HomeMy WebLinkAboutSubsoils Report for Foundation Designrcnfffiffi:lffiix';**
An Ernp{oyea Ornsd Compa*y
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-798&
lax: (970) 945-8454
email : kaglenrvood @-kumarusa.com
wu'u'.kumatusa.cont
Office Locations: Den'er (HQ), Parker, Colorado Springs, Fort Collins, Gle.nr",'ood Springs, and Surrnit Coulfy, Colorado
October 26,2A20
Chris Shaw Construction
Attn: Chris Shaw
P.O.Box2724
Glenwood Springs, Colorado 81602
cshaw8 1 *?@hotmail.ccrn
Project No. 20-7-537
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot73, Filing 7,Elk
Springs, Garfield County, Colorado
Dear Mr. Shaw:
As requested, Kumar and Associates 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 September 18, 2020. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report. Hepworth-Pawlak Geotechnical, Inc., previously perfonned a
preliminary geotechnical study for Filings 6 through 9, Elk Springs (fonnerly Los Amigos Ranch
PUD) and reported our findings on February 14, 1997 ,Iob No. 197 617.
Proposed Consfruction: The proposed residence will be one to two story wood frame
construction above a crawlspace with an attached garage. The house will be located on the site
as shown on Figure l. Garage floor will be slab-on-grade. Cut depths are expected to range
between about 3 to 6 feet. Foundation loadings for this type of construction are assumed to be
relatively light and typicai of the proposed type of construction.
Ifbuilding conditions or foundation loadings are siguificantly different from those described
above, we should be notified to re-evaluate the recomrnendations presented in this report.
Site Conditions: The lot was vacant at the time of our field exploration. Vegetation consists of
sage brush, grass and weeds, with scattered pinion and juniper trees south of the building
envelope. The ground surface is moderateiy sloping down to the south at grades of about
10 percent in the building area. Three pits had been excavated prior to our site visit.
Subsurface Conditions: The subsurface conditions at the site were evaluated by observing
three exploratory pits at the approximate locations shown on Figure l. The logs of the pits are
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presented on Figure 2. The subsoils encountered, below about I foot of topsoil, consist of 2 to
4 feet ofsandy silty ciay overlying basalt cobbles and boulders in a calcareous sand and silt
matrix down to the maximurn depth explored, 6 feet. Results of swell-consolidation testing
performed on a relatively undisturbed sample of the sandy silty clay, presented on Figures 3,
indicate low expansion under existing moisture conditions and light loading. No free water was
observed in the pits at the time of excavation and the soils were slightly moist.
Foundation Recommendafions: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread footings
placed on the undisturbed nafural soil designed for an allowable soii bearing pressure of
2,000 psf for support of the proposed residence. The soils tend to expand after wetting and there
could be some post-consffuction foundation movement. Footings should be a rninirnum width of
18 inches for continuous walls and 2 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
should be reinforced top and bottom to span local anomalies such as by assuming an unsupported
lengtlr of at least 12 feet. Foundation walls acting as retaining strucfures 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 lightly loaded
slab-on-grade construction. To reduce the effects of some differential movement, floor slabs
should be separated frorn all bearing wails 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 rninirnurn 4 inch
layer of free-draining gravel should be placed beneath garage level slabs. This rnaterial should
consist of minus 2-inch ag$egate with less than 5Ao/o passing the No. 4 sieve and less thanZYo
passing the No. 200 sieve.
All filImaterials for support of floor slabs should be cornpacted to at least 95olo of rnaxnnum
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. @ Project No.20-7-537
-J-
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 reconunend below-grade construction, such as retaining walls and crawlspace
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 gtanular rnaterial. The drain should be placed at each level of
excavation and at least 1 foot below lowest adjacent finish grade and sloped at a minimurn l% to
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2olo passingthe No. 200 sieve, less than 50% passing the No. 4 sieve and have a
maxinrurn 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:
l) Inundation ofthe foundation excavations and underslab areas should be avoided
during construction.
2) Exterior backfill should be adjusted to near optinrum moisture and compacted to
at least 95Ya 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 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 recomrnend a rninirnum
slope of 12 inches in the first l0 feet in unpaved areas and a minimum slope of
3 inches in the first 10 feet in pavement and walkway areas. A swale may be
needed uphill to direct surface runoffaround the residence.
4) Roof downspouts and drains should discharge well beyond the lirnits 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 irrigation.
Limitations: This study has been conducted in accordance with generally accepted geotechnical
engineering principles and practices in this areaatthis time. We make no warranff either
express or implied. The conclusions and recommendations submitted in this report are based
Kumar & Associates, lnc. @ Project No.20-7-537
4
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 elient 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 cofftruction 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 consultatian and field services during construction to review and
monitor the implementation of our recommendationso and to verify 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 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 Submified,
K{rx'ns!: & AsswEE*t**, .trnc"
k.k
David Noteboom, Staff Engineer
Reviewed by:
Daniel E. Hardin, P.E.
attachrnents Figure I
Figure 2
Figure 3 *
Pits
Pits
Test Results
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APPROXIMATE SCALE_FEET
2A-7 -537 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
PIT 1 PII 2 PIT 3
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LEGEND
TOPSOIL; SANDY SILTY CLAY WITH ROOTS AND ORGANICS, MEDIUM STIFF, SLIGHTLY
MOIST, BROWN.
CLAY (CL); SANDY, SILTY, VERY STIFF, SLIGHTLY MOIST' BROWN
BASALT COBBLES AND BOULDERS (GM); IN A SILT AND SAND MATRIX, DENSE, SLIGHTLY
MOIST, WHITISH.
F HAND DRIVEN LINER SAMPLE
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE PRIOR TO SEPTEMBER 18,2024,
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 NOT MEASURED AND THE LOGS OF THE
EXPLORATORY PITS ARE PLOTTED TO DEPTH.
4. THE EXPLORATORY PIT LOCATIONS 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 (PCI) (NSTU D 2216).
2A-7 -537 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2
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SAMPLE OF: Sondy Silty Cloy
FROM:Pit1@2.5'
WC = 7.5 %, DD = 99 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
ft.r. i.* reruit! oppt ont to &.
smplG ted.d. Tb. iGding repoil
.hall not b qrcduc.d, €xept in
full. wlthod th6 wd{.n omrcYol of
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1001,0 APPLIED PRESSURE - KSF 10
SWTLL_CONSOLIDATION TEST RESULT Fig. 320-7-537 Kumar & Associates
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