HomeMy WebLinkAboutSoils Report 11.14.2016H-PKUMAR
Geotechnical 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: hpkglenwoodOkumarusa.com
Office Locations: Parker, Glenwood Springs, and Silverthome, Colorado
November 14, 2016H
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4,0
Rob Schober wri ty C[)& i
198 Monarch Road
Glenwood Springs, Colorado 81601
(rwschober@gmail.com)
Project No.16-7-512
Subject: Subsoil Study for Foundation Design, Proposed Residence, Lot 39, Filing 5, Elk
Springs, 198 Monarch Road, Garfield County, Colorado
Dear Mr. Schober:
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 October 10, 2016. The data obtained and our recommendations based on
the proposed construction and subsurface conditions encountered are presented in this report.
Hepworth-Pawlak Geotechnical, Inc., (now H-P/Kumar) previously performed a preliminary
geotechnical study for Filings 6 through 9, Elk Springs (formerly Los Amigos Ranch PUD) and
reported our findings on February 14, 1997, Job No. 197 617.
Proposed Construction: The proposed residence will be one story wood frame construction
over a walk -out basement located within the building envelope as shown on Figure 1. Ground
floor will be slab -on -grade. Cut depths are expected to range between about 2 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 vacant lot is vegetated with a pinion and juniper forest, sage brush, grass
and weeds. The site is located on a rolling upland mesa. The ground surface slopes slightly
down to the south. Numerous basalt cobbles and boulders are visible on the ground surface.
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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 one foot of topsoil, consist of
basalt cobbles and boulders in a silty sandy gravel matrix. Results of a gradation analysis
performed on a sample of clayey gravel (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.
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 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. Loose and 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 soils. Voids created from
boulder removal at footing grade should be filled with a structural material such as road base
compacted to 98 percent standard Proctor density at a moisture content near optimum or
concrete. 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 50 pcf for the on-site soil as backfill.
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 basement 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 the area that local perched groundwater can develop during times of
heavy precipitation or seasonal runoff. Frozen ground during spring runoff can also create u
perched condition. We recommend below -grade construction, such as retaining walls,
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Project No. 16-7-512
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crawlspace and 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 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.
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. 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 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
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Project No. 16-7-512
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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 -R s KUMAR
12
Louis E. Eller
Reviewed by:
Daniel E. Hardin, P.E. f , '. /'/s/.
LEE/ljf
attachments Figure 1 — Location of Exploratory Pits
Figure 2 — Logs of Exploratory Pits
Figure 3 -- Gradation Test Results
H -P z KUMAR
Project No. 16-7-512
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LOT 39
}
1 r PIT 2 i I
I IN 1
I J
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1
1
I y
LOT 38 J LOT 40
1 I
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1 }
I I PIT 1 1
l I • I
L BUILDING ENVELOPE J
25 0 25 50
APPROXIMATE SCALE -FEET
16-7-512
H-Pw-KUMAR
MONARCH ROAD
LOCATION OF EXPLORATORY PITS
Fig. 1
— 0
— 10
PIT 1
LEGEND
TOPSOIL.
WC=7.5
-I +4=46
-200=27
PIT 2
BASALT ROCKS (GM); IN SILTY SANDY GRAVEL MATRIX, MEDIUM DENSE, SLIGHTLY MOIST,
LIGHT BROWN, CALCAREOUS.
DISTURBED BULK SAMPLE.
t PRACTICAL REFUSAL TO DIGGING WITH BACKHOE.
NOTES
0 —
10
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON OCTOBER 17, 2016.
2. THE LOCATIONS OF THE EXPLORATORY PITS WERE MEASURED APPROXIMATELY BY PACING FROM
STAKES IN THE FIELD.
3. 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.
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).
16-7-512
H -P- KUMAR
LOGS OF EXPLORATORY PITS
Fig. 2
p H�, FpIYUFIT1ME READINGS METERANALYS[5 U.S. STANDARD SERIESSIEVE ANALYSIS1 CLEAR SOUARE OPENINGS 1
0 45 MIN. 15 H.
60MIN19MIN.4 MIN 1 MIN
*325 *140 #60 *35 #18 *10 *4 315' 314' 1 1/2' 3' 5'6' 8' 100
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DIAMETER OF PARTICLES IN MILOMETERS
f 1 Ic1 1 of DIM IODA Ffi1
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16-7-512
GRAVEL 46 %
SAND 27 %
USDA SOIL TYPE: Silty Sandy Gravel
H -P- KU MAR
SILT AND CLAY 27 %
FROM: Pit 1 at 6 Feet
USDA GRADATION TEST RESULTS
Fig. 3