HomeMy WebLinkAboutSubsoil Study for Foundation Design 03.06.17H-PVKUMAR
Geotecñnical 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 Loætions: Parker, Glenwood Springs, and Summit County, Colorado
SUBSOIL STUDY
FOR FOUNDATION DESTGN
PROPOSED RESIDENCE
LOT H39, ASPEN GLEN
HOMESTEAD ROAD
GARFIELD COUNTY, COLORADO
PROJECT NO. 17-7-187
MARCH 6,2017
REVISED MARCH 7,2017
PREPARED FOR:
TOM PALIZZT
P.O. BOX 1404
RIFLE, CO 81650
(tompalizzi @ hotmail.com)
RECEIVN}
No\, 2 I lolt
GARFIELD COUNW
]MMUNIW DEVELOPMENT
TAtsI,E OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
STTE CONDITIONS
SUBSIDENCE POTENTIAL
FIELD EXPLORATION..
SUBSURFACE CONDÍI'IONS
DESIGN RECOMMENDATIONS
FOI.'NDATIONS
FOUNDATION AND RETAINING WALLS
FLOOR SLABS
UNDERDRAIN SYSTEM .........
SURFACE DRAINAGE ............
LIMITATIONS
FIGURE I - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - GRADATION TEST RESULTS
TABLE 1 - SUMMARY OF LABORATORY TEST RESULTS
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H-PNKUMAR Pfoject Na. 1l-/-181
PURPOSD AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed residence to be located on Lot
H39, Aspen Glen, Homestead Road, Galfield Count!, Colorado. The project site is shown on
Figure 1. The pllrpose of the study was to develop recommendations for the foundation design.
The study was conducted in accoldance with our agreement for geotechnical engineering
services to Tom Palizzi dated Febmary L7,2017.
A field exploration program consisting of exploratory borings was conducted to obtain
information on the subsurface conclitions. Samples of the subsoils obtained cluring the field
exploration were tested in the labomtory 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 pressurcs for
the proposed building foundation. This report summarizes the data obtained during this study
and presents our conclusions, design rccommendations and other geotechnical engineering
considerations based on the ploposed construÇtion and the subsulface conditions encounterecl.
PROPOSED CONSTRUCTION
The proposed residence will be a 1 to 2 story structure with a full basement, a covered porch and
an attached garage. Ground floor will be slab-on-grade in the living areas, the covered porch and
the garage. There will be a shallow swimming pool in the basement about 4 feet deep. Grading
for the structure is assumed to be relatively minor with cr¡t depths between about 3 to 13 feet.
'We assume relatively light founclation 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 vacanl at the time of the field exploration. The terain was gently sloping down to
the north. There was about 2 feet of elevation change across the lot. An open irrigation ditch
was on the eastern part of the lot. Vegetation consisted of grass and weeds.
H-P\KUMAR Project No, 17-7-187
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SUBSIDENCE POTENTIAI,
Bedrock of the Pennsylvanian age Eagle Valley Evapolite underlies the Aspen Glen
development. These rocks are a seqllence of gypsiferous shale, fine-grained sandstone and
siltstone with some massive beds of gypsum and limestone. There is a possibility that massive
gypsum deposits associatecl 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 wolk in the area, several sinkholes werc
observed scatterecl throughout the development, mostly east of the Roaring For.k River. These
sinkholes appear similar to CItheß 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 werc relatively
shallow, for foundation design only. Based on our plesent knowledge of the subsurface
conditions at the site, it cannot be said for certain that sinkholes will not develop. The risk of
fttture ground subsidence on Lot H39 throughout the service life of the proposed rcsidence, 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 Februaly 21,2017. Two exploratory
borings were drilled at the locations shown on Figure I to evahiate the subsurface conditions.
The borings were advanced with 4 inch diameter continuous flight augers powered by a truck-
mot¡nted CME-458 drill rig. The borings were logged by a representative of H-PlKumar.
Samples of the subsoils were taken with a L% tnch 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
H-PNKUMAR Project No. 17-7-187
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penetration resistance values are an indication ofthe relative density ol consistency ofthe
subsoils. Depths at which the samples were taken and the penetlation resistance values are
shown on the Logs of Exploratory Borings, Figure 2. The samples were returned to our
laboratory fol review by the project engineel and testing.
SUBSURFACE CONDITIONS
Graphic Iogs of the subsurface conditions encountercd at the site are shown on Figurc 2. The
strbsoils consist of about Vz feet of topsoil overlying nil to lVz feet of stiff, silty sandy clay with
scattered gravel underlain by relatively dense, slightly silty to silty sandy gravel ancl cobbles with
small boulders to the maximum drilled depth of l3 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 performecl on samples obtained from the borings included natural moistule
content and gradation analyses. Results of gradation analyses performed on small diameter drive
samples (minus IVz inch fraction) of the coarse granular subsoils are shown on Figure 4. The
laboratory testing is summarized in Table 1.
No fi'ee water was encountercd in the borings at the time of drilling and the subsoils were moist
to slightly rnoist with depth.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the nature of
the ploposed constrnction, 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.
H.PTKUMAR Project No. 17-7-'187
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2)
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3)
4)
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Footings placed on the undisturbed natural granular soils should be designed for
an allowable bearing pressurc of 3,000 psf. Based on experience, we expect
settlement of footings designed and constructed as discussed in this section will
be about I inch or less.
The footings should have a minimum width of l6 inches fol 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 plotection. Piacement
of foundations at least 36 inches below exterior grade is typically used in this
aÍea.
Continuous foundation walls should be reinforced lop 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 designecf to resist
lateral earth pressures as discussed in the "Fonndation and Retaining Walls"
section of this report.
The topsoil and any loose or disturbed soils should be lemoved ancl the footing
bearing level extended down to the relatively dense natural granulal soils, The
exposed soils in footing area should then be moistened and compacted.
A representative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
s)
FOUNDATION AND RETAINING WALLS
Foundation wallS, pool walls and letaining structures r,vhich are latelally supported and can be
expected to undergo only a slight amount of deflection should be designed for a lateral earth
pressllre computed on the basis of an equivalent fluid unit weight of at least 50 pcf fo¡ backfill
consisting of the on-site granular soils. Cantilevered retaining structlrres which are separate from
the residence and can be expected to deflect sufficiently to mobilize the full active earth pressure
condi¡ion should be clesigned for a lateral earth presslrre computed on the basis of an equivalent
fluicl unit weight of at least 40 pcf for backfill consisting of the on-site granular soils. Backfill
shoulcl not contain any organics, clay soils or rock larger than about 5 inches.
H.P\KUMAR Project No. 17-7-187
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All founda¡ion and retaining strlrctures should be designed fol appropriate hydrostatic and
surchalge pressures such as adjacent footings, traffic, construction materials and equipment. The
pl€ssltres recommended above assume dl'ained conditions behind the walls ancl a horizontal
backfill surface. The buildup of water behind a wall ol an upwatd sloping backfill surface will
increase the lateral pressure imposed on a foundation wall or retaining structure. An underdrain
should be provided to prcvent hydrostatic plessllÍe buildup behind walls.
Backfill should be placed in uniforn lifts and compacted to at least 9ATa of the maximum
standard Proctor density at a moisture content near optimum. Backlill placecl in pavement and
walkway areas should be compacted to at Least 95Va of the maximum standard Proctor density.
Care should be taken not to overcompact the backfill or ttse large equipment near the wall, since
this could cause excessive lateral pressure on the wall. Some settlement of deep founclation wall
backfill should be expected, even if the material is placed corectly, 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 matelials and passive earth pressure against
the sicle 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 plessure of compacted backfill against the
sides of the footings can be calculated using an eqnivalent fluid unit weight of 400 pcf. The
coefficient of friction and passive pressure values recommended above assume ultimate soil
strength. Suitable factorc of safety should be included in the design to limit the strain which wiil
occur at the ultimate strength, particr"rlarly in the case of passive resistance. Fill placed against
the sides of the footings to resist lateral loads should be a gmnular material compacted to at least
95% of the maximum standard P¡octor density at a moisture content near optimum.
FLOOR SLABS
The natr¡ral on-site soils, exclusive of topsoil, are suitable to sLrpport lightly loaded slab-on-grade
construction. To reduce the effects of some differential movement, floor slabs should be
H-P*¡19¡y¡¡p Project No. 17-7-14/
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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 r¡sed to reduce damage due to shrinkage
cracking. The requirements for joint spacing ancl slab reinforcement shoulcl be established by the
designer based on experience and the intended slab use. A minimum 4 inch layer of fi'ee-
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 than2Vo passing the No. 200 sieve.
All fill materials for support of floor slabs shoulcl be compacted to at least957o of maximum
standard Proctor density at a moisture contenl near optimum. Required fill can consist of the on-
site granular soils devoid ofvegetation, topsoil and oversized rock.
UNDERDRAIN SYSTEM
Although free water was not encounterecl during onr exploration, it has been our expedence in
the aïea that local perched groundwater can develop during times of heavy precipitation or
seasonal runoff. Frozen ground during spling runoff can create a perched condition. 'We
recommencl below-grade construction, such as retaining walls, crawlspace ancl basement areas,
and the swimrning pool bottom, be protected from wetting and hydrostatic pressule buildup by
an underdrain system. A blanket drain should also be provided below the swimming pool
bottom slab.
The drains should consist of drainpipe placed in the bottom of the wall backfill surounded above
the invert level with fi'ee-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 mininlu m lVo to
a suitable gravity outlet, sump and pllmp or perforated surnp/drywell. Free-draining granular
material used in the underdrain system should contain less than 27o 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 lYzteet deep. The blanket drain below the swimming pool bottom
slab should be a minimum 8 inches thick. A laterai subdrain should be provided down the
middle of the blanket drain gravel that discharges to suitable outlet.
H.P\KUMAR ProJect Na. 17-7-187
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SURFACE DRAINAGE
The following cirainage precautions should be observed during construction and maintained at all
times after the residence has been compleled:
l) 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 957o of the maximum standard Proctor density in pavement and slab areas
anci to at least 9A7o of the maximum standard Proctor density in landscape ateas.
3) The gronnd surface surrounding the exterior of the building should be sloped to
dlain away from the foundation in all directions. We recommend a minimum
slope of 6 inches in the firsf 10 feet in unpaved aleas and a minimum slope of 3
inches in the first l0 feet in paved areas. Free-dlaining wall backfill should be
covered with filter fabric and capped r,vith about 2 feet of the on-site finer grained
soils to recluce surface water infiltration.
4) Roof downspouts and drains shoulcl discharge well beyond the limits of all
backfill.
LIMITATIONS
This study has been conclncted in accordance with generally accepted geotechnical engineering
principles and practices in this area at this time. We make no warranty either express ol implied.
The conclusions and recommendations submitted in this report arc based Llpon the clata obtained
from the exploratory borings drilled at the locations indicated on Figure 1, the ploposed 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 fi¡ture. If the client is concemed about MOBC, then a professional in this special field of
practice should be consulted. Our findings include interpolation and extrapolation oi 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
H.PVKUMAR Project No. 17-7-187
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during construction appear different from those described in this repoft, we shor.rld be notified so
that re-evaluation of the recommenclations may be made.
This report has been prepared for the exclusive use by our client for design purposes. We arc 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 ancl
monitor the implementation of our rccommendations, and to verify that the recommendations
have been appropriately interpreted. Significant design changes may require additional analysis
or modifications to the recommendations presented helein. We recommend on-site observation
ofexcavations and foundation bearing strata and testing ofstructural fill by a representative of
the geotechnical engineer.
Respectfully Submitted,
H.P\ KUMAR
4r"''#/,,fr
Shane M. Mello, Staff Engineer
Reviewed by:
Steven L. Pawlak, P.
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17 -7 -187 H.PryKUMAR LOCATION OF TXPLORATORY BORINGS Fig. 1
BORING
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17 -7 -187 H-PryKUMAR LOGS OF TXPLORATORY BORINGS Fig. 2
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LEGEND
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ToPSolL; 0RGANIC SANDY SILTY CLAY, MOIST, BRoWN
CLAY (CL); S|LTY, SANDY, SCATTERED GRAVEL, ST|FF, MO|ST, BROWN. LOW pLASTtCtTy
GRAVEL ANO COBBLgS (CU-CP); SLIGHTLY SILTY TO SILTY, SANDY, BOULDERS, DENSE,
SLIGHTLY MOIST, BROWN, ROUNDED ROCK.
I DRIVE SAMPLE; STANDARD PENETRATI0N TEST (SPT), 1 3/8 INCH LD. SPLTT SPO0N
SAMPLE, ASTM D-I586.
1¿712 DRIVE SAMPLE BLOW COUNT. |NÐICATES IHAT 34 BLOWS OF A 14O-POUND HAMMER-,, '- FALLING 50 INCHES WERE REQUIRED TO DRIVE THE SPT SAMPLER 12 INCHES.
f nnacrrcal AUGER REFUSAL.
NOTES
I. THE EXPLORATORY BORINGS WERE DRILLED ON FEBRUARY 21,2017 WITH Â 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 TXPLORATORY BORINGS WERE MEASURED BY HAND LEVEL ANÐ REFER
TO BORING 1 AS lOO FEET, ASSUMED.
4. THE EXPLORATORY BORING LOCATIONS AND ELEVATIONS SHOULD BE CONSIDERED ACCURATE
ONLY TO THE DECREE 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 Ð 2216);
+4 = PERCENTAGE RETAINED ON NO, 4 SIEVE (ASTM Ð A22);
_2OO= PERCENTAGE PASSING NO. 2OO SIEVE (ASTM D 1140).
17 -7 -187 H-PryKUMAR LEGEND AND NOTES Fig. 3:
SIEVS ANALYSIS
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CLAY TO SILT COBBLES
GRAVTL 60 % SAND 30 %
LIQUID LIMIT PLASTICITY INDEX
SAMPLE OF: Silly Sondy Grovel
SILT ANO CLAY 10 %
FROM:Boringl@2.5
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I{YOROMEfER ANALYSIS
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FINE MEDIUM FINE COARSE
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GRAVEL 45 % SAND
LIQUIO LIMIÏ
SAMPLE 0F: Silly Sond ond Grovel
44%
PLASIICITY INDEX
SILT ANO CLAY 11 %
FROM:Boring2@10'
Ìh¡¡¡ lcrt rrlulls opply only lo lhc
!ompl€! whlch w€.s l€!i.d. Thol.ttlñg r.porl shqll not b! r.Þroducrd,
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opp.ovol ol Kumqr & Arsoclotrs, lne.Sl.vr onolysi! l.sllng l! plrform.d ln
occordonc! wlth ASTM 0422. ÀSTM Cl56ond/or ASTM Dll,l0.
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HYDROMETER ANALYSIS
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FINE MEDIUM COARSE FINE COARSE
17 -7 -187 H-PryKUMAR GRADATION TTST RESULTS Fís. 4
H.PTI(UMARTABLE 1SUMMARY OF LABORATORY TEST RESULTSProject No. 17-7-187 "SOIL TYPESilty Sandy GravelSilty Sand and GravelUNCONFINEDCOMPRESSIVESTRENGTH(PSF}ATTERBËRG LIMITSPLASTICINDEX(%lLIQUIDLIMIT(%lPERCENTPASSINGNO.200SIEVE603010l1GRADATIONSAND%t44GRAVEL(%)45NATURALDRYDENSITY(pcOSAMPLENATURALMOISTURECONTENTBORINGDÊPTH2.02.52v,10I2