HomeMy WebLinkAboutSoils Report 12.12.2017H.PVKUMAR
Geotechnical Enginucring I Engineerlng Geology
Materials Testing I Environmental
5020 County Road 154
Glenwood Springs, CO 81601
Phune: (970) 945-7988
Fax; (970) 94S8454
Email: hpkglenwood@kumarusa.com
Office Locations: Denver (HQ), Parker, Colorado Springs, Fort Collins, Glenwood Springs, Summit County, Colorado
RECEIVED
MAY 2 2 2018
GARFIELD COUNTY
c-o r¡ rrr u H rrY D EvE Lo P MEt'lT
ST]BSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT 13, ROCK CREEK ST]BDIVISION
574 CRYSTAL RIVER ROAD
GARFIELD COUNTY, COLORADO
PROJECT NO. 17-7-807
DECEMBERt2,20t7
PREPARED FOR:
ED & MICHELLE BUCHMAN
P.O. BOX 1400
CARBONDALE, COLORADO 81623
ecl.buchman @ smail.com
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
STTE CONDITIONS
SUBSIDENCE POTENTTAL
FIELD EXPLORATION
SUBSURFACE CONDITIONS
DES IGN RECOMMENDATIONS
FOLINDATIONS
FOUNDATION AND RETAINING WALLS
FLOOR SLABS
UNDERDRAIN SYSTEM
SITE CRADING
SURFACE DRAINAGE ...
LIMITATIONS................
FIGURE I - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - SWELL-CONSOLIDATION TEST RESULTS
TABLE 1. SUMMARY OF LABORATORY TEST RESULTS
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H.PVKUMAR
Project No.17-7-807
PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot
13, Rock Creek Subdivision, 574 Crystal River Road, 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 Ed & Michelle Buchman, dated October 26,2017.
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. Ttris 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 replace the existing house. Design plans have not been developed.
We assume that the new house will be a one to two story wood frame structure over a crawlspace
or basement level. Ground floor may be slab-on-grade. Grading for the structure is assumed to
be relatively minor with cut depths between about 4 to 9 feet. We assume relatively light
foundation loadings, typical of the proposed type of construction.
When building location, grading and loading information have been developed, we should be
notified to re-evaluate the recommendations presented in this report.
SITE CONDITIONS
The site is occupied by an existing one story wood frame residence over a partial basement with
an attached garage. There is also a two story log round barn located west and uphill of the
house. The site is accessed by a paved driveway. The buildin g areais relatively flat with a
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gentle slope down to the east. The building area is vegetated with landscaped lawn and
evergreen and deciduous trees. At the east side of the existing house there is a steep slope down
to the east at SOTo grade. The steep slope is about 15 feet high. The Crystal River borders the
east side of the lot.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the site. 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
Carbondale area and along the Crystal River. These sinkholes appear simila¡ to others associated
with the Eagle Valley Evaporite in areas of the Roaring Fork Valley.
Sinkholes were not observed in the inutrediaLe area of the subject lot. No evidence of cavities
was encountered in the subsurface materials; however, the exploratory borings were relatively
shallow, for foundation clesign 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 [,ot 13 throughout the service life ofthe proposed residence, in our
opinion, is low; 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 November 27,2017. 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 CME458 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
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inches. This test is similar to the standard penetration test described by ASTM Method D-l586.
The penetration resistance values are an indication of the relative density or consistency of the
subsoils. Depths at which the samples werc 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.
ST]BSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2. The
subsoils,below aboutVzto l footof topsoil,consistof about lYzto3Vzfeetof mediumstiff,
sandy silty clay overlying relatively dense, slightly silty sandy gravel with cobbles. Drilling in
the dense granular soils with auger equipment was difficult due to the cobbles and possible
boulders and drilling refusal was encountered in the deposit.
Laboratory testing performed on samples obtained from the borings included natural moistnre
content, density and percent finer than sand size gradation analyses. Results of swell-
consolidation testing performed on a relatively undisturbed drive sample, presented on Figure 3,
indicate moderate compressibility under conditions of loading and wetting. 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 to moist.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the proposed construction, we recommend the residence 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 placecl on the undisturbed natural granular soils should be designed for
an allowable bearing pressure of 3,000 psf. Based on experience, we expect
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2)
settlement of footings designed and constructed as discussed in this section will
be about I inch orless.
The footings should have a minimum width of 16 inches for continuous walls and
2 feet for isolated pads.
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.
Continuous foundation walls should be reinforced top and bottom to span local
anomalies such as by assuming an unsupported length of at least l0 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.
All existing fill, debris, clay, 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.
A representative of the geotechnical engineer shoulcl observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
3)
4)
FOUNDATION AND RETAINING }VALLS
Foundation walls and retaining structures which are laterally supported and can be expected to
undergo only a slight amount of deflection should be designetl 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.
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
s)
6)
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backfill surface. The buildup of water behind a wall or an upward sloping backfill surface will
increase the late¡al 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 907o of the maximum
standard Proctor density at a moisture content near optimum. Backfill in pavement and walkway
areas should be compacted to at least95Vo 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 corectly, and coukl result in distress to
facilities constructed on the backfill. Backfill should not contain organics, debris or rock larger
than about 6 inches.
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 425 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 95Vo 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
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 placecl beneath basement level slabs to facilitate drainage. This
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material should consist of minus 2 inch aggregate with at least 507o retained on the No. 4 sieve
and less than2To passing the No, 200 sieve.
All fill materials for support of floor slabs should be compacted to at least 95Vo of maximum
standard Proctor density at a moisture content near optimum. Required fill can consist of the on-
site 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
this area that local perched groundwater can develop during times of heavy precipitation or
seasonal runoff. Frozen ground during spring runoff can also 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 surounded 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%o to
a suitable gravity outlet. Free-draining granular material used in the underdrain system should
contain less than 2Vo passing the No. 200 sieve, less than 507o passing the No. 4 sieve and have a
maximum size of 2 inches. The drain gravel backfill should be at least lVz feet deep.
STTE GRADING
The risk of construction-induced slope instability at the site appears low provided the building is
located abovc the steep slope as planned and cut and fill depths are limited. We assume the cut
depths for a basement level will not exceed one level, about 9 feet. Fills should be limited to
about I to 10 feet deep, especially at the downhill side of the residence where the slope steepens.
Embankment fills should be compacted to at least95Vo of the maximum standard Proctor density
near optimum moisture content. Prior to fill placement, the subgrade should be carefully
prepared by removing all vegetation and topsoil and compacting to at least 95Vo of the maximum
standard Proctor density. The fill should be benched into the portions of the hillside exceeding
ZOVo grade.
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Permanent unretained cut and fill slopes should be graded at 2 horizontal to 1 vertical or flatter
and protected against erosion by revegetation or other means. The risk of slope instability will
be increased if seepage is encountered in cuts and flatter slopes may be necessary. If seepage is
encountered in permanent cuts, an investigation should be conducted to determine if the seepage
will adve¡sely affect the cut stability. This office should review site grading plans for the project
prior to construction.
SURFACE DRAINAGE
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 compactecl to
at least 95Vo of the maximum standard Proctor density in pavement and slab areas
and to at least 9OVo of the maximum standard Proctor density in landscape areas.
3) The ground surface sunounding 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 feú of the on-site 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 a¡e 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 ficld of
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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 pu{poses. We are not
responsible for technical interpretations by othe¡s 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
Daniel E. Hardin, P.E.
Reviewed by:
L. Pawlak, P.E.
DEHlkac
cc Tim Hagman, Architect tim@hagmanarchitects.com
H.PÈKUÍVIAR
Project No. 17-7-807
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17 -7 -807 H.PVKUMAR LOCATION OF EXPLORATORY BORINGS Fig. 1
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LEGEND
TOPSOIL, ORGÀNIC CLAYEY SAND AND SILT, FIRM, SLIGHTLY MOIST, ÐARK 8ROWN.
CLAY (cL): SILTY, SANDY, SCATTERED GRAVEL, MEDIUM STIFF, MOIST, BROWN
GRAVEL ANû C0EBLES (ËM-GP): sANuY, SLIGHTLY slLTY, DENst, SLIGHTLY MorsT, BRowN
RELATIVELY UNÐISTURBED DRIVE SAMPLE; 2-INCH l.D. CAL|F0RNtA LTNER SAMpLE
DRTVE SAMPLE; STANÐARD PENETRATTON TEST (SpT), r 3/s tNcH LD. spltï spooN
SAMPLE, ASTM D_t586.
¡¡12 DRIVE SAMPLE BLOW COUNT. INDICATES THAT I BLOWS OF À 14O-POUND HAMMER-,.- FALLING 30 INCHES WERE REQUIRED TO ÐRIVE THE CALIFORNIA OR SPT SAMPLER 12 INCHES
PRACTICAL AUGTR REFUSAL.
NOTES
THE EXPLORATORY BORINGS WIRT DRILLTD ON NOVTMBER 27,2017 WITH A 4-INCH DIAMETER
CONTINUOUS TLIGHT POWER AUGER.
2. THE LOCATIONS OF lHE EXPLORATORY BORINGS WERT MEASURED APPROXIMÀTTLY BY PACINO
rROM TEATURES SHOWN ON THI SITE PLAN PROVIDED.
3. THE ELEVATIONS OF THE EXPLORATORY BORINGS WERE MTASUREÐ BY HAND LEVEL AND REFTR
TO THE BENCHMARK ON FIG. 1.
4. THE EXPLORATORY BORING LOCATIONS AND ELÊVATIONS SHOULD BE CONSIDERED ACCURATE
ONLY TO THE ÐEGREE IMPL'ED BY THE METHOD USTD.
5. THE LINES EETWËEN MATERIÄLS SHOWN CIN THE EXPLORATORY BORING LOGS REPRESENT THE
APPROXIMATE BOUNÐARIES SETWEEN MATERIAL TYPES ANÐ THE TRANSITIONS MAY BE GRADUAL.
6. LABORATORY TESÍ RESULTST
WC = WATER CONTENT (%) (ASTM Ù 2216);
DD = DRY DENSITY (PCf) (ASTM I) 2216);
-200= PTRCENTAGE PASSING NO. 200 SIEVE (ASTM D 1 1 40).
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17 -7 -807 H.PVKUMAR LOGS OF IXPLORATORY BORINGS Fig. 2
SAMPLE OF: Sondy Silty Clcy
FROM:Boringl@2.5'
WC = 15.A %, DD = 111 pcf
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ADDITIONAL COMPRESSION
UNDER CONSTANT PRESSURE
DUE TO WETTING
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17 -7 -8A7 H-PryKUMAR SWTLL-CONSOLIDATION TEST RESULTS Fig. 3
9
H-P\KUMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSProject No. 17-7-807SOILTYPESandy Silty ClaySlightly Silty Sand andGravelUNCONFINEÐCOMPRESS¡VESTRENGTHIPSF}ATTERBERG LIMITSPLASTICINDEX(o/"1LIQUIDLIMIT(o/olPERCENTPASSINGNO.200SIEVE6II0GRADATIONSAND(o/olGRAVEL$lNAÏURALDRYDENSITYlocf)111NATURALMOISTURECONTENÏ(%l12V"15.06.9SAMPLELOCATIONDEPTH{ftt2V2BORING2