HomeMy WebLinkAboutSoils Report 10.19.2016H-P�INMAR
Geotechnical Engineering ; Engineering Geology
Materials Testing 1 Environmental
60Es W IT it f /4Ac
Email:
5020 County Road 154
Glenwood Springs, CO 81601
Phone: (970) 945-7988
Fax: (970) 945-8454
hpkglenwood@kumarusa.com
Office Locations: Parker, Glenwood Springs, and Silverthorne, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 28, FOUR MILE RANCH
GARFIELD COUNTY, COLORADO
PROJECT NO. 16-7-464
OCTOBER 19, 2016
REVISED: NOVEMBER 18, 2016
PREPARED FOR:
McK COMPANY
ATTN: EARL McKERRIHAN
11 SOUTH PAINTED HORSE CIRCLE
NEW CASTLE, COLORADO 81647
wcgmck@ sopris.net
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
PROPOSED CONSTRUCTION - 1 -
SITE CONDITIONS - 2 -
SUBSIDENCE POTENTIAL - 2 -
FIELD EXPLORATION - 2 -
SUBSURFACE CONDITIONS - 3 -
FOUNDATION BEARING CONDITIONS - 3 -
DESIGN RECOMMENDATIONS - 4 -
FOUNDATIONS - 4 -
FOUNDATION AND RETAINING WALLS - 5 -
FLOOR SLABS - 5 -
UNDERDRAIN SYSTEM - 6 -
SURFACE DRAINAGE - 6 -
LIMITATIONS - 7 -
FIGURE 1 - LOCATIONS OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 THROUGH 6 - SWELL -CONSOLIDATION TEST RESULTS
TABLE 1 - SUMMARY OF LABORATORY TEST RESULTS
H -P ; KUMAR
Project No. 16-7-464
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located at Lot
28, Four Mile Ranch, 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 McK
Company dated September 19, 2016. Hepworth-Pawlak Geotechnical, Inc. (now
H-P/Kumar) previously performed a subsoil study for foundation design at the site and reported
our findings April 25, 2006, Job No. 106 0284.
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 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.
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Project No. 16-7-464
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SITE CONDITIONS
The property is vacant and vegetated with sage brush, grass and weeds. The ground surface is
relatively flat and slopes moderately down to the south at a grade of about 8 percent. An old
ranch road crosses the west part of the site. Scattered basalt cobbles and boulders are visible on
the ground surface.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian Age Eagle Valley Evaporite underlies the Four Mile Ranch
subdivision. 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.
No evidence of subsidence or sinkholes were 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 can not
be said for certain that sinkholes will not develop. The risk of future ground subsidence at the
site throughout the service life of the 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 September 21 and November 15, 2016.
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.
H -P = KUMAR
Project No. 16-7-464
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Samples of the subsoils were taken with 13/8 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 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.
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils, below about one foot of topsoil, consist of sandy silty clay to about 8 to 9 feet in depth
overlying basalt cobbles and boulders in a sandy silty clay matrix. Drilling in the dense granular
soils with auger equipment was difficult due to the cobbles and boulders.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and percent finer than sand size gradation analyses. Swell -consolidation testing was
performed on relatively undisturbed drive samples of the clay subsoils. The swell -consolidation
test results, presented on Figures 4 through 6, indicate low to moderate compressibility under
relatively light surcharge loading and a low to moderate expansion potential when wetted under a
constant light surcharge. 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 to moist.
FOUNDATION BEARING CONDITIONS
The sandy silty clay subsoils encountered at typical shallow foundation depths at the site possess
low to moderate expansion potential when wetted. A shallow foundation placed on the clay soils
will have a high risk of movement 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
drainage and subsurface drainage contained in this report be followed. The amount of
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Project No. 16-7-464
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movement, if the bearing soils become wet, will mainly be related to the depth and extent of
subsurface wetting. Surface runoff, landscape irrigation, and utility leakage are possible sources
of water which could cause wetting. The expansion potential can probably he mitigated by
placing 3 feet of structural fill below the spread fooling foundation.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory boring and the nature of
the proposed construction, we recommend the building be founded with spread footings bearing
on at least 3 feet of structural fill with a risk of movement, mainly if the bearing soils become
wetted. The footing areas should be subexcavated down about 3 feet below design footing grade
and footing grade re-established with compacted imported 3/4 -inch road base.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on a minimum of 3 feet of compacted structural fill should be
designed for an allowable bearing pressure of 2,000 psf. Based on experience, we
expect settlement of footings designed and constructed as discussed in this section
will be about 1 inch or less. Additional movements of 1/z to 1 inch could occur if
the clay soils below the structural fill become wetted.
2) The footings should have a minimum width of 16 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. The
foundation should be configured in a "box like" shape to help resist differential
movements. Foundation walls acting as retaining structures should also be
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Project No. 16-7-464
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designed to resist a lateral earth pressure corresponding to an equivalent fluid unit
weight of at least 50 pcf.
5) All existing fill, topsoil and any loose or disturbed soils should be removed and
the footing bearing level extended down to the relatively undisturbed soils. The
exposed soils in footing areas after subexcavation should then be moistened and
compacted. Structural fill should consist of imported 3/4 -inch road base
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 a distance equal to about 1/2 the fill depth below the footing.
6) A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FOUNDATION AND RETAINING WALLS
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% 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.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab -on -grade
construction. The clay soils possess a heave potential and could cause slab distress if wetted.
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Project No. 16-7-464
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Three feet of structural fill similar to the fill placed below footings should be placed below the
garage slab to help mitigate potential movement due to the underlying expansive clays. 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.
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 should consist of
imported granular soils such as 3/4 -inch road base.
UNDERDRAIN 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 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 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/ 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
The following drainage precautions should be observed during construction and maintained at all
times after the residence has been completed:
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Project No. 16-7-464
-7-
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
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.
H -P KUMAR
Project No. 16-7-464
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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,
11 -P --t; KU AR
Louis Eller
Reviewed by:
(
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Daniel E. Hardin, P.E. '" 24443 z,
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H -P ; KUMAR
Project No. 16-7-464
5
3
LOT 27
16-7-464
MAROON DRIVE
I, I
BORING 1
6 nn
H-P-K1JMAR
30 0 30 60
APPROXIMATE SCALE—FEET
J I LEGEND:
• EXPLORATORY BORING
FOR THIS STUDY.
O EXPLORATORY BORING
B1 FOR PREVIOUS STUDY
DATED 6/12/2006,
JOB NO. 106 0498.
LOCATION OF EXPLORATORY BORING
Fig. 1
0
5
CL
w
w
0
15
BORING 1
EL. 6101'
BORING 2
EL. 6103'
/
/
// 22/12 // 9/12
/� WC=6.8 WC=7.5
DD=104 /_1 DD=91
/ /
/ /
/ /-' 46/12 / 52/12
✓ WC=6.7 / /-. WC=8.0
/ 00=121 V DD=110
/ /
r
23/12
WC=3.2
DD=115
-200=29
50/2
17/12
WC=2.7
-200=32
Al 58/12
0 ---
5 -
15
15 -
20 20-
16-7-464
0-
16-7-464
H -P- KUMAR
LOGS OF EXPLORATORY BORINGS
Fig. 2
LEGEND
ti
r
i
TOPSOIL; ORGANIC SANDY SILTY CLAY, FIRM, MOIST, DARK BROWN.
CLAY (CL); SANDY, SILTY, VERY STIFF TO HARD, SLIGHTLY MOIST TO MOIST, BROWN.
SAND (SM); SILTY, MEDIUM DENSE, SLIGHTLY MOIST, BROWN.
BASALT GRAVEL, COBBLES AND BOULDERS (GM), IN A SANDY SILTY CLAY MATRIX, DENSE,
SLIGHTLY MOIST, BROWN, CALCAREOUS.
RELATIVELY UNDISTURBED DRIVE SAMPLE; 2—INCH I.D. CALIFORNIA LINER SAMPLE.
DRIVE SAMPLE; STANDARD PENETRATION TEST (SPT), 1 3/8 INCH I.D. SPLIT SPOON
SAMPLE, ASTM D-1586.
22/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 22 BLOWS OF A 140—POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE CALIFORNIA OR SPT SAMPLER 12 INCHES.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON SEPTEMBER 21 AND NOVEMBER 15, 2016 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 D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422);
—2b0= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
16-7-464
H-P-KUMAR
LEGEND AND NOTES
Fig. 3
CONSOLIDATION - SWELL
2
0
5
4
3
J
— J
2
CONSOLIDATION
1
0
—1
SAMPLE OF: Sandy Silt Clay
FROM: Boring 1 ® 2.5'
WC = 6.8 %, DD = 104 pcf
e
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
1.0 APPLIED PRESSURE — KSF 10
100
SAMPLE OF: Sandy Silty Clay
FROM: Boring 1 ® 5'
WC = 6.7 %, DD = 121 pcf
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
ih... MM r..unn nppn wrly Io 1h.
namp 3.. Sra1.d. Th. to ling ropwl
Mol` net be ropedue 4. NC.pt In
run, .nhovt IM .ntt.n eppnn,01 nr
K umar pod Anon:atm Ire. $$.NI
b. ilotnn Wing y.Monrwd In
• rdonn. with ATM 0-4646.
1.0 APPLIED PRESSURE — KSF
10
100
16-7-464
H -P- KUMAR
SWELL -CONSOLIDATION TEST RESULTS
Fig. 4
SAMPLE OF: Sandy Silty Clay
FROM: Boring 2 0 2.5'
WC = 7.5 %, DD = 91 pcf
Thee. tat reeu1L1 apPrY 4Nr 10 the
ompfn l.tl.4. The testing report
Man not be ryrad.Jc.. e.upt in
fell, eitneut !4e .raln rppwwl at
Komar and M•112,L.t, InC 5.111
Cenralipaiian teebnq partwmed In
accordance. with A511t 0-4544.
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
16-7-464
1.0 APPLIED PRESSURE - KSF t0 1C
H-P=�KUMAR
SWELL -CONSOLIDATION TEST RESULTS
Fig. 5
X.aa.nc.\(.111^9\I 67
SAMPLE OF: Sandy Silty Clay
FROM: Boring 2 0 5'
WC = 8.0 %, DD = 110 pcf
MIR* 1111 rHYRa appy Only lO Na
Owl np
Sanded Th. (..rims vert
ino
t N rcd.t.d, eget In
rax, .iuwut (h..ntt.n apprerar of
Namur and 1..nei.t.., roe. Swan
eanwfidatla; l.rtlrp p.rfann.d in
eeerdene. %h 15TH SP -454a.
EXPANSION UNDER CONSTANT
PRESSURE UPON WETTING
16-7-464
1.6 APPLIED PRESSURE — KSF 10 100
H -PKU MAR
SWELL -CONSOLIDATION TEST RESULTS
Fig. 6
H-P�KUMAR
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 16-7-464
SAMPLE LOCATION
NATURAL
MOISTURE
CONTENT
(%)
NATURAL
DRY
DENSITY
(pa)
GRADATION
1 PERCENT
PASSING
NO. 200
SIEVE
ATTERBERG LIMITS
UNCONFINED
COMPRESSIVE
STRENGTH
(PSF)
SOIL TYPE
BORING
DEPTH
eft)
GRAVEL
(%)
SAND
(%)
LIQUID
LIMIT
(!e)
PLASTIC
INDEX
Cy.)
1
21/2
6.8
104
Sandy Silty Clay
5
6.7
121
Sandy Silty Clay
10
3.2
115
29
Silty Sand
2
2'/2
7.5
91
Sandy Silty Clay
5
8.0
110
Sandy Silty Clay
10
2.7
32
Silty Sand
1