HomeMy WebLinkAboutSubsoil Study for Foundation Design 10.31.2005RHTäIVËMNfiV I4?ßO$
Heor¡,ortlr-Pawlak Georechnical, Inc'
50i0 County Roacl 154
Glenwood Springs, Colorado 81601
Phone: 970-945-7988
H
HEPWORTH-PAWLAK GEOTECHNICAL
October 3t,2005
Ron York
13091 Riverchase Court
Alva, Florida 33920
Fax 970-945'8454
ernail: hpgeo@hpgeotech'coln
.Tob No.105 758
Subject
Dear Mr. York:
As requested, Hepworth-Pawlak Geotechnical, Inc. performed a subsoil study and
percolation testing for foundation and septic disposal designs at the subject site' The
study was conducted in accordance with ouf agleement for geotechnical engineering
services to you dated Augu st23,2005. The data obtained and our recommendations
based on the proposed construction and subsufface conditions encountered are presented
in this report. 'we previously performed a subsoil study for a residence located several
hundred feet south of this site and pressûted our findings in a report dated october 26,
1998, Job No' 198 613'
proposed construction: Design of the residence has not been determined' For the
purposed of this report, we assume that the proposed residence will be atwo story wood
frame structure located in the area of Pits 1-4 as shown on Figure 1' Ground floor will be
slab-on-grade" cut depths are expected to be about 3 feet' Foundation loadings for this
type of construction are assumed to be relatively light and typical of the proposed type of
construction. The septic disposal system is proposedto be located south ofthe residence'
If buitding conditions or foundation loadings are significantly different from those
described above, we should be notified to re-evaluate the recommendations presented in
this report'
SiteConditions:Thesitewasvacantatthetimeofoursitevisit.Topographically,the
site consists of two relatively flat aliuvial terraces which slope slightly down to the east'
There is a steep slope between the terraces which is about 15 feet high' The septic field
site is on the uppff tefiaceand the residence site is on the lower tercace' Two irrigation
ditches cross the lot, one along the western side of the lot and the other on the lower
terrace. The Roaring Fork River is located east of the lot' vegetation consists of
cottonwood trees, brush, grass and weeds'
SubsoilStudyforFoundationDesignandPercolationTesting'Proposed
n.ri¿.o"", iot Z1,Tel1er Springs, Garfreld County, Colorado
parker 303-g4r-7r19 . coloradoSprings 719-633-5562 r silverth'-e 970'468-1989
..,subsidence Potential: Teller springs is underlain by Pennsylvania Age Eagle valleyEvaporite becirock. The evaporite contains gypsum deposits' Dissolution of the gypsumunder certain conditions can cal]se sinkholes to dcvelop and can producc areas oflocalized subsidence. During previotts worlc in the area, a few sinkholes were observed inthe terraces close to the Roaring Forlc River at Teller Springs' Sinkholes were notobserved in the immediate area of the subject lot. No evidence of cavities wasencountered in the subsurface materials; however, the expioratory pits were relativelyshallow, for foundation design on-ly. Based on our present knowiedge of the site, itcannot be said for certain that sintholes will not develop' In our opinion, the risk offuture ground subsidence tluoughout the scrvice iife of the residence at Lot 21 is low andsimiiar to other lots in the area but the owner should be aware of the potential for sinkholedevelopment. If further investigation ol'possible cavities in the bedrock trclow the site isdesired, we should be contacted.Subsurface Conditions: The subsurface conditions at the site were evaluated byexcavating four exploratory pits in the building area and one profile pit in the septicdisposal area atthe approximate locations shov¡n on Figure 1' The logs of the pits arepresented on Figure 2. The subsoils encountered, below about 7 to lYz feet oftopsoil'consist of \yzto 3 feet of ioose silty sand and sandy silt overlying reiativeiy dense slightlysilty sandy gravei with cobbles and boulders down to the bottom of the pits,.4l/zto 5%f'eet. Results of swell-consoliciation testing performed on relatively undisturbed samplesof the sandy silt an<l siþ sand, presented on Figures 3 and 4, indicate modcratc to highcompressibility under loading and wetting. Results of gradation analyses performed onsamples of the slightly silty sancly gravel (minus 3 to 5 inch fraction) obtained from thesite are preseuted on Figure 5. The laboratory test results afe summarized in Tabie 1'Free water was observed in Pits l-4 at 4 to 4Yzfeet deep at the tirne of excavation' Thesoils above the water level were moist to very moist'Foundation Recommendations: considering the subsoil conditions encountered in theexploratory pits and the nature of the proposed construction, we recolnmend spreadfoåtirrg, placed on the undistu¡bed natural gravel soil or gtanular structural fill designedfor an allowable soil bearing pfessule of 2,500 psf for support of the proposed residence'Footings should be a minimum width of 16 inches for continuous walls and 2 feet forcolumns. Loose and disturbed soils and existing loose sand and silt encountered at thefoundation bearing ievel within the excavation should be removed and the footing bearinglevel ex{.ended down to the undisturbed natural gravel soils. structural fiil used to re-establish design beari[g lcvel should cxtcnd beyond the edges of the footings a distanceuc1ua1 to at least thc dcpth of fill belou, the footing ancl he compacted to at least 100% ofIob No,1 05 758cåStectr
-3 -
standard Proctor density atnearoptimum moisture content' Exterior footings should be
provided with adequate cover above their bearing elevations for frost protection'
Placement of footings at least 36 inches below the exterior grade is typically used in this
area. continuous foundation walls should be reinforced top and bottom to span local
anomaliessuchasbyassuminganunsupportedlengthofatleastl0feet.Foundation
walls acting as retaining structures should be designed to resist a laleral earth pressure
based on an equivalent fluid unit weight of at least 45 pcf for the on-site soil as baclcfili'
Floor slabs: The natural on-site soils, exclusive of topsoil' are suitable to support lightly
loaded slab-on-grade construction. The loose sand and silt soils may be suitable for
support of floor slabs but should be fi.rther evaluated at the tirne of construction' To
reducetheeffectsofsomedifferentialmovement,floorslabsshouldbeseparatedfromall
bearing wa1ls and columns with expansion joints which allow unrestrained veriical
movement. Floor slab control joints should be used to reduce damage due to shrinkage
cracking'Therequirementsforjointspacingandslabreinforcemerrtshouidbe
established by the designer based on experience and the intended siab use' A minimum 4
inch layer of free-drairing gravel should be piaced beneath basement level slabs to
facilitate drainage. This material should consist of minus 2 inch aggregate with less than
50% passing the No. 4 sieve and less than2Yopassing the No' 200 sieve'
All fill 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 gravel soils or imported granular soils devoid of vegetation' topsoil
and oversized rock.
Underdrain System: Free water was encountered at relatively shallow depth and it has
been our experience that the water level will rise during spring runoff and seasonal
inigation. since it is not practicalto permanently dewater the site or even temporarily
during a flood event, *. ,."o*end below-grade construction' such as crawlspace and
basement aïeas, be avoided. we assurne the ground floor will be slab-on-grade' elevated
slightly above the surrounding ground. An underdrain system is not required for this slab-
on-grade condition.
surface Drainage: The following drainage precautions should be.obsewed during
construction and maintained at all times aÍ1er the residence has been completed:
1)Inundationofthefoundationexcavationsandunderslabareasshouldbe
avoided during construction'
2)Exteriorbackfillshouldbeadjustedtonearoptimummoistureand
compactedtoatleastglYoolthemaximumstandardProctordensityin
Job No.105 758 cåFtecn
-4-3)pavement and slab aleas and to at lcast 90o/o of the ma.ximum standardProctor density in landscape areas'The ground surface surrounding the exterior of the building should besloped to drain away from the f'ounclation in all directions. werecommend a minimum slope of 6 inches in the first 10 feet in unpavedareas and a minimum slope of 3 inches in the first 10 feet in pavement andwalkway areas.Roof downspouts and drains should discharge well beyond the limits of allbackfill.4)Pcrcolation Testing: Percolation tests were conducted on october i 5' 2005 to evaluatethe feasibility of an infiltration septic disposal system at the site' One profile pit and threepercolation holes were clug at the locations shown on Figure 1' The test holes (nominal12 inch diameter by llinch deep) were hand dug at the bottom of shallow backhoe pitsand were soaked with water one day prior to testing. The soiis exposed in the percoiationholes are similar to those exposed in the Profiie Pit shown on Figure 2 at¡d consist of %foot of topsoil overlying slightly siity sand¡' gravel with cobbles and boulders down to thepit depth of 8 feet. The percolation test results are presented in Table 2 and rangedbetween 2 to 2lminutes per inch. Based on the subsurface conditions encounterecl andthe percolation test results, we recommend that a civil engineer design the infiitrationseptic disposal sYstem.Limitations: Tiús study has been conducted in ac'cor<lance with generally acceptedgeotechnical engineering principles and practices in this area atthis time' We make nowarranty either express or implied. The conclusions and recommendations submitted inthis report are basecl upon the data obtained from the exploratory pits excavated at thelocations indicated on Figure 1, the assumed type of construction and our experience inthe area. Our services do not include determining the presence, prevention or possibilþof mold or other biological contaminants (MOBC) developing in the future' If the clientis concerned about MOBC, then a professional in this special field of practice should beconsulted. Our firrdings include interpolation and exhapolation of the stlbsurfaceconditions identified at the exploratory pits and variations in the subsurface conditionsmay not become evident until excavation is performed- If conditions encountered duringconstruction appear different from those described in this report, we should be notified atonce so re-evaluation of the recommendations may be made'This report has been prepared for tire exclusivc use by our client for design purposes' 'Weare not responsible for technical interpretations by others of our information' As theproject evolves, we should provide continued consultation and field services dulingJob No.105 758cåEtecl.
5-
const*¡ction to review and monitor the implementation of our recommendations, and to
verify that the recommendations have been appropriateiy 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 Ïepresentative of the geotechnical
engmeer
If you have any questions or if we may be of further assistance' please let us know'
RespectfullY Submitted,
HEPWORTH - PAWLAK GEOTECHNICAL' INC'
Daniel E. Hardin, P
Reviewed bY:
fl--l¡^
Steven L. Pawlak, P'E
DEH/ksw
attachments Figurel*LocationofExploratoryPitsandPercolationTestHoles
Figure 2 -Logs of ExPloratorY Pits
Figures 3 to 4 - Swell-Consoiidation Test Results
Figure 5 - Gradation Test Results
Table i - Summary of Laboratory Test Results
Table 2- Percolation Test Results
GambaAssociates - Attn: Mike Gamba
*444S
u /t{oi
Job No.105 758 cåFtecn
1 05 758LOCATIOI{ OF EXPLORATONYPËRCO I-ATI ON TF'ST HO LESPITS ANDFigure 1PIT 2t\TPIT 3¡--PIT 1PIT 4'ooáY9APPROXIMATE SCALE1": 100'PONDt'oa.t"ô'/.q"((a\AróAPROPERTYLINEP2\AP1
PIT 3 PIT 4 PROFILË PIÏ
PIT 1 PIT 2
0
0
31.0
WC:34'7
DD:85
-200:8-l
DD=84
-200:34 \NÇ:37.4
DD=84
-2Q0=73 't4:70 0)
0)II
I
_ca
0)rl
J - - '200=8
I(l)oLL
I
.Caoc)
J ñ
E
+4:64
-200:8
10
IU
LEGEND:
TOPSOIL; silt, sandy' clayey, organic, firm' moisl' dark brown'
SANDANDSILT(SM-ML);interlayeredsandysiltandsiltysand'loose'moisttoverymoist'brown
w GRAVEL(GP-GM);sandy,slightlys¡lty,w¡thcobblesandboulders'dense'wet'brown'roundedrock'
þ
L--fi
-=
2" Diameter hand driven liner sample'
Disturbed bulk samPle.
Free water level in pit at time of excavating'
NOTES:
1'Exploratorypitswereexcavatedonoctober14,zooswithaCat416Bbackhoe.
2. Locations of exploratory p1s 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.Theexploratorypitlocationsshouldbeconsideredaccurateonlytothedegreeimpliedbythemethodused.
5. The rines between materiars shown on the exproratory pit rogs represent the approximate boundaries between
- rJ.ii"l types and transitions may be gradual'
6. water rever readings shown on the rogs were made at the time and under the conditions indicated' Fluctuations in
water level may occur with time'
7, Laboratory Testing Results:
WC: Water Content (%)
DD : Dry DensitY (Pcf)
+4 = Percent retained on the No' 4 sieve
-200 : Percent Passing No' 200 sieve
Figure 2LOGS OF EXPLORATORY PITS
1 05 758
I 05 758SWELL-ÇONSOI II]ATION TEST RESULTSFigure 30òeCo'6Ø0)oËoO2.l4tr671.0101000.1APPLIED PRESSURE - ksf0I2\oo\c'6Ø0)a-EoC)4t610APPLIED PHTSSUHË - ksf)ì\\l.\No movementupon-wettingMoisture Content = 34.7Dry DensitY : 85Sample of: SandY SiliFrom: PiT 1 at 2,5 Feetpercentpcf)\(\\\Compressionuponwetting(,_Moisture Content = 31'0Dry DensitY : 84Sample of: SìltY SandFrom: Pit 2 at 2 Feetpercentpcf70.11.0100
Moisture Content : 37.4
Dry DensitY : 84
Sample of: Sandy Silt
From: Pit 4 aI2Feet
percent
pcf
Compression
-uponwetting
\
\
\
\
(
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\)
0
1
rôo\
C
"6
(t)o
o-
Eo
2
J
4
Ã
o
7
I
I
10
APPLIED PRESSURE - ksf
0.1 1.0
'100
Figure 4SWELL-CON SOLIDATION TEST R ESU LTS
1 05 758
1 05 758Figure 5GRADATION TEST HESULTSU,S. STANDARD SËRJËSCLEAR SOUARE OPENINGSTIME READINGSâ-#f,¡rru. rLtñ¡rru. 60MrN1 eMtN.4 MtN 1MrN. #200 #100 #50#30 #16 #8 #4a/B' gl4, 1 1/2 3' 5'6' 8"ozU)cnn-FzLIJOÉ.ttlo-ÊulzaFLUEF_zLUC)ELUo-01020304A50607A8090'10010090û0706050402010.005 .0ûg .019 .037 .ot4 .150 300 600 1 18 2'96 175 n u 1' u tn o 37'5 762152203127.001 .002DIAMETER OF PARTICLES IN MILLIMETERS--++-GRAVEL 64 %LIOUID LIMIT %SAMPLE OF: Slightly Silty Sandy GravelTIME READINGSrã ilfr'r. oor,¡rr'rlsMtN.4 MtN, 1 MtNCLAY TO SILT.001 .002 .005 .009SAND 28 % SILT AND CLAY 8 %PLASIICITY INDEX %FROM: Pit 2 at 3 thru 3.5 FeetU.S, STANDAHIJ SEHIESCOBBLESCLEAR SOUAÊE OPENINGSs/B' 314, I 112' 3' s'6'8"onBOlıtoZct)a60Íf,--^2"" LUO40ffiÊ_24450102AâUJ^Z JUt--LU 40EF250LUrlÉ. 60LUo_7080#200 +100 #50 #30#16 +8 #401s .0g7 .O74 .150 ,300 600 118 2'36DIAMETER OF PARTICLES IN MILLIMETERS4]5 9.s12.519,0 37.5 76.2 p\52 2O3100901003020100_----l-------4-------l-----{-----+---+------b-.æ4------14-CLAY TO SILTGRAVEL 70 %LIQLIIN I IMITSAI\/PI F OFSAND 22 O/"Gravelwith Cobbleso//aCOBBIESSILT AND CLAY 8 %PLASTICITY INDEX %FROM: Profile Pit at 4 thru 5 Feei
H EPWORTH-PAWLAK GEOTECH NICAL, INC.TABLE 1SUMMARY OF I.ABORATORY TEST RESULTSlob No. 105 758cobblesSandy siltSlightþ silty sandy gravelSilty sandSandy siltSOIL ORBEDROCK TYPEUNCONRNEDCOMPRESSIVESTRENGTHPLASTICINDÐ(LTQUiDUMITI73I3481PERCENTPASSINGNO.2û0SÏEVE2228SAND(o/o)7064GRAVEL(o/o)848485NATURALDRYDENSIÏY37.431.034.7NATURALMOISTURECONTENT24-53-3r/z)ZVzDEPTHProfile421PIT
H EPWORTH.PAWLAK GEOTECH NTCAL, INC.TABLE 2PERCOI.ATION TEST RESU LTSJOB NO. 105 758Note: percolation test holes were hand dug in the bottom of backhoe píts and soaked onOctober L4,2005. Percolation tests were conducted on October 1_5, 2005. Theaverage percolation rates were based on the last three readings of each test.2Vz3V2410 water added10 Water added10 Water added10 Water added1 Water added1 Water added1 Water added30P-3Vz44V2Vz4Vz55+055+055+0055+3 3/q520Vz3 1/+10Water added35P-2th3 3/+4 1/cth4 1/+4 3/qVz4 3/+5Vq15lh6Vq?/+4V4515620Vz33Vz10Water added27P-1Vz3Vz4Vz44Vzth41i25I563/q44 3/+IVq4 3/a6AVERAGEPERCOI-ATIONRATE(MrN./rNCH)DROP INWATERLEVEL(rNcHES)WATERDEPTH ATENQ OFINTERVAL(INCHES)WAT'ËRDEPTH ATSTART OFINTERVALüNCHES)LENGTH OFINTERVAL(MfN)HOLEDEPTH(rNcHES)HOLE NO.