HomeMy WebLinkAboutSoils Report 08.10.2017H-PKUMAR
Geotechnical Engineering 1 Engineering Geology
Materials Testing 1 Environmental
RECEIVED
AUG 0 8 2019
GARFIELD COUNTY 5020 County Road 154
COMMUNITY DEVELOPMENT Glenwood Springs, CO 81601
Phone: (970) 945-7988
Fax: (970) 945-8454
Email: hpkglenwood@kumarusa.com
August 10, 2017
Ed Kitselman
1460 East Valley Road
Basalt, Colorado 81621
(ed kitselmanC conicast.net)
Office Locations: Parker, Glenwood Springs, and Silverthorne, Colorado
Project No.17-7-569
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 43, Filing 6, Elk
Springs, 0301 Woodruff Road, Garfield County, Colorado
Dear Mr. Kitselman:
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 July 21, 2017. The data obtained and our recommendations based on the
proposed construction and subsurface conditions encountered are presented in this report.
Hepworth-Pawlak Geotechnical (now H-P/Kumar) previously performed a preliminary
geotechnical study for Filings 6 through 9, Elk Springs (formerly Los Amigos Ranch PUD) and
reported the findings on February 14, 1997, Job No. 197 617.
Proposed Construction: The proposed residence will be one and two story wood frame
construction with an attached garage and located on the site as shown on Figure 1. Ground
floors will be slab -on -grade with a turned -down thickened edge. Cut depths are expected to
range between about 2 to 5 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 lot was vacant and the property corners and building envelope corners
were staked at the time of our site visit. Vegetation consists of scattered juniper trees, sage
brush, cactus, grass and weeds. The ground surface is moderately sloping down to the west at a
grade of about 8 percent in the building area. A dry swale and drainage easement border the
south side of the building envelope.
Subsurface Conditions: The subsurface conditions at the site were evaluated by observing four
exploratory pits excavated at the approximate locations shown on Figure 1. The logs of the pits
are presented on Figure 2. The subsoils encountered, below about 1/2 to 1 foot of topsoil, consist
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of sandy silty clay down to a depth of about 2 feet overlying basalt gravel, cobbles and boulders
in a sandy silt and clay matrix down to the maximum depth excavated of 4 feet. Results of a
gradation analysis performed on a sample of sandy clayey gravel with cobbles (minus 5 inch
fraction) obtained from Pit 1 at 3 to 4 feet are presented on Figure 3. The laboratory testing
results are summarized in Table 1. No free water was observed in the pits and the soils were
slightly moist.
Foundation Recommendations:
Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread footings or
thickened edge slab -on -grade placed on the undisturbed natural granular 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 16 inches for continuous walls and 2 feet for columns. Utility
trenches and deep cut areas below about 3 feet may require rock excavating techniques such as
chipping or blasting. 'Topsoil, sandy silty clay and loose or 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. Voids created from boulder removal at
footing grade should be filled with a structural material such as road base compacted to at least
98 percent standard Proctor density at a moisture content near optimum or with concrete.
Exterior footings or tuned -down edges should be provided with adequate cover above their
bearing elevations for frost protection or with rigid insulation. Placement of footings at least 36
inches below the exterior grade is typically used in this area. Continuous foundation walls and
turn -down sections 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 (if any) 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, excluding organics and rock
larger than about 6 inches.
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
separated from bearing walls and columns should have expansion joints which allow
unrestrained vertical movement. This would not apply to thickened edge slabs. 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 relatively well graded sand and gravel
such as road base should be placed beneath slabs for support. This material should consist of
minus 2 inch aggregate with less than 50% passing the No. 4 sieve and less than 12% passing the
No. 200 sieve.
H-P%-KUMAR
Prniart Nn 17-7-r,FQ
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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:
It is our understanding the finished floor elevation at the lowest level will
be at or above the surrounding grade. Therefore, a foundation drain system is not required. 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 also 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 and wall drain system.
If the finished floor elevation of the proposed structure has a floor level below the surrounding
grade, we should be contacted to provide recommendations for an underdrain system. All earth
retaining structures should be properly drained.
Surface Drainage: The following drainage precautions should be observed during construction
and maintained at all times after the residence has been completed:
1)
2)
3)
4)
5)
Inundation of the foundation excavations and underslab areas should be avoided
during construction.
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.
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. A swale may be
needed uphill to direct surface runoff around the residence.
Roof downspouts and drains should discharge well beyond the limits of all
backfill.
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
H-PkKUMAR
Pre -Nine -4 Mn 17_7 $ & O
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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,
H-PKUMAR
Steven L. Pawlak, P.E; 16 2 21 6
Ip
Reviewed by:
Daniel E. Hardin, P.E.
SLP/kac
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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:
Silver Town Structures - Attn: Matt Monger Cmonger2O021sopris.net)
F&M Architects LLC - Attn: Flynn Stcwart-Scvery (flynu( fandrarchitects_com)
H -P -KUMAR
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APPROXIMATE SCALE -FEET
LOCATION OF EXPLORATORY PITS
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PIT 1
EL. 7916'
0
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LEGEND
+4=42
200=40
PIT 2
EL, 7917'
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PIT 3
FI . 7913'
WC=9.2
DD=88
-200=77
PIT 4
EL. 7911'
LJ
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'- -tel TOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, SLIGHTLY MOIST, DARK BROWN.
1
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CLAY (CL); SANDY, SILTY, MEDIUM STIFF, MOIST, REDDISH BROWN, LOW PLASTICITY.
BASALT GRAVEL, COBBLES AND BOULDERS (GC); CLAYEY, SILTY, SANDY, DENSE, SLIGHTLY
MOIST, LIGHT BROWN, CALCAREOUS.
0
SI HAND DRIVEN LINER SAMPLE.
DISTURBED BULK SAMPLE.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE PRIOR TO OUR OBSERVATION ON
AUGUST 1, 2017.
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 OBSERVED IN THE PITS AT THE TIME OF OUR FIELD OBSERVATION.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422);
-200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
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17-7-569 H -P- KUMAR
LOGS OF EXPLORATORY PITS Fig. 2
100
90
BO
70
80
50
40
30
20
10
HYDROMETER ANALYSIS
SIEVE ANALYSIS
71ME REWINDS 1 D.S. STANDARD SEAIEB
24 HRS 7 HRS
43 MIN 15 MIN 4OMIN 191.IN 4414 1MIN f 0 1100 /50 /40 /30
1
/16 110 y8 14 3/e" 3/4" 1 1/2" 3"
clEA71 SONARC OPENINGS
0
10
20
30
40
50 II
8
80
70
e0
90
0 I I I I I I I 1 1 1 1 1 1 1 1 1 11 1 1 1 1 I I I I I I I I I 1 1 1 1 1 1 1 1 100
.001 .002 .005 .009 .019 .037 .075 .150 .300 .800 1.18 2.39 4.75 9.5 19 35.1 78.2 127 200
DIAMETER OF PARTICLES IN MILLIMETERS 152
CLAY TO SILT
SAND
FINE 7 MEDIUM COARSE FINE
GRAVEL
COARSE
COBBLES
GRAVEL 42 X SAND 18 X SILT AND CLAY 40 X
LIQUID LIMIT PLASTICITY INDEX
SAMPLE OF: Sandy Silty Clayey Gravel with Cobbles
FROM: Pit 10 3-4'
These test results apply only to the
samples whloh were tailed. The
testing report shall not be reproduced,
except In full, without the written
approval o1 Kumar & Associates, Inc.
Sieve analysts testing Is performed In
accordance with ASTM D422, ASTM C136
and/or ASTM 01140.
17-7-569
H-P-MWMAR
GRADATION TEST RESULTS
Fig. 3
H-PI<UMAR
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 17-7-569
SAMPLE LOCATION
NATURAL
GRADATION I
ATTERBERG LIMITS
PIT
DEPTH
(Ft)
MOISTURE
CONTENT
(%I
NATURAL
DRY DENSITY
(Pct)
GRAVEL
(%)
SAND
(%)
PERCENT
PASSING NO.
200 SIEVE
LIQUID LIMI
(%)
PLASTIC
INDEX
(%)(PSF)
UNCONFINED
COMPRESSIVE
STRENGTH
SOIL TYPE
1
3 to 4
42
18
40
Sandy Silty Clayey Gravel
with Cobbles
3
1
9.2
88
77
Sandy Silty Clay