HomeMy WebLinkAboutSoils Report 01.17.2017H-PKUMAR
Geotechnical Engineering i Engin enng Geology
Materials Testing Environmenta.
5020 County Road 154
Glenwood Springs, CO 81601
Phone: (970) 945-7988
Fax: (970) 945-8454
Email: hpkglenwood@kumarusa.com
Office Locations: Parker, Glenwood Springs, and Silverthome, Colorado
January 17, 2017
Alpen Daniel Badgett and Dina Bowers
956 County Road 106
Carbondale, Colorado 81623
(alpendaniel @yahoo.com)
Project No.17-7-101
Subject: Subsoil Study for Foundation Design, Proposed Residence, 956 County Road
106, Garfield County, Colorado
Dear Alpen Daniel and Dina:
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 January 4, 2017. 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 one story and partial two story wood
frame construction. Ground floor will be slab -on -grade. Cut depths are expected to range
between about 3 to 4 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 property is occupied with two existing residences and outbuildings.
Vegetation consists of landscaped lawn area with scattered cottonwood and aspen trees. There
was about 6 inches of snow cover at the time of our exploration. The ground surface is relatively
flat with a slight slope down to the west. A shallow irrigation ditch crosses the property.
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 31/2 feet of man placed fill, consist
of silty sandy gravel with cobbles. Results of a gradation analysis performed on a sample of
sandy gravel with cobbles (minus 5 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 to moist.
-2 -
Foundation Bearing Conditions: The man placed fill encountered at the site is not suitable for
support of foundations and should be removed from beneath the proposed building area. The
proposed foundation can be extended down to the natural granular soils or the grade can be
returned with the compacted on-site soils devoid of vegetation and over size rock. The structural
fill should be compacted to 100 percent of standard Proctor density at a moisture content near
optimum.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we recommend spread footings or
thickened slab placed on the undisturbed natural granular soil or compacted structural fill be
designed for an allowable soil bearing pressure of 2,000 psf for support of the proposed
residence. Footings or thickened portion of slab should be a minimum width of 16 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 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 walls should be reinforced top and bottom to span local anomalies such as by
assuming an unsupported length of at least 10 feet. Foundation wails 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 45 pcf for the on-site soil as backfill.
Floor Slabs: The natural on-site soils, exclusive of topsoil and existing fill, 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 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 separate from the foundation, 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 topsoil, 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 and crawlspace
areas be protected from wetting and hydrostatic pressure buildup by an underdrain system. It is
our understanding the finished floor elevation at the lowest level is at or above the surrounding
grade. Therefore, a foundation drain system should not be required.
H -P = KUMAR
Project No. 17.7.101
-3 -
Lf needed, 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.
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.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
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 -P KUMAR
Project No. 17.7-101
4
If you have any questions or if we may be of further assistance, please let us know.
Respectfully Submitted,
H -Pt #SJMAR
Louis Eller
Reviewed by:
Daniel E. Hardin, P.E.
LEE/ksw
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13 f/ 7/1 w' ,
attachments Figure 1 — Location of Exploratory Pits
Figure 2 — Logs of Exploratory Pits
Figure 3 — Gradation Test Results
H -P ti KUMAR
Project No. 17-7-101
20 0 20 40
APPROXIMATE SCALE—FEET
17-7-101
i
SHED 'er
DRIVEWAY
EXISTING
PIT 1 RESIDENCE
BUILDING
AREA
■
PIT 2
EXISTING
RESIDENCE
H-PkKUMAR
LOCATION OF EXPLORATORY PITS
Fig. 1
W
1
,w
u.i
0
— 0
--5
PIT 1 PIT 2
1 +4=73
—200=6
0
5 —
— 10 10
LEGEND
EFILL: ABOUT 12 INCHES OF TOPSOIL OVERLAYING SILTY CLAYEY SAND AND GRAVEL WITH
COBBLES, LOOSE TO MEDIUM DENSE, MOIST, DARK BROWN.
i
GRAVEL AND COBBLES (GM—GP); SANDY, SILTY TO SLIGHTLY SILTY, DENSE, SLIGHTLY
MOIST, LIGHT BROWN, ROUNDED ROCK.
DISTURBED BULK SAMPLE.
NOTES
1. THE EXPLORATORY PITS WERE EXCAVATED WITH A BACKHOE ON JANUARY 11, 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 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:
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM 0 422);
—200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
DEPTH-FEET
17-7-101
H-PWUMAR
LOGS OF EXPLORATORY PITS J Fig. 2
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