HomeMy WebLinkAboutSoils Report 11.14.2019Gr�r nl Ali, M
Geoff& A and M te$ I Engineers 5020 County Road 154
and En lranrnenfai Scien3isis Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@kumarosa.com
An Empioyee Owned Company ;•ww.f;umarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs; and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 35
IRONBRIDGE PHASE 3
RIVER BEND WAY
GARFIELD COUNTY, COLORADO
PROJECT NO. 19-7-649
NOVEMBER 14, 2019
PREPARED FOR:
JEFFREY MOORE
1824 SOUTH BROADWAY
DENVER, COLORADO 80210
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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 - 3 -
FOUNDATIONS - 3 -
FOUNDATION AND RETAINING WALLS - 4 -
FLOOR SLABS - 5 -
UNDERDRAIN SYSTEM - 6 -
SURFACE DRAINAGE - 6 -
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. 19-7-649
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot
35, Ironbridge Phase 3, 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 general accordance with our agreement for geotechnical
engineering services to Jeffrey Moore dated October 10, 2019.
A field exploration program consisting of exploratory borings was conducted to obtain
information on the subsurface conditions. Samples of the subsoils 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 not available at the time of this study. Based on our conversations with the
client, we assume the proposed residence will be a one-story structure with a bonus room above
the garage. 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 are significantly different than described
above, 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 and weeds. The terrain is gently sloping down to the north with around 2 feet of elevation
difference across the assumed building area.
Kumar & Associates, Inc. Project No. 19-7-649
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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 work
in the area, several sinkholes were observed scattered throughout the Ironbridge Subdivision.
The nearest mapped sinkhole is at the northeast comer of Lot 63, about 750 feet from Lot 35.
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 boring was 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 35, 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. 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 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. 19-7-649
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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 about 7%2 feet of stiff to very stiff, slightly
sandy to sandy clay and silt, underlain by medium dense to dense, slightly silty sand and gravel
with cobbles. 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 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 relatively undisturbed drive samples of the slightly sandy to sandy clay and
silt, presented on Figure 4, indicate low compressibility under light loading and minor expansion
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 to moist.
FOUNDATION BEARING CONDITIONS
The upper clay and silt soils possess low bearing capacity and low to moderate settlement
potential. It has been our experience that the soils typically are compressible when wetted. The
expansion potential should be further evaluated at the time of excavation. The underlying sandy
gravel and cobble soils possess moderate bearing capacity and relatively low settlement
potential. At assumed excavation depths, the subgrade will consist of the fine-grained silt and
clay soils. Spread footings bearing on the fine-grained soils can be used for support of the
residence with the accepted risk of movement and distress mainly if the bearing soils are wetted.
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 soils.
Kumar & Associates, Inc. Project No. 19-7-649
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The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural fine-grained soils should 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 differential movement of % to 1 inch could
occur if the bearing soils are wetted.
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 firm natural soils. 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.
Kumar & Associates, Inc.
Project No. 19-7-649
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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. Backfill should not contain organics, debris or rock larger
than about 6 inches.
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 0.35. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 350 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 a nonexpansive 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 with the accepted risk of movement and distress. The settlement/heave potential of
the subgrade soils and the need for mitigation of movement potential should be evaluated at the
time of excavation. To reduce the effects of some differential movement, floor slabs should be
Kumar & Associates, Inc. Project No. 19-7649
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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 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 (if used) will be 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.
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.
Kumar & Associates, Inc, Project No. 19-7-649
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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. Consideration should be given to the use of xeriscape
to limit potential wetting of soils below the building 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 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 inay 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.
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
Kumar & Associates, Inc. Project No, 19-7-649
8
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.
4has,
Shane J. Robat, P.E.
Reviewed by:
Steven L. Pawla
SJR/kac
Kumar & Associates, Inc.: Project No. 19-7-649
_ PROPERTY
LINE
PROPERTY
LINE
15 ¢ 15 30
APPROXIMATE SCALE -FEET
19-7-649
Kumar & Associates
LOCATION OF EXPLORATORY BORINGS
Fig. 1
BORING 1
BORING 2
F-
w
W
li
a
W
— 5
-- 10
15
20
15/12
WC=6.8
DD=101
16/12
WC=10.7
DD=101
-200=98
26/12
58/12
19-7-649
30/12
WC=8.6
DD=114
-200=92
12/12
WC=9.5
DD=96
27/6, 50/6
0
5
10
15
20
Kumar & Associates LOGS OF EXPLORATORY BORINGS
Fig. 2
LEGEND
disc
I
/
TOPSOIL; SANDY SILTY CLAY, FIRM, MOIST, DARK BROWN, ORGANICS.
CLAY AND SILT (CL—ML); SLIGHTLY SAND TO SANDY, STIFF TO VERY STIFF, SLIGHTLY MOIST,
BROWN.
SAND AND GRAVEL (SM—GM); SLIGHTLY SILTY WITH COBBLES, MEDIUM DENSE TO DENSE,
SLIGHTLY MOIST, MIXED BROWN, SAND LAYER AT 10' IN BORING 1.
DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
DRIVE SAMPLE, 1 3/8—INCH I.D. SPLIT SPOON STANDARD PENETRATION TEST.
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.
t 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 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 D221 6);
OD = DRY DENSITY (pcf) (ASTM D2216);
—200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D1140).
19-7-649
Kumar & Associates
LEGEND AND NOTES
Fig. 3
1
s
ri
a
Fa
CONSOLIDATION - SWELL
ces
1
0
-2
- 3
- 4
J
— J
W
1# 0
Z
O —1
1-
0
J
0
N —2
Z
0
0
SAMPLE OF: Slightly Sandy Silt and Clay
FROM: Boring 1 0 2.5'
WC = 6.8 %, DD = 101 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
1.0
APPLIED PRESSURE - KSF 10
too
NNtriel idlN b.n',`sd Inv 1wus ran n
Mpf nol be npro0x.d. ueNN In
lu0. rMhoul the wrhuen a peep of
Wither fed M ocrblr. 3pc, 5111111.
Cen,aOdatiien liefhe wdom�ed 1n
a[wteooce .bt D..4bi
19-7-649
SAMPLE OF: Slightly Sandy Silt and Clay
FROM: Boring 2 ® 5'
WC = 9.5 %, DD = 96 pcf
1.0 APPLIED PRESSURE — KSF
Kumar & Associates
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
10 Too
SWELL —CONSOLIDATION TEST RESULTS
Fig. 4
IC -FA
Kumar & Ate, Mc.'"
C-eatechnical and Materials Engineers
and Envircnmentai Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
SAMPLE LOCATION
BORING
DEPTH
(#)
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
(pcf)
GRADATION
GRAVEL SAND
(%) (%)
PERCENT
PASSING NO.
200 SIEVE
ATTERBERG LIMITS
LIQUID LIMIT
(%)
PLASTIC
INDEX
UNCONFINED
COMPRESSIVE
STRENGTH
(lst)
r'rajecl N0.19.7-649
SOIL TYPE
1
2%
6.8
101
5
10.7
101
98
Slightly Sandy Silt and
Clay
Silt and Clay
2
2'/z
5
8.6
9.5
114
96
92
Slightly Sandy Silt and
Clay
Slightly Sandy Silt and
Clay