HomeMy WebLinkAboutSoils Report 02.14.2019ic+A & cia ,1.
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
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 29, IRONBRIDGE, PHASE III
1797 RIVERBEND WAY
GARFIELD COUNTY, COLORADO
PROJECT NO. 19-7-120
FEBRUARY 14, 2019
PREPARED FOR:
RED DEER REALTY
ATTN: LEO CARMICHAEL
151 PRINCE DRIVE
CARBONDALE, COLORADO 81623
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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 -
FLOOR SLABS - 4 -
UNDERDRAIN SYSTEM - 5 -
SURFACE DRAINAGE - 5 -
LIMITATIONS - 6 -
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURES 4 AND 5 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Kumar & Associates, Inc. Project No. 19.7-120
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot
29, Ironbridge, Phase III, 1797 Riverbend 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 Red Deer Realty dated January 25, 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
The proposed residence will be a two-story wood frame structure over a crawlspace. The
attached garage will have a slab -on -grade floor. 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 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 lot was vacant and covered with about 6 inches of snow at the time out our site visit. The
surface of the lot slopes gently down to the north. Vegetation consists of grass and weeds below
the snow.
Kumar & Associates, Inc. Project No. 19.7.120
2
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Ironbridge development.
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 sinkholes to develop and can produce areas of
localized subsidence. During previous work in the area, several sinkholes were observed
scattered throughout the Ironbridge development. These sinkholes appear similar to others
associated with the Eagle Valley Evaporite in areas of the Roaring Fork 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 29 throughout the service life of the proposed residence, in our
opinion, is low and similar to other 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 January 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
shown on the Logs of Exploratory Borings, Figure 2. The samples were returned to our
laboratory for review by the project engineer and testing.
Kumar & Associates, Inc. Project No. 19-7-120
3
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils consist of up to about 1 foot of gravelly sandy clay and silt fill overlying 2 to 12 feet of
very stiff, sandy clay and silt soils. Dense, slightly silty sandy gravel with cobbles was
encountered below the clay and silt at depths of 3 to 12 feet. Drilling in the dense granular soils
with auger equipment was difficult due to the cobbles and drilling refusal was encountered in the
deposit at 131/2 feet in Boring 1.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and percent finer than sand size gradation analyses. Results of swell -consolidation
testing performed on relatively undisturbed drive samples, presented on Figures 4 and 5, indicate
low to moderate compressibility under conditions of loading and wetting. The samples had a
low swell or collapse (settlement under constant load) 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.
FOUNDATION BEARING CONDITIONS
The upper clay and silt soils have low bearing capacity and generally low to moderate
compressibility when wetted. Shallow spread footings placed on the natural clay and silt soils
can be used with a risk of settlement as described below. The footing bearing level on Lot 29
should be deepened below existing ground surface so there is no more that 4 feet of silt and clay
soils below the bearing level as a foundation settlement mitigation measure. In sub -excavated
areas below design footing level, the on-site soils could be replaced compacted. Extending the
footing bearing level down or use of a deep foundation placed on the underlying gravel and
cobble soil could be used to achieve a low settlement risk.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, the building can be founded with spread footings bearing on the
natural clay and silt or granular soils or compacted structural fill with a settlement risk.
Kumar & Associates, Inc. Project No. 19.7-120
The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab -on -grade
4
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 or structural fill 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 about 1/2 to 1 inch or less. Additional differential settlement up
to about 1 inch could occur if the bearing soils are wetted.
2) The footings should have a minimum width of 20 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 14 feet.
Foundation walls acting as retaining structures should also be designed to resist a
lateral earth pressure corresponding to an equivalent fluid unit weight of at least
55 pcf for the onsite silt and clay soil as backfill.
5) All existing fill, topsoil and any loose or disturbed soils should be removed in
footing areas. The exposed soils in footing areas should then be moistened and
compacted. Structural fill should extend laterally beyond the footing edges at
least 1/2 the fill depth below the footing and be compacted to at least 98% of the
standard Proctor density at near optimum moisture content. The soils should be
protected from frost and concrete should not be placed on frozen soils.
6) A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FLOOR SLABS
construction with a risk of settlement if the bearing soils are wetted. Structural fill about 2 feet
deep consisting of the on-site soils can be used to limit the settlement risk.
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
Kumar & Associates, Inc. Project No. 19-7-120
5
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.
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 silt and clay soils devoid of vegetation and topsoil.
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 also 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.
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 with the drain invert elevation at least 1 foot below lowest adjacent finish grade and
sloped at a minimum 1% to a suitable gravity outlet or sump. 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. An impervious membrane such as 20 mil PVC should be placed
beneath the pipe and drain gravel in a trough shape and attached to the foundation wall with
mastic to prevent wetting of the bearing soils.
SURFACE DRAINAGE
Providing proper surface grading and drainage is very important to the satisfactory performance
of the building. 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. 19.7-120
-6
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
reduce the potential for 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 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.
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
Kumar & Associates, Inc. Project No. 19-7-120
7 -
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.
D
Daniel E. Hardin, P.E.
DEH/kac
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Kumar & Associates, Inc. Project No. 19-7-120
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PROPERTY LINE -1
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15 0 15 30
APPROXIMATE SCALE -FEET
19-7-120
BENCHMARK:
SEWER MANHOLE RIM
A. ELEVATION=100 FEET ASSUMED
BORING 2
PROPOSED
RESIDENCE
r SETBACK
LOT 29
BORING 1
/
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LOT 30
Kumar & Associates
LOCATION OF EXPLORATORY BORINGS
Fig. 1
DEPTH-FEET
- - 0
10
BORING 1
EL. 104'
19/12
WC=5.2
DD=106
15/12
WC=7.0
DD=96
25/12
WC=9.2
DD=99
-200=86
BORING 2
EL. 105.5'
50/6
WC=1.3
-200=6
0
5 -
10 -
15 15
19-7-120 19-7-120
Kumar & Associates
LOGS OF EXPLORATORY BORINGS
Fig. 2
LEGEND
FILL: GRAVELLY SANDY CLAY AND SILT, MEDIUM DENSE TO STIFF, MOIST, BROWN.
/ 1 CLAY AND SILT (CL—ML); SANDY, VERY STIFF, SLIGHTLY MOIST, LIGHT BROWN.
19/12
GRAVEL (GM—GP); SANDY WITH COBBLES, SLIGHTLY SILTY, DENSE, SLIGHTLY MOIST, MIXED
BROWN.
DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA LINER SAMPLE.
DRIVE SAMPLE, 1 3/8—INCH I.D. SPLIT SPOON STANDARD PENETRATION TEST.
DRIVE SAMPLE BLOW COUNT. INDICATES THAT 19 BLOWS OF A 140—POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
PRACTICAL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON JANUARY 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 THE BENCHMARK; SEWER MANHOLE IN FRONT OF LOT EL. 100' ON FIG. 1.
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 D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216);
—200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
19-7-120
Kumar & Associates
LEGEND AND NOTES
Fig. 3
2
CONSOLIDATION - SWELL
Theo !ell reevne op* only to lh.
Iprnplep !.pled. Thn leptInq report
oha1I nM be roprndund. orcepl In
full, niNp.l Ihp .rrttlon approval of
Kumar and Meoclbtal, Ina. $w.i1
CoaecCdctlon t.niing performed In
accordance .4A P.511.1 D-4568,
SAMPLE OF: Sandy Silty Clay
FROM: Boring 1 ® 2.5'
WC = 5.2 %, DD = 106 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
19-7-120
1.0 APPLIED PRESSURE - KSF 10 100
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 4
se FACrellnA'97: 20 -Cd to
CONSOLIDATION - SWELL
—4
— 6
— 8
—10
—12
Thee. Seal refine ee7sy only ie lbw
•ompin teole0 The taltlnq renen
obeli not be t, t ducted, except In
full, w:lheui the +ellen criplcrel of
Aimee and Neocotaf, fns. Swell
Cnn.Wfdellen 1nLnp pert earned In
ecco•donce with WSTRI 0— 45.46.
19-7-120
SAMPLE OF: Sandy Silty Clay
FROM: boring 1 5'
WC = 7.0 %, DD = 96 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1.0 APPLIED PRESSURE - KSF 10 100
Kumar & Associates
SWELL—CONSOLIDATION TEST RESULTS
Fig. 5
IC -FA
•
R de ASSOCIates, inc
Geotechnical and Materials Engineers
and Environmental Scientists
kumarusa.com
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 19.7-120
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
(MO
GRADATION [
PERCENT
PASSING NO.
200 SIEVE
1 ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
(psi
SOIL TYPE
BORING
DEPTH
(ft)
GRAVEL
(/0)
SAND I
1
ro)
LIQUID LIMIT
i (%)
PLASTIC
INDEX
(%)
1
21/2
5.2
106
Sandy Silty Clay
5
7.0
96
Sandy Silty Clay
10
9.2
99
86
Sandy Silty Clay
2
10
1.3
6
Slightly Silty Sandy Gravel
i