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Providence Properties, LLC
Attn: Randy Clarno
PO Box 2648
Eagle, ID 83616
Dear Mr. Clarno:
July 9, 2013
File: BO13253A
RE: Geotechnical Engineering Evaluation
Eastwood Subdivision
Meridian, Idaho
Strata, A Professional Services Corporation (STRATA) is pleased to present our
authorized Geotechnical Engineering Evaluation for the proposed residential development
located to the southwest of the intersection of East Wrightwood Drive and South Locust Grove
Road, at 4515 South Locust Grove Road in Meridian, Idaho. Our Geotechnical Engineering
Evaluation's purpose was to explore the subsurface conditions in the proposed development
area and provide geotechnical recommendations to assist project planning, design and
construction. The attached report summarizes our field and laboratory test results and presents
our geotechnical engineering opinions and recommendations.
The following report provides specific geotechnical recommendations for preparing the
site, including earthwork activities, pavement design and stormwater design recommendations.
It is our opinion that geotechnical continuity with the project team throughout construction will
lessen the potential for errors and omissions related to our geotechnical recommendations.
The project design, owner, and construction team must read, understand and implement
this report in its entirety. Portions of the report cannot be relied upon individually without the
supporting text of remaining sections, appendices and plates. Our opinion is the success of the
proposed construction will depend on following the report recommendations, good construction
practices, and providing the necessary construction monitoring, testing and consultation to
verify that work has been constructed as recommended. We recommend STRATA be retained
to provide monitoring, testing, and consultation services to verify our report recommendations
are being followed.
We appreciate the opportunity to work with
involvement on this project throughout construction.
have any questions or comments.
Sincerely,
STRATA, Inc.
4t
Steve Worsley
Geologist
i
Gl � v�-
P.G.( ashington)
you and we look forward to our continued
Please do not hesitate to contact us if you
Cc: Mr. Kevin McCarthy/KM Engineering
SW/MGW/nm
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E.
TABLE OF CONTENTS
INTRODUCTION............................................................................................................1
PROJECT UNDERSTANDING.......................................................................................2
ExistingSite Conditions..................................................................................................
2
ProposedConstruction...................................................................................................2
SUBSURFACE EVALUATION PROCEDURES..............................................................2
SUBSURFACE CONDITIONS........................................................................................3
LABORATORYTESTING...............................................................................................
3
GEOTECHNICAL OPINIONS AND RECOMMENDATIONS...........................................4
Earthwork....................................................................................................................4
Site and Subgrade Preparation................................................................................4
Wet Weather/Soil Construction................................................................................5
Excavation Characteristics.......................................................................................6
Utility Trench Construction........................................................................................
6
StructuralFill and Compaction..................................................................................6
Table 1. Structural Fill Specifications and Allowable Use.............................................7
Geosynthetics...........................................................................................................
8
PavementSection Design............................................................................................8
General....................................................................................................................
8
Trafficand Subgrade................................................................................................
9
Table 2. Pavement Design Parameters.. ............... - ...............................................
.... 9
Asphalt, Aggregate Base Course and Subbase Materials........................................9
Pavement Section Thickness.................................................................................10
Table 3. Asphalt Pavement Design Section...............................................................
10
PavementMaintenance..........................................................................................
10
SiteDrainage.............................................................................................................10
ExteriorGrading.....................................................................................................10
InfiltrationRates.....................................................................................................11
Groundwater...........................................................................................................11
GEOTECHNICAL DESIGN CONTINUITY....................................................................12
EVALUATIONLIMITATIONS........................................................................................
12
Eastwood Subdivision
4515 South Locust Grove Road
Meridian, Idaho
File: B013253A
Page 2
Site Drainage
• Exterior grading
• Infiltration rates
• Groundwater
g Geotechnical Design Continuity
• Groundwater Monitoring
• Plan and specification review
• Construction observation and testing
5. Prepared and provided an electronic copy of our final report of geotechnical findings,
opinions and recommendations, including exploration logs and an exploration location plan.
Hard copies are available upon request.
PROJECT UNDERSTANDING
Existing Site Conditions
The proposed construction development is located southwest of the intersection of East
Wrightwood Drive and South Locust Grove Road. The proposed subdivision will be accessed
from East Wrightwood Drive. The site is currently undeveloped, and is bounded by residential
properties to the north, south east and west. East Wrightwood Drive parallels the proposed
subdivision to the north in an east -west orientation, and South Locust Grove Road parallels the
site to the east in a north -south orientation.
Proposed Construction
We understand the approximate 7.35 -acre development will consist of 22 buildable lots
with proposed asphalt paved roadways providing access to the development. Although
structures are not currently defined, we anticipate buildings will be supported by shallow
foundations and joist supported floors. We also anticipate stormwater will be disposed of via
seepage beds or swales.
SUBSURFACE EVALUATION PROCEDURES
STRATA accomplished subsurface exploration on July 1, 2013 via 3 exploratory test pits
extending 14.5 to 15 feet below existing ground surface. The approximate exploration locations
are illustrated on Plate 1, Exploration Location Plan, which also delineates the proposed
development. Test pit locations were established in the field by taping from existing site
features.
A professional geologist visually evaluated the soil encountered in each test pit and
logged the soil profile referencing the USCS. We provide a brief USCS explanation in Appendix
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Eastwood Subdivision
4515 South Locust Grove Road
Meridian, Idaho
File: B013253A
Page 4
We will retain soil samples for 90 days and discard after this time period unless we are notified
to store the samples for an extended period of time.
GEOTECHNICAL OPINIONS AND RECOMMENDATIONS
We present the following geotechnical recommendations to assist planning, design and
construction of the proposed Eastwood Subdivision, to be located southwest of the intersection
of East Wrightwood Drive and South Locust Grove Road in Meridian, Idaho as illustrated on
Plate 1 attached to this report. This report provides geotechnical design criteria for the
development which the design and construction teams must review to verify the applicability to
the planned construction. We base our recommendations on the results of our field evaluation,
laboratory testing, our experience with similar soil conditions and our understanding of the
proposed construction. If design plans change or if the subsurface conditions encountered
during construction vary from those observed during our field evaluation, we must be notified to
review the report recommendations and make necessary revisions.
Earthwork
Site and Subgrade Preparation
We currently do not have a grading plan for the proposed subdivision, but we anticipate
final grades will generally be within approximately 1 -foot of existing grades. At the time of
exploration, surficial vegetation and organic material was observed to a depth of approximately
6 to 10 inches. We recommend a minimum of 10 inches of topsoil with organic matter be
stripped beneath all planned improvements, including structural fill areas. This topsoil is not
suitable for use as structural fill and should be wasted or stockpiled on-site for landscape areas.
Test pits have been marked in the field with labeled standpipe piezometers or stakes.
Test pit locations should be surveyed prior to any earthwork site grading activities for future
remediation. Test pits which are located beneath paving, structural fill or building lot areas
should be re -excavated and replaced with structural fill in accordance with the
recommendations in this report.
The stripped subgrade in proposed structural fill, pavement and sidewalk areas should
be proof -rolled with a minimum of 5 passes from a heavy 5 -ton roller or equivalent. If weaving
or pumping is observed, those areas should be removed and replaced with structural fill.
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Eastwood Subdivision
4515 South Locust Grove Road
Meridian, Idaho
File: B013253A
Page 6
Excavation Characteristics
Based on exploration results, it appears the near surface soil encountered in exploratory
test pits may be excavated with conventional equipment. Excavations can cave and slough and
must be sloped back in accordance with Occupational Health and Safety Act (OSHA)
guidelines. Fine to coarse-grained soil is expected to be exposed in excavations throughout the
development area and should be temporarily sloped at 1.5HAV (horizontal to vertical). Due to
the potential for varying soil conditions at the time of construction, we recommend earthwork
contractors evaluate each excavation configuration specific to OSHA guidelines and seek
appropriate professional guidance to ensure excavation safety and stability.
Utility Trench Construction
Structural fill for backfilling utility trenches and all bedding should conform to Idaho
Standards for Public Works Construction (ISPWC) specifications, except that all trench backfill
must be placed and compacted to the structural fill requirements presented herein. Loose soil
must be removed from the base of utility trenches prior to placing pipe bedding. In addition, if
water is encountered, it must be removed from the base of the utility trench before placing pipe
bedding. We recommend utility pipes be placed on at least 4 inches of bedding placed over
undisturbed native soil, structural fill or otherwise supported according to the pipe manufacturer's
specifications and ISPWC requirements.
After bedding the pipe, place structural fill and compact it from the pipe invert to 1 -foot
above the top of the pipe with tamping bars and/or plate compactors to render the backfill in a firm
and unyielding condition. Thoroughly place and compact bedding below pipe haunches or the
zone between the pipe invert and the spring line. To accomplish backfilling, the distance between
the side of the pipe at the spring line and the trench wall should be at least 12 inches. The
remainder of the utility trench should be backfilled in accordance with the Structural Fill section of
this report.
Structural Fill and Compaction
All fill placed for the development must be placed as structural fill. The structural fill
requirements described in Table 1 below, in general, correlate to ISPWC material
specifications. Project structural fill products are described in Table 1 below.
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Eastwood Subdivision
4515 South Locust Grove Road
Meridian, Idaho
File: B013253A
Page 8
to the materials and conditions encountered. At a minimum, STRATA recommends coarse,
granular fill be placed in maximum 10 -inch lifts and compacted with 6 complete passes of a 10 -
ton vibratory or grid roller. Vibratory rollers must have a dynamic force of at least 30,000
pounds per impact per vibration and at least 1,000 vibrations per minute. Coarse fill must be
compacted to a dense, interlocking and unyielding surface. We recommend STRATA review
the soil and aggregate material planned for fill use and monitor compaction effort during
construction.
Geosynthetics
If earthwork contractors are unable to achieve subgrade compaction requirements
outlined in this report's Site Preparation section, geosynthetic fabrics may be used to improve
subgrade support when constructing on soft or wet soil. We recommend woven geosynthetics
at pavement subgrade elevation where moisture -conditioning and re -compaction as
recommended in the Site Preparation section of this report is not possible due to wet soil
conditions. Where required, apply geosynthetics directly on approved subgrade, taut, free of
wrinkles and over -lapped at least 12 inches. Woven geosynthetic fabrics for subgrade
stabilization and soil improvements shall have the following minimum properties of 700 pounds
(CBR Puncture, ASTM D6241) and 200 pounds (Grab Tensile Strength ASTM D4632).
STRATA must be consulted prior to using geosynthetics for subgrade stabilization. Further, we
recommend contractors carefully review subsurface conditions prior to bidding and recommend
the design team include a unit price for woven geosynthetics for the earthwork portion of the
project.
We recommend non -woven geosynthetic fabrics for filtration and for stormwater
facilities. Non -woven fabrics should have a maximum apparent opening size equivalent to the
U.S. No. 70 sieve (ASTM D4751), a minimum weight of 3.5 ounces per square yard and
minimum CBR puncture resistance of 200 pounds (ASTM D6241).
Pavement Section Design
General
The following flexible asphalt pavement section design is provided referencing the Idaho
Transportation Department (ITD) Gravel Equivalent Design Method using Ada County Highway
District substitution ratios. STRATA estimated traffic loading and design parameters based on
our proposed construction understanding and our understanding of the subsurface conditions.
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Eastwood Subdivision
4515 South Locust Grove Road
Meridian, Idaho
File: B013253A
Page 10
Pavement Section Thickness
STRATA evaluated the pavement sections utilizing the ITD pavement design
methodology, soil -engineering parameters from laboratory testing and the estimated traffic -
loading conditions. Based on subgrades prepared as recommended and the traffic criteria
provided, Table 3 provides the recommended asphalt section for the anticipated pavement
application. If subgrade conditions change as design is finalized or during construction, or traffic
loading is different than we have assumed, STRATA must review our pavement analyses and
resulting sections.
Table 3. Asphalt Pavement Design Section
Pavement Maintenance
We recommend crack maintenance be accomplished on all pavement surfaces every 3
to 5 years to reduce the potential for surface water infiltration into the underlying pavement
subgrade. Surface and subgrade drainage are extremely important to the performance of the
pavement section. Therefore, we recommend the subgrade, base and asphalt surfaces slope at
no less than 2 percent to an appropriate stormwater disposal system or other appropriate
location that does not impact adjacent buildings or properties. The pavement's lifespan is
dependent on achieving adequate drainage throughout the section, especially at the subgrade
elevation. Ponding water at the pavement subgrade surface can induce heaving during the
freeze -thaw process.
Site Drainage
Exterior Grading
We recommend the ground surface adjacent to structures slope a minimum of 5 percent
away within 10 feet of the structure. The ground surface beyond 10 feet of structures should be
sloped at least 2 percent away. Improper management of near -surface water, by not providing
an effective grading and drainage design, can result in moisture or water entering foundation
areas. Possible sources of near -surface water include pressurized irrigation water, rainwater,
snowmelt, or leaking water lines. These water sources can be transmitted to the foundation
stem wall and pond beneath the structure via precipitation, roof downspout discharge, and
snowmelt. Possible conduits for water to enter into crawlspaces can include loose or porous
14
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Asphalt
Aggregate Base
Granular
Asphalt Pavement Application
Concrete
Course (inches)
Subbase
(inches)
(inches)
Local Roads (TI = 6)
2.5
1 4.0
12.0
Pavement Maintenance
We recommend crack maintenance be accomplished on all pavement surfaces every 3
to 5 years to reduce the potential for surface water infiltration into the underlying pavement
subgrade. Surface and subgrade drainage are extremely important to the performance of the
pavement section. Therefore, we recommend the subgrade, base and asphalt surfaces slope at
no less than 2 percent to an appropriate stormwater disposal system or other appropriate
location that does not impact adjacent buildings or properties. The pavement's lifespan is
dependent on achieving adequate drainage throughout the section, especially at the subgrade
elevation. Ponding water at the pavement subgrade surface can induce heaving during the
freeze -thaw process.
Site Drainage
Exterior Grading
We recommend the ground surface adjacent to structures slope a minimum of 5 percent
away within 10 feet of the structure. The ground surface beyond 10 feet of structures should be
sloped at least 2 percent away. Improper management of near -surface water, by not providing
an effective grading and drainage design, can result in moisture or water entering foundation
areas. Possible sources of near -surface water include pressurized irrigation water, rainwater,
snowmelt, or leaking water lines. These water sources can be transmitted to the foundation
stem wall and pond beneath the structure via precipitation, roof downspout discharge, and
snowmelt. Possible conduits for water to enter into crawlspaces can include loose or porous
14
www.stratageotech.com
Eastwood Subdivision
4515 South Locust Grove Road
Meridian, Idaho
File: B013253A
Page 12
GEOTECHNICAL DESIGN CONTINUITY
Geotechnical design continuity will be an important aspect of this project's successful
completion. In our opinion, geotechnical continuity can occur in 4 stages in the planning, design
and construction project aspects. Specifically, we recommend STRATA maintain the
geotechnical design continuity in the following aspects:
@�i Groundwater Monitoring: The groundwater level should be monitored during the
current irrigation season to verify the seasonal high groundwater level beneath the
site. Piezometers were installed to monitor groundwater levels. Monitoring typically
should be accomplished on a monthly basis between July and October. STRATA
remains available to perform groundwater monitoring at your request.
Plan and Specification Review: We recommend STRATA be retained to review
final design and construction plans and specifications to verify our geotechnical
recommendations are incorporated into project bidding and construction documents
as well as to provide additional recommendations based on the final design
concepts. These efforts can help provide document continuity across the
engineering disciplines and reduce the potential for errors as the project concepts
evolve.
ISF Construction Observation and Testing: We recommend STRATA be retained to
observe site grading and fill compaction testing. Having STRATA provide testing and
oversight during this process will reduce the potential for an unforeseen construction
error which may ultimately impact the project. STRATA can also provide
construction material testing of pavement sections and asphalt surfaces. If we are
not retained to perform the recommended services, we cannot be responsible for
related construction errors or omissions.
EVALUATION LIMITATIONS
This report has been prepared to assist project planning design and construction of the
proposed Eastwood Subdivision to be located at 4415 South Locust Grove Road in Meridian,
Idaho. Our geotechnical findings and opinions have been developed based on the authorized
subsurface exploration and laboratory testing, as well as our understanding of the project at this
time. Our geotechnical design recommendations are specific to the planned design and
infrastructure construction and should not be extrapolated to other future site developments
without allowing adequate geotechnical consultation by STRATA.
Our services consist of professional opinions and findings made in accordance with
generally accepted geotechnical engineering principles and practices in southwest Idaho at the
time of this report. The geotechnical recommendations provided herein are based on the
premise that appropriate geotechnical consultation during subsequent design phases is
implemented and an adequate program of tests and observations will be conducted by
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UNIFIED SOIL CLASSIFICATION SYSTEM
MAJOR DIVISIONS
GRAPH
SYMBOL
LETTER
SYMBOL
TYPICAL NAMES
Baggie Sample
Split—Spoon Sample
..
GW
Well—Graded Gravel,
California Modified 3—Inch
OD Split—Spoon Sample
CLEAN
"<
Bulk Sample
Gravel—Sand Mixtures.
O:.
GP
Poorly—Graded Gravel,
IIRock
GRAVELS0.
Groundwater
RG
Ring Sample
:
Gravel—Sand Mixtures.
GRAVELS
Shelby Tube 3—Inch OD
_
Silty Gravel, Gravel—
Undisturbed Sample
GRAVELS
GM
Sand—Silt Mixtures.
WITH
Clayey Gravel, Gravel—
COARSE
FINES
GC
Sand—Clay Mixtures.
GRAINED
� C 0 0 0 C
Well—Graded Sand,
SOILS
CLEAN
°° " ° ° °
co 0000
SW
Gravelly Sand.
• ° • ° • •
Poorly—Graded Sand,
SANDS
• •
SP
Gravelly Sand.
SANDS
�.
�+
Silty Sand,
SANDS
SM
Sand—Silt Mixtures.
WITH
• •
Clayey Sand,
FINES
. •• •� .
SC
Sand—Clay Mixtures.
•
Inorganic Silt, Sandy
ML
or Clayey Silt.
SILTS AND CLAYS
Inorganic Clay of Low
CL
to Medium Plasticity,
LIQUID LIMIT
Sandy or Silty Clay.
LESS THAN 50%
Organic Silt and Clay
OL
of Low Plasticity.
FINE
Inorganic Silt, Mica—
GRAINED
MH
ceous Silt, Plastic
SOILS
Silt.
SILTS AND CLAYS
Inorganic Clay of High
CH
Plasticity, Fat Clay.
LIQUID LIMIT
GREATER THAN 50%
OH
Organic Clay of Medium
to High Plasticity.
Peat, Muck and Other
_
PT
Highly Organic Soils.
BORING LOG SYMBOLS GROUNDWATER SYMBOLS TEST PIT LOG SYMBOLS
Shorthand Notation:
BGS = Below Existing Ground Surface
N.E. = None Encountered
Standard 2—Inch OD
- GroundwaterBG
Baggie Sample
Split—Spoon Sample
= After 24 Hours
California Modified 3—Inch
OD Split—Spoon Sample
(7-3-07) Indicates Date ofBK
Bulk Sample
Reading
IIRock
Core
Groundwater
RG
Ring Sample
=_ at Time of Drilling
Shelby Tube 3—Inch OD
_
Undisturbed Sample
Shorthand Notation:
BGS = Below Existing Ground Surface
N.E. = None Encountered
=
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REMARKS
USCS Description
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Note: BGS =Below Ground
z
T
o `o
o
Surface
(J
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SANDY SILT, (ML) brown, stiff,
moist to dry
2.5
Grass roots to 6 inches BGS
ML
>4.5
SILT, (ML) tan, hard, moist to dry
>4.5
2.5
II
$6
>4.5
>4.5
Moderate cementation 5 to 8
5.0
feet BGS
ML
Z5
Strong cementation from 8.0 to
11.0 feet BGS
Difficult excavation 8.0 - 11.0
feet BGS
i
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i
10.0
I
'
i POORLY GRADED GRAVEL, With
Sand And Slit, (GP) tan, very
dense, moist
a D'
Q
12.5
i
GP
a �p,
.
s
Q
Cj
� Test Pit Terminated at 14.0 Feet.
S
i
Client: KMENGINEEERING
Test Pit Number. TP -2
"'
EXPLORATOR
TEST PIT LOG
Project: B013253A
Date Excavated: 07-01-2013,..�.�
r Backhoe: CASE 580K
Bucket Width: 2
S
Depth to Groundwater: N.E.
Logged By: SW
Sheet 1 Of 1
APPENDIX B