HomeMy WebLinkAboutGeotechnical Study 9.20.2018J ,-tatf'F*rt^***
RECEIVED
FEB 0 q 20ß
GARF¡ELD COUNTY
COMMUNITY DEVELOPMENT
640 White Avcnue
Grand Junst¡otr, Colorado 81501
Phone: 970-255-8005
Pax:970-255{818
Info@huddlestonberry.com
Huddle ston-Berry
Enginecriog & Tcotln¡r LLC
September 20,2418
Project#01303-0017
Clayton Homes
671 23 Road
Grand Junction, Colorado 81505
Attention: Mr. David Mahovsþ
Subject:Geotechnical Investigation
Mountain Shadow Place
Glenwood Springs, Colorado
Dear Mr. Mahovsky,
This letter presents the results of a geotechnical investigation conducted by Huddleston-Berry
Engineering A festing, LLC (IIBET) for the Mountain Shadow Place project in Glenwood
Springs, Colorado. The site location is shown on Figure 1 - Site Location Map. The prop-osed
cónstruction is anticipated to consist of three new residential structures. The scope of our
investigation included evaluating the subsurface conditions at the site to aid in developing
foundation recommendations for the proposed consfuction.
Site Conditions
At the time of the investigation, the site was occupied by an existing residential structure. The
site was fairly flat. Vegetation consisted primarily of weeds and grasses, \Ãrith a few trees. The
site was bordered to the north, south, and west by existing residences, and to the east by Cactus
Drive.
Subsur{rce Investlsation
The subsurface investigation included three test pits as shown on Figure 2 - Site Plan. The test
pits were excavated to a depth of 8.0 feet below the existing ground surface. T¡.ped test pit logs
are included in Appendix A.
As indicated on the logs, the subsurface conditions at the site were slightly variable. Test Pit TP-
I , conducted on Lot l, encountered I .0 foot of topsoil above brown, moist, stiff sandy lean clay
soils to the bottom of the excavation. Groundwater was not encountered in TP-l at the time of
the investigation.
Test Pit TP-2, conducted on Lot 2, encountered 1.0 foot of topsoil above brown, moist, stiff
sandy lean clay to a depth of 3.0 feet. The clay was underlain by tan, moist, dense siþ gravel
with sand to the bottom of the excavation. Groundwater was not encountered in TP-z at the time
ofthe investigation.
Mountain Shadow Place
#01303-0017
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addition, fill materials were encountered in
Therefore, in order to provide a uniform
Test Pit TP-3, conducted on Lot 3, encouutered 3.0 feet of sandy lean clay fill materials above a
thin layer of asphalt pavement. The asphalt was underlain by tan, moisto medium dense to dense
silty gravel with sand to the bottom of the excavation. Gror¡ndwater was not encourtered in TP-
3 at the time of the investigation.
Laboreto¡"y Testine
Laboratory testing was conducted on sanples of the native soils encountered in the test pits. The
testing included grain size analysis, Atterberg limits determination, natural moistr¡re content
water soluble sulfates content determination, and ma¡<imum dry densþ and optimum moisture
content (Proctor) detemrination. The laboratory testing results are included in Appendix B.
The laboratory testing results indicate that tlre native clay soils are moderately plastic. Due to
the presence of gravels, undisturbed samples of the clays were unable to be collected for
swell/consolidation testing. However, based upon the Atûerberg limits of the materials, the
native clay soils are anticipated to be slíghtly expansive. 'Water soluble sulfates were not
detected in the site soils.
The native gravel soils were indicated to be slightly plastic. In general, the native gravel soils
are anticipaûed to be fairþ stable under loading.
Foundetion Recommend¡tions
Based upon the results of the subsurface investigation and nature of the proposed constructior¡
shallow foundations are recommended.Spread footings and monolithic (turndown) sfuctural
are However, as discussed previousþ, the native
clay soils are anticipated to be
TP-3 and the actual extent rs
bearing statm and limit the potential for excessive difflerential movements, it is recommended
that the foundations be constructed above a minimum of 24-inches of structural fill.
Due to their plasticity, the ûative clay soils are not suitable fbr reuse as structural fill. The
existing fill and pavement materials are also not suitable for reuse as sfructural fill. However, the
native gravel soils are suiøble for reuse as stuctural fill; provided particles in excess of 3-inches
in diameter a¡e removed. Imported structural fill should consist of a granular, non-expansive,
non-ftee drainlns material such as crusher fines or CDOT Class 6 base course. Unless it can be
demonstrated that the maærials are not ûee-draining, pit-run materials should not be used as
structual fill.
For spread fnoting foundations, the footing areas may he trenched" However, for moncllithic slab
foundations, the strucfi.nal fill should extend across the entire building pad area to a depth af 24-
inches below the bottom of the turndown edge. Structural fill should extend laterally beyond the
edges of the foundations a distance equal to the thickness of structrnal fill for both foundation
types.
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Prior to placement of structural fill, all fill materiats should be completely removed from below
the foundations. It is recommended that the bottom of the foundation excavation be scarified to
a depth of 6 to 9 inches, moisture conditioned, and compacted to a minimum of 95o/o of the
standard Proctor maximum dry density, within + ZYo of the optimum moisü¡re content as
detersrined in accordance with ASTM D698. Structural fill should be moisture conditioned,
placed in maximum 8-inch loose lifts, and compacted to a minimum of 95% of the standard
Proctor maximum dry density for fine grained soils and modified Proctor ma¡cimum dry density
for coarse grained soils, within + zyo of the optimum moisture content as determined in
accordance with ASTM D698 and D1557, respectively.
Structural fitl should be extended to within O,I-feet of the bottom of the foundation. No more
than Q.I-feet of gravel should be placed below the footings or tumdown edge as a leveling
course.
For structural fill consisting of suit¿ble native soils or imporæd granular materials, and
foundation building pad preparation as recommended,a marimum allowable
may be used. In addition, a modulus of may
fîll consisting of the native gravel soils and a modulus of 250 pci may be used for
structural fill consisting of crusher fines or base course. Foundations subject to frost should be at
least 36-inohes below the finished grade.
Any stemwalls or retaining walls should be designed to resist lateral earth pressures. For backfill
consisting of the native soils or imported granular, non-ûee draining, non-expansive material, we
recommend that the walls be designed for an active equivalent fluid unit weight of 50 pcf in
areas where no surcharge loads are present. An at-rest equivalent fluid unit weight of 70 pcf is
recommended for braced walls. Latenl earth pressures should be increased as necessary to
reflect any surcharge loading behind the walls'
As discussed prevíously, v¡ater soluble sulfates were not detected in the site soils. However,
water soluble sulfate concentrations can vary widety in lñ/estem Colorado. Therefore, at a
minimum, Type I-II sulfate resistant cement is recommended for construction at this site.
Non-Structural Floor Slab and Exterior Fl¡twork Recommendations
In order to reduce the potential for excessive differential movements, it is recommended that
non-süuctural floating floor slabs be constructed above a minimum of l8-inches of stuctural fill
with subgrade preparation, structural fill materials, and fill placement be in accordance with the
Foundation RecommendafÍozs section of this report. It is recommended that exterior flatwork be
constructed above a minimum of l2-inches of süuctural fill.
I)rain¡ee Recommendations
Grudínp and draínøse øre crütìcal for the lone-term nerforrrunce of the structures and grading
aroun¿ the structures should be designed to carry precipitation and runoff away from the
structures. It is recommended that the finished ground surface drop at least twelve inches within
the first ten feet away from the structures. It is also recommended that landscaping within five
feet of the structu¡es include primarily desert plants with low water requirements. In addition, it
is recommended that automatic inigation, including drip lines, within ten feet of foundations be
of
1,500 psffficEil
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IIBET recommends that downspout extensions be used which discharge a minimum of l0 feet
from the structures or beyond the backfill zone, whichever is grcatcr. However, if subsurface
downspout drains are utilized, they should be carefully coustnrcted of solid-wall PVC and should
daylight a minimum of 15 feet from the structures. In addition, an imperrneable membrane is
recommended below subsuface downspout drain lines. Dry wells should not be used.
General Notes
The recommendations included above are based upon the results of the subsurface investigation
and on our local experience. These conclusions and recommendations are valid only for the
proposed coustruction.
As discussed previously, the subsurface conditions in the test pits were slightly variable.
However, the precise nature and extent of subsurface variability may not become evident until
construotion. The recommendations contained herein are designed to reduce the risk and
magnitude of structural movements and it is extrernely critical thatALLof the recommendations
herein be applied to the design and constuction. Howeven HBET cannot øredict lonp-tetm
changes ín subsa¡faee n oisture condlllons ønd/ot the o¡ecíse ,no.míludc or úent of anv
volume chønse ín the native soíls. llhe¡e slsníficant lncreases ín subsutface ,noßture occar
du¿ to ooor sradíns, improoer sto¡mwater ntnnaøement. uÍ¡lìtv lìne faìlure, scess Ûnísatíon,
or other cause, du¡íns o¡ øfter construction. sígnilicønt rrrovemenß are possíble.
In additioq the success of the structure foundations, slabs, etc. is critically dependent upon
proper constuction. Therefore, HBET should be retained to provide materials testing, special
inqpections, md engineering oversight during ALL phases of the construction to ensure
conformance with the recommendations herein. In addition, the homeowners should be provided
a copy of this report and infomred of the risks associated with living in an area of moisture
sensitive soils.
We are pleased to be of service to your project. Please contact us if you have any questions or
comments regarding the contents of thls repoÍt.
Respectfi rlly Submitted :
Huddleston-Berry Engineering and Testing, LLC
Michael A. Berry, P.E.
Vice President of Engineering
4
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APPENDIX A
Typed Test Pit Logs
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Á,PPENDD( B
Laboratory Testing Results
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Huddleston-Berry Engineering & Testing; LLC
6¿10 White Arcnue, Unit B
Grand hrnction, CO 81501
970-255-8005
970-255.6818
GRAIN SIZE DISTRIBUTION
CLlEilT Clavton Homes PROJECTMÍr,E l[ountai¡lhadqüv_Plaæ --***
PROJECT LOCATION Glen'¡tood Sr¡inqs, COPROJECT NUMBER 01303-OO.I7
U S SIËVE OPÊNING IN INCHES I U S SIEVE NUMBERS
510 1416 20 30 40 50 60 1001
HYDROMETER8 43 2 3i41i23l8346
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85
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75
70
65
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55
50
45
40
35
30
26
20
15
10
5
0
100 10 1
GRAIN SIZE IN MILLIMETERS
0.1 0.01 0.001
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COBBLES GRAVEL SAND SILT OR CLAY
co6fse fine coarge mEdium fine
Spccimen ldentification Classification LL
SANDY LEAN 32
SILTY GRA\rEL wiül 23
PL PI Cc Cu
o TP-1, GBt 8fi8 18 14
E TP-2, cBl 8fi8 21 2
Specimen ldentification D100 D60 D30 D10 %Gralal %Sand o/oSilt %Clay
o TP-î. GB1 Iñ8 25 0.082 t4.9 26.0 59.0
E TP-2, GBI 8/18 97.6 9.7t9 0.fl 46.0 27.2 26.8
Huddleston-Berry Engineering & Testing LLC
ó40 White Awnue, UnitB
Grand Junction, CO 81501
970-255-8005
970-255óß18
ATTERBERG LIIT'IITS' RESULTS
PRO.ECT LOCÂTIONPROJECT N$iBER
PRO.ECT l,lAftlE Mounlâ¡n Shadol PlaceCLENTClâvton
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LIQUID LIMIT
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ClassificationPLPI#200LLSpecimen ldentification
SANDY LEAN CLAY{CL)N2 18 14 59TP-1, GBI 813112018
27 SILTY GRAVEL w¡th SAND(GM)23 21 2TP-2, GB{ 8/3112018
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PRO.ECT NAME fVlountain Shado,v Place
PRO.TECT LOCATION Gbnwood SprinEs, e,O
Junotion, CO 8150t
CLIENT Clej4on Hofies
FRO.'ECT NtitBËR 01301,0017
Huddleston-Berry Engineering & Testing LL,C
640 White Arænue, Unit B
970-255-800s
970-2ss.68r I
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Sample Date:
Sample No.:
Source of Materiah
Description of Material
8/31/2018
GBI
145 TP-{ __ *-*
SANDY LEAN CLAY{CLI
Test Method:ASTM D698A
140
135 TEST RESULTS
Maximum Dry Density 115.0 PCF
Optimum WaterConÞnt 14.A olo
130
125
GRADAflON RESULTS (7o P¡{SS|NG)
#200 #4 3t4"
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ATTERBERG LMÍTS
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LL PL PI
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115
Gunæs of I 00% Saturation
for Specific Gravig Equalto:
110
2,80
2.70
2.60
105
100
9ı
90
5 15
WATERCONTENT %
0 10 20 25 30