HomeMy WebLinkAboutGeotechnical Investigation 12.20.16Huddleston-Berry
Engineering & Testing, LLC
Clayton Homes
2394 Highway 6 & 50
Grand Junction, Colorado 81505
Attention:
Subject:
Mr. Steve Snyder
Geotechnical Investigation
1851 County Road 306
Parachute, Colorado
Dear Mr. Snyder,
640 White Avenue, Unit B
Grand Junction, Colorado 8150 I
Phone: 970-255-8005
Fax: 970-255-6818
lnfo ,ahuddlcstonhl!n .com
December 20, 2016
Proj ect#O 13 03-0007
This letter presents the results of a geotechnical investigation conducted by Huddleston-Berry
Engineering & Testing, LLC (HBET) at 1851 County Road 306 in Parachute, Colorado. The
proposed construction is anticipated to consist of a single-family residence. The site location is
shown on Figure 1 -Site Location Map. The scope of our investigation included evaluating the
subsurface conditions at the site to aid in developing foundation recommendations for the
proposed construction.
Site Conditions
At the time of the investigation, most of the site was open. However, an existing residence and
outbuildings were present at the site. Vegetation consisted primarily of grasses and weeds with a
few bushes and trees. The site was bordered to the north and south by rural residential
properties, to the east by rural residential property and County Road 306, and to the west by a
property with a gas well pad.
Subsurface Investigation
The subsurface investigation included two test pits as shown on Figure 2. Test Pits TP-1 and TP-
2 were excavated to depths of 10.0 and 8.0 feet below the existing ground surface, respectively.
Typed test pit logs are included in Appendix A.
As indicated on the logs, the subsurface conditions were variable. Test Pit TP-1 encountered 1.0
foot of topsoil above tan, moist, medium dense sandy fat clay with trace gravel and cobbles to a
depth of 7.5 feet. Below the clay, tan, moist, dense clayey gravel with sand, cobbles, and
boulders extended to the bottom of the excavation. Groundwater was not encountered in TP-1 at
the time of the investigation.
1851 County Road 306
#01303-0007
12/20/16
Test Pit TP-2 encountered 1.0 foot of topsoil above tan, moist, dense clayey gravel with sand,
cobbles, and boulders to the bottom of the excavation. Groundwater was not encountered in TP-
2 at the time of the investigation.
Laboratory Testing
Laboratory testing was conducted on samples of the native soils collected from the test pits. The
testing included grain-size analysis, Atterberg limits determination, natural moisture content
determination, water soluble sulfates content determination, and maximum dry density and
optimum moisture content (Proctor) determination. The laboratory testing results are included in
Appendix B.
The laboratory testing results indicate that the native clay soils are highly plastic and that the
native gravel soils are moderately plastic. Due to the presence of large particles, undisturbed
samples of the native soils were unable to be collected for swell/consolidation testing. However,
based upon the Atterberg limits of the materials and upon our experience with similar soils in the
vicinity of the subject site, the native clay soils are anticipated to be moderately expansive and
the native gravel soils are anticipated to be slightly expansive.
Foundation Recommendations
In general, based upon the results of the subsurface investigation and nature of the proposed
construction the recommended foundation alternatives include spread footings, voided spread
footings, and isolated pads and grade beams. However, as discussed previously, the native soils
are anticipated to be expansive. Therefoue, in order to help limit the potential for excessive
differential movements, it is recommended that the foundations be constructed above a minimum
of 36-inches of structural fill.
Due to the potential for expansion of the native soils, the native soils are not suitable for reuse as
structmral fill. Imported structural fill should consist of a granular, non-expansive, non-free
draining material such as crusher fines, pit-run with high fines content, or CDOT Class 6 base
course. However, if pit-run is proposed to be used as structural fill, due to the wide variability in
pit-run materials in Western Colorado, HBET should be contacted to evaluate the pit-run and
ensure that the material contains an appreciable quantity of fines. In addition, for pit-run
structural fill, a minimum of six inches of crusher fines or Class 6 base course should be placed
on top of the pit-run to prevent large point stresses on the bottoms of the foundations due to large
particles in the pit-run.
Prior to placement of structural fill, it is recommended that the bottom of the foundation
excavation be proofrolled to the Engineer's satisfaction. No moisture should be added to the
subgrade. Structural fill should extend laterally beyond the edges of the foundation a distance
equal to the thickness of structural fill. 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 maximum dry density for
coarse grained soils, within ±2% of the optimum moisture content as determined in accordance
with ASTM D698 and Dl557C, respectively. Pit-run materials should be proofrolled to the
Engineer's satisfaction.
X :\2008 ALL PROJECTS\01303 -Clayton Homes\01303-0007 1851 CR 306\200 -Geo\01303-0007LR122016 doc 2
1851 County Road 306
#01303-0007
12/20/16
For structural fill consisting of imported granular materials, and foundation building pad
preparation as recommended, a maximum a1lowable bearing capacity of 2,500 psf may be used.
However, a minimum dead load pressure of 750 psf is recommended. Where the minimum dead
load is not achievable, such as for interior foundations, the dead load should be maximized to the
extent practical. Footings subject to frost should be at least 36-inches below the finished grade.
As discussed previously, water soluble sulfates were. detected in the site soils in a concentration
of 0.2%. This concentration of sulfates represents a severe degree of potential sulfate attack on
concrete. The International Building Code (IBC) specifies Type V cement for this concentration
of sulfates. However, Type V cement can be difficult to obtain in Western Colorado. Where
Type V cement is unavailable, Type I-II sulfate resistant cement is recommended.
Any stemwalls or retaining walls should be designed to resist lateral earth pressures. For backfill
consisting of the native soils or imported granular, non-free draining, non-expansive material, we
recommend that the walls be designed for an active equivalent fluid unit weight of 65 pcf in
areas where no surcharge loads are present. An at-rest equivalent fluid unit weight of 85 pcf is
recommended for basement walls or other braced walls. Lateral earth pressures should be
increased as necessary to reflect any surcharge loading behind the walls.
Non-Structural Floor Slab and Exterior Flatwork Recommendations
As mentioned above, expansive soils are present at the site. Therefore, a wood framed floor or
other structural floor system should be considered. However, where a floor slab is utilized, it is
important to note that due to the fact that slabs-on-grade do not generate sufficient loads to resist
heave, differential movement o{s/abs-on-grade sflould be anticipated. However, to help limit
the magnitude of movement, it is recommended that non-structural floor slabs be constructed
above a minimum of 24-inches of structural fill with subgrade preparation and fill placement in
accordance with the Foundation Recommendations section of this report. It is recommended that
exterior slabs-on-grade be constructed above a minimum of 12-inches of structural fill.
Slabs-on-grade should not be tied into or otherwise connected to the foundations in any manner.
In addition, where a floor slab is used, interior, non-bearing partitions should include a framing
void or slip joint which permits a minimum of 2-inches of vertical movement.
Drainage Recommendations
Grading and drainage are critical to the long-term performance of the foundations and slabs-on-
grade. Where grading and drainage permit moisture to infiltrate around the structure and down
below the foundations, sig11ifica11t structural movement is likelv. As a result, grading around
the structure should be designed to carry precipitation and runoff away from the structure. It is
recommended that the finished ground surface drop at least twelve inches within the first ten feet
away from the structure. It is also recommended that landscaping within ten feet of the structure
include primarily desert plants with low water requirements. In addition, it is recommended that
automatic irrigation within ten feet of foundations be minimized or controlled with automatic
shut off valves.
X \2008 ALL PROJECTS\01303 -Clayton Homes\01303-0007 1851 CR 306\200 -Geo\01303-0007 LR122016 doc 3
1851 County Road 306
#01303-0007
12/20/16
Huddleston-Berry @ t .,;~ ... 1 .\ f(•frc.11( .
It is recommended that conventional downspouts be utilized with extensions that terminate 5 feet
from the structure or beyond the backfill zone , whichever is greater. However, if subsurface
downspout drains are utilized, they should be carefully constructed of solid wall PVC pipe and
daylight at least 10 feet from the structure . In addition, an impermeable membrane 1s
recommended below subsurface downspout drain lines. Dry wells should not be used.
As discussed previously, groundwater was not encountered at the site. However, a perimeter
foundation drain is recommended to limit the potential for surface moisture to impact the
structure. In general, the perimeter foundation drain should consist of prefabricated drain
materials or perforated pipe and gravel systems with the flowline of the drain at the bottom of the
foundation (at the highest point). The perimeter drain should slope at a minimum of 1 % to
daylight or to a sump. An impermeable membrane is also recommended at the base of the drain
to limit the potential for moisture to infiltrate into the subsurface below the foundations.
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 construction.
As discussed previously, the subsurface conditions at the site were variable. However, the
precise nature and extent of any subsurface variability may not become evident until
construction. In addition, expansive soils were encouNtered in the subsurface and this resents a
risk of structural mo vement due to heave. The recomme11datio11s contained herein are designed
to reduce tile risk a11d magnitude of anv movements and it is extremelv critical that ALL oftlle
recommendations llereill be applied to tile design and construction. However, HBET cannot
predict long-term changes in subsurface moisture conditions and/or tile precise magnitude or
extent of swelling. Where significant increases in subsurface moisture occur due to poor
grading, improper stormwater management, utility line failure, excess irrigation, or other
cause, during or after construction, significant movements are possible .
In addition, the success of the structure foundations, slabs, etc. is critically dependent upon
proper construction. Therefore, HBET should be retained to provide materials testing and
engineering oversight during ALL phases of the construction to ensure conformance with the
recommendations herein. In addition, the homeowner should be provided a copy of this report
and made fully aware of the risks associated with living in an area of expansive 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 this report.
Respectfully Submitted:
Huddleston-Berry Engineering and Testing, LLC
Michael A. Berry, P.E .
Vice President of Engineering
X \2008 ALL PROJECTS\01303 -Clay ton Homes\01303 -0007 1851 CR 3061200 -Geo\0 13 03-0007 LR122016 doc 4
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APPENDIX A
Typed Test Pit Logs
CLIENT Clayton Homes
PROJECT NUMBER 01303-0007
DATE STARTED _1'--'1_,__./2,_,,3'--'/1-"'6 __ _ COMPLETED 11 /23/16
EXCAVATION CONTRACTOR --'C=l=le""'"nt'------------
EXCAVATION METHOD _T'--'-r=ac=k=h'-'/B"""'a'""c""k""'ho""'e'-----------
LOGGED BY CM CHECKED BY ___,M=A'--'B=----
NOTES 39 22 .576 ' -108 05 .4 91 '
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MATER IAL DESCR IPT ION
L:"' Sandy Fat CLAY with Organ ics (TOPSO IL) ;/,:4 .
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TEST PIT NUMBER TP-1
PROJECT NAME 1851 County Road 306
PROJECT LOCATION Parachute . CO
PAGE 1 OF 1
GROUND ELEVATION ____ _ TEST PIT SIZE ------
GROUND WATER LEVELS:
AT TIME OF EXCAVATION --'d=-'-------------
AT END OF EXCAVATION ___,d=-'-------------
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CLIENT C layton l'lomes
PROJECT NUMBER 01303-0007
DATE STARTED 11 /23/16 COMPLETED 11 /23/1 6
EXCAVATION CONTRACTOR ....:C::,,l"-"ie::..:.nt,,__ _________ _
EXCAVATION METHOD _T'-'r""'ac::::.k""h""'/B,._,a.,,c::.:.k'""ho,,__,e'------------
LOGGED BY CM CHECKED BY _,M.:.::A....::B=------
NOTES 39 22.593' -108 05.495'
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MATERIAL DESCRIPTION
Sandy Fat CLAY w ith Organ ics (TOPSO IL)
TEST PIT NUMBER TP-2
PROJECT NAME 1851 County Road 306
PROJECT LOCATION Parachute . CO
PAGE 1 OF 1
GROUND ELEVATION TEST PIT SIZE ------
GROUND WATER LEVELS:
AT TIME OF EXCAVATION -'d=--------------
AT END OF EXCAVATION _d~-----------
AFTER EXCAVATION ---------------
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APPENDIXB
Laboratory Testing Results
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970-255-6818
CLIENT Cla~ton Homes PROJECT NAME 1851 Count~ Road 306
PROJECT NUMBER 01303-0007 PROJECT LOCATION Parachute CO
U.S. SIEVE OPENING IN INCHES I U.S. SIEVE NUMBERS .1 HYDROMETER
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GRAIN SIZE IN MILLIMETERS
COBBLES I GRAVEL SAND SILT OR CLAY I I coarse fine coarse medium I fine
Specimen Identification Classification LL PL Pl Cc Cu
• TP-1, GB1 11/16 SANDY FAT CLAY(CH) 64 30 34
Ill TP-1, GB2 11/16 CLAYEY GRAVEL with SAND(GC) 39 21 18
Specimen Identification 0100 060 030 010 %Gravel %Sand %Silt %Clay
• TP-1, GB1 11/16 9.5 0.3 35.9 63.8
Ill TP-1, GB2 11/16 37.5 5.942 41.8 24.9 33.3
~ Huddl~on-B e-ry En gineeri ng & T esting, LLC ATTERBERG LIMITS' RESULTS ®~~ 640 Wh;teA"'""' Uo;t B ··, Grand Junction, CO 81501 J 970-255-8005
~ 970-255-6818
CLIENT Cla~ton Homes PROJECT NAME 1851 Count'.)'. Road 306
PROJECT NUMBER 01303-0007 PROJECT LOCATION Parachute CO
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Specimen Identification LL PL Pl #200 Classification
e TP1, GB1 11/23/2016 64 30 34 64 SANDY FAT CLAY(CH)
1Z1 TP-1, GB2 11/23/2016 39 21 18 33 CLAYEY GRAVEL with SAND(GC)
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CLIENT Clayton Homes
PROJECT NUMBER 01303-0007
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MOISTURE-DENSITY RELATIONSHIP
PROJECT NAME 1851 County Road 306
PROJECT LOCATION Parachute CO
Sample Date : 11/23/2016
Sample No.: GB1
Source of Material: TP-1
Description of Material : SANDY FAT CLAY(CH)
Test Method : ASTM D698A
TEST RESULTS
Maximum Dry Density 78.0 PCF
Optimum Water Content 31.5 %
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