HomeMy WebLinkAboutSoils Report 11.11.2019I(+A
Geolechrdcal 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
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SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 96, IRONBRIDGE
RIVER BEND WAY
GARFIELD COUNTY, COLORADO
PROJECT NO. 19-7-653
NOVEMBER 11, 2019
PREPARED FOR:
KEN KULWIEC
185 MONARCH ROAD
GLENWOOD SPRINGS, COLORADO 81601
kkuIwiec(a sopris.net
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 1 -
SUBSIDENCE POTENTIAL - 2 -
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 3 -
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 4 -
FOUNDATIONS - 4 -
FOUNDATION AND RETAINING WALLS - 5 -
FLOOR SLABS - 6 -
UNDERDRAIN SYSTEM - 6 -
SURFACE DRAINAGE - 7 -
LIMITATIONS - 7 -
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - SWELL -CONSOLIDATION TEST RESULTS
FIGURE 4 - GRADATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Kumar & Associates, Inc. Project No. 19-7-653
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
Lot 96, Ironbridge, River Bend Way, 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 Ken Kulwiec dated October 29, 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, design
recommendations and other geotechnical engineering considerations based on the proposed
construction and the subsurface conditions encountered.
PROPOSED CONSTRUCTION
Design plans were conceptual at the time of this study. We understand the proposed residence
will generally be a one-story structure. Ground floors will be either structural over crawlspace or
slab -on -grade. Grading for the structure is assumed to be relatively minor with cut depths
between about 3 to 5 feet. We assume relatively light foundation loadings, typical of the
proposed type of construction.
If building location, grading or loading information change significantly, we should be notified
to re-evaluate the recommendations presented in this report.
SITE CONDITIONS
The site was vacant at the time of our field exploration. The ground surface was vegetated with
grass, weeds, and scattered sage brush with scattered cobbles at the surface. The terrain is gently
sloping across the building site to moderately sloping down to the north-northeast.
Kumar & Associates, Inc. Project No. 19-7-653
-2 -
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Ironbridge Subdivision.
These rocks are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some
massive beds of gypsum and limestone. There is a possibility that massive gypsum deposits
associated with the Eagle Valley Evaporite underlie portions of the lot. Dissolution of the
gypsum under certain conditions can cause areas of localized subsidence. During previous
studies for the subdivision development, several sinkholes were observed scattered throughout
the Ironbridge Subdivision. These sinkholes appear similar to others associated with the Eagle
Valley Evaporite in other areas of the Roaring Fork River valley.
Sinkholes were not observed in the immediate area of the subject lot. No evidence of cavities
was encountered in the subsurface materials; however, the exploratory borings were relatively
shallow, for foundation design only. Based on our present knowledge of the subsurface
conditions at the site, it cannot be said for certain that sinkholes will not develop. The risk of
future ground subsidence on Lot 96, throughout the service life of the proposed structure, in our
opinion, is low and similar to other platted lots in the area; however, the owner should be made
aware of the potential for sinkhole development. If further investigation of possible cavities in
the bedrock below the site is desired, we should be contacted.
FIELD EXPLORATION
The field exploration for the project was conducted on October 31, 2019. Three 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 13/8 inch and 2 inch I.D. spoon samplers. The samplers
were driven into the subsoils 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. Depths at which the samples were taken and the penetration resistance values are
Kumar & Associates, Inc. Project No. 19-7-653
-3 -
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 6 -inches of topsoil overlying 1 to 31/2 feet of very stiff, sandy to very
sandy silt, underlain by dense, slightly silty, sandy to very sandy gravel, cobbles and boulders.
Drilling in the coarse granular soils with auger equipment was difficult due to the cobbles and
boulders and drilling refusal was encountered in the deposit.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and gradation analyses. Results of swell -consolidation testing performed on
a relatively undisturbed drive sample of the sandy to very sandy silt, presented on Figure 3,
indicate low compressibility under light loading and low collapse (settlement under constant
load) when wetted and moderate compressibility when additionally loaded. Results of gradation
analyses performed on small diameter drive samples (minus 11/2 -inch fraction) of the coarse
granular subsoils are shown on Figure 4. 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.
FOUNDATION BEARING CONDITIONS
The fine-grained silt soils possess low bearing capacity and low to moderate settlement potential.
The underlying coarse granular, sandy gravel and cobble soils possess moderate bearing capacity
and relatively low settlement potential.
At assumed excavation depths, the subgrade could transition the silt and coarse granular soils.
Spread footings bearing entirely on the coarse granular soils are recommended for foundation
support of the residence to limit settlement potential.
Kumar & Associates, Inc. Project No. 19-7-653
-4_
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, we recommend the building be founded with spread footings bearing
on the natural granular soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural granular soils should be designed for
an allowable bearing pressure of 3,000 psf. Based on experience, we expect
settlement of footings designed and constructed as discussed in this section will
be about 1 inch or less.
2) The footings should have a minimum width of 16 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 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 should also be designed to resist
lateral earth pressures as discussed in the "Foundation and Retaining Walls"
section of this report.
5) The topsoil and any loose or disturbed soils should be removed and the footing
bearing level extended down to the relatively dense natural granular soils. The
exposed soils in footing area should then be moistened and compacted. Structural
fill placed to reestablish design bearing level should consist of a relatively well
graded granular soil compacted to at least 98% of standard Proctor density at near
optimum moisture content.
6) A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
Kumar & Associates, Inc. Project No. 19-7-653
-5 -
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 50 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 40 pcf for backfill consisting of the on-site soils. Backfill should not contain organics,
debris or rock larger than about 6 inches.
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 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 0.50. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 400 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
Kumar & Associates, Inc. Project No. 19-7-653
-6 -
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 a granular material 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. 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 interior 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 granular soils devoid of vegetation, topsoil and oversized rock.
UNDERDRAIN SYSTEM
It is our understanding the proposed finished floor elevation at the lowest level is at or above the
surrounding grade and the crawlspace is relatively shallow. 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 create a perched condition. We recommend below -grade construction, such as
retaining walls and basement areas, be protected from wetting and hydrostatic pressure buildup
by an underdrain and wall drain system.
If the finished floor elevation of the proposed structure is revised to have 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.
Kumar & Associates, Inc. Project No. 19-7-653
7
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.
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.
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
during construction appear different from those described in this report, we should be notified so
that re-evaluation of the recommendations may be made.
Kumar & Associates, Inc. Project No. 19-7-653
-8 -
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.
1411a44 -
Shane J. Robat, P.E.
Reviewed by:
Steven L. Pawla
SJR/kac
Kumar & Associates, Inc. Project No. 19-7.653
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LEGEND
BORING 1
EL. 100'
63/12 COMBINED
WC=1.5
+4=54
—200=12
59/6
BORING 2
EL. 95'
18/12
WC=5.1
DD=107
—200=50
50/0.5
BORING 3
EL. 100'
0
COMBINED
10
TOPSOIL; ORGANIC, SANDY SILT AND CLAY, FIRM, SLIGHTLY MOIST TO MOIST, DARK BROWN.
SILT (ML); SANDY TO VERY SANDY, VERY STIFF, SLIGHTLY MOIST, BROWN.
GRAVEL (GM—GP); SANDY TO VERY SANDY, SLIGHTLY SILTY WITH COBBLES AND PROBABLE
BOULDERS, DENSE, SLIGHTLY MOIST, BROWN. ROUNDED ROCK.
DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
DRIVE SAMPLE, 1 3/8—INCH I.D. SPLIT SPOON STANDARD PENETRATION TEST.
63/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 63 BLOWS OF A 140—POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
f PRACTICAL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON OCTOBER 31, 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 MEASURED BY HAND LEVEL AND REFER
TO BORING 1 AS ELEVATION 100'.
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 D2216);
DD = DRY DENSITY (pcf) (ASTM 02216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM 06913);
—200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM 01140).
19-7-653 19-7-653
Kumar & Associates
LOGS OF EXPLORATORY BORINGS
Fig. 2
—' 0
CONSOLIDATION - SWELL
— 2
— 3
—4
—5
SAMPLE OF: Slightly Clayey. Sand and Siltl
FROM: Boring 2 2.5'
WC = 5.1 %, DD = 107 pcf
—200 = 50 %
Th.as tett 'mai apdh ..to o EM
larepir, tested. The Wang r
shall not be ryredo.avd, trnpt 1n
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ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1.0 APPLIED} PRESSURE — KSF' 10 Opp
19-7-653
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 3
na...a1.9 07, 2019 - 11 S
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19-7-653 Kumar & Associates GRADATION TEST RESULTS
GRAVEL 47 X SAND 40 X SILT AND CLAY 13 X
LIQUID LIMIT PLASTICITY INDEX
Thee. fest resuHs apply only 10 the
samples which were tested. The
SAMPLE OF: Slightly Silty, Very Sandy Gravel FROM: Boring 3 0 2.5' & 5' (Combined)
testing report shall not be reproduced.
except In full, without the written
approval of Kumar & Associates. Inc.
Sieve analysts testing Is performed In
accordanto with ASTM D6915, !.STM 07928,
ASTM C15G and/or ASTM 01140.
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i DIAMETER OF PARTICLES IN MILLIMETERS j
GRAVEL 54 % SAND 34 % SILT AND CLAY 12 X
LIQUID LIMIT PLASTICITY INDEX
SAMPLE OF: Slightly Silty. Sandy Gravel FROM: Boring 1 0 2.5 & 5' (Combined)
CLAY TO SILT
90 r 1 , . : 1D
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.001 .002 .005 .009 .019 .037 .076 .150 .300. 1 .669 1.18 1 x.36 4.75 9.5 19 38.1 78J 127: pan
DIAMETER OF PARTICLES IN MILLIMETERS
8
HYDROMETER ANALYSIS
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SIEVE ANALYSIS
FINE MEDIUM COARSE
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FINE COARSE
GRAVEL
COBBLES
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Gecieci�nical and Materials Engineers
and Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
(acf)
GRADATION
PERCENT
PASSING NO.
ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
(Pati)
SOIL TYPE
BORING
DEPTH
_ (ft)
GRAVEL
SAND
LIQUID LIMB
1941
PLASTIC
INDEX
(%)
1
2/Z & 5
Combined
1.5
54
34
12
Slightly Silty, Sandy
Gravel
2
21/2
5.1
107
50
Slightly Clayey, Sand and
Silt
3
21/2 & 5
Combined
2 1
47
40
13
Slightly Silty, Very Sandy
Gravel
f