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TABLE OF CONTENTS
PITRPOSE AND SCOPE OF STUDY....................,.
SITE CONDITIONS.
1
SUBSIDENCE POTENTIAL
FIELD EXPLORATION.,.......,.
2-
SUBSUMACE CONDITIONS....
DESIGN RECOMME}{DATIONS.. ..
FOUNDATIONS..........
UNDERDRAIN SYSTEM...
SITE GRADING
SURFACE DRAINAGE.......................
FIGURE 1 - LOCATION OF HGLORATORY BORINGS
FIGURE 2 . LOGS OF DGLORATORY BORINGS
FIGTJRE 3 - LEGEND AND NOTES
FIGTJRE 4 . GRADATION TEST RESULTS
TABLE 1- SUMMARY OF LABORATORY TEST RESULTS
-?_
FOUNDATION AND RETAINING WALLS. ...14'
FLOOR SLABS .......6-
6-
-7-
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PURPOSE AND SCOPE OF STUDY
This report presents the rezults of a subsoil study for a proposed residence to be located at
Lot 3, Coryell Ranch, Garfield County, Colorado. The project site is shown on Figure 1.
The purpose of the study was to develop recommendations for the foundation desrgn.
The study was conducted in accordance with orn proposal for geotechnical engineering
services to you dated June 8, 2015.
A field explorationprogram consisting of exploratoryborings 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 classifioation and other
engingering characteristics. The results ofthe field exploration and laboratory testing
were anallzed to develop recorrmendations for foundation types, dopths and allowable
pressures for the proposed building foundation. This report zumrnarizes the data obtained
during this study and presents our conclusions, design recommendations and other
geotechnical engineering considerationsbased on theproposed construction and the
sub$ufase conditions encountered.
PROPOSED CONSTRUCTION
The proposed residence building plans are conceptual. Tlpical homes in the area are one
and two story wood frame construction above a crawlspace or basement with an attached
gara$e. Basement and garage floors would typicallybe slab-on-grade. Grading for the
structure is assumed to be relatively minor with cut depths between about 3 to 9 feet. We
assurne relatively light foundation loadings, typical of the proposed tlpe of construction.
when building location, grading and loading information have been developed, we
should be notified to re-evaluate the recommendations presented in this report.
JobNo. l15268.4 e&Btectr
SITE CONDITIONS
The property is located between Stonefly Drive and the Roaring Fork River and is vacant
of structures. Vegetation consists of grass and weeds. Topography consists ofupper and
lower relatively flat benches. The front part of the site is about 4 higher than the lower,
rear buildin g ffiea. The ground surface in the building area is relatively flat with a slight
slope down to the northeast. A drainage ditch is located along the west property line and
between the building envelope and top of steep slope down to the Roaring Fork River.
The area has historically been used as irrigated pashue. Minor grading was done during
subdivision development.
SUBSIDENCE POTENTIAL
Coryell Ranch is underlain by Pennsylvania Age Eagle Valtey Evaporite bedrock. The
evaporite contains g)?sum deposits. Dissolution of the gypzum under certairr conditions
car cause sinklroles to develop and can produce areas of localized subsidence. During
previous work in the area, sinkholes havebeen observed in tbe lower Roaring Fork
Valley. Sinlilroles were'not observed in the irnmediate area of the subject lot, although
the lot has been graded during subdivision development. Based on our present
knowledge of the site, it cannot be said for certain that sinkholes will not develop. In our
opinion, the risk of ground subsidence at Lot 3 is low and similar to other lots in the area
but the owner should be aware ofthe pote,ntial for sinli*role development.
FTELD EXPLORATION
The field exploration for the project was conducted on June 12,2015- Three exploratory
borings were drilled at the locations shown on Figure 1 to evaluate the subsurface
conditions. The borings were advanced with 4 ineh diameter continuous flight augers
powered by a truck-mounted CME-458 dlill rig. The borings were logged by a
representative of Hepworthf awlak Geotechnical, Inc.
JobNo. ll5268A e$tecft
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Samples of the subsoils were taken .uurrthl%inch and 2 inch LD. spoon samplers. The
samplers were driven into the subsoils at various depths with blows from a 140 pound
hammer falling 30 inches. This test is similar to the standard penehation test descrilied
by ASTM Method D-1586. The penetration resistance values are an indication of the
relative density or consistency of the subsoils. Depths at which the samples were taken
and the penetration resistance values are shoum on the Logs of Exploratory Borings,
Figure 2. Ttre samples were retumed to our laboratory for review by the project engineer
and testing.
STJBSTIRFACE CONDMONS
Graphic logs of the subzurface conditions encountered at the site are shown on Figure Z.
The subsoils consist of about 6 inches ofman-placed filUtopsoil overlying relatively
dense silty sandy gravel with cobbles and boulders. About ZYzfeetof man-placed fiIl was
encountered ut eotiog 2 overllng tbe gravel. Drilling in the dense granular soils with
auger equipment was diffieult due to the cobbles and boulders and drilling refusal was
e,neountered in the deposit.
Laboratorytesting performed on samples obtained from the borings included. natural
moisture content and gradation analyses. Resrrlts of gradation analyses.performed on
small diameter drive samples (minus l%inchfraction) ofthe coarse granular subsoils are
shown on Figure 4. The laboratory testing is summari zed in Table 1.
No free water was encountered in the borings at the time of drilling or when checked 1l
days later and the subsoils were slightlymoist.
DESIGN RECOMMEI\DATIONS
FOIINDATIONS
Considerin$ the subsurface conditions encountered in the exploratoryborings and the
nature of the proposed consh-uctiorl we recommend the building be founded with spread
footings bearing on the natural granular soils.
JobNo. 115268A e&&ech
4
The design and consffuction criteriapresented below should be observed for a spread .
footing foundation system.
1) Footings placed on the undisturbed naftual granular'soils should be
designed for an allowable bearingpressure of 2,500 psf. Based on
experiencg we expect setflement of footings designed and constructed as
discussed in this section will be about t inch or less.
2) The footinp should have a minimurn width of 16 inches for continuous
walls and2 feetforisolatedpads.
-'
3) Exterior footings and footings beneath unheated areas should be provided
with adequate soil cover above their bearing elevation for frost protection.
Iacennent offoundations at least 36 inches below exterior grade isG
tSpicaliyused in this area.
4> Continuous foundation walls strould be reinforced top and bottorn to span
local anomalies such as by assuming'an unsupported length of at least 10
feel Foundation walls acting as lstaining structures should also be
designed to resist lateral earth pressures as discussed in the "Formdation
and Retaining Walls" section of this report.
5) All existing fill, topsoil and any loose or disturbed soils should be rernoved
and the footingbearing level extended down to the relatively dense natural
granular soils. The exposed soils in footing area should then be moistened
andsompacted.
6) A represe,ntative of the geotechnical engineer should observe all footing
excavations prior to concrete placement to evaluate beaiing conditions.
FOI.INDATION AND RETAINING WALLS
Foundation walls and retaining stnrctures which are laterally supported and san be
expected to undergo only a slight anount of deflection should be designed for a lateral
earth pressure computed on the basis of aa equivalent fluid unit weight of at least 45 pcf
for backfill consisting of the on-site soils. Cantilevered retaining structures which are
JobNo.115268A e&Btecrr
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separats from theresidence and can be expected to deflect zufficientlyto mobilize the fun
active earth preszure condiiion should be designed for a lateral earth pressure computed
on the basis of an equivalent fluid unit weiglt of at least 40 pcf for baclcfill consisting of
the on-site granular soils.
Ail foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, &affic, construction materials and
equipment. Thepressures recontmended above assume drained conditions behind the
walls and a horizontal backfill surface. The buildup of water behind a wall or an upward
sloping backfill surface will increase the lateral pressure imposed on a foundation wall or
retaining structure. An underdrain should be provided to prevent hydrostatic pressure
buildup behind walls.
Backfill should be placed in unifonn lifts and compacted to at least 90of the maximum
standard Proctor density at a moisture content near optimum. Backfill in pavement and
walkway areas should be compacted to at least 95Yo of the maximum standard Proctor
density. Care should be taken not to overcompact the backfill or use large equipment
near the wall, since this could cause excessive lateral pressnre on the wall. Some
settle,lnent of deep {oundation wall backfill should be expected, even if the material is
placed correcfly, and could result in distress to faoiiities constructed on the backfill.
The lateral resistance of foundation or retaining wall footings will be a combination of the
sliding resisknce of the footing on the foundation materials and passive earth preszure
against the side of the footing. Resistance to sliding at the bottoms of the footings can be
calculated based on a coeffioient of friction of 0.50. Passive pressure of compacted.
backfill against the sides of the footings can be calculated using an equivalent fluid unit
weight of 400 pcf. The coefficient offriotion andpassive pressure values recommended
above assume ultimate soil strength. Suitable factors of safety shouldbe included in the
design to limit the sfrain which will occur at the ultimate strength, particularly in the case
of passive resistance. Fili placed against the sides of the footings to resist lateral loads
Job No. l15268A e&Btecrr
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should be compacted to at 1east95% of the maximum standard Proctor density at a
moisture content near optimum.
FLOOR SLABS
The natural on-site soils, exclusive of topsoil, are suitable to support lightly loaded slab-
on-grade consffuction. To reduce the offects of some differential movement, floor slabs
should be separated from all bearing walls and columns with expansion joints which
allow unrestrained vertical movement. Floor slab contol joints should be used to reduee
damage due to shrinkage cracking. The requirements for joint spasing and slab
reiaforce,rnent should bo established by the designe,rbased on experience and the intended
slab use. A minimum 4 inch layer of free-draining gravel should ba placed beneath
basement lovel slabs to facilitate drainage. This material should consist of minus 2 inch
aggtegate with at least 50% retained on the No. 4 sieve and less than 2a/o passingthe No.
200 sieve.
Atl fill materials for support of floor slabs should be compacted to at least 95% of
maximum standard Proctor density at a moisture content near optimu:n. Required fill can
consist of the on-site ganulff soils devoid ofvegetation, topsoil and oversized rock.
IINDERDRAIN SYSTEM
Although free water was not encountered during our exploration" it has been our
experience in the area that local perched groundwater can develop during times ofheavy
precipitation or seasonal runoff. Frozen ground during springrunoffcan create aperched
condition. We recommend below-grade eonskuction, such as retaining walls, crawlspace
and basement areas, be protected from wetting and hydrostatic pressure buildup by an
underdrain system.
The dreins should consist of drainpipe placed in the bottom of the wall backfill
surrounded above the invert level with free-draining granular material. The drain should
JobNo. l15268A'c&Ftecn
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be placed at each level of excavation and at least 1 foot below lowest adjacent finish
grade and sloped at a minimum L%oto a suitable gravity outlet. 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 sieve and have a maximum size of Zinches. The
drain gravelbackfill should be at least 172 feet deep.
SITE GRADING
The risk of construction-induced slope instability at the site appears low provided the sut
and fill depths are limited. The building envelope is located about 55 feet away from the
top of slope and,25 feet from the drainage ditch on a relatively flat terrace. We assume
the cut depths for the basement level will not exceed one level, about 10 fest, and fill
depths above existing grade will be a few feet. Embanlonent fillsshould be compacted to
at least 95% of tJre nnaximum standard Proctor density near optimum moisture content.
Prior to fill placeurent, the subgrade should be carefirlly prepared by removing all
vegetation and topsoil and compacting to at least 95Yo of the maximum standard proctor
density. The fill should be benched into the portions of the hillside exceeding Z0o/o grade.
Permanentwtretained cut and fill slopes should be graded at2hortzontalto 1 vertical or
flatter and protected against erosion by revegetation or other means. The risk of slope
instabilitywill be increased if seepage is encountered in cuts and flatter slopes maybe
necessary. If seq:age is encoutrtered in permanent cuts, an investigation should be
conducted to determine if the seepage will adversely affect the cut stabiiity. This office
should review site gradingplans for theproject prior to construction.
SURFACE DRAINAGE
The followingdrainageprecautions should be observed during sonstruction and
maintained at all times after the residence has been completed:
1) Inundation of the foundation excavations and underslab areas should be
avoided during conshuction
JobNo.1t5268A e&Btecrr
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3)
Exterior backfill should be adjusted to near optimum moisture and
compacted to al least 95% of the maximum standard Proctor density in
pavement and slab areas and to at least 90% of the maximum staqdard
Proctor densrty in landscape areas-
The ground surface surrounding the exterior of the building should be
sloped to drain away from the foundation in all directions. We
recommend aminimum slope of at least 6 inohes in the first 10 feet in
unpaved areas and a minimum slope of 3 inches in the first 10 feet in
paved areas. Free-draining wall backfill should be capped with about 2
feet of the on-site finer grained soils to reduce surface water infiltation.
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 borings drilled at the locations
indicated on Figure 1, the proposed type of construction and our experience in tbe area.
Our services do not include determining the presence, prevention or possibility of mold or
other biological contaminants (MOBC) developing in the future. If the clipnt is
concerned about MOBC, then aprofessional in this special field of practice should be
consulted. Our findings include interpolation and extrapolation of the subsurface
conditions identified at the explora'tnry borings and variations in the subsurface
conditions may not become evident until excavation is perfonned. If conditions
encountered duing construction appear different from those described in this report, we
should be notifed so that re-evaluation of the recommendations may 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 information. As the
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JobNo. 115 26EA cElBtecn
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projeet evolves, we shonld provide contitiued consriltaficn and ficlcl scrvices during
cor*truction t* review and rnonitor the implenenlaticr of oul recom*rendatians, and to
r'*rify th*t tlie recommendations lrave bcen applopriately inte4xeted. Sigrrificant t{esign
changes nray require additisnal analysis ol rnodifications to lhe recommendafisns
preseirted herejn" We rec*mmen{l fill-site oirservation of excavatiq:ns antl fbunclation
bearing straia anr,l testing r:f strus:tural filt by a represenl*tive of tlie geotechnical
engineer.
Respectfu lly $ ubmitted,
HEPWOR'I'}I - PAWLAK GEOTECH]\ICAL, INC.
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Reviewed bv:
Dnniei E. I{ardin, F.E.
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STONEFLY DRIVE
115 268A LOCATION OF EXPLORATORY BOHINGS Figure 1
BORING 1
ELEV.: 100.7'
BORING 2
ELEV.- 100.9'
BOBING 3
ELEV.: 101.1'
10s 105
100
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WC:2.0
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WC:2.5
+4:51
-20A=12
95
90 90
Note: Explanation of symbols is shown on Figure g.
1 15 2684 LOGS OF EXPLORATORY BORINGS Figure 2
LEGEND:
FILL; organic sandy gravelly clay, stiff, moist, brown
lE'l
ffi GRAVEL, COBBLES AND BOULDERS (GM-GP); sandy, silty, dense, slightly moist, light brown, rounded rocks.
Relatively undisturbed drive sample; 2-inch LD. California liner sample.
j Drive sample; standard penetration test (SPT), 1 3/8 inch l.D. split spoon sampte, ASTM D-1586,
7At12 Drivg sapnlg blow count; indicates lhal74 blows of a 140 pound hammer falling 30 inches wereIat te required to drive the California or SPT sampler '12 inches.
T 1?91]Fl drilling refusal. Where shown above bottom of log, indicates that muttipte attempts were
I made to advance the boring.
NOTES:
1' Rploratory borings were drilled on June 12,2015 with 4-inch diameter continuous flight power auger.
2. Locations of exploratory borings were measured approximately by pacing from features shown on the site plan
provided.
3. Elevations of exploratory borings were measured by instrument level and refer to the Bench Mark shown on Figure 1
4. The exploratory boring locations and elevations should bs considered accurate only to the degree implied by the
method used.
5. The lines between materials shown on the exploratory boring logs represent the approximate boundaries between
materialtypes and transitions may be gradual.
6. No free water was encountered in the borings at the time of drilling or when checked 11 days later. Fluctuatjon in
water level may occur with time.
7. Laboratory Testing Results:
WC : Water Content (%)
+4 : Percent retained on ths No. 4 sieve
-ZAQ = Psrcent passing No. 200 sieve
m
1 15 2684 LEGEND AND NOTES Figure 3
TIME BEADINGS
7 lt8
15 MtN.@MINIgMIN MtN. 1 MtN. #200
U.S. STANDARD SERIES
#50 #30 #16 #8'
CLEAR SQUARE OPENINGS
v8" 3//4', 1112', 3' 5'80
tsa
127
#4 8"
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z
LU
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LU
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10
20
30
40
50
60
70
80
90
100
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LU
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100
g0
80
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60
50
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20
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DNMETER OF PABTICLES IN MILUMETERS
+
#
--+-F--
CI.AYTOSILT
GRAVEL 51 O/O
. LIOUID LIMIT %
SAMPLE OF: Sitty Sandy Gravet
NME READINGS7HR
15 MtN.60MtN1
.00r .002
SAND 37 7O SILTANDCLAY 12 OA
PLASTICIry]NDEX %
FROM: Borlng 2 atS Feet
U.S. STANDARD SERIES
#100 #60 #30 #.t6 #8
coBB.ES
CIEAR SQUAFE OPENINGS
#4 3/8' g!4' 1 112' 9" 5n6" 8,
24
45
0
10
MIN. 1 MIN.
.005.009 .019 .o$ .074 .150 .300 .600 1.18 2.36 4.75
DIAMETER OF PARTICLES IN MILUMETEBS
9.q2.51e.0 37.5 76.2 1;t52 203
100
90
80 o7n z_
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30
20
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C)rr 60
uJ(L
70
80
90
100
10
0
CLAYTOgLT
GRAVEL 57 %
LIQUID LIMIT O/O
SAMPLE OF: Silty Sandy Gravel
COEEIEB
SAND 33 "/O SILTANDCI.AY 10 %
PLASTICIry INDEX %
FROM: Boring B at2/rFeet
1 15 2684 GRADATION TEST RESULTS Figure 4
HEPWORTH-PAW.AK GEOTECHNICAL, INC.
TABLE 1
SUMMARY OF LABOMTORY TEST RESULTS
Job No. 115 268A
soll oR
BEDROCK TYPE
Silty Sandy Gravel
Silty Sandy Gravel
UNCONFINED
COMPRESSIVE
STRENCTTI
(PSF)
ATTMBERG IIMITS
PTASTIC
INDEX
(o/o\
UQUID
UMIT
(o/o\
PERCENT
PASSING
NO.200
SIR'E
12
10
-
GRADATION
SAND
(Vo)
37
33
GRAVEL
e/')
5 1
57
NATUML
MOISTURE
CONTENT
NATURAL
DRY
DENSITY
2.5
2.4
DEPTH
5
2u2
BORING
.,
3