HomeMy WebLinkAboutSubsoil Study for Foundation Design 11.26.2004StxE-o52t-6832
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SI]BSOIL STUDY
T'OR FOUNDATION DESIGN
PROPOSED RESIDENCE
LOT F'7, ASPEN GLEN
GARFTELD COUNTY, COLORADO
JOB NO. tL4 437A
NOVEMBER.26,20t4
PREPARED FOR:
}VOODBRIDGE MORTGAGE INTVESTMENT F',UND z,LLC
ATTN: RICK SALVATO
22 CENTER STREET, FRONT SUITE
IREEIIOLD, NEIV JERSEY A7728
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TABLE OF CONTENTS
PLJRPOSE ÂND SCOPE OF STUDY..................
PROPOSED CONSTRUCTION..........
SITE CONDITIONS
SUBSIDENCE POTENTIAL ....
FIELD EXPLORATION.
SUB SURFACE CONDITIONS ..
DESIGN RECOMMENDATIONS..........,......
FOLINDATIONS.........
FOI-INDATION AND RETAININC WALLS.
FLOOR SLABS
TINDERDRAIN SYSTEM...
SITE GRADING .................
SURFACE DRAINAGE ......
LIMITATIONS
REFERENCES
FIGURE 1 - LOCATION OF EXPLORATORY BORINGS
FIGURE 2 - LOGS OF EXPLORATORY BORINGS
FIGIIRE 3 . LEGEND AND NOTES
FIGURE 4 - GRADATION TEST RESI'LTS
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PURPOSE AND SCOPE OF STT"IDY
This report presents the results ofa subsoil study for a proposed residence to be located at
Lot F 7, Aspen Glen Subdivision, Garfield Countg Colorado. The project site is shown
on Figure 1. The purpose of the study was to develop recommendations for the
foundation design. The study was conducted in accordance with our proposal for
geotechnical engineering services to Woodbridge Mortgage Investment Fund 2,LLC
dated october 2,2014. chen-Northern, Inc. (1991 and lgg3)previously conducted
preliminary geotechnical engineering studies for the development and preliminary plat
design.
A fie1d exploration program consisting of exploratory borings was conducted to obtain
information on the subsurface conditions. Samples of the subsoils obtained during the
field exploration rvere tested in the laboratory to determine their classification and other
engineering characteristics. The results of the field exploration and laboratory testing
were analyzed to develop recommendations for foundation fires, depths and allowable
pressures for the proposed building foundation. This report surnmarizes the data obtained
dwing this study and presents our conclusions, design recommendations and other
geotechnical engineering considerations based on the proposed construction and the
subsurface conditions encor¡ntered,
PROPOSED CONSTRUCTION
Building plans for the proposed residence are conceptual. Typical residences in the area
are one and two story wood frame above a basement or crawlspace with an attached
garage. Ground floors are typically slab-on-grade. Grading for the proposed structure is
assumed to be relatively minor with cut depths befween about 3 to 10 feet. We assume
relatively light foundation loadings, typical of the assumed type of eonstruction.
If building loadings, location or grading plans change significantly from those described
above, we should be notified to re-evaluate the recommendations contained in this report.
JobNo. tl4437A eåBtec¡
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SITE CONDITIONS
The vacant property is locatcd at the cul-de-sac of River Park Lane. Vegetation consists
of sparse grass and weeds. Topography at the site consists of relatively flat upper and
lower terraces separated with by a steep slope. The terraces have a slight slope down to
the northwest' Elevation difference bsfween the terraces is about 15 feet. A wetland area
and drainage are located beyond the site to the northwest. The uppor terrace appears to
have been graded with minor cuts during subdivision development and gravel and cobbles
are exposed on the ground swface. A golf coursc fairway is located along the northern
property line.
SUBSIDENCE POTENTIAL
Bedrock of the Pennsylvanian age Eugle Valley Evaporite underlies the Aspen Glep
development. These rocks are a sequence of gypsiferous shale, fine-grained
sandstonelsiltstone and limestone with some massive beds of gypsum. There is a
possibility that massive gypsum deposits associated with the Eagle Valley Evaporite
underlie portions of the lot. Dissolution of the gypsum uncler certain conclitions can cause
sinkholes to develop and canproduce areas oflocalized subsidence. Duringprevious
studies in the area, sevsral broad subsidence areas and smaller size sinktrole areas were
observed scattered throughout the Aspen Glen development, predominantly on the east
side of the Roaring Fork Rivor (Chen-Northcrn,Inc., 1993). These siukhules äppeðr
similar to others associated with the Eagle Valley Evaporite in areas of the Roaring Fork
River valley.
Lot F 7 is located just outside of one of the broad subsidence areas mapped by Chen-
Northern. Signs of active ground movements have not been observed in the zubsidence
area. The neârest sinkhole wâs mapped about 900 feet to the northeast of Lot F 7.
Sinkholes were not observed in the immediate area of the subject lot. No evidence of
cavities was encountered in the subsurface materials; however, the exploratory borings
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\¡rere relatively shallow, for foundation design only. Based on our present knowledge of
the subsu¡face conditions at the site, it cannot be said for certain that sir*holes will not
develop. The risk of fi.rture ground subsidence an Lot F 7 throughout the service life of
the proposed residence, in our opinion, is low but the site should not be considered totaily
risk free. If furfher investigation of possibie cavities in the be&ock helow the site is
desired, we should tre contacted.
FIELD EXPLORATION
The field exploration for the project was conducted on Octob er 7,2014. Two exploratory
borings were drilled at the locations shom on Figure 1 to evaluate the subsur-face
conditions. Tlie borings u/ere advanced witb 4 inch diameter continuous flight augeîs
powered by a truck-mounted cME-458 drill rig. The borings were logged by a
representative of Hepwortli-Pawlak Geotechnical, Inc. .À previous boring (B-5-g3) was
drilled near the û'ont of the lot by Chen-Northerno Inc.
Samples of the subsoils were taken with a 1% irich I.D. spoon sampler. The sanpler was
driven into the subsoils at various depths with blows fiom a 140 pouncl hammer falling 30
inches. T'his test is similar to the standard penetration test described by ASTM Method
D- 1586. The penetration resistance values a1'e an indication of the relative density or
consistency of the subsoils. Depths at which the samples were taken and the penetration
resistance values ate shown on the Logs of Exploratory Bcrings, Figure 2. The samples
rvere retumed to our laboratory for review by the proiect enginecr an<l testing.
SUBSURFACE CONDITIONS
Graphic logs of the subsurface conditions encountered at the site are shown on Figure 2.
T'he subsoils encountered consist of silty sandy gravel with cobbles and boultiers. Results
of gradation analyses performed on a small diameter drive sample {minus 1% inch
fiaction) of the coarse granular subsoiis are shown on Figure 4. Drilling in the dense
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granulil soils witfu uuger equipmsflt was dtfllcult tlue to the cobbles antl boulders and
drilling refusal was encountered in the deposit at relatively shallow depths.
No free water was encountered in the borings at the time of drilling and thc subsoils were
slightly moist to moist. Chen-Northern, Inc. Boring 8-5-93 indicates the granular soils
extend down to about 60 feet and are underlain by Eagle Valley Evaporite Bedrock.
DESIGN RECOMMENDATIONS
FOUNDATIONS
Considering the zubsurface conditions encountered in the exploratoryborings and the
nature of the proposed construction, we recofirmend thc building be founded with spread
footings bearing on the nafural granular soils.
The design and construction criteria presented below should be observed for a spread
fo oting foundation system.
1) Footings placed on the undisturbed natural granular soils should be
designed for an allowable bearing plessure
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prf,- Based on
experience, we expect settlement of footings designed and construeted as
discussed in this section will be about I inch or less.
2) The footings shoultl have a minimum width of l6 inches for continuous
walls and 2 feet for isolated pads.
3) .Exterior tbotings and footings beneath unheated areas should be provided
with adequate soil cover above their bearing elevation for frost protection.
Placement of foundations at least 36 inches below exterior grade is
typically used in this area. r'-r--
4) Continuous foundation walls should be reinforced top and bottom to span
local anomalies such as by assuming an unsupported length of at least 10
feet. Foundation walls acting as retaining structures should also be
designed to resist lateral earthpressures as discussed in the "Foundation
and Retaining Walls" section of this report.
5) All topsoil and any loose or disturbed soils should be removed and the
footing bearing lcvcl extended down to the relatively dense natural
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granular soils. The exposed soils in footing area should then be moistened
and compacted. If water seepage is encountered, the footing areas should
be dewatered before concrete placement.
A representative ofthe geotechnical engineer should observe all foofing
excavations prior to concrete placement to evaluate bearing conditions.
FOLINDATION AND RETAINING WALLS
Foundation walls and retaining structures which are laterally supported and can be
expected to undergo only a slight amount of deflection should be designed for a lateral
earth pressure computed on the basis of an equivalent fluid unit weight of at least 43 pcf
for backfill consisting of the on-site soils. Cantilevered retaining structures which are
separate from the residence and can be expected to deflect sufficiently to mobilize the full
active earth pressure condition should be designed for a lateral earth pressure computed
on the basis of an equivalent fluid unit weight of at least 40 pcf for backfill consisting of
the on-site soils.
All foundation and retaining structures should be designed for appropriate hydrostatic and
surcharge pressures such as adjacent footings, fraffic, construction materials and
equipment. The pressures recouìmended above assurne 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 skucture. An underdrain should be provided to prevent hydrostatic pressure
buildup behind walls.
Backfill should be placed in uniform lifts and cornpacted to at least 90% of the maximum
standard Proctor density at a moisture content near optimum. Backfill in pavement and
walkway areas should be compacted to at least 95o/o af themaximum standard Proctor
density. Care should be taken not to overcompact the backfill or use large equipment
near the wall, since this could cause sxcessive lateral pressure on the wall. Some
settlement of deep foundation wall backfill should be expected, even if the material is
placed correctly and could result in distress to facilities constructed on the backfill.
6)
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The latcral rcsistance of fouutlutiurr ur retainirg wall footings will be a combination of the
sliding resistance of the footing on the foundation matorials anrl passive carth pressure
against the side of the footing. Resistance to sliding at the bottoms of the footings can be
calculated based on a coefficient of friction of 0.50. Passive plessure of compacted
backfill against the sides of the footings can be calculated using an equivalent fluid unit
weight of 400 pcf. The coefficient of friction and passive pressure values recommended
above assume ultimate soil strength. Suitable factors of safety should be includeri in the
design to limit the strain which will occur at the ultimate strength, particularly in the casc
of passive resistance. Fill placed against the sides of the footings to resist lateral loads
should be compacted to at least 95olo of the maxímum standard proctor density at a
moisfure content near optimum.
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, floor slabs
should be separated from all bearing walls and columns with expansion joints which
allow unreshained vertical movement. Floor slab control joints should be used to reduce
damage due to shrinkage cracking. The requiremsnts 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 level slabs to facilitate drainage. This material should consist of minus 2 inch
aggregate with at least 50% retained on the No. 4 sieve and less than 2% passing the No.
200 sieve.
AII 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 ofthe on-site granular soils devoid ofvegetation, topsoil and oversized rock.
TINDERDRAIN SYSTEM
Although free water was not cncountered durùrg our exploration, it has been our
experience in the areathat local perched groundwater can develop during times of heavy
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precipitation or seâsonal runoff. Frozen grouncl during spring runoff can also create a
perched conclition. W'e recornmenci below-gpade construction, such as retaining walls,
crawlspace and basemenl âreas, be protected from wetting and. hyclrostatic pressure
buildup by an underdrain system
The drains should consist of in the bottom of the wall backfill
surrounded above the invert level with free-draining granular material. The drai' should
be placed at each level of excavation and at least I fbot below lawest adjacent finish
grade and sioped at a minimum lYo to a suitable gravity outlet. Free-drain.ing granular
material used'in the underdrain system should contaiu less tha:r Z% passing the No. 2û0
sieve, less than 50% passing the No, 4 sieve and have a maximul size of Z inches. The
drain gravel backfill shoulcl be at least l% feet <leep.
SITE GRADING
The risk of conskuction-induced siope instability at the site appears low pr-ovided cut and
filI depths are limited. We assume the cut depths for the basement levei (if any) rviil ¡rot
exceed one level, about 10 to 12 feet, Fills should be limitcd to about I to 10 feet tleep at
the dnwnhili side of the residence where the slope steepens" Embankrne't fills shor¡ld be
oompacted to at ieast 95o1a oT the maximum standarrl Proctor density near optimum
mois{ure content. Prior to fill placement, the subgra<le should be carefully prepared by
removing all vegetation and topsoii ancl cornpacting to at least g5yo af themaximum
standard Proctor density. The fill shoulcl be benchecl into the portigns of the hiilsicle
exceecii ng 20a/o gr ad,e.
Pennanetrt unretained cut and fîll slopes should be graded at 2 hoúr-antal to 1 vertical or
flatter and protecled against erosion by revegetation or other means. The ri.sk o{. slope
instability will be increase¡l if seepage is encounteled in csfs and flatte¡ slopes may ¡e
nscessary. Ifseepage is encountered inpennanent cuts, an investigation shoulcl be
conducted to cletermine if the seepage will adversely affect the cqt stabiliiy. This officc
should review site grading plans for the project prior to conshr¡cfion,
Job No. 114 437A cåFtecr¡
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SURFACtr DRAINAOE
The following tlrainage precautions should he observed dwing construction and
maintained 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 a-djusted 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.
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 slope of 12 inches in the first l0 feet in unpaved
areas and a minimum slope of 3 inches in the first l0 feet in paved areas.
Free-draining wall backfill should be capped with about 2 feet of the on-
site soils to reduce surface water infilftation.
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
er(fresñ nr implied. The conclusions and recommondations submittcd in this rcport æc
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 the 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 client is
concerned about MOBC, then a professional in this special ñeld of practice should be
consulted' Our findings include interpolation and extrapolation of the subswface
conditions identified at the exploratoryborings and variations in the subsurface
conditions may not become evidetrt until excavation is performed. If conditions
JobNo. l14417A eåStecr¡
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encountered during construction appear different from those described in this report, we
should be notified 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
project evolves, we should provide continued consultation and field servicçs during
construction to review and monitor the implernentation of our recommendations, and to
verify that the recommendations have been appropriately interpreted. Significant design
changes may require additional analysis or modifications to the recommendations
presenfed herein. We recommend on-site observation of excavations and foundation
bearing shata and testing of structural fill by a representative of the geotechnical
engineer.
Respectfully Submitted,
HEPWORTH - PAWLAK GEOTECHNICAL, INC
Louis E. Eller
Reviewed by:
Daniel E. Hardin, P.E
LEE/ksw
REFERENCES
chen-Northern, rnc., 1991, Prelimínary Geotechnícal Engineeríng study, proposed
Aspea Glen Development, Garfield counfii, colorado, prepared for Aspen Glen
Company, dated December 20, Tggl,Job No. 4 ll2 gZ.
Chen-Northem, Inc., 1993, Geoîechnical EngÌneering Studjtfor Preliminary PIat Design,
Aspen Glen Development, Gørfield county, colorado, prepared for Aspen Glen
Company, dated }lday 28,1993, Job No. 4 n2 gZ,
JobNo. ll4437A ceFtecr'
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APPROXIMATE SCALE'1": 50'RIVEB
PARK I.ANE
114 4374 LOÇATION OF EXPLORATORY BORINGS Figure 1
BORING 1
ËLEV.= 102.3'
BORING 2
ELEV,: 99.5'
105 105
100 100
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95 95
90 90
Note: Explanation of symbols is shown on Figure 3.
114 4374 LOGS OF EXPLORATORY BORINGS Figure 2
LEGEND:
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ffi GRAVEL, COBBLES AND BOUTDEHS (GP-GM); sandy, silty, dense, slightly moist, brown, subrounded rocks.
i Drive sample; standard penetration test (SPT), 1 3/8 inch l.D. split spoon sample, ASTM D-1586.
39112
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Drive sample blow count; indicates that 39 blows of a 140 pound hammer falling 30 inches were
required io drive the SPT sampler 12 inches.
Practical drilling refusal
NOTES:
1. Exploratory borings were drilled on October 7,2014 with 4-inch diameter continuous flight power auger.
2. Locations of exploratory borings were measured approximately by pacing lrom fealures 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 be 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
rnaterial types and transitions may be gradual,
6. No Tree water was encountered in the borings at the time of drilling. Fluctuation in water level may occur with time.
7. Laboratory Testing Results:
+4 : Percent retained on the No. 4 sieve
-200 : Percent passing No. 200 sieve
1 l4 4374 LEGEND AND NOTES Figure 3
24 HF. 7 HR
o 45 MlN. 15 MtN.
TIME BEADINGS U.S. STANDARD SERIES
00 #50 #30 #16 #8
CLEAR SOUARE OPEN¡NGS
3/8" 3/4' 1 112', 3', 5'6u60MtN19MtN.4MtN. 1MrN. #204 #1 #4 8',100
10 90
80
30 7Q
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70
80
40
30
20
1090
100 0
00j .OO2 .00s.009 .01s .0S7 .O74 .150 .900 .6üû l.l8 2.36
DIAMETER OF PARTICLES IN MILLIMETERS
4.75 9.5 1S.0 37 .5
12.5
76.2 152 2A3
127
ctÀYTo srlf I SAND I GRA\,IL II |INE I MED,UM I COAFSE I FINE I ruffi I coBBr,Es
GRAVEL 54 %SAND 35 %SILT AND CLAY 11 %
LIOUID LIMIT %PLASTIC|TY INDEX %
FROM:Boring2aì0Feet
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SAMPLE OF: Slightly Silty Sandy Gravel
114 4374 GRADATION TEST RESULTS Figure 4