HomeMy WebLinkAboutSoils Report for Foundation Design, Lot SD-23 08.13.2018HP<L \/r]AR
Geotechnlcal Engineering I Engineering Geology
Materials Testing I 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 Silverthome, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT SD -23, ASPEN GLEN
SUNDANCE TRAIL
GARFIELD COUNTY, COLORADO
PROJECT NO. 18-7-493.02
AUGUST 13, 2018
PREPARED FOR:
MARTIN HOFFMAN
6906 EAST ARCHER PLACE
DENVER, COLORADO 80230
(dochoffi a@ g m a i l .cam)
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 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 - GRADATION TEST RESULTS
TABLE 1 - SUMMARY OF LABORATORY TEST RESULTS
H-PMKUMAR
Project No. 18-7-493.02
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot
SD -23, 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, 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. 18-7-493.02
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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 south with about 2 feet of elevation change across the general building area. A pond with
perimeter drainage easement is located immediately south of the lot. Small boulders were
observed in the southeast part of the lot. Vegetation consisted of grass and weeds with cattails in
the drainage easement.
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 couple hundred feet north of Lot SD -23. 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 -23 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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Project No. 18-7-493.02
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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 a 13/8 inch I.D. spoon sampler. The sampler was 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 1 foot of topsoil, consist of relatively dense, slightly silty sandy gravel and
cobbles with small boulders to the maximum drilled depth of 61/2 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 gradation analyses. Results of gradation analyses performed on small diameter drive
samples (minus 11/ inch fraction) of the coarse granular subsoils are shown on Figure 3. 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.
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.
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Project No. 18-7-493.02
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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 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 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
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Project No. 18-7-493.02
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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
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, floor slabs should be
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Project No. 18-7-493.02
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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.
The drains should consist of drainpipe placed in the bottom of the wall backfill surrounded above
the invert Ievel 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 11/2 feet deep.
SURFACE DRAINAGE
The following drainage precautions should be.observed during construction and maintained at all
times after the residence has been completed:
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Project No. 18-7-493.02
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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
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
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Project No. 18-7-493.02
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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-tKUMAR
Steven L. Pawlak, P.E.
Reviewed by:
73-n
Daniel E. Hardin, P.E.
SLP/ksw
H-PKUMAR
Project No. 18-7-493.02
LOCATION OF EXPLORATORY BORINGS
H-PMKUMAR
`\' '
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BENCHMARK:_
MANHOLE RIM'
EL. 100' ASSUMED tic
BORING 2
BORING 1
Sll-23
22,433 SQ. FT
laze, u;g tea, N.
HOA Acccss Easement
SD -2
21,796 SQ.
] and
15 0 15 30
APPROXIMATE SCALE -FEET
18-7-493.02
Fig. 1
1-
L.1
w
L-
0_ a
0
1-0
5
- 10
BORING 1
EL. 97'
24/6. 15/3
50/6
WC=1.2
+4=51
-200=13
BORING 2
EL. 99'
33/6, 50/6
0
5
10-
1-
w
w
L�
x
0-
0 -
LEGEND LEGEND
rTOPSOIL, ORGANIC SANDY SILT AND CLAY, SCATTERED GRAVEL AND COBBLES, SLIGHTLY
MOIST, BROWN.
7
•
GRAVEL AND COBBLES (GM -GP); SLIGHTLY SILTY, SANDY, BOULDERS, DENSE, SLIGHTLY
MOIST, BROWN, ROUNDED ROCK.
DRIVE SAMPLE; STANDARD PENETRATION TEST (SPT), 1 3/8 INCH I.D. SPLIT SPOON
SAMPLE, ASTM D-1586.
24/6 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 24 BLOWS OF A 140 -POUND HAMMER
FALLING 30 INCHES WERE REQUIRED TO DRIVE THE SPT SAMPLER 6 INCHES.
PRACTICAL AUGER REFUSAL. WHERE SHOWN ABOVE BOTTOM OF BORING, INDICATES THAT
MULTIPLE ATTEMPTS WHERE MADE TO ADVANCE THE HOLE.
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);
+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D 422);
-200= PERCENTAGE PASSING NO. 200 SIEVE (ASTM 11 1140).
18-7-493.02
H -P- KUIIAR
LOGS OF EXPLORATORY BORINGS
Fig. 2
100
10
60
70
60
SO
30
20
10
CLAY TO SILT
SAND
FINE 1 MEDIUM ICOARSE
GRAVEL
FINE COARSE
COBBLES
18-7-493.02
GRAVEL 51 X SAND 36 X
LIOUID LIMIT PLASTICITY INDEX
SAMPLE OF: Silty Gravel with Sond
H-PtiKLIMAR
SILT AND CLAY 13 X
FROM: Boring 1 0 2.5' & 5' Combined
20
]D
w
eD
60
70
ea
62
100
These lel results apply only to Ihs
samples which were lasted. The
Meting report shall nal be reproduced,
ecepl In full, without the woIlten
approval 01 I:4990r • Aa. aei0tes, Inc.
Sipe 0901010 felting In performed In
accordance wllh ASTM b422. ASTM C136
and/or A51M 181540.
GRADATION TEST RESULTS
Fig. 3
HYDROMETER ANALYSIS
SIEVE ANALYSIS
34 HRS 7 HRS
TIME READINGS
.1.3,
00080.170
SE11100
Cl01.6 32}LA60 OrLIONae
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300. .eoo
1.
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,31 7,75
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.3
0 11
e 361 RI
311
M
7 27
102
22
CLAY TO SILT
SAND
FINE 1 MEDIUM ICOARSE
GRAVEL
FINE COARSE
COBBLES
18-7-493.02
GRAVEL 51 X SAND 36 X
LIOUID LIMIT PLASTICITY INDEX
SAMPLE OF: Silty Gravel with Sond
H-PtiKLIMAR
SILT AND CLAY 13 X
FROM: Boring 1 0 2.5' & 5' Combined
20
]D
w
eD
60
70
ea
62
100
These lel results apply only to Ihs
samples which were lasted. The
Meting report shall nal be reproduced,
ecepl In full, without the woIlten
approval 01 I:4990r • Aa. aei0tes, Inc.
Sipe 0901010 felting In performed In
accordance wllh ASTM b422. ASTM C136
and/or A51M 181540.
GRADATION TEST RESULTS
Fig. 3
H-P�I<UMAR
TABLE 1
SUMMARY OF LABORATORY TEST RESULTS
Project No. 18-7-493.02
SAMPLE LOCATION
BORING
DEPTH
(ft)
1 2%2&5
NATURAL
MOISTURE
CONTENT
(%)
1.2
NATURAL
DRY
DENSITY
(pcf)
J
GRADATION
GRAVEL
(%)
SAND
(%)
PERCENT
PASSING
NO. 200
SIEVE
51 36 13
J
ATTERBERG LIMITS
LIQUID
LIMIT
(%)
PLASTIC
INDEX
(%)
UNCONFINED
COMPRESSIVE
STRENGTH
(p5()
SOIL TYPE
Silty Gravel with Sand