HomeMy WebLinkAboutSubsoil Report for Foundation DesignI (tn $j,ffilfl#tf,'#f*iiyi*' "
An Employcc owncd Compony
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email : kaglenwood@kumarusa.com
www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
F'OR FOUNDATION DESIGN
PROPOSED RESIDENCE
LO'r 44, SPRTNG RrDGE RESERVE
1284 IIIDDEN VALLEY DRIVE
GARFIELD COUNTY, COLORADO
PROJECT NO.21-7-795
NOVEMBER 30, 2o2L
PREPARBD FOR:
TREVOR FRENCH
239 BUCKTIIORN ROAD
NEW CASTLE, COLORADO 81647
trevor@ boilercreek.com
TABLE OF'CONTENTS
PURPOSE AND SCOPE OF STUDY............
PROPOSED CONSTRUCTION
SITE CONDITIONS.....
GEOLOGY..
SUBSURFACE CONDITIONS
LIMITATIONS..........
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
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1
1
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......,...........,. 2 .
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FIELD EXPLORATION ............,- 2 -
FOUNDATION BEARING CONDITIONS
DESIGN RECOMMENDATIONS
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FOLINDATION AND RETAINING WALLS ..............- 4 -
FLOOR SLABS .....- 5 -
UNDERDRAIN SYS'I'EM ......- 5 -
-6-
FOUNDATIONS
Kumar & Associates, lnc. @ Project No. 21-7-795
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on
Lot 44, Spring Ridge Reserve, 1284 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 Trevor French dated Octobet 6,2021.
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 one- and two-story structure over crawlspace with attached
slab-on-grad e garage. Grading for the structure is assumed to be relatively minor with cut depths
between about2 to 5 feet. We assume relatively light foundation loadings, typical of the
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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 in the
building area is strongly sloping down to the north and moderately steep near the road.
Vegetation consists of grass and weeds with some sage brush and rabbit brush near Hidden
Valley Drive. Maroon Formation sandstone is exposed on the hillside to the west of the lot.
GEOLOGY
According to the Geologic Map of the Cattle Creek Quadrangle, Garfield County, Colorado, by
Kirkham, R.M., Streufert, R.K., Hemborg, Thomas, and Stelling, dated2014, the site soils
Kumar & Associates, lnc. @ Project No. 2'l-7-795
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consist of alluvium and colluvium of the Holocene age underlain by Maroon Formation
sandstone.
FIELD EXPLORATION
The field exploration for the project was conducted on October 13 and 21,2021. 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, Inc.
Samples of the subsoils and bedrock were taken with l%-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-I586. The penehation 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 foot of topsoil overlying stiffto hard, sandy silty clay to between 4
and l7% feet deep. About 2 feet of silty sandy gravel with cobbles (rock fragments) was
encountered in Boring 2 below the clay soil. Hard to very hard sandstone/siltstone bedrock was
encountered at depths of6 to lTYzfeet down to the boring depths ofabout l5 to 20 feet.
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 sandy clay, presented on Figures
4 and 5, indicate low to moderate compressibility under conditions of loading and wetting. The
lehnraforv fecfino ic srrrnrncrizerl in Tnhle 1
No free water was encountered in the boring at the time of drilling and the subsoils and bedrock
were slightly moist.
Kumar & Associates, lnc. o Project No. 21-7-795
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F'OUNDATION BEARING CONDITIONS
At assumed excavation depths, we expect the subgrade will expose natural sandy clay soils. The
natural soils at the site possess low bearing capacity and relatively low settlement potential when
wetted. Deeper portions of the excavation may expose sandstone/siltstone bedrock. If bedrock
is encountered, lightly loaded spread footings transitioning from natural soils to bedrock will
have a potential for differential movement due to the variable bearing conditions. Excavation
within the very hard sandstone/siltstone bedrock will be diffrcult and may require specialized or
heavy-duty equipment such as splitting, rock spade, blasting or other methods.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed constructiono we recommend the building be founded with spread footings bearing
on natural soils or bedrock materials.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
l) Footings placed on natural sandy clay soils should be designed for an allowable
bearing pressure "flp!, Based on experience, we expect initial settlement
of footings designed and constructed as discussed in this section will be about
I inch or less. Additional differential settlement of around Y, or I inch could
occur in soil bearing areas that become wetted after construction.
2) The footings should have a minimum width of 18 inches for continuous walls and
2'9to' 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, especially across any material transitions, such as by assuming
an unsupported length of at least 14 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, lnc. @ Project No. 21-7-795
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s)Topsoil and any loose disturbed soils should be removed and the footing bearing
level extended down to the relatively firm natural soils. The exposed soils in
footing areas should then be moistened and compacted.
A representative ofthe 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 slightly above optimum. Backfill placed in
pavement and walkway areas should be compacted to at least 95%o 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.
Thc lqferql rpcisfqnnc nf fnrrnrlofinn nr rafaininc.troll fnnfincc.trill Lo a nnmhinafi^- ^f +horb Yrsrr vvrrr vv
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
sidcs of thc 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
6)
Kumar & Associates, lnc. o Project No. 21-7-795
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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 95Yo of the
maximum standard Proctor density at a moisture content near optimum.
FLOOR SLABS
The natural on-site soils and bedrock, 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 free-draining gravel should be placed beneath basement level slabs to facilitate drainage.
This material should consist of minus 2-inch aggregate with at least 50% retained on the No. 4
sieve and less than 2o/o passing the No. 200 sieve.
All fill materials for support of floor slabs should be compacted to at least95%6 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.
LINDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
the area and where bedrock is shallow or clay soils are present that local perched groundwater
can develop during times of heavy precipitation or seasonal runoff. Frozen ground during spring
runoffcan create a perched condition. We recommend below-grade construction, such as
retaining walls, crawlspace and basement 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 lYoto
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2o/o passingthe No. 200 sieve, less than 50oZ passing the No. 4 sieve and have a
maximum size of 2 inches. The drain gravel backfill should be at least l% feet deep.
Kumar & Associates, lnc. @ Project No. 21-7-795
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SUMACE DRAINAGE
The following drainage precautions 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 95Yo of the maximum standard Proctor density in pavement and slab areas
and to at least 90Vo of the maximum standard Proctor density in landscape areas.
3) The ground surface sumounding 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
covered with filter fabric and capped with about 2 feet of the on-site soils to
rcducc surfacc watcr infiltration.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Landscaping which requires regular heavy inigation should be located at least
5 feet from foundation walls. Consideration should be given to the use of
xeriscape to limit potential wetting of soils below the foundation caused by
irrigation.
LIMITATIONS
This study has been conducted in accordance with generally accepted geotechnical engineering
principlcs and practices in this area at this time. We make no war:ranty either express or implied.
The conclusions and recommendations submitted in this repoft are based upon the data obtained
from the exploratory borings drilled at the locations indicated on Figure I, 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 concemed 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 reporto we should be notified so
that re-evaluation of the recommendations may be made.
Kumar & Associates, lnc. o Project No. 21-7-795
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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 evolveso we
should provide continued consultation and field services during construction to review and
monitor the implementation of our recommendations, and to verifr 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 f.oundation bearing strata and testing of structural fill by a representative of
the geotechnical engineer.
Respectfully Submitted,r
Kumar & Associates, Inc.
James H. Parsons, P
Reviewed by:
ffi-/.
Steven L. Pawlak, P.E.
JHP/kac
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Kumar & Associates, lnc. 6)Project No. 21-7-795
H LOI 44
SPRING RIDGE RESERVE
1284 HIDDEN VALLEY DRIVE
HIDDEN VALLEY DRIVE
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APPROXIMATE SCALE-FEET
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21 -7 -795 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
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BORING 1 BORING 2
0 0
32/ 12
WC=8.1
DD= 1 01
20/ 12
WC=5.0
DD= 1 05
-200=50
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-2OO=54
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21 -7 -795 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fig. 2
LEGEND
ToPSOll : SllT, cl AYFY, VFRY SANDY, R0OT 7oNF, ORGANICS, FIRM, MolST,
DARK BROWN.
Wlw
CLAY (CL): SANDY TO VERY SANDY, SCATTERED GRAVEL, SILTY, STIFF TO VERY STIFF,
SLIGHTLY POROUS, SLIGHTLY CALCAREOUS, SLIGHTLY MOIST, RED_BROWN.
GRAVEL AND COBBLES (OU): SANDY, StLTY, DENSE, SLTGHTLY MoIST, RED.
SANDSTONE/SILTSTONE BEDROCK: CLAYEY, WEATHERED TO VERY HARD, SLIGHTLY MOIST,
MAROON.
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE
I DRtvE sAMpLE, 1 J/8-tNcH t.D. spLtr spooN STANDARD PENETRAT|oN TEST
2.ti. DRIVE SAMPLE BLOW COUNT. INDICATES THAT 32 BLOWS OF A 140-POUND HAMMERr1/ tz FALLTNG 30 TNCHES WERE REQUTRED To DRrvE THE SAMPLER 12 rNcHES.
NOTES
1 THE EXPLORATORY BORINGS WERE DRILLED ON OCTOBER 13 AND 21, 2021 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 D2216);
DD = DRY DENSITY (PCf) (ASTM D2216);
-200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM 01140).
21 -7 -795 Kumar & Associates LEGEND AND NOTES Fig. 5
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SAMPLE OF: Sondy Siliy Cloy
FROM:Boringl@2.5'
WC = 8.1 %, DD = 101 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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21 -7 -795 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 4
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SAMPLE OFr Slightly Grovelly Sondy Clcy
FROM:Boring2@2.5'
WC = 5.0 %, DD = 'l 05 pcf
-2OO = 50 %
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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21 -7 -795 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig. 5
I(+A Kumar & Associatesn lnc.'
Geotechnical and Materials Engineers
and Environmental Scientists
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
No. 21-7-795
Slightly Gravelly Sandy
Clay
SOIL TYPE
Sandy Silty Clay
Sandy Silty Clay with
Gravel
(psfl
UNCONFINED
COMPRESSIVE
STRENGTH
(olrl
Pt-ASTIC
INDEX
ATTERBERG LIMITS
(o/ol
LIQUID LIM]T
54
50
PERCENT
PASSING NO,
200 stEVE
SAND
(%)
GRADATION
{%)
GRAVEL
locfl
NATURAL
DRY
DENSITY
118
105
ll"l
NATURAL
MOISTURE
CONTENT
13.8
5.0
(ftI
DEPTH
1018.1al/z/2
5I
2%
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2
SAMPLE LOCATION
BORING