HomeMy WebLinkAboutSoils Report 07.21.2020K±A
Kumar & Associates, Inc..
Geotechnical and Materials Engineers
and Environmental Scientists
An Employee Owned Company
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarusa.com
www.kumarusa.corn
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
1151 HIDDEN VALLEY DRIVE
LOT 38, SPRING RIDGE RESERVE
GARFIELD COUNTY, COLORADO
PROJECT NO. 20-7-342
JULY 21, 2020
PREPARED FOR:
MATT JURMU
2906 HAGER LANE
e GLENWOOD SPRINGS, COLORADO 81601
matt a,ianckilaconstruction.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 1 -
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 - 5 -
SURFACE DRAINAGE - 6 -
LIMITATIONS - 6 -
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. 20-7-342
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
Lot 38, Spring Ridge Reserve, 1151 Hidden Valley Drive, Garfield County, Colorado. The
project site is shown on Figure 1. The purpose of the study was to develop recommendations for
the foundation design. The study was conducted in accordance with our agreement for
geotechnical engineering services to Matt Jurmu dated June 12, 2020.
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, design
recommendations and other geotechnical engineering considerations based on the proposed
construction and the subsurface conditions encountered.
PROPOSED CONSTRUCTION
The proposed residence will generally be a one and two story structure with attached garage cut
at shallow depth into the hillside. The approximate location of the residence is in the area of the
borings shown on Figure 1. Ground floors are assume to be structural over crawlspace or slab -
on -grade. Grading for the structure is assumed to be relatively minor with cut depths between
about 2 to 8 feet. We assume relatively light foundation loadings, typical of the proposed type of
construction.
If building loadings, location or grading plans change significantly from those described above,
we should be notified to re-evaluate the recommendations contained in this report.
SITE CONDITIONS
The subject site was vacant at the time of our field exploration. The ground surface is gently to
moderately sloping down to the northeast at a grade of about 10 to 20 percent. Vegetation
consists of sagebrush, grass and weeds.
Kumar & Associates, Inc. ® Project No. 20-7-342
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FIELD EXPLORATION
The field exploration for the project was conducted on June 15, 2020. 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 augers powered by a truck-
mounted CME -45B drill rig. The borings were logged by a representative of Kumar &
Associates, Inc.
Samples of the subsoils were taken with 1% inch and 2 inch I.D. spoon samplers. The samplers
were 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 conditions encountered at the site are shown on Figure 2. The
subsoils consist of about 1/2 foot of topsoil overlying very stiff, sandy to very sandy clay and silt
to between 4 and 5 feet underlain by hard to very hard siltstone/sandstone bedrock to the
maximum explored depth of 16 feet. Weathered siltstone/sandstone bedrock was encountered in
Boring 2 from about 4 to 6 feet in depth. Drilling in the very hard bedrock with auger equipment
was difficult and drilling refusal was encountered in the deposit at Boring 2.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and finer than sand -size gradation analyses. Results of swell -consolidation
testing performed on a relatively undisturbed drive sample of the upper soil, presented on
Figure 4, indicate low to moderate compressibility under existing moisture conditions and light
loading and a low collapse potential when wetted. The laboratory testing is summarized in
Table 1.
No free water was encountered in the borings at the time of drilling and the subsoils were
slightly moist.
Kumar & Associates, Inc. ® Project No. 20-7-342
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FOUNDATION BEARING CONDITIONS
The upper soils encountered at the site generally possess low bearing capacity and low to
moderate compressibility potential mainly under wetted conditions. 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. Extending the foundations down to
the bedrock should be used if the risk of movement cannot be tolerated.
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 bearing on the
undisturbed natural soils or bedrock 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 or 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. Footings placed entirely on the bedrock should be designed
for an allowable bearing pressure of 4,000 psf. Additional settlement on the order
of %2 inch could occur for footings placed on the upper soils under wetted
conditions.
2) The footings should have a minimum width of 18 inches for continuous walls and
2 feet for isolated pads.
3) 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 exterior grade is typically used in this
area.
4) Continuous foundation walls should be heavily 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 also be designed to resist
lateral earth pressures as discussed in the "Foundation and Retaining Walls"
section of this report.
Kumar & Associates, Inc. ® Project No. 20-7.342
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5) Topsoil and any loose or disturbed soils should be removed and the footing
bearing level extended down to the natural soils or bedrock. The exposed soils in
footing area should then be moistened and compacted.
6) 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
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 a moisture content near optimum. 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 350 pcf. The
Kumar & Associates, Inc. ® Project No. 20-7-342
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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, are suitable to support lightly loaded slab -on -grade
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.
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 free water was not encountered during our exploration, it has been our experience in
the area and where there are clay soils 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. 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 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
Kumar & Associates, Inc. ® Project No. 20-7-342
6
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 1'/2 feet deep.
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) 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.
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. Free -draining wall backfill should be
capped with about 2 feet of the on-site soils to reduce surface water infiltration.
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 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 encountered
Kumar & Associates, Inc. ® Project No. 20-7-342
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during construction appear different from those described in this report, we should be notified so
that 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.
Respectfully Submitted,
Kumar & Associates, Inc.
Pvt,'44"/Z
James H. Parsons, E.I.
Reviewed by:
Steven L. Pawlak,
JHP/kac
cc:
Kumar & Associates, Inc.
Project No. 20.7.342
G
5
A
LOT 36
LOT 38
BORING 1
•
•
BORING 2
is m
30 0 30 00
APPROXIMATE SCALE -FEET
LOT 39
LOT 37
20-7-342
Kumar & Associates
LOCATION OF EXPLORATORY BORINGS I Fig. 1
DEPTH-FEET
0
5
10
15
BORING 1
EL. 100'
28/12
WC=7.7
DD=98
- 200=40
50/4.5
WC=3.9
- 200=37
50/0
50/1
BORING 2
EL. 106'
50/5
50/1
0
5 --
10
15 -
- 20 20
20-7-342
Kumar & Associates
LOGS OF EXPLORATORY BORINGS
Fig. 2
Vtrntf]nq\207342-02 to 03.thol
LEGEND
TOPSOIL; SANDY, CLAY AND SILT, ORGANICS, FIRM, SLIGHTLY MOIST, RED.
CLAY AND SILT (CL—ML); SANDY TO VERY SANDY, SLIGHTLY CALCAREOUS, VERY STIFF TO
HARD, SLIGHTLY MOIST, RED.
WEATHERED BEDROCK, SILTSTONE, SANDSTONE, HARD, SLIGHTLY MOIST, RED.
BEDROCK, SILTSTONE, SANDSTONE, HARD TO VERY HARD, SLIGHTLY MOIST, RED.
L
DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
28/12
DRIVE SAMPLE, 1 3/8—INCH I.D. SPLIT SPOON STANDARD PENETRATION TEST.
DRIVE SAMPLE BLOW COUNT. INDICATES THAT 28 BLOWS OF A 140—POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
DEPTH AT WHICH BORING CAVED.
PRACTICAL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON JUNE 15, 2020 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 MEASURED BY HAND LEVEL AND REFER
TO BORING 1 AS AN ASSUMED 100' BENCHMARK.
4. THE EXPLORATORY BORING 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 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).
20-7-342
Kumar & Associates
LEGEND AND NOTES
Fig. 3
1
.. 0
CONSOLIDATION - SWELL
—1
— 2
—3
— 4
— 5
6
0
20-7-342
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULT
Fig. 4
SAMPLE OF: Silty Clayey Sand
FROM: Boring 1 0 2.5'
WC = 7.7 %, DD = 98 pcf
—200 = 40
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
N
)111
These test results apply only to the
ampler tested. The testing epart
shall not be reproduced, evc pt In
!lull, without the written approval or
Kumar and Aseoclates, Inc. Swell
Consolidation testing performed In
/accordance with ASTM D-4546.
1 0 APPLIED PRESSURE - KSF 10 10
0
20-7-342
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULT
Fig. 4
1(+A
Kumar & Associates, Inc.®
Geotechnical and Materials Engineers
and Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Proiect No. 20-7-342
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
(pcfl
GRADATION
PERCENT
PASSING NO.
200 SIEVE
ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
(psi)
SOIL TYPE
BORING
DEPTH
(ft)
GRAVEL
(%)
SAND
(%)
LIQUID LIMIT
(%)
PLASTIC
INDEX
(°lo)
1
2 1/2
7.7
98
40
Silty Clayey Sand
5
3.9
37
Sandstone