HomeMy WebLinkAboutSoils Report for Foundation Design, Lot SD-21 08.13.2018Geotechnical 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 SD -21, ASPEN GLEN
SUNDANCE TRAIL
GARFIELD COUNTY, COLORADO
PROJECT NO. 18-7-493
AUGUST 13, 2018
PREPARED FOR:
MARTIN HOFFMAN
6906 EAST ARCHER PLACE
DENVER, COLORADO 80230
(dochoffie gmai i.com)
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY 1
PROPOSED CONSTRUCTION 1
SITE CONDITIONS 2
SUBSIDENCE POTENTIAL 2
FIELD EXPLORATION 2
SUBSURFACE CONDITIONS 3
DESIGN RECOMMENDATIONS 4
FOUNDATIONS 4
FOUNDATION AND RETAINING WALLS 5
FLOOR SLABS 6
UNDERDRAIN SYSTEM 6
SURFACE DRAINAGE 7
LIMITATIONS 7
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - SWELL -CONSOLIDATION TEST RESULTS
FIGURE 5 - GRADATION TEST RESULTS
TABLE 1 - SUMMARY OF LABORATORY TEST RESULTS
H-P*KUMAR
Project No. 18-7-493
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot
SD -21, Aspen Glen, Sundance Trail, 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 Martin Hoffman dated July 26, 2018.
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
expansion potential, gradation 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
Development plans for the lot had not been determined at the time of our study. We understand
the findings of our study will be considered in the purchase of the lot. For the purpose of our
study, we assume the proposed residence will be a 1 to 2 story structure with or without a
basement level and an attached garage. Ground floors could be slab -on -grade or structural above
crawlspace. Grading for the structure is assumed to be relatively minor with cut depths between
about 3 to 12 feet. We assume relatively light foundation loadings, typical of the proposed type
of construction.
When building loadings, location and grading plans have been developed, we should be notified
to re-evaluate the recommendations contained in this report.
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Project No. 18-7-493
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SITE CONDITIONS
The lot was vacant at the time of the field exploration. The terrain was gently sloping down to
the northwest with about 2 feet of elevation change across the general building area. A pond
with perimeter drainage easement is located immediately west of the lot. Small boulders were
observed in the north part of the lot. Vegetation consisted of grass and weeds.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Aspen Glen
development. 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 development, mostly east of the Roaring Fork River and one
located a few hundred feet north of Lot SD -21. These sinkholes appear similar to others
associated with the Eagle Valley Evaporite in areas of the Roaring Fork River 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 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 on Lot SD -21 throughout the service life of the proposed residence, in
our opinion, is low and similar to other lots in Aspen Glen; 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.
FIELD EXPLORATION
The field exploration for the project was conducted on August 1, 2018. Two exploratory borings
were drilled at the locations shown on Figure 1 to evaluate the subsurface conditions. The
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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 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 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 '/ to 21/ feet of mixed clay and gravel fill, consist of 21/ to 3 feet of stiff,
silty sandy clay underlain by relatively dense, slightly silty sandy gravel and cobbles with small
boulders to the maximum drilled depth of 16 feet. Drilling in the dense granular soils with auger
equipment was difficult due to the cobbles and boulders and drilling refusal was encountered in
the deposit.
Laboratory testing performed on samples obtained from the borings included natural moisture
content and density and gradation analyses. Results of swell -consolidation testing, presented on
Figure 4, indicate low compressibility potential under light loading and moderate collapse
potential (settlement under constant load) when wetted. Results of gradation analyses performed
on a small diameter drive sample (minus 11/ inch fraction) of the coarse granular subsoils are
shown on Figure 5. 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.
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Project No. 18-7-493
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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 granular soils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on the undisturbed natural granular soils should be designed for
an allowable bearing pressure of 3,000 psf. Based on experience, we expect
settlement of footings designed and constructed as discussed in this section will
be about 1 inch or less.
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 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) The fill soils, sandy silty clay 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.
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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 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 40 pcf for backfill consisting of the on-site soils. Backfill should not contain organics
or rock larger than about 6 inches.
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 0.50. Passive pressure of compacted backfill against the
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Project No. 18-7-493
, floor slabs should be
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sides of the footings can be calculated using an equivalent fluid unit weight of 400 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 a granular material 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
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 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
onsite 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
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.
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Project No. 18-7-493
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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, sump and pump or perforated sump/drywell. 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 P/2 feet deep.
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.
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 6 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 finer grained
soils to reduce surface water infiltration.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
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
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Project No. 18-7-493
8
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
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: KU MAR
Steven L. Pawlak, P.E.
Reviewed by:
Daniel E. Hardin, P.E.
SLP/ksw
H=P%KUMAR
Project No. 18-7-493
9
dt
a•:
SD -23
?2,433 SQ. 7.
,1rrigotioa,
:ss Easemm[
'ond
�yG
SD -21
a 1 �- i BORING
21,796 SQ. FT. - I
uru
wfj
az
ttY
lPofcl
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15 0 15 30
APPROXIMATE SCALE—FEET
/+cf-
1- J�0-
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1 1 Com]
4- \ Ari
BENCHMARK:
MANHOLE RIM
\ EL. 100', ASSUMED
18-7-493
H -P- iKU MAR
LOCATION OF EXPLORATORY BORINGS
Fig. 1
- 5
10
L
— 15
20
BORING 1
EL. 98.5'
18/12
18/6, 26/6
WC=6.3
DD=87
58/12
WC=1.1
+4=58
-200=9
50/1
BORING 2
EL. 96.5'
25/6, BOUNCE
WC=7.5
DD=85
0-
5
10
15 -
20
w
w
i
a
w
0
18-7-493
H-R-KUMAR
LOGS OF EXPLORATORY BORINGS
Fig. 2
LEGEND
FILL: MIXED CLAY AND GRAVEL, SANDY, SOME ORGANICS, LOOSE, SLIGHTLY MOIST, BROWN.
CLAY (CL); SILTY, SANDY, STIFF, SLIGHTLY MOIST, BROWN, LOW PLASTICITY.
GRAVEL AND COBBLES (GM—GP); SLIGHTLY SILTY, SANDY, BOULDERS, DENSE, SLIGHTLY
MOIST, BROWN, ROUNDED ROCK.
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.
18/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 18 BLOWS OF A 140—POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE CALIFORNIA OR SPT SAMPLER 12 INCHES.
f PRACTICAL AUGER REFUSAL
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON AUGUST 1, 2018 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 THE BENCHMARK ON FIG. 1.
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);
—200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
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H -P- KUMAR
LEGEND AND NOTES
Fig. 3
CONSOLIDATION - SWELL
CONSOLIDATION - SWELL
— 10
— 12
—10
—12
SAMPLE OF: Sandy Silty Clay
FROM: Boring 1 CO 5'
WC = 6.3 %, DD = 87 pcf
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
1.0 APPLIED NRLSSURE - KSF
10 100
TN.* lint mai. eoe.V w U.
'+ee n1 ten a Per twang neer_
41R venue t� ' 4 onemeel or
Cent
a al n {.�y .Ml ernef :n
YuSW
wJmn u. A$,hl D-1 .0
SAMPLE OF: Sandy Silty Clay
FROM: Boring 2 (P 2.5'
WC = 7.5 %, DD = 85 pcf
to APPLIE° PRESSURE - KSF
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
10 - - - —100
1
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H-P:A5KUMAR
SWELL -CONSOLIDATION TEST RESULTS
Fig. 4
7
100
90
t o
70
S O
30
g
aD
30
20
0
DIAMETER OF PARTICLES IN MILLIMETERS
CLAY TO SILT
SAND
FINE L MEDIUM
COARSE
182
GRAVEL
FINE
COARSE
COBBLES
GRAVEL 58 X SAND 33 X SILT AND CLAY 9 X
LIQUID LIMIT PLASTICITY INDEX
SAMPLE OF: Slightly Silty Gravel with Sand FROM: Boring 1 0 10'
10
20
30
40
so E
V
00
70
BO
00
100
These lest results apply only to the
samples which were lasted. The
I.oUnyy report shall not be reproduced,
swept In lull, without the wriNen
approval of Kumar & Assorlolee. Inc.
Sieve °nafyele Wing Is performed In
accordance wllh AST' D422, A551 C136
and/or ASTM DI 140.
18-7-493
H-P-� KUMAR
GRADATION TEST RESULTS
Fig. 5
HYDROMETER ANALYSIS
— .. IIS,
.. _/
STANDARD
• 11i 4.4_1
1
S1R.E5
SIEVE
L alp.a
ANALYSIS
CLEAR
-
Sal1AOE
A. 1
_..._
- i
i
or a
2e Hgl6 7 14115
49 YIN WN SOAK
5114E READINGS
19
/IN
OPENINGS
7•
,29
1
t
I
]
}
1
—J
I
1
1 -
1 '1 1
1
1L_1
.037
1 .1•
,073
.150
AOC
L
1
_ .100
11
1.
I
1-
8 _1_888
-(
,73
4
I 11
1
,
01 .009
.000 409
,019
9.9
t9
].11 I/ T''
39.1 71.2 est
7a
DIAMETER OF PARTICLES IN MILLIMETERS
CLAY TO SILT
SAND
FINE L MEDIUM
COARSE
182
GRAVEL
FINE
COARSE
COBBLES
GRAVEL 58 X SAND 33 X SILT AND CLAY 9 X
LIQUID LIMIT PLASTICITY INDEX
SAMPLE OF: Slightly Silty Gravel with Sand FROM: Boring 1 0 10'
10
20
30
40
so E
V
00
70
BO
00
100
These lest results apply only to the
samples which were lasted. The
I.oUnyy report shall not be reproduced,
swept In lull, without the wriNen
approval of Kumar & Assorlolee. Inc.
Sieve °nafyele Wing Is performed In
accordance wllh AST' D422, A551 C136
and/or ASTM DI 140.
18-7-493
H-P-� KUMAR
GRADATION TEST RESULTS
Fig. 5
H-PKUMAR
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 18-7-493
SAMPLE LOCATION
BORING
DEPTH
(ft)
NATURAL
MOISTURE
CONTENT
(Y.)
NATURAL
DRY
DENSITY
(pcf)
GRADATION
GRAVEL 1 SAND
(%) (%)
PERCENT
PASSING
NO. 200
SIEVE
ATTERBERG LIMITS
LIQUID PLASTIC
LIMfT INDEX
(%) i CA)
UNCONFINED
COMPRESSIVE
STRENGTH
(psf)
SOIL TYPE
5
6.3
87
10
1.1
58
33
9
L
21/4
7.5
85
Sandy Silty Clay
Slightly Silty Gravel with
Sand
Sandy Silty Clay