HomeMy WebLinkAboutSubsoils Report for Foundation DesignlGnHi.r*fi'f,11'ffttrillrd""'
An Employcc Owncd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
wwwkumarusa. coln
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Surnrnit County, Colorado
January 19,202I
Todd Sievers
5648 West Long Place
Littleton, Colorado 80 123
tws i ev ers (@c om cast. n et
Project No. 20-7-761
Subject Subsoil Study for Foundation Design, Proposed Residence, Lot 8, Elder
Amended, Ranch at the Roaring Fork, TBD Surrey Street, Garfield County,
Colorado
Dear Todd:
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 December I1,2020. 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 wood frame structure over
a crawlspace located in the area of the pits on the site as shown on Figure 1. The attached garage
will have a slab-on-grade floor. Cut depths are expected to range between about 2 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 site was vacant at the time of our field work. The lot is relatively flat and
slopes gently down at about 5o/o grade for about 80 feet into the site. Then there is a2/z foot
drop in elevation (about 10 feet into the building envelope) and the southern portion of the
building envelope is relatively flat and slopes gently down to Blue Creek on the south side of the
lot.
Subsurface Conditions: The subsurface conditions atlhe site were evaluated by excavating two
exploratory pits at the approximate locations shown on Figure 1. The logs of the pits are
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presented on Figure 2. The subsoils encountered, below about 6 to 14 inches of topsoil, consist
of medium dense, slightly silty sandy gravel with cobbles down to the maximum depth explored,
7t/z feet. Results of a gradation analysis performed on a sample of sandy gravel (minus 3-inch
fraction) obtained from the site are presented on Figure 3. Free water was observed in Pit 1 at
5% feet at the time of excavation and the soils above the water level and in Pit 2 were 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 soil bearing pressure of
?,000 psf for support of the proposed residence. Footings should be a minimum width of
16 inches for continuous walls and2 feet for columns. 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 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 is typically used in this area. Continuous foundation walls
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should be reinforced top and bottom to span local anomalies such as by assuming an unsupporled
length of at least 10 feet. Foundation walls acting as retaining structures should be designed to
resist alateral earth pressure based on an equivalent fluid unit weight of at least 45 pcf for the
on-site gravel soil as backf,rll.
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 slabs to facilitate drainage. This material
should consist of minus 1-inch aggregate with less than 50Yo passing the No. 4 sieve and less
than2oh 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 can consist of the on-
site gravel soils devoid of vegetation, topsoil and oversized rock.
Underdrain System: The proposed shallow crawlspace and garage slab-on-grade should not
require an underdrain system.
Kumar & Associates, lnc. @ Project No. 20-7-761
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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 of the foundation excavations and underslab areas should be avoided
during construction.
2) Exterior backhll should be adjusted to near optimum moisture and compacted to
at least 95oh 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.
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 6 inches in the first 10 feet in unpaved areas and a minimum slope of
2/z inches in the first 10 feet in pavement and walkway areas.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
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 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
f,rndings 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
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 recommendations presented herein. We recommend on-site observation
Kumar & Associates, lnc, o Project No, 20-7-761
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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
Respectfu lly Submitted,
Kumar & Associates, Inc.
Daniel E. Hardin, P.
Reviewed by:
i
Steven L. Pawlak, P.E.
DEHlkac
attachments Figure I - Location of Exploratory Pits
Figure 2 -Logs of Exploratory Pits
Figure 3 - Gradation Test Results
Kumar & Associates, lnc, 0 Project No. 20-7-761
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LS# 25947
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REC# 476659
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LOT 7
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APPROXIMATE SCALE-FEET
20-7 -761 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
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LEGEND
TOPSoIL; ORGANIC CLAY AND SILT, SANDY, GRAVELLY, ROoTS, FIRM, MOIST, BROWN
GRAVEL (op); SnNoy WITH COBBLES AND SCATTERED BOULDERS, DENSE, SLIGHTLY MOIST
TO WET WITH DEPTH, BROWN.
DISTURBED BULK SAMPLE
9 oEprH To wATER LEVEL ENcouNTERED AT THE TIME oF DIGGING.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH AN EXCAVATOR ON DECEMBER 51,2020.
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 WERE MEASURED BY HAND LEVEL AND REFER TO
GROUND SURFACE AT NORTHEAST LOT CORNER AS 1 OO" 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.
5. GROUNDWATER LEVELS SHOWN ON THE LOGS WERE MEASURED AT THE TIME AND UNDER
CONDITIONS INDICATED. FLUCTUATIONS IN THE WATER LEVEL MAY OCCUR WITH TIME.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422);
-2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1 1 4O).
20-7 -761 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2
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PARTICLES IN M
152
DIAMETER OF
CLAY TO SILT COBBLES
GRAVEL 69 %
LIQUID LIMIT
SAMPLE OF: Sondy Grovel
SAND 50 %
PLASTICITY INDEX
SILT AND CLAY 1 %
FRoM:Plt1@2'-3'
Th€se l.sl rosulls qpply only lo lhc
sqmpl6s whlch w6re lssled. Th€
l€sllng roport shqll nol bo roproduc€d,
oxcept ln full, wllhoul lhe wrlll6nqpprovql of Kumqr & Assoclol€s, lnc.
Slovo onqlysls lesllng ls p.rform€d ln
qccordqnco wlth ASTM D6915, ASTM D7928,
ASTM C156 qnd/or ASTM Dll4o.
HYDROMETER ANALYSIS SIEVE ANALYSIS
U.S. STANDARD SERIES CLEAR SQUARE OPENINOS
t/A, 1/^6 t 1/a'24 HRS 7 HRS
TIME READINGS
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MEDTUM lCOanSr FINE COARSEFINE
20-7 -761 Kumar & Associates GRADATION TEST RESULTS Fig. 3