HomeMy WebLinkAboutSoils Report 10.03.2019Kiffitar & Ass=!Age, int.."'
Geotechnical and Materials Engin' rs
and Environmental Scientists
An Employee Owned Company
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
October 3, 2019
Regina Piccione
1213 County Road 112
Carbondale, CO 81623
(regi naw22[a7,gniail .com)
RECEIVED
DEC 3 1 2019
GARFIELD COUNTY
COMMUNITY DEVELOPMENT
Project No.19-7-518
Subject: Subsoil Study for Foundation Design, Proposed Shop/Residence, 1213 County
Road 112, Carbondale, Colorado
Dear Ms. Piccione,
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 Regina Piccione dated August 26, 2019. The data obtained and our
recommendations based on the proposed construction and subsurface conditions encountered are
presented in this report.
Proposed Construction: The proposed building will be a steel frame single -story over a
walkout basement located on the site as shown on Figure 1. Cut depths are expected to range
between about 3 to 8 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 a vacant pasture at the time of our field investigation. The
ground surface was vegetated with grass and weeds. The terrain is strongly sloping down to the
east at an approximate 10% grade. An irrigation ditch is located approximately 40 feet uphill
from the proposed building location.
Subsurface Conditions: The subsurface conditions at the site were evaluated by excavating two
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 a''/ foot of topsoil, consist of
medium stiff, slightly sandy, silty clay. Results of swell -consolidation testing performed on
relatively undisturbed samples of the slightly sandy silty clay, presented on Figure 3, indicate
-2 -
low compressibility under existing moisture conditions and light loading and a minor expansion
or collapse potential when wetted. No free water was observed in the pits at the time of
excavation and the soils were slightly moist to 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 2,000
psf for support of the proposed building. The soils tend to compress after wetting and there
could be some post -construction foundation settlement. Footings should be a minimum width of
18 inches for continuous walls and 2 feet 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 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 length of at least 12 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 55 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 basement level
slabs to facilitate drainage. This material should consist of minus 2 -inch aggregate with less than
50% passing the No. 4 sieve and less than 2% passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95% 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 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, crawlspace and
Kumar & Associates, Inc. Project No. 19-7-518
3
basement 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 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 1% to
a suitable gravity outlet. Free -draining granular material used in the underdrain system should
contain less than 2% 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 11/2 feet deep. An
impervious membrane such as 20 mil PVC should be placed beneath the drain gravel in a trough
shape and attached to the foundation wall with mastic to prevent wetting of the bearing soils.
Surface Drainage: The following drainage precautions should be observed during construction
and maintained at all times afler the building 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 95% 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 10 feet in pavement and walkway areas. The grading above
the building should be sloped so that (in the event of) water overflowing from the
irrigation ditch will be routed away from the structure.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy irrigation should be located at least
10 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 area at this time. We make no warranty either
express or implied. The conclusions and recommendations submitted in this report are based
Kumar & Associates, Inc.'," Project No. 19-7-518
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 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 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 Submitted,
Kumar & Associates, Inc.
Shane J. Robat, P.E.
Reviewed by:
Daniel E. Hardin, P.
SJR/kac
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attachments Figure 1 • a [ on ; f: : loratory Pits
Figure 2 - Lb s ui_E*foratory Pits
Figure 3 — Swell -Consolidation Test Results
Table 1 — Summary of Laboratory Test Results
Kumar & Associates, Inc. a
-
Project No. 19.7-518
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ELEVATION 100' \
25 0 25 50
APPROXIMATE SCALE—FEET
19-7-518
Kumar & Associates
LOCATION OF EXPLORATORY PITS
Fig. 1
LEGEND
F -
w
w
M
a
w
0
-0
— 5
PIT 1 PIT 2
EL. 100' EL. 108'
WC=7.9
DD=96
-200=89
WC=9.7
DD=89
0
5
10 10
TOPSOIL; SILTY CLAY, ORGANICS, ROOTS, SOFT, MOIST, DARK BROWN.
CLAY (CL); SLIGHTLY SANDY, SILTY, MEDIUM STIFF, SLIGHTLY MOIST, CALCAREOUS, BROWN.
HAND DRIVE SAMPLE.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON SEPTEMBER 11, 2019.
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
PIT 1 AS ELEVATION 100.0 FEET.
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 AFTER SAMPLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216);
-200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
19-7-518
Kumar & Associates
LOGS OF EXPLORATORY TEST PITS
Fig. 2
CONSOLIDATION - SWELL
CONSOLIDATION - SWELL
0
—1
— 2
— 3
0
— 1
— 2
4
SAMPLE OF: Slightly Sandy, Silty Clay
FROM: Pit 1 ® 2'
WC = 7.9 %, DD = 96 pcf
—200 = 89 %
-- EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
1.0 APPLIED PRESSURE. - 3[SF 10 100
zw �ini�iy w101 77.11;,:11,144.1; I'I
f 09l Gu!
fhW proritinn unp1 !1
l lI. w1U L( IM wr$tI,n nppnpepl d
Miner ond M.o. F,hw. Inc. Swdl
rpmpidcbon l.i410 M in
dpn
oc4olca wit D-4548-4546
SAMPLE OF: Slightly Sandy, Silty Clay
FROM: Pit 2 CO 5'
WC = 9.7 %, DD = 89 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1.0 APPLIED PRESSURE - KSF 10 100
19-7-518
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 3
•
Kumar & Associates. Inc.
Geotechnical and Materials Engineers
and Environmental SCienlists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
SAMPLE LOCATION
BORING
DEPTH
NATURAL NATURAL
MOISTURE DRY
CONTENT DENSITY
(%) (vcfl
GRADATION
GRAVEL
(%)
SAND
(%)
ATTERBERG LIMITS
PERCENT
PASSING N0. LIQUID LIMB
200 SIEVE
PLASTIC
INDEX
(%)
UNCONFINED
COMPRESSIVE
STRENGTH
(asfl
Project No. 19-7-518
SOIL TYPE
1
2 7.9
96
89
2
5
9.7
89
Slightly Sandy, Silty Clay
Slightly Sandy, Silty Clay