HomeMy WebLinkAboutSubsoils Study for Foundation DesignlGrf åffirffiffini':,iå**5020 County Road 154
Glenwood Springs, CO 81601
phone: (970)945-7988
fax: (970) 945-8454
emai I : kaglenwood@J<umarusa.com
www.kumarusa.comAn Emdoycc olrncd Compony
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Snmmit Cormty, Colorado
March 7,2023
Peter Glauber
444 Girdle Road
East Aurora, New York 14052
glauberp@starktech'com
project No. 23-7-135
Subject: Subsoil Study for Foundation Design, Proposed Residence, 3499 Elk Springs
Drive, Lot 58, Filing 9, Los Amigos Subdivision, Garfield County, Colorado
Dear Mr. Glauber:
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 February 2,2023. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: We assume that the proposed residence will be a two-story wood
frame structure over a crawlspace located on the site as shown on Figure 1. Ground floor in the
garage will be slab-on-grade. Cut depths are expected to range between about 2to 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
aboveo we should be notifïed to re-evaluate the recommendations presented in this report.
Site Conditions: The site was vacant with about 2 feet of snow on it. The lot slopes down to
the south at between 5 and 10% grade. The site is vegetated with juniper trees with an
understory of scattered bushes, grass and weeds.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating
three 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 I fo 1,% feet of topsoil, consist of
1 foot of clayey sand with basalt gravel and cobbles overlying relatively dense, basalt rocks up
to boulder size. Backhoe digging refusal was encountered in all three pits at depths of 2Yzto
3%feet. Results of a per cent finer than sand size gradation analysis and Atterberg Limits testing
performed on a sample of clayey sand (minus 3-inch fraction) obtained from the site are
presented on Figure 3. No free water was observed in the pits at the time of excavation and the
soils were slightly moist.
a
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
2,000 psf for support of the proposed residence. Footings should be a minimum width of
î6Tr"he.-f for continuous walls and2feet for columns. Loose and disturbed soils and existing
fill 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 [!1gþ1þlow 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 10 feet. Foundation walls acting as retaining
structures should be designed to resist alateruI 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 to
moderately 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 below grade slabs
(if any) to facilitate drainage. This material should consist of minus 2-inch aggregate with less
than 50% passing the No. 4 sieve and less than2Vo passing the No. 200 sieve.
All fìll materials for support of floor slabs should be compacted to at least 95o/o of maximum
standard Proctor density at a moisture content near optimum. Required fìIl can consist of the
on-site soils devoid of vegetation, topsoil and oversized rock or a suitable imported sandy gravel
such as 3/¿-inchroad base.
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
heavy 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 (if any), 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 1 foot below lowest adjacent fïnish grade and sloped at a minimw lo/oto
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
Kumar & Associates, lnc. o Project No. 23-7-135
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contain less than 2% passing the No. 200 sieve, less than 50oá passing the No. 4 sieve and have a
maximum size of 2 inches. The drain gravel backfill should be at least 1% feet deep.
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. Drying could increase the expansion potential of the soils.
2) 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 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 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. A swale may be
needed uphill to direct surface runoff around the residence.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfïll.
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
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
monitor the implementation of our recommendations, and to veriff that the reconìmendations
have been appropriately interpreted. Significant design changes may require additional analysis
Kumar & Associates, lnc. @ Project No. 23-7-135
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or modifications to the recoÍrmendations 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 & Associates, lnc.
Daniel E. Hardin, P.
Reviewedby:
Steven L. Pawlak, P.E.
DEH/kac
attachments Figure I - Location of Exploratory Pits
Figure 2 * Logs of Exploratory Pits
Table I - Summary of Laboratory Test Results
Kumar & Associates, lnc. @ Project No. 23-7-135
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23-7 -135 Kumar & Associates LOCATION OF EXPLORATORY PITS Fig. 1
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LEGEND
TOPSOIL; ORGANIC CtiYEY SAND, FIRM, MOIST, DARK BROWN
SAND (SC); CLAYEY, GRAVELLY, SMALL BASALT COBBLES, MEDIUM DENSE,
SLIGHTLY MOIST, BROWN.
BASALT GRAVEL, COBBLES AND BOULDERS IN SAND SILT MATRIX (GM); CALCAREOUS, DENSE,
SLIGHTLY MOIST, LIGHT BROWN MATRIX WITH GRAY ROCKS.
DISTURBED BULK SAMPLE.
PRACTICAL DIGGING REFUSAL.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON FEBRUARY 23, 2023.
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 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:
-200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D
LL = LIQUID LIMIT (ASTM D A31E);
PI = PLASTICITY INDEX (ASTM D 4318).
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Fig. 223-7-135 Kumar & Associates LOGS OF EXPLORATORY PITS
IC U**rOggnf*å-*
TABLE 1
SUMMARY OF LABORATORYTEST RESULTS
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PIT
I to2
rftì
DEP'IH
SA¡IPLE LOCATION
f%t
NATURAL
tttosTuRE
CONTENT
focff
NATURAL
DRY
DENSITY
GRAI
(%)
GRAVEL
(%)
sAt¡D
noN
37
PERCENT
PASSING NO.
200 stEvE
39
{Y")
LIQUID LI]SIT
T4
(olol
PLASTIC
INDÐ(
{osf}
UNCONFINED
coilPRESSnÆ
STRENGTH
Clayey Sand with Gravel
SOIL TYPE
No. 23-7-135