HomeMy WebLinkAboutSoils Report 07.07.2017H -P KUMAR
Geotechnlcal Engineering 1 Engineering Geology
Materials Testing 1 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 Silverthorne, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 61, FILING 2, PINYON MESA
TBD PAINTBRUSH WAY
GARFIELD COUNTY, COLORADO
PROJECT NO. 17-7-387
JULY 7, 2017
PREPARED FOR:
RECEIVED
FEB 0 9 2018
GARFIELD COUNTY
COMMUNITY DEVELOPMENT
INTEGRATED MOUNTAIN DEVELOPMENT, INC.
ATTN: JIM GORNICK
P.O. BOX 908
GLENWOOD SPRINGS, COLORADO 81602
(jeornick@ opris.net)
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 2 -
SUBSIDENCE POTENTIAL - 2 -
FIELD EXPLORATION - 3 -
SUBSURFACE CONDITIONS - 4 -
FOUNDATION BEARING CONDITIONS - 4 -
DESIGN RECOMMENDATIONS - 4 -
FOUNDATIONS - 5 -
FOUNDATION AND RETAINING WALLS - 5 -
FLOOR SLABS -6-
UNDERDRAIN SYSTEM - 7 -
SURFACE DRAINAGE - 7 -
LIMITATIONS - 8 -
FIGURE 1 - LOCATION OF EXPLORATORY BORING
FIGURE 2 - LOG OF EXPLORATORY BORING
FIGURE 3 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
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Project No. 17-7-387
PURPOSE AND SCOPE OF STUDY
This report presents the results of u subsoil study for a proposed residence to be located al Lot
61, Filing 2, Pinyon Mesa, TBD Paintbrush 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 Integrated Mountain Development, Inc. dated May 11, 2017.
An exploratory boring was drilled 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 structure above a basement and with an attached
garage. Basement and garage floors will be slab -on -grade. Grading for the structure is assumed
to be relatively minor with cut depths between about 3 to 10 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 property is vacant and vegetated with sage brush, grass and weeds. Vegetation in the front
part of the lot has been removed during the subdivision development. The ground surface in the
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building envelope is relatively flat with a slight slope down to the west. The building envelope is
about 3 feet below the roadway grade. A deep gully is located in the rear of the lot beyond the
building envelope line.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian Age Eagle Valley Evaporite underlies the Pinyon Mesa
Development. These rocks are a sequence of gypsiferious shale, fine-grained sandstone/siltstone
and limestone with some massive beds of gypsum. There is a possibility that massive gypsum
deposits associated with the Eagle Valley Evaporite underlie portions of the property.
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, sinkholes have been
observed scattered throughout the lower Roaring Fork River valley.
No evidence of subsidence or sinkholes was observed on the property or 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 at the
site throughout the service life of the proposed structure, in our opinion is low, however the
owner should be 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 June 7, 2017. One exploratory boring
was drilled at the location shown on Figure 1 to evaluate the subsurface conditions. The boring
was advanced with 4 -inch diameter continuous flight augers powered by a truck -mounted CME -
45B drill rig. The boring was logged by a representative of H-P/Kumar.
Samples of the subsoils were taken with a 2 inch E.D. spoon sampler. The sampler was driven
into the subsoils at various depths with blows from a 140 pound hammer falling 30 inches. This
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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 Log of Exploratory Boring, Figure 2. The samples were returned to our laboratory
for review by the project engineer and testing.
SUBSURFACE CONDITIONS
A graphic log of the subsurface conditions encountered at the site is shown on Figure 2. The
subsoils, below about 6 inches of topsoil, consist of sandy clay to 12 feet and sandy silt and clay
to 23 feet underlain by medium dense, silty to very silty sand with gravel and silt zones. The
deeper gravelly soils below about 27 feet are possibly weathered formation rock but are logged
as soil from a foundation support viewpoint.
Laboratory testing performed on samples obtained from the boring included natural moisture
content and density and percent finer than sand size gradation analyses. Results of swell -
consolidation testing performed on relatively undisturbed drive samples, presented on Figure 3,
indicate low to moderate compressibility under conditions of loading and wetting with a low to
moderate expansion potential when wetted. The laboratory testing is summarized in Table 1.
No free water was encountered in the boring at the time of drilling and the subsoils were slightly
moist.
FOUNDATION BEARING CONDITIONS
The upper sandy clay soils encountered at typical shallow foundation depth and the underlying
sandy silt and clay soils mainly tend to settle when they become wetted based on test results of
nearby lots. The clay soils tested for the current study showed an expansion potential when
wetted. A shallow foundation placed on these soils will have a risk of settlement or heave if they
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
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foundation system.
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structure that the recommendations for surface grading and subsurface drainage contained in this
report be followed. The amount of settlement, if the bearing soils become wet, will mainly be
related to the depth and extent of subsurface wetting. We expect initial settlements will be less
than 1 inch. Wetting of the shallow soils could result in additional settlements of 1 to 2 inches
which would likely cause building distress. Mitigation methods such as a deep foundation (piles
or piers extending down at least 30 feet below existing ground surface) or removing and
replacing the bearing soils as compacted structural fill should be used to support the proposed
house with a lower risk of settlement. If a deep foundation is desired, we should be contacted to
provide additional design recommendations.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory boring and the nature of
the proposed construction, the building can be founded with spread footings bearing on
compacted structural fill.
The design and construction criteria presented below should be observed for a spread footing
1) Footings placed on compacted structural fill should be designed for an allowable
bearing pressure of 1,200 psf.
The basement and garage footing areas should be
sub -excavated down about 6 to 10 feet below existing ground surface and the
excavated soil replaced with compacted structural fill back to design grade. The
sub -excavated areas should extend down at least 3 feet below the footing bearing
level. 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
settlements of about 1/2 to 1 inch could occur if the bearing soils are wetted. A '/,
increase in the allowable bearing pressure can be taken for toe pressure of
eccentrically loaded (retaining wall) footings.
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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 heavily reinforced top and bottom to span
Iocal anomalies such as by assuming an unsupported length of at least 14 feet.
The foundation should be configured in a box like shape to help resist differential
movements. 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, sub -excavation depth and any loose or disturbed soils should be
removed below the foundation area. The exposed soils in footing areas after sub -
excavation should then be moistened and compacted. Structural fill should
consist of low permeable soil (such as the on-site sandy clay and silt soils
compacted to at least 98% of standard Proctor density within 2% of optimum
moisture content. The structural fill should extend laterally beyond the footing
edges equal to at least '/2 the fill depth below the footing.
6) A representative of the geotechnical engineer should evaluate the fill placement
for compaction and observe all footing excavations prior to concrete placement.
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 fine-grained 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 fine-grained soils.
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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.
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 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 with a settlement/heave risk similar to the foundation
if the underlying soils are
wetted. To reduce the effects of some differential movement, floor slabs should be separated
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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 2%
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 and topsoil.
UNDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
the area and where clay soils are present, 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
system. An underdrain should not be provided around slab -at -grade garage and crawlspace areas
to help limit potential wetting of bearing soils from shallow water sources.
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 or sump and pump. 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
drain gravel in a trough shape and attached to the foundation wall with mastic to prevent wetting
of the bearing soils.
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Project No. 17.7.387
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SURFACE DRAINAGE
The following drainage precautions should be observed during construction and maintained at alI
times after the residence has been completed:
1) Inundation of the 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 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 at least 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. Graded surface swales should have a minimum slope of 3%.
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 the time of this study. 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 boring drilled at the location 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
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extrapolation of the subsurface conditions identified at the exploratory boring 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
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 t ; U MAR
Louis E. Eller
Reviewed by:
Steven L. Pawlak, P. L
erif
SLP/kac "q ,.'• -,, •
cc: Oddo Engineering -- Bob Oddo bob@oddogws.com)
H -P i KUMAR
Project No. 17.7-387
LOT 62
1
r
OPEN SPACE
LOT 61
0
BORING 1
Mi
Ell
15 0 15 30
APPROXIMATE SCALE -FEET
17-7-387
'1 -
PAINTBRUSH WAY
H-P-� ICUMAR
J
LOT 60
LOCATION OF EXPLORATORY BORING
Fig. 1
3
—
— 5
— 10
— 15
W
�
_
W
G
— 20
L_25
— 30
--- 35
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BORING 1 LEGEND
r -c-
TOPSOIL; ORGANIC SILT AND CLAY, FIRM, SLIGHTLY MOIST, BROWN.
L.
/
/
/
/
/
/
30/12
21/12
] WC=6.7
00=111
—7
7
7
CLAY (CL); SILTY, SANDY, VERY STIFF, SLIGHTLY MOIST, BROWN, LOW
PLASTICITY. CALCAREOUS TRACES.
SILT AND CLAY (ML -CL); SANDY, VERY STIFF, SLIGHTLY MOIST, LIGHT
BROWN, CALCAREOUS.
/ SAND AND SILT (SM -ML); GRAVELLY, MEDIUM DENSE, SLIGHTLY MOIST,
r' BROWN TO LIGHT BROWN. VERY FIRM DRILLING BELOW 27 FEET.
f
/ 51/12 DRIVE SAMPLE, 2 -INCH I.D. CALIFORNIA UNER SAMPLE,
/ WC=10.0
/1 00=109
/ / -200=91 2 /12 DRIVE SAMPLE BLOW COUNT, INDICATES THAT 21 BLOWS OF A
140 -POUND HAMMER FALLING 30 INCHES WERE REQUIRED TO DRIVE THE
SAMPLER 12 INCHES.
1-] 36/12
NOTES
/ I. THE EXPLORATORY BORING WAS DRILLED ON JUNE 7, 2017 WITH A
4 -INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER.
/ 34/12
WC6.=
WCfi.S
00=118
37/12
WC=4.7
21 00=117
-200=82
2. THE LOCATION OF THE EXPLORATORY BORING WA5 MEASURED
APPROXIMATELY 9Y PACING FROM FEATURES SHOWN ON THE SITE PLAN
PROVIDED.
3. THE ELEVATION OF THE EXPLORATORY BORING WAS NOT MEASURED AND
THE LOG OF THE EXPLORATORY BORING IS PLOTTED TO DEPTH,
4, THE EXPLORATORY BORING LOCATION SHOULD BE CONSIDERED ACCURATE
ONLY TO THE DEGREE IMPLIED BY THE METHOD USED.
5. THE LINES BETWEEN MATERIALS SHOWN ON THE EXPLORATORY BORING LOG
REPRESENT THE APPROXIMATE BOUNDARIES BETWEEN MATERIAL TYPES AND
THE TRANSITIONS MAY BE GRADUAL.
6. GROUNDWATER WAS NOT ENCOUNTERED IN THE BORING AT THE TIME OF
DRILLING.
7, LABORATORY TEST RESULTS:
WC = WATER CONTENT (X) (ASTM D 2216);
DD = DRY DENSITY (pct) (ASTM D 2216);
-200 = PERCENTAGE PASSING N0. 200 SIEVE (ASTM D 1140).
H-PWLIMAR
LOG OF EXPLORATORY BORING
Fig. 2
CONSOLIDATION - SWELL
—2
CONSOLIDATION -- SWELL
1..
1.0
SAMPLE OF: Sandy Cloy
FROM: Boring 1 ® 5'
WC = 6.7 %. DD = 111 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
APPLIED PRESSURE — KSF IC IOC
SAMPLE OF: Sandy Clay
FROM: Boring 1 ® 20'
WC = 6,5 %, OD = 118 pcf
11.4r gni no111 wait Ny to N,
.sryn 1..141. Tht lnlnd r.fpl
1*41 rpl M npt[n:uc,6. ann.; ;n
fig. .UcN 114 `Alyn 449ICro1 of
.1.4.4? 1041 Mur:Mn. lac. 1.0
Canouretetwt l..rp 15,4w1w4d
•...erdAik 1h 'STU U +544.
17-7-387
1,0 APPLIED PRESSURE • KSF 10
Kumar & Associates
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
SWELL—CONSOLIDATION TEST RESULTS
10Q
Fig. 3
H-PKUMAR
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 17-7-387
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
(PO
GRADATION
PERCENT
PASSING
N0.200
SIEVE
ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
(PSF)
SOIL TYPE
BORING
DEPTH
(ft)
GRAVEL
(°�,1
SAND
(%)
LIQUID
LIMIT
(%)
PLASTIC
INDEX
(%)
1
5
6.7
111
Sandy clay
10
10.0
109
91
Slightly sandy silty clay
20
6.5
118
Sandy clay
25
4.7
117
82
Sandy silt