HomeMy WebLinkAboutSoils Report 03.16.2017H-P1<UMAR
Geotechnical 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 Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 50, CERISE RANCH
26 CERISE RANCH ROAD
GARFIELD COUNTY, COLORADO
PROJECT NO. 17-7-200
MARCH 16, 2017
PREPARED FOR:
BUILDINGLOGIC, LLC
ATTN: KEITH JOHNSON
P.O. BOX 1542
BASALT, COLROADO 81623
ki.buildinglogic(c amail.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 1
FIELD EXPLORATION - 2 -
SUBSIDENCE POTENTIAL. - 2 -
SUBSURFACE CONDITIONS - 3 -
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 THROUGH 6 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
Project No. 17-7-200
H-PNKUMAR
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot
50, Cerise Ranch, 26 Cerise Ranch Road, 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 Keith Johnson dated February 7, 2017.
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 or walkout
basement. The attached garage and basement 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 proposed development area is currently vacant with terraced levels with about two feet of
elevation difference between them. The site lies at an elevation of around 6,3$0 feet. The
existing topography is shown by the contour lines (2 -foot contour interval) on Figure 1. The
Project No. 17.7-200
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slope across the development area is gentle down to the south. The vegetation on the site
consists of grass and weeds. There was about 'A foot of snow on the site.
FIELD EXPLORATION
The field exploration for the project was conducted on March Is', 2017. 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 H-P/Kumar.
Samples of the subsoils were taken with a l% -inch I.D. spoon sampler and a 2 -inch I.D.
California liner sampler. 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.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies Cerise Ranch. 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
Roaring Fork Valley. These sinkholes appear similar to others associated with the Eagle Valley
Evaporite in areas of the Eagle 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 nnr present knowledge of the subsurface
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PrtfiArt Nrf 17-7-2Q{]
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conditions at the site, it cannot be said for certain that sinkholes will not develop. The risk of
future ground subsidence on Lot 50 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.
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils consist of about 6 inches of topsoil overlying interlayered sandy, silty clay and clayey,
silty sand with gravel. Based on our experience in the area, dense gravel alluvial soil occurs at
depths of around 35 to 40 feet with groundwater close to that depth.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and percent finer than sand size gradation analysis. Results of swell -
consolidation testing performed on relatively undisturbed drive samples, presented on Figures 4
through 6, indicate low to moderate compressibility under light loading and a low to moderate
collapse potential (settlement under constand load) when wetted. The samples were moderately
compressible under increased loading after wetting. The laboratory testing is summarized in
Table 1.
No free water was encountered in the borings at the time of drilling or when checked 2 days later
and the subsoils were slightly moist to very moist with depth.
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 subsoils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
H-PtKUMAR
Pmjart No 12-7-7flrj
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1) Footings placed on the undisturbed natural subsoils should be designed for an
allowable bearing pressure of 1,400 psf. Based on experience, we expect
settlement of footings designed and constructed as discussed in this section will
be about 1 inch or less.
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 12 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) All existing fill, topsoil and any loose or disturbed soils should be removed and
the footing bearing level extended down to the relatively dense natural granular
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 50 pcf for backfill consisting
of the on-site fine-grained 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
H-PKUMAR
Prnject Nn 17.7-20Q
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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 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.
We recommend on-site granular soils for backfilling foundation walls and retaining structures
because their use results in lower lateral earth pressures. Subsurface drainage recommendations
are discussed in more detail in the "Underdrain System" section of this report.
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 350 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, 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
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PwAfPClt1in 17 7 Of1
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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 Tess 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 granular soils devoid of vegetation, topsoil and oversized rock.
UNDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
mountainous areas 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, 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 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 l'/2 feet deep. A pvc 30 -
mil liner should be placed under the drain gravel in a trough shape and attached to the footing
with mastic to reduce the filtration of water in the drain gravel to the underlying bearing soils.
SURFACE DRAINAGE
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
Prnjart Wn 17-7-700
-7-
2) Exterior backfill should be adjusted to near optimum moisture and compacted to
at Ieast 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 finer -grained 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.
H -Pk KIJMAR
Prrjar.! N _172-2of)
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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 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. KUJMAR
ftthoP---
Robert L. Duran, Staff Engineer
Reviewed by:
Daniel E. Hardin, A.E.
RLD/kac
H-P€KUMAR
QrnjPrt No 47.7.7f11
tn
APPROXIMATE SCALE -FEET
rn
Mig
LOCATION OF EXPLORATORY BORINGS
lUr�sogw►wwww. — .VMWPC .i S.-L-aUla M�[ia
rO0441.41 - clic v[ trK
CD
CD
DEPTH -FEET
-- 0
5
- 10
15
--- 20
- 25
17-7-200
BORING 1
BORING 2
EL. 6379.5' EL. 6378.5'
24/12
WC=5.5
-1 00=129
-i -200=14
20/12
10/12
WC=14.3
DD=105
15/12
-1 WC=8.7
DD=112
- 200=41
13/12
WC=17.7
DD=106
-200=62
8/12
WC=20.5
D0=102
- 200=89
H-P�KUMAR
1-
30/12
14/12
'WC=6.4
DD=107
12/12
WC=10.9
00=119
50/12
Li6/12
WC=15.0
-200=74
14/12
WC=20.0
DD=103
LOGS OF EXPLORATORY BORINGS
0
5-
15
25
30
DEPTH -FEET
Fig. 2
LEGEND
7
24/12
TOPSOIL, ORGANIC SILT AND CLAY, SAND WITH COBBLES, FIRM, MOIST, DARK BROWN.
SC—SM; INTERLAYERS SANDY CLAY AND SILTY, CLAYEY SAND WITH GRAVEL AND SCATTERED
COBBLES, STIFF TO MEDIUM DENSE, MOIST TO VERY MOIST WITH DEPTH, BROWN.
RELATIVELY UNDISTURBED DRIVE SAMPLE; 2—INCH I.D. CALIFORNIA LINER SAMPLE.
DRIVE SAMPLE; STANDARD PENETRATION TEST (SPT), 1 3/8 INCH 1.D. SPLIT SPOON
SAMPLE, ASTM D-1586.
DRIVE SAMPLE BLOW COUNT. INDICATES THAT 24 BLOWS OF A 140—POUND HAMMER
FALLING 30 INCL -EES WERE REQUIRED TO DRIVE THE CALIFORNIA OR SPT SAMPLER 12 INCHES.
—IP- DEPTH AT WHICH BORING CAVED FOLLOWING DRILLING.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON MARCH 1, 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 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 OR WHEN
CHECKED 2 DAYS LATER.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (pct) (ASTM D 2216);
—200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
17-7-200
H-PKUMAR
LEGEND AND NOTES
Fig. 3
CONSOLIDATION - SWELL
-4
SAMPLE OF: Clayey Silty Sand
FROM: Boring 1 0 10'
WC = 14.3 %, DO = 105 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1MM sIW, 4mt7.MLAI.1ld Th . ly W
.et r.,1 r.pndvld...cp
IM wets/
naw/._liry. 63% 51.4
Ce.ws. a.
NUlN
Lh A.51 1 13-1 n,a N
aaye smw. rn ,* 11J p-1711
17-7-200
1.0 APPLIED PRESSURE - KSF 10 1110
H -P KU MAR
SWELL -CONSOLIDATION TEST RESULT
Fig. 4
0
—1
.. —2
— 3
—4
— 5
— 6
— 7
— 8
— 9
CONSOLIDATION - SWELL
lwr u4 nwR. W.! wr to t.
ane. Th. a.t.r.o ..�
Odd rre e. npod:Ac.e...t.pt r
full .Rheas !h..ras.. e.r.ored or
IRAN, pd Mwo.r... 1.t. 5.A
R.nn.d n
}CcprdO�� •silo -.54
SAMPLE Of: Clayey Sand and Gravel
FROM: Boring 2 ® 5'
WC= 6.4 %,0D=107 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1.0 APPLIED PRESSURE - KSF 10 Too
17-7-200
H - P-1KU MAR
SWELL—CONSOLIDATION TEST RESULT
Fig. 5
CONSOLIDATION - SWELL
1
0
— 2
— 3
— 4
1
ae
0
CONSOLIDATION - SWELL
—1
— 2
—3
—4
5
SAMPLE OF: Sandy Silty Clay
FROM: Boring 2 0 10'
WC = 10.9 %, DD = 119 pcf
1.0 APPLIED PRESSURE — NSF 10
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
100
SAMPLE OF: Sandy Silty Clay
FROM: Boring 2 0 25'
WC = 20.0 %, DD = 103 pcf
r".a inn r“Lilk A' ony W m.
..mid., intoe 1h4 wing s000rl
rnos nos no hweakned, n.rcl In
NI Hew( 11.• .1140•01 .e
wr.r ane arwelal., Mc. 1.w
R.M0.1.1.fr.L . Mka„wa i,
.�a.K.nn 'T4
17-7-200
NO MOVEMENT UPON
WETTING
1.0 APPLIED PRESSURE - KS, 10 100
H -P--KU MAR
SWELL—CONSOLIDATION TEST RESULT
Fig. 6
KuMLA.R
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No.17-7-200
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
(pct)
GRADATION
PERCENT
PASSING
NO. 200
SIEVE
ATT ER BERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
(PSF)
501E TYPE
BORING
DEPTH
((t)
GRAVEL
(%)
SAND
(azul
LIQUID
LIMIT
(%)
PLASTIC
INDEX
(%)
1
2.5
5.5
129
14
Silty Sand and Gravel
10
14.3
105
Clayey Silty Sand
15
8.7
112
41
Silty Sand and Gravel
20
17.7
106
62
Sandy Silty Clay
25
20.5
102
89
Slightly Sandy Silty Clay
2
5
6.4
107
Clayey Sand and Gravel
10
10.9
119
1
Sandy Silty Clay
20
15.0
74
Sandy Silty Clay
25
20,0
103
Sandy Silty Clay