HomeMy WebLinkAboutSubsoil StudyKumar & Associatesn lnc.'
Geotechnical and Materials Engineers
and Environmental Scientisls
An Ëmployêe Owned Çampcny
Office Locations: Denver (HQ), Parker, Colorado Splings, Fort Collins, Glenwood Springs, and Summit County, Colorado
December 14,2020
Drs. Carol & John Wise
1815 Forest Grove Road
Lucas, Texas 15002
docj ohn@wiseorthodonti cs. com
Project No.20-7-670
Subject: Subsoil Study for Foundation Design, Proposed Residence, 0044 Kingbird Drive,
Lot 19, Filing 9, Elk Springs, Los Amigos Ranch, Garfield County, Colorado
Dear Carol & John:
As requested, Kumar & Associates, Inc. performed a subsoil study for design of foundations at
the subject site. The study was conducted in accordance with our agreement for geotechnical
engineering services to you dated November 3,2020. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: Design plans have not been developed. The proposed residence will
be located on the site in the area of the pits shown on Figure 1. We expect that the house will be
I to 2 stories over a crawlspace or walkout basement. Basement and garage floors will be slab-
on-grade. Cut depths are expected to range between about 4 to 10 feet. Foundation loadings for
this type of construction are assumed to be relatively light and typical of the proposed type of
construction.
If building conditions or foundation loadings are significantly different from those described
above, we should be notified to re-evaluate the recommendations presented in this report.
Site Conditions: The lot was vacant and vegetated with grass and weeds in the building area at
the time of our study. The western, upper part of the lot, nearer the street, is vegetated with
sagebrush. The eastern part of the site is vegetated with scattered pinon and juniper trees with
basalt rocks on the ground surface. The building arca is on a southeast-facing hillside with
slopes of about 15% down to the southeast. A dry drainage crosses the site from north to south
just to the east of the building envelope.
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970)945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
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Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two
exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are
presented on Figure 2. The subsoils encountered, below about 10 inches of topsoil, consist of
very stiff to hard sandy silty clay. The backhoe had difficulty penetrating the clay due to its
hardness and digging was stopped at3 fo 4 feet deep. Results of swell-consolidation testing
performed on relatively undisturbed samples of the clay soils, presented on Figure 4, indicate
low compressibility under existing moisture conditions and light loading and a moderate
expansion potential when wetted. Two weeks later, we drilled a boring with our drill rig which
penetrated the clays down 19 feet. Results of finer than sand size gradation analysis and
Atterberg limits testing performed on two disturbed samples of the clay soils obtained from the
boring are presented on Table 1. The Atterberg limits test results indicated the clay soils have
medium to high plasticity. No free water was observed in the pits or boring at the time of
excavation/drilling and the soils were slightly moist to moist"
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and boring and the nature of the proposed construction, we recommend spread
footings placed on at least 3 feet of structural fill over the undisturbed natural soils designed for
an allowable soil bearing pressure of 3,000 psf for support of the proposed residence. The clay
soils tend to expand after wetting and there could be some post-construction foundation
movement depending on the depth and extent of wetting. Footings should be a minimum width
of 16 inches for continuous walls and2 feet for columns. The clay soils encountered at the
foundation bearing level within the excavation should be removed down to a depth of 3 feet
below design bearing elevation. The footing bearing level can be re-established with imported
34-inch road base compacted in lifts to at least 98o/o of the maximum standard Proctor density at a
moisture content near optimum. Exterior footings should be provided with adequate cover above
their bearing elevations for frost protection. Placement of footings at least 36 inches below the
exterior grade is typically used in this area. Continuous foundation walls should be reinforced
top and bottom to span local anomalies such as by assuming an unsupported length of at least
12 feet. Foundation walls acting as retaining structures should be designed to resist alaferal
earth pressure based on an equivalent fluid unit weight of at least 55 pcf for the on-site soil as
backfill.
Kumar & Associates, lnc. o Project No. 20-7-670
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Floor Slabs: The natural on-site clay soils, exclusive of topsoil, should also be removed to a
depth of at least 3 feet below slab subgrade and replaced with 3 feet of 3/a inch road base
compacted to at least 95o/o of the maximum standard Proctor density at a moisture content near
optimum. 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 basement level slabs to facilitate drainage. This material should
consist of minus 2-inch aggregate with less Than 50%o passing the No. 4 sieve and less than2o/o
passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95Yo of maximum
standard Proctor density at a moisture content near optimum. Required fill should consist of
imported 3/+-inch road base.
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.
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 lo/o to
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2%o 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 Ilz 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.
Kumar & Associates, lnc. @ Project No. 20-7-670
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Surface Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the residence has been completed:
1) Inundation ofthe foundation excavations and underslab areas should be avoided
during construction. Drying could increase the expansion potential of the soils.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95Yo of the maximum standard Proctor density in pavement and slab areas
and to at least 90Yo of the maximum standard Proctor density in landscape areas.
Free-draining wall backfill should be capped with about 2 feet of the on-site, finer
graded soils to reduce surface water infiltration.
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 f,rrst 10 feet in pavement and walkway areas.
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 the building. Consideration should be given to the use of xeriscape
to limit potential wetting of soils below the foundation caused by inigation.
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 reoommendations submitted in this report are based
upon the data obtained from the exploratory pits excavated and boring drilled at the locations
indicated on Figure 1 and to the depths shown on Figure 2,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 pits and variations in the subsurface conditions may not become
evident until excavation is performed. If conditions encountered during construction appear
different from those described in this report, we should be notified at once so re-evaluation of the
recommendations may be made.
Kumar & Associates, lnc. @ Project No. 20-7-670
5
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 recoÍrmendations, and to veri$r that the recommendations
have been appropriately interpreted. Significant design changes may require additional analysis
or modifications to the recommendations presented herein. We recommend on-site observation
of excavations and foundation bearing strata and testing of structural fill by a representative of
the geotechnical engineer.
If you have any questions or if we may be of further assistance, please let us know.
Respectfully Submitted,
Kum*r & Åss$ciaÉes, årac.
Daniel E. Hardin, P
Reviewed by:
Steven L. Pawlak, P.E.
DEH/kac
attachments Figure 1 - Location of Exploratory Boring and Pits
Figure 2 - Logs of Exploratory Boring and Pits
Figure 3 - Legend and Notes
Figure 4 - Swell-Consolidation Test Results
Table I - Summary of Laboratory Test Results
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20-7 -670 Kumar & Associates LOCATION OF EXPLORATORY
BORING AND PITS Fig. 1
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20-7 -670 Kumar & Associates LOGS OF EXPLORATORY
BORING AND PITS Fig. 2
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LEGEND
TOPSOIL. ORGANIC SANDY SILTY CLAY, MEDIUM STIFF, MOIST, DARK BROWN
CLAY
SLIGH
(cl-cu): SANDY, srLTY, MEDIUM TO HIGH PLASTTCtTY, VERY STtFF,
TLY MOIST TO MOIST WITH DEPTH, BROWN.
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HAND DRIVEN 2-INCH DIAMETER LINER SAMPLE.
DISTURBED BULK SAMPLE.
NOTES
THE EXPLORATORY PITS WERE EXCAVATED ON NOVEMBER 1 1, 2O2O WITH A JD_35G MINI
EXCAVATOR. THE BORING WAS DRILLED ON NOVEMBER 17,2020 WITH A 4-INCH DIAMETER
CONTINUOUS_FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY PITS AND BORING WERE MEASURED APPROXIMATELY BY
PACING FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY PITS AND BORING WERE NOT MEASURED AND THE LOGS
OF THE EXPLORATORY PITS AND BORING ARE PLOTTED TO DEPTH.
4. THE EXPLORATORY PIT AND BORING LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO
THE DEGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIT AND BORING LOGS
REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS
MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS OR BORING
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM OZZIA);
DD = DRY DENSTTY (pct) (nSrV D2216);
_2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D1 1 4O);
LL = LIQUID LIMIT (ASTM O¿SIA);
PI = PLASTICITY INDEX (ASTM D4518).
20-7 -670 Kumar & Associates LEGTND AND NOTES Fig. 5
SAMPLE OF: Sondy Silty Cloy
FROM:Pit1@-2'
WC = 9.0 %, DD = 108 pcf
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EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
1.0 APPLIED PRESSURE - KSF 10 100
1.0 APPLIED PRESSURE - KSF t0 100
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SAMPLE 0F: Sondy Silty Cloy
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20-7 -670 Kumar & Associates SWELL_CONSOLIDATION TEST RESULTS Fig. 4
I (*rt åifu,'*:nËsn'rË;'*'*TABLE 1SUMMARY OF LABORATORY TEST RESULTSNo. 20-7-670Sandy Silty ClaySandy Silty ClaySOIL TYPESandy ClaySandy Clay(o/olEXPANSION2.5ATTERBERG LIMITSLIQUID LIMITEXPANSIVEPRESSUREPLASTICINDEX1.6450062001aJ271549PERCENTPASSING NO.200 stEVE1875(%)SAND%tGRAVELNATURALDRYDENSITY10811122DEPTH12PIT9.010.1t7.819.65-914-18NATURALMOISTURECONTENTBoring1