HomeMy WebLinkAbout1.17 Geotechnical Report -AMD 101A Airpark Dr., Unit 9, PO Box 464, Gypsum, CO 81637 Phone (970) 524-0720 Fax (970) 524-0721 www.groundeng.com
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Subsurface Exploration Program
Geotechnical and Pavement Section Recommendations
New Creation Church Preschool
Glenwood Springs, Colorado
Prepared for:
Colorado River Engineering
136 East 3rd Street
Rifle, Colorado 81650
Attention: Mr. Gregory Shaner, P.E.
Job Number: 13-6017 August 23, 2013
TABLE OF CONTENTS
Page
Purpose and Scope of Study ..................................................................................... 1
Proposed Construction ................................................................................................ 1
Site Conditions ............................................................................................................ 2
Geologic Setting .......................................................................................................... 3
Geologic Hazard Review ............................................................................................. 3
Subsurface Exploration ............................................................................................... 7
Laboratory Testing ...................................................................................................... 8
Subsurface Conditions ................................................................................................ 8
Seismic Classification ................................................................................................. 9
Geotechnical Considerations for Design ................................................................... 10
Foundation Systems
Deep Foundation Systems .................................................................................. 11
Drilled Piers ................................................................................................... 11
Driven Piles ................................................................................................... 14
Screw Piles/Helical Piers ............................................................................... 16
Aggregate Piers ............................................................................................. 17
Shallow Foundation System ................................................................................ 18
Floor Systems ........................................................................................................... 18
Mechanical Rooms/Mechanical Pads ........................................................................ 23
Water-Soluble Sulfates ............................................................................................. 23
Soil Corrosivity .......................................................................................................... 24
Lateral Earth Pressures ............................................................................................ 27
Project Earthwork ...................................................................................................... 28
Excavation Considerations ........................................................................................ 31
Utility Pipe Installation and Backfilling ....................................................................... 33
Surface Drainage ...................................................................................................... 35
Subsurface Drainage ................................................................................................ 37
Pavement Sections ................................................................................................... 39
Exterior Flatwork ....................................................................................................... 38
Closure ...................................................................................................................... 43
Locations of Test Holes .................................................................................... Figure 1
Logs of Test Holes ................................................................................... Figures 2 – 3
Legend and Notes ............................................................................................ Figure 4
Gradation Test Results .............................................................................. Figure 5 – 6
Swell/Consolidation Test Results ............................................................. Figures 7 – 9
Laboratory Compaction Test Result ............................................................... Figure 10
R-Value Test Result ....................................................................................... Figure 11
Summary of Laboratory Test Results ................................................................ Table 1
Pavement Section Calculations ................................................................. Appendix A
New Creation Church Preschool
Glenwood Springs, Colorado
Job No. 13-6017 GROUND Engineering Consultants, Inc. Page 1
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsurface exploration program performed by
GROUND Engineering Consultants, Inc. (GROUND) to provide geotechnical and
pavement section recommendations for the proposed new preschool and associated
parking lot located at 44761 Highway 6 & 24 in Glenwood Springs, Colorado. Our study
was conducted in general accordance with GROUND Proposal Number 1305-0928
dated May 23, 2013.
Field studies provided information regarding surface and subsurface conditions,
including existing site improvements and groundwater. Material samples retrieved
during the subsurface exploration were tested in our laboratory to assess the
engineering characteristics of the site earth materials, and assist in the development of
our geotechnical recommendations. Results of the field and laboratory studies for the
proposed renovations are presented below.
This report has been prepared to summarize the data obtained and to present our
conclusions and recommendations based on the proposed construction and the
subsurface conditions encountered. Design parameters and a discussion of engineering
considerations related to construction of the proposed school facility are included herein.
PROPOSED CONSTRUCTION
Based on the provided conceptual site plan prepared by WL Perry Associates, Ltd.
dated July 23, 2013, we understand the proposed construction includes improvements to
the existing New Creation Church property. Specifically, a new preschool building
measuring about 10,971 square feet in size is proposed. An asphalt surfaced parking lot
will replace the existing gravel surfaced parking to the west of the new preschool, and
the existing gravel parking located to the south of the proposed preschool will be
removed. Additionally, it appears an adjustment in lot line location to increase the size
of Parcel C is planned, which will result in the proposed construction being included
within Parcel C.
Building loads were not available for our review at the time this report was prepared,
however, building loads are anticipated to be comparatively light. No below grade
spaces (basements) were assumed. Development is also anticipated to include
installation of underground utilities to service the proposed structure.
New Creation Church Preschool
Glenwood Springs, Colorado
Job No. 13-6017 GROUND Engineering Consultants, Inc. Page 2
SITE CONDITIONS
At the time of our field exploration, the project area consisted of two Parcels
approximately 15.8 acres in size located between County Road 138 and State Highway
6 & 24. The site generally slopes down to the south with a maximum elevation
difference of about 50 feet across the site and an average slope of around 9 percent.
Upward sloping, steeper slopes covered by fire debris are located on a hill north and
across County Road 138. Topography within the site includes rolling hills that are gentle
to moderately sloping. The Colorado River is located south across State Highway 6 &
24 and Interstate 70, and is about 40 feet lower and 400 feet away from the property at
the closest.
The western 5.8 acre Parcel C has been previously developed. It includes an existing
single-story masonry church and two-story administration building, as well as asphalt
paved and gravel surfaced parking areas, access roads and drive lanes were located
within the south portion of the Parcel. A basketball court, a volley ball court, and fire ring
were located in a grassed and irrigated area in the northern portion of Parcel C.
The 10 acre Parcel B was located east of Parcel C, and was largely undeveloped with
the exception of some gravel and asphalt surfacing in the southwest corner abutting
Parcel C. The ground surface in the remainder of Parcel B was sparsely covered by
native vegetation. A few mature trees were scattered along the edges of the Parcel.
The previous development in the southwestern corner of the Parcel included some fill
placement most likely associated with the development and grading of Parcel C. The fill
section surface is generally level and flat, partially gravel surfaced, and appears to have
been used as a yard for construction material and equipment storage. It is thickest at
the southeastern edge and pinches out against the natural slopes to the west and north.
New Creation Church Preschool
Glenwood Springs, Colorado
Job No. 13-6017 GROUND Engineering Consultants, Inc. Page 3
GEOLOGIC SETTING Published maps, e.g. Bryant, et. al., (20021), depict the site as
underlain by Holocene to late Pleistocene age alluvial (river-deposited) and debris flow
deposits. The alluvial materials generally consist of fine to medium grained clayey sands
with gravel, cobble and boulders derived from nearby streams and rivers. The debris
flow deposits typically represent larger flow events generally mobilizing larger quantities
of larger sized materials. The overburden materials are mapped as underlain by the
Lower Permian to Middle Pennsylvania age Maroon Formation, which consists of
interbedded siltstone and sandstone bedrock with lenses of conglomerates.
GEOLOGIC HAZARD REVIEW
Expansive Soils The shallow earth materials underlying the site included silt/clay and
sands over sandy to silty/clayey and sandy gravels. Swelling clayey soils and bedrock
change volume in response to changes in moisture content that can occur seasonally, or
in response to changes in land use, including development. Expansion potentials vary
with moisture contents, density and details of the clay chemistry and mineralogy. The
swell potential in any particular area can vary markedly both laterally and vertically due
to complex interbedding of the site soil and bedrock materials. Moisture changes also
occur erratically, resulting in conditions that cannot always be predicted.
1 Bryant, B., Shroba, R.R., Harding, A.E., and Murray, K.E. l., 2002, Geologic map of the Storm King
Mountain quadrangle, Garfield County, Colorado, U.S. Geological Survey, Miscellaneous Field Studies
Map MF-2389.
Interstate 70
Approximate
Project Site
New Creation Church Preschool
Glenwood Springs, Colorado
Job No. 13-6017 GROUND Engineering Consultants, Inc. Page 4
The site soils had generally non-plastic to low plasticity, and swell/consolidation testing
indicated a low potential for post-construction heave (Table 1). Based on the properties
of the materials encountered on-site, we do not anticipate damage from post-
construction swell to be a significant concern in the project area.
Collapsible Soils Certain surficial deposits, typically eolian (wind-blown) materials
including loess, are known to be susceptible to local hydro-consolidation or “collapse.”
Hydro-consolidation consists of a significant volume loss due to re-structuring of the
constituent grains of the soil to a more compact arrangement upon wetting under a
surcharge load.
Site surficial soils are interpreted to be collapsible. Results of swell/consolidation tests
indicated compressions in all of the test samples ranging from 0.6 to 6 percent under
various surcharge loads after wetting. Additionally, the index parameters for site soils
assessed for this study generally fell into the range typically associated with collapsible
soils (e.g. Naval Facilities Engineering Command, 1986)2. Therefore, the presence of
collapsible soils is deemed to be a geologic hazard within the site and should be
considered during any proposed development/improvements.
Radon is a naturally occurring, colorless, odorless, radioactive gas that can cause lung
cancer, according to the U.S. Environmental Protection Agency (EPA). The occurrence
of radon is difficult to predict, and structures with all types of foundations can be affected
by radon build up. Radon represents a potential hazard where it is allowed to
concentrate in an enclosed structure. However, it is not a hazard that can be mitigated
by geotechnical measures.
Testing for the possible presence of radon gas prior to project development does not
yield useful results regarding the potential accumulation of radon in completed
structures. Radon accumulations are most typically found in basements, crawl spaces
or other enclosed portions of buildings built in areas underlain at relatively shallow
depths by granitic crystalline rock. Additional information regarding radon and radon-
resistant building design can be obtained from the EPA (e.g., www.epa.gov/radon) as
well as from many local building and/or health departments.
GROUND recommends that radon testing be performed in each building, particularly
where basements or below grade spaces are included, after construction is completed.
2 Naval Facilities Engineering Command, 1986, Design Manual 7.01, Soil Mechanics, 348 pp.
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Glenwood Springs, Colorado
Job No. 13-6017 GROUND Engineering Consultants, Inc. Page 5
However, we understand that incorporating sufficient ventilation and other measures into
a structure to address radon accumulation during construction is significantly less costly
than installing them after construction has been completed. We recommend that the
Architect or Developer consider radon mitigative measures for any proposed structures
and incorporate appropriate systems into the design.
Seismic Activity / Faulting Review of available geologic maps did not indicate the trace
of an active or potentially active fault traversing or immediately adjacent to the site. In
this regard, the likelihood of surface fault rupture at the site is considered to be low.
However, at greater horizontal distance, a magnitude 3.8 earthquake was recorded in
February 2006, approximately 2.9 miles to the southwest of the project site. Damage
was not reported with this event. Other similar magnitude earthquakes have also been
recorded but at greater distances.
In addition, the closest mapped faults to the site are located approximately 1.5 miles to
the northeast, which has an estimated movement age of about 23.7 million years ago.
The risk of these faults giving rise to damaging, earthquake-induced ground motions at
the site is considered to be relatively low, given the previously recorded seismic
magnitudes and frequencies.
Slope Stability and Erosion The site consists of rolling slopes descending to the south
with steeper slopes located north as previously discussed. During our reconnaissance
of site area, no evidence was noted of mass-wasting processes associated with steep
slopes, such as landslides, slumps or unusual soil creep. Therefore, the likelihood of
project developments being affected by large scale, unanticipated slope instabilities is
considered low.
However, we estimate short term erosion potential, associated with the previous fire of
the slopes on the hill to the north, to be elevated until vegetation is re-established. Such
erosion will likely occur mostly during storm events and will likely include slope wash and
sediment deposition on the property near drainages. Drainage cutting and widening
may also occur until native vegetation is re-established.
Flooding A review of the preliminary October 2011 Flood Insurance Study for Garfield
County and Incorporated Areas indicates the subject property lies outside of Special
Flood Hazard Areas, which are subject to inundation by the 1 percent annual chance
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Glenwood Springs, Colorado
Job No. 13-6017 GROUND Engineering Consultants, Inc. Page 6
flood. However, some flooding due to seasonal heavy rainfall may occasionally occur.
Also, significant fluctuation in the flow of drainages can be expected during such
seasonal run periods. Flooding potential is believed to be limited to local, surface
saturation during episodes of heavy rainfall and associated temporary ponding of run-off
in areas of relatively slow surface drainage. However, flooding potential should be
evaluated by the Civil Engineer.
Groundwater was not encountered at the time of subsurface exploration to the depths
explored. Therefore, we anticipate groundwater will not be a factor during construction
in the project area. Groundwater levels can fluctuate, however, in response to annual
and longer-term cycles of precipitation, irrigation, snowmelt, surface drainage and land
use, and the development and drainage of transient, perched water conditions.
Wetlands Potential No evidence of wetlands areas were observed within the project
area. However, during site development all regulations concerning wetland protection,
as well as any other areas designated as wetlands by the Federal Wetlands Protection
Act should be adhered to. Explicit designation of wetlands was not included as part of
the scope of this study.
Mining Activity and Subsidence Review of available U.S. Geological Survey
information covering the site (e.g., Bryant, et. al., 2002) did not indicate past mining
activities on or adjacent to the subject parcel. No indications of mining activities were
apparent on the site during the site reconnaissance. Therefore, there appears to be little
potential for surface subsidence associated with consolidation of former mine workings
at depth.
Sinkholes The City of Glenwood Springs, including the project site, generally lies within
the ‘Carbondale Collapse Center,’ a geologic structure occupying a large area of west-
central Colorado apparently formed by dissolution and/or flow of the water-soluble
minerals in the sedimentary formations there. The risk of damage to structures, while
present, has been estimated to be very low for the design life of normal residential
structures3. No sinkholes or subsidence features were observed during our fieldwork,
therefore we estimate the risk of sinkhole or subsidence feature development to be no
greater than typically exists within the Glenwood Springs area. If this geologic hazard is
a significant consideration to the Owner, or if additional information is desired regarding
3 White, Jonathon L., Colorado Map of Potential Evaporite Dissolution and Evaporite Karst Subsidence
Hazards Map Discussion, Colorado Geologic Survey Department of Natural Resources 2013
New Creation Church Preschool
Glenwood Springs, Colorado
Job No. 13-6017 GROUND Engineering Consultants, Inc. Page 7
the potential risk of sinkhole/subsidence feature development, we recommend a
comparatively deep (on the order of several hundred feet) test hole be drilled/cored to
evaluate the risk from dissolution of evaporate deposits underlying the Maroon
Formation.
Based on the published information reviewed for the site and the findings of this
assessment, with allowance for the conditions and risks discussed above, the site
appears to be feasible for development with respect to potential geologic hazards
and general geotechnical design concerns.
SUBSURFACE EXPLORATION
The subsurface exploration for the project was conducted on July 25 and 26, 2013. A
total of six (6) test holes were drilled with a truck-mounted drill rig advancing continuous
flight auger equipment to evaluate the subsurface conditions as well as to retrieve soil
samples for laboratory testing and analysis. Four (4) of these test holes were drilled
within the proposed building footprint and the remaining two (2) test holes were drilled
within the areas proposed for pavements. The test holes were advanced to depths
ranging from approximately 5 to 24 feet below existing grades. A GROUND engineer
directed the subsurface exploration, logged the test holes in the field, and prepared the
soil samples for transport to our laboratory.
Samples of the subsurface materials were retrieved with a 2-inch I.D. California liner
sampler. The sampler was driven into the substrata with blows from a 140-pound
hammer falling 30 inches. This procedure is similar to the Standard Penetration Test
described by ASTM Method D1586. Penetration resistance values, when properly
evaluated, indicate the relative density or consistency of soils. Depths at which the
samples were obtained and associated penetration resistance values are shown on the
test hole logs.
The approximate locations of the test holes are shown in Figure 1. Logs of the
exploratory test holes are presented in Figures 2 and 3. Explanatory notes and a legend
are provided in Figure 4.
The test hole locations were approximately placed in the field based on the proposed
construction as shown in the provided conceptual site plan. The locations should only
be assumed to be accurate to the degree implied by the method used. If detailed
New Creation Church Preschool
Glenwood Springs, Colorado
Job No. 13-6017 GROUND Engineering Consultants, Inc. Page 8
information regarding test hole locations and elevations are desired, the test holes
should be professionally surveyed.
LABORATORY TESTING
Samples retrieved from our test holes were examined and visually classified in the
laboratory by the project engineer. Laboratory testing of soil samples obtained from the
subject site included standard property tests, such as natural moisture contents, dry unit
weights, grain size analyses, swell-consolidation potential, and liquid and plastic limits.
Water-soluble sulfate and corrosivity tests were completed on selected samples of the
soils as well. Standard Proctor and R-Value testing was completed on a composite bulk
sample. Laboratory tests were performed in general accordance with applicable ASTM
and AASHTO protocols. Results of the laboratory testing program are summarized in
Figures 5 through 11 and on Table 1.
SUBSURFACE CONDITIONS
The subsurface conditions encountered in the test holes generally consisted of either
approximately 3 inches of gravel surfacing (test holes TH-1, P-1, and P-2) or fill soils at
the ground surface. The fill soils appeared to consist of remolded native soils from on-
site, and although it was difficult to delineate the transition from fill to native materials in
the boreholes, were estimated to be 2 to 8 feet in thickness where encountered (test
holes TH-2, TH-3, and TH-4). The gravel surfacing and fill materials were underlain by
native soils consisting of silt/clay and sand to depths of 5 feet in the pavement test holes,
and depths of 10 to 18 feet in the building test holes, which were underlain by
silty/clayey and sandy gravels with cobbles to the test hole termination depths of 11.5 to
24 feet below existing grades. It should be noted that practical drill rig refusal was
encountered in test holes TH-1 and TH-3 at respective depths of 11.5 and 18 feet.
It should be noted that while it is generally not possible to determine the presence of
boulders from comparatively small diameter boreholes, based on our experience
boulders should be expected to exist within the gravel layer as well as scattered
throughout the overlying silt/clay and sand.
Delineation of the complete extents, limits, and compositions of site fills were beyond our
present scope of services. If fill extents or compositions are of significance to a
contractor, they should be evaluated using test pits.
New Creation Church Preschool
Glenwood Springs, Colorado
Job No. 13-6017 GROUND Engineering Consultants, Inc. Page 9
The surficial soils are interpreted to be eolian (wind-blown) sands grading irregularly
downward into alluvial (stream-laid) materials of the Broadway Alluvium. The bedrock
deposits are interpreted to be Maroon Formation materials.
Fill generally consisted of silt/clay and sand, with fine to coarse grained sand, was
slightly moist to moist, had low plasticity, was loose to medium dense or medium stiff to
very stiff, and reddish in color.
Silt/Clay and Sand were interlayered with fine to coarse grained sand, were slightly
moist to moist, had low plasticity, were loose to medium dense or medium stiff to very
stiff, and reddish in color. May contain scattered cobbles and boulders.
Gravel was slightly silty/clayey and sandy to silty/clayey and sandy, with fine to coarse
grained sand, fine to coarse gravel and cobbles and likely boulders, was slightly moist to
moist, had nil to low plasticity, was very dense, and reddish brown to brown in color.
Groundwater was not encountered in the test holes at the time of drilling within the
depths explored. Therefore, groundwater is not anticipated to be a factor during
construction at this site. Groundwater levels can fluctuate, however, in response to
annual and longer-term cycles of precipitation, irrigation, surface drainage and land use,
and the development and drainage of transient, perched water conditions.
Swell-Consolidation Testing of samples of the on-site materials indicated
consolidations ranging from approximately 0.6 to 6.0 percent under surcharge loads of
200 and 1,000 psf after loading (Figures 7 – 9 and Table 1). Such magnitudes generally
represent a low to high risk of poor post-construction performance.
SEISMIC CLASSIFICATION
Based on extrapolation to depth of the subsurface data obtained for this study, and our
experience in the project area, GROUND estimates that the site will meet the
characteristics of a Site Class D site, according to the 2006/2009 IBC classification
(Table 1613.5.2). To determine the site class quantitatively would require drilling and
testing to a depth of at least 100 feet. GROUND can provide a proposal for this
additional service upon request. However, based on the subsurface conditions
encountered and our experience we estimate the likelihood of achieving at Site Class
higher than D to be low.
New Creation Church Preschool
Glenwood Springs, Colorado
Job No. 13-6017 GROUND Engineering Consultants, Inc. Page 10
Based on the site coordinates, the USGS’s Earthquake Ground Motion Tool v.5.0.9a
indicates an SDDS value of 0.358 g and an SD1 value of 0.119 g, for a Site Class D.
GEOTECHNICAL CONSIDERATIONS FOR DESIGN
The gravel underlying the silt/clay and sand soils appears to be an excellent stratum for
bearing. However, the overlying silt/clay and sand soils are variable in strength, ranging
from loose to medium dense or medium stiff to very stiff, have comparatively low
densities, and appear to be susceptible to hydro-consolidation/settlement. Additionally,
the thickness of the settlement prone silt/clay and sand soils is variable, increasing in
thickness to the northwest.
Given the land use of the existing construction, which includes irrigated grasses, the
subsurface moisture content will most likely increase following the completion of
proposed construction. The magnitude of settlement will be dependent on how deep the
moisture increase changes penetrate the subsurface as well as the adequacy of the site
drainage. We estimate settlement due to hydro-consolidation of the in-place soils to
potentially range from 2.5 inches where the gravels are within 10 feet of the ground
surface to as much as 5 inches where the gravels are deeper. This implies that a large
differential settlement potential will exist across the building footprint for any shallow
foundation on the in-place soils, or any remedial over-excavation and replacement depth
unless the entire section of silt/clay and sand soils beneath the building are removed to
the top of gravel and replaced. We estimate this option would involve the excavation
and replacement of an estimated rough volume of 9,000 cubic yards.
The on-site soils appear suitable for re-use as backfill of such an excavation, however
these types of soils can be difficult to work with and tend to be sensitive to moisture
content to achieve proper compaction. Additionally even with a complete removal and
replacement strategy, since the fill section will not be of uniform thickness, a differential
settlement potential across the building footprint will still exist but will be much reduced.
If high quality granular backfill is used, this differential settlement potential will likely be
on the order of 0.75 inches and up to 1.5 inches for on-site soils. Based on this, we
have assumed that the removal and replacement scenario is less feasible from a cost
standpoint and less desirable from a performance standpoint than other available
options. In the event the Owner elects to utilize over-excavation and replacement, we
should be contacted to provide additional foundation design criteria.
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Glenwood Springs, Colorado
Job No. 13-6017 GROUND Engineering Consultants, Inc. Page 11
Given the soil conditions, we anticipate feasible foundation options for this site to include
foundation soil improvements to mitigate the settlement from hydro-consolidation and
allow the use of shallow foundations, or the use of deep foundations. Foundation
improvements are recommended to consist of aggregate piers. Deep foundation
systems could likely include drilled piers, screw piles/helical piers, or driven piles.
Consideration should also be given to the floor system type. We assume a slab-on-
grade floor would be preferred, however slab settlements of up to 5 inches relative to the
foundation are possible if a deep foundation system is used with a slab-on-grade floor.
While it is possible slab settlements of these magnitudes may not have negative impacts
on the structural performance of the building, such magnitudes of settlement are
generally not acceptable to Owners. Any mechanical equipment resting on these slabs
would also need to be designed and constructed to accommodate such settlements.
Based on the results of the laboratory testing, we anticipate that in-situ silt/clay and sand
soils will undergo approximately 20% shrinkage when placed as fill materials as
compared to 100% compaction of the standard Proctor, or 15% shrinkage at 95%
standard Proctor compaction. We also anticipate the addition of approximately 7 to 8
percent construction water will be necessary to achieve optimum moisture contents.
FOUNDATION SYSTEMS
Deep Foundation Systems
A deep foundation system would result in the least risk of post-construction movement of
structures normally associated with consolidation potential. Although a deep foundation
system will not eliminate the risk of post-construction structure movement, if the
recommendations below are followed, the likelihood of acceptable structure performance
will be well within the local industry standards for construction of a deep foundation
system.
Drilled Piers We recommend drilled piers utilize comparatively low skin friction values
in the on-site soils and be founded in the on-site gravels. Driller pier borehole stability
may be problematic in the gravels and refusal conditions may be frequently encountered
on large cobbles and boulders. Drilled pier contractors should anticipate such difficult
conditions.
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Glenwood Springs, Colorado
Job No. 13-6017 GROUND Engineering Consultants, Inc. Page 12
The design criteria presented below should be observed for a straight-shaft pier
foundation system. The recommendations should be considered when preparing project
documents and construction details.
1) Piers may be designed for an allowable end bearing pressure of 20,000 psf and
a skin friction value of 120 psf in the on-site soil and 1,200 psf in the gravels.
The upper 3 foot of soils should be ignored in all load calculations.
2) A minimum deadload is not required for this site.
3) We recommend piers penetrate a minimum length of 5 feet into the gravels.
However, the actual pier lengths should be based on the specific design loads as
determined by the Structural Engineer, as well as the actual conditions
encountered in the field at each pier location during installation.
4) A minimum pier diameter of 18 inches is recommended to facilitate proper
cleaning and observation of the pier hole.
5) Void form should be provided beneath grade beams to concentrate loads and to
provide space for seasonal frost heave. Void form should be a minimum of 4-
inches in thickness.
6) Shear rings are not required for drilled piers on this site.
7) Groups of piers required to support concentrated loads will require an
appropriate reduction of the estimated bearing capacity based on the effective
envelope area of the pier group.
Reduction of axial capacity can be avoided by spacing piers at least 3 diameters
center to center. Pier groups spaced less than 3 diameters center to center
should be studied on an individual basis to determine the appropriate axial
capacity reductions(s).
To avoid reduction of the capacity of piers to resist the component of lateral
loading parallel to the line connecting the pier centers, piers should be spaced at
least 6 diameters apart. Groups of piers spaced less than 6 diameters center to
center should be studied to determine the appropriate lateral capacity
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Glenwood Springs, Colorado
Job No. 13-6017 GROUND Engineering Consultants, Inc. Page 13
reduction(s). It should be noted, however, that 2012 IBC specifies a minimum
spacing of 8 diameters, however this is overly conservative in our opinion.
8) Piers may be designed to resist lateral loads assuming a soil horizontal modulus
of 50 tcf in overburden sands and silts/clay. Alternatively the L-Pile parameters
presented below may be used.
Estimated Geotechnical Parameters for Lateral Load Analysis
Soil Type
Sand and
Silt/Clay
(Sand Reese)
(Above Water
Table)
Gravel
(Sand Reese)
(Above Water
Table)
Density
(pci) 0.061 0.078
Friction Angle
(degree) 28 34
Kh
(pci) 25 225
9) We do not anticipate any significant tensile loads on piers from swelling soils.
Therefore, we recommend steel reinforcement be provided and sized based on
axial and lateral load considerations, and conform to industry reinforcement
criteria based on pier cross sectional area. If the soils are subjected to hydro-
consolidation, down drag forces on piers from hydro-consolidation may be
evaluated using 27 pcf acting on the perimeter of the pier in the silt/clay and
sand.
10) Groundwater was not encountered at the time of drilling. Caving and refusal
conditions may be encountered in the gravel below the silt/clay and sand.
Therefore, the use of slurry drilling or casing may be necessary for pier
installation. However, the requirements for casing can sometimes be reduced by
placing concrete immediately upon cleaning and observing the pier hole. In no
case should concrete be placed in more than 3 inches of water, unless placed
through an approved tremie method.
11) Pier holes should be properly cleaned prior to placement of concrete.
12) Concrete utilized in the piers should be a fluid mix with sufficient slump so that it
will fill the void between reinforcing steel and the pier hole wall. We recommend
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Job No. 13-6017 GROUND Engineering Consultants, Inc. Page 14
the concrete have a minimum slump in the range of 5 to 7 inches. Concrete
should be placed by an approved “tremie”-type method or other methods such as
the utilization of a long steel pipe or “elephant trunk” to reduce mix segregation.
The “tremie” should be extended down into the center of the drilled pier shaft in
order to provide a clear pathway through the reinforcement cage. A centering
chute that extends to shallow depths may not be sufficient.
13) Concrete should be placed in piers the same day they are drilled. Failure to
place concrete the day of drilling will normally result in a requirement for
additional penetration. The presence of groundwater or caving soils at the time
of pier installation may require that concrete be placed immediately after the pier
hole drilling is completed.
14) The Contractor should take care to prevent enlargement of the excavation at the
tops of piers, which could result in mushrooming of the pier top. Mushrooming of
pier tops can increase uplift pressures on the piers from swelling soils and frost
heave.
15) The soils beneath the site are generally loose to very dense. Additionally,
practical drill rig refusal was encountered in test holes TH-1 and TH-3.
Therefore, we recommend the use of a high-torque, commercial rig in good
working order. If refusal is encountered in these materials, the Geotechnical
Engineer should evaluate the conditions to establish that true refusal has been
met with adequate drilling equipment.
Driven Piles The following geotechnical parameters and recommendations are
provided for design of driven, steel driven pile foundations. Post-construction
settlements of a properly designed and installed driven pile foundation system are
estimated to be on the order of ½ inch or less.
1) The piles should be reinforced with commercial, heavy duty, pile tips.
2) Piles may be designed for an allowable service stress of 9,000 psi based on the
pile cross-sectional area for 36 ksi steel piles.
3) We recommend piles be installed into the gravels underlying the sand and
silt/clay soils. We recommend a minimum gravel penetration depth of 5 feet.
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4) We anticipate that post-installation ‘down-drag’ on steel piles will be moderate
due to the collapsible overburden soils. ‘Down-drag’ may be calculated taking an
equivalent fluid pressure of 73 pcf as characteristic of the site soils acting on the
portion of each pile above the gravels with a negative soil/pile skin friction
coefficient of 0.37. The perimeter of the pile may be used to calculate ‘down-
drag.’ GROUND also recommends, however, re-striking of the piles to evaluate
their capacity at least 24 hours after (initial) driving has been completed.
5) Uplift capacity on driven piles should be limited to 25 percent of the indicated
vertical load capacities.
6) Lateral loads may be resisted using the parameters outlined in the Drilled Pier
section,or they can also be resisted by battered piles. The vertical and horizontal
components of the load will depend on the batter inclinations. Batters should not
exceed 1:4 (horizontal : vertical).
7) Groups of piles should be spaced apart as indicated in the Drilled Pier section to
avoid reductions in capacity.
8) A Wave Equation Analysis should be performed to determine if the driving
hammer is sized adequately for the type of pile selected and the soils and
materials into which the piles are driven.
9) We suggest that a test pile installation program be performed to better define the
driving conditions and installation depths and conditions.
10) We recommend that at the start of pile installation a Geotechnical Engineer
perform pile dynamic testing at each pier and abutment in order to:
a. Assess whether piles are being over-stressed relative to the allowable
service stress of 9,000 psi.
b. Develop virtual refusal criteria for gravel penetration based on the design
capacity of the piles.
11) Additional pile footage should be included in project planning to allow for
additional piles locally where offsets were required due to potential obstructions
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to pile driving in the gravel materials (i.e. cobbles and boulders) or damage to
piles.
12) A quality control representative should be retained to observe pile driving
operations. We are available to perform pile driving observation upon request.
13) Piles should be evaluated for corrosion potential and provided with adequate
corrosion protection such as sacrificial thickness, cathodic protection, protective
coatings or combinations of these methods.
14) Where a pile cannot be advanced to at least the anticipated tip elevation, it
should be evaluated with regard to its capacity by the Geotechnical Engineer and
the structural engineer.
Screw Piles/Helical Piers Screw piles/helical piers appear to be feasible for this site.
Screw piles and helical piers differ primarily in the amount of capacity they can provide,
with screw piles typically capable of higher capacities than helical piers. Screw piles can
typically achieve capacities of up to 300,000 lbs, while helical piers are generally limited
to around 100,000 lbs.
Helical piers sometimes need to be pre-drilled to achieve minimum penetration depths,
which would likely be necessary for any significant amount of penetration into the gravel
layer. We recommend screw piles/ helical piers be founded in the gravel layer rather
than achieving torque in the overlying, consolidation prone, silt/clay and sand soils
through the use of multiple helices on the piles/piers.
Both screw piles and helical piers typically utilize hydraulic pressure converted to toque
to determine when capacities have been achieved. The conversion from drive head
pressure to torque is often based on a drive head calibration. We recommend contractor
submittals include a current drive head pressure torque calibration performed within the
last six months. Torque is also sometimes verified through the use of shear pins, or
periodically verified on a few piles/piers during installation. The drive head calibration
submittal requirement may be waived if shear pin torque verification is used on at least
50% of the piles/piers.
To determine capacity, design/builders use an empirical torque coefficient (ETC) which
is largely based on the available geotechnical data and experience. Therefore, true
capacity is unknown unless a load test is performed to verify the ETC used in the design.
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We highly recommend a load test be performed if screw piles/helical piers are used on
the project. In the absence of a load test, we recommend a highest ETC of 7 ft-1 be
accepted from a design/builder and preferably not more than 5 ft-1. We also recommend
full time observation of installation by a quality control representative. We are available
to review screw pile/helical pier designs, and perform load test and installation
observations upon request.
Lateral loads are often handled by the installation of battered piles/piers, or alternatively
the L-Pile parameters or horizontal soil modulus value design parameters presented in
the Drilled Pier section may be used. We recommend groups of piles/piers be spaced
apart as outlined in the Drilled Pier section based on the diameter of the largest helix.
Screw piles/helical piers should also be evaluated for corrosion and provided with
adequate corrosion protection similarly to the recommendations presented in the Driven
Piles section.
Screw piles/helical piers are typically handled by specialty design/build contractors, who
should be provided with a copy of the available geotechnical data as well as the
foundation plan, structural loads, and movement tolerances.
Aggregate Piers One option that appears to be feasible for this site includes the use of
aggregate piers as a cost effective foundation improvement alternative to drilled piers or
screw piles/helical piers. Aggregate pier systems are typically handled by specialty
design/build contractors, similar to screw piles/helical piers, and consist of a drilled shaft,
backfilled with coarse rock in lifts and compacted with a high frequency tamper. This
has the effect of strengthening the surrounding soils, thereby increasing bearing capacity
and reducing post-construction settlements. Post-construction settlements of ½-inch or
less are possible if the available geotechnical data, foundation plan, structural loads (or
target bearing capacity), and movement tolerances are supplied to the design/build
contractor. The placement of a bottom reaction plate and vertical reinforcement in the
aggregate piers can also provide resistance to uplift forces.
Aggregate pier systems are capable of producing bearing capacities of up to 6,000 psf
and supporting column loads of up to 100,000 lbs. Aggregate pier installation time is
comparable to that for screw piles/helical piers. If an aggregate pier system is selected,
we recommend a quality control representative perform full-time observation of
aggregate pier installation. GROUND is available to provide pier observation upon
request.
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Shallow Foundation System
Based on our field and laboratory analysis and the nature of the proposed construction,
it is GROUND’s opinion the materials encountered in our exploration are suitable to
support the proposed structure on a shallow foundation consisting of spread footings
only if foundation improvements such as complete over-excavation or aggregate piers
are used. The following recommendations are based on the use of aggregate piers. In
the event an over-excavation option is desired, we should be contacted to provide
additional recommendations. To use these recommendations, the Owner must accept
the risk of post-construction foundation movement associated with shallow foundation
systems. Utilizing the above recommendations as well as other recommendations in this
report, GROUND estimates potential movements may be on the order of ½ to 1 inch.
Actual movements may be more or less.
Although aggregate piers are capable of achieving bearing capacities up to 6,000 psf,
based on the proposed construction, we do not anticipate such a bearing capacity will be
necessary to support the structural loads. We recommend a minimum footing width of
12 inches for footing foundations on aggregate piers. Based on footing width and
structural loads, the specialty design/build contractor should be supplied with the target
bearing capacity, which should help to determine the necessary spacing and depth of
aggregate pier foundation improvements to achieve required bearing capacity. Where
pads or footings are located beyond the perimeter of the aggregate piers, we
recommend either providing sufficient soil cover for frost penetration considerations, or
that gaps between piers be spanned with a 4-inch void form. Foundation walls should
be designed to span unsupported lengths between piers.
FLOOR SYSTEMS
Slab-on-Grade Floors
Slab-on-grade construction should be used only if the Owner understands and accepts
the risk of post-construction slab movements. Additionally, we would only recommend a
slab-on-grade floor if foundation improvements such as over-excavation or aggregate
piers are installed below foundation and floor areas. The following recommendations
are based on the assumption of the use of aggregate piers. In the event over-
excavation is selected, we should be contacted to provide additional recommendations.
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We anticipate post-construction movements of approximately ½ to 1 inch if slab-on-
grade construction is utilized with aggregate pier foundation soil improvements.
1) Floor slabs should be adequately reinforced. Floor slab design, including slab
thickness, concrete strength, jointing, and slab reinforcement should be
developed by the specialty design/build contractor.
2) The specialty design/build aggregate pier contractor should also determine the
vertical modulus of subgrade reaction. However, we anticipate values on the
order of 200 to 300 pci will likely be achievable.
3) Floor slabs should be separated from all bearing walls and columns with slip
joints, which allow unrestrained vertical movement.
Slip joints should be observed periodically, particularly during the first several
years after construction. Slab movement can cause previously free-slipping
joints to bind. Measures should be taken to assure that slab isolation is
maintained in order to reduce the likelihood of damage to walls and other interior
improvements.
4) Concrete slabs-on-grade should be provided with properly designed control
joints.
ACI, AASHTO and other industry groups provide guidelines for proper design
and construction concrete slabs-on-grade and associated jointing. The design
and construction of such joints should account for cracking as a result of
shrinkage, curling, tension, loading, and curing, as well as proposed slab use.
Joint layout based on the slab design may require more frequent, additional, or
deeper joints, and should reflect the configuration and proposed use of the slab.
Particular attention in slab joint layout should be paid to areas where slabs
consist of interior corners or curves (e.g., at column blockouts or reentrant
corners) or where slabs have high length to width ratios, significant slopes,
thickness transitions, high traffic loads, or other unique features. The improper
placement or construction of control joints will increase the potential for slab
cracking.
5) Interior partitions resting on floor slabs should be provided with slip joints so that
if the slabs move, the movement cannot be transmitted to the upper structure.
This detail is also important for wallboards and doorframes. Slip joints, which will
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allow 2 or more inches of vertical movement, should be considered. If slip joints
are placed at the tops of walls, in the event that the floor slabs move, it is likely
that the wall will show signs of distress, especially where the floors and interior
walls meet the exterior wall.
6) Post-construction soil movements may not displace slab-on-grade floors and
utility lines in the soils beneath them to the same extent. Design of floor
penetrations, connections and fixtures should accommodate up to 2 inches of
differential movement.
7) Moisture can be introduced into a slab subgrade during construction and
additional moisture will be released from the slab concrete as it cures. GROUND
recommends placement of a properly compacted layer of free-draining gravel, 4
or more inches in thickness, beneath the slabs. This layer will help distribute
floor slab loadings, ease construction, reduce capillary moisture rise, and aid in
drainage.
The free-draining gravel should contain less than 5 percent material passing the
No. 200 Sieve, more than 50 percent retained on the No. 4 Sieve, and a
maximum particle size of 2 inches.
The capillary break and the drainage space provided by the gravel layer also
may reduce the potential for excessive water vapor fluxes from the slab after
construction as mix water is released from the concrete.
We understand, however, that professional experience and opinion differ with
regard to inclusion of a free-draining gravel layer beneath slab-on-grade floors. If
these issues are understood by the owner and appropriate measures are
implemented to address potential concerns including slab curling and moisture
fluxes, then the gravel layer may be deleted.
8) A vapor barrier beneath a building floor slab can be beneficial with regard to
reducing exterior moisture moving into the building, through the slab, but can
retard downward drainage of construction moisture. Uneven moisture release
can result in slab curling. Elevated vapor fluxes can be detrimental to the
adhesion and performance of many floor coverings and may exceed various
flooring manufacturers’ usage criteria.
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Per the 2006 ACI Location Guideline, a vapor barrier is required under concrete
floors when that floor is to receive moisture-sensitive floor covering and/or
adhesives, or the room above that floor has humidity control.
Therefore, in light of the several, potentially conflicting effects of the use vapor-
barriers, the owner and the architect and/or contractor should weigh the
performance of the slab and appropriate flooring products in light of the intended
building use, etc., during the floor system design process and the selection of
flooring materials. Use of a plastic vapor-barrier membrane may be appropriate
for some building areas and not for others.
In the event a vapor barrier is utilized, it should consist of a minimum 15 mil
thickness, extruded polyolefin plastic (no recycled content or woven materials),
maintain a permeance less than 0.01 perms per ASTM E-96 or ASTM F-1249,
and comply with ASTM E-1745 (Class “A”). Vapor barriers should be installed in
accordance with ASTM E-1643.
Polyethylene (“poly”) sheeting (even if 15 mils in thickness which polyethylene
sheeting commonly is not) does not meet the ASTM E-1745 criteria and is not
recommended for use as vapor barrier material. It can be easily torn and/or
punctured, does not possess necessary tensile strength, gets brittle, tends to
decompose over time, and has a relatively high permeance.
Construction Recommendations for Slab-on-Grade Floors
9) Loose, soft or otherwise unsuitable materials exposed on the prepared surface
between aggregate piers on which the floor slab will be cast should be excavated
and replaced with properly compacted fill.
10) Concrete floor slabs should be constructed and cured in accordance with
applicable industry standards and slab design specifications.
11) All plumbing lines should be carefully tested before operation. Where plumbing
lines enter through the floor, a positive bond break should be provided.
Structural Floors
Structural floors should be constructed to span above a well-ventilated crawl space. The
crawl space should be adequate to allow access and maintenance to utility piping.
Piping connections through the floor should allow for differential movement between the
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piping and the floor system. If a wooden structural floor system is used, particular care
should be taken to design and maintain the under-floor ventilation systems in order to
reduce potential deterioration of the wooden structural members.
A vapor barrier meeting ASTM E-1745 (Class “A”) should be considered for installation
below all structurally supported floors and if utilized, should be properly attached/sealed
to foundation walls/drilled piers above the void material. The sheet material should not
be attached to horizontal surfaces such that condensate might drain to wood or
corrodible metal surfaces.
Use of polyethylene (“poly”) sheeting as a vapor barrier is not recommended.
Polyethylene (“poly”) sheeting (even if 15 mils in thickness which polyethylene sheeting
commonly is not) does not meet the ASTM E-1745 criteria and is not recommended for
use as vapor barrier material. It can be easily torn and/or punctured, does not possess
the necessary tensile strength, gets brittle, tends to decompose over time, and has a
relatively high permeance.
New buildings generally lack ventilation due primarily to systematic efforts to construct
airtight, energy-efficient structures. Therefore, areas such as crawl spaces beneath
structural floors are typically areas of elevated humidity which never completely dry.
This condition can be aggravated in some locations by shallow groundwater or a
perched groundwater condition, which can result in, saturated soils within close proximity
of finished building pad grades. Persistently warm, humid conditions in the presence of
cellulose, which is the base material found in many typical construction products, creates
an ideal environment for the growth of fungi, molds, and mildew. Published data
suggest links between molds and negative health affects. Therefore, GROUND
recommends that crawl spaces beneath structural floors be provided with adequate,
positive active ventilation systems or other active mechanisms such as specially
designed HVAC systems (as well as properly constructed and maintained underdrains)
to reduce the potential for mold, fungus and mildew growth. Crawl spaces should be
inspected periodically so that remedial measures can be taken in a timely manner,
should mold, fungus or mildew be present and require removal.
The Owner must be willing to accept the risks of potential mold, fungus, and mildew
growth when electing to utilize a structural floor system. Additionally, the Contractor is
solely responsible for the construction means and methods, and any observation or
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testing performed by a representative of the Geotechnical Engineer during construction
does not relieve the Contractor of that responsibility.
Mold Growth Areas/Conditions for Growth for Structural Floors
1) Water damaged building materials or high moisture/humidity areas where cellulose-
containing materials are used:
i. Wallboard/Sheetrock
ii. MDF/OSB/Plywood
iii. Fibrous Ceiling Tiles
iv. Paper-backed Insulation
v. Jute-backed Carpet
vi. Hardwood Flooring
2) Condensation inside buildings from pipes, baths, heaters, and dryer vents
3) Relative humidity greater than 55%
4) Temperatures of 36 to 104 ºF.
5) “Wet” areas that do not dry out after 24 hours.
Mold does not require a light source in order to grow and can grow inside walls, behind
tubs/showers, under carpet and flooring undetected.
MECHANICAL ROOMS / MECHANICAL PADS
Often, slab-bearing mechanical rooms/mechanical equipment are incorporated into
projects. Our experience indicates these commonly are located as partially below-grade
or adjacent to the exterior of a structure. GROUND recommends these elements be
founded on the same type of foundation systems as the associated primary structure.
Furthermore, mechanical connections must allow for potential differential movements.
WATER-SOLUBLE SULFATES
The concentration of water-soluble sulfates measured in a selected sample retrieved
from the test holes was less than the detectable limit of 0.01 percent by weight (Table 1).
Such concentrations of soluble sulfates represent a ‘negligible’ environment for sulfate
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attack on concrete exposed to these materials. Degrees of attack are based on the
scale of 'negligible,' 'moderate,' 'severe' and 'very severe' as described in the “Design
and Control of Concrete Mixtures,” published by the Portland Cement Association
(PCA). The Colorado Department of Transportation (CDOT) utilizes a corresponding
scale with 4 classes of severity of sulfate exposure (Class 0 to Class 3) as described in
the published table below.
REQUIREMENTS TO PROTECT AGAINST DAMAGE TO
CONCRETE BY SULFATE ATTACK FROM EXTERNAL SOURCES OF SULFATE
Severity of
Sulfate
Exposure
Water-Soluble
Sulfate (SO4)
In Dry Soil
(%)
Sulfate (SO4)
In Water
(ppm)
Water
Cementitious
Ratio
(maximum)
Cementitious
Material
Requirements
Class 0 0.00 to 0.10 0 to 150 0.45 Class 0
Class 1 0.11 to 0.20 151 to 1500 0.45 Class 1
Class 2 0.21 to 2.00 1501 to 10,000 0.45 Class 2
Class 3 2.01 or greater 10,001 or greater 0.40 Class 3
Based on this data GROUND, makes no recommendation for use of a special, sulfate-
resistant cement in project concrete.
SOIL CORROSIVITY
The degree of risk for corrosion of metals in soils commonly is considered to be in two
categories: corrosion in undisturbed soils and corrosion in disturbed soils. The potential
for corrosion in undisturbed soil is generally low, regardless of soil types and conditions,
because it is limited by the amount of oxygen that is available to create an electrolytic
cell. In disturbed soils, the potential for corrosion typically is higher, but is strongly
affected by soil conditions for a variety of reasons but primarily soil chemistry.
A corrosivity analysis was performed to provide a general assessment of the potential for
corrosion of ferrous metals installed in contact with earth materials at the site, based on
the conditions existing at the time of GROUND’s evaluation. Soil chemistry and physical
property data including pH, oxidation-reduction (redox) potential, sulfides, and moisture
content were obtained. Test results are summarized on Table 1.
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Reduction-Oxidation: Testing indicated a red-ox potential of -55 millivolts. A low
potential typically creates a more corrosive environment.
Sulfide Reactivity: Testing indicated a result of “positive” in a sample of test soil. The
presence of sulfides in the alignment soils suggests a more corrosive environment.
Soil Resistivity: A sample of material retrieved from the test holes was tested for
resistivity in the in the laboratory, at the as-received moisture content, rather than in the
field. Resistivity varies inversely with temperature. Therefore, the laboratory
measurements were made at a controlled temperature. It should also be noted that
increases in moisture content will likely result in lower resistivity values.
A measurement of electrical resistivity indicated a value of 2,928 ohm-centimeters in a
sample of retrieved soil. The following table presents the relationship between resistivity
and a qualitative corrosivity rating4:
Corrosivity Ratings Based on Soil Resistivity
Soil Resistivity (ohm-cm)Corrosivity Rating
>20,000 Essentially non-corrosive
10,000 – 20,000 Mildly corrosive
5,000 – 10,000 Moderately corrosive
3,000 – 5,000 Corrosive
1,000 – 3,000 Highly corrosive
<1,000 Extremely corrosive
pH: Where pH is less than 4.0, soil serves as an electrolyte; the pH range of about 6.5
to 7.5 indicates soil conditions that are optimum for sulfate reduction. In the pH range
above 8.5, soils are generally high in dissolved salts, yielding a low soil resistivity5.
Testing indicated a pH value of approximately 8.21.
The American Water Works Association (AWWA) has developed a point system scale
used to predict corrosivity. The scale is intended for protection of ductile iron pipe but is
valuable for project steel selection. When the scale equals 10 points or higher,
4 ASM International, 2003, Corrosion: Fundamentals, Testing and Protection, ASM Handbook, Volume 13A.
5 American Water Works Association ANSI/AWWA C105/A21.5-05 Standard.
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protective measures for ductile iron pipe are recommended. The AWWA scale is
presented below. The soil characteristics refer to the conditions at and above pipe
installation depth.
Table A.1 Soil-test Evaluation3
Soil Characteristic / Value Points
Resistivity
<1,500 ohm-cm 10
1,500 to 1,800 ohm-cm 8
1,800 to 2,100 ohm-cm 5
2,100 to 2,500 ohm-cm 2
2,500 to 3,000 ohm-cm 1
>3,000 ohm-cm 0
pH
0 to 2.0 5
2.0 to 4.0 3
4.0 to 6.5 0
6.5 to 7.5 0 *
7.5 to 8.5 0
>8.5 3
Redox Potential
< 0 (negative values) 5
0 to +50 mV 4
+50 to +100 mV 3½
> +100 mV 0
Sulfide Content
Positive 3½
Trace 2
Negative 0
Moisture
Poor drainage, continuously wet 2
Fair drainage, generally moist 1
Good drainage, generally dry 0
* If sulfides are present and low or negative redox-potential results (< 50 mV) are
obtained, add three points for this range.
We anticipate that drainage at the site after construction will be good. Based on the
values obtained for the soil parameters, the overburden soils appear to comprise a
borderline corrosive environment for metals (up to 9.5 points).
If additional information or recommendations are needed regarding soil corrosivity,
GROUND recommends contacting the American Water Works Association or a
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Corrosion Engineer. It should be noted, however, that changes to the site conditions
during construction, such as the import of other soils, or the intended or unintended
introduction of off-site water, may alter corrosion potentials significantly.
LATERAL EARTH PRESSURES
Structures which are laterally supported can be expected to undergo only a limited
amount of deflection, i.e., an “at-rest” condition, should be designed to resist lateral earth
pressures computed on the basis of an equivalent fluid unit weight of 73 pounds per
cubic foot (pcf) where on-site materials are placed as backfill. The lateral earth
pressures may be computed using an equivalent fluid unit weight of 57 pcf, if select,
granular backfill, (meeting the criteria for CDOT Class 1 Structure Backfill) is used as
backfill.
Structures designed to deflect sufficiently to mobilize the full, active earth pressure
condition may be designed for an active lateral earth pressure computed on the basis of
an equivalent fluid unit weight of 51 pcf where the backfill consists of on-site materials,
or 35 pcf where select, granular backfill is used.
Passive earth pressures may be computed taking an allowable equivalent fluid unit
weight of 230 pcf to be characteristic of the on-site soils. The upper 1 foot of
embedment should be neglected for passive resistance, however. Sliding may be
evaluated using a sliding coefficient of 0.33 for the on-site soils.
The parameters recommended above assume well drained conditions behind foundation
walls based on a properly functioning wall drain system and a horizontal backfill surface.
Wall design should incorporate any upward sloping backfills, live loads such as
construction equipment, material stockpiles, etc., and other surcharge pressures. The
build-up of hydrostatic pressures behind a wall also will increase lateral earth pressures
on the walls.
The above parameters should be considered preliminary with regard to design of MSE
walls, etc., that are not part of building foundations. In the event that such retaining
walls are added once project design begins, retaining wall parameters should be
requested and the New Creation Church should realize that additional subsurface
exploration may be necessary.
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PROJECT EARTHWORK
The following information is for private improvements; public roadways or utilities should
be constructed in accordance with applicable municipal / agency standards.
General Considerations: Site grading should be performed as early as possible in the
construction sequence to allow settlement of fills and surcharged ground to be realized
to the greatest extent prior to subsequent construction.
Prior to earthwork construction, existing structures, vegetation and other deleterious
materials should be removed and disposed of off-site. Relic underground utilities should
be abandoned in accordance with applicable regulations, removed as necessary, and
properly capped.
Topsoil present on-site should not be incorporated into ordinary fills. Instead, topsoil
should be stockpiled during initial grading operations for placement in areas to be
landscaped or for other approved uses.
Existing Fill Soils: As previously mentioned man-made fill was encountered in the test
holes. The fill materials generally appeared suitable for reuse, however, actual contents
and composition of the man-made fill materials are not completely known; therefore,
some of the excavated man-made fill materials may not be suitable for replacement as
backfill. A geotechnical engineer should be retained during site excavations to observe
the excavated fill materials and provide recommendations for its suitability for reuse.
Use of Existing Native Soils: Overburden soils that are free of trash, organic material,
construction debris, and other deleterious materials are suitable, in general, for
placement as compacted fill. Organic materials should not be incorporated into project
fills.
Fragments of rock, cobbles, and inert construction debris (e.g., concrete or asphalt)
larger than 3 inches in maximum dimension will require special handling and/or
placement to be potentially incorporated into project fills. In general, such materials
should be placed as deeply as possible in the project fills. We anticipate cobbles and
boulders will likely be encountered. These oversize materials should be removed from
project fills or spread evenly throughout the fill section. The placement of large size
materials in such a configuration as to leave open spaces between individual clasts not
filled by surrounding and compacted soil should be avoided. Standard
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recommendations that likely will be generally applicable can be found in Section 203 of
the current CDOT Standard Specifications for Road and Bridge Construction.
Imported Fill Materials: If it is necessary to import material to the site as common fill,
the imported soils should be free of organic material, and other deleterious materials.
Imported material should consist of soils that have less than 60 percent passing
the No. 200 Sieve and should have a liquid limit of less than 25. We recommend
imported granular or structural fill consist of approved pit run, or CDOT Class 1 structure
backfill. Representative samples of the materials proposed for import should be tested
and approved by the Geotechnical Engineer prior to transport to the site.
Fill Platform Preparation: Prior to filling, the top 8 to 12 inches of in-place materials on
which fill soils will be placed should be scarified, moisture conditioned and properly
compacted in accordance with the recommendations below to provide a uniform base for
fill placement. If over-excavation is to be performed, then these recommendations for
subgrade preparation are for the subgrade below the bottom of the specified over-
excavation depth.
If surfaces to receive fill expose loose, wet, soft or otherwise deleterious material,
additional material should be excavated, or other measures taken to establish a firm
platform for filling. The surfaces to receive fill must be effectively stable prior to
placement of fill.
Fill Placement: Fill materials should be thoroughly mixed to achieve uniform moisture
contents, placed in uniform lifts not exceeding 8 inches in loose thickness, and properly
compacted.
We recommend soils be compacted to 95 or more percent of the maximum standard
Proctor dry density at moisture contents from 2 percent below to 2 percent above the
optimum moisture content as determined by ASTM D698.
No fill materials should be placed, worked, rolled while they are frozen, thawing, or
during poor/inclement weather conditions.
Care should be taken with regard to achieving and maintaining proper moisture contents
during placement and compaction. Materials that are not properly moisture conditioned
may exhibit significant pumping, rutting, and deflection at moisture contents near
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optimum and above. The contractor should be prepared to handle soils of this type,
including the use of chemical stabilization, if necessary.
Compaction areas should be kept separate, and no lift should be covered by another
until relative compaction and moisture content within the recommended ranges are
obtained.
Use of Squeegee: Relatively uniformly graded fine gravel or coarse sand, i.e.,
“squeegee,” or similar materials commonly are proposed for backfilling foundation
excavations, utility trenches (excluding approved pipe bedding), and other areas where
employing compaction equipment is difficult. In general, GROUND does not recommend
this procedure for the following reasons:
Although commonly considered “self compacting,” uniformly graded granular materials
require densification after placement, typically by vibration. The equipment to densify
these materials is not available on many job-sites.
Even when properly densified, uniformly graded granular materials are permeable and
allow water to reach and collect in the lower portions of the excavations backfilled with
those materials. This leads to wetting of the underlying soils and resultant potential loss
of bearing support as well as increased local heave or settlement.
GROUND recommends that wherever possible, excavations be backfilled with approved,
on-site soils placed as properly compacted fill. Where this is not feasible, use of
“Controlled Low Strength Material” (CLSM), i.e., a lean, sand-cement slurry (“flowable
fill”) or a similar material for backfilling should be considered.
Where “squeegee” or similar materials are proposed for use by the contractor, the
design team should be notified by means of a Request for Information (RFI), so that the
proposed use can be considered on a case-by-case basis. Where “squeegee” meets
the project requirements for pipe bedding material, however, it is acceptable for that use.
Settlement: will occur in filled ground, typically on the order of 1 to 2 percent of the fill
depth. If fill placement is performed properly and is tightly controlled, in GROUND’s
experience the majority of that settlement will typically take place during earthwork
construction, provided the contractor achieves the compaction levels recommended
herein. The remaining potential settlements likely will take several months or longer to
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be realized, and may be exacerbated if these fills are subjected to changes in moisture
content.
Cut and Filled Slopes: We recommend permanent site slopes supported by on-site
soils up to 20 feet in height be constructed no steeper than 3 : 1 (horizontal : vertical).
Minor raveling or surficial sloughing should be anticipated on slopes cut at this angle
until vegetation is well re-established. Surface drainage should be designed to direct
water away from slope faces.
Soft and Wet Subgrade Conditions: The following recommendations should be
considered where soft, wet, and unstable subgrade conditions are encountered in areas
on which fill will be placed:
1) Cement treating or chemical stabilization may be performed.
2) Pockets of weak or pumping soils can be excavated and replaced with clean,
coarse, aggregate (e.g., crushed rock or “pit run” materials) or road base, or
stabilized by “crowding” the aggregates into the subgrade. The depth of
excavation and replacement likely will be 1 to 2 feet or more to provide a stable
surface. The use of recycled concrete aggregate may be a cost effective
material in this application.
3) Geo-textile or geo-grid (e.g., Mirafi® HP370 / Tensar® BX 1100 or equivalent) can
be placed below a minimum of 8 inches of removed soil. Soil or aggregate
placed on top of the geosynthetics to achieve subgrade elevations should be
placed on the drier side of the moisture content specification and well
compacted. Stabilization geo-textile / geo-grid should be placed and lapped in
accordance with the manufacturer’s recommendations.
We recommend a test section be performed to adjust the stabilization procedure as
necessary to achieve subgrades capable of passing proof-rolls prior to stabilizing large
areas.
EXCAVATION CONSIDERATIONS
The test holes for the subsurface exploration were excavated to the depths indicated by
means of truck-mounted, flight auger drilling equipment. As previously discussed,
practical drill rig refusal was encountered in the underyling gravels. However, we
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anticipate no significant excavation difficulties in the majority of the site for shallow
excavations with conventional heavy-duty excavation equipment in good working
condition.
We recommend that temporary, un-shored excavation slopes up to 20 feet in height be
cut no steeper than 1.5 : 1 (horizontal : vertical) in the on-site soils in the absence of
seepage. Sloughing on the slope faces should be anticipated at this angle. Local
conditions encountered during construction, such as groundwater seepage and loose
sand, will require flatter slopes. Stockpiling of materials should not be permitted closer
to the tops of temporary slopes than 5 feet or a distance equal to the depth of the
excavation, whichever is greater.
Should site constraints prohibit the use of the recommended slope angles, temporary
shoring should be used. The shoring should be designed to resist the lateral earth
pressure exerted by building, traffic, equipment, and stockpiles. GROUND can provide
shoring design upon request.
Groundwater was not encountered at the time of drilling to the depths explored.
Therefore, groundwater is not anticipated to be a significant factor for shallow
earthworks during construction of this project. If seepage or groundwater is encountered
in shallow project excavations, slopes should be flattened as necessary to maintain
stability and/or excavation should be dewatered.
Good surface drainage should be provided around temporary excavation slopes to direct
surface runoff away from the slope faces. A properly designed drainage swale should
be provided at the top of the excavations. In no case should water be allowed to pond at
the site. Slopes should also be protected against erosion. Erosion along the slopes will
result in sloughing and could lead to a slope failure.
Excavations in which personnel will be working must comply with all OSHA Standards
and Regulations. Project excavations and shoring should be observed regularly
throughout construction operations. The Contractor’s “responsible person” should
evaluate the soil exposed in the excavations as part of the Contractor’s safety
procedures. GROUND has provided the information above solely as a service to the
New Creation Church, and is not assuming responsibility for construction site safety or
the Contractor’s activities.
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UTILITY PIPE INSTALLATION AND BACKFILLING
Pipe Support: The bearing capacity of the site soils appeared adequate, in general, for
support of the proposed underground utilities. The utilities are generally less dense than
the soils which will be displaced for installation. Therefore, GROUND anticipates no
significant pipe settlements from loading in these materials where properly bedded and
where a firm platform for fill placement is present.
Excavation bottoms may expose soft, loose or otherwise deleterious materials, including
debris. Firm materials may be disturbed by the excavation process. All such unsuitable
materials should be excavated and replaced with properly compacted fill. Areas allowed
to pond water will require excavation and replacement with properly compacted fill. The
contractor should take particular care to ensure adequate support near pipe joints which
are less tolerant of extensional strains.
Where thrust blocks are needed, they may be designed for an allowable passive soil
pressure of 230 psf per foot of embedment. Sliding friction at the bottom of thrust blocks
may be taken as 0.33 times the vertical dead load.
Trench Backfilling: Some settlement of compacted soil trench backfill materials should
be anticipated, even where all the backfill is placed and compacted correctly. Typical
settlements are on the order of 1 to 2 percent of fill thickness. However, the need to
compact to the lowest portion of the backfill must be balanced against the need to
protect the pipe from damage from the compaction process. Some thickness of backfill
may need to be placed at compaction levels lower than recommended or specified (or
smaller compaction equipment used together with thinner lifts) to avoid damaging the
pipe. Protecting the pipe in this manner can result in somewhat greater surface
settlements. Therefore, although other alternatives may be available, the following
options are presented for consideration:
Controlled Low Strength Material: Because of these limitations, we recommend
backfilling the entire depth of the trench (both bedding and common backfill zones) with
“controlled low strength material” (CLSM), i.e., a lean, sand-cement slurry, “flowable fill,”
or similar material along all trench alignment reaches with low tolerances for surface
settlements.
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We recommend that CLSM used as pipe bedding and trench backfill exhibit a 28-day
unconfined compressive strength between 50 to 200 psi so that re-excavation is not
unusually difficult.
Placement of the CLSM in several lifts or other measures likely will be necessary to
avoid ‘floating’ the pipe. Measures also should be taken to maintain pipe alignment
during CLSM placement.
Compacted Soil Backfilling: Where compacted soil backfilling is employed, using the
site soils or similar materials as backfill, the risk of backfill settlements entailed in the
selection of this higher risk alternative must be anticipated and accepted by the
Client/Owner.
We anticipate that the on-site soils excavated from trenches will be suitable, in general,
for use as common trench backfill within the above-described limitations. Backfill soils
should be free of vegetation, organic debris and other deleterious materials. Fragments
of rock, cobbles, and inert construction debris (e.g., concrete or asphalt) coarser than 3
inches in maximum dimension should not be incorporated into trench backfills.
If it is necessary to import material for use as backfill, the imported soils should be free
of vegetation, organic debris, and other deleterious materials. Imported material should
consist of relatively impervious soils that have less than 50 percent passing the No. 200
Sieve and should have a plasticity index of less than 15. Representative samples of the
materials proposed for import should be approved prior to transport to the site.
Soils placed for compaction as trench backfill should be conditioned to a relatively
uniform moisture content, placed and compacted in accordance with the
recommendations in the Project Earthwork section of this report.
Pipe Bedding: Pipe bedding materials, placement and compaction should meet the
specifications of the pipe manufacturer and applicable municipal standards. Bedding
should be brought up uniformly on both sides of the pipe to reduce differential loadings.
As discussed above, we recommend the use of CLSM or similar material in lieu of
granular bedding and compacted soil backfill where the tolerance for surface settlement
is low. (Placement of CLSM as bedding to at least 12 inches above the pipe can protect
the pipe and assist construction of a well-compacted conventional backfill, although
possibly at an increased cost relative to the use of conventional bedding.)
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If a granular bedding material is specified, GROUND recommends that with regard to
potential migration of fines into the pipe bedding, design and installation follow ASTM
D2321. If the granular bedding does not meet filter criteria for the enclosing soils, then
non-woven filter fabric (e.g., Mirafi® 140N, or the equivalent) should be placed around
the bedding to reduce migration of fines into the bedding which can result in severe,
local surface settlements. Where this protection is not provided, settlements can
develop/continue several months or years after completion of the project. In addition,
clay or concrete cut-off walls should be installed to interrupt the granular bedding section
to reduce the rates and volumes of water transmitted along the utility alignments which
can contribute to migration of fines and settlements.
If granular bedding is specified, the contractor should anticipate that significant volumes
of on-site soils may not be suitable for that use. Materials proposed for use as pipe
bedding should be tested by a geotechnical engineer for suitability prior to use.
Imported materials should be tested and approved by a geotechnical engineer prior to
transport to the site.
Other Considerations: Because of the potential for settlements to result in significant,
extensional strains to utility pipes, all utility pipes should be provided with restrained
joints to reduce the potential for failure at joints. Connections to the building or other
structures on deep foundations should be flexible and easily replaced or adjusted. Non-
pressurized lines should be evaluated periodically for deformations such as pipe ‘bellies’
that would impair their efficiency, and appropriate repairs made. Maintenance plans
should anticipate greater than typical utility line maintenance and replacement.
SURFACE DRAINAGE
The following drainage measures are recommended for design, construction, and should
be maintained at all times after the project has been completed:
1) Wetting or drying of the foundation excavations, subgrade soils, and underslab
areas should be avoided during and after construction as well as throughout the
improvements’ design life. Permitting increases/variations in moisture to the
adjacent or supporting soils may result in a decrease in bearing capacity and an
increase in volume change of the underlying soils and/or differential movement.
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2) Positive surface drainage measures should be provided and maintained to
reduce water infiltration into foundation soils. The ground surface surrounding
the exterior of each building should be sloped to drain away from the foundation
in all directions. We recommend a minimum slope of 12 inches in the first 10 feet
in the areas not covered with pavement or concrete slabs, or a minimum 3
percent in the first 10 feet in the areas covered with pavement or concrete slabs.
Reducing the slopes to comply with ADA requirements may be necessary but
may result in an increased potential for moisture infiltration and subsequent
volume change of the underling soils. In no case should water be allowed to
pond near or adjacent to foundation elements. However, if positive surface
drainage is implemented and maintained directing moisture away from the
building, lesser slopes can be utilized. In no case should water be allowed to
pond near or adjacent to foundation elements.
3) On some sites it is common to have slopes descending toward buildings. Such
slopes can be created during grading even on comparatively flat sites. In such
cases, even where the recommendation above regarding slopes adjacent to the
building is followed, water may flow to and beneath the building with resultant
additional post-construction movements. Where the final site configuration
includes graded or retained slopes descending toward the building or flatwork,
interceptor drains should be installed between the building and the slope. In
addition, where irrigation is applied on or above slopes, drainage structures
commonly are needed near the toe-of-slope to prevent on-going or recurrent wet
conditions.
4) In no case should water be permitted to pond adjacent to or on sidewalks,
hardscaping, or other improvements as well as utility trench alignments, which
are likely to be adversely affected by moisture-volume changes in the underlying
soils or flow of infiltrating water.
5) Roof downspouts and drains should discharge well beyond the perimeters of the
structure foundations (minimum 10 feet), or be provided with positive conveyance
off-site for collected waters.
6) Vegetation that may require watering should ideally be located 10 or more feet
from building perimeters, flatwork, or other site improvements. Even so, we
understand that some municipalities and developments have certain
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requirements for landscaping near the building. Therefore, less than 10 feet is
acceptable provided that positive, effective surface drainage is initially
implemented and maintained throughout the life of the facility. Irrigation sprinkler
heads should be deployed so that applied water is not introduced near or into
foundation/subgrade soils. The area surrounding the perimeter of the building
should be constructed so that the surface drains away from the structure.
Additionally, it is very important that landscape maintenance is performed such
that the amount of moisture is strictly controlled so that the quantity of moisture
applied is limited to that which is necessary to sustain the vegetation; in no case
should saturated or marshy conditions be allowed to occur near any of the site
improvements (including throughout the landscaped islands in parking areas).
7) Use of drip irrigation systems can be beneficial for reducing over-spray beyond
planters. Drip irrigation can also be beneficial for reducing the amounts of water
introduced to foundation/subgrade soils, but only if the total volumes of applied
water are controlled with regard to limiting that introduction. Controlling rates of
moisture increase in foundation/subgrade soils should take higher priority than
minimizing landscape plant losses.
8) Where plantings are desired within 10 feet of a building, GROUND recommends
that the plants be placed in water-tight planters, constructed either in-ground or
above-grade, to reduce moisture infiltration in the surrounding subgrade soils.
Planters should be provided with positive drainage and landscape underdrains.
Colorado Geological Survey – Special Publication 43 provides additional
guidelines for landscaping and reducing the amount of water that infiltrates into
the ground.
9) Plastic membranes should not be used to cover the ground surface adjacent to
foundation walls. Perforated “weed barrier” membranes that allow ready
evaporation from the underlying soils may be used.
SUBSURFACE DRAINAGE
Perimeter Underdrains: Below grade areas (if any) for the selected foundation system
should be protected by a perimeter underdrain system. Geotechnical recommendations
for a perimeter underdrain system are provided below. The actual components and
layout of the underdrain system should be designed by a civil engineer.
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1) An underdrain system for the building should consist of perforated PVC collection
pipe at least 4 inches in diameter, non-perforated PVC discharge pipe at least 4
inches in diameter, free-draining gravel, and filter fabric.
The free-draining gravel should contain less than 5 percent passing the No. 200
Sieve and more than 50 percent retained on the No. 4 Sieve, and have a
maximum particle size of 1 inch. Each collection pipe should be surrounded on
the sides and top only with 6 or more inches of free-draining gravel.
The gravel surrounding the collection pipe(s) should be wrapped with filter fabric
(MiraFi 140N® or the equivalent) to reduce the migration of fines into the drain
system.
2) The high point(s) for the collection pipe flow lines should be at least 6 inches
below the bottom of the grade beam (deep foundations) or footing (shallow
foundations). Drain trenches should not encroach within a 1 : 1 (Horizontal :
Vertical) slope from footings to avoid undermining the supporting materials. The
collection and discharge pipe for the underdrain system should be laid on a slope
of 2 percent or more.
3) Underdrain ‘clean-outs’ should be provided at regular intervals to facilitate
maintenance of the underdrains. In general, GROUND recommends that
cleanouts be placed at approximately 200-foot centers along the
system. Cleanouts also should be located at pipe elbows that entail angles
greater than 30 degrees.
4) The underdrain discharge pipes should be connected to one or more sumps from
which water can be removed by pumping, or to outlet(s) for gravity
discharge. We suggest that collected waters be discharged directly into the
storm sewer system, if possible.
The underdrain system should be tested by the contractor after installation and after
placement and compaction of the overlying backfill to verify that the systems function
properly.
If below-grade or partially below-grade structures such as short foundation walls,
elevator pits, etc., are included in the project, those structures should be damp-proofed
on their exterior sides and provided with similar, local underdrain systems. Spray-
applied waterproofing membranes, wall drain / drain board, and other systems may be
integral to the design, based on input from the structure engineer and/or architect.
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These systems should be evaluated in respect to performance of the perimeter
underdrain system.
PAVEMENT SECTIONS
A pavement section is a layered system designed to distribute concentrated traffic loads
to the subgrade. Performance of the pavement structure is directly related to the
physical properties of the subgrade soils and traffic loadings. The standard care of
practice in pavement design describes the recommended flexible pavement section as a
“20-year” design pavement: however, most flexible pavements will not remain in
satisfactory condition without routine maintenance and rehabilitation procedures
performed throughout the life of the pavement. Pavement designs for the private
pavements were developed in general accordance with the design guidelines and
procedures of the American Association of State Highway and Transportation Officials
(AASHTO).
Subgrade Materials: Based on the results of our field exploration and laboratory
testing, the potential pavement subgrade materials classify typically as A-4 soils in
accordance with the American Association of State Highway and Transportation Officials
(AASHTO) classification system.
For the site soils, an R-value of 32 was measured on a bulk sample collected from the
test holes and tested in our laboratory. An R-value of 32 correlates to an approximate
soil Resilient Modulus (MR) value of 6,500 psi. It is also important to note that significant
decreases in soil support have been observed as the moisture content increases above
the optimum. Pavements that are not properly drained may experience a loss of the soil
support and subsequent reduction in pavement life.
Anticipated Traffic: Specific traffic loadings were not available at the time of this report
preparation. Based on our experience with similar development, an equivalent 18-kip
daily load application (EDLA) value of 5 was assumed for parking stall areas. The EDLA
value of 5 was converted to an equivalent 18-kip single axle load (ESAL) value of 36,500
for a 20-year design life. An EDLA of 10, corresponding to an ESAL value of 73,000,
was assumed for ‘driveways and general parking’ such as entrances/exits, drive lanes,
and other areas subject to heavier traffic. An EDLA of 30, corresponding to an ESAL
value of 219,000, was assumed for heavy vehicle traffic loads such as trash collection
zones, loading docks, and other areas subject to heavier high turning stresses. If design
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traffic loadings differ significantly from these assumed values, GROUND should be
notified to re-evaluate the recommended pavement sections.
Pavement Sections: The soil R-Value and the assumed ESAL value were used to
determine the required design structural number for the project pavements. The
required structural number was then used to develop recommended pavement sections.
Pavement designs were based on the DARWin™ computer program that solves the
1993 AASHTO pavement design equations. A Reliability Level of 75 percent and a
terminal serviceability of 2.0 were utilized for design of the pavement sections. A
structural coefficient of 0.40 was used for hot bituminous asphalt and 0.12 was used for
aggregate base course. The minimum pavement sections recommended by GROUND
are tabulated below.
Recommended Minimum Pavement Sections
Pavement
Minimum Minimum Composite
Full Depth Asphalt Section
(Inches Hot Mix Asphalt)
(Inches Hot Mix Asphalt / inches
Aggregate Base Course)
Parking Lot (automobile) 5.0 3.0 / 6.0
Driveways and General
Parking 5.5 4.0 / 5.0
High Turning Stresses &
Heavy Traffic 6.0 (Portland Cement Concrete) / 4.0 (Aggregate Base Course)
We recommend that primary delivery truck routes such as the dock area, trash collection
area, as well as other pavement areas subjected to high turning stresses or heavy truck
traffic be provided with rigid pavements consisting of 6.0 or more inches of Portland
cement concrete.
Asphalt pavement should consist of a bituminous plant mix composed of a mixture of
aggregate and bituminous material. Asphalt mixture(s) should meet the requirements of
a job-mix formula established by a qualified Engineer.
Concrete pavements should consist of a plant mix composed of a mixture of aggregate,
Portland cement and appropriate admixtures meeting the requirements of a job-mix
formula established by a qualified engineer. Concrete should have a minimum modulus
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of rupture of third point loading of 650 psi. Normally, concrete with a 28-day compressive
strength of 4,500 psi should develop this modulus of rupture value. The concrete should
be air-entrained with approximately 6 percent air and should have a minimum cement
content of 6 sacks per cubic yard. Maximum allowable slump should be 4 inches.
In areas of repeated turning stresses we recommend that the concrete pavement joints
be fully tied or doweled. We suggest that civil design consider joint layout in accordance
with CDOT’s M Standards. Standard plans for placement of ties and dowels, etc.,
(CDOT M Standards) for concrete pavements can be found at the CDOT website:
http://www.dot.state.co.us/DesignSupport/
If composite flexible sections are placed, the aggregate base material should meet the
criteria of CDOT Class 6 aggregate base course. Base course should be and
compacted in accordance with the recommendations in the Project Earthwork section of
this report.
Subgrade Preparation: Shortly before placement of pavement, including aggregate
base, the exposed subgrade soils should be excavated and/or processed to a depth of 8
to 12 inches, mixed to achieve a uniform moisture content and then re-compacted in
accordance with the recommendations provided in the Project Earthwork section of this
report. Greater depths (i.e. 24 inches) of subgrade mitigation to reduce distress
associated with the overburden materials should be considered for enhanced
performance. Subgrade preparation should extend the full width of the pavement from
back-of-curb to back-of-curb or three feet beyond pavement edges where there is no
curb.
The contractor should be prepared either to dry the subgrade materials or moisten them,
as needed, prior to compaction. It may be difficult for the contractor to achieve and
maintain compaction in some on-site soils encountered without careful control of water
contents. Likewise, some site soils likely will “pump” or deflect during compaction if
moisture levels are not carefully controlled. The Contractor should be prepared to
process and compact such soils to establish a stable platform for paving, including use
of chemical stabilization, if necessary.
Immediately prior to paving, the subgrade should be proof rolled with a heavily loaded,
pneumatic tired vehicle. Areas that show excessive deflection during proof rolling should
be excavated and replaced and/or stabilized. Areas allowed to pond prior to paving will
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require significant re-working prior to proof-rolling. Passing a proof roll is an additional
requirement, beyond placement and compaction of the subgrade soils in accordance
with the recommendations in this report. Some soils that are compacted in accordance
with the recommendations herein may not be stable under a proof roll, particularly at
moisture contents in the upper portion of the acceptable range.
Additional Observations: The collection and diversion of surface drainage away from
paved areas is extremely important to the satisfactory performance of the pavements.
The subsurface and surface drainage systems should be carefully designed to ensure
removal of the water from paved areas and subgrade soils. Allowing surface waters to
pond on pavements will cause premature pavement deterioration. Where topography,
site constraints, or other factors limit or preclude adequate surface drainage, pavements
should be provided with edge drains to reduce loss of subgrade support. The long-term
performance of the pavement also can be improved greatly by proper backfilling and
compaction behind curbs, gutters, and sidewalks so that ponding is not permitted and
water infiltration is reduced.
Landscape irrigation in planters adjacent to pavements and in “island” planters within
paved areas should be carefully controlled or differential settlement and/or rutting of the
nearby pavements will result. Drip irrigation systems are recommended for such
planters to reduce over-spray and water infiltration beyond the planters. Enclosing the
soil in the planters with plastic liners and providing them with positive drainage also will
reduce differential moisture increases in the surrounding subgrade soils. In our
experience, infiltration from planters adjacent to pavements is a principal source of
moisture increase beneath those pavements. This wetting of the subgrade soils from
infiltrating irrigation commonly leads to loss of subgrade support for the pavement with
resultant accelerating distress, loss of pavement life and increased maintenance costs.
This is particularly the case in the later stages of project construction after landscaping
has been emplaced but heavy construction traffic has not ended. Heavy vehicle traffic
over wetted subgrade commonly results in rutting and pushing of flexible pavements,
and cracking of rigid pavements. In relatively flat areas where design drainage gradients
necessarily are small, subgrade settlement can obstruct proper drainage and yield
increased infiltration, exaggerated distress, etc. (These considerations apply to project
flatwork, as well.)
Also, GROUND’s experience indicates that longitudinal cracking is common in asphalt-
pavements generally parallel to the interface between the asphalt and concrete
structures such as curbs, gutters or drain pans. This of this type is likely to occur even
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where the subgrade has been prepared properly and the asphalt has been compacted
properly. The use of a thickened base course or reinforced concrete pavement can
reduce this effect. GROUND should be contacted if these alternates are desired.
The design traffic loading does not include excess loading conditions imposed by heavy
construction vehicles. Consequently, heavily loaded concrete, lumber, and building
material trucks can have a detrimental effect on the pavement.
A pavement section cannot be anticipated to achieve its design life without regular
maintenance and rehabilitation. Maintenance and rehabilitation measures preserve,
rather than improve, the structural capacity of the pavement structure. Therefore,
GROUND recommends that an effective program of regular maintenance be developed
and implemented to seal cracks, repair distressed areas, and perform thin overlays
throughout the lives of the pavements. The greatest benefit of pavement overlaying will
be achieved by overlaying sound pavements that exhibit little or no distress.
Crack sealing should be performed at least annually and a fog seal/chip seal program
should be performed on the pavements every 3 to 4 years. After approximately 8 to 10
years after construction, patching, additional crack sealing, and asphalt overlay may be
required. Prior to overlays, it is important that all cracks be sealed with a flexible,
rubberized crack sealant in order to reduce the potential for propagation of the crack
through the overlay. If actual traffic loadings exceed the values used for development of
the pavement sections, however, pavement maintenance measures will be needed on
an accelerated schedule.
EXTERIOR FLATWORK
Proper design, drainage, construction and maintenance of the areas between individual
buildings and parking/driveway areas are critical to the satisfactory performance of the
project. Sidewalks, entranceway slabs and roofs, fountains, raised planters and other
highly visible improvements commonly are installed within these zones, and distress in
or near these improvements is common. Commonly, soil preparation in these areas
receives little attention because they fall between the building and pavement (which are
typically built with heavy equipment). Subsequent landscaping and hardscape
installation often is performed by multiple sub-contractors with light or hand equipment,
and over-excavation / soil processing is not performed. Therefore, GROUND
recommends that the design team, contractor, and pertinent subcontractors take
particular care with regard to proper subgrade preparation around the structure exteriors.
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Similar to slab-on-grade floors, exterior flatwork and other hardscaping placed on the
soils encountered on-site may experience post-construction movements due to volume
change of the subsurface soils. Both vertical and lateral soil movements can be
anticipated as the soils experience volume change as the moisture content varies.
Distress to rigid hardscaping likely will result. The following measures will help to reduce
damages to these improvements.
Ideally, subgrade soils beneath project sidewalks, paved entryways and patios, masonry
planters and short, decorative walls, and other hardscaping should be placed on the
same depth of properly compacted fill as discussed for slab-on-grade floors. Where this
is not practical, the owner should understand that additional risk, some of which may be
significant, will be inherent in these areas and movements will occur.
Provided the owner understands the risks identified above, we believe that subgrade
under exterior flatwork or other (non-building) site improvements could be processed
and/or excavated to a minimum depth of 12 inches, mixed to achieve a uniform moisture
content and then re-compacted in accordance with the recommendations provided in the
Project Earthwork section of this report. Greater depths (i.e. 24 inches) of subgrade
mitigation to reduce distress associated with the overburden materials should be
considered for enhanced performance, as discussed in the Geotechnical Considerations
for Design section. This should occur prior to placing any additional fill required to
achieve finished design grades. This processing depth will not eliminate potential
movements. The excavated soil should be replaced as properly moisture-conditioned
and compacted fill as outlined in the Project Earthwork section of this report. As stated
above, greater depths of moisture-density conditioning of the subgrade soils beyond the
above minimum will improve hardscape performance. Movement will occur, some of
which could be significant, especially if sufficient surface drainage is not maintained.
Prior to placement of flatwork, a proof roll should be performed to identify areas that
exhibit instability and deflection. The soils in these areas should be removed and
replaced with properly compacted fill or stabilized.
In no case should exterior flatwork extend to under any portion of the building where
there is less than 2 inches of vertical clearance between the flatwork and any element of
the building. Exterior flatwork in contact with brick, rock facades, or any other element of
the building can cause damage to the structure if the flatwork experiences movement.
New Creation Church Preschool
Glenwood Springs, Colorado
Job No. 13-6017 GROUND Engineering Consultants, Inc. Page 45
As discussed in the Surface Drainage section of this report, proper drainage should be
maintained after completion of the project, and re-established as necessary. In no case
should water be allowed to pond on or near any of the site improvements or a reduction
in performance should be anticipated.
Concrete Scaling: Climatic conditions in the project area including relatively low
humidity, large temperature changes and repeated freeze – thaw cycles, make it likely
that project sidewalks and other exterior concrete will experience surficial scaling or
spalling. The likelihood of concrete scaling can be increased by poor workmanship
during construction, such as ‘over-finishing’ the surfaces. In addition, the use of de-icing
salts on exterior concrete flatwork, particularly during the first winter after construction,
will increase the likelihood of scaling. Even use of de-icing salts on nearby roadways,
from where vehicle traffic can transfer them to newly placed concrete, can be sufficient
to induce scaling. Typical quality control / quality assurance tests that are performed
during construction for concrete strength, air content, etc., do not provide information
with regard to the properties and conditions that give rise to scaling.
In GROUND’s experience the measures below can be beneficial for reducing the
likelihood of concrete scaling. It must be understood, however, that because of the other
factors involved, including weather conditions and workmanship, surface damage to
concrete can develop, even where all of these measures were followed.
1) Maintaining a maximum water/cement ratio of 0.45 by weight for exterior
concrete mixes.
2) Include Type F fly ash in exterior concrete mixes as 20 percent of the
cementitious material.
3) Specify a minimum, 28-day, compressive strength of 4,500 psi for all exterior
concrete.
4) Include ‘fibermesh’ in the concrete mix also may be beneficial for reducing
surficial scaling.
5) Cure the concrete effectively at uniform temperature and humidity. This
commonly will require fogging, blanketing and/or tenting, depending on the
weather conditions. As long as 3 to 4 weeks of curing may be required, and
possibly more.
New Creation Church Preschool
Glenwood Springs, Colorado
Job No. 13-6017 GROUND Engineering Consultants, Inc. Page 46
6) Avoid placement of concrete during cold weather so that it is not exposed to
freeze-thaw cycling before it is fully cured.
7) Avoid the use of de-icing salts on given reaches of flatwork through the first
winter after construction.
Frost and Ice Considerations Nearly all soils other than relatively coarse, clean,
granular materials are susceptible to loss of density if allowed to become saturated and
exposed to freezing temperatures and repeated freeze – thaw cycling. The formation of
ice in the underlying soils can result in heaving of pavements, flatwork and other
hardscaping (“ice jacking”) in sustained cold weather of 2 inches or more. This heaving
can develop relatively rapidly. A portion of this movement typically is recovered when
the soils thaw, but due to loss of soil density some degree of displacement typically will
remain. This can result even where the subgrade soils were prepared properly.
Where hardscape movements are a design concern, e.g., at doorways, replacement of
the subgrade soils with 3 or more feet of clean, coarse sand or gravel with a drain should
be considered, or the element supported on foundations similar to the building and
spanning over a void. Detailed recommendations in this regard can be provided upon
request. It should be noted that where such open graded granular soils are placed,
water can infiltrate and accumulate in the subsurface relatively easily, which can lead to
increased settlement or heave from factors unrelated to ice formation. The relative risks
from these soil conditions should be taken into consideration where ice jacking is a
concern. GROUND will be available to discuss these concerns upon request.
CLOSURE
Geotechnical Review: The author of this report should be retained to review project
plans and specifications to evaluate whether they comply with the intent of the
recommendations in this report. The review should be requested in writing.
The geotechnical recommendations presented in this report are contingent upon
observation and testing of project earthworks by representatives of GROUND. If another
geotechnical consultant is selected to provide materials testing, then that consultant
must assume all responsibility for the geotechnical aspects of the project by concurring
in writing with the recommendations in this report, or by providing alternative
recommendations.
New Creation Church Preschool
Glenwood Springs, Colorado
Job No. 13-6017 GROUND Engineering Consultants, Inc. Page 47
Materials Testing: The client should consider retaining a Geotechnical Engineer to
perform materials testing during construction. The performance of such testing or lack
thereof, in no way alleviates the burden of the contractor or subcontractor from
constructing in a manner that conforms to applicable project documents and industry
standards. The contractor or pertinent subcontractor is ultimately responsible for
managing the quality of their work; furthermore, testing by the geotechnical engineer
does not preclude the contractor from obtaining or providing whatever services they
deem necessary to complete the project in accordance with applicable documents.
Limitations: This report has been prepared for Colorado River Engineering as it
pertains to the proposed school facility as described herein. It may not contain sufficient
information for other parties or other purposes. The owner or any prospective buyer
relying upon this report must be made aware of and must agree to the terms, conditions,
and liability limitations outlined in the proposal.
In addition, GROUND has assumed that project construction will commence by Winter
2013. Any changes in project plans or schedule should be brought to the attention of a
geotechnical engineer, in order that the geotechnical recommendations may be re-
evaluated and, as necessary, modified.
The geotechnical conclusions and recommendations in this report relied upon
subsurface exploration at a limited number of exploration points, as shown in Figure 1,
as well as the means and methods described herein. Subsurface conditions were
interpolated between and extrapolated beyond these locations. It is not possible to
guarantee the subsurface conditions are as indicated in this report. Actual conditions
exposed during construction may differ from those encountered during site exploration.
If during construction, surface, soil, bedrock, or groundwater conditions appear to be at
variance with those described herein, a geotechnical engineer should be advised at
once, so that re-evaluation of the recommendations may be made in a timely manner. In
addition, a contractor who relies upon this report for development of his scope of work or
cost estimates may find the geotechnical information in this report to be inadequate for
his purposes or find the geotechnical conditions described herein to be at variance with
his experience in the greater project area. The contractor is responsible for obtaining
the additional geotechnical information that is necessary to develop his workscope and
cost estimates with sufficient precision. This includes current depths to groundwater,
etc.
New Creation Church Preschool
Glenwood Springs, Colorado
Job No. 13-6017 GROUND Engineering Consultants, Inc. Page 48
The materials present on-site are stable at their natural moisture content, but may
change volume or lose bearing capacity or stability with changes in moisture content.
Performance of the proposed structure and pavement will depend on implementation of
the recommendations in this report and on proper maintenance after construction is
completed. Because water is a significant cause of volume change in soils and rock,
allowing moisture infiltration may result in movements, some of which will exceed
estimates provided herein and should therefore be expected by the owner.
This report was prepared in accordance with generally accepted soil and foundation
engineering practice in the project area at the date of preparation. GROUND makes no
warranties, either expressed or implied, as to the professional data, opinions or
recommendations contained herein. Because of numerous considerations that are
beyond GROUND’s control, the economic or technical performance of the project cannot
be guaranteed in any respect.
ALL DEVELOPMENT CONTAINS INHERENT RISKS. It is important that ALL aspects
of this report, as well as the estimated performance (and limitations with any such
estimations) of proposed project improvements are understood by the Client, Project
Owner (if different), or properly conveyed to any future owner(s). Utilizing these
recommendations for planning, design, and/or construction constitutes understanding
and acceptance of recommendations or information provided herein, potential risks,
associated improvement performance, as well as the limitations inherent within such
estimations. If any information referred to herein is not well understood, it is imperative
for the Owner or anyone using this report to contact the author or a company principal
immediately.
Sincerely,
GROUND Engineering Consultants, Inc.
Carl Henderson, P.E. Reviewed by James B. Kowalsky, P.E.
Indicates test hole number and approximate location.
(Not to Scale)
LOCATION OF TEST HOLES6017SITE.DWG
CADFILE NAME:JOB NO.:
13-6017
FIGURE:
1
1
P-2
P-1
4
3 2
1
Depth - feet
Test Hole
0
1
Test Hole
2
Test Hole
3
Test Hole
4
Test Hole
P-1
JOB NO.:
CADFILE NAME:
FIGURE:213-6017
LOGS OF TEST HOLES
6017LOG01.DWG
5
10
15
20
25
6/12
50/9
50/6
11/12
9/12
50/5
20/12
10/12
16/12
12/12
14/12
50/3
5/12
5/12
3" RB3" RB
Depth - feet
Test Hole
0
P-2
JOB NO.:
CADFILE NAME:
FIGURE:313-6017
LOGS OF TEST HOLES
6017LOG02.DWG
5
10
15
20
25
3" RB
5/12
5/12
JOB NO.:
CADFILE NAME:
FIGURE:
LEGEND AND NOTES
13-6017
6017LEG.DWG
4
LEGEND:
7) The material descriptions on this legend are for general classification purposes only.
See the full text of this report for descriptions of the site materials and related recommendations.
Road Base
Drive sample blow count, indicates 23 blows of a 140-pound hammer falling 30 inches were
required to drive the sampler 12 inches.
23/12
Drive sample, 2-inch I.D. California liner sample
Small disturbed sample
Practical Rig Refusal
with 4-inch diameter continuous flight augers.
4) The test hole locations and elevations should be considered accurate only to the degree
3) Elevations of the test holes were not measured and the logs of the test holes are drawn to
2) Locations of the test holes were measured approximately by pacing from features shown on
boundaries between material types and the transitions may be gradual.
5) The lines between materials shown on the test hole logs represent the approximate
implied by the method used.
the site plan provided.
1) Test holes were drilled on 07/25 and 07/26/2013
depth.
NOTES:
6) Groundwater was not encountered during drilling. Groundwater levels can fluctuate seasonally
and in response to landscape irrigation.
Large disturbed sample.
Fill:
Gravel:
Silt/Clay and Sand:
Generally consisted of silt/clay and sand, fine to coarse grained sand, slightly moist to moist, low
plasticity, loose to medium dense or medium stiff to very stiff, reddish.
Interlayered with fine to coarse grained sand, slightly moist to moist, low
plasticity, loose to medium dense or medium stiff to very stiff, reddish. May
contain scattered cobbles and boulders.
Slightly silty/clayey and sandy to silty/clayey and sandy, fine to coarse grained
sand, fine to coarse gravel and cobbles and likely boulders, slightly moist to
moist, nil to low plasticity, very dense, reddish brown to brown.
SIEVE ANALYSIS: ASTM C 136 with C 117 or D 1140
HYDROMETER ANALYSIS: ASTM D 422
Sieve Openings
U.S. Standard Sieves
Time Readings
1009080706050403020100
DIAMETER OF PARTICLE IN MILLIMETERS
PERCENT PASSING
0
102030405060708090
100
PERCENT RETAINED
3"
1.5"
0.75"
0.5"
0.37"
#4
#10
#16
#40
#50
#100
#200
Coarse
Fine
Coarse
Medium
Fine
SILT
CLAY
GRAVEL
SAND
COBBLES
100
5
2
10.0
1.0
0.1
0.01
0.001
LL = PI =
#8
#30
5
2
5
2
5
2
5
2
2"
1"
GRADATION TEST RESULTSCADFILE NAME:JOB NO.:
FIGURE:
13-6017
5
6017GRAD01.DWG
Sample Description:
Gravel: % Sand: % Silt and Clay: %
Silt/Clay and Sand
48 41 1122 4
Sample Location:
Test Hole 1 at 10 feet
SIEVE ANALYSIS: ASTM C 136 with C 117 or D 1140
HYDROMETER ANALYSIS: ASTM D 422
Sieve Openings
U.S. Standard Sieves
Time Readings
1009080706050403020100
DIAMETER OF PARTICLE IN MILLIMETERS
PERCENT PASSING
0
102030405060708090
100
PERCENT RETAINED
3"
1.5"
0.75"
0.5"
0.37"
#4
#10
#16
#40
#50
#100
#200
Coarse
Fine
Coarse
Medium
Fine
SILT
CLAY
GRAVEL
SAND
COBBLES
100
5
2
10.0
1.0
0.1
0.01
0.001
LL = PI =
#8
#30
5
2
5
2
5
2
5
2
2"
1"
GRADATION TEST RESULTSCADFILE NAME:JOB NO.:
FIGURE:
13-6017
6
6017GRAD02.DWG
Sample Description:
Gravel: % Sand: % Silt and Clay: %
very Sandy SILT and CLAY
3 36 6122 4
Sample Location:
Test Hole P-1 and P-2 at 0-5 feet
CONSOLIDATION - % - SWELL
APPLIED PRESSURE - ksf
0.11.010 100
Moisture Content
Dry Unit Weight
Sample of:
From:
= pcf
= percent
SWELL-CONSOLIDATION
TEST RESULTS
CADFILE NAME:
JOB NO.:FIGURE:
10
0
2
4
6
8
2
4
6
8
with Constant Pressure
Consolidation
Upon Wetting
SC-SM
Test Hole 1 at 5 ft
7.2
100.6
13-60177
6017SWL01.DWG
CONSOLIDATION - % - SWELL
APPLIED PRESSURE - ksf
0.11.010 100
Moisture Content
Dry Unit Weight
Sample of:
From:
= pcf
= percent
SWELL-CONSOLIDATION
TEST RESULTS
CADFILE NAME:
JOB NO.:FIGURE:
10
0
2
4
6
8
2
4
6
8
with Constant Pressure
Consolidation
Upon Wetting
SC-SM
Test Hole 4 at 8 ft
3.4
92.7
13-60178
6017SWL02.DWG
CONSOLIDATION - % - SWELL
APPLIED PRESSURE - ksf
0.11.010 100
0
1
2
3
1
2
3
4
4
Moisture Content
Dry Unit Weight
Sample of:
From:
= pcf
= percent
SWELL-CONSOLIDATION
TEST RESULTS
CADFILE NAME:
JOB NO.:FIGURE:
5
with Constant Pressure
Consolidation
Upon Wetting
CL-ML
Test Hole P-1 at 2 ft
12.2
92.7
13-60179
6017SWL03.DWG
Dry density, pcf
70
80
90
100
110
120
130
140
Water content, %
0510152025303540
100% SATURATION CURVES
FOR SPEC. GRAV. EQUAL TO:
2.8
2.7
2.6
Test specification:
ASTM D 698-07 Method A Standard
13-60177/26/13
New Creation Church Preschool
Colorado River Engineering
A-4(0)CL-ML
224
61.3 %
Maximum dry density = 116.1 pcf
Optimum moisture = 12.2 %
10
Project No.:Date:
Project:
Client:
Location: P1-P2 0-5'
Remarks:
MATERIAL DESCRIPTION
Description:
Classifications -USCS:AASHTO:
Nat. Moist. =Sp.G. =
Liquid Limit =Plasticity Index =
% < No.200 =
TEST RESULTS
Figure
GROUND ENGINEERING CONSULTANTS, INC.
COMPACTION TEST REPORT
Location:
P-1 and P-2; 0-5 feet
Sample ID No.
GROUND
ENGINEERING CONSULTANTS
123Job No.
13-6017
R-VALUE TEST RESULT
16.218.019.2
ASTM D 2844-07e1
512617Soil Type:
very Sandy Silt/Clay
630216143***Material will be considered "unstable" if optimum moisture is greaterthan 300 psi exudation moisture and the decrease in R-value from 400 psi to 300 psi exudation pressure is 10 or greater
Test SpecimenMoisture (%)R-ValueExudation Pressure
0102030405060708090100
0
100
200
300
400
500
600
700
800
R‐Value
Exudation Pressure
(PSI)
R-Value32 at
300 PSI
Figure 11
TABLE 1
SUMMARY OF LABORATORY TEST RESULTSSample LocationNaturalNaturalPercentAtterberg LimitsPercentWaterRedoxSulfidesUSCSAASHTO
TestMoistureDryPassingLiquidPlasticitySwellSolublepHPotentialContentResistivityClassifi-Classifi-Soil orHole
Depth
ContentDensityGravelSandNo. 200LimitIndex(
SurchargeSulfatescationcationBedrock Type
No.
(feet)(%)(pcf)(%)(%)
SievePressure)
(%)(mV)(ohm-cm)
(GI)
TH-157.2100.648204-5.5 (1ksf)SC-SMA-4(0)Silt/Clay and SandTH-1102.6SD484111224
GW-GCA-1-a(0)sl. Silty, Sandy, Gravel
TH-297.490.941204
SC-SMA-4(0)v. Silty/Clayey SandTH-335.2105.146205<0.018.21-55Positive2,928SC-SMA-4(0)Silt/Clay and SandTH-483.492.743204-6.0 (1ksf)SC-SMA-4(0)v. Silty/Clayey SandTH-4193.4106.235227
GW-GCA-1-a(0)Silty/Clayey, Sandy GravelP-1212.2101.567224-0.6 (0.2ksf)CL-MLA-4(0)Sandy Silt/ClayP-247.998.951215
CL-MLA-4(0)Silt/Clay and Sand
P-1, 20-5*12.2*116.133661224
CL-MLA-4(0)v. Sandy Silt/Clay*Indicates Opt. WC and Max Dry Density of a Bulk Sample, SD = Sample Disturbed, NV = Non-Viscous, NP = Non-PlasticJob No. 13
-6017
Gradation
APPENDIX A
PAVEMENT SECTION CALCULATIONS
Page 1
1993 AASHTO Pavement Design
DARWin Pavement Design and Analysis System
A Proprietary AASHTOWare
Computer Software Product
Network Administrator
Flexible Structural Design Module
New Creation Church Preschool
Job No. 13-6017
Parking Stalls
Full Depth Section
Flexible Structural Design
18-kip ESALs Over Initial Performance Period36,500
Initial Serviceability4.5
Terminal Serviceability2
Reliability Level75 %
Overall Standard Deviation0.44
Roadbed Soil Resilient Modulus6,500 psi
Stage Construction1
Calculated Design Structural Number1.87 in
Specified Layer Design
Layer
Material Description
Struct
Coef.
(Ai)
Drain
Coef.
(Mi)
Thickness
(Di)(in)
Width
(ft)
Calculated
SN (in)
1Asphalt0.415122.00
Total---5.00-2.00
Page 1
1993 AASHTO Pavement Design
DARWin Pavement Design and Analysis System
A Proprietary AASHTOWare
Computer Software Product
Network Administrator
Flexible Structural Design Module
New Creation Church Preschool
Job No. 13-6017
Parking Stalls
Composite Section
Flexible Structural Design
18-kip ESALs Over Initial Performance Period36,500
Initial Serviceability4.5
Terminal Serviceability2
Reliability Level75 %
Overall Standard Deviation0.44
Roadbed Soil Resilient Modulus6,500 psi
Stage Construction1
Calculated Design Structural Number1.87 in
Specified Layer Design
Layer
Material Description
Struct
Coef.
(Ai)
Drain
Coef.
(Mi)
Thickness
(Di)(in)
Width
(ft)
Calculated
SN (in)
1Asphalt0.413121.20
2Class 6 ABC0.1216120.72
Total---9.00-1.92
Page 1
1993 AASHTO Pavement Design
DARWin Pavement Design and Analysis System
A Proprietary AASHTOWare
Computer Software Product
Network Administrator
Flexible Structural Design Module
New Creation Church Preschool
Job No. 13-6017
General Parking Areas
Full Depth Section
Flexible Structural Design
18-kip ESALs Over Initial Performance Period73,000
Initial Serviceability4.5
Terminal Serviceability2
Reliability Level75 %
Overall Standard Deviation0.44
Roadbed Soil Resilient Modulus6,500 psi
Stage Construction1
Calculated Design Structural Number2.10 in
Specified Layer Design
Layer
Material Description
Struct
Coef.
(Ai)
Drain
Coef.
(Mi)
Thickness
(Di)(in)
Width
(ft)
Calculated
SN (in)
1Asphalt0.415.5122.20
Total---5.50-2.20
Page 1
1993 AASHTO Pavement Design
DARWin Pavement Design and Analysis System
A Proprietary AASHTOWare
Computer Software Product
Network Administrator
Flexible Structural Design Module
New Creation Church Preschool
Job No. 13-6017
General Parking Areas
Composite Section
Flexible Structural Design
18-kip ESALs Over Initial Performance Period73,000
Initial Serviceability4.5
Terminal Serviceability2
Reliability Level75 %
Overall Standard Deviation0.44
Roadbed Soil Resilient Modulus6,500 psi
Stage Construction1
Calculated Design Structural Number2.10 in
Specified Layer Design
Layer
Material Description
Struct
Coef.
(Ai)
Drain
Coef.
(Mi)
Thickness
(Di)(in)
Width
(ft)
Calculated
SN (in)
1Asphalt0.414121.60
2Class 6 ABC0.1215120.60
Total---9.00-2.20
Page 1
1993 AASHTO Pavement Design
DARWin Pavement Design and Analysis System
A Proprietary AASHTOWare
Computer Software Product
Network Administrator
Rigid Structural Design Module
New Creation Church Preschool
Job No. 13-3017
Heavy Traffic
PCCP Section
Rigid Structural Design
Pavement TypeJPCP
18-kip ESALs Over Initial Performance Period219,000
Initial Serviceability4.5
Terminal Serviceability2
28-day Mean PCC Modulus of Rupture650 psi
28-day Mean Elastic Modulus of Slab3,400,000 psi
Mean Effective k-value20 psi/in
Reliability Level75 %
Overall Standard Deviation0.34
Load Transfer Coefficient, J3.6
Overall Drainage Coefficient, Cd1
Calculated Design Thickness5.69 in
Effective Modulus of Subgrade Reaction
Period
Description
Roadbed Soil
Resilient
Modulus (psi)
Base Elastic
Modulus
(psi)
116,50020,000
223,50020,000
333,50020,000
446,50020,000
Base TypeClass 6
Base Thickness4 in
Depth to Bedrock18 ft
Projected Slab Thickness6 in
Loss of Support Category2.5
Effective Modulus of Subgrade Reaction20 psi/in
101A Airpark Dr., Unit 9, PO Box 464, Gypsum, CO 81637 Phone (970) 524-0720 Fax (970) 524-0721 www.groundeng.com
Office Locations: Englewood Commerce City Loveland Granby Gypsum Grand Junction Casper, WY
September 30, 2013
Subject: Supplemental Design Criteria and
Geotechnical Recommendations Addendum,
New Creation Church Preschool, Glenwood
Springs, Colorado
Job No. 13-6017
Mr. Greg Shaner, P.E.
Colorado River Engineering
136 East Third Street, Suite 101
Rifle, Colorado 81650
Dear Mr. Shaner:
GROUND Engineering Consultants, Inc. (GROUND) is pleased to present an addendum to our
August 23, 2013 geotechnical report containing supplemental design criteria and associated
geotechnical recommendations for the proposed Preschool to be constructed at the New
Creation Church facility located at 44761 Highway 6 & 24 in Glenwood Springs, Colorado.
Based on a September 25th, 2013 meeting with representatives from our office, CRE, and the
Owner present, we understand that a footing foundation would be preferred if movement
potentials could be reduced from those outlined in the August report. Options to realize this
were discussed at the meeting including the elimination of irrigation within the vicinity of the
Preschool as well as the provision of excellent surface and subsurface drainage.
Discussion
We anticipate a footing foundation is feasible in these circumstances, although such a
foundation type carries a higher risk of poor post-construction foundation performance than the
deep foundation alternatives outlined in the August report. The movement potentials in the
August report were based on a depth of moisture increase of approximately 10 feet below grade
beams, or roughly 13.5 feet from the ground surface. By eliminating irrigation in the vicinity of
the proposed Preschool and providing excellent surface and subsurface drainage, a shallower
depth of moisture increase appears achievable. To limit differential settlement from the sloping
gravel surface, subsurface moisture increases must be limited to within 10 feet of the ground
surface or about 6.5 feet from the bottom of footings. In this condition, settlements on the order
of 2.5 inches are still anticipated although they should be more uniform. To reduce these
settlements to the range of 1 inch, we recommend removal and re-compaction of the on-site
soils below footings and slab areas to a depth of 3.5 feet below footing bearing elevation. The
over-excavation should extend laterally at full thickness a minimum of 3.5 feet beyond the edges
of the footings. Scarification and fill section compaction should conform to the
recommendations in the Project Earthwork section of the August report.
NCC Preschool Addendum
Glenwood Springs, Colorado
Job No. 13-6017 GROUND Engineering Consultants, Inc. Page 2
Foundation
To use these recommendations, the Owner must accept the risk of post-construction foundation
movement associated with shallow foundation systems placed on the on-site soils. Utilizing the
above recommendations as well as other recommendations in this report, GROUND estimates
settlement will be on the order of approximately 1 inch. Actual movements may be more or
less.
The design and construction criteria presented below should be observed for a spread footing
foundation system. The recommendations should be considered when preparing project
documents and construction details. The precautions and recommendations provided below will
not prevent movement of the footings if the underlying materials are subjected to alternate
wetting and drying cycles. However, the recommended measures will tend to make the
movement more uniform, and reduce resultant damage if such movement occurs.
1) Footings bearing on 3.5 feet of on-site soil fill may be designed for an allowable bearing
pressure (Q) of 2,000 psf. The recommended allowable bearing pressure was based on
an assumption of drained conditions. If foundation materials are subjected to
fluctuations in moisture content, the effective bearing capacity may be reduced and
larger post-construction movements than those estimated above may result.
2) Footing excavation bottoms may expose loose, organic or otherwise deleterious
materials, including debris. Footing subgrade materials may be disturbed by the
excavation process. All such loose or unsuitable materials should be excavated and
replaced with properly compacted fill.
3) In order to reduce differential settlements between footings or along continuous footings,
footing loads should be as uniform as possible. Differentially loaded footings will settle
differentially. Similarly, differential fill thicknesses beneath footings will result in
increased differential settlements.
4) Spread footings should have a minimum footing dimensions of 16 or more inches and
isolated pads should have minimum dimensions of 24 inches. Actual footing
dimensions, however, should be determined by the Structural Engineer, based on the
design loads.
5) Footings should be provided with adequate soil cover above their bearing elevation for
frost protection. Footings should be placed at a bearing elevation 3.5 or more feet below
the lowest adjacent exterior finish grades.
6) Continuous foundation walls should be reinforced top and bottom to span an
unsupported length of at least 10 feet.
NCC Preschool Addendum
Glenwood Springs, Colorado
Job No. 13-6017 GROUND Engineering Consultants, Inc. Page 3
7) The lateral resistance of spread footings will be developed as sliding resistance of the
footing bottoms on the foundation materials and by passive soil pressure against the
sides of the footings. Sliding friction at the bottom of footings may be taken as 0.33
times the vertical dead load on the on-site soils.
8) Backfill placed against the sides of the footings should be well compacted by vibratory
compaction equipment and in accordance with the recommendations in the Project
Earthwork section of this report.
9) Care should be taken when excavating the foundations to avoid disturbing the
supporting materials. Hand excavation or careful backhoe soil removal may be required
in excavating the last few inches.
10) All footing areas should be compacted with a vibratory plate compactor prior to
placement of concrete.
11) The Civil Design Engineer(s) and contractor should evaluate the possible sources of
water in the project area over the life of the structure, to provide a grading plan and
construct in a manner that minimizes the amount of moisture that infiltrates the
foundation/structure supporting materials.
Surface Drainage
Slopes should be as steep as feasibly possible, although we realize ADA requirements may
necessitate some areas be flatter than the minimum slopes outlined in the August report. Flat,
non-sloping areas within 20 feet of the building should be avoided, particularly where the site
slopes down to the building, and a swale may be necessary between the toe of the slope and
backfill sloped away from the foundation to adequately convey surface water around the
building. Roof downspouts should be routed to at least 20 feet away and downslope from the
building. Irrigation should be eliminated within a minimum 20 foot perimeter of the building, and
we recommend this buffer zone be extended to a minimum of 35 feet on the uphill side.
Subsurface Drainage
Although no below-grade areas are planned for the Preschool, we recommend a foundation
perimeter drain be included in the construction given how critical the control of subsurface
moisture increase will be to satisfactory post-construction performance. We also recommend
any backfilled excavations be provided with interceptor drains to reduce the tendency of water
to accumulate in perched conditions between native soil and fill interfaces. This includes the
over-excavation section, which we recommend be sloped at minimum 2 percent to the
interceptor drains. Utility trenches sloping toward the building should also be provided with
cutoff trench walls/plugs at the edges of the irrigation perimeter buffer zone.
NCC Preschool Addendum
Glenwood Springs, Colorado
Job No. 13-6017 GROUND Engineering Consultants, Inc. Page 4
Interceptor drains in infiltration areas should be constructed similarly to foundation drains,
generally consisting of a 1 square foot cross section of clean gravel containing perforated drain
pipe, surrounded by filter fabric, and laid on a minimum 2 percent slope. We recommend filter
fabric consist of Mirafi 140N or approved equivalent and overlap at least 12 inches. Outside of
infiltration areas, the gravel and filter fabric should be eliminated and non-perforated pipe should
be used.
Closure
This report has been prepared as an addendum to the geotechnical report dated August 23rd
2013 (Job No. 13-6017). All recommendations from the August 23rd report not explicitly
superseded herein shall remain valid. If you have any questions, please contact our office.
Sincerely,
GROUND Engineering Consultants, Inc.
Carl Henderson, P.E.