HomeMy WebLinkAboutSubsoils Report for Foundation Design (2)HEPWORTH - PAWLAK .G EOTECHNICAL
Hep*'ordr-Fawlak Ceotechnical, Inc.
5020 County Road t$4
Glenrvood Springs, Colorado 81601
Phoner 970.94j-?988
Fax: 970.945,8154
ernaih hpgeo@hpge gteclr,cbnr
H
Novernber 28, 2005
Revised December 16, ?005 RECEIVED
LS Homes,Inc.
Atur: Sheila Kennedy Wills'
1800 Medicine Bow Road
Aspen, Colorado 81611
Jou- No.106 0023
Subsoil Study for Foundation D€sign, Proposed Residence, Lot 14, Blue
Creek Ranch Ponderosa Pass, Ggrfield County, Colorado.
DearMs. Wills:
As,requested Hepworth-Pawlak GeotecJrnioal,Inc. performed a subsoil study for desigR
of foundations at the subject site. The study was condlcted in accordanee with our
proposal for geotechnical engineering services to LS Homes,Inc, dated Novenrber 14,
2005. The data obtained and our recommendations based on the proposed eonstruction
and subsurface sondition$ enceurxtered are presented rn this report. Hepworth-Pawlak
Geotechnisal, Inc, previously conducted a prelindnary g€otechdoal study for the
developrnent of the subdivision and presented our findings in a reporl dated September
11" 2000" Jsb No, 100 601.
Proposed Construction: The proposed resifunce will be atwo story wood frame
struoture with an attached garage located on the site as shown on Figure 1, Gtound floor
will be either structural over a crawlspace or slab-on-grade. Cut depths are e:rpected to be
about 3 to 4 feet. Foundation loadings forthis type of constuetion are assumed to be
relatively light and b"ical of the proposed fype of construction,
If building conditiorrs or fouridation ioadings are significantly different from those
described above, ws should be notified to re-evaluate the recommendations presented in
this report.
Site Conditionsr The site was vacant at the time of our field e>,ploration. There could be
some minor fill on the lot from overlot grading as part of the subdivision developmenl.
The ground surfacs is relatively flat with a slight slope dowa to the northeast and less
than about 2 feet of elevation difference ,across the lot, There is a steeper slope down to
the south anil a pond on the south side of the lot. The water level in the pond is about I to
10 feet below the elevation of the site. Vegetation consists of grass and weeds. There are
large aspen and evergreen trees in the southwest comer ofthe lot. Occasional cobbles
'and small boulders are exposed on the ground surface.
"triil 2 0 2024
GARFIHLD COt,'NTY
COMiS{UNIIY I]EVEL,)PMENT
Subject:
Parker 303-841"7L19 r Colorado Springs 719"633"5567, r Silverthorne g?0.468"1989
-2-
Subsidence Fotentia} Elue Creek Ranch is undedain by Perrnsylvania Age Eagle
Valley Evaporite bpdrock. The evaporite contains gypsum deposits. Dissolution of the
gJpsum qnder certain conditions can cause sfukholes to develop and can produce areas of
localized subsidence. Sinkholes were not observed in the irnmediate area of the subjoct
lot. The exploratory pits were relativell' shallow, for foundation design only. Based on
our present knowledge of th€ site, it.cannot,he said for eertain that sinkholes will not
develop. ln our opinion, the risk of ground subsidence.at Lot 14 is. low and similar to
other lots in the area but the owner should be arpare,of the potential for sinkhole
developrnent.
Subsur{aee Conditions.. The subsurface conditions at the site were evaluated by
excavating two expioratory pits at the approxitnate locations shor,vn on Figure 1. The
logs ofthe pits arc pre.sented on Figure 2. The subsoils encoultered, below about 1/z ts I
foot oftopsoil, consist ofrelatively dense, slighfly siltysandy gravel with eobbles and
occasional boulders to the pit depths of 7 feet. Results of a gradation ianalysisperformed
on a saurple of the Savels (minus 5 inch fraction) obtained from the site are presented on
Figure 3. No frse w&terwas observed in the pits at the time of excavation and the. soils
were moist. The grourdwater level could be slose'to the pond water surface eievation but
could be higher due to seasonal flucfirations.
Foundation Recommendations; Considering the subsoil conditions encountered in the
exploratory pits and thenature of the proposed constructien, we recomrnend spread
footings plased on the undisturbed natural soil designed,for an allowable soil bearing
pressure €3,000psf for suppott of theproposed residence. Footings should be a
minimumldffi c,nes fs: oontinuous walls and 2 feet for oolumns, Loosp rrnd
disturbed soils enceuntered at the foundation bearing lwel wiJhin the excavation shouid
be removed.and the footing bearing level extended down to fhe undisnrbed natural soils.
Exterior footings should be provided with adequate cover above their bearing elevatiorrs
for frsst protection. Placement of footings at least 35 uroheg below the exterior grade is
lvpically used in lhis area. The foundation should b ively shallow to avoid
possible groundwater irnpacts to below grade areas such as the crawlspace. For
crawlspace construction, an rhderdrain system daylighting to the south could be provided
in the event of higher seasonal groundwater levels. Continuous foundation walls should
be reinforced top and bottom to span local anomalies such as by assurning an unsupported
leng.th of at least 10 feet. Foundation ualls ac{ing as retaining struatures should be
designed to resist a lateral earth pressure baseil or an equivalent fluid unit weight of at
least 45 pcf for the on-site soil, excluding vegetation, topsoil or oversized rock, as
backfill.
Floor Slabs: The natural on'site soils,. exclusive of topsoil, are suitable to support lighAy
loaded slab-on-Erade construction. To reduce the effects of sotne differential moveme{
floor slabs should be,separated from all bearing walls and columns with expansionjoints
Job No.106 0023
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which allow unrestained vertical movement. Floor slab conttol joints should be.used to
reduce darnage due to s}rinkage cracking. The requirements forjoint spacing and slab
reinforcement should be.established by the designer based or exper-ience and the intended
slab use, A minimum 4 incfr layer of fiee-draining gravel should be placed below slabs'
on-grade as a leveling course and to limit capillar)'moisture rise. This material sbould
consist of minus 2 inch aggregate with less than 50% passing the No. 4 sieve and less
than2o/o passing the No. 200 sieve.
,All fill matetials for support sf floor slabs should be compacted to at ieast g50h of.
maximum standard Proctor density at a moisture content near optimum. Required fill can
consist of the on-site soils devoid of vegetation, topsoil and oversized rock.
Surface Drainage; The following drainage precautions should be observed during
construstion and rnaintained at all times after the residence has been completed:
1) 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 95% of the merximum standard Proctor dens.ity in
paaement arrd slab areas and to at least907o ofthe maximum standard
Proetor density in landscape areas.
3) The ground surface surrounding the exterior of the building should be
sloped to drain away frorn the foundation'in ail directions. We
recofirmend amfuimurn slope of 6 inches in the fust l0 feet:inunpaved
areas and a minimum slope of 3 inches,in the fitst l0 feet in pavement and
walJaruay areas.
4I Roof downspouts and drains should discharge well beyond the limits of all
backfil1.
Limitationsr This study has been eonducted in accordance with generally accepted
geotechnical engineering principles and practices in this area afthis time, We make no
war-ranly eithq express or implied. The conclusions and recomrnendations submitted in
this report are based upon the data obtained from the exploratory pits excavated at the
locations indicated on.Figure 1 and to the depths shorryn on:Figure 2,the proposed type of
construction, and our experience in the area, Our services do not inolude determining the
presence, prevention or possibility ofmold or other biological contaminants (lr{OBC)
developing in the firture. If the client is ooncemsd about MOBC, then a professional in
this special field of practice should be consulted. Our fin-dings include interyolation and
extrapolation ofthe subsqdaee conditions identified atthe 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.
Job No.106 0023
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This report has been prepared for the exclusive use by our client for design purposes. We
are not responsible for technical interpretations h1' others of our information. As the
project evolves, we should provicle continued cousultation and fielcl sen'ices cluring
construotion to review and monitor the irnplementation of our recomrnendations. and to
veri$' that the reconunendations have been appropriately interpreted. Significant design
changes may require additional analysis or modifications to the rccornmendations
presented herein. \\/e recommend on-site obsen'ation of excavations and foundation
bearing strata and testing of structural filI by a representative of the geotechnical
engineer.
If you have any questions or if we may be of further assistance, please let us know
Respectfu lly Submitted,
HEPWORTI{ - PA\TI,AK
Jordy Z. Adamson, Jr., P
Reviewed by:
INC
S{.r-* * Ale
Steven L. Pawlak, P.E.
JZAlksw
atlacllnents Figure 1 - Location of Exploratory Pits
Figure 2 - Logs of Exploratory Pits
Figure 3 - Gradation Test Results
t-u.Alloy Architectural Design, Inc. - Attrr: Stephanie Gerwin
Job No. I 06 0023
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APPB0XfI\,{ATE SCALE
:l'i = 30'
/PlT 1
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FIT2 T
6A88*
6287"-
6285*
LOT 14
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LOT 13
6286** *
-t\\"\ \'- -8289
\6297
\6296\ * 6285
6284
6984
6283
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B2B3
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PROPOSED
FESIDENCE
106'0023 G
Haowort
LOCATION OF EXPLORATOHY PITS Figure 1
,6?82- -**
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rl)ll.
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PIT 1 ?lT 2
0 0
5 5
+4*71
-200i*5
10 10
LEGEND:
TOPSOIL; sllry sand, scattererl gravel and cobbles, organics, {irrn, moist, brown.
ffiH
E'!r&I
GRAVELAND COBBLES (GP-GM); sandy, slightly sflty, occasional bouldera up to 3 feet in slze, dense, moist,
brown, $rbrounded to rounded roek,
0)
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J Disturbed bulk sample,
NOTES:
1. Expluratory plts were excavated on Norember 81,, 8005 with a Bobeat 435 2HS trackhoe.
2. Locatlons of exploratory pits were measured approxirnatslV W pacing from features shown on ths site plan
Brovided,
3, Elevations of exploratory pits were.not measuied and'the logs of explDratory pits are draun to depth. Fit 2 is about I
foat highrer than Pit 1,
4. The exploratory pit locations shnuld be oonsidered accurate only to the degree impiied by the method used.
5. The lines between matelals shovvn on the exploratory pit logs reBlesent the approximate boundaries between
material types and transitions nnay be gradual.
6. No free water was encountsred in liro pits at ilre time of excavating, Fluctuation iir vuiltor ia,rel rnair occur uilth tirne.
7. t-aboratory Testing Hesulis:
+4 = Percent retained on the No. 4 siwe
-200 = Perceni passing No. 200 sieve
106 0023 I,H LOG$ OF EXPLORATOHY PITS Figure z
TIME HEADINGS
24 HF. 7 HR
0 4t MiN, 15 MIN.MtN. 1 MtN. #200 #'100 #6060MlMsMlN.4
,001 ,002 .006 ,009 .019 .037 ,074 ,150 ,C00 '600
DIAMETEH OF PAFTIOLES IN MII LIMETER$
cuYro ErLl'
GBAVEL 71 V,SAND 24 %
CLEAF SOUABE OFENING$
tr4 3/s. ala, r 1 Eu 3r SnGi' 6u 100
37,5
127
203
coEelEs.
SILT AND CLAY 5 %
U.$,.STANDAHD SERIES
g0
8D
70
602
tr+th{
50Fz
Hutrl
40 n-
15.br dnz.
F
L!,t.E
F50zIJ(,
trId[60
10
,t0
00
70
80
80
EO
l0s
9.5
12,5
LIOUID LIMIT "A PLA$TICITY INDEX %
SAMPLE OF: S$ghtly Siliy Sandy Gravelwith Cobbles FROM; Pit 1 at 5 to 7 Feet
1 06 0023 ,e
tlap\yartl
GRADATION TEST RESULTS Figure 3