HomeMy WebLinkAboutSubsoils Report for Foundation Designl(+n Kumar & Associates, lnc.'
Geotechnical and Materials Engineers
and Environmental Scientists
An Employcc O^/nsd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-1988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
wwwkumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Splings, and Summit County, Colorado
March 7,2023
Mark and Christine Matson
2299 Elk Springs Drive
Glenwood Springs, Colorado 81601
rnarkrnatson6 @ gm ail. com
Project No.22-l-789
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 5, Filing 8,
Elk Springs,2299 Elk Springs Drive, Garfield County, Colorado
Dear Mark and Christine:
As requested, Kumar & Associates, lnc. performed a subsoil study for design of foundations at
the subject site. The study was conducted in accordance with our proposal for geotechnical
engineering services to you dated December 28,2022. 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 generally be a one and two-story wood-
frame structure with attached garage located on the site as shown on Figure 1. Ground floor will
likely be structural over crawlspace for the living areas and slab-on-grade for the garage. 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 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 site was vacant with approximately 1 to 3 feet of snow cover atthe
time of our field exploration. The ground surface was gently sloping down to the south at a
grade ofabout 5 percent.
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 %to l% feet of topsoil, consist of
dense, basalt cobbles and boulders in a calcareous sandy silt matrix down to the maximum
explored depth of 3 feet and practical digging refusal. Results of a gradation analysis performed
on a sample of the calcareous matrix soil (minus I%-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 below a frozen layer of topsoil.
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 ol]J,99-pgl_
for support of the proposed residence. The matrix soils tend to compress after wetting and there
could be some post-construction foundation settlement. Footings should be a minimum width of
16 inches for continuous walls and2 feet for columns. The topsoil 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 is typically used in this area.
Continuous foundation 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 alateral earth pressure based on an equivalent fluid unit
weight of at least 50 pcf for the on-site soil as backfill excluding organics and rock larger than
6 inches. Our experience in this area is that alarge trackhoe, typically used for house excavation
can usually excavate around 2 feet deeper than we could get with a small backhoe in our pits.
Deeper excavations will likely require chipping or blasting of the basalt rocks.
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-on-grade to facilitate drainage. This
material should consist of minus 2-inch aggregate with less than 50%o passing the No. 4 sieve and
less than 2oh 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 soils devoid of vegetation, topsoil and oversized (plus 6-inch) 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
heavy precipitation or seasonal runoff. Frozen ground during spring runoff can create a perched
Kumar & Associates, lnc, o Project No, 22-7-789
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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 rigid perforated PVC 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 finish grade and
sloped at a minimum/ro/o 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 Yz 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 ofthe foundation excavations and underslab areas should be avoided
during construction.
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at least 95o/o of lhemaximum 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.
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
2Yz inches in the first 10 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
backfill.
5) Landscaping which requires regular heavy inigation should be located at least
5 feet from the building.
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 concemed
Kumar & Associates, lnc. o Project No. 22-7-789
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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 verifo that the recommondations
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 fuither assistance, please let us know.
Respectfully Submitted,
Kumar & Associates, lnc,
James H. Parsons, P.E.
Reviewed by:
Steven L. Pawlak, P.E.
JHP/kac
attachments Figure 1 - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Gradation Test Results
Table 1 - Summary of Laboratory Test Results
cc Olaf Jean Architecture - Cassandra Westerlind - (cassandra(golaflean.com)
/0/23
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Kumar & Associates, lnc. !Project No. 22-7-789
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APPROXIMATE SCALE-FEET
LOCATION OF EXPLORATORY PITS Fig. 122-7 -789 Kumar & Associates
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PIT 2
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LEGEND
TOPSOIL; CLAY, SANDY TO VERY SANDY, ORGANICS, FIRM/FROZEN, SLIGHTLY MOIST,
BROWN.
GRAVEL AND COBBLES (GM); BOULDERS, CALCAREOUS SANDY SILTY MATRIX, DENSE,
SL|GHTLY MOTST, PALE GRAY/BROWN.
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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.
3. 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);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422);
_2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1140).
o ."/
22-7 -789 Kumar & Associates LOGS OF EXPLORATORY PITS Fig. 2
SIEVE ANALYSISHYDROMETER ANALYSIS
TIME READIN6S
7 HRS24 HRS
I UtN
U.S, STANDARD SERIES CLEAR SOUARE OPENINGS
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90
80
70
60
50
40
30
10
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70
80
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.o37 ,075 .t 50
.125
PARTICLES
152
DIAMETER OF IN
CLAY TO SILT COBBLES
GRAVEL 50 % SAND 59 %
LIQUID LIMIT - PLASTICITY INDEX
SAMPLE 0F: Colcorsous Silty Sdnd ond Grovel Motrix
SILT AND CLAY 11 %
FROM:Pll 3@1'-1.5'
These l€sl rasulls qpply only lo lhe
somplos whlch wors lsslgd. Ths
losllng roporl sholl nol b€ rcproducod'
sxcopl ln full, wllhoul lho wrlllen
qpprovol ol Kumor & Assoclql€s, lnc.
Slevs onolysls lesllng 13 perlorm€d ln
occordonc€ wlth ASTM 06913, ASTM D7928,
ASTM C156 ond/or ASTM D1140.
GRAVELSAND
COARSE FINE COARSEFINEMEDIUM
22-7 -789 Kumar & Associates GRADATION TEST RESULTS Fig. 3
rcn f;ffi[*'ir:lttr1iiy;'*"
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
No.22-7-789
Calcareous Silty Sand and
Gravel Matrix
SOIL TYPE
(psfl
UNCONFINED
COMPRESSIVE
STRENGTH
(%l
PLASTIC
INDEX
ATTERBERG LIMITS
("/"1
LIQUID LIM]T
PERCENT
PASSING NO.
200 stEVE
113950
GRADATIONSAMPLE LOCATION
DEPTHPIT
NATURAL
DRY
DENSITY
NATURAL
MOISTURE
CONTENT
SAND
(:/")
GRAVEL
(Y"l
2t.tI to LV,-J