HomeMy WebLinkAboutSubsoil Study for Foundation Design 08.10.21l&rtffi:H'r*.
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August 10,2021
Uriel Mellin
144 Cliffrose Way
Glenwood Springs, Colorado 81601
i¡ncl.lllcll l¡olnrail,eorn
Job No. 2l-7-313
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 17, Callicotte
Ranch, Sopris Lane, Garfield County, Colorado
Dear Mr. Mellin:
As requested, Kumar and Associates, Inc. performed a subsoil study for design of foundations at
the subject site on July 22,2021. The study was conducted in accordance with our agreement for
geotechnical engineering services to you dated April 1,2A21. The data obtained and our
recommendafions based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: The proposed residence will be a two story, wood frame structure over
a crawlspace with an attached garage. The garage floor will be slab-on-grade. Cut depths are
expected to range between about 3 to 5 feet. Foundation loadings for this type of construction
are assumed to be relatively light and typical of the proposed type of construction. A septic
disposal system is proposed to be located southwest of the residence.
If building location, conditions, or foundation loadings are significantly different from those
described aboveo we should be notified to re-evaluate the recommendations presented in this
report.
Site Conditions: The site is vacant and forested with juniper and pinyon trees, with areas of
grasses, sage and cactus. The lot is gently to moderately sloping down to the west-southwest and
the surface appears natural with visible basalt cobbles and boulders. The lot is bordered on the
northeast by Sopris Lane.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two
exploratory pits in the building area and two profile pits for septic design at the approximate
locations shown on Figure 1. The logs of the pits are presented on Figure 2. The subsoils
encountered in exploratory Pits 1 and2, and Profile Pit 1, below about 1 to 1% feet of topsoil,
consist ofdense basalt cobbles and boulders in a pale tan and gray highly calcareous sand, silt,
and clay matrix down to the maximum explored depth of 3 feet. In Profile Pit 2, below about
I foot of topsoil, a hard, pale tan and gray gravelly sandy clayey silt was encountered down to
the explored depth of 4% feet. Digging in the basalt rock was difficult, and practical digging
refusal was encountered in all four pits'
2-
Results of a finer than sand sized gradation analysis and a USDA gradation analysis performed
on a sample of the natural coarse granular soils (minus 3-inch fraction) obtained from the site are
presented on Figure 3. The laboratory test results are summarized in Table 1. No free water was
observed in the pits at the time of excavation and the soils were slightly moist.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread footings
the undisturbed natural granular soil designed for an allowable soil bearing pressure of
for suppof of the proposed residence. Footings should be a minimum width of
for continuous walls and 2 feet for columns. Utility trenches and cut areas below
about 3 to 4 feet may require rock excavating techniques such as chipping or blasting. Loose and
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 granular soils.
Voids created from boulder removal at footing grade should be filled with concrete or a
structural material such as roadbase compacted to 98o/o of the maximum standard Proctor density
at a moisture content near optimum. We should observe the completed foundation excavation
for bearing conditions. Exterior footings should be provided with their
bearing elevations for frost protection. Placement of footings at the
exterior grade is typically used in this area. Continuous foundation 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 a lateral
earth pressure based on an equivalent fluid unit weight of at least 50 pcf for the on-site soil as
backfill.
Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support moderately
loaded slab-on-grade construction. To reduce the effects of some differential movernent, 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 slabs for support. This material should
consist of minus 2-inch aggregate with less than 50% passing the No. 4 sieve and less than l2o/o
passing the No. 200 sieve.
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 filI can consist of the
on-site soils devoid of vegetation, topsoil and oversized rock or a suitable imported granular
material.
Underdrain System: Although free water was not encountered during our exploration, it has
been our experience in mountainous areas that local perched groundwater can develop during
times ofheavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a
perched condition. We recommend below-grade construction, such as retaining walls, deep
crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup by
an underdrain system.
36 inches
Kumar & dssociates, lnc,Prôiect No. 2'l-7-313
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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 I foot below lowest adjacent finish grade and sloped at a minimum |o/oto
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 50% passing the No. 4 sieve and have a
maximum size of 2 inches. The drain gravel backfill should be at least l% 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: 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 backfrll should be adusted to near optimum moisture and compacted to
at least 95o/o 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 capped with filter fabric and 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 lirst 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
5 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.
Septic Disposal Area: Two Profile Pits were dug at the locations shown on Figure 1. The
subsurfacc profile mainly consists of a gravelly sandy loam. Results of a USDA gradation test
performed on a sample of the coarse grained soils are shown on Figure 3 and the test results are
summarized on Table 2. Based on these findings, the tested area should be suitable for an
infiltration septic disposal system. A civil engineer should be engaged to design the septic
disposal system.
Limítations: This study has been conducted in accordance with generally accepted geotechnical
engineering principles and practices in this area at this time. We rnake no warranty either
express or implied. 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 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
Kumar & Associates, lnc.Project No. ¿1-7-313
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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.
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 veri$ 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 filIby 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,
Kunrar & Àssociates. Inc.
David A. Noteboom, Staff Engineer
Reviewed by:
Daniel E. Hardin, P.E.
DEH/kac
Attachments: Figure 1 - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - USDA Gradation Test Results
Table I - Summary of Laboratory Test Results
Kumar & A¡sociales, lnc. 'Project No. 21-7.31?
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21 -7 -313 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
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ñ ror-so-tL; sANDy sllî wtrH BA'ALT .'BBLES AND BouLDERs, Roors AND oRcANrcs, F'RM,hV sucprLy Motsr, BRowN.
CoBBLES AND souLDER:..(cM)¡_ Bf:sArT RocKS tN A SAND AND stLT MATRtx, DENSE,SLIGHÏLY MOIST, PALE TAN AÑD GRAY, HIGHLY CALCAREOUS.
IIII(ITI)i S4NÐY, SLIGHTLY CLAYEY, GRAVELLY, EECOMING ROCKIER WITH DEPîH, HARD,SLIGHTLY MOIST, PALE TAN AND CRAY.
DISTUREED BULK SAMPLE.I
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NOTES
I. THE EXPLORATORY PITS WERE EXCAVATED WITH A MINI EXCAVATOR ON JULY 22,2021.
2' THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROMFEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE NOT MEASURED AND THE LOGS OF THEEXPLORATORY PITS ARE PLOTTED TO DEPTH.
4. THE EXPLORATORY PIT LOCATIONS SHOULO BE CONSIDERED ACCURATE ONLY TO THE DEGRETIMPLIED 8Y THE METHOD USED.
5' THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY PIl LOGS REPRESENT THEAPPROXIMATE BOUNDARIES BETWEEN MATERIAT TYPES AND THE TRANS'TIONS MAY BE GRADUAL.
6' GROUNDWATER WAS NOT ENCOUNTERED IN THE PITS AT THE TIME OF EXCAVATION. PITS WERESACKFILIED SUBSEQUENT TO SAMPLING.
7. LABCIRATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM Ù 2?16);
-2AO= PERCENTAGE pASstNG NO. 200 STEVE (ASTM D ilao);LL = LIQUID LIMIT (ASTM Ð 4318);Pl = PLAST|CITy TNDEX (ASTM D aJiB);
GRAVEL = PERCENT RETAINED ON NO. íO SIEVE;sAND = PERCENT pÀsstN0 No. ro stEvE AND RETATNED oN No. 325 sIEVE;slLT = PEROËNT PASSTNG No. g2s srEVE To PARTTCLE srzE .oo2MM;CLAY = PERCENT SMALLER THAN PART|CLE SIZE .OO2MM.
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21 -7 -31s Kumar & Associates LOGS OF EXPLORATORY PI,ïS Fig. 2
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DIAMETER OF PABTCLES IN MILLIMEÎEBS
CLAY COBBLES
GRAVËL 22 %SAND 42 %SILT 26 %CLAY 10 0/"
USDA SOIL TYPE: Gravelly Sandy Loam FROM: PP-1 @ 2.5'-3.5'
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21-7-313 Kumar & Associates USDA GRADATION TIST RESULTS Fig. 3
lGrfiffilffi*;**TABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.21.73SOILTYPËSandy Gravelly HighJlastisity SiltSandy LoanPtASncFI¡EX061I8uQutoLmftIt¿)52sttTcr¡YPERCEilTPASSII{G T{O:ãN$E!E51I026sAt¡0t%)42GRAVELg.l22¡ÂlURAJ-NOFruREcot{tEtffV.l1 1.8IDEPTHftt2*2y,zVz -3y,PtÌIPPl