HomeMy WebLinkAboutGeotechnical InvestigationI
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Geotechnical Investigation
Lots 3 and 4
Creek Side Estates
Garfield County, Colorado
Project No. 27-135
May 18, 2007
Prepared for:
Mr. Tom Heuen
Empty Enterprises, LLC
898 SH 133, Suite 303
Carbondale, Colorado 81623
Prepared by:
Yeh and Associates, Inc.
170 Mel Ray Road
Glenwood Springs, Colorado 81601
Phone: 970-384-1500
Fax: 970-384-1501
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Lots 3 std 4, Creek Side Eatalell
TABLE OF CONTENTS
PURPOSE ANO SCOPE ................................................................................................ 1
PROPOSED CONSTRUCTION ...................................................................................... 1
SITE CONDITIONS ........................................................................................................ 2
SUBSURFACE CONDITIONS ........................................................................................ 2
EX.PANSIVE SOIL RISK ·······--·············•·························· ........................................................ 3
SITE DEVELOPMENT .................................................... , .................................. ···-........... 4
FOUNDATION RECOMMENDATIONS ........................................................................... 4
Footings with Mlnimu~ Oeadload ........................................................................ 4
BELOW-GRADE CONSTRUCTION ................................................................................ 5
SLABS-ON-GRADE ........................................................................................... : ............ 6
SUBSURFACE DRAINAGE ....................................................................................... : •... 6
SURFACE DRAINAGE ................................................................................................... 6
PERCOLATION TEST RESULTS ................................................................................... 7
LIMITATIONS .............................................................................. ,, ................ ~ ........................ 7
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Lois 3 and 4, creek Side Estates Project No. 27-135
PURPOSE AND SCOPE
This report presents the results of our geotechnlcal Investigation and recommendations
for design and construction of single-family residences on Lots ~ and 4 In Creek Side Estates In
Garfield County, Colorado. The subsurface Investigation was conducted to provide
recommendations for foundation design, subsurface drainage, below grade construction, and
backfilling/compaction procedures for the construction of the residential structure. The findings
of our Investigation and recommendations for construction of the proposed residence on the
subject site are presented in this report.
The site Investigation consisted of geologic reconnaissance and drilling of two
exploratory test holes to Investigate subsurface conditions. One test hole was dnlled within the
building envelope on both Lot 3 and Lot 4. Additionally, a profile hole and a group of percolation
test holes were drilled on Lot 3, outside the building envelope to estimate a percolation rate for
the proposed leach field . A representative of Yeh and Associates observed drilling of the test
holes end performed the percolation tests. The proj~ct personnel examined samples obtained
during the field exploration and representative samples were subjected to laboratory testing to
determine the engineering characteristics of materials encountered.
Based on our investigation, Yeh and Associates completed an engineering analysis of
the subsurface conditions. This report summarizes our field Investigation, the results of our
analysis, and our conclusions and recommendations based on the proposed construction, site
reconnaissance, subsurface investigation, and results of the laboratory testing.
PROPOSED CONSTRUCTION
We understand the proposed construction will consist of a one or two-story residential
wood framed structure on each lot. Each house will likely be supported on footing foundations.
Crawlspace areas and/or basements are planned for each residence. Cuts on the order of 3 to
5 feet below existing grade for crawlspace areas, and cuts on the order of 8 to 10 feet below
existing grade for basements are planned to achieve foundation elevation for each residence.
We anticipate minor grading around the building to establish drainage and fletwork. Foundation
loads will likely be on the order of 1,000 to 3,000 pounds per linear foot.
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Lots 3 and 4, Creek Side Estates Project No. 27-135
SITE CONDITIONS
Creek Side Estates Is located northeast of Rifle, Colorado. in Garfield County. about one
mile northeast ot the Intersection of Highway's 13 and 325 on the east side of Highway 325.
Lots 3 and 4 were located in a low lying area . An existing residence is located on Lot 6 to the
north and one residence Is located to the south on an adjacent parcel. The lots are located
between Highway 325 end Rifle Creek. The sites were recently graded and were void of
vegetation. A swampy area was located between the subject lots. and a soil stockpile was
located on Lot 4 . The lots are fairty flat, and gently slope down to the east towards Rifle Creek.
UtiHties were in the process of being installed.
SUBSURFACE CONDITIONS
Subsurface conditions were investigated by drilling three exploratory borings on April 25,
2007. The approximate location of the exploratory test~ is presented on Figure 1. The test
holes were drilled using a Dietrich D-50 to pre-determined depths where modified California
samples were obtained. The results are shown on Agure 2.
Modified California samples were collected u.sing a 2-lnch 1.0. sampler driven Into the
subsoils with a 140-pound hammer falling 30 Inches. The number of blows needed to drive the
sampler constitutes the blow count. For example. a value on the log (Appendix A) of 13/12
Indicates the sampler was driven 12 inches with 13 blows of the hammer. The blow count can
be used as a relative measure of material stiffness or density. The collected samples were
transported to our laboratory where they were examined and classified. Laboratory tests
included moisture content, dry density. swelVconsolidation, grain size analysis and Atterberg
limit testing.
The subsoils encountered in the test holes consisted of 9 to 14 feet of clay underlain by
sandy silt and clay. The upper clay was medium stiff to very stiff, the sandy silt was loose. and
the lower clay was medium stiff to stiff. Bedrock was not encountered in any of the test holes.
The clay sample tested had 70 percent fines (material passing the No . 200 sieve). Atterberg
limit test results Indicated the clay had a llquld limit of 27 percent and plastlclty Index of 9
percent. The sandy silt samples tested had 74 to 79 percent fines, and were non-liquid and
non-plastic. Two clay samples exhibited slight compression to low swell (-0.6 to 1.3 percent)
and one sample tested exhibited moderate swell (2.6 percent) when wetted under an applied
pressure of 1,000 psf. One silt sample exhibited compression of-1.8 percent wetted under an
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Lois 3 and 4, Creek Side Estates Project No. 27-135
applied pressure of 1,000 psf. The laboratory test results are presented on Figures 3 and 4 and
are summarized In the Summary of Laboratory Test Results table.
Groundwater was encountered In the test holes at depths of 10 and 14.5 feet on Lots 3
and 4, respectively. Based on existing grades and measured groundwater levels, we
recommend foundations be placed no deeper than 5.feet below existing grade for Lot 3 and 9
feet for Lot 4. Variations in groundwater conditions may occur seasonally. The magnitude of the
variation will be largely dependent upon the amount of spring snowmelt, duration and intensity
of precipitation, local landscape Irrigation practices, site grading changes, and the surface and
subsurface drainage characteristics of the surrounding area. Perched water tables may be
present, but were not encountered in any of the test holes.
EXPANSIVE SOIL RISK
The site appeared suitable for the proposed construction. Potentially expansive soils will
require particular attention in the design and construction. We believe there is a low to
moderate risk of poor slab-on-grade performance due to swelling soils. We estimate potential
movements of basement slabs and exterior flatwork of about 1 to 2 Inches could occur. We
anticipate foundation movements of about 1-lnch or less. Expansive soils are stable at current
moisture conditions. Upon wetting these soils Increase in volume and could cause movement of
slabs-on-grade and foundations. The amount of movement Is dependent on the availability of
water due to landscape irrigation and surface drainage and the structural tolerances to
movement.
Slab-on-grade construction for basement or garage areas is considered acceptable
provided the owner accepts the risk of potential slab movement The expansive soils can be
mitigated by subexcavatlon. Subexcavatlon consists of removal of the expansive soils, moisture
conditioning of the soils and placement as a moisture conditioned, controlled fill. If selected, we
recommend subexcavation to a depth of 5 feet below slab level. Subexcavation can also be
performed by removing 3 feet of the expansive clay below improvements and replacing the
material with a non-expansive granular fill. We estimate potential movements of less then 1-
inch, If subexcavation is performed.
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Lois 3 and 4, Creek Side Estates Project No. 27-135
SITE DEVELOPMENT
We anticipate cuts of about 3 to 5 feet for crawlspace areas and/or 8 to 10 feet for
basements from existing grade to reach foundation level Jn both Lots 3 and 4. Groundwater
was encountered at relatively sheHow depths on both lots. We recommend foundations be
placed no deeper than 5 feet below existing grade for Lot 3 and 9 feet for Lot 4. Areas to
receive fill should be stripped of vegetation, organic soils and debris. The on-site solls free of
organic matter, debris and rocks larger than 6 Inches can be used in fills. Fill should be placed
In thin, loose lifts of 8 inches thick or less, moisture conditioned to 0 to 3 percent above optimum
moisture content and compacted to at least 95 percent of maximum standard Proctor dry
density (ASTM D 698). Placement and compaction of fill should be observed and tested by a
representative of the geotechnlcal engineer.
FOUNDATION RECOMMENDATIONS
Based on the materials encountered in the test holes and our laboratory test results, we
anticipate foundation soils would consist of low to moderate swelling clay solls. We believe
there is a low to moderate risk of heave related damage due to expansive soils and therefore a
moderate risk of foundation movement. We anticipate foundation movements of about 1-inch or
less. If the owner Is not willing to accept the risk, a deep foundation altemative is recommended
and should be considered. If the owner is willing to accept the risk of foundation movement, the
structure can be supported on a footing foundation designed to maintain a minimum deadload.
Recommended design and construction criteria for footings with minimum deadload ere
presented below.
Footings with Minimum Dead/oad
1. Foundations should be constructed on undisturbed, natural soils. Loose,
disturbed soils encountered at foundation level should be removed and replaced
wilh compacted fill or the foundation should be extended to undisturbed soils.
2. Footing foundations can be designed for a maximum allowable soil pressure of
3,000 psf. The footing foundation should be designed wHh a minimum deadload
pressure of 1,000 psf.
3. Continuous wall footings should have a minimum width of at least 16 inches.
Foundation pads for isolated columns should have a minimum dimension of 20
Inches by 20 inches.
4. Jn order to maintain the minimum dead load pressure, it may be necessary to
design and construct a system of grade beams and Isolated footing pads. To
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Lots 3 and 4, Craelc Side Estates Project No. 27-135
maintain the minimum dead load pressure on footings, a minimum 4 Inch void
space should be provided beneath the grade beams between footing pads (if
utilized}.
5. Resistance to sliding at the bottom of the footing can be calculated based on a
coefficient of friction of 0.30. Passive pressure against the side of the footing can
also be considered for the sliding resistance if it is properly compacted. Passive
pressure can be estimated based on an equivalent fluid density of 250 pcf for a
level backfill.
6. Grade beams and foundation walls should be reinforced to span undisclosed
loose or soft soil areas. We recommend reinforcement sufficient to span an
unsupported distance of at least 10 feel
7. The soils below exterior footings or exterior edges of slabs should be protected
from freezing. We recommend the bottom of footings be constructed at least 3
feet below finished exterior grade or as required by local municipal code.
8. All foundation excavations should be observed by an experienced engineering
geologist or geotechnical engineer prior to placement of concrete.
BELOW·GRADE CONSTRUCTION
Crawlspace areas and/or basements are planned for the residences planned on Lots
3 and 4. Foundation waifs that extend below grade should be designed for lateral earth
pressure where backfill Is not present at about the same level on both sides of the wall. Walls
that can deflect or rotate about 0.5 to 1 percent of the wall height can be designed for "active•
earth pressure conditions. For a very rigid wall where negligible deflection will occur, an "at-
resr lateral earth pressure condition can be used. Typically, below-grade walls In residences
can rotate under normal design loads, and deflections result in acceptable perfonnance.
If on-site soils are used as backfill, we recommend using an equivalent fluid density of
50 pcf for design of below grade walls for "active" conditions. This value assumes that some
minor cracking fs acceptable. If negligible deflections are desired, a higher ("at rest") equivalent
fluid density should be used for design. For •at rest" conditions, an equivalent fluid density of 60
pcf can be used for design. These equivalent fluid densities do not account for sloping backfill,
surcharges or hydrostatic pressure.
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Lots 3 and 4, Creelc Side Estates Project No. 27-135
SLABS-ON·GRADE
Based on our investigation, garage and driveway slabs will likely be underlain by low to
moderate swelllng clay soils. We believe there Is a moderate risk of poor slab-on-grade
performance due to swelling soils. Slab-on-grade movements of 1 to 2 Inches could occur if
subgrade soils become saturated. If a finished basement Is planned for the residence, given the
engineering characteristics of clays, consideration should be given to use of structural floor
systems In basement areas or ground modification, such as subexcavatlon and moisture
conditioning, to the depths recommended above. The on-site soils, free of organics and debris,
are suitable to support llghUy loaded slabs-on-grade. Slabs should be separated from all load
bearing waifs and columns with expansion joints that allow at least 2 inches of vertical
movement. Control joints should be used to reduce damage from shrinkage cracking. All fill
below slabs should be compacted to at least 95 percent of maximum standard Proctor dry
density at 0 to 3 percent above optimum moisture content.
SUBSURFACE DRAINAGE
Surface water typically flows through permeable wall backfill and collects et the backfill
and natural soil Interface resulting In saturated foundation solls and/or wet crawlspace areas
and/or basement conditions. To reduce water accumulation outside foundation walls and In
crawlspace areas and/or basements, a foundation drain should be Installed around the exterior
of foundation walls. If foundations are planned at depths greater than that recommended, we
should be contacted to provide additional subsurface drain recommendations.
The drain should consist of a 4-inch diameter, perforated pipe encased in free draining
gravel. The gravel should be % to 1.5-inch washed rock with less than 5 percent fines. The
drain should be provided with a gravity discharge such as a sump pit where water can be
removed by pumping or daylighted. The pipe should be sloped at a minimum of 0.5 percent and
be installed 12 to 18 Inches away from and parallel to the footing foundation. The bottom of the
pipe should be at least 4 inches below the bottom of footing level at the high point. Crawlspace
areas should also be provided with adequate ventilation.
SURFACE DRAINAGE
Surface drainage is crucial to the performance of foundations and flatwork. We
recommend the ground surface surrounding the building be sloped to drain away from the
structure. We recommend a slope of at least 6 Inches in the first 10 feet for landscape areas.
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Lota 3 and 4, Creek Side Estates PRljed No. 27-135
Paved areas can be sloped at 1 to 2 percent away from the structure. Backfl~ around
foundations should be moisture conditioned and compacted as recommended In the SITE
DEVELOPMENT section. Roof downspouts and drains should discharge beyond the backfill
area .
PERCOLATION TEST RESULTS
Three percolation tests were performed near Boring P-1. The following table presents
the overall (4 hour) percolation rates for each of the three percolation holes. Each percolation
hole was orlglnaUy drilled to 3 feet with a 6-lnch auger and the holes were presoaked overnight
The following day, all three holes were still holding water. Holes were cleaned out with a hand
auger, pea gravel was added to prevent scour, and then sk>tted (environmental) pipe was
placed In each hole for accurate measurements.
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r --i.--' .-_--~,, ·,.·-·a··~) :.-i )-.. r·~1· .... :·:::-.,-~ .. ,~.-.;.~.;---l faJ.;1-1}-_:~ • '~€_i~·::~l"1:L:Jrla~r!'. ~,:_J;l Jb '.~Q~'.!~!~D~~~t:::: _:r~
South 448
Adiacent 1250
North 833
Average 844
LIMITATIONS
The analyses and recommendations presented In this report are based upon our data
obtained from the test holes at the indicated locations, field observations, laboratory testing, our
understanding of the proposed construction and other information discussed in this report. It is
possible that subsurface conditions may vary between or beyond the points explored. The
nature and extent of such variations may not become evident until construction. If variations
appear, we should be contacted Immediately so we can review our report in light of the
variations and provide supplemental recommendations as necessary. We should also review
the report if the scope of the proposed construction, Including the proposed loads, finished
elevations or structure locations , change from those described in this report. The conclusions
and recommendations contained In this report shall not be considered valid unless Yeh and
Associates reviews the changes and either verifies or modifies the conclusions of this report in
writing.
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Loi! 3 and 4, Creek Side Ea1ates ProJect No. 27-135
The scope of services for this project did not include, specifically or by impllcation, any
environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or Identification or
prevention of pollutants, hazardous materials or conditions or blologlcal conditions. If the owner
Is concerned about the potential for such contamination, conditions or pollution, other studies
should be undertaken.
The report was prepared In substantial accordance with the generally accepted
standards of practice for geotechnlcal engineering as exist In the site area at the tlme of our
Investigation. No warranties, expressed or Implied, are Intended or made. The
recommendations in this report are based on the assumption that Yeh and Associates will
conduct an adequate program of construction testing and observation to evaluate compliance
with our recommendations.
Respectfully Submitted,
Keith E. Asay
Staff Engineer
Reviewed By:
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Project No. 27-135
100 0 ~D 100 ... --·1--1-•1
SCALE• 1' = 100'
LEGEND:
Tli-1 e Indicates Approximate Test Hole Location
P-1 Indicates Approximate Percolation Profile e Hole Location
Approximate Loca~ions of
Exploratory Borings
Figure 1
Tfl.1
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P..1
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............................ 0 Legend
UlllZ tW ................ ......................... 5
7112 1an2
$ample Types
D MDdllledClllbnfl ..... lbt.,.nllcl 13"2 lndic.t llll II
llllMI flam I 1<40paunll111-""'9 30 lndm-UMd lo
"""'2ft:h L0.--12 lndm.
Soll Lithology
~ a.y,llly, ,,.,..,,.,..,, llltldlutrldto d, 11..-1tnc11t1o
~ •"'-lollf!IY(a.).
mn 111, l/lfl'llf undy ............ .,,,,, lllOlll loWll. llnlMI.,.., WU ,,.,.
1 ............ ,s .. .. ....................... 10
7112 1 .............. . ......................... 15
= -I 7112 1112 20 .............. . ......................... 20
2 .............. .
30 .............. . ~~~ ....................... ,.,4 .................................................... 30
..................... ,. •• ~ ................................... 9 ............................................. 35
Groundwater
~ lndlcalol ~c11p1111t• of drllng on 411H<fT.
~ ~ dlll)1ld ll"IU,....,dlpll an 4/Zl/(/f.
. Lots 3 and 4, Creek Side Estates I , jYEH AND ASSOCIATES INC.
.GEOTECHNICAL ENGINEERING CONSUfrANTs P
eel Number: 27-135
3 .0
IGraph 1
• ••
~ • 2.0 .. WATER ADDED +" I •
't'
f ~ a
1.0
A
0 u o.o
•
-1.0
0.1 1 10 100
Applied Normal Pressure, kif
1.0
fGnph2
0.0 .,
-1.0
t.. • '\
f -2.0 ~ -• I -3.0
I' 4.0 "'" Cl • ~\
I C> ~ -5 .0 ...
:i ~ ~~ -·6.0 C> a • C> WATER ADDED u -7.0 -
•
-8.0 •
·9.0
0.1 1 10 100
Applied Normal Pressure, ksf
Graph Boring Natural Dry Mollture Swell(+)/ SWELL/
Depth(ft, Content Coasolidadon(-) Soll Delcripdon CONSOLIDATION Number Number Density (pd) (%) (%) GRAPH
1 TH-1 4 109 11.7 2.6 Clay, silty (CL) Drawn By: KEA
2 TH-1 9 98 20.7 ·1.8 Silt, sandy (ML) Checked By: RDJ
Job No: 27-135 Project Name: Lots 3 and 4, Creek Side Estates Figure3 YEH & ASS()I ·1 ~TE~. INL.
t.O
Grapbl
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~ . +' 0.0 -~ ! \ ~ WATER ADDED
'ii' ' \ ! ~ "'-:; -1.0 .. ~ a ~ t.J ~r--
~ ~
-2.0
0.1 1 10 100
Applied Normal Prasure, ksr
1.0
IGraphl
~
0.0
~ ~ • "' +' I -1.0 '\ 'i' • ~ .. I -2.0 t "" ~ • ,,
d -3.0 ~
~
-
~
WATER ADDED
' I I 111 11 -4.0
O.J 1 10 100
Applied Normal .Pressure, kif'
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Gnph Boring Natural Dry Moisture Swell(+)/ SWELL/
Depth(ft] Content ConsoUdatlon(-) Soll Destrlptloo CONSOLIDATION Number Number Density (pc( (%) (%) GRAPH
1 m-2 4 99 13.S 1.3 Clay, silty (CL) Drawn By: KEA
2 Til-2 9 99 20.1 -0.6 Clay, silty (CL) Checked By: RDJ
Job No: 27-13S Project Name: Lots 3 and 4, Creek Si de Estates Figure4 l'EH &A iSUCIAl·E~. JNt..:.
-~ YEH &ASSOCIATES, INC
Project No: 27-135
Samole Location Moisture
Test Depth Sample Content Dry Density
(pd) Hole (ft) Type (%)
TH-1 4 CA 11.7 109
9 CA 20.7 98
14 CA 27.0 97
P-1 4 CA 10.1 108
TH-2 4 CA 13.5 99
9 CA 20.1 99
14 CA 21.6 103
19 CA 28.2 93
r.11 -lnrl~ mnttmeo C".Allfnm!A !lt::IMnlP.
NL -Indicates non-liquid
NP -Indicates non-plastic
Summary of Laboratory Test Results
Project Name: Lots 3 and 4, Creek Side Estates
Grain Size Anelvsis Atterberu llmitS Water swell(+)/
Gravel Sand Fines Soluble Consoldation (-)
>#4 <#200 LL PL Pl Sulfate under 1,000 J>8f
(%) (%) (%) (%) (%)
0.294 2 .6
-1.8
76
70 27 18 9
1.3
-0.6
74 NL NP NP
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son Description
Clay, allty (CL)
Slit. slghUy sandy (ML}
Slit, slghUy sandy (ML)
Clay, silty (CL)
Clay, silly (CL)
Clay, silty (Cl)
Slit, slightly sandy (ML)
Slit, slightly sandy (Ml)
;