HomeMy WebLinkAboutSubsoil Study for Foundation Design 04.30.2021Receíved rlz-zlrc *'ç1ffiäfúfr,TË;;**
An Employcc Owncd Compony
5020 Countv Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglanwood@kunarusa. com
www.kurnanrsa.com
Qffrce L¡cations: Denver (HQ), Parker; Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
Apnl 30,2021
Janice James & Sherman Muller
c/o MataDesign
Attn: Martin Mata
P.O. Box 189
Carbondale, Colorado 81623
matadesisn@mac.com
Project Na. 2l-7-234
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot24, Stirling
Ranch, Clipper Place, Garfield County, Colorado
Dear Martin:
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 Janice James and Sherman Muller dated March 3,2021. The data
obtained and our recommendations based on the proposed construction and subsurface
conditions encountered are presented in this report.
Proposed Construction: The proposed residence will be a one-story wood-frame structure over
lower walkout level with attached garage at the lower level located on the site as shown on
Figure 1. Ground floor will b":$-on-ry!1cut depths are expected to range between about
2 to l0 feet. Foundation loadings for this type of construction are assumed to be relatively light
and brpical 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 subject site was vacant at the time of our field exploration. The ground
surface in the building areas is gently sloping down to the northeast at gradegþþgllto ._
5 percent. Vegetation consists of sage brush and weeds and there was approximately 3 to
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4 inches of snow cover.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two
exploratory pits at the approximate locations shor¡'n on Figure l. The logs of the pits are
presented on Figure 2. The subsolls encountered below about I feet of topsoil, consist of 4 to
4Yz feet of stiff, silty sandy clay underlain by very stiff, sandy silt wrth scattered basalt fiagments
2-
to the ma:rimum excavated depth of 8 feet. Results of swell-consolidation testing performecl on
relatively undisturbed samples of the silty sandy clay soils, presented on Figure 3, indicate low
compressibility under existing moisture conditions and light loading and a minor expansion or
collapse (settlement under constant load) potential v¡hen wetted under constant light surcharge.
No free water was observed in the pits at the time of excavation and the soils were slightly moist
to moist.
X'oundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread footings
placed on the undisturbed natural soil designed for an allowable soil bearing pressure of
1,000 psf for support of the proposed residence. The soils tend to compress after wetting and
there could be some post-construction foundation settlement. Footings should be a minimum
width of 16 inches for continuous walls and 2 feet for columns. Topsoil and loose disturbed soils
encountered at the foundation bearing level within the excavation should be removed and the
footing bearing level extended down to the undisturbed natural soils. Exterior footings should be
provided with adequate cover above their bearing elevations for frost protection. Placement of
footings at least 36 inches beþw the exterior grade is typically used in this area. Continuous
foundation walls should be well reinforced top and bottom to span local anomalies such as by
assuming an unsupported length of at least 12 feet. Forurdation walls acting as retaining
structures should be designed to resist a lateral earth pressure based on an equivalent fluid unit
weight of at least 50 pcf for the on-site soil as backfill.
X'loor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded
slab-on-grade construction. To reduce the effects of some differential movement, floor slabs
should be sepalated from all bearing walls and colulurs 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 50Yo passing the No. 4
sieve and less than ZYopassingthe No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 959/o of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the on-
site soils devoid of vegetation, topsoil and oversized rock.
Kumar & Associates, lnc. @ Projec't No. 21-7-234
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Underdrain System: Although free water was not encountered during our exploration, it has
been our experience in the area and where clay soils are present 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 adj acent finish grade and sloped at a minimum IYo to
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2o/o passingthe No. 200 sieve, less than 50olo passing the No. 4 sieve and have a
maximum size of 2 inches. The drain gravel backfill should be at least lYz feet deep.
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. 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 90% of the maximum standard Proctor density in landscape areas.
Free-draining wall backfill should be cover with filter fabric and capped with
about2 feet of the on-site, finer graded soils to reduce surface water infiltration.
3) The ground surface sunounding 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 l0 feet in unpaved areas and a minimum slope of
3 inches in the fïrst 10 feet in pavement and walkway areas.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping r,vtrich requires regular heavy irrigation should be located at least
l0 feet from the building. Consideration should be given to the use of xeriscape
to limit potential wetting of soils below the foundation caused by irigation.
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
Kumar & Associates, lnc. @ Project No. 21-7-234
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express or irnplied. The conclusions and recommendations submitted in this report are based
upon the data obtained from the exploratory pits excavated 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 prcsence, prevention or possibility of mokl
or other biological contaminaats {MOBC) developing in the future. If the client is concerned
about MOBC, then a professional in this special fîeld 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 mty not become evidcnt until
excavation is perfonned, lf conditions encûuntered during construction appsar different from
those described in this repo*, we should be notified at once so re-evaluation of the
recommendations may be made.
This report has been prepared for the exclusive use by our client for design pulposes. 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 recommenclalions, and to vnrifor that the recommendations
have been appropriately interpreted. Significant design changes may require additional analysis
ur moclifioations to the recommendations presented herein. We recommend on-site observation
of excavations and foutdation bearing strata and testing of structural fill by a representative of
the geotechnical engineer.
If you have any questions or if we rnay be of further assistance. please let us know.
Respectful ly Submitted,
Kunrar &
James H. Parsons, P
Reviewed by:
\
Daniel E.Ilardin, P.E.
JHP/kac
attachments Figure I - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Swell-Consolidation Test Rssults
Table 1 - Summary of Laboratory Test Results
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Kumar & Associates, lnc. n Project t'lo. 21-7-234
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PROFILE PITS 1 AND 2 LOGGED BY OTHERS FOR SEPTIC DESIGN
NOT TO SCALE
21 -7 -234 Kumar & Associates LOCATION OF EXPLORATORY PIÏS 1Fig.
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PIT 1
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7 1
2
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0 0
WC=6.8
DD= I 03 WC=7.4
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10 10
LEGEND
TOPSOIL: CLAY, SANDY, ORGANlCS, FIRM, SLTGHTLY MOtST, BROWN
CLAY (CL); SILTY, SANDY, STtFF, SL|GHTLY MO|ST, BROWN
srLT (M
MOIST,
L);
WH
SANDY TO VERY SANDY, SCATTERED BASALT FRAGMENT, VERY STIFF, SLIGHTLY
ITISH TAN.
F
t
HAND DRIVE SAMPLE
DISTURBED BULK SAMPLE.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A RUBBER TRACKED EXCAVATOR ON MARCH 16,
2021.
2, THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY PITS ARE BASED ON TOPOGRAPHIC LINES ON SITE PLAN
PROVIDED.
4. THE EXPLORATORY PIT 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 PIT LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION. PITS WERE
BACKFILLED SUBSEQUENT TO SAMPLING.
7. LABORATORY TFST RFSiJLTSTwc = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (PCf) (ASTM D 2216);
-200= PERCENTAGE PASSING No. 200 SIEVE (ASTM D l1a0);LL = LIQUID LIMIT (ASTM D4518);Pl = PLASTICITY INDEX (ASTM 04318).
21 -7 -234 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2
Ê:
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SAMPLE OF: Silty Sondy CloY
FROM:Pít1E^2'
WC = 6.8 %, DD = 103 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
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SAMPLE OF: Silty SondY CloY
FROM:Pìt2@-2.5'
WC = 7.4 %, DD = 91 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
ln
D-45Æ.
21 -7 -234 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 3
ICrt iffilråffifffifniifü*-'TABLE 1SUMMARY OF LABORATORY TEST RESULTS]1o.21-7-2ASOIL TìtrESilty Sandy ClaySilt and SandSilty Sandy ClaylpsñUNCOI,¡FIHEDcof¡lPRESstvESTRENGTH(o/"1PLASTtCINDEX8ATTERBERG LIIIITSIo/olLIqUID LIiIIT14PERCENTPASSING NO200 stEvE42("/ùSANDGRADATION(wGRAVEL(pcûNATURALDRYDE¡¡SITY103I9fo/"\NATURALTTIOISTURECONTENT6.89.57.4DEPTHPIT26)1,/-SÀllPLE LOCATIONI2