HomeMy WebLinkAboutSubsoils Report for Foundation Design
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
www.kumarusa.com Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 23, FIRST EAGLES POINT SUBDIVISION
BATTLEMENT MESA
325 EAGLE RIDGE DRIVE
PARACHUTE, COLORADO
PROJECT NO. 22-7-174
MARCH 29, 2022
PREPARED FOR:
VALENTINO WAUNEKA
90 BENT CREEK CIRCLE
PARACHUTE, COLORADO 81635
tinowauneka@gmail.com
Kumar & Associates, Inc. ® Project No. 22-7-174
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY ....................................................................................... - 1 -
PROPOSED CONSTRUCTION ................................................................................................ - 1 -
SITE CONDITIONS ................................................................................................................... - 1 -
FIELD EXPLORATION ............................................................................................................ - 1 -
SUBSURFACE CONDITIONS ................................................................................................. - 2 -
FOUNDATION BEARING CONDITIONS .............................................................................. - 2 -
DESIGN RECOMMENDATIONS ............................................................................................ - 2 -
FOUNDATIONS .................................................................................................................... - 2 -
FLOOR SLABS ...................................................................................................................... - 3 -
UNDERDRAIN SYSTEM ..................................................................................................... - 4 -
SURFACE DRAINAGE ......................................................................................................... - 4 -
LIMITATIONS ........................................................................................................................... - 5 -
FIGURE 1 - LOCATION OF EXPLORATORY BORING
FIGURE 2 - LOG OF EXPLORATORY BORING
FIGURE 3 - GRADATION TEST RESULTS
TABLE 1 - SUMMARY OF LABORATORY TEST RESULTS
Kumar & Associates, Inc. ® Project No. 22-7-174
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
Lot 23, First Eagles Point Subdivision, Battlement Mesa, 325 Eagle Ridge Drive, Parachute,
Colorado. The project site is shown on Figure 1. The purpose of the study was to develop
recommendations for the foundation design. The study was conducted in accordance with our
agreement for geotechnical engineering services to Valentino Wauneka dated February 8, 2022.
An exploratory boring was drilled to obtain information on the subsurface conditions. Samples
of the subsoils obtained during the field exploration were tested in the laboratory to determine
their classification and other engineering characteristics. The results of the field exploration and
laboratory testing were analyzed to develop recommendations for foundation types, depths and
allowable pressures for the proposed building foundation. This report summarizes the data
obtained during this study and presents our conclusions, design recommendations and other
geotechnical engineering considerations based on the proposed construction and the subsurface
conditions encountered.
PROPOSED CONSTRUCTION
Plans for the proposed residence were not developed at the time of our study. The proposed
residence is expected to be a one- or two-story wood-framed structure with an attached garage.
Ground floors could be a combination of slab-on-grade and structural over crawlspace. Grading
for the structure is assumed to be relatively minor with cut depths between about 2 to 5 feet. We
assume relatively light foundation loadings, typical of the proposed type of construction.
If building loadings, location or grading plans change significantly from those described above,
we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The subject site was vacant and had scattered snow cover at the time of our field exploration.
The ground surface was gently to moderately sloping down to the north and became steeper as it
approached the property line near Eagle Ridge Drive. Vegetation consists of scattered grasses
and weeds with a few scattered sage brushes and junipers along the rear property line. Scattered
basalt cobbles and boulders were present on the ground surface of the lot.
FIELD EXPLORATION
The field exploration for the project was conducted on February 11, 2022. One exploratory
boring was drilled at the location shown on Figure 1 to evaluate the subsurface conditions. The
boring was advanced with 4-inch diameter continuous flight augers powered by a truck-mounted
CME-45B drill rig. The boring was logged by a representative of Kumar & Associates, Inc.
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Kumar & Associates, Inc. ® Project No. 22-7-174
Samples of the subsoils were taken with a 1⅜-inch I.D. spoon sampler. The sampler was driven
into the subsoils at various depths with blows from a 140-pound hammer falling 30 inches. This
test is similar to the standard penetration test described by ASTM Method D-1586. The
penetration resistance values are an indication of the relative density or consistency of the
subsoils. Depths at which the samples were taken and the penetration resistance values are
shown on the Log of Exploratory Boring, Figure 2. The samples were returned to our laboratory
for review by the project engineer and testing.
SUBSURFACE CONDITIONS
A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. The
subsoils consist of about 1 foot of loose to medium dense existing fill overlying about 6 feet of
dense, silty sand and gravel with cobbles overlying about 5½ feet of dense, sandy, silty gravels
and cobbles down to the maximum explored depth of 12½ feet. Drilling in the coarse granular
soils with auger equipment was difficult due to the cobbles and possible boulders and drilling
refusal was encountered in the deposit.
Laboratory testing performed on samples obtained from the boring included natural moisture
content and gradation analyses. Results of gradation analyses performed on small diameter drive
samples (minus 1½-inch fraction) of the coarse granular subsoils are shown on Figure 3. The
laboratory testing is summarized in Table 1.
No free water was encountered in the boring at the time of drilling and the subsoils, excluding
the moist to very moist fill, were slightly moist. The upper layer of fill was very moist due to
snowmelt.
FOUNDATION BEARING CONDITIONS
Existing fill (and topsoil where present) is unsuitable to support building foundations. The
underlying natural granular materials are relatively dense and have low settlement potential.
Placing the foundation entirely on the natural granular soils should provide a relatively low risk
of foundation movement.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory boring and the nature of
the proposed construction, we recommend the building be founded with spread footings bearing
on the natural granular soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural granular soils or compacted structural
fill should be designed for an allowable bearing pressure of 2,000 psf. Based on
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Kumar & Associates, Inc. ® Project No. 22-7-174
experience, we expect settlement of footings designed and constructed as
discussed in this section will be about 1 inch or less.
2) The footings should have a minimum width of 16 inches for continuous walls and
2 feet for isolated pads.
3) Exterior footings and footings beneath unheated areas should be provided with
adequate soil cover above their bearing elevation for frost protection. Placement
of foundations at least 36 inches below exterior grade is typically used in this
area.
4) Continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least 10 feet.
Foundation walls acting as retaining structures should also be designed to resist a
lateral earth pressure corresponding to an equivalent fluid unit weight of at least
45 pcf for the on-site soils as backfill excluding organics and rock larger than
6 inches.
5) The fill and any loose disturbed soils or topsoil should be removed and the footing
bearing level extended down to the relatively dense natural granular soils. The
exposed soils in footing area should then be moistened and compacted. As an
alternative, design bearing level can be re-established with structural fill
compacted to at least 98% of standard Proctor density at a moisture content near
optimum. The fill can consist of on-site sand and gravel soils, sorted to remove
organics and oversized (plus 6-inch) rock or a suitable imported material such as
¾-inch base course. The fill should extend laterally beyond the edge of footings a
minimum distance of at least ½ the depth of fill below footings.
6) A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FLOOR SLABS
Any existing fill, topsoil, and loose or disturbed soils should be removed from slab-on-grade
areas. The underlying natural granular soils and structural fill are suitable to support lightly
loaded slab-on-grade construction. To reduce the effects of some differential movement, floor
slabs should be separated from all bearing walls and columns with expansion joints which allow
unrestrained vertical movement. Floor slab control joints should be used to reduce damage due
to shrinkage cracking. The requirements for joint spacing and slab reinforcement should be
established by the designer based on experience and the intended slab use. A minimum 4-inch
layer of free-draining gravel should be placed beneath interior slabs to facilitate drainage. This
material should consist of minus 2-inch aggregate with at least 50% retained on the No. 4 sieve
and less than 2% passing the No. 200 sieve.
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Kumar & Associates, Inc. ® Project No. 22-7-174
All fill materials for support of floor slabs should be compacted to at least 95% of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the
on-site granular soils devoid of vegetation, topsoil and oversized rock.
UNDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
the area that local perched groundwater can develop during times of heavy precipitation or
seasonal runoff. Frozen ground during spring runoff can create a perched condition. We
recommend below-grade construction, such as retaining walls, crawlspace and basement areas,
be protected from wetting and hydrostatic pressure buildup by an underdrain system. A
perimeter foundation drain around shallow crawlspace areas (less than 3 feet deep) should not be
needed with adequate compaction of foundation backfill and positive drainage away from
foundation walls as recommended below.
Where required, the drains should consist of drainpipe placed in the bottom of the wall backfill
surrounded above the invert level with free-draining granular material. The drain should be
placed at each level of excavation and at least 1 foot below lowest adjacent finish grade and
sloped at a minimum 1% to a suitable gravity outlet or sump and pump. Free-draining granular
material used in the underdrain system should contain less than 2% passing the No. 200 sieve,
less than 50% passing the No. 4 sieve and have a maximum size of 2 inches. The drain gravel
backfill should be at least 1½ feet deep and be covered with filter fabric.
SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at all
times after the residence has been completed:
1) Inundation of the foundation excavations and underslab areas should be avoided
during construction.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95% of the maximum standard Proctor density in pavement and slab areas
and to at least 90% of the maximum standard Proctor density in landscape areas.
3) The ground surface surrounding the exterior of the building should be sloped to
drain away from the foundation in all directions. We recommend a minimum
slope of 6 inches in the first 10 feet in unpaved areas and a minimum slope of
3 inches in the first 10 feet in paved areas. Free-draining wall backfill should be
covered with filter fabric and capped with about 2 feet of the on-site soils to
reduce surface water infiltration.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
Kumar & Associates
Kumar & Associates
Kumar & Associates
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 22-7-174
SAMPLE LOCATION NATURAL MOISTURE CONTENT
NATURAL DRY DENSITY
GRADATION
PERCENT
PASSING NO. 200 SIEVE
ATTERBERG LIMITS UNCONFINED COMPRESSIVE STRENGTH SOIL TYPE BORING DEPTH GRAVEL SAND LIQUID LIMIT PLASTIC INDEX (%) (%)
(ft) (%) (pcf) (%) (%) (psf)
1 2½ & 5
combined 4.2 49 21 30 Sandy Silty Gravel