HomeMy WebLinkAboutSubsoil Study for Foundation DesignJuly 29, 2014
Gru e ncfcldl Constructio n
Attn: Dan Grucnefclclt
P. 0. Box 19 10
Ba salt , Co lorado 8 1621
(d Il l'</ "1 llU ll'kl d! U llll)
Job No.114 279 A
Subject: Subso il Study i'or Foundation De s ign, Prop osed Residence, Lot E-2, Aspe n
Equ estrian Es tate s, Garfield Co unt y, Co lorado
Dear Mr. Gruc nefcldt:
As req uested, Hepworth-Pawlak Geotec hni ca l, In c. perfonned a su bso il st udy for design
of fo und at io ns at the s ubj ec t s ite . The s tud y was co ndu cted in accordance with our
agreement fo r geotechni ca l engineering serv ices to Gruenefc ldt Construct ion dat ed July
16 , 2014. The data obtai ned and o ur recomme ndati o ns based on the proposed
co nstr uct ion and sub s urfa ce con diti ons encoun tered are present ed in thi s reporl.
Proposed C on struction : The proposed res idence will be two sto ry wood frame
construct ion with an attached garage. Gro und flour s wi II be s lab-o n-grade. Cut depths
are ex pected to range between about 2 to 5 feet. Fo und ation loadings fo r thi s type of
construct io n a re assu med to be re latively li ght and typical ol'thc propo sed type of
co nstruction.
If bui ld ing cond iti ons or fo und at ion loadin gs arc signifi cant ly diffe rent from those
described above, we s hould be notified to re-evaluate the re co mmcnd a t.ions prese nted in
thi s report.
S ite Cond ition s: The prop erty is vaca nt of structures and vegetated \Vi th grass and
weeds. The ground s urfa ce is s li ght ly rollin g and re lativ ely flat with a slig ht s lope down
to the so uthwest.
S ubsidence Potentia l: The site is unde rl ain by Pennsylvania Age Eagle Va ll ey
Evapo rite be drock. The eva porite con tain s gyps um dep osits. Dis so luti on of th e gyps um
und er certain condition s can cause s inkhol es to develop and ca n prod uce areas of
loca lize d sub siden ce . During prev iou s work in the area , sinkholes ha ve been o bserved in
the Ro arin g Fork Ri ve r va ll ey to th e north and east of the Cath erin e Sto re area . Sinkhol es
were not observed in th e imm ediat e area of th e s ubje ct lot. Th e ex ploratory pits we re
shallow , for foundation des ign only. No ev idence of undergrou nd void s we re
e nco unt e red . Based o n our pr ese nt knowled ge of th e site, it cannot be said fo r certa in that
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sinkholes will not develop. In our opinion, the risk of ground subsidence at Lot E-2
throughout the service life of the residence is low and similar to other lots in the area but
the owner should be aware of the potential for sinkhole development.
Subsurface Conditions: The subsurface conditions at the site were evaluated by
excavating eight exploratory pits at the approximate locations shown on Figure I. The
logs of the pits are presented on Figure 2. The subsoils encountered, below about I to I Yz
feet of topsoil, consist of Yz to 5 feet of sandy silty clay overlying silty sandy gravel with
cobbles and small boulders. Results of swell-consolidation testing perfonned on a
relatively undisturbed sample of sandy silty clay, presented on Figure 4, indicate
moderate compressibility under conditions of loading and wetting. Results of a gradation
analysis performed on a sample of the silty sandy gravel (minus 5 inch fraction) obtained
from the site are presented on Figure 5. Free water was observed in the pits generally
between 2 and 4 feet at the time of excavation. Ground water depths are shown on Figure
2. The upper soils were slightly moist to moist. Our experience in the area is that shallow
groundwater conditions are typical and are related to irrigation of nearby properties in the
valley.
Foundation Bearing Conditions: The natural silty sandy gravel soils are adequate for
support of spread footing foundations. The topsoil and sandy clay soils should be
removed from beneath footings. The granular soils could be below proposed excavation
grade and the over excavated areas could be reestablished with a structural fill such as pit
run. The structural fill should be compacted to 98 percent standard Proctor density at a
moisture content.near optimum.
Dewatering of the excavation will likely be required and can probably be accomplished
by pumping from shallow sump pits adjacent to the ex.cavation. If the excavation is made
prior to irrigation season, it is possible that dewatering can be avoided. Crawlspaces and
basement levels are not recommended at this site due to the seasonal relatively high
groundwater.
Foundation Recommendations: Considering the subsoil conditions encountered in the
exploratory pits and the nature of the proposed construction, we reoommend spread
footings placed on the undisturbed natural granular soil or compacted structural fill
designed for an allowable soil bearing pressure of2,500 psffor support of the proposed
residence. Footings should be a minimum width of 16 inches for continuous walls and 2
feet for columns. Topsoil, sandy clay and loose or disturbed soils encountered at the
foundation bearing level within the excavation should be removed and the footing bearing
level extended down to the undisturbed natural gravel soils. 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
anomalies such as by assuming an unsupported length of at least I 0 feet. Foundation
walls acting as retaining structures (if any) should be designed to resist a lateral earth
pressure based on an equivalent fluid unit weight of at least 50 pcf for the on-site
predominantly granular soil as backfill.
JobNo,Jl4279A
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Floor Slabs: The natural on-site soils, exclusive of topsoil, are suitable to support lightly
loaded slab-on-grade construction. To reduce the effects of some differential movement,
non-structural floor slabs should be separated from all bearing walls and columns with
expansion joints which allow unrestrained vertical movement. Floor 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 designer based on experience
and the intended slab use. A minimum 4 inch layer of free-draining gravel should be
placed beneath slabs to act as a break for capillary moisture rise. This material should
consist of minus 2 inch aggregate with less than 50% passing the No. 4 sieve and less
than 2% passing 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 granular soils or a suitable imported gravel devoid of vegetation,
topsoil and oversized rock.
Perimeter Drain: A perimeter drain should not be needed for the proposed slab-on-
grade floor construction.
Surface Drainage: The following drainage precautions should.be observed during
construction and maintained at all times after the residence has been completed:
1) Inundation of the foundation excavations and unders!ab areas should be
avoided during construction.
2) Exterior backfill should be adjusted to near optimum moisture and
compacted to at least 95% of the maximum standard Proctor density in
pavement and slab areas and to at least 90% of the maximum standard
Proctor density in landscape areas. Free-draining wall backfill (if any)
should be capped with about 2 feet of the on-site, finer graded soils to
reduce surface water infiltration.
3) The ground surface surrounding the exterior of the building should be
sloped to drain away from the foundation in all directions. We
recommend a minimum sl9pe of 6 inches in the first 10 feet in unpaved
areas and a minimum slope of 3 inches in the first 1 0 feet in pavement and
walkway areas.
4) Roof downspouts and drains should discharge well beyond the limits of all
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
warranty either express or implied. The conclusions and recommendations 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 shown on Figure 2, the proposed type of
construction, and our experience in the area. Our services do not include detennining the
presence, prevention or possibility of mold or other biological contaminants (MOBC)
developing in the future. If the client is concerned about MOBC, then a professional in
this special field of practice should be consulted. Our findings include interpolation and
extrapolation of the subsurface conditions identified at the exploratory pits and variations
Job No.114 279 A
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in the sub sur face co nd it io ns may not become evi dent until exc a vatio n is performed. If
co ndition s enco un tered du ri ng co nstructi on appear different fro m those descr ibed in this
re po rt , \.Ve should be notified at o nce so re-evaluat io n or the recommendat ions may be
mad e .
This repor t has bee n pre pared for the exc lu sive use by ou r cl ient for des ign purp oses. We
arc not res po ns ibl e fo r techni ca l inte rp retat ions by olh crs of o ur in formation. As the
project evo lves, we sho uld provide con tinu ed cons ult atio n and field se rvices during
co nstructi o n lo rev iew and monito r th e impl ementation of our recommendation s, and to
ve ri fy that the reco mm endation s have bee n ap propriate ly int erp reted. Significa nt design
change s may requi re add iti ona l ana lys is or modifi cati ons to the recom mendations
prese nt ed herein . We recomm end o n-s it e obse rva ti on of excavat ions and fo und atio n
bearing s trata and test in g o f stru ctural fill by a rep rese ntati ve of the gcotec hnical
engin eer.
If yo u ha ve any qu es tion s or i f we may be of further ass is tance , pl ease let us know.
Respectfu ll y Submitt ed,
HEPWORTH -PAWL AK GEOTECHN ICA L, INC.
Loui s Ell er
at tac hm e nt s
Joh No.11 4 2 79 ,\
~tec h
APPROXIMATE SCALE
I"~ 30'
LOT E 3
I
I
PIT 1 •
PIT5 • !
PIT 2 •:
•PIT?
EQUESTRIAN WAY
LOT E 2
!. PIT4
I
!•PIT 6
'
'PIT3
PIT 8 • '
EXISTING
FENCE
LOT E 1
PIT 1 PIT2 PIT 3 PIT 4
0 [i
0
-WC=23.2
00=101
1i) ~ if --, +4=61 -5 ' 5 -200=14 ' .c .t;;
Ci @-Q)
Cl 0
10 10
PIT 5 PIT6 PIT7 PITS
0 0
~ -~ --
' 5 5 ' .c ,;
Ci -a.
Q) Q)
0 0
10 10
Note: Explanation of symbols Is shown on Figure 3.
114 279A LOGS OF EXPLORATORY PITS Figure 2
LEGEND:
TOPSOIL; organic sandy slit and clay, roots, soft, slightly moist to moist. dark brown.
CLAY (CL); sandy, silty, medium stiff to soft, slightly moist to very moist, to wet, brown.
GRAVEL (GM-GP); with cobbles and small boulders, sandy, silty, dense, moist to wet, brown, subrounded
rocks.
2' Diameter hand driven liner sample.
Disturbed bulk sample.
Free water level in pit at time of excavating.
NOTES:
1. Exploratory pits were excavated on July 18, 2014 with a Yan Mar 850 mini-excavator.
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 should be considered accurate only to the degree implied by the method used.
5. The lines between materials shown on the exploratory pit Jogs represent the approximate boundaries between
material types and transitions may be gradual.
6. Water level readings shown on the logs 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 (pcij
+ 4 = Percent retained on the No. 4 sieve
-200 = Percent passing No. 200 sieve
114 279A c~St.ecti
Heoworth-Povtlok Geotechntccl
LEGEND AND NOTES Figure 3
Moisture Content = 23.2 percent
Diy Density = 101 pcf
Sample of: Sandy Silly Clay
From: Pit 1 at 2 Feet
0 -.........
1 r--.. ....
"' ---c.--./ No movement
/' --"upon
* 2 f'. wetting
c
"""
.Q
"' \. ~ 3 a. \ E
0 \ 0 4
\
5
0.1 1.0 10 100
APPLIED PRESSURE -ksf
114 279A G"cMech Hnnworth-Paw/ak Geotechnle<H
SWELL-CONSOLIDATION TEST RESULTS Figure 4
I HYDROMETER ANALYSIS I SIEVE~LYSIS I
10
20
30
40
60
60
70
80
90
100
.001 .()()2 .005 .009 .G19 .()37 .074 .150 .300 .600 1.18 2.36 4.75 9.5 19.0 37.5 76.2 152 203
12.5 127
DIAMETER OF PARTICLES IN MIWMETERS
CtAYTOSll.T
GRAVEL 61 % SAND 25 % SILTANDCLAY 14 %
LIQUID LIMIT % PLASTICITY INDEX %
SAMPLE OF: Silty Sandy Gravel with Cobbles FROM: Pit 2 at 4 to 4 ~ Feet
90
80
70
60
50
40
30
20
10
0
114 279A ~ Heoworlh-Pawlak Gootedmlcal
GRADATION TEST RESULTS Figure 5
HEPWORTH-PAWLAK GEOTECHNICAL, INC.
TABLE 1 Job No. 114 279A
SUMMARY OF LABORATORY TEST RESULTS
SAMPLE l.OCA TION NATURAL NATURAL GRADATION PERCENT ATTERBERG LIMITS UNCONFJNED
MOISTURE ORY GRAVEL SAND PASSING UQUID PlASTIC COMPRESSM SOIL OR PIT DEPTH CONTENT DENS!lY N0.200 UMIT INDEX STRENGTH BEDROCK TYPE (%) (%) SIEVE
(ft) (%\ (pd) (%\ {%) {PSF)
1 2 23.2 101 Sandy Silty Clay
2 4-4 112 61 25 14 ;:;uty Sandy urave1 wltll
Cobbles