HomeMy WebLinkAboutSoils Report 03.23.2018H-PKUMAR
Geotechnlcal Engineering 1 Engineering Geology
Materials Testing 1 Environmental
5020 County Road 154
Glenwood Springs, CO 81601
Phone: (970) 945-7988
Fax: (970) 945-8454
Email: hpkglenwood@kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado
March 23, 2018
Nic Lough
637 North Bridge Lane
Carbondale, Colorado 81623
nlridgerunner@ginail.com
RECEIVED
MAY 0 4 2018
GARFIELD COUNTY
COMMUNITY DEVELOPMENT
Project No.18-7-207
Subject: Subsoil Study for Foundation Design, Proposed Residence, MJN Lot B, MJN
Road, South of Carbondale, Garfield County, Colorado
Dear Nic:
As requested, H-P/Kumar 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 March 16, 2018. 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 one story wood frame structure over
a full basement with an attached garage located on the site as shown on Figure 1. Ground floor
will be slab -on -grade. Cut depths are expected to range between about 3 to 10 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 is open grass pasture land which slopes moderately down to the north
at grades of 5 to 7%. North of the building area, the lot becomes moderately steep down to a
west -trending ephemeral drainage. West and north of the building area, the vegetation consists
of cedar and pinyon trees and brush.
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
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presented on Figure 2. The subsoils encountered, below about 1 foot of topsoil, consist of sandy
silty clay with occasional seams of cobbles. Results of swell -consolidation testing performed on
relatively undisturbed samples of the sandy silty clay, presented on Figures 3 and 4, indicate low
compressibility under existing moisture conditions and light loading and a low to moderate
expansion potential in Pit 1 or collapse potential (settlement under constant load) in Pit 2 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 3 feet of structural fill placed on the undisturbed natural soil designed for an allowable
soil bearing pressure of 2,000 psf for support of the proposed residence. The natural soils tend to
expand or compress after wetting and there could be some post -construction foundation
settlement. Footings should be a minimum width of 16 inches for continuous walls and 2 feet for
columns. Structural fill can consist of the on-site non -expansive soils or a suitable imported
material such as 3/4 -inch road base. The structural fill should be compacted to at least 98% of the
maximum standard Proctor density at a moisture content near optimum. 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 14 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 or 45 pcf if imported 3/4 inch road base is
used as backfill.
Floor Slabs: Slabs -on -grade should be placed on at least 3 feet of structural fill overlying the
natural on-site soils. The structural fill should consist of on-site non -expansive soils or imported
3/4 -inch road base compacted to at least 95% of the maximum standard Proctor density at a
moisture content near optimum. 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
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Project No. 18-7-207
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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.
Underdrain System: Although free water was not encountered during our exploration, it has
been our experience in mountainous areas that local perched groundwater can develop during
times of heavy precipitation or seasonal runoff. Frozen ground during spring runoff can also
create a perched condition. We recommend below -grade construction, such as retaining walls,
crawlspace and basement areas, be protected from wetting and hydrostatic pressure buildup by
an undcrdrain systcm.
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 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 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
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Project No. 18-7-207
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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.
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
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.
H-PKUMAR
Project No. 18-7-207
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If you have any questions or if we may be of further assistance, please let us know.
Respectfully Submitted,
H -P- KUMAR
Daniel E. Hardin, P.
Rev. by: SLP
DEH/kac
attachments Figure 1 — Location of Exploratory Pits
Figure 2 — Logs of Exploratory Pits
Figures 3 and 4 — Swell -Consolidation Test Results
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cc: Dale Kaup dale@kaupengineering.coin
H-PMCUMAR
Project No. 18-7-207
LOCATION OF EXPLORATORY PITS
,, t
25 0 25
_......_ 50
APPROXIMATE SCALE -FEET
18-7-207
H -P- KUIVIAR
Fig. 1
0
— 5
10
15
LEGEND
PIT 1
EL. 99'
WC=15.0
DD=111
PIT 2
EL. 93'
WC=7.2
DD=93
-200=77
TOPSOIL, ORGANIC SANDY SILTY CLAY, ROOT ZONE, FIRM, MOIST, DARK BROWN.
0
5-
10 —
10
15
11 CLAY (CL); SILTY, SANDY, SCATTERED COBBLEY ZONES, MEDIUM STIFF TO STIFF, SLIGHTLY
MOIST, BROWN, LOW PLASTICITY.
HAND DRIVEN 2 -INCH DIAMETER LINER SAMPLE.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON MARCH 16, 2018.
2. THE EXPLORATORY PITS WERE LOCATED BY THE CLIENT.
3. THE ELEVATIONS OF THE EXPLORATORY PITS WERE PROVIDED BY THE CLIENT.
4. THE EXPLORATORY PIT LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE ONLY
TO THE DEGREE IMPLIED BY THE METHOD USED.
1-
w
w
0
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 DIGGING. PITS WERE
BACKFILLED SUBSEQUENT TO 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).
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H - PvKl1 MAR
LOGS OF EXPLORATORY PITS
Fig. 2
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CONSOLIDATION - SWELL
rhet• Mt twain* VP*IY 1.
6.1401•I lasted. Thwt temlinc• tripes!
ocean:41nel, with AS114 D-4546,
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n n n—%KUMAR
SAMPLE OF: Sandy Cloy
FROM: Pit 1 7.5'
WC = 15.0 %, DU ~ 111 pcf
•
EXPANSION UNDER CONSTANT
' PRESSURE UPON WETTING
m
SWELL -CONSOLIDATION TEST RESULTS
1 00
Fig. 3
2
0
2
4
V)
—6
z
0
—12
4
18-7-207
H -P KUMAR
10
SWELL -CONSOLIDATION TEST RESULTS
100
Fig. 4
SAMPLE OF: Sandy Silty Clay
FROM: Pit 2 c 7'
WC = 7.2 %, DD = 93 pcf
—200 = 77 %
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
•
These (e.t ieautl! upply MI. 14 the
'ampler (aging Thei lsfii fo irpe•rt
holt not b feweutocH, e. Irl in
full, without Pa wpilton approval of
Kumarv, Inc, Swell
Kumar and testing
d testingq 10.414 In
...old. a with AiM 0 •-•0114
T
I. —`
._
—._
..........
—
.... __
...............--
.
18-7-207
H -P KUMAR
10
SWELL -CONSOLIDATION TEST RESULTS
100
Fig. 4