HomeMy WebLinkAboutSoils Report 04.18.2019KA
Kumar
Geotechnical and Materials Engineers
and Environmental Scientists
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
An Employee Owned Company www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
RECEIVED
JUN 0 6 2019
GARFIELD COUNTY
COMMUNITY DEVELOPMENT
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 39, SPRING RIDGE RESERVE
GARFIELD COUNTY, COLORADO
PROJECT NO. 19-7-196
APRIL 18, 2019
PREPARED FOR:
KEITH WITTENBERG
243 ELK RIDGE DRIVE
GLENWOOD SPRINGS, COLORADO 81601
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TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 2 -
GEOLOGY -2-
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 2 -
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 3 -
FOUNDATIONS - 3 -
FOUNDATION AND RETAINING WALLS - 4 -
FLOOR SLABS - 5 -
UNDERDRAIN SYSTEM - 6 -
SITE GRADING - 6 -
SURFACE DRAINAGE - 7 -
LIMITATIONS - 7 -
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Kumar & Associates, Inc. Project No. 19-7-196
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PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot
39, Spring Ridge Reserve, Hidden Valley Drive, Garfield County, Colorado. The project site is
shown on Figure 1. The purpose of the study was to develop recommendations for foundation
design. The study was conducted in accordance with our agreement for geotechnical engineering
services to Keith Wittenberg, dated March 28, 2019.
A field exploration program consisting of exploratory borings was conducted to obtain
information on the subsurface conditions. Samples of the subsoils and bedrock obtained during
the field exploration were tested in the laboratory to determine their classification,
compressibility or swell and other engineering characteristics. The results of the field
exploration and laboratory testing were analyzed to develop recommendations for foundation
types, depths and allowable pressures for the proposed building foundation. This report
summarizes the data obtained during this study and presents our conclusions, recommendations
and other geotechnical engineering considerations based on the proposed construction and the
subsurface conditions encountered.
PROPOSED CONSTRUCTION
The proposed single-family residence will be a single -story house with an attached garage.
Below -grade level is not currently planned. The approximate location of the residence is
between the borings shown on Figure 1. We assume excavation for the building will have a
maximum cut depth of one level, about 5 to 8 feet below the existing ground surface. For the
purpose of our analysis, foundation loadings for the structure were assumed to be relatively light
and typical of the proposed type of construction.
If building loadings, location or grading plans are significantly different from those described
above, we should be notified to re-evaluate the recommendations contained in this report.
Kumar & Associates, Inc. Project No. 19-7-196
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SITE CONDITIONS
The property was vacant at the time of our field exploration. The site is vegetated with grass,
weeds and sage brush. The ground surface in the general building area slopes moderately down
to the northeast. Maroon Formation sandstone is exposed on the hillside to the west of the lot.
GEOLOGY
According to the Geologic Map of the Cattle Creek Quadrangle, Garfield County, Colorado, by
Krikham, Steufert, Hemborg, and Stelling, dated 2014, the site is underlain by alluvium and
colluvium deposits of the Holocene age overlying Maroon Formation.
FIELD EXPLORATION
The field exploration for the project was conducted on April 8, 2019. Two exploratory borings
were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions. The
borings were advanced with 4 -inch diameter continuous flight auger powered by a truck-
mounted CME -45B drill rig. The borings were logged by a representative of Kumar &
Associates.
Samples of the subsoils were taken with a 2 -inch I.D. spoon sampler. The sampler was driven
into the subsurface materials at various depths with blows from a 140 -pound hammer falling 30
inches. This test is similar to the standard penetration test described by ASTM Method D-1586.
The penetration resistance values are an indication of the relative density or consistency of the
subsoils and hardness of the bedrock. Depths at which the samples were taken and the
penetration resistance values are shown on the Logs of Exploratory Borings, Figure 2. The
samples were returned to our laboratory for review by the project engineer and testing.
SUBSURFACE CONDITIONS
Graphic logs of the subsurface profiles encountered at the site are shown on Figure 2. Below
about 1 to 2 feet of organic topsoil, the subsoils consist of stiff to very stiff, sandy, silty, clay,
underlain by hard sandstone/siltstone bedrock. In Boring 1, medium dense/very stiff sandy clay
and gravel with cobbles layer was encountered under the silty, sandy clay.
Kumar & Associates, Inc. Project No. 19-7-196
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Laboratory testing performed on samples obtained during the field exploration included natural
moisture content and density, unconfined compressive strength, and percent silt and clay (percent
passing the No. 200 sieve). Swell -consolidation testing was performed on relatively undisturbed
drive samples of the clay subsoils. The swell -consolidation test results, presented on Figure 4,
indicate low compressibility under relatively light surcharge loading and no expansion to minor
expansion potential when wetted under a constant light surcharge. Undisturbed sampling of the
clayey gravel soils was not possible due to the rock content. The laboratory testing is
summarized in Table 1.
No free water was encountered in the borings at time of drilling. The subsoils were slightly
moist to moist.
FOUNDATION BEARING CONDITIONS
The subsoil materials encountered at the site generally possess low to moderate compressibility
potential when wetted. Surface runoff, landscape irrigation, and utility leakage are possible
sources of water which could cause wetting. Footing foundations can be used with the accepted
risk of movement. Deep foundations, such as drilled piers or micropiles, can be used if the risk of
movement cannot be tolerated. We should be contacted if deep foundation recommendations are
desired.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction,
the residence can be founded with spread footings placed on
undisturbed natural soils with a risk of settlement mainly if the bearing soils are wetted.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural soils/bedrock can be designed for an
allowable bearing pressure of 1,500 psf. Based on experience, we expect initial
settlement of footings designed and constructed as discussed in this section will
be up to about 1 inch. Additional movement could be on the order of 1 inch for a
limited wetted depth of around 10 feet below the footings.
Kumar & Associates, Inc. Project No. 19-7-196
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3) '1'he footings should have a minimum width of 16 inches for continuous footings
and 24 inches for isolated pads.
4) Continuous foundation walls should be reinforced top and bottom to span local
anomalies and limit the risk of differential movement. One method of analysis is
to design the foundation wall to span an unsupported length of at least 12 feet.
Below grade level are not currently planned. If a basement level is planned, the
foundation walls acting as retaining structures should also be designed to resist a
lateral earth pressure as discussed in the "Foundation and Retaining Walls"
section of this report.
5) Exterior footings and footings beneath unheated areas should be provided with
adequate soil cover above their bearing elevation for frost protection. Placement
of foundations at least 36 inches below the exterior grade is typically used in this
area.
6) Prior to the footing construction, the topsoil and loose or disturbed soils should be
removed and the footing bearing level extended down to competent bearing soils.
7) A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FOUNDATION AND RETAINING WALLS
Foundation walls and retaining structures which are laterally supported and can be expected to
undergo only a slight amount of deflection should be designed for a lateral earth pressure
computed on the basis of an equivalent fluid unit weight of at least 55 pcf for backfill consisting
of the on-site soils. Cantilevered retaining structures which are separate from the residence and
can be expected to deflect sufficiently to mobilize the full active earth pressure condition should
be designed for a lateral earth pressure computed on the basis of an equivalent fluid unit weight
of at least 45 pcf for backfill consisting of the on-site soils.
All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffic, construction materials and equipment. The
pressures recommended above assume drained conditions behind the walls and a horizontal
backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will
Kumar & Associates, Inc. Project No. 19-7-196
5
increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain
should be provided to prevent hydrostatic pressure buildup behind walls.
Backfill should be placed in uniform lifts and compacted to at least 90% of the maximum
standard Proctor density at near optimum moisture content. Backfill placed in pavement and
walkway areas should be compacted to at least 95% of the maximum standard Proctor density.
Care should be taken not to overcompact the backfill or use large equipment near the wall, since
this could cause excessive lateral pressure on the wall. Some settlement of deep foundation wall
backfill should be expected, even if the material is placed correctly, and could result in distress to
facilities constructed on the backfill.
The lateral resistance of foundation or retaining wall footings will be a combination of the
sliding resistance of the footing on the foundation materials and passive earth pressure against
the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated
based on a coefficient of friction of 0.40. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 325 pcf. The
coefficient of friction and passive pressure values recommended above assume ultimate soil
strength. Suitable factors of safety should be included in the design to limit the strain which will
occur at the ultimate strength, particularly in the case of passive resistance. Fill placed against
the sides of the footings to resist lateral loads should be compacted to at least 95% of the
maximum standard Proctor density at a moisture content near optimum.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, can be used to support lightly loaded slab -on -grad(
construction. There could be differential settlement potential from wetting of the bearing soils
similar to that described above for footings. 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 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
at least 50% retained on the No. 4 sieve and less than 12% passing the No. 200 sieve.
Kumar & Associates, Inc. Project No. 19-7-196
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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 (plus 6 inch) rock.
UNDERDRAIN SYSTEM
Although groundwater was not encountered during our exploration, it has been our experience in
the area and where clay soils are present and bedrock is shallow that local perched groundwater
can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring
runoff can create a perched condition. Therefore,
we recommend below -grade construction,
such as crawlspace and basement areas, be protected from wetting by an underdrain system
drain should also act to prevent buildup of hydrostatic pressures behind foundation walls.
The
The underdrain system should consist of a drainpipe surrounded by free -draining granular
material placed at the bottom of the wall backfill. The drain lines should be placed at each level
of excavation and at least 1 foot below lowest adjacent finish grade, and sloped at a minimum
1% grade to a suitable gravity outlet. Free -draining granular material used in the drain system
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. The drain gravel should be at least 11/2 feet deep. An
impervious liner such as 20 mil PVC should be placed below the drain gravel in a trough shape
and attached to the foundation wall with mastic to keep drain water from flowing beneath the
wall and to other areas of the building.
SITE GRADING
The risk of construction -induced slope instability at the site appears low provided cut and fill
depths are limited. We assume cut and fill depths for foundation construction will not exceed
about 5 to 8 feet. Embankment fills should be compacted to at least 95% of the maximum
standard Proctor density near optimum moisture content. Prior to fill placement, the subgrade
should be carefully prepared by removing all vegetation and topsoil and compacting to at least
95% of the maximum standard Proctor density. The fill should be benched into the portions of
the hillside exceeding 20% grade. Permanent unretained cut and fill slopes should be graded at
2 horizontal to 1 vertical or flatter and protected against erosion by revegetation or other means.
This office should review site grading plans for the project prior to construction.
Kumar & Associates, Inc. Project No. 19-7-196
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SURFACE DRAINAGE
Providing proper surface grading and drainage will be critical to prevent wetting of the bearing
soils and limiting building settlement and distress. The following drainage precautions should be
observed during construction and maintained at all times after the residence has been completed:
1) Excessive wetting or drying 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 areas and to at
least 90% of the maximum standard Proctor density in landscape areas.
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 paved 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 foundation walls. Consideration should be given to use of xeriscape to
prevent wetting of bearing soils from landscape 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 borings drilled excavated at the locations indicated on Figure 1, 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 borings and variations in
the subsurface conditions may not become evident until excavation is performed. If conditions
Kumar & Associates, Inc. Project No. 19-7-196
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encountered during construction appear to be 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 of 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.
Respectfully Submitted,
Kumar & Associates, Inc.
Shane J. Robat, P.E.
Project Manager
Reviewed by:
Steven L. Pawlak,
SJR/kac
Kumar & Associates, Inc. Project No. 19-7-196
-PROPOSED
RESIDENCE
50 0 50 mo
APPROXIMATE SCALE—FEET
19-7-196
Kumar & Associates
LOCATION OF EXPLORATORY BORINGS
Fig. 1
w
z
w
0
0
- 5
10
- 15
20
BORING 1
15/12
WC=12.1
DD=117
34/12
WC=8.6
DD=118
-200=72
} 75/9
73/8
50/2
BORING 2
110140
5/12
WC=23.0
DD=99
UC=3,000
37/12
WC=5.6
DD=120
96/11
50/1
0
5-
10 -
10
15 -
20
- 25 25
1-
w
w
0
w
w
0
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Kumar & Associates
LOGS OF EXPLORATORY BORINGS
Fig. 2
LEGEND
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TOPSOIL; ORGANIC, CLAY AND SILTY, SANDY, FIRM, MOIST, DARK BROWN.
CLAY (CL); SANDY, SILTY, STIFF TO VERY STIFF, SLIGHTLY MOIST TO MOIST, BROWN.
CLAY AND GRAVEL (GC—CL); SANDY WITH SCATTERED COBBLES, MEDIUM DENSE, SLIGHTLY
MOIST, MIXED BROWN.
SANDSTONE/SILTSTONE BEDROCK; HARD, SLIGHTLY MOIST, RED. MAROON FORMATION.
11 DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
15/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 15 BLOWS OF A 140—POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON APRIL 8, 2019 WITH A 4—INCH—DIAMETER
CONTINUOUS—FLIGHT POWER AUGER.
2. THE LOCATIONS OF THE EXPLORATORY BORINGS WERE MEASURED APPROXIMATELY BY PACING
FROM FEATURES SHOWN ON THE SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE NOT MEASURED AND THE LOGS OF THE
EXPLORATORY BORINGS ARE PLOTTED TO DEPTH.
4. THE EXPLORATORY BORING LOCATIONS SHOULD BE CONSIDERED ACCURATE ONLY TO THE
DEGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOGS REPRESENT THE
APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM 02216);
DD = DRY DENSITY (pcf) (ASTM D2216);
—200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D1140);
UC = UNCONFINED COMPRESSIVE STRENGTH (psi) (ASTM D 2166).
19-7-196
Kumar & Associates
LEGEND AND NOTES
Fig. 3
CONSOLIDATION - SWELL
CONSOLIDATION - SWELL
3
SAMPLE OF: Sandy Silty Clay
FROM: Boring 1 0 2.5'
1II WC = 12.1 %, DD = 117 pcf
1 4 1.1_
1 t NO MOVEMENT UPON
I li r
l_ , 1 ._
WETTING
1.0 APPUED PRESSURE -- KSF 10 1P0
SAMPLE OF: Sandy Silty Clay
FROM: Boring 2 ® 5'
WC = 5.6 %, DD = 120 pcf
Uel ....t1. oyper W rh.
IO .IM I.,unp r tim. Irk
efu14 without VW oyWvwl of
%71Numm and A. odn1n In.. Si.nI
..tl.n .of nmmcn In
aenn<..Ine ti u••;ste.
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
APPLIED PRESSURE — KSF
10 100
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Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 4
K±A
Kumar & Associates, Inc.
Geotechnical and Materials Engineers
and Environmental Scientists
kumarusa.com
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
SAMPLE LOCATION
BORING
DEPTH
NATURAL
MOISTURE
CONTENT
NATURAL
DRY
DENSITY
flit
GRADATION
GRAVEL SAND
(%)
ATTERBE
RG LIMITS
PERCENT
PASSING NO. LIQUID LIMIT
200 SIEVE
_J%)
PLASTIC
INDEX
f�1
UNCONFINED
COMPRESSIVE
STRENGTH
(ast)
Protect No. 19-7-196
SOIL TYPE
1 2Y2
5
12.1
8.6
117
118
72
2 2'/2
23.0
99
3,000
Sandy Silty Clay
Sandy Silty Clay
Sandy Silty Clay
5
5.6
120
Sandy Silty Clay
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