HomeMy WebLinkAboutSubsoil Studylc'ti**i*ffi:ffi'qÊú**
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Ëmgoyaü Own¡d Cørpcny
5020 County Road 154
Glenwood Springs, CO 81601
phone: (970) 945-7988
fax: (970) 945-8454
email: kaglenwood@Jcumarusa.com
www.kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT S-12, FILTNG I, ASPEN GLEN
SADDLEBACK ROAI)
GARFIELD COUNTY, COLORADO
PROJECT NO.21-7-384
JUNE 23,2021
PREPARED FOR:
RUSLAN FARADZHOV
408 AABC, UNIT 1A
ASPEN, COLORADO 81611
(aspencarcare@¡ahoo )
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION .........
SITE CONDITIONS
SUBSIDENCE POTENTIAL
SUBSURFACE CONDITIONS
FOUNDATION BEARING CONDITIONS ......
DESIGN RECOMMENDATIONS
FOUNDATIONS
FOUNDATION AND RETAINING WALLS
FLOOR SLABS
UNDERDRAIN SYSTEM
SURFACE DRAINAGE...
LIMITATIONS
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 I- SUMMARY OF LABORATORY TEST RESULTS
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Kumar & Associates, lnc. o Project No. 21-7-384
PURPOSE AND SCOPE OF STUDY
This report presents the results ofa subsoil study for a proposed residence to be located on
Lot S-12, Filing 8, Aspen Glen, Saddleback Drive, 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 proposal for geotechnical
engineering services to Ruslan Faradzhov dated April 27 ,2021.
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. Garage
floor will be slab-on-grade. Grading for the structure is assumed to be relatively minor with cut
depths between about 4 to 6 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 field exploration. The terrain is relatively flat with a slight
slope down to the north. The ground surface is natural with minimal grading from road
construction. There is a berm with landscaped trees along the north side of the lot. Vegetation
Kumar & Associates, lnc. @ Project No. 2'l-7-384
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consists of grass and weeds and the trees planted on the berm. Nearby buildings include one and
two story singlc family rcsidences.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the subject site and the
nearby areas of 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
pottions of the property. Dissolution of the gypsum under certain conditions can callse sinkholes
to develop and can produce areas of localized subsidence. During previous work in the area,
sinkholes have been observed scattered throughout the Roaring Fork River valley. These
sinkholes appear similar to others associated with the Eagle Valley Evaporite in other areas of
the Roaring Fork River valley. The nearest mapped sinkhole is located about %mile southeast
of this lot.
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 S-14 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 May 10, 2021. Two exploratory borings
were drilled at the locations shown on Figure I to evaluate the subsurface conditions. Thc
borings were advanced with 4 inch diameter continuous flight augers powered by a truck-
mounted CME-458 drill rig. The borings were logged by a representative of H-P/Kumar.
Samples of the subsoils were taken with l% inch and 2 inch l.D. spoon samplers. 'l'he samplers
were driven into the subsoils at various depths with blows from a 140 pound hammer falling 30
inchcs. This tcst is similar to the standard penetration test described by ASTM Method D-1586,
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The penetration resistance values aÍe 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 I foot of topsoil consist of I0% feet of stiff, sandy clay overlying slightly
silty sand and gravel with cobbles at a depth of IlYz feet down to the maximum depth explored,
lSVz feet. Four feet of clay fill with scattered gravel was encountered in Boring 2 overlying the
natural clay soils. Drilling in the dense granular soils with auger equipment was difficult due to
the cobbles and drilling refusal was encountered in the deposit.
Laboratory testing performed on samples obtained from the borings included natural moisture
content, density and gradation analyses. Results of swell-consolidation testing performed on
relatively undisturbed drive samples of the clay soils, presented on Figure 4, indicate low to
compressibility under light loading and a low to moderate expansion potential when wetted
under a constant light surcharge. Results of gradation analyses performed on a small diameter
drive sample (minus lYr-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
FOUNDATION BEARING CONDITIONS
The sandy clay soils possess an expansion potential when wetted which could result in
movement of footings bearing on the clay soils. Surface runoff landscape irrigation, and utility
leakage are possible sources of water which could cause wetting. A lower risk alternative would
be to place the foundation entirely on the underlying relatively dense river gravels or remove and
replace a certain depth of silty sandy clay soils with compacted structural fill. The subgrade
should be observed for bearing conditions and further evaluated for heave potential at the time of
construction.
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DN,SIGN RECOMMENDATIONS
I.OUNDA'I'IONS
Consiclering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed constructiono we recommend the building be founded with spread footings bearing
on at least 3 feet of compacted structural fill or on the natural gravel subsoils.
The design and construction criteria presented below should be observed for a spread footing
foundation system.
1) Footings placed on at least 3 feet of structural fill over the clay soils should be
designed for an allowable bearing pressure of 2,000 psf. Based on experience, we
expect initial settlement of footings designed and constructed as discussed in this
section will be about 1 inch or less. There is a heave potential for the soils if the
clay soils were to become wetted. The movement would be differential and could
be about %to I inch f'or a wetted depth on the order of l0 f'eet below fboting
bearing level. Use of a full depth basement would reduce the heave potential with
less depth of clay soils below the foundation bearing level.
2) The footings should have a minimum width of 16 inches for continuous walls and
2 feú 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
afea.
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.
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 loosc or disturbcd soils should bc rcmovcd and
the footing bearing level extended down to the natural soils. The clay soils should
be removed for 3 feet below footing grade and the design bearing level re-
established with compacted structural fill to reduce heave potential. The
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structural fill should be a well graded granular material such as 3/¿ inch road base
(CDOT Class 6) and compacted to at least 98% of standard proctor density at a
moisture content near optimum. The fill should extend laterally beyond the
footing a distance at least equal to one-half the depth of fill below the footing.
Structural fill placed to reduce the potential heave risk should be at least 3 feet
deep below the footings.
A representative ofthe geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FOLINDATION 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 55 pcf for backfill consisting
of the on-site fine-grained 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 45 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
backhll 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%o 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%o 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. Backfill should not contain organics, debris or rock larger than about
6 inches.
6)
Kumar & Associates, lnc. @ Project No. 21-7-384
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The lateral resistance of foundation or retaining rvall footings will be a combination of the
sliding resistance of the footing on the foundation matcrials and passivc carth prcssurc against
the side of the footing. Resistance to sliding at the bottoms of the footings can be calculated
basecl on a coefficient of friction of 0.45 for gravel fill bearing soils. 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 ocour 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
nonexpansive material compacted to at least 95Yo 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. The clay soils possess a heave potential when wetted which could result in slab
movement and distress if the bearing soils become wetted. The risk of slab movement can be
reduced by removing the clay soils and placing at least 2 feet of compacted structural fill, such as
road base, below the slab. 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 least95Yo of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of
imported 3/a-inch road base devoid of vegetation, topsoil and oversized rock.
UNDERDRAIN SYSTEM
Although free water was not encountered during our exploration, it has been our experience in
this 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
Kumar & Associates, lnc. @ Project No. 21-7-384
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recommend below-grade construction, such as retaining walls, deep 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 I foot below lowest adjacent finish grade and sloped at a minimum l%oto
a suitable gravity outlet or sump and pump. Free-draining granular material used in the
underdrain system should contain less than 2o/o 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 Yz 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
Proper surface drainage will be critical to limit potential for wetting below the building. The
following drainage precautions should be observed during construction and maintained at all
times after the residence has been completed:
1) Inundation ofthe 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%o of the maximum standard Proctor density in pavement and slab areas
and to at least 90Yo 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 frrst 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
6 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 inigation.
Kumar & Associates, lnc. @ Project No. 21-7-384
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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 consùted. 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 pu{poses. Vy'e 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
ofexcavations and foundation bearing strata and testing ofstructural fill by a representative of
the geotechnical engineer.
Respectfully Submitted,
Kuuuar & ÅssoeåæÉeso äaec,
Daniel E. Hardin,
DEH/kac
Cc: JeffJohnson
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21 -7 -384 Kumar & Associates LOCATION OF EXPLORATORY BORINGS Fig. 1
BORINC 1EL. t0 r .6
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21 -7 -384 Kumar & Associates LOGS OF EXPLORATORY BORINGS Fîg. 2
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LEGEND
TOPSOIL: SLIGHTLY SANDY SILTY CLAY, ORGANIC, ROOTS, SOFT, MOIST, DARK BROWN.
FILL: SANDY SILTY CLAY, SCAïïERED GRAVEL, MEDIUM STIFF, SLIGHILY MOIST, LIGHT BROWN.
CLAY (CL); SILTY, SANDY, STIFF TO HARD, SLIGHTLY MOIST TO MOIST, LIGHT BROWN,
CALCAREOUS.
W
GRAVEL (GM): SANDY TO VERY SANDY, DENSE TO VERY DENSE, SLIGHTLY MOIST, BROWN
DRIVE SAMPLE, 2-INCH I.D. CALIFORNIA LINER SAMPLE
i DRTVE SAMPLE, 1 3/8-|NCH t.D. SPLTT SPOON STANDARD PENETRATTON TEST
.-;.^ DRIVE SAMPLE BLOW COUNT. INDICATES THAT 17 BLOWS OF A 140-POUND HAMMER"/ '' FALLTNG 30 TNCHES WERE REQUTRED To DRrvE THE SAMPLER 12 rNcHEs.
I eucrrclL AUGER REFUSAL.
NOTES
1. THE EXPLORATORY BORINGS WERE DRILLED ON MAY 10, 2021 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 PLÄN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MEASURED BY INSTRUMENT LEVEL AND
REFER TO THE BENCHMARK ON FIG. 1.
4. THE EXPLORATORY BORING LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE
ONLY TO TI{E DEGREE IMPLIED BY TIIE 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 WÄS NOT ENCOUNTERED IN THE BORINGS AT THE TIME OF DRILLING.
7. LABORATORY TEST RESULTS:
WC = WATER CONTENT (%) (ASTM D2216);
DD = DRY DENSITY (PCt) (ISTV D2216);+4 = PERCENTAGE RETAINED ON NO. 4 SIEVE (ASTM D6913);
_2OA= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM 01140);
21 -7 -384 Kumar & Associates LTGEND AND NOTES Fig. 3
SAMPLE OF: Sondy Silty Cloy
FROM:Boringl@4'
WC = 8.5 26, DO = 1 10 pcf
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PRESSURE UPON WETTING
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21 -7 -384 Kumar & Associates SWELL-CONSOLIDATION TEST RESULTS Fig.4
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DIAMETER IN MILLIMETERS
CLAY TO SILT COBBLES
GRAVEL 16 % SAND 13
LIQUIO LIMIT
SAMPLE OF: Slightly Silty Sond ond Grovgl
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PLASTICITY INDEX
SILT AND CLAY 11 %
FROM:Boríng1O15'
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FINE MEDTUM lCOlnSe FINE COARSE
21 -7 -384 Kumar & Associates GRADAÏION TTST RESULTS Fis. 5
rcÂiåm[.mfmifd-."TABLE 1SUMMARY OF LABORATORY TEST RESULTSNo.21-7.384SOIL TYPESandy Silty ClaySandy Silty ClaySlightly Silty Sand andGravelClay FillSandy Silty ClaySandy Silty ClayP/"1EXPANSION2.48,0000.5fosflEXPANSIONPRESSURE2,000(o/"1PLASTICINDEXATTERBERG LIMITSlo/olLIQUID LIMITPERCENTPASSING NO.2()f) SIEVE8511IJ4346DÊPTHBORINGSANDl:/"1GRA\ELlo/"1NATURALDRYDENSITYNATURALMOISTURECONTENTlt0rt71061081048.5.5l13.09.0tt.79.2475I2%7Vz011nL