HomeMy WebLinkAboutSubsoil StudyI Crt i'*iïfi'trf:iÉtri'Yn ; *' *
An Employcc Ownad Gompany
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-1988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
www.kumarusa.com
Offrce Locations: Denver (HQ), Parker', Colorado Springs, Foft Collins, Glenwood Springs, and Summit County, Colorado
June2l,202l
David Rowley
8310 Banpo Bridge Way
Delray Beach, Florida 33446
dsrowle]¡@gmail'com
project No.2r-i-444
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot25, Callicotte
Ranch, Il21 Callicotte Ranch Road, Garfield County, Colorado
Dear Mr. Rowley:
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 RM Construction dated March 12,2021. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: Development plans were preliminary aL the time of our study. In
general, the proposed residence will be a single-story structure over a walkout basement level
and attached garage located on the site as shown on Figure 1. Ground floors could be structural
over crawlspace or slab-on-grade. Cut depths are expected to range befween about 2 to 8 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 subject building site was vacant and vegetated with sage brush, grass and
cactus at the time of our site visit. The uphill, south part of the lot is a broad hilltop with a gentle
to moderate slope down to the north-northwest and around 6 feet of elevation difference in the
proposed building area.
Subsidence Potential: Callicotte Ranch is underlain by Pennsylvania Age Eagle Valley
Evaporite bedrock. The evaporite contains gypsum deposits. Dissolution of the gypsum under
certain conditions can cause sinkholes to develop and can produce areas of localized subsidence.
Sinkholes are scattered throughout the general area but were not observed in the immediate area
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of the subject lot or in this part of Callicotte Ranch. Based on our present knowledge of the site,
it cannot be said for certain that sinkholes will not develop. In our opinion, the risk of ground
subsidence at Lot 25 is low throughout the service life of the proposed residence and similar to
other lots in the area but the owner should be aware of the potential for sinkhole development.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
4 exploratory pits and2 profile pits at the approximate locations shown on Figure 1. The logs of
the pits are presented on Figure 2. The subsoils encountered, below about lzto llz feet of
topsoil, consist of very stiff to hard, sandy calcareous silt and clay with scattered gravel
underlain by basalt gravel and cobbles in a highly calcareous sandy silt matrix at a depth of 7 feet
in Pit 3. Practical refusal to backhoe digging due to the soil hardness was encountered in the pits
as shown on Figure 2. Results of swell-consolidation testing performed on relatively undisturbed
samples of upper clay and silt soils, presented on Figure 4,indicate low compressibility under
existing low moisture conditions and light loading and a low collapse potential when wetted with
moderate compressibility under additional loading after wetting. Results of gradation analyses
performed on a sample of sandy silt v/ith gravel matrix soils (minus 3-inch fraction) obtained
from the site are presented on Figure 5. The laboratory test results are summarizedin Table 1.
No free water was observed in the pits at the time of excavation and the soils were typically
slightly moist.
Foundation 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 bearing pressure of 1,500 psf
for support of the proposed residence. The soils typically tend to compress after wetting under
load and there could be around l-inch of post-construction foundation settlement depending on
the depth and extent of wetting. Precautions should be taken with surface grading and
subsurface drainage to prevent wetting of the bearing soils. Footings should be a minimum
width of 18 inches for continuous walls and2 feet for columns. 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. We should observe the
completed excavation for bearing conditions prior to forming footings. 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 72 feet. Foundation walls acting as retaining
Kumar & Associates, lnc. @ Project No. 21-7-444
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structures should be designed to resist alateral earth pressure based on an equivalent fluid unit
weight of at least 55 pcf for the on-site soil as backfill excluding organics and rock larger than
6-inches.
Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded
slab-on-grade construction with a differential settlement risk mainly if the subgrade soils are
wetted. 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 50o/o passing the No. 4 sieve and less than2Yo
passing the No. 200 sieve.
All fillmaterials 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 can consist of the on-
site 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 areathat local perched groundwater can develop during times of
hear,y 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 I foot below lowest adjacent finish grade and sloped at a minimum lo/o to
a suitable gavity 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 llz feet deep. An
impervious membrane such as 20 mil PVC should be placed below 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:
Kumar & Associates, lnc. @ Project No. 21-7-444
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1)Inundation of the foundation excavations and underslab areas should be avoided
during construction.
Exterior backfill should be adjusted 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 90o/o of the maximum standard Proctor density in landscape areas.
Free-draining wall backfill should be covered with filter fabric and capped with
about 2 feet of the on-site, finer graded soils to reduce surface water infiltration.
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 l0 feet in pavement and walkway areas.
Roof downspouts and drains should discharge well beyond the limits of all
backfill.
Landscaping which requires regular heavy irrigation should be located at least
i0 feet from the building. Consideration should be given to the use of xeriscape
to limit potential wetting of soils below the foundation caused by irrigation.
2)
3)
4)
Septic System Suitability: The USDA gradation testing results presented on Figures 5 and 6,
indicate a soil type of 3 (Sandy Clay Loam) for the sample taken from Profile Pit I and 2A (Silt
Loam) for the sample taken from ProfilePit2. It appears the clay loam is localized and the
septic system can be designed for type 2A soils provided it is based in the underlying silt loam.
A civil engineer should design the infiltration septic disposal system.
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 pits excavated at the locations indicated on Figure I
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 appeãr different from
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Kumar & Associates, lnc. o Project No. 21-7-444
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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 putposes, 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 veriff that the recommendations
have been appropriately interpreted. Significant design changes may require additional analysis
or modifications to the recoÍtmendations presented herein. We recommend on-site observation
of excavations and foundation bearing strata and testing of structural filI by a representative of
the geotechnical engineer.
If you have any questions or if we may be of further assistance, please let us know.
Respectfu lly Submitted,
Kumar & Associates,Inc"
Steven L. Pawlak, P
Reviewed
Ð
1 I
Danial E Hardin, P.E.
SLPikac
attachments Figure 1 - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Legend and Notes
Figure 4 - Swell-Consolidation Test Results
Figure 5 - Gradation Test Results
Figures 6 and 7 - USDA Gradation Test Results
Table 1 - Summary of Laboratory Test Results
cc:RM Construction - Blake Piland (blake&åuil$¡vit )
Kumar & Associates, hc. @ Pmject No. 21.7.444
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PIT 1
ELEV.=105'
PIT 2
ELEV.=106'
PIT 3
ELEV.=100'
PIT 4
ELEV.=103'
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5 WC=7.6
DD=9'l
WC=7.5
DD=9 1
WC=6.8
DD=83 5
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PROFILE PIT 1 PROFILE PIT 2
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- SAND=49
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SILT=36
CLAY= 1 6
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21 -7 - 444 Kumar & Associates LOGS OF EXPLORATORY PITS Fi1. 2
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LEGEND
TOPSOIL; ORGANIC SANDY SILT AND CLAY, SLIGHT MOIST, BROWN
slLT AND CLAY (ML-CL); SANDY, VERY STIFF TO HARD, SLIGHTLY MOIST, LIGHT BROWN,
SLIGHTLY POROUS, SLIGHTLY CALCAREOUS.
SILT AND CLAY (ML_CL); SANDY, SCATTERED GRAVEL AND COBBLES, VERY STIFF TO HARD,
SLIGHTLY MOIST, LIGHT BROWN.
GRAVEL AND SILT (GM-ML); SANDY, COBBLES, DENSE/HARD, SLIGHTLY MOIST, PALE/TAN,
HIGHLY CALCAREOUS.
F
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HAND DRIVEN 2-INCH DIAMETER LINER SAMPLE
DISTURBED BULK SAMPLE
PRACTICAL DIGGING REFUSAL.
NOTES
1. EXPLORATORY PITS 1 _4 WERE EXCAVATED WITH A BACKHOE ON MAY 20, 2021. PROFILE PITS 1
AND 2 WERE EXCAVATED WITH A BACKHOE ON JUNE 9,2A21.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED AND DESIGNATED BY CLIENT.
3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE MEASURED BY HAND LEVEL AND REFER TO
PIT 3 GROUND SURFACE AS ELEVATION = 100', ASSUMED.
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 ÏHE TIME OF EXCAVATION.
7. LABORATORY TEST RESULïSr
WC = WATER CONTENT (%) (ASTM O ZZIA);
DD = DRY DENSITY (PCi) (NSTU D 2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (NSTV O +ZZ);
_2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM O II¿O);
GRAVEL = PERCENT RETAINED ON NO. 10 SIEVE;
SAND = PERCENT PASSING NO. 1 0 SIEVE AND RETAINED ON No. 325 SIEVE;
SILT = PERCENT PASSING NO. 525 SIEVE TO PARTICLE SIZE .002MM;
CLAY = PERCENT SMALLER THAN PARTICLE SIZE .002MM.
21 -7 -444 Kumar & Associates LEGEND AND NOTES Fis.3
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1.0 PRESSURE - KSF t0 t00
SAMPLE OF: Sondy Sîlt ond Cloy
FROM: Pit 1 Gt 5'
WC = 7,6 %, DD = 91 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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SAMPLE OF: Sondy Silt ond Cloy
FROM:Pit2@^4.5'
WC = 7.5 %, DD = 91 pcf
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ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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21 -7 -444 Kumar & Associates SWELL-CONSOLIDATION TEST RTSULTS Fig. 4
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=
100
90
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70
60
50
ß
30
20
t0
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to
20
30
10
50
60
70
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r00
=
,o37 .075 .t 50
DIAMETER OF IN MI RS
CLAY TO SILT COBBLES
GRAVEL 4 % SAND 24 %
LIQUID LIMIT - PLASTICITY INDEX
SAMPLE OF: Cqlcoreous Sondy Silt wilh Grovel (MolrÎx)
SILT AND CLAY 72 %
FROM:Plt3O7'-8'
Thcsc i6sl r.sulb qpply oñly lo lh.
somplcs whlch wcrc lcslcd, Thcl.sllng r.porl shqll nol bs r6producld,
sxcopl lñ full, wllhoul'lho wrlllÊnqpprovql of Kumor & Assoclolcs, lnc.
Slcv. onolylls lostlng ls pcrformcd ln
occordqñcå wllh ASTM 06913, ASTM D7928,
ASTM C136 ond/or ASTM Dl1,+0.
HYDROMETER ANALYSIS SIEVE ANALYSIS
U.S. STAXDARD SERIES CLEAR SQUARÊ OPENINGS
2,I HRS 7 HRS lvlN It
ÎIHE REÀDINGS
âôútN lcvtN ¡utN
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lltiilliti ll:rl:lttrrflìl,ll,l tttf;,ti.
GRAVELSAND
FINE MEDIUM COARSE FINE COARSE
Fig. 521 -7 -444 Kumar & Associates GRADATION TEST RESULTS
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SIEVE ANALYSISHYDROMETER ANALYSIS
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. ..........t.. - .-.. t................ .t.... .....:.
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TIN/E U,S. STANDARD SERIES CLEAR SQUARE OPENINGS
24 HR. 7 HR 1MIN.
#325
045
4 MIN,#35 #1A #10 #4 'f1 3" 5" 6" B'
100
10 90
20 BO
30 70
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50 50
60 40
30
BO 20
90 10
100 0.001 .002 .005 .009 .019 .045 .106 .425 .500 1.00 2.00 4.75 S.5 19.0 37.5 76.2 152 203
DIAMETËR OF PARTICLES IN IVILLIN/ETERS
CLAY COBBLES
GRAVEL 2 %SAND 49 %SILT 23 %CLAY 26 %
USDA SOIL TYPE: Sandy Clay Loam FROM: PP-1 @ 3'-4'
SILT
21 -7 -444 Kumar & Associates USDA GRADATION TTST RTSULTS Fig.6J
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SIEVE ANALYSISHYDROMETER ANALYSIS
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TIME READI U.S. STANDARD SERIES CLEAR SQUARE OPENINGS
24 HR. 7 HÊ 1 À/rN.
+325 #140 #60 #1A #10 +4 1 3" 5" 6'. B'
100
'10 90
20 BO
30 70
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50 50
60 40
70 30
80 20
90 10
100 .00r .002 .005 .009 .019 .045 106 .025 .500 1.00 2,00 4.75 9.5 19.0 37.5 76.2 152 203
DIAMETER OF PARTICLES IN MILLIIVETERS
CLAY COBBLES
GRAVEL O %SAND 48 %SILT 36 %CLAY 16 %
USDA SOIL WPE: Loam FROM: PP-2 @ 2'-3'
GRAVEL
SILT
USDA GRADATION TEST RISULTS Fis.721 -7 -444 Kumar & Associates
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K+rfKumar & Associales, lnc"@Geotechnical and Materials Engineersand Environmental ScientistsTABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.21-7-444J21Profile124Pit4%5L--t3-44y,7-86.81.57.6NATURALMOISTURECONTENT$tNATURALDRYDENSITY(pcr)GRAVEL(/"1SAND(%)PIT(ft)DEPTH("/"1SILT&CLAY83919142484722492326Sandy Clay LoamSandy Silt and ClaySandy Silt and ClaySandy Silt and ClaySOIL TYPE(%)GRAVELUSDA SOIL TEXTURECalcareous Sandy Siltwith GravelCLAY{%tSAND%tSILT(%)t604836Loam