HomeMy WebLinkAboutSoils Report 11.17.2016H-PKUMAR
Geotechnical Engineering 1 Eng neenng 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 277, IRONBRIDGE
0255 BLUE HERON VISTA
GARFIELD COUNTY, COLORADO
PROJECT NO. 16-7-558
NOVEMBER 17, 2016
PREPARED FOR:
RM CONSTRUCTION
ATTN: ERIC LINTJER
5030 COUNTY ROAD 154
GLENWOOD SPRINGS, CO 81601
(eric @ buildwithrm.com)
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY - 1 -
BACKGROUND INFORMATION - 1 -
PROPOSED CONSTRUCTION - 2 -
SITE CONDITIONS - 2 -
SUBSIDENCE POTENTIAL - 2 -
FIELD EXPLORATION - 3 -
SUBSURFACE CONDITIONS - 3 -
FOUNDATION BEARING CONDITIONS - 4 -
DESIGN RECOMMENDATIONS - 5 -
FOUNDATIONS - 5 -
FOUNDATION AND RETAINING WALLS - 6 -
NONSTRUCTURAL FLOOR SLABS - 7 -
UNDERDRAIN SYSTEM - 8 -
SURFACE DRAINAGE - 8 -
LIMITATIONS - 9 -
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
H -P ti KUMAR
Project No. 16-7-558
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be Iocated
on Lot 277, Ironbridge, 0255 Blue Heron Vista, 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 RM Construction dated October 31, 2016.
Hepworth-Pawlak Geotechnical (now H-P/Kumar) previously performed a preliminary
geotechnical study for the Ironbridge Villas where Lot 277 is located and presented the
findings in a report dated September 14, 2005, Job No. 105 115-6.
A field exploration program consisting of an exploratory boring 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.
BACKGROUND INFORMATION
The proposed residence is located in the existing Ironbridge subdivision development.
Hepworth-Pawlak Geotechnical (now H-P/Kumar) previously conducted subsurface
exploration and geotechnical evaluation for development of Villas North and Villas South
parcels, Job No. 105 115-6, report dated September 14, 2005, and performed observation
and testing services during the infrastructure construction, Job No. 106 0367 between
April 2006 and April 2007. The information provided in these previous reports has been
considered in the current study of Lot 277.
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Project No. 16-7-558
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PROPOSED CONSTRUCTION
The proposed residence will be a one story, wood frame structure with an attached garage
and located as shown on Figure 1. Ground floor is proposed to consist of a structural
slab -on -grade with no basement or crawlspace. Grading for the structure is proposed to
be relatively minor with cut depths between about 2 to 3 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 lot was vacant at the time of the field exploration. The terrain was relatively flat with
about 2 feet of elevation difference down to the southeast. Fill had been placed to elevate
the lot and surrounding area by the previous subdivision grading. Vegetation had been
stripped from the lot at the time of the field exploration.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Ironbridge
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.
A sinkhole opened
in the cart storage parking lot located east of the Pro Shop and west of the Villas North
parcel in January 2005. Other irregular bedrock conditions have been identified in the
affordable housing site located to the northwest of the Villas North parcel. Irregular
surface features that could indicate an unusual risk of future ground subsidence were not
observed in the Villas North parcel, but localized variable depths of debris fan soils and
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Project No. 16-7-558
3
bedrock quality encountered by the previous September 14, 2005 geotechnical study in
the Villas North development area could be the result of past subsidence.
The subsurface
exploration performed in the area of the proposed residence on Lot 277 did not encounter
voids but
the alluvial fan depth encountered was generally greater than encountered on
nearby Tots which could indicate past ground subsidence. In our opinion, the risk of
future ground subsidence on Lot 277 in the Villas North parcel throughout the service life
of the proposed residence is low and similar to other areas of the Roaring Fork River
valley where there have not been indications of ground subsidence, but 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 current project was conducted on November 1, 2016. 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 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 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 13 feet of relatively dense, mixed sand, silt and gravel fill
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consist of about 8 feet of medium dense, silty sand and gravel underlain by about 15 feet
of medium dense/stiff, silty sand to sandy silt with scattered gravel. Below the sand and
silt at about 36 feet deep was dense, slightly silty sandy gravel and cobbles to the
maximum drilled depth of 41 feet.
Laboratory testing performed on samples obtained from the boring included natural
moisture content and density and finer than sand size gradation analyses. Results of
swell -consolidation testing performed on a relatively undisturbed drive sample of the
sandy silt, presented on Figure 3, indicate low to moderate compressibility under loading
and minor collapse potential (settlement under constant load) when wetted. The
laboratory testing is summarized in Table 1.
Free water was not encountered in the boring at the time of drilling or when checked 14
day later. The upper soils were slightly moist to moist with depth.
FOUNDATION BEARING CONDITIONS
The upper 13 feet of soils consist of fill placed mainly in 2006 as part of the subdivision
development. The field penetration tests (blow counts) and laboratory tests performed for
the current study, and review of the field density (compaction) tests performed during the
fill construction indicate the structural fill was placed and compacted to the project
specified 95% of standard Proctor density. Debris fan soils which tend to collapse (settle
under constant load) when wetted were encountered below the fill. The amount of
settlement will depend on the thickness of the compressible soils due to potential collapse
when wetted, and potential compression of the underlying soils after wetting. Relatively
deep structural fill will also have some potential for long term settlement but should be
considerably less than the alluvial fan deposit. Sources of wetting include irrigation,
surface water runoff and utility line leaks. A heavily reinforced structural slab or post -
tensioned slab foundation designed_for significant differential settlements is
recommended for the building support.
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Project No. 16-7-558
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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 a
heavily reinforced structural slab foundation bearing on at least 10 feet of compacted
structural fill. A post -tensioned slab foundation could also be used.
The design and construction criteria presented below should be observed for a structural
slab foundation system.
1) A heavily reinforced structural slab placed on about 10 feet of structural
fill should be designed for an allowable bearing pressure of 1,500 psf or
subgrade modulus of 125 tcf. A post -tensioned slab if used should be
designed for a wetted distance of 10 feet but at least half of the slab width,
whichever is more. Based on experience, we expect initial settlement of
the slab foundation designed and constructed as discussed in this section
will be about 1 inch or less. Additional settlement could occur if the
bearing soils were to become wetted. The magnitude of the additional
settlement would depend on the depth and extent of wetting but may be on
the order of 1 to 11/2 inches.
2)
The thickened sections of the slab for support of concentrated loads should
have a minimum width of 20 inches.
3) The perimeter turn -down section of the slab should be provided with
adequate soil cover above the bearing elevation for frost protection.
Placement of foundations at Ieast 36 inches below exterior grade is
typically used in this area. If a frost protected foundation is used, the
perimeter turn -down section should have at least 18 inches of soil cover.
4) The foundation should be constructed in a "box -like" configuration rather
than with irregular extensions which can settle differentially to the main
building area. The foundation walls, where provided, should be heavily
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Project No. 16-7-558
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reinforced top and bottom to span local anomalies such as by assuming an
unsupported length of at least 14 feet. Foundation walls acting as retaining
structures (if any) should also be designed to resist lateral earth pressures
as discussed in the "Foundation and Retaining Walls" section of this
report.
5) The organic root zone and any loose or disturbed soils should be removed.
Additional structural fill placed below the slab bearing level should be
compacted to at least 98% of the maximum standard Proctor density at a
moisture content near optimum.
fi)
A representative of the geotechnical engineer should evaluate the
compaction of fill materials and 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 building 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.
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.
M -P KUMAR
Project No. 16-7-558
7
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 300 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.
NONSTRUCTURAL FLOOR SLABS
Compacted structural fill can be used to support lightly loaded slab -on -grade construction
separate from the building foundation. The fill soils can be compressible when wetted
and result in some post -construction settlement. To reduce the effects of some
differential movement, slabs -on -grade should be separated from the building to 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
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Project No. 16-7-558
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slab use. A minimum 4 -inch layer of well -graded sand and gravel, such as road base,
should be placed beneath slabs for support. This material should consist of minus 2 -inch
aggregate with at least 50% retained on the No. 4 sieve and less than I2% 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, topsoil and oversized rock.
UNDERDRAIN SYSTEM
It is our understanding that the finished floor elevation at the lowest level of the proposed
residence will be at or above the surrounding grade. Therefore, a foundation drain system
is not required. 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,
be protected from wetting and hydrostatic pressure buildup by an underdrain system.
If finished floor elevation of the proposed residence has a floor level below the
surrounding grade, we should be contacted to provide recommendations for an underdrain
system. All earth retaining structures should be properly drained.
SURFACE DRAINAGE
Precautions to prevent wetting of the bearing soils, such as proper backfill construction,
positive backfill slopes, restricting landscape irrigation and use of roof gutters need to be
taken to limit settlement and building distress. The following drainage precautions
should be observed during construction and maintained at all times after the residence has
been completed:
H -P KUMAR
Project No. 16-7-558
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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 5 feet in unpaved
areas and a minimum slope of 21 inches in the first 10 feet in paved areas.
Graded swales should have a minimum slope of 3%.
4) Roof downspouts and drains should discharge well beyond the Iimits 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 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 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
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Project No. 16-7-558
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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 KUMAR
Steven L. Pawlak, P.E.
Reviewed by:
Daniel E. Hardin, P.E.
SLP/ljf
H -P KUMAR
Project No. 16-7-558
BLUE HERON
VISTA
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APPROXIMATE SCALE—FEET
16-7-558
3
14'
H-PKUMAR
LOCATION OF EXPLORATORY BORING
Fig. 1
W
W
LA_
z
0
J
LLJ
BORING 1
EL. 5959'
59 60
— 5955
— 5950
— 5945
— 5940
— 5935
5930
5925
— 5920
5915
16-7-558
PROPOSED FLOOR
EL. 5958.65'
56/6
52/6
50/5
WC=1.1
—200=71
46/12
WC=8.5
DD=114
—200=56
1 4/1 2
20/12
1 2/1 2
WC=17.5
DD=105
20/12
WC=13.8
DD=108
—200=62
46/12
H-P==�KUMAR
LEGEND
7
X
FILL: MIXED SILT, SAND AND GRAVEL SCATTERED COBBLES,
COMPACTED, SLIGHTLY MOIST, BROWN.
SAND AND GRAVEL (5M—GM); SILTY, SCATTERED COBBLES, MEDIUM
DENSE, MOIST, MIXED BROWN.
SAND AND SILT (SM—ML); VERY SANDY, SCATTERED GRAVEL,
MEDIUM DENSE, MOIST, BROWN.
GRAVEL AND COBBLES (GM—GP); SUGHTLY SILTY, DENSE, MOIST,
BROWN, ROUNDED ROCK.
DRIVE SAMPLE, 2—INCH I.D. CALIFORNIA UNER SAMPLE.
DRIVE SAMPLE, 1 3/8—INCH I.D. SPLIT SPOON STANDARD
PENETRATION TEST.
46/12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT 46 BLOWS OF
A T40—POUND HAMMER FALLING 30 INCHES WERE REQUIRED
TO DRIVE THE SAMPLER 12 INCHES.
NOTES
1. THE EXPLORATORY BORING WAS DRILLED ON NOVEMBER 1, 2016
WITH A 4—INCH DIAMETER CONTINUOUS FLIGHT POWER AUGER.
2. THE LOCATION OF THE EXPLORATORY BORING WAS MEASURED
APPROXIMATELY BY PACING FROM FEATURES SHOWN ON THE
SITE PLAN PROVIDED.
3. THE ELEVATION OF THE EXPLORATORY BORING WAS OBTAINED
BY INTERPOLATION BETWEEN CONTOURS ON THE SITE PLAN
PROVIDED.
4. THE EXPLORATORY BORING LOCATION AND ELEVATION SHOULD
BE CONSIDERED ACCURATE ONLY TO THE DEGREE IMPUED BY
THE METHOD USED.
5. THE UNES 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 DRIWNG OR WHEN CHECKED 14 DAYS LATER.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D 2216);
DD = DRY DENSITY (pcf) (ASTM D 2216);
—200 = PERCENTAGE PASSING NO. 200 SIEVE (ASTM D 1140).
LOG OF EXPLORATORY BORING
Fig. 2
1
0
—2
z
0
1-
0 —3
J
0
en
z
0
`-, —4
URE - KSF
I0
TOO
16-7-558
H-P45KUMAR
SWELL -CONSOLIDATION TEST RESULT
Fig. 3
SAMPLE OF: Sandy Silt
FROM: Boring 1 0 25'
WC = 17.5 %, DD = 105 pcf
IIIIII
ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
I
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tem hat mita app/ •n7 to Vn
run*. Naiad. mo WAIN impost
.nal net in np,Wugp. aecwt I.
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£ p o—i .tA N
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URE - KSF
I0
TOO
16-7-558
H-P45KUMAR
SWELL -CONSOLIDATION TEST RESULT
Fig. 3
Project No. 16-7-558
0
H
J
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rt
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W
2i_
>_ix
= °
1_a
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cn
SOIL OR
BEDROCK TYPE
Sandy Gravelly Silt (Fill)
Very Sandy Gravelly Silt
(Fill)
Sandy Silt
Very Sandy Silt
UNCONFINED
COMPRESSIVE
STRENGTH
(PSF)
ATTERBERG LIMITS
PLASTIC
INDEX
(%)
01_
J J
PERCENT
PASSING
NO. 200
SIEVE
71
VD
CN1
z
o
0
co
0
a
a
0
GRAVEL
(%)
NATURAL
DRY
DENSITY
(pcf)
-
in
CP
108
1 NATURAL
MOISTURE
CONTENT
(%)
17.5
co
11 SAMPLE LOCATION
DEPTH
I (ft)
V)
o
o
BORING