HomeMy WebLinkAboutSubsoils Study for Foundation DesignHepworth-Pawlak Geotechnical, Inc.
5020 County Road 154
Glenwood Springs, Colorado 81601
Phone: 970,945-7988
HEPWORTH . PAWLAK GEOTECHNICAL Fax:970-945-8454
email hpgeo@hpgeotech. com
June 30,2006
Chad Jeweli
0026 Buckskin Drive
Carbondale, Colorado 8 1 623
Job No. 106 0513
Subject Subsoil Study for Foundation Design, Proposed Residence, Lot F-l1,
Aspen Olen,72 River Par* Lane, Garfield Counfy, Colorado
Dear Chad:
As requested, Hepwortlr-Pawlak Geotechnical, Inc. performed a zubsoil study for design
of foundations at the subject site. The study was conducted in accordance rvith our
agreement for geotechnical engineering services to you dated Ma1, 26,2AA6. The d.ata
obtained and our recommendations based on tle proposed construction and subsurface
conditions encountered are presented in this rqrort. Chen-Northem, Inc. previously
eonducted apreliminary geotechnical study for the development at Aspen Gien, report
dated December 20, 79.91, and a geotechnical engineering study for preliminary plat
design dated May 28, 1993, Job No. 4 l1'2 92.
Proposed Construction: Plans for the residence have been developed at this time and
we understand the findings of our sfudy will be considered in purchase of the properfy.
The residence will probably be a two story wood frame structme over crawlspace. A
basement may be considered depending on our findings. Cut depths are expected to
range between about 3 to 6 feet. Foundation loadings for this tytrle of construction are.
assumed to be relatively.light and typical of the proposed type of conskuction.
If buildins conditions or fouaclation loadings are significantly different from those
described above, we should be notified to re-evaluate t}re recornmendations presented in
this report.
Site Conditions: The 1ot is vacant and has undergone apparent rninor overlot grading
consisting of shallow fillplacement. The ground surface is relatively flat with a slight
slope down.to the southwest. Vegetation consists of grass and weeds. .There is an
irrigation ditch along the north side of the lot that wps flowing water at the time of our
field exploration.
H
Parker 303"841-7119 . Colorado Springs 7L9-633-5562 . Silverthorne 970-468-1989
-2-
Subsidenee potential: Aspen Glen is underlain by Perursylvania Age Eagle Valiey
Evaporite bedrock. The erraporite contains gypsum deposits. Dissolution of the gypsum
under certain conditions can cause sinkholes to develop and can produce areas of
iocaiized subsidence. The chen-Norfhern stud5r found two broad depression areas and
several sinkholes scatiered through the Aspen Glen development' Sinljroles were not
observed in the immediate area of the subject lot. The 1ot is along the northem side of the
southem broad depression area and the closest knovt'n sinkhole is about 1'600 feet to the
north. The exploratory pits were relativeiy shallorn' and for foundation design oniy'
Based on our present knowledge of the site, it cannot be said fbr certain that sinkholes
wiil not develop. In our opinion, the risk of ground subsi<lence at Lot F-i 1 is 1ow and
simi.lar to other nearby lots but the owner should be aware of the potential for sinkhole
development'
Subsurface Conditions: The subsutface contlitions at the site were evaluated by
excavating two exploratory pits at the approximate locations shown on Figure 1' The
logs of the pits are presented on Figure 2. The subsoils encountered, below about )lfoot
of overlot fitl mixed with topsoii, consistecl of medium stiff sandy silty clay underlain at
depths from about 2to ZYzfeet by relatively dense, silty sandy gravel and cobbles with
bouiders that extended to the pit depths of g% feet. Results of swell-consolidation testi'g
performed on areiatively undisturbed sa:nple of the siity clay soils' presented on Figure
3,indicatelowcompressibilityunderexistingmoistureconditionsandlightloadingand
low to moderate potential urhen vretted under a constant light surcharge' The sanlple
showed moderate compressibility when loaded after wetting' Results of a gradation
analyses perfonned on a disturbed bulk sample of the natural coarse granular soils (rninus
3 inch fraction) are provided on Figure 4. No free watff was observed in the pits at the
time of excavation and the soils were slightly moist'
Foundation Bearing Conditions: The silty ciay soils possess lowbearing capacity and
generally moderate settlement potential. The natural coarse granular soils possess
moderate bearing capacity and relatively low settlement potential' Spread footings
bearing entirely on the underlying gravel and cobble soils should be used for foundation
support of the residence'
We expect the irrigation dilch adjacent the lot is lined' Based on the relatively deep
groundwateratthesite,atypical6toSfeetdeepbasementshouldbefeasibiervitharisk
ofwettingifthenearbyditchdevelopsaieak'Aperimeterunderdrainshouldbeprovided
around the basement 1evel'
JobNo, 106 0513 c&Eteclr
Foundation Reeommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nafure of the proposed construction' we fecolnmend spread
footings placed entirelv on the undisturbed natural gravel and cobble soils designed for an
allowable bearing pressureaf 3,Q9 gtf fot topport of the proposed residence' Spread
footingsshou1db.u*iniffiforcontirruouswa11sand2feetfor
coiumns. A1l topsoil, existing fill, silty clay and loose disturbed soils encountered at the
foundation bearing level within the excavation should be removed and the footing bearing
le'el extended dorvn to the undisfurbed natural gravel and cobble soils. Exterior footings
should be provided with adequate cover above their bearing elevations for frost
protection. Placement of footings at leasl,36 inches below the exterior grade is typically
used in this area. Continuous fcundation rvalls should be tl'ell reinforced top and bottom
to span local anomalies such as by assuming an unsupported length of at least 72 feet'
Foundation wails acting as retaining structures should also be designed to resist a latsral
earth pressure based on an equivalent fluid unit weight of at least 5 0 pcf for the on-site
soil, excluding topsoil and oversized rocks, as backfiil'
Floor slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly
to moderately loaded slab-on-grade construction, Slab areas underlail by the silty ciay
could seftle some if the subgrade trecomes v'etted. To reduce the effects of some
diffefential movement, floor slabs shouid be separated from all bearing walis and
columns rvith expansion joints which allow unrestrained verlical movernent' Floor slab
control joints should be used to reduce darnage due to shrintr<age 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 placed beneath basement levei slabs to facilitate drainage. This
material should consist of nrinus 2 :rrtch aggregate wjth less than 50% passing the No' 4
sieve and less than Zn/opasstngthe No' 200 sieve'
All fiil 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 sand and gravel soils devoid of topsoil and oversized rocks.
Underdrain System: Although free water was not encountered during clr exploration, it
has been our expcrience in the area where clay soils are present that locai perched
groundwater can deyelop during times of hearry precipitation or seasonal runoff. Frozen
ground during spring runoff can also create a perched condition. we recommend below-
grade construction, such as retaining walls and basement areas, be protected from wetting
and hydrostatic pressure buildup by an underdrain system' A:r underdrain around shallow
crawlspace areas (less than 4 feet deep) may not be needed with adequate compaction of
Job No. 106 0513 c&Ftecrt
-4-
foundation wall backfill and positive surface away from the exterior of the foundation
wal1s
The drains, if used, should consist of drainpipe placed in the bottom of the wall backfill
surounded above the invert lerrel with free-draining granular material' The drain should
be placed at eachievel of excavation and at least 1 foot below lowest adjacent finish
gadeand sloped at a rninimum 7Yato a suitable gravi4 outlet or a sump where the water
can be collected and pumped. Free-draining granular material used in the underdrain
system should contain less than 2% passing the No' 200 sieve, less than 50% passing the
No. 4 sjeve and have a maximum size of 2 inches. The drain gravel backfill should be at
least 1'/z feet deeP.
Surfaee Drainage: The foliowing drainage precautions should be observed during
construction and rnaintained at all times after the residence has been completed:
l) Inundation ofthe fcundation excavations and underslab areas should be
avoi ded during construction'
2) Exterior backfil1 should be adjusted to near optimum moisture and
compacted to at least 95% of the ma^:rimum standard Proctor density in
pavement and slab areas and to at least 90To of t}Ie mruiimum standard
Proctor density in iandscape areas'
r)The ground surface surrounding the exterior of the building should be
sioped to drain away from the foundation in all directions' we
reconrmend a mininrum slope of 6 inches in the first 10 feet in unpaved
areas and a minimum slope of 3 inches in the first 10 feet in pavement and
4)
walkway_areas.
Roof downspouts and drains should discharge well beyond the limits of all
backfill.
Landscaping which requires regular heavy irrigation, such a sod, and lawn
sprinkler heads shouid be located at least 5 feet fronr the building'
Liruitations: This study has been conducted in accordance with generally accepted
geotechnical engineering principles eurd practices in this area at this time' we rnake no
warranty either express or implied. The conciusions and reeommendations submitted in
this report are based upon the data obtained from the exploratory pits excavated at the
locations ir:dicated on Figure 1 and to the depths shown on Figure 2,t}re proposed type of
construction, and our experience in the area. Our services do not include deterrLining the
pfesence, prevention or possibility of mold or other biological contaminants (h{OBC)
developing in the future. If the client is concerned about MOBC, then a professionai in
this special field of practice should be consulted. our findings include interpolation and
s)
JobNo. 106 05i3 c&Ftecr'
-)-
exfrapolation of the subsurface eonditions identified at the exploratory pits 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 at once so re-evaluation of the recommendations may be
made.
This report has been prepared for.the exclusive use try our client for design purposes' we
are not responsible for technical inteqpretations by others of our infonnation' As the
pro.iect evolves, we should prov'ide coltinued consultation and field services during
co'struction to review and monitor the implementation of our recomrnendations, and to
verify that the recornmendations have been appropriately interpreted' Significant desigu
changes may require additional analysis or modifications to the recommendations
presented herein. we recommend on-site abservation of excavations and foundation
bearing strata and testing of structural filI by a representative of the geotecbnical
engineer.
If you have any questions or if we maybe of further assistance, please let us know'
RespectfullY Subrnitted,
HEPWORTH . PAWLAK GEOTECTINICAL, TNC.
David A. Young, P.E'
Rev. by: DEH
DAY,4<sw
attachments Figure 1 - Location of Exploratory Pits
Figure 2-Logs of ExPloratory Pits
Figure 3 - Swell-Consolidation Test Results
Figure 4 - Gradation Test Resuits
Fell Real Estate - Attn: Chris Striefel (e-mail only)cc:
JobNo. 106 0513 e&Ftecr,
APPROXIMATE SCALE
1":20'
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LOT F-11
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Figure 1LOCATTON OF EXPLOBATORY PITS(3d
HEPIYORT'{
106 0513
PIT 1 PIT 2
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LEGEND:
WC=5.7
DD=102
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FILL; sandy silt with topsoil, soft, slightly moist, dark brown'
CLAY (CL); silty, sandy, medium stiff, slightly moist' red-brown'
ffi GRAVEL AND COBBLES (GM-GP); with boulders, sandy, silty, dense, slightly moist' brown', rocks are primarily
subrounded to rounded
2" Diameter hand driven liner sample
Disturbed bulk samPle.
NOTFS:
l.ExploratorypitswereexcavatedonJune20,2006withaCat4168backhoe.
2. Locations of exploratory pits were measured approximately by pacing from features shown on the site plan
provided.
3, Elevations of exploratory pits were not measured and the logs of exploratory pits are drawn to depth'
4. The exploratory pit locations and elevations should be considered accurate only to the degree implied by the method
used.
5. The lines between materials shown on the exploratory pit logs represent the approximate boundaries between
material types and transitions may be gradual'
6. No free water was encountered in the pits at the time of excavating. Fluctuation in water level may occur with time'
7. Laboratory Testing Results:
WC : Water Content (%)
DD : Dry DensitY (Pcfl
+4 : Percent reiained on the No. 4 sieve
-200 = Percent passing No' 200 sieve
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Figure 2LOGS OF EXPLORATORY PITS(3.
HEPWORTH
106 0513
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U.S. STANDARD SEBIES CLEAH SAUARE OPENINGS
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TIME READINGS
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DIAI\{ETEH OF PAFTICLES IN MILLIMF|ERS
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Figure 4GRADATION TEST RESULTS
CLAYTO SILT
GRAVEL 57 %
LIAUID LIMlr %
SAMPLE OF: SiltY SandY Gravel
COBBLE8
SILT AND CLAY 11 O/"
PLASTICIW INDEX %
FROM:Pit 1 at 7 ihrough 8.5 Feet
SAND 32 %
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106 0513