HomeMy WebLinkAboutSubsoil Study.-.¡
HEPWORTH - PAWLAK GEOTECHNICAL
Heprvorth-Pau'lak Geotechnical, lnc.
5020CounryRoad 154
Glenu'ood Springs, Colorado 81601
Phone: 970-945-7988
Fax,970-945.8454
email: hpgeo@hpgeotech.com
SUBSOIL STUDY
FOR FOUNDATION DESIGN
PROPOSED RESII}ENCE
LOT 56, X'IRST E^ÀGLES POINT
35 EAGLE RIDGE DRTYE
BÂTTLEMENT MESA, COLORADO
JOB NO. W A4A7
JU¡rE 27,2t07
PREPARED FOR¡
CIIì{aRRONI,A}II) & IIOMES, LLC
Ä.TTN: BILL IMILDE
73 SIPPRELLE DRryE, SUITE E_3
BA,TTLEMENT MESA, COLOR^ÀDO 81635
H
Parker 303'841-?119 ' CcrloracloSprings ?19-633-5562 r Silçerrhome 920.46g-lggg
SITE CONDITIONS 2-
FIELD EXPLORATION
SUBSURFACE CONDITIONS .....,......-2-
FO{JNDATION BEARING CONDITIONS .............3 -
DESIGN RECOMMENDATIONS..
TABLE OF CONTENTS
PURPOSE A}TD SCOPE OF STUDY...,...
PROPOSED CONSTRUCTION.
FOTINDATIONS......,..
FLOOR SLABS
SURFACE DRAINAGE ...............
FIGURE I - LOCATION OF EXPLORATORY BORINC
FIGURE 2 -LOG OF EXPLOR.A,TORY BORING
FIGURE 3 - LEGEND AND NOTES
FIGURE 4 - SV/ELL.CONSOLIDATION TEST RESULTS
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PT]RPOSE AND SCOPE OF STT.JDY
This report presents the results of a subsoil study for a proposed residence to be located
on Lot 56, First Eagles Point, 35 Eagle Ridge Drive, Battlement Mesa, Colorado. The
projeet site is shown on Figure l. The purpose of the study vyas to develop
recommendations for the foundation design. The study was conducted in accordance
with our agreement for geotechnícal engineering services to Cimarron Land & Homes,
LLC dated May 27,2007. Hepworth-Pawlak Geotechnical, Inc. previously conducted a
preliminary geotechnical study for development of the subdivision and presented our
findings in a report dated November 2l,ZAA3,Job No. 103 6g0.
An exploratory boring w'as drilled on the lot to obtain information on the general
subsurface conditions. A sample of the subsoils obtained during the field exploration was
tested in the laboratory to determine their classification, compressibility or swell and
other engineering characteristics. The results ofthe field exploration and laboratory
testing were analyzed to develop recommendations for foundation types, depths and
allowable pressures for the proposed building foundation. This report summarizes the
data obtained during this study and presents our conclusions, design recommendations
and other geotechnical engineering considerations based on thc proposed construction and
the subsurface conditions encountered.
PROPOSED CONSTRUCTION
The proposed residence will be a single story wood frame structure with an attached
garage and located on the lot as shou¡n on Figure l. Ground floor will be structural over a
crawlspace for the residence and slab-on-grade in the garage. Grading for the srructure is
assumed to be relatively minor with cut depths between about 3 to 4 feet- 'We assume
relatively light foundation loadings, typical of the proposed type of consrruction.
If building loadings, location or grading plans change significantly from those described
above, we should be notified to ¡e-evaluate the recommendations contained in this report.
Job No- 107 0407 eå5te*,
SITE CONDITIONS
The site'was vacânt at the time of our field exploration. The ground surface is relatively
flat with a gentle slope down to the northwest. There appears to be some fill on the lot
from overlot grading as pan ofthe subdivision development. Vegetation consists of
spârse gmss and weeds. Scauered basait cobbles were exposed on the ground surface.
FIELD E}PLORATION
The field exploration for the project was conducted on June I 1,2007. One exploratory
boring was drilled at the location shown on Figure I to evaluate the subsurface
conditions. The boring was advanced with 4 inch diameter continuous flight augers
powered by a truck-rnounted CfuIE-458 driil rig. The boring was logged by a
representative of H epworth-Pawl ak Geotechnical, Inc.
Samples of the subsoils were taken with 11/' inch and 2 inch I.D. 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 penetration test described
by ASTM Method D-l586. 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 penetfirtion resistance values are shown on the Log of Exploratory Boring, Figure
2. The samples were returned to our laboratory for review by the project engineer and
testing.
STTBSI]RFACE COIIDITIONS
A graphic log of the subsu¡face conditions encountered at the site is shovyn on Figure 2.
The subsoils consist of about 2 feet of sandy silty clay with basalt fragment fill overlying
stiff to very stifi, sandy silty clay. Relatively dense, basalt gravel, cobbles and boulders
in a sandy clay rnatrix was encountered beneath the clays at a depth of ó fect. Drilling in
the basalt rock soils with auger equipment was difficult due to rock hardness and size and
drilling refusal was encountered in the deposit. A boring drilled to the northwest of Lot
JobNo. 107 0407 eå&ecrr
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56 as part of the preliminary study encountered about SYzfeet of clay overlying the basalt
gravel and no ûee water to the drilled depth of 12 feet in Ocrobe¡ 2003.
Laboratory testing performed on a sample obtained from the boring included natural
moisture content and density. Results of swell-consolidation testing perfonned on a
relatively undisrurbed drive sample of the clay soils, presented on Figure 4, indicate low
compressibility under existing moisture conditions and light loading and a minor collapse
potential (settlement under constant load) when wetted. The sample showed moderate
compressibility upon increased loading after wetting.
No free water was encountered in the boring at the time of drilling and the subsoils were
slightly moist.
F'O[]ND,A.TION BEARING CONDITIONS
Some of the clay zubsoils encounlered in the First Eagles Point development possess an
expansion potential when wetted. Surface runoff, landscape irrigation, and utility leakage
are possible sources of water which could cause wetting. The settlement/heave potential
of the subgrade should be further evaluated at the time of construction. Placing the
foundation entirely on the basalt gravels or compacted structural fill placed on the basalt
gravels should provide a relatively low risk of foundation movement.
DESIGN RECOMME¡TDATIONS
FOTINDATIONS
Considering the subsurface conditions encountered in the exploratory boring and the
nature of the proposed construction, we recommend tbe building be founded with spread
footings bearing on the natural gravel subsoils or compacted structu¡al fill.
The design and construction criteria presented below should be observed for a spread
footing foundation system.
1) Footings placed on the undisturbed natural gravel subsoils or compacted
structural fill should be designed for an allowable bearing presswe of
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3)
2,000 psf. Based on experience, we expect settlemenilheave of,footings
designed and constructed as discussed in this section will be about I inch
or less.
The footings should have a minimum width of 16 inches for continuous
walls and 2 feet for isolated pads.
Exterior footings and footings beneath unheared areas should be provided
with adequate soil cover above their bearing elevation for f¡ost protcction.
Placemenl of foundations at least 36 inches below 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 l2
feer. Foundation walis acting as retaining stn¡cnres (such as for the
crawlspace area) should also be designed to resist a lateral earth pressure
corresponding to an equivalent fluid unit weight of at least 50 pcf.
The topsoil, clay soils and any loose or disturbed soils should be removed
and the footing bearing level extended down to the natural gravel soils. As
an altemative design bearing levels ca¡r be re-established with compacted
structural fill, compacted to at least 98% of standard proctor density at a
moisture content near optimum. The fill should consist of a granular
material, such as ve ínch road base. The fiil should extend laterally beyond
the edge of the footings ar least equal to the deprh of fill below the
footings. Voids created by the removal of large rocks should be backfilled
with compacted sand and gravel or with concrete. The exposed soils in
footing area should then be moistened and compacted.
A representative of the geotechnical engineer should observe alt footing
excavations prior to concrete placement to evaluâte bearing conditions.
4)
FLOOR SLABS
The nahral clay soils possess an expansion potential and slab heave could occur if the
subgrade soils were to become wet. Slab-on-grade construction may be used for clay
subgrade conditions provided precautions are tâken to limit potential movernent and the
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.lob No. 107 0407 cå5íecr'
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risk of distress to the building is accepted by the owner. A positive way to reduce the risk
of slab movement is to conslruct structurally supported floors over crawlspace and is
recolnmended for the clay subgrade conditions. The settlement{heave potential of the
garage slab subgrade should be further evaluated at the time of construction.
Slab-on-grade constn¡ction may be used in the garage area provided the risk of distress is
understood by the olvner. We recommend placing at least 3 feet of nonexpansive
structural fill, such as3/o-inch road base, below the garage floor slab in order to help
mitigate slab movement due to expansive soils.
To reduce the effects of some differential movement, nonstructural floor slabs should be
separated from all bearing walls a¡rd columns with expansion joints which allow
unrestrained vertical movement. Interior non-bearing partitions resting on floor slabs
should be provided with a slipjoint at the bottom of the wall so that, if the slab moves,
the movement cannot be transmiued to rhe upper structure- This detail is also important
for wallboards, stairways and door frames. Slip joints which will allow at least l% inches
of venical rnovement are resorlmended. Floor slab control joints should be used to
reduce damage due to shrinkage cracking. SIab reinforcement and control joints should
be established by the designer based on experience and the intended slab use.
Required fill beneath slabs should consist of a suitable imported granular mate¡ial, such
as 3/" inch road base. The fill should be spread in thin horizoffal lifrs, adjusted to at or
above optimum moisture content, and compacted to at least 95% ofthe maximum
standard Proctor densiry. All vegetation, topsoil and loose or disturbed soil should be
removed prior to fill placement.
The above recomrnendations will not prevent slab heave if the expansive clay soils
underlying slabs-on-grade become wet. However, the recommendations will reduce the
effects if slab heave occurs- All plurnbing lines should be pressure tested before
backfilling to help reduce the porential for weting.
Job No. lO7 0407 cåBtecrt
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SURFACE DR¡.INAGE
The following drainage precautions should be observed during const¡:r¡ction and
maintained at all tirnes after the residence has been completed:
1) Inundation ofthe foundation excavations and underslab areas should be
avoided during construction.
2) Exterior backfill should be adusted to near optimum moisture and
compacted to at least 95% of the maximum standard Proctor density in
pavement and slab areas and to at ieast 90% ofthe 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 forundation in all directions. \Ve
recorÌunend a minimum slope of 6 inches in the fîrst l0 feet in unpaved
areas and a minimum slope of 3 inches in the first l0 feet in paved areas.
4) Roof downspouts and drains should discharge well beyond the limits of all
backfill.
5) Irrigation sprinkler heads and landscaping which requires regular heavy
irrigation, such as sod, should be located at least 5 feet from foundation
walls.
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 irnplied. The conclusions and recommendations submitted in this report are
based upon the data obtained from the exploratory boring drilled ar the location 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. Ifthe client is
concerned about MOBC, then a professional in this special field ofpractice should be
consulted. Our findings include extrapolation of the subsurface conditions identified at
the exploratory boring and variations in the subsurface conditions may not become
Job No. 107 0407 cå5ree,
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evident until excavation is performed. If conditions 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 infor¡nation. As the
project evolves, we should provide continued consultation and field services during
construction to review and monitor the irnplementation 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
presented herein. We recommend on-site observation of excavations and foundation
bearing strata and testing of structural fill by a representative of the geotechnical
engineer.
Respectfully Submitted,
HEPWORTH - PAIü/LAK GEOTËCHN]CAL, INC
Jordy Z. Adamson, Jr., P.E.
Reviewed by:
Daniel E. Hardin, P.E.
IZNcay
JobNo. ¡07 0407 eå5'tecrr
APPROXIMATE SCALE
1" = 30'
EAGLE COURT
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BENCH MARK: GROUND AT PROPËBTY
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LOCATION OF EXPLORATORY BORING Figure 1
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BORING 1
PROPOSED
RESIDENCE
9595
100
90
B5
80
BORING 1
ELF/.: 96.1'
25112
27/12
WC = 6.'l
DD = 101
1816,2012
NOTE: Explanation of symbots ís shown on Figure 3.
100
90
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LOG OF EXPLORATOBY BORING Figure 2
LEGEND
m
FILL; sandy silty clay with basalt fragments up to small boulder size, firm, slightly moist, light brown.
CIAY (CL); silty, sandy, stiff to very stiff, slightly moist, light brown.
ffi iffiåT"ffi:.ANÐ coBBLEs (GC); in a sandv clav matrix, with boulders, dense, slighuy moist, tishr brown to
Relatively undisturbed drive sample; 2-inch l.D. California tiner sample.
Drive sample; standard penetration test (SPT), 1 3/8 inch l.D. split spoon sampte, ASTM,15g6.
Drive samplg þlory colntt indicates that2í blows gf a 140 pound hamrner falling 30 inches wererequired to drive the California or SPTsampler l2 inches.
NOTES:
1. Ïhe exploratory boring was drilled on June 11,2OAl wíth a 4-inch diameter continuous flight power auger.
2- The exploratory boríng location was measured approximately by pacing from features shown on the site planprovided.
3. The exploratory boring elevation was measured by instrument feveland refers tothe Bench Mark shown on Figure 1.
4. The eçloratory boring location and elevatíon should be considered accuraie onþ to the degree implied bythemethod used.
5. The línes between materials shown on the exploratory boring log represent the approximate boundaries betweenmaterial types and transitÍons may be gradual.
6' No free water was encountered in the boring at the time of drilling. Fluctuation in water level may occur with time.
7. Laboratory Testing Results:
WC - WaterContent (%)
DD = Dry Density (pc0
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107 0407 G(
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LEGEND AND NOTES Figure 3
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