HomeMy WebLinkAboutGeotechnical Investigation Letter 09.04.2018I{udelleston-Berry
Engineerlng & Testing, LLC
640 White Avenue
Grand Junction, Colorado 81501
Phone: 970-255-8005
Fax: 970-255-68 I 8
In fo@huddl estonberry. com
Subject
September 4,2018
Project#O1 509-0021
RC Schneider Construction
90 Caballo
Carbondale, Colorado 81623
Attention: Mr. Bob Schneider
Geotechnical Investigation
307 Pinyon Mesa Drive
Glenwood Springs, Colorado
Dear Mr. Schneider.
This letter presents the results of a geotechnical investigation conducted by Huddleston-Berry
Engineering & Testing, LLC (HBET) at 307 Pinyon Mesa Drive in Glenwood Springs,
Colorado. The site location is shown on Figure 1. The proposed construction is anticipated to
consist of a residential structure. 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, the site was generally open and fairly flat. Vegetation consisted
primarily of grasses and weeds. The site was bordered to the north by open land, to the east and
west by vacant lots, and to the south by Pinyon Mesa Drive.
Subsurface Investigation
The subsurface investigation included one test pit on the lot. Test Pit TP-l was excavated to a
depth of 9.0 feet below the existing ground surface. A typed test pit log is included in Appendix
A.
The test pit encountered 1.0 foot of topsoil above brown, moist, medium stiff to soft lean clay
with sand soils to the bottom of the excavation. Groundwater was not encountered in the test pit
at the time of the investigation.
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Laboratory Testins
Laboratory testing was conducted on samples of the native soils encountered in the test pit. The
testing included grain-size analysis, Atterberg limits determination, and natural moisture content
determination. The laboratory testing results are included in Appendix B.
The laboratory testing results indicate that the native clays are moderately plastic. Based upon
the laboratory testing results and upon our experience in the vicinity of the subject site, the native
clay soils are anticipated to be slightly expansive. V/ater soluble sulfates were detected in the
sites soils in a concentration of 0.23%.
Foundation Recommendations
Based upon the results of the subsurface investigation and nature of the proposed construction,
shallow foundations are recommended. Spread footings and monolithic (turndown) structural
slabs are both appropriate foundation alternatives. However, as discussed previously, the native
clay soils are anticipated to be slightly expansive. Therefore, in order to limit the potential for
excessive differential movements, it is recommended that spread footing foundations be
constructed above a minimum of 24-inches of structural fill and that monolithic structural slab
foundations be constructed above a minimum of 36-inches of structural fill.
Due to the plasticity of the native clay soils, the native clay soils are not suitable for reuse as
structural fill. Imported structural fill should consist of a granular, non-expansive, non-free
drainins material such as crusher fines or CDOT Class 6 base course. Unless it can be
demonstrated that the materials are not free-draining, pit-run materials should not be used as
structural fill.
For spread footing foundations, the footing areas may be trenched. However, for monolithic slab
foundations, the structural fill should extend across the entire building pad area to uniform depth
below the turndown edges. Structural fill should extend laterally beyond the edges of the
foundation a distance equal to the thickness of structural fill.
Prior to placement of structural fill, 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 95% of the standard Proctor maximum dry density, within + 2Yo of the optimum
moisture content as determined in accordance with ASTM D698. Structural fill should be
moisture conditioned, placed in maximum 8-inch loose lifts, and compacted to a minimum of
95o/o of the standard Proctor maximum dry density for fine grained soils and modified Proctor
maximum dry density for coarse grained soils, within*2o/o of the optimum moisture content as
determined in accordance with ASTM D698 and Dl557, respectively.
For structural fill consisting of imported granular materials and foundation building pad
preparation as recommended, a maximum allowable bearing capacity of 1,500 psf may be used.
In addition, a modulus of subgrade reaction 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-inches below
the finished grade.
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Water Soluble Sulfates
As discussed previously, water soluble sulfates were detected in the site soils in a concentration
of 0.23%. 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 should be used.
Lateral Earth Pressures
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 drøínins, non-expansive material,
we reconìmend that the walls be designed for an active equivalent fluid unit weight of 55 pcf in
areas whers no surcharge loads are present. An at-rest equivalent fluid unit weight of 75 pcf is
recommended for braced walls. Lateral earth pressures should be increased as necessary to
reflect any surcharge loading behind the walls.
Floorins Svstem and Exterior Flatwork Recommendations
In general, slabs-on-grade cannot develop sufficient bearing pÍessures to resist swelling
pressures. Therefore, some movement of slabs-on-srøde should be expected. As a result,
framed floor are recoÍrmended for living areas. However, to reduce the risk of large scale
movements of slabs-on-grade, such as the garage slab, it is recommended that non-structural
floor slabs be constructed above a minimum of l8-inches of structural fill with subgrade
preparation, structural fill materials, and fill placement be in accordance with the Foundation
Recommendations section of this report. It is recommended that exterior flatwork be constructed
above a minimum of l2-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 partition walls should include a
framing void or slip joint which permits a minimum of 2-inches of vertical movement.
Drainase Recommendations
Proper grading and drainage is criticalto the long-term performance of the structure. 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 frst ten feet away from the structure. It is also recommended that landscaping within five
feet of the structure include primarily desert plants with low water requirements. In addition, it
is recommended that irrigation, including drip lines, within ten feet of foundations be minimized.
HBET recommends that downspout extensions be used which discharge a minimum of 10 feet
from the structure. However, if subsurface downspout drains ate used, they should be carefully
constructed of solid wall PVC pipe and daylight a minimum of 15 feet from the structure. In
addition, an impermeable membrane is recommended below subsurface downspout drain lines.
Dry wells should not be used.
aJX:U008 ALL PROJECTS\01 509 - RC Schneider Construction\01509-0021 307 Pinyon MesaU00 - Geo\o1509-0021 LRo829l 8.doc
307 Pinyon Mesa Drive
#0 I 509-002 I
09104/r8
As discussed previously, shallow groundwater was not encountered at the time of the
investigation. However, a perimeter foundation drain is recommended to limit the potential for
surface water to impact the structure. In general, the perimeter foundation drain should consist
of prefabricated drain materials or perforatecl pipe ancl gravel 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 1.0% to daylight or to a sump with pump. An impermeable membrane should be placed at the
base of the drain to limit the potential for moisture to infiltrate vertically down 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, only one test pit was conducted at the site. Therefore, the precise
natnre ancl extent of any subsurface variability may not become evident until constnrction. The
recommendations contained herein are designed to reduce the risk and magnitude of movements
and it is extremely critical thaf ALL of the recommendations herein be applied to the design and
construction. However, HBET cannot predict long-term changes in subsurface moisture
conditions andlor the precise magnitude or extent of any volume change in the subsurface
materials. Where sìgníficant increases in subsurface moisture occur due to poor gradíng,
ìmproper stormwater mdnagement, utilitv líne føilure, excess irrìgation, or anv other cause,
during or øfter constructíon. signilicant movements are øossíble.
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, special
inspections, and engineering oversight during ALL phases of the construction to ensure
conformance with the recommendations herein. In addition, the homeo\¡r'ners should be provided
a copy of this report and made fully aware 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 this report.
Respectfully Submitted:
Huddleston-Berry Engineering and Testing, LLC
Michael A. Berry, P.E.
Vice President of Engineering
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FIGURES
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F¡GURE 2Site Plan
APPENDIX A
Typed Test Pit Log
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APPENDIX B
Laboratory Testing Results
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640 Write Avenue, Unit B
Grand Junction, CO 81501
970-255-8005
970-2ss-6818
GRAIN SIZE DISTRIBUTION
CLIENT RC Schneider Construction PROJECT NAME 307 Pinvon Mesa Dr
PROJECT NUMBER 01509-OO2I PROJECT LOCATION Glenwood Sr:rinqs. tü
U.S. SIEVE OPENING IN INUHES I u.s. sth.vh. NUMljblìs HYDROMËTER
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GRAIN SIZE IN MILLIMETERS
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COBBLES GRAVEL SAND SILT OR CLAYcoarsefinecoarsemediumfine
Specimen ldentification Classification LL PL PI Cc Cu
O TP-1, GB1 gt201g LEAN CLAYwith SAND(CL)32 19 13
Specimen ldentification D100 D60 D30 D10 %Gravel %Sand %sitt o/oClay
o TP-1, GBI 8t2018 2 0.0 17.2 82.8
Huddleston-Berry Engineering & Testing, LLC
640 White Avenue, Unit B
Grand Junction, CO 81501
970-255-8005
970-2ss-68t8
ATTERBERG LIMITS' RESULTS
CLIENT RC Schneider Construction PROJECT NAME 307 Pinvon Mesa Dr
PROJECT NUMBER 01509-0021 PROJECT LOCATION Glenwood Sorinos. CO
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Specimen ldentification LL PL PI #200 Classification
o TP-1, GB1 812018 32 19 13 83 LEAN CLAYwith SAND(GL)
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CLIENT RC Schneider Construction PROJECT NAME
MOISTU RE-DENSITY RELATIONSHIP
PROJECT NUMBER 01509-0021 PROJECT LOCATION Glenwood Sprinqs, CO
307 Pinvon Mesa Dr
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Samplc Datc:
Sample No.:
Source of Material:
Description of Material
8t17t2018
18-0627
145 TP.1
LEAN CLAYwith SAND(CL)
Test Method:ASTM D698A
140
135 TEST RESULTS
Maximum Dry Density 110.0 PCF
Optimum Water Content 16.0 %
130
125
GRADATTON RESULTS (% PASS¡NG)
#200 #4 3t4"
80 100 100
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ATTERBERG LIMITS
1 20
LL PL PI
32 t9 13
115
110
105
100
95
90
Curves of 100% Saturation
for Specific Gravity Equalto:
2.80
2.70
2.60
0 5 15
WATER CONTENT, %
10 20 25 30