HomeMy WebLinkAboutSubsoils Report for Foundation DesignI(fiA $#$lfi','ii:ll]$nn'Ysd
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An Emdoyri Ourncd Sompgny
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
wwwkumarusa.com
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Office Locations: Denver (HQ), Palker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT H-4
29 SAGES COURT
ASPEN GLEN SUBDIVISION
GARFIELD COUNTY, COLORADO
PROJECT NO.22-7-532
ocToBER 12,2022
PREPARED FOR:
LARISSA AND MICHAEL BUSO
9084 EAST WAGON WHEEL WAY
PARKER' COLORADO 80138
buso.larissa@gmail.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
SITE CONDITIONS...
SUBSIDENCE POTENTIAL
FIELD EXPLORATION
SUBSURFACE CONDITIONS
FOUNDATION BEARING CONDITIONS
DESIGN RECOMMENDATIONS
FOUNDATIONS
FLOOR SLABS
UNDERDRAIN SYSTEM ........
SURFACE DRAINAGE............
LIMITATIONS ..........
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGTIRE 3 - LEGEND AND NOTES
FIGURES 4 and 5 - SWELL-CONSOLIDATION TEST RESTILTS
TABLE 1 - SUMMARY OF LABORATORY TEST RESULTS
1
1
1
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J
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4
5
5
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Kumar & Associates, lnc. o Project No.22-7-532
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
Lot H-4 within Aspen Glen Subdivision, 29 Sages Court, Garfield County, Colorado. The
project site is shown on Figure 1. The pu{pose of the study was to develop recommendations for
foundation design. The study was conducted in general accordance with our agreement for
geotechnical engineering services to Larissa and Michael Buso dated July 27,2022.
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 development will be a single-family residence located as shown on Figure I and
consist of a 1 and 2-story structure with an attached garage. The ground floors willbe structural
over crawlspace in living areas and slab-on-grade in the garage. 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 site was vacant and vegetated with grass and weeds at the time of our field exploration. The
terain ranges from relatively flat to gently sloping down to the east with about 2 feet of
elevation difference across the building footprint. Sages Court is to the southeast and Aspen
Glen golf course is to the west.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian-age Eagle Valley Evaporite underlies the subject site. These rocks
are a sequence of gypsiferous shale, fine-grained sandstone and siltstone with some massive beds
Kumar & Associates, lnc. o Project No. 22-7.532
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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 oflocalized subsidence.
During prcvious work in the area, sinkholes have been observed scattered throughout the lower
Roaring Fork Valley. The nearest mapped sinkhole is about 1,000 feet southeast of this lot.
These sinkholes appear similar to others associated with the Eagle Valley Evaporite in this area.
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 H-4 throughout the service life of the proposed residence, in our
opinion, is low; 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 August 16,2022. 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-458 drill rig. The borings were logged by a representative of Kumar &
Associates.
Samples of the subsoils were taken with l%-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 ate 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.
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils encountered, below about 1 foot of topsoil, consist of about 6%to7 feet of stiff, sandy
silty clay, underlain by dense, silty sandy gravel and cobbles with probable boulders. Drilling in
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the dense coarse granular soils with auger equipment was difficult due to the cobbles and
probable boulders and drilling refusal was encountered in the deposit at depths of about 1 I and
12 feet.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and finer than sand size gradation analysis. Results of swell-consolidation
testing performed on relatively undisturbed drive samples of the clay soil, presented on Figures 4
and 5, indicate low compressibility under existing low moisture conditions and light loading and
minor expansion upon wetting or moderate to high compressibility after wetting under increased
loading. The natural moisture content and relatively low dry density indicates the clay soils may
be prone to settlement (collapse potential) when wetted. Our experience in this area indicates the
clay soils typically have a low collapse potential when wetted under load and not expansion.
The laboratory test results are summarizedin 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 natural sandy silty clay soils within about the upper 6 to 7 feet are typicaliy low density and
compressible especially when wetted. The underlying coarse granular soils possess a moderate
bearing capacity and a relatively low settlement potential. At assumed excavation depths, we
expect the subgrade will expose sandy silty clay soils. Spread footings should be feasible for
foundation support of the residence with a risk of settiement if the clay soils become wet.
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 or properly compacted structural fill. The bearing level could be extended
down through the clay soils to the underlying dense, coarse granular soils to reduce the
settlement potential and should be further evaluated at the time of construction,
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural clay soils should be designed for an
allowable bearing pressure of 1,500 psf. Footings placed entirely on the natural
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2)
granular soils or compacted structural fill should be designed for an allowable
bearing pressrue of 3,000 psf. Based on experience, we expect initial settlement
of footings designed and constructed as discussed in this section will be about
1 inch or less. There could be additional settlement of around % to 7 inch if the
clay bearing soils are wetted.
The footings should have a minimum width of 18 inches for continuous walls and
2 feet for isolated pads.
Exterior footings and footings beneath unheated areas should be provided with
adequate soil cover above their bearing elevation for fi'ost protection. Placement
of foundations at least 36 inches below exterior grade is typically used in this
area.
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 rctaining structures should also be designed to resist
lateral earth pressure coffesponding to an equivalent fluid unit weight of at least
55 pcf for the on-site fine-grained soil as backfill.
The topsoil and any loose or disturbed soils should be removed and the footing
bearing level extended down to the nafural soils. The exposed soils in footing
area should then be moistened and compacted to a minimum of 95Y, of the
standard Proctor density. If needed, structural fill used to reestablish design
footing bearing level in sub-excavated clay soil areas should consist of imported
'/+-inch road base that extends at least 1/z feet beyond footing edges and
compacted to at least 98% of standard Proctor density atnear optimum moisture
content.
A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
3)
4)
s)
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 rnovement with clay soil subgrade. The risk of movernent
can be reduced by placing slabs-on-grade on a minimum of 2 feet of compacted structural fill or
by using structural floors over crawlspace, which is commonly done in the area. The structural
fill should consist of CDOT Class 5 or 6 base course material.
6)
Kumar & Associates, lnc. o Project No.22-7.532
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To reduce the effects of some differential movement, floor slabs should be separated from al1
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 sand and gravel base
course should be placed beneath floor slabs-at-grade for support. This 4-inch thickness can be
included in the recommended 2 feet of base course below the slabs. A minimum -inch layer of
free-draining gravel should be placed beneath basement level slabs (if any) to facilitate drainage.
This material should consist of minus 2-inch aggregate with at least 50Yo retained on the No. 4
sieve and less than 2Yo passing the No. 200 sieve.
All fiIl materials for support of floor slabs should be compacted to at least 95Yo of maximum
standard Proctor density at a moisture content near optimum. Required fill, below the
recommended depth of base course, can consist of the on-site soils devoid of debris, topsoil and
oversized rocks (plus 4-inch).
LINDERDRAIN 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 and at least 1 foot below lowest adjacent finish grade and sloped at a minimum lo/o to
a suitable gravity outlet or drywell based in the underlying gravel. Free-draining granular
material used in the underdrain system should contain less than 2o/opassing 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 I1/zfeet deep. An impervious membrane such as 20 mil PVC should
be placed beneath the 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 will be very important to limiting wetting of the
bearing soils and potential building movement and distress. The following drainage precautions
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should be observed during construction and maintained at all times after the residence has been
completed:
1) Inundation ofthe 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 95o/o 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 6 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 iuigation should be located at least
5 feet from foundation walls.
LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
pr:inciples 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 concetned about MOBC, then aprofessional 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
monitor the implementation of our recommendations, and to verify that the recommendations
Kumar & Associates, lnc. @ Project No, 22-7-532
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have been appropriately interpreted. Significant design changes rnay require additional analysis
or mo<iifications to the recommendations presented herein. We recommend on-site observation
of excavations end foundation bearing strata and testing of structural filI by a re,presentative of
the geotechnical engineer.
Respectfu lly Submitted,
Knngar & Associa{es,
Steven L" Pawlak,
Reviewed By:
Daniel E. Hardin, P.E.
Hinge Architects * Kurt Camrth (kgf{#hr$ge:srchite+.1s"c*ir*
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Lot H
22-7 -532 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
BORING 1
EL. 6053'
BORING 2
EL. 6064.5'
0 0
18/ 12
\,l,,lC=7.4
DD=92
20/ 12
WC=9.4
DD= 1 05
-200=78
4 5
13/ 12 11/12
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DD= 1 02
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22-7 -532 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
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LEGEND
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TOPSOIL; SANDY SILTY CLAY WITH ORGANICS, FIRM, SLIGHTLY MOIST, BROWN
CLAY (CL) SANDY TO VERY SANDY WITH DEPTH, SILTY, STIFF TO VERY STIFF, SLIGHTLY
MOIST, LIGHT BROWN, TRACE TO SLIGHTLY POROUS, TRACE CALCAREOUS.
GRAVEL AND COBBLES (GM_GP) SANDY, SILTY, WITH PROBABLE BOULDERS, DENSE, SLIGHTLY
MOIST, LIGHT GRAY AND BROWN ROUNDED ROCK.
DRIVE SAMPLE, 2_INCH I.D. CALIFORNIA LINER SAMPLE
i DRTVE SAMPLE, 1 3/1-|NCH t.D, SPLTT SPOON STANDARD PENETRATTON TEST.
18/12 ?
RIVE SAMPLE BLOW COUNT. INDICATES THAT 1 8 BLOWS OF A 1 4O_POUND HAMMER
ALLING 30 INCHES WERE REQUIRED TO DRIVE THE SAMPLER 12 INCHES.
t PRACTICAL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON AUGUST 16, 2022 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 OBTAINED BY INTERPOLATION BETWEEN
CONTOURS ON THE SITE PLAN PROVIDED.
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 D2216);
-200= PERCENTAGE PASSING No. 200 SIEVE (ASTM 01140).
22-7 -532 Kumar & Associates LEGEND AND NOTES Fig.3
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SAMPLE OFr Sondy Silty Ctcy
FROM:Boringl@2.5'
tNC = 7.4 %, DD = 92 pcl
sholl hot
fr6
inbo
full.tho
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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anzoo
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-2
-3
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-8
't.0 APPLIED PRESSURE - KSF 10 100
22-7 -532 Kumar & Associates SWELL_CONSOLIDATION TEST RTSULTS Fig. 4
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DD = 102 pcl
Sondy Cloy
\NC = 7.2 %,
SAMPLE OF:
FROM: Boring
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in
D-4546.
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
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1 1.0 APPLIED PRESSURE - KSF 10 100
22-7 -532 Kumar & Associates SWELL-CONSOLIDATION TTST RESULTS Fig. 5
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TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
SOIL TYPE
Sandy Silty Clay
Sandy Clay
Sandy Clay
{psfl
UNCONFINED
COMPRESSIVE
STRENGTH
%l
PI-ASTIC
INDEX
ATTERBERG LIMITS
{%t
LIQUID LIMtT
PERCENT
PASSING NO.
200 srEVE
78
SAND
{%)
GRADATION
(%)
GRAVEL
NATURAL
DRY
DENSITY
(ocfl
7.4 92
105
702
(%)
NATURAL
MOISTURE
CONTENT
9.4
7.2
(fr)
DEPTH
at/L/2
al/L/2
5
SAMPLE LOCATION
BORING
I
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No.22-7-532