HomeMy WebLinkAboutSoils Report 04.04.2017H-PKUMAR
Geotechnical Engineering 1 Engineering Geology
Materials Testing ( Environmental
5020 County Road 154
Glenwood Springs, CO 81601
Phone: (970) 945-7988
Fax: (970) 945-8454
Email: hpkglenwood@kumarusa.com
Office Locations: Parker, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 76, SPRINGRIDGE RESERVE
76 HIDDEN VALLEY DRIVE
GARFIELD COUNTY, COLORADO
JOB NO. 17-7-235
APRIL 4, 2017
PREPARED FOR:
TREVOR RUONAVAARA
160 SPRING RIDGE DRIVE
GLENWOOD SPRINGS, COLORADO 81601
(trfnnishes @ gmai i.com)
1.1
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - I -
PROPOSED CONSTRUCTION - 1
SITE CONDITIONS - 1 -
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 2 -
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
FIGURES 4 AND 5 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
H-PitKUMAR
Project No. 17-7-235
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot
76, Springridge Reserve, 76 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 general accordance with our agreement for
geotechnical engineering services to Trevor Ruonavaara dated March 15, 2017. Hepworth-
Pawlak Geotechnical previously performed a preliminary geotechnical study for the subdivision
and reported the findings in a report dated February 26, 2001, Job No. 101 126 and updated the
study in a report dated June 22, 2004.
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 above a crawlspace and with
an attached garage. Garage floor will be 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 loadings, location or grading plans change significantly from those described above,
we should be notified to re-evaluate the recommendations contained in this report.
H -Pk KUMAR
Project No. 17-7-235
-2 -
SITE CONDITIONS
The property was vacant and free of snow at the time of our field exploration. The site is
vegetated with grass and weeds with small stands of scrub oak to the northeast above the
building area. The ground surface at the building envelope slopes gently to moderately down to
the southwest and is bisected by an abandoned irrigation ditch, see Figure 1. The ground surface
above the building envelope is steeply sloping down to the southwest. Maroon Formation
sandstone is exposed on the hillside to the northeast of the lot.
FIELD EXPLORATION
The field exploration for the project was conducted on March 17, 2017. 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 -55 drill rig. The borings were logged by a representative of H-P/Kumar
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 lest 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 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 an Figure 2. The
subsoils were variable and below about one foot of topsoil consist of sand and silt in Borings 1
and 3 overlying sandstone bedrock at depths of 61 and 13 feet, respectively. In Boring 2, about
11 feet of sandy silty clay was encountered above the sand and silt soils with sandstone bedrock
at a depth of about 22 feet. Drilling in the bedrock with auger equipment was difficult due to its
hardness and cemented condition and practical drilling refusal was encountered in the formation.
H-PkKUMAi2
Project No. 17-7-235
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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 soils, presented on Figures 4
and 5, generally indicate low to moderate compressibility under light loading and a low collapse
potential (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 to moist.
FOUNDATION BEARING CONDITIONS
The top of bedrock slopes down to the west and may be encountered in the upper part and
transition to sand, silt and clay in the remaining areas of the excavation. The sand, silt and clay
soils are of variable compressibility potential and could tend to settle especially when they
become wetted. A shallow foundation placed on the sand, silt and clay soils will have a risk of
settlement if the soils become wetted and care should be taken in the surface and subsurface
drainage around the house to prevent the soils from becoming wet. It will be critical to the long
term performance of the structure that the recommendations for surface grading and subsurface
drainage contained in this report be followed. Presented below are recommendations for shallow
spread footings with a risk of settlement. A low settlement risk foundation support can be
achieved by extending the bearing down into the underlying bedrock such as with straight -shaft
drilled piers. If a drilled pier foundation is desired, we should be contacted for additional
recommendations.
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 soils below topsoil provided the owner accepts the risk of settlement and potential
building distress.
H-PisKUMAR
Project No. 17-7-235
-4 -
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1)
2)
Footings placed on the undisturbed natural soils should be designed for an
allowable bearing pressure of 1,200 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. Additional differential settlement could be on the order of
1/2 to 11/2 inches for a limited wetted depth of around 10 feet below the footings.
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
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.
H-P%KUMAR
Project No. 17-7-235
-5 -
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 near optimum moisture content. 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.
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 0.40. Passive pressure of compacted backfill against the
sides of the footings can be calculated using an equivalent fluid unit weight of 325 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 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, can be used to support lightly loaded slab -on -grade
construction. There could be differential settlement potential from wetting of the bearing soils
similar to that described above for footings. 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
H-P%KUMAR
Project No. 17-7-235
-6 -
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 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 (plus 6 inch) rock.
UNDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
the area and where there are clay soils 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
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 1% to
a suitable gravity outlet. Free -draining granular material used in the underdrain system should
contain Tess 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 drain gravel in a trough
shape and attached to the foundation wall with mastic to prevent wetting of the bearing soils.
SURFACE DRAINAGE
Proper surface grading and drainage will be critical to limiting subsurface wetting below 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.
H-PkKUMAR
Project No. 17-7-235
-7-
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
covered with filter fabric and 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
H-PtINMAR
Project No. 17-7-235
-8 -
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,
H -P= KIJMAR
Steven L. Pawlak, P.
Reviewed by:
David A. Young, P.E.
SLP/kac
H-PxKUMAR
Project No. 17-7-235
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17-7-235
HIDDEN VALLEY DRIVE
H-P=-KUMAR
LOCATION OF EXPLORATORY BORINGS
Fig. 1
BORING 1
EL. 103.5'
BORING 2 BORING 3
EL. 100' EL. 101.5'
105 105
- 100
20/12
WC=3.4
00=107
-200=60
-- 95
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- 85
- 80
- 75
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WC=10.7
DD=94
20/12
WC=8.1
DD=105
8/12
WC=11.3
OD=109
-200=76
14/12
WC=6.0
00=109
9/12
WC=10.6
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17-7-235
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IH-P%KUMAR
LOGS OF EXPLORATORY BORINGS
Fig. 2
LEGEND
MTOPSOIL; ORGANIC SANDY SILT AND CLAY, FIRM, MOIST, DARK REDDISH BROWN.
—7
L
CLAY (CO; SANDY, SILTY, VERY STIFF, SLIGHTLY MOIST, DARK REDDISH BROWN, POROUS, LOW
PLASTICITY.
rzi
SAND AND SILT (SM -ML); MEDIUM DENSE, SLIGHTLY MOIST, RED.
SANDSTONE BEDROCK; WEATHERED TO VERY HARD WITH DEPTH, SLIGHTLY MOIST, RED,
MAROON FORMATION.
h
F
20/12
NOTES
RELATIVELY UNDISTURBED DRIVE SAMPLE; 2 -INCH I.D. CALIFORNIA LINER SAMPLE.
DRIVE SAMPLE; STANDARD PENETRATION
SAMPLE, ASTM D-1586.
DRIVE SAMPLE BLOW COUNT. INDICATES
FA..LIN G 30 INCHES WERE REQUIRED TO
PRACTICAL AUGER REFUSAL.
TEST (SPT), 1 3/8 INCH I.D. SPLIT SPOON
THAT 20 BLOWS OF A 140 -POUND HAMMER
DRIVE THE CALIFORNIA OR SPT SAMPLER 12 INCHES.
1. THE EXPLORATORY BORINGS WERE DRILLED ON MARCH 17, 2017 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 2 AS EL. 100' ASSUMED.
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.
FLUCTUATIONS IN THE WATER LEVEL MAY OCCUR WITH TIME.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
OD = DRY DENSITY (pcf) (ASTM D 2216);
-200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
17-7-235
H-Pk4KUMAR
LEGEND AND NOTES
Fig. 3
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SWELL—CONSOLIDATION TEST RESULTS
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CONSOLIDATION - SWELL (%)
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CONSOLIDATION - SWELL (%)
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CONSOLIDATION - SWELL
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—1
— 2
— 3
—4
SAMPLE OF: Sand and SIR
FROM: Boring 2 0 15'
WC = 6.0%, DD = 109 pct
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WNW MOM. rm wan.* hal
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17-7-235
Kumar & Associates
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
APPUEO PRESSURE —KSS ID 100
SWELL—CONSOLIDATION TEST RESULT
Fig. 5
H-PKUMAR
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 17-7-235
SAMPLE LOCATION
NATURAL
NATURAL
DRY
DENSITY
(pc{)
GRADATION
ATTERBERG LIMITS
T
SOIL TYPE
BORING
DEPTH
(111
MOISTURE
CONTENT
(%)
GRAVEL
(,�o)
SAND
('�o)
PERCENT
PASSING
NO. 200
SIEVE
LIQUID
LIMIT
(%1
PLASTIC
INDEX
(%)
UNCONFINED
COMPRESSIVE
STRENGTH
(PSF)
1
4
3.4
107
60
Sandy Silt
2
2
10.7
94
1
Sandy Silty Clay
5
8.1
105
Sandy Silty Clay
10
11.3
109
76
Sandy Silty Clay
15
6.0
109
Sand and Silt
20
10.6
110
Sand and Silt
C