HomeMy WebLinkAboutSoils Report 02.03.2017H-PKUMAR
Geotechnical Engineering 1 Engineering Geology
Materials Testing j Environmental
5020 County Road 154
Glenwood Springs, CO 81601
Phone: (970) 945-7988
Fax: (970) 945-8454
Email: hpkglenwood@kumarusa.com
Office Locations: Parker, Glenwood Springs, and Silverthome, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 24, SPRING RIDGE RESERVE
43 HIDDEN VALLEY DRIVE
GARFIELD COUNTY, COLORADO
PROJECT NO. 17-7-143
FEBRUARY 3, 2017
PREPARED FOR:
NICK DALEY
4249 LENOX BOULEVARD
VENICE, FLORIDA 34293
(npdale v @pcisys.net)
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 2 -
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 2 -
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 3 -
FOUNDATIONS - 3 -
FOUNDATION AND RETAINING WALLS -4-
FLOOR SLABS - 5 -
UNDERDRAIN SYSTEM - 6 -
SURFACE DRAINAGE - 6 -
LIMITATIONS - 7 -
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
H -P ` KUMAR
Project No. 17-7-143
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located at Lot
24, Spring Ridge Reserve, 34 Hidden Valley Drive, Garfield County, 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 Nick Daley dated January 25, 2017. Hepworth-Pawlak Geotechnical
(now H-P/Kumar) previously conducted a preliminary geotechnical study for the Spring Ridge
Reserve Subdivision development and presented the findings in a report dated June 22, 2004, Job
No. 101 126.
A field exploration program consisting of exploratory borings was conducted 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, compressibility or
swell 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
The proposed residence will be a one story wood frame structure with an attached garage.
Ground floor will be slab -on -grade. Grading for the structure is assumed to be relatively minor
with cut depths between about 3 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.
H-P�KUMAR
Project No. 17-7-143
SITE CONDITIONS
The lot was vacant and covered with about 18 inches of snow at the time of our field exploration.
The site is vegetated with grass and weeds. The ground surface slopes down to the east at about
13 percent in the rear of the lot and flattens to about 3 percent in the front. An abandoned potato
cellar is located in the northwest part of the property. Siltstone bedrock outcrops are visible in
the northwest part of the property.
FIELD EXPLORATION
The field exploration for the project was conducted on January 26, 2017. Two exploratory
borings were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions.
The borings were advanced with 4 inch diameter continuous flight augers powered by a truck-
mounted CME -45B drill rig. The borings were logged by a representative of H-P/Kumar.
Samples of the subsoils were taken with a 2 inch I.D. spoon sampler. The sampler was driven
into the subsurface materials 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 and hardness of the bedrock. Depths at which the samples were taken and the
penetration resistance values are shown on the Logs of Exploratory Borings, Figure 2. The
samples were returned to our laboratory for review by the project engineer and testing.
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils, below about 6 inches of topsoil, consist of sandy silty clay overlying siltstone bedrock.
The depth to bedrock varied from 22 feet at Boring 1 to 2 feet at Boring 2. Drilling in the very
hard bedrock with auger equipment was difficult due to its apparent cemented condition and
drilling refusal was encountered in the formation.
H -P ` KUMAR
Project No. 17-7-143
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and finer than sand size gradation analyses. Results of swell -consolidation
testing performed on relatively undisturbed drive samples of the clay soils, presented on Figure
4, indicate low to moderate compressibility under conditions of loading and wetting. The sample
of blocky clay tested from Boring 1 at 21/2 feet showed a moderate expansion potential when
wetted. The laboratory testing is summarized in Table 1.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist to moist with depth.
FOUNDATION BEARING CONDITIONS
The siltstone bedrock dips deeply down to the east. The excavation will likely expose siltstone
bedrock in the upper portion transitioning mostly to sandy silty clay. About the upper 4 feet of
the sandy silty clay is blocky and expansive when wetted. We recommend the upper 4 feet of
sandy silty clay be removed from beneath proposed footing and floor slab areas. The underlying
sandy silty clay soils could tend to settle or heave when they become wetted. A shallow
foundation placed on the sandy silty clay soils will have a risk of settlement if the soils become
wetted and care should be taken in the surface and subsurface drainage around the house to
prevent the soils from becoming wet. It will be critical to the long term performance of the
structure that the recommendations for surface grading and subsurface drainage contained in this
report be followed.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, the building can be founded with spread footings bearing on the sandy
silty clay soils below 4 feet or siltstone bedrock.
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Project No. 17-7-143
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The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the sandy silty clay soils should be designed for an allowable
bearing pressure of 1,500 psf. Based on experience, we expect settlement of
footings designed and constructed as discussed in this section will be about 1 inch
or less and differential across the building.
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. PIacement
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 Iocal
anomalies such as by assuming an unsupported length of at least 12 feet.
Foundation walls acting as retaining structures should also be designed to resist
lateral earth pressures as discussed in the "Foundation and Retaining Walls"
section of this report.
5) The topsoil, blocky clay soils (about the upper 4 feet) and any loose or disturbed
soils should be removed and the footing bearing level extended down to
undisturbed natural soils. The exposed soils in footing area should then be
moistened and compacted.
6) A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FOUNDATION AND RETAINING WALLS
Foundation walls and retaining structures which are laterally supported and can be expected to
undergo only a slight amount of deflection should be designed for a lateral earth pressure
computed on the basis of an equivalent fluid unit weight of at least 55 pcf for backfill consisting
of the on-site soils.
H -P= KUMAR
Project No. 17-7-143
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All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The
pressures recommended above assume drained conditions behind the walls and a horizontal
backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will
increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain
should be provided to prevent hydrostatic pressure buildup behind walls.
Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum
standard Proctor density at a moisture content slightly above optimum. Backfill placed in
pavement and walkway areas should be compacted to at least 95% of the maximum standard
Proctor density. Care should be taken not to overcompact the backfill or use large equipment
near the wall, since this could cause excessive lateral pressure on the wall. Some settlement of
deep foundation wall backfill should be expected, even if the material is placed correctly, and
could result in distress to facilities constructed on the backfill.
The lateral resistance of foundation or retaining wall footings will be a combination of the
sliding resistance of the footing on the foundation materials and passive earth pressure against
the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated
based on a coefficient of friction of 0.35. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 350 pcf. The
coefficient of friction and passive pressure values recommended above assume ultimate soil
strength. Suitable factors of safety should be included in the design to limit the strain which will
occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against
the sides of the footings to resist lateral loads should be compacted to at least 95% of the
maximum standard Proctor density at a moisture content near optimum.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil and expansive blocky clay soils, can be used 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
H -P = KUMAR
Project No. 17.7-143
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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 basement level
slabs to facilitate drainage. This material should consist of minus 2 inch aggregate with at Ieast
50% retained on the No. 4 sieve and less than 2% passing the No. 200 sieve.
Alt 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 silty clay soils or imported 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 and basement areas, be protected
from wetting and hydrostatic pressure buildup by an underdrain system.
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 I % to
a suitable gravity outlet. 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 11/2 feet deep. An
impervious membrane such as 20 mil PVC should be placed beneath the drain gravel in a trough
shape and attached to the foundation wall with mastic to prevent wetting of the bearing soils.
SURFACE DRAINAGE
Providing proper surface grading and drainage will be critical to keeping the bearing soils dry
and limiting potential building movement and distress. The following drainage precautions
H -P z KUMAR
Project No. 17-7-143
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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 12 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
capped with at least 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.
5) Landscaping which requires regular heavy irrigation should be located at least 10
feet from foundation walls. Consideration should be given to use of xeriscape to
reduce the potential for wetting of soils below the building caused by irrigation.
LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
principles and practices in this area at this time. We make no warranty either express or implied.
The conclusions and recommendations submitted in this report are based upon the data obtained
from the exploratory borings drilled at the locations indicated on Figure 1, the proposed type of
construction and our experience in the area. Our services do not include determining the
presence, prevention or possibility of mold or other biological contaminants (MOBC) developing
in the future. If the client is concerned about MOBC, then a professional in this special field of
practice should be consulted. Our findings include interpolation and extrapolation of the
subsurface conditions identified at the exploratory borings and variations in the subsurface
conditions may not become evident until excavation is performed. If conditions encountered
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Project No. 17-7-143
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during construction appear different from those described in this report, we should be notified so
that re-evaluation of the recommendations may be made.
This report has been prepared for the exclusive use by our client for design purposes. We are not
responsible for technical interpretations by others of our information. As the project evolves, we
should provide continued consultation and field services during construction to review and
monitor the implementation of our recommendations, and to verify that the recommendations
have been appropriately interpreted. Significant design changes may require additional analysis
or modifications to the recommendations presented herein. We recommend on-site observation
of excavations and foundation bearing strata and testing of structural fill by a representative of
the geotechnical engineer.
Respectfully Submitted,
H -P k• KUMAR
Louis E. Eller
Reviewed by:
Steven L. Pawlak, P.E. (`1 •'4 1X2:2 l'*411
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H -P KUMAR
Project No. 17.7-143
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1005 FINISHED FLOOR EL. 1004.5'
1000
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BORING 2
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990 --
985
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975
17-7-143
H-PtiKUI IAR
LOGS OF EXPLORATORY BORINGS
Fig. 2
LEGEND
—7
//
T7
./
TOPSOIL; ORGANIC SILT AND CLAY, SANDY, FIRM, MOIST, BROWN.
CLAY (CL); SANDY, SILTY, VERY STIFF AND SLIGHTLY MOIST TO STIFF AND
MOIST WITH DEPTH, RED.
SILTSTONE BEDROCK; VERY HARD, SLIGHTLY MOIST, RED. MAROON FORMATION.
11 RELATIVELY UNDISTURBED DRIVE SAMPLE; 2—INCH I.D. CALIFORNIA LINER SAMPLE.
20/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 20 BLOWS OF A 140—POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE CALIFORNIA SAMPLER 12 INCHES.
I PRACTICAL AUGER REFUSAL IN CEMENTED ROCK.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON JANUARY 26, 2017 WITH A 4—INCH DIAMETER
CONTINUOUS FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING
FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
4. THE EXPLORATORY BORING LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE
ONLY TO THE DEGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (X) (ASTM D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216);
—200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM 0 1140).
17-7-143
H -P- KUMAR
LEGEND AND NOTES
Fig. 3
CONSOLIDATION - SWELL
CONSOLIDATION - SWELL
1
0
—1
—2
—3
SAMPLE OF: Blocky Sandy Clay
FROM: Boring 1 0 2.5'
WC = 10.5 %, DD = 108 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
1,0 APPLIED PRESSURE — KSF $0
100
SAMPLE OF: Sandy Silty Clay
FROM: Boring 1 0 5'
WC = 10.2'/., DO = 96 pcf
NO MOVEMENT UPON
WETTING
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17-7-143
IA APPLIED PRESSURE - KV
H -P- KUMAR
10
SWELL -CONSOLIDATION TEST RESULTS
!00
Fig. 4
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 17-7-143
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
(Pcf)
GRADATION
PERCENT
PASSING
NO. 200
SIEVE
ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE STRENGTH
(PSF)
SOIL TYPE
BORING
DEPTH
(ft)
GRAVEL
(%)
SAND
(%)
LIQUID
LIMIT
(%)
PLASTIC
INDEX
(%)
1
2%
10.5
108
BIocky Sandy Clay
5
I0.2
96
Sandy Silty Clay
10
8.3
108
55
Very Sandy Silty Clay
20
22.3
76
Sandy Silty Clay