HomeMy WebLinkAboutSubsoil Studyl*rtHiffi'*ffiEii*lå;*"'
An Employcc Owncd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970)945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
www.kumarusa.com
Office l¡cations: Denver (HQ), Parker, Colorado Springs, Fort Colling Glenwood Springs, and Summit County, Colorado
December 9,2020
Jeff and Becky Zimmermann
6936 East Archer Place
Denvero Colorado 80230
i zimmermann@desi gnworkshoo. com
Project No.20-7-654
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot22, Coryell
Ranch, 37 Cutbow Lane, Garfield County, Colorado
Mr. and Mrs. Zimmermann:
As requested, Kumar & Associates, Inc. performed a subsoil study for design of foundations at
the subject site. The study was conducted as additional services to and in accordance with our
proposal for geotechnical engineering services to you dated October 23,2020. 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 two-story structure with an attached
garage located on the site as shown on Figure l. Ground floors will be structural above
crawlspace in the living area and slab-on-grade in the garage. Cut depths are expected to range
between about 3 to 4 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 at the time of our field exploration. Vegetation consists of
grass and weeds. The ground surface is relatively flat to gently rolling with a gentle slope
generally down to the north. Elevation difference across the building area is about 5 feet.
Shallow ditches cross the properly including roadside ditches and a field ditch adjacent the east
side of the lot. The ground surface is moderately sloping down to the northeast beyond the field
ditch as indicated by the contour lines on Figure l.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
3 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 % to I foot of topsoil, typically
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consist of dense, sandy gravel with cobbles to the maximum explored depth of 7 feet. AtPitz,
about 2/zfeet of stiffi sandy clay was encountered below the topsoil. Results of gradation
analyses performed on samples of the sandy gravel (minus S-inch fraction) obtained from the site
are presented on Figure 3. The laboratory test results are sunìmarized in Table 1. No free water
was observed in the pits at the time of excavation and the soils were slightly moist.
Subsidence Potential: Coryell Ranch is underlain by Pennsylvania Age Eagle Valley Evaporite
bedrock. These rocks are a sequence of gypsiferious shale, fine-grained sandstone/siltstone and
limestone with some massive beds of gypsum. There is a possibility that massive gypsum
deposits associated with the Eagle Valley Evaporite underlie portions of the property.
Dissolution of the gypsum under certain conditions can cause sinkholes to develop and can
produce areas of localized subsidence. During previous work in the area, sinkholes have been
observed in the lower Roaring Fork Valley. Sinkholes were not observed in the immediate area
of the subject lot. Based on our present knowledge of the subsurface conditions at the site, it
cannot be said for certain that sinkholes will not develop. The risk of future ground subsidence
at Lot 22 throughout the service life of the structure, in our opinion is low, however the owner
should be aware of the potential for sinkhole development. If further investigation of possible
cavities in the bedrock below the site is desired, we should be contacted.
Foundation Bearing Conditions: The natural granular soils below the topsoil and sandy silt
and clay soils are adequate for support of spread footing foundations. The sandy silt and clay
encountered in the exploratory pits was relatively shallow (less than 2%feet) and should be
removed from beneath proposed foundation areas and the bearing grade extended down to the
granular soils.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recoÍlmend spread footings
placed on the undisturbed natural granular soil designed for an allowable soil bearing pressure of
2,500 psf for support of the proposed residence. The granular soils have low compressibility
potential and post-construction foundation settlement should be minor. Footings should be a
minimum width of,lljchsg.for continuous walls and ? feelfor columns. The silt and clay soils
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
granular soils. 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
Kumar & Associates, lnc. @ Project No. 20-7-654
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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 10 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 45 pcf for the on-site soil as backfill
Floor 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 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 interior slabs to facilitate drainage. This
material should consist of minus 2-inchaggregate with less than 50% passing the No. 4 sieve and
less than 2Yo passing the No. 200 sieve.
Al1fill 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 can consist of the
onsite 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 crawlspace
areas (excluding the slab-at-grade garage), 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 1olo to
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2o/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 l%feetdeep.
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. 20-7-654
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l)Inundation ofthe foundation excavations and underslab areas should be avoided
during construction.
Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95%o of the maximum standard Proctor density in pavement and slab areas
and to at least 90o/o of the maximum st¿ndard 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.
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 6 inches in the first 10 feet in unpaved areas and a minimum slope of
3 inches in the first 10 feet in pavement and walkway 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.
Roof downspouts a¡rd drains should discharge well beyond the limits of all
backfill.
Landscaping which requires regular heavy irrigation should be located at least
5 feet from the building.
3)
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Limitations: This study has been conducted in accordance with generally accepted geotechnical
engineering principles and practices in this area at this time. V/e 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 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
2)
Kumar & Associates, lnc. @ Project No. 20-7-654
5
monitor the implementation of our recommendations, and to veriry that the recommendations
have been appropriately interpretd. 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,
Kumar & Associateso Inc.
Steven L. Pawlak, P.E
Reviewed by:
Daniel E. Hardin, P.E.
SLP/kac
Attachments: Figure I - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Gradation Test Results
Table l- Summary of Laboratory Test Results
tn 15222
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Kumar & Associates, lnc. @ Project No. 20.7.654
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PIT 1
EL. 6079.5'
PIT 2
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PIT 5
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LEGEND
TOPSOIL; ORGANIC, SANDY SILT AND CLAY, FIRM, DARK BROWN.
stLT AND CLAY (ML-CL); SANDY, STIFF, SLIGHTLY MOIST, BROWN.
GRAVEL (OU-CP); SLIGHTLY SILTY, SANDY, COBBLES, DENSE, SLIGHTLY MOIST, BROWN,
ROUNDED ROCKS.
HAND DRIVEN 2-INCH DIAMETER LINER SAMPLE.
DISÏURBED BULK SAMPLE.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A MINI-EXCAVATOR ON NOVEMBER 18, 2O2O
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
FEATURES SHOWN ON THE SITE PLAN PROVIDED.
5. THE ELEVATIONS OF THE EXPLORATORY PITS WERE OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE 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 TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422);
_2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1140).
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20-7 -654 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2
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HYOROMEIER ANALYSIS SIEVS ANALYSIS
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IN MILLIMETERS
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DIAMETER OF IN
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PLASTICITY INOEX
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SAMPLE OF:Sllghtly Silþ Sondy Grovol wilh
Cobbles
FROM:PIt3O1.5'-2.5'
Those tcsl rolulls opply only lo lhe
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SAND GRAVEL
FINE MEDTUM ICOARSE FINE COARSE
HYDROMETER ANALYSIS SIÊVÊ ANALYSIS
TI¡E RE^OTNOS
t{Rs 7 HRS
U.S. STANDARO CI'EAR SOUARE OPENINGS
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20-7 -654 Kumar & Associates GRADATION TEST RESULTS Fig. 3
rc iffiirffi#snüËü"*TABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.20-7-654SOILTYPESandy Gravel with CobblesSandy Silt and ClaySlightly Silty Sandy Gravelwith CobbleslosflUNCOT{F¡NÊDcotPRESSwESTREI{GTHG LITITSlPlolPLASÏICINDEXATTERBE(ololLIQUID LfiTTPERCENTPASSIÌ{G NO.200 stEvE5I('/.)SAND24GRADAÏIONlf/"|GRAVEL68(Dcf)NATURALDRYDEilSTY257086lolNATURÄLfIIOISTURECONTENT4.6tfttDEPTH5-72ry2-2%Pll123