HomeMy WebLinkAboutSubsoil StudyHEPWORTH - PAWLAK GEOTECHNICAL
Hepworrh-Pa.r'iak Geotechnical, lnc.
5020 Ccunty Road 154
Gienwood Springs, Colo¡ado .81601
Phone: 970-945-7988
Fa>::970-945.8454
email: hpgeo@hpgeotech, com
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RECEIVED
APR ! g ?fr1r
GARFIELD COUNTY
TOMMI'IIITY DËVFLOPMENT
SUBSOIL STTIDY
FOR F'OUNDATION DESIGN
PROPOSEI} CLUBHOUSE A.T{D POOL
LOT 1, CERISE RANCH
GARFIELD COUNTY, COLORADO
JOB NO. 104 300
MAY 14,2004
PREPARED FOR:
WINTERGR.EEN HOMES
ATTN: JEFF SPANEL
P.O. BOX 1s30
AVON, COLORADO 81620
Parker 303-841-7119 . Colorado Springs 719-633"5562 o Silverthone 970-468-1"989
TABLE OF CONTENTS
PURPOSE AND SCOPE OF STUDY
PROPOSED CONSTRUCTION
SITE CONDITIONS....
SUBSIDENCE POTENTIAL ...
FIELD EXPLORATION........-..
SUBSURFACE CONDITIONS ....,....
BEARING AND GROIINDWATER CONDITIONS .........
DESIGN RECOMMENDATIONS
FO{.INDATIONS......
FOUNDATION AND RETAINING 1VALLS
FLOOR SLABS ...,...
I.INDERDRAIN SYSTEM......... -......,....
SIJRFACE DRAINAGE
LIMITATIONS ..,..........
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF ÐGLORATORY BORINGS
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - GRADATION TEST RESULTS
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PURPOSE AND SCOPE OF STUDY
This report presents the results of a subsoil study for a proposed clubhouse and pool to be
located on lotl, Cerise Ranch, Garfield County, Colorado. The project site is shown on
Figure l. 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 Wintergreen llomes dated April 12,2004. CTl/Thompson' Inc.
prepared a revised geologic hazard evaluation for Cerise Ranch and reported their
findings February 3, 2000, Job No. GS-7953. Hepworth-Pawlak Geotechnical Inc.,
previously performed a subsoil study for foundation design on the northern portion of Lot
1 and reported our findings December 10,2001, Job No. 101 755.
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 werc analyzed to develop recommendations for
foundation t14les, de,pths and allowable presswes for the proposed building foundation-
This report sumrnarizes 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 clubhouse will be a single story structure with a slab-on-grade floor and
Iocated as shown on Figure 1. we assume relatively light foundation ioadings, typical of
the proposed type of conskuction, A below grade swimrning pool will be located
adjacent to the southside of the clubhouse'
If building loadings, location or grading plans change significantly from those described
above, we should be notified to re-evaluate the recomrnendations contained in this report'
Job No. 104 300 cåfrecrr
''
SITE CONDITIONS
Lot I is located on the east side of Cerise Ranch Road between State Highway 82 and
Larkspur Drive. Vegetation consists of grass and weeds. The ground surface is relatively
flat with less than about I foot of elevation difference in the building area. Shallow fill
rnay have been placed across part of the lot. An existing lake is located in the south part
ofLot 1.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eagle Valley Evaporite underlies the Cerise Ranch
subdivision. These rocks are a sequence of gypsiferous shale, fine-grained sandstone and
siltstone with some massive beds of gypsum zurd limestone. There is a possibility that
massive gypsgm deposits associated with the Eagle Valley Evaporite underlie portions of
the |ot. Dissolution of the gypsum under certain conditions can cause sinkholes to
develop and canproduce areas of localized subsidence. During previous work for the
development, subsidence areas were obsçrved in the Cerise Ranch Subdivision. These
subsidence areas appeÍlr similar to others associated with the Eagle Valley Evaporite in
areas of the lower Roaring Fork River valley.
Sinllholes 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 prese,nt knowledge of
the zubsurface conditions at the site, it cannot be said for certain that sinkloles will not
develop. The risk of future ground subsidence on Lot 1 throughout the service life of the
proposed clubhouse, in ouropinion, is low; however, the owner shouldbe made aware of
the potential for sinlhole development. If further investigation ofpossible cavities in the
bedrock below the site is desired, we should be contacted.
ii¡BNr,Ifr43fr8
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FIELD EXPLORATION
The field exploration for the project was conducted on Apdl 20,2004. Three exploratory
borings were drilled at the locations shown on Figure 1 ta evaiuate the subsurface
conditions. The borings ïyere advanced with 4 inch diameter continuous flight augers
powered by a truck-mounted CME-458 drill rig. The borings were logged by a
repres entative o f Hepworth-Pawlak Geotechnical, Inc.
Samples of the subsoils were taken with a 1 inch and2 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 \ryere taken
and the penehation resistance values are shown on the Logs of Exploratory Borings,
Figure 2. T1¡e samples were retumed to our laboratory for review by the project engineer
a¡d testing. Slotted PVC pipe was installed in the borings for future groundwater level
monitoring.
SUBST]RFÄCE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2.
The subsoils consist of about fwo to tluee feet of topsoil overlying silty sandy gravel wíth
cobblss and scattered boulders. 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 anaþses. Results of gradation analyses performed on
small diameter drive samples (minus 11/z inchfraction) of the coarse granular subsoils are
shown on Figure 3,
Job No. 104 300 <så5tecn
-4-
Free water ìüas encoulttered ín the borings at depths between 4 and 4Yz feet. The upper
soils were generallY moist.
BEARING AND GROT]NDWÄTER CONDITIONS
The natural granular soils below the topsoil should provide adequate support for a spread
footing foundation. Groundwater was measured at 4 to 4V, feetbelow the ground surface
on April 29,2Q04. The groundw¿ter level could rise during spring runoffor the summer
irrigation season. 'We recornmend shallow crawlspace or siab-on-grade construction'
The ground floor or crawlspace grade should be kept at least two feet above the high
water level. Ventilation and a moisture barrier should be provided for a crawlspace.
DESIGN RECOMMENDATIONS
FOI,INDATIONS
Considering the subsurface conditions encountered in the exploratory borings and the
nature of the proposed consfruction, lve recommend the clubhouse building be founded
with spread footings bearing on the natural granular soils.
The design and conskuction criteria presented below shouid be observed for a spread
footing foundation sYstem.
1) Footings placed on the undisturbed natural granular soils should be
designed for an allowable bearing pressufe of 3000 psf. Based on
experience, we expect settlement of footings designed and constructed as
discussed in this section will be about 1 inch or less'
Z) The footings should have aminimurn width of 16 ínches 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.
JobNo. 104 300 <¡Stec¡
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s)
Placernent 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 ieast 10
feet. Foundation walis acting as retaining structufes should also be
designed to resist lateral earth pressures as discussed in the "Foundation
and Retaining Walis" section of this report-
A1l existing fill, 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
compacted. If water seepage is encountered, the footing areas should be
dewatered before concrete placement. A thin layer of crushed rock can be
placed in footing a¡eas to facilitate dewatering and for fine grading
purposcs.
A representative of the geotecllrical engineer should observe all footing
excavations prior to concrete placement to evaluate bearing conditions.
FOIJNDATION AND RETAINING ÏYALLS
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 45 pcf
for backfill consisting of the on-site granular soils. Cantilevered retaining structurcs
which are separate from the clubhouse and can be expected to deflect sufficiently to
rnobilize the futl 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 granular soils.
All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, traffic, construction rnaterials and
equipment, The pressures recortmended above assume drained conditions behind the
4)
6)
Job No. 104 300 cåFtecn
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walls and a horizontal backfill surface. The buildup of water behind a wall or an upward
sloping backfill surface will increase the lateral pressure irnposed on a foundation wall or
retaining structure. An underdrain should be provided to prevent hydrostatic pressure
buildup behind walls.
Backfill should beplaced in uniform tifts and compacted to at least 90% of the maximum
standard proctor density at a moisfure content near optimum. Backfill in pavement and
walkway areas should be cornpacted to at least 95% of the maximum standard Proctor
density. Care should be taken not to overcompact the backfill or use large equipment
'ear
the wall, since this could cause excessive lateral pr€ssure on the wali. Some
settlement of deep foundation wall backfill shouldbe 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 wail footings will be a combination of the
sliding resistarice 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 coeffrcicnt of friction of 0,45. Passive pressure of compacted
backfill against the sides of the footings can be calculated using an equivalent fluid unit
weight of 400 pcf for dry backfill and275 pcf for submerged backfill condiitons. The
coefficient of friction and passive pressì¡re values recoÍrmended above assulr.e ultirnate
soil strength. Suitable factors of safety should be included in the design to limit the strain
which wiil occur at the ultimate strength, particularly in the case ofpassive resistance.
Fill placed against the sides of the footings to resist lateral loads should be a granular
material compacted to at least 95Yo of themaximum standard Proctor density at a
rnoisture content near oPtimum'
FLOOR SLABS
The naturai oû-site soils, exclusive of topsoil, are suitable to support lightly loa<led slab-
on-grade construction. To reduce the effects of sorne differential movement, floor slabs
should be separated from all bearing walls and columns with expansion joints which
dMjshNs, lB13B8
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ailow unresh.ained vertical movement. Fioor 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 desiguer based on experience and the intended
slab use. A minirnurn 4 inch layer of free-draining gravel should be placed beneath
interior slabs to facilitate drainage, This material should consist of minus 2 inch
aggregatewith at least 5To/o retained on the No, 4 sieve and less than 2Yo passing the No-
200 sieve.
Ali fill rnaterials for support of floor slabs should be compacted to at least 95Yo 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.
LINDERDRAIN SYSTEM
Free water was encountered at relatively shallow depth and it has been our experience in
the area that the water level can rise and local perched groundwater can develop during
tirnes of healy precipitation or seasonal runoff. Frozen ground during spring runoff can
create a perched condition. We recommend below-grade construction, such as retaining
walls and crawlspace areas, be protected from wetting and hydrostatic pressure buildup
by an underdrain system. The underdrain should not be expected to lower the
groundwater level and the pool should be designed to resist hydrostatic pressure uplift'
If drains are placed, they should consist of drainpipe placed in the bottom of the wall
backfill surrounded above the invert level with free-draining granular material. Thq drain
should be placed at least 1 foot below lowest adjacent finish grade and sloped at a
minimurn lVoto a suitable gfavlty outlet or sump and punp. Free-draining granular
material used in the underdrain system should contain less than 2% passing the No. 200
sievg less than 50% passing the No. 4 sieve and have a maximum size of 2 inches. The
drain gravel backfill should be at least lYz feet deep'
Job No. 104 300 såFtacrr
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SURFACE DRAINAGE
The following drainage precautions should be observed during construction and
maintained at all times after the clubhouse and pool havebeen completed:
l) Inundation of the foundation excavations and underslab areas should be
avoided during construction'
Z) Exterior backfill should be adjusted to near optimum moisture and
compacted to at least 95% of the maximum standard Proctor densþ in
pavernent and slab areas and to at least 90Yo of the maximum standard
Proctor density in landscape aleas'
3) The ground surface surrounding the exterior of the building should be
sloped to drain away from the foundation in all directions. we
recommend aminimum siope of 6 inches inthe first 10 feetinunpaved
areas and a minimum slope of 3 inches in the first 10 feet in paved are&s.
Free-draining wall backfill shouldbe capped with about 2 feet of the on-
site finer graded soiis to reduce surface water infiltration.
4) Roof downspouts and drains should discharge well beyond the iimits of ail
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 warrauty either
express or irnplied. 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 nat include determining the presence, prevention or possibilþ of rnold or
other biological contaminants (MOBC) developing in the future. If the client is
concemed about M6BC, then a professional in this special freld of practice should be
consulted. Our findilgs include interpolation and extlapolation of the subsurface
conditions identified at the exploratory borings and variations in the subsurface
'JobNo. ti]4 300
Job No. I 04 300 #n
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conditiols 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 rnay 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 infonnation. 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
veriff that the recoïïrmendations have been appropriately interpreted. Signifrcant design
changes may require additional analysis or modifi.cations to the recorlmendations
presented herein. !V'erecomrnend on-site observation of excavations and foundation
bearing strata and testing of structural fill by a representative of the geotechnical
engrneer.
Respectfuliy Submitted,
HEPWORTH - PA\MLAK GEOTECTINICAL, INC.
Louis E. Elier
Reviewed by:
Steven L. Pawlak, P.E,
LEE(djb
cc: Eric Smith Architects - Attn: Scott Nunnery
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APPROXIMATE SCALE
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PATH
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--*-./ BORING 2 6344
PROPOSED
CLUBHOUSE
PROPOSED
POOL
PROPOSED
PLAYGROUND
6344
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Figure 1LOCATON OF EXPLORATORY BORINGSHEPWORTH_PAWLAK
GEOTECHNICAL, INC.104 300
BORING 1
ELEV.:6344'
BORING 2
ELEV.=6344
BORING 3
ELEV.:6344'
6345
6340 s
6335
6330
6/6,12/2
'n/t2
22/12
tflC=I1.9
+¡+-55
-2OO-13
I:
s8/12
CLUBHOUSE POOL
Note: Explonct¡on of symbols is shown on Figure 3'
+
NEARBY LAXE I.EIEL
20/12
1+/6,12/5
*4=53
-2AO-12
6345
6340
6535
6350
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Figure 2LOGS OF EXPLORATORY BORINGSHEPWORTH_PAWLAK
GEOTECHNICAL, INC.104 300
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LEGEND:
ToPSolL;orgonicsondysiltondcloywithgrovel,firm,moist,darkbrowntoblock'
GRAIEL (GM); ssnoy, slightly silty to,silty, cobbles ond scsttered boulders' medium dense to dense'
rnoist to'wei, brown, subrounded rock'
Relotively undisturbed drive somple; 2-inch l'D' Colifornio liner somple'
Drive somple; stondsrd penetrotion test (sPT), 1 3/8 inch l'D' split spoon somple' ASTM D-1586'
Drive somple blow count; indicoteslhot 4o blows of o 14O pound hommer folling 30 inches were
;;ä;tJ ü ¿.ìu" tne boíitornio or sPT sompler 12 inches'
Free woter level in boring ond nurnber of doys ofter drilling meosurement wos mode'
Procticol rig refusol- tvhere shown obove bottom of log' multiple ottempts were mode to odvonce
the boring-
lndicoted slotted PVC pipe instolled to the depth shown'
NOTES:
1- Explorotory borings were drilled on April 20, 2OO+ with o 4-inch diometer continuous flight power ouger'
2. Locotions of explorotory borings were meosured opproximotely by toping from feotures shown on the
site Plon Provided.
3. Elevotions of erplorotory borings. were obtoined by interporotion between contours on the site pron provided
ond checked bY instrument level'
4. The explorotory boring locotions ond elevotions should be considered occurste only to the degree implied
by the method used-
5- The lines between moteriols shown. on the exploro-torytoring logs represent the opproximote boundories
-Uet*""n
moteriol types ond tronsitions moy be groouor'
6, ltster level reodings shown on the logs-.were mode of the time ond under the conditions índicsted'
fiuctuot¡on in wotir level moy occur with time'
7. LoborotorY Testíng Resulfs:
WC:WoterContent(%)i+ = Percent retqineð on the No' 4 sieve
-2OO = Percent possing No' 2OO sieve
Figure 3LEGEND AND NOTESHEPWORTH-PAWLAK
GEOTECHNICAL, INC.104 300
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DIAMETER OF PARTCLES IN MILLÍMETERS
coæ-E
CLAY ÍO SLI
% SILT AND CLAY 13
PLASTICITY INDEX %
FROM: Boring 1 ot 5 Feet
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100
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GRAVEL 55 % SAND 32
LIQUID LIMIT %
SAMPLE OF:SiltY SondY Grovel
lil¡E ¡ÉADll¡cs!&
r&ù
7 llR
15 ldil 6d¡t{.{5û
GRAVEL 55 % SAND 35
LIQUID LIMIT %
SAMPLE OF:SiltY SondY Grqvel
ct-ËtR SOITARE OPEI¡NôS
3/t 3/+ t t/2' ¡. s'ð'
lflo
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-0tn -ø2 .0o5 .l¡os .Otg .O5-, .o71 .t5o .J{x' 'æo l'lt 2'Jlô 1'75 s'512S leo 37'5 7#.t l3? ?û-:'t??
DIAMETER OF PARTICLES IN MILLIMETERS
q-^Y TO S¡LT
% SILT AND CLAY 12
PLASTCITY INDEX %
FROM:Boring 3 ot 1O Feet
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Fígure 4GRADATION TEST RESULTSI.IEPWORTH_PAWLAK
GEOTECHNICAL, INC104 JOo
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