HomeMy WebLinkAboutHacienda South Sub - Geotechnical Engineering Evaluation14
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A PROFESSIONAL SERVICES CORPORATION
Y+4-1ear14X 1 rvo t 4-A, <*roaA,A UP
Doug Jayo
Jayo Development
10564 W. Business Park Lane
Boise, Idaho 83709
doug@jayoconstruction.com
Dear Mr. Jayo:
November 1, 2013
File: B013258A
RE: Geotechnical Engineering Evaluation
Hacienda South Subdivision
North Meridian Road
Meridian, Idaho
STRATA, A Professional Services Corporation (STRATA) is pleased to present our
authorized Geotechnical Engineering Evaluation for the proposed Hacienda South Subdivision
to be located northeast of the intersection of North Meridian Road and East Producer Drive 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 of planned project
infrastructure. The attached report summarizes our field and laboratory test results and presents
our geotechnical engineering opinions and 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. 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.
We appreciate the opportunity to work with Jayo Development. We look forward to our
continued involvement on this project throughout construction. Please do not hesitate to contact
us if you have any questions or comments.
Sc,�ONAC�H Sincerely,
STRATA, Inc.
1425a i�j���
Adrian Mascorro, P.E.9gTF�PtD��Q O Michael G. Woodworth, P.E.
Project Engineer 'Q/itis q�r,{Q. Engineering Manager
AM/MGW/am
wvvw.stratag eotec h. com
REPORT
Geotechnical Engineering Evaluation
Hacienda South Subdivision
North Meridian Road
Meridian, Idaho
Prepared For:
Mr. Doug Jayo
Jayo Development
10564 W. Business Park Lane
Boise, Idaho 83709
Prepared By:
STRATA, Inc.
8653 W. Hackamore Drive
Boise, Idaho 83709
P.208.376.8200
F.208.376.8201
November 1, 2013
TABLE OF CONTENTS
Wet Weather/Soil Construction.................................................................................. 5
Excavation Characteristics.........................................................................................6
UtilityTrench Construction......................................................................................... 6
Structural Fill and Compaction...................................................................................
Page
INTRODUCTION...................................... ............................... ..................................
....... 1
PROJECT UNDERSTANDING.........................................................................................2
8
ExistingSite Conditions....................................................................................................2
................ 9
ProposedConstruction.....................................................................................................
2
SUBSURFACE EVALUATION PROCEDURES...............................................................
2
SUBSURFACE CONDITIONS..........................................................................................3
9
LABORATORY TESTING.................................................................................................
3
GEOTECHNICAL OPINIONS AND RECOMMENDATIONS............................................4
10
Earthwork....................................................................................................................
4
Site and Subgrade Preparation... ----.............................................. ..._.....................4
10
Wet Weather/Soil Construction.................................................................................. 5
Excavation Characteristics.........................................................................................6
UtilityTrench Construction......................................................................................... 6
Structural Fill and Compaction...................................................................................
7
Table 1. Structural Fill Specifications and Allowable Use ..............................................
7
Geosyntheti cs.............................................................................................................
8
Pavement Section Design.........................................................................
................ 9
General.......................................................................................................................
9
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
Pavement Maintenance, ................................................................. .........................
10
SiteDrainage...............................................................................................................
11
InfiltrationRate.........................................................................................................11
Seasonal High Groundwater (estimated) .......... .................. ..................__...............
11
GEOTECHNICAL DESIGN CONTINUITY .......... ............. :....... .......................................
11
EVALUATION LIMITATIONS..........................................................................................
12
Geotechnical Engineering Evaluation
Hacienda South Subdivision
North Meridian Road and East Producer Drive
Meridian, Idaho
INTRODUCTION
STRATA, A Professional Services Corporation (STRATA) has performed our
Geotechnical Engineering Evaluation for the proposed Hacienda South Subdivision located
northeast of the intersection of North Meridian Road and East Producer Drive in Meridian,
Idaho. Our evaluation's purpose was to explore the subsurface soil conditions at the project site
and to prepare geotechnical recommendations to assist project planning, design and
construction for the planned project infrastructure. We accomplished our services referencing
our authorized geotechnical proposal dated May 29, 2013. To accomplish our evaluation,
STRATA performed the following services:
1. Coordinated exploration with the Idaho Digline Utility Notification Center to help reduce the
potential for damage to existing utilities.
2. Observed the excavation of 5 exploratory test pits within the planned development area.
Test pit exploration extended 11 to 12.5 feet below existing grades. Standpipe piezometers
were installed in 3 of the test pits. Our field engineer visually described, classified and
logged soil encountered referencing the Unified Soil Classification System (USCS).
3. Performed two infiltration tests within gravel to assist with stormwater disposal design.
4. Performed laboratory tests with reference to ASTM International (ASTM) procedures
including in-situ moisture content, Atterberg limits and grain size evaluation. We utilized
these laboratory results to help characterize engineering parameters and to correlate soil
engineering characteristics used in our design.
5. Performed engineering analyses in order to provide geotechnical design and earthwork
construction recommendations. Our engineering analyses provides geotechnical
recommendations and opinions for:
I -s Earthwork
• Site and subgrade preparation
• Wet weather/soil construction
• Excavation characteristics
• Utility trench construction
• Structural fill and compaction
• Geosynthetics
60 Pavement section design
• Traffic and subgrade
• Asphalt, aggregate base course and subbase materials
• Pavement section thickness
;.653 West R;ack,ar c &e, Boise, idahu 83708 rax_208,376.x201
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Hacienda South Subdivision
File: B013258A
Page 2
• Pavement maintenance
Site drainage
• Infiltration rate
• Seasonal high groundwater (estimated)
6. 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 approximate 20 -acre site scheduled for development is relatively flat and is currently
occupied by a single family residence with associated outbuildings, fencing and asphalt access
way that will be demolished as part of the development. The site is bounded by existing
subdivision development to the north, east, and south and by North Meridian Road to the west.
Proposed Construction
We understand the development will consist of approximately 97 residential lots, a
community park, common areas, and proposed asphalt paved roads providing access to
individual lots. The subdivision will be accessed via existing subdivision development to the
north, east and south. Stormwater will be retained and disposed of on-site. Our proposed
project approach, scope of service, schedule and fees are presented below.
SUBSURFACE EVALUATION PROCEDURES
STRATA accomplished subsurface exploration on October 4, 2013 via 5 exploratory test
pits extending 11 to 12.5 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 geotechnical engineer 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
A to help interpret the terms on individual test pit logs. Individual test pit logs are also provided
in Appendix A. The test pits were backfilled with the excavated material following the completion
of excavations.
040
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SUBSURFACE CONDITIONS
Topsoil rooting was observed to a depth of approximately 6 inches below grade.
Multiple, non -pressurized, 2 -inch -diameter PVC pipes were also observed throughout the site at
approximately 12 inches below ground surface. Soil conditions encountered within test pits
generally consist of surficial sandy lean clay, underlain by silty sand, silty gravel with sand, and
poorly -graded gravel with sand. We provide more specific discussion of each soil unit
encountered below:
Sandy lean clay (native) — We encountered sandy lean clay at the ground surface to
depths of 0.7 to 4 feet below existing grade. The clay was described as light brown to
brown, firm to hard, and moist
Silty sand — Underlying sandy clay, we encountered light brown to tan, very dense,
moist, silty sand to depths of 1.2 to 6 feet below existing grade, with the exception of TP -
2 where silty sand was not observed below clay soil. Calcium cementation was observed
at varying depths and thicknesses.
Silty gravel with sand — Underlying silty sand, or sandy clay in TP -2, we encountered
orange -brown, dense to medium dense, moist, silty gravel with sand to depths of 3.7 to
7.5 feet below existing grade. Calcium cementation was observed at varying depths and
thicknesses.
0% Poorly -graded gravel with sand — Underlying silty gravel with sand, we encountered
poorly -graded gravel with sand described as orange brown, medium dense and moist to
test pit termination depths.
Groundwater — Groundwater was not encountered during exploration within test pits to
maximum depths of 12.5 feet below existing ground surface.
Specific soil contacts and descriptions are further described on individual test pit logs
provided as Appendix A to this report, along with a USCS explanation to assist with test pit log
information. Temporary standpipe piezometers were installed in test pits TP -1, TP -2 and TP -4
for future groundwater monitoring. Groundwater has the potential to vary with seasonal changes
in irrigation, precipitation, infiltration and development to the project site.
LABORATORY TESTING
We returned soil samples collected in the field to our laboratory for further classification
and testing, and accomplished laboratory testing referencing ASTM Intemational (ASTM)
procedures. We developed our laboratory testing program for this project primarily to evaluate
subsurface soil characteristics and engineering properties. Specifically, we accomplished
moisture content, Atterberg limits, and grain size analysis. We present laboratory test results on
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Hacienda South Subdivision
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individual test pit logs in Appendix A. We will retain soil samples for 90 days and discard after
this time period unless we are notified to store samples for longer periods of time.
GEOTECHNICAL OPINIONS AND RECOMMENDATIONS
We present the following geotechnical recommendations to assist planning, design and
construction of the proposed Hacienda South Subdivision to be located 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. Subsurface
variations may exist between exploration locations and may not be apparent until construction.
Test pits only allow us to observe a portion of the site subsurface conditions. Where such
variations exist, they may impact opinions and recommendations presented in this report, as
well as construction timing and costs.
Earthwork
Site and Subgrade Preparation
We currently do not have a grading plan for the proposed development, but we
anticipate grading will be limited with cut and fill of less than 1 foot. At the time of exploration,
surficial vegetation and organic material was observed to a depth of approximately 6 inches. We
also observed an unpressurized irrigation system throughout the site consisting of
approximately 2- to 3 -inch -diameter PVC and aluminum pipes at approximately 12 inches below
existing ground. As such, we recommend a minimum of 6 inches of topsoil with organic matter
and the existing pipe system be removed beneath all planned improvements. In our opinion, this
topsoil is not suitable for use as structural fill and should be wasted or stockpiled on-site for
landscape areas.
All existing fill on-site is considered undocumented and uncontrolled fill. Any and all
undocumented fill associated with the demolition of existing structures and infrastructure, should
also be removed to native soil. Undocumented fill may be associated with existing residential
development and subsurface utilities which will be demolished/removed as part of the
development.
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Also, we have evidence of existing drainfields located in the north central portion of the
site northwest of test pit TP -4 that will require removal and remediation. All existing fill within
planned improvements, including structural fill areas, must be over -excavated and replaced with
structural fill as indicated in the Structural Fill section of this report. Test pits have been marked
in the field with labeled stakes and/or standpipe piezometers. The test pits should be located
prior to any earthwork site grading and 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, sidewalk areas, and for
over -excavations should be scarified for a minimum of 8 inches, moisture conditioned and
recompacted to structural fill criteria, as indicated in the Structural Fill section of this report. If
weaving or pumping is observed, those areas should be over -excavated and replaced with
structural fill as indicated in this report.
Wet Weather/Soil Construction
We strongly recommend earthwork construction take place during dry weather
conditions. Native clay and silt soil is susceptible to pumping or rutting from heavy loads such as
rubber -tired equipment or vehicles when the soil is above optimum moisture content. Earthwork
should not be performed immediately after rainfall or until soil can dry sufficiently to allow
construction traffic without disturbing the subgrade. During and after achieving subgrade
elevation, the contractor must take precautions to protect the subgrade from becoming
disturbed or saturated. We recommend the contractor limit construction traffic to any prepared
subgrade and reduce exposure to precipitation and water. Specifically, the contractor should:
Grade subgrades to aggressively direct surface water away from construction areas
that could be adversely affected by infiltration.
04i After adequate moisture conditioning efforts have failed, remove exposed subgrade
soil, which becomes soft or begins to pump, to firm soil and replace it with structural
fill as described in the Site and Subgrade Preparation section above for over -
excavations.
Never attempt structural fill placement during or immediately following a significant
precipitation event.
Never allow subgrades to freeze or become saturated prior to fill placement.
The final subgrade conditions, and careful construction procedures, are critical to the
long-term project performance. We recommend earthwork specifications specifically identify the
contractor's responsibility to protect and maintain prepared subgrades. It may improve project
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economy to retain STRATA to observe the subgrade preparation activities to identify techniques
or construction activities that may be attributing to unstable subgrades and contributing to the
need for over -excavations. If significant soft/wet soil conditions are encountered, the use of a
woven geotextile fabric may be necessary. These material requirements are presented in the
Geosynthetics report section below.
Allowing time for proper moisture -conditioning during dry weather is critical to reducing
excessive over -excavations and importing structural fill. However, depending on the weather
and moisture conditions during construction, drying fine-grained soil may not be practical, and
over -excavation in conjunction with the use of geosynthetics may be necessary to help maintain
project schedule. In short, working with on-site, near surface soil may be impractical during
certain weather or soil conditions and we recommend contingencies are in place to remove and
replace wet soil.
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 and coarse-grained soil is expected to be exposed in excavations throughout
the development area and should be temporarily sloped at 1.5H:1V (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 to 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 and soft
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
Oki
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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.
Table 1. Structural Fill Specifications and Allowable Use
Structural Fill Product
Sieve
%
• Allowable Use
Material Specifications
Size
Passing
• Soil classified as GW, GP, GP -GM, GM, SW, SP,
General Structural Fill
SP -SM, SM, or ML according to the USCS.
General site grading
• Maximum particle size must be less than 6 inches.
• Soil consisting of inert earth materials with less
than 3 percent organics or other deleterious
substances wood, metal, plastic, waste, etc).
Granular Structural Fill
• Soil classified as GW, GP, GP -GM, according to
6 Inch
100
3 Inch
90-100
• General structural fill
the USCS, and meeting the gradation provided.
No. 4
30-60
• Over -excavations
• Soil meeting requirements stated in the latest
• Pavement section
edition of the Idaho Standard for Public Works
No. 200
<10
Construction (ISPWC), Section 801—Aggregate
granular subbase
Subbase.
• Soil may not contain particles larger than 1 inch in
1 Inch
100
% Inch
80-100
Utility Trench Bedding
median diameter and must meet the required
3/8 Inch
20-70
• Utility trench
gradation.
No. 4
5-20
construction
• Soil meeting requirements stated in the latest
No. 8
0-5
edition of the Idaho Standard for Public Works
Construction (ISPWC), Section 305— Pipe
No. 200
0-3
Bedding.
• Soil may not contain particles larger than 1 inch in
1 Inch
100
Aggregate Base Course
median diameter and must meet the required
'/. Inch
90-100
• General structural fill
gradation.
No. 4
40-65
• Granular structural fill
• Soil meeting requirements stated in the latest
• Pavement section
edition of the Idaho Standard for Public Works
No. 8
30-50
base course
Construction (ISPWC), Section 802 —Aggregate
No. 200
3-9
Base.
All structural fill from on-site or imported sources should be placed in maximum 10 -inch -
thick lifts, and each lift shall be moisture -conditioned to within 3 percent of optimum moisture
content and compacted to a minimum of 95 percent of ASTM D 1557 (Modified Proctor). The
maximum, loose -lift thickness is based on using large, 5- to 10 -ton, smooth -drum vibratory
rollers. The maximum loose lift thickness should be reduced where smaller and/or lighter
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compaction equipment is used. STRATA should be retained to perform field density testing of
structural fill to verify contractor compliance with the above minimum compaction criteria.
Structural fill with greater than 30 percent retained above the '/< inch sieve is too coarse
for proctor density testing, but may be used as granular structural fill provided it meets the
above specification. Coarse fill must be compacted using a "method specification" developed
during construction, based on the material characteristics and the contractor's means and
methods. It is common that "method specifications" are developed during construction, specific
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 efforts during construction.
Geosvnthetics
If earthwork contractors are unable to achieve subgrade compaction requirements
outlined in this report's Site and Subgrade 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 and Subgrade Preparation section of this report is not possible due
to wet soil conditions. Where required, apply geosynthetics directly on approved subgrade, 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 D 6241) and 200 pounds (Grab Tensile Strength ASTM D 4632).
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 D 4751), a minimum weight of 3.5 ounces per square yard and
minimum CBR puncture resistance of 200 pounds (ASTM D 6241).
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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 (ACHD) substitution ratios. STRATA estimated traffic loading and design parameters
based on our proposed construction understanding and our understanding of the subsurface
conditions.
Traffic and Subgrade
The following tables present our traffic loading, geotechnical design parameters and
references, as well as the resulting flexible pavement section design recommendations.
Table 2. Pavement Design Parameters
Design Parameter
Value Used
References
Traffic Loading
33,000 ESALS
Ada County
Highway
District Standard
Design Life
20 years
Assumed
Sub rade R -value
5
Assumed
see section below
Asphalt Layer Substitution Ratio
1.95
Ada County
Highway
District Standard
Base Course Substitution Ratio
1.1
Ada County
Highway
District Standard
Subbase Course Substitution Ratio
1.0
Ada County
Highway
District Standard
'Equivalent Single Axle Loads (ESALS).
From correlations to laboratory testing, our experience with similar soil, and utilizing
sandy clay for roadway subgrade, we assumed an R -value of 5 for roadway subgrade. To help
improve subgrade characteristics, the pavement subgrade should be prepared as
recommended in this report's Site Preparation section. Subgrades must be shaped (crowned)
and graded to facilitate positive drainage and inverted crowns must be avoided.
Asphalt Aggregate Base Course and Subbase Materials
Crushed aggregate base course and granular subbase shall conform to the Structural
Fill requirements above and be placed directly over a properly prepared subgrade. A woven
geotextile should be used for constructability during wet and inclement weather and to increase
performance at the subgrade. The woven geotextile should have material properties and be
placed as outlined in this report's Geosynthetics section. We recommend STRATA observe final
subgrade preparations, geotextile placement and all aggregate placements.
Asphalt concrete must be compacted to 92 percent of the maximum density for a Hveem
or Superpave mix design. The final traveling surface of asphalt concrete shall meet ISPWC'/<-
inch asphalt mix design requirements. Asphalt mix designs and all appropriate aggregate
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source certificates should be accepted by STRATA at least 5 days prior to initiating asphalt
paving. Asphalt construction and final surface smoothness, joints and density should meet
ISPWC specifications. If subgrade conditions appear significantly different during construction,
traffic loading conditions change or traffic volumes increase from what was assumed, STRATA
should be notified to amend our design accordingly.
Pavement Section Thickness
STRATA evaluated the pavement sections utilizing the ACHD pavement design
methodology, correlated 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.
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Asphalt
Aggregate. Base
Granular
Asphalt Pavement Application
Concrete
(inches)
Subbase
(inches)
(inches)
Local Roads
2.5
4.0
14.0
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.
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Site Drainage
Infiltration Rate
We understand on-site stormwater will be retained using subsurface seepage beds or
swales. All seepage beds or swales should be located a minimum 25 feet away from structures.
We performed infiltration tests in test pits TP -1 and TP -4 within medium dense gravel at
9 and 6.5 feet below grade, respectively. We measured a field infiltration rate of 30 inches per
hour (in/hr) in the medium dense gravel with sand at both locations. All infiltration facilities
should be constructed a minimum of 12 inches into poorly -graded gravel and sand. Based on
test pit exploration, we anticipate excavation depths of 4 to 7.5 feet may be required to expose
poorly -graded gravel and sand. We recommend the following allowable design infiltration rate
be utilized for infiltration facilities constructed into poorly -graded gravel and sand:
Allowable Infiltration Rate (gravel and sand) = 8 in/hr
Seasonal High Groundwater (estimated)
The appropriate separation between seasonal high groundwater and the base of the
stormwater disposal facilities should be maintained. As discussed above, we observed no
groundwater to depths of 12.5 feet below existing grade. Based on our experience in the area
and review of nearby well logs, we anticipate seasonal high groundwater levels will occur at a
depth of 15 to 20 feet below existing ground surface. Therefore, we recommend subsurface
infiltration facilities are designed assuming seasonal high groundwater occurs at a depth of 15
feet below existing site grades.
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 3 stages in the planning, design
and construction project aspects. Specifically, we recommend STRATA maintain the
geotechnical design continuity in the following aspects:
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.
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W Geotechnical Design Confirmation: The potential soil variation may have a
significant impact on construction of the planned development. As such, we
recommend STRATA be retained to provide geotechnical observation during
earthwork construction to observe the potential variability in the soil conditions and
provide consultation regarding potential needs for over -excavations and compaction.
45 Construction Observation and Testing: We recommend STRATA be retained to
provide observation and compaction testing during structural fill placement, as
required. 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 and
special inspection for concrete, masonry, reinforcement, and asphalt. 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 Hacienda South Subdivision to be located northeast of the intersection of North
Meridian Road and East Producer Drive 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. STRATA's scope only provides recommendations for infrastructure
construction, which does NOT include recommendations for individual lots, and STRATA does
NOT assume the role of geotechnical engineer of record for individual lot construction.
Our services consist of professional opinions and findings made in accordance with
generally accepted geotechnical engineering principles and practices as they exist 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 STRATA
during construction to verify compliance with our recommendations and to confirm conditions
between exploration locations. This acknowledgment is in lieu of all express or implied
warranties.
The following plate and appendix accompany and complete this report:
Plate 1: Exploration Location Plan
Appendix A: Unified Soil Classification System (USCS) &
Exploratory Test Pit Logs
www.stratageotech.com
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APPENDIX A
UNIFIED SOIL CLASSIFICATION SYSTEM
MAJOR DIVISIONS
GRAPH
SYMBOL
LETTER
SYMBOL
TYPICAL NAMES
— After 24 Hours
California Modified 3—Inch
OD Split—Spoon Sample
Q'.-.-:
GW
Well—Graded Gravel,
Reading
CLEAN
Groundwater
RG Ring Sample
Gravel—Sand Mixtures.
=_ at Time of Drilling
GRAVELS
Q
Poorly—Graded Gravel,
i..
CP
Gravel—Sand Mixtures.
GRAVELS
Silty Gravel, Gravel—
GRAVELS
GM
Sand—Silt Mixtures.
COARSE
WITH
FINES
GC
Clayey Gravel, Gravel—
Sand—Clay Mixtures.
GRAINED
°
Well—Graded Sand,
SOILS
CLEAN
o
SW
Gravelly Sand.
Poorly—Graded Sand,
SANDSSP
°
GravellySand.
SANDS
Silty Sand,
SANDS
SM
Sand—Silt Mixtures.
WITH
FINES
; •g m;
Sc
Clayey Sand,
Sand—Clay Mixtures.
Inorganic Silt, Sandy
ML
or Clayey Silt.
SILTS AND CLAYS
Inorganic Clay of Low
LIQUID LIMIT
\ \
CL
to Medium Plasticity,
LESS THAN 50%
Sandy or Silty Clay.
Organic Silt and Clay
OL
of Low Plasticity.
FINE
GRAINED
Inorganic Silt, Mica—
SOILS
MH
ceous Silt, Plastic
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
IStandard 2—Inch OD
Split—Spoon Sample
- Groundwater
BG Baggie Sample
— After 24 Hours
California Modified 3—Inch
OD Split—Spoon Sample
(7-3_07) Indicates Date of
BK Bulk Sample
Reading
I� Rock 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
G
Oca 12
'
REMARKS
Description
F
a
Co
m
T
¢❑ .,
QJ -�
N -
oNo
ou
Note: BGS = Below Ground
ZU3
o
2 0
Surface
ao
SANDY LEAN CLAY, (native), (CL)
Moderate vegetation and
light brown, hard, moist
organics to about 6 inches BGS
CL
ATTERBERG LIMITS
BG
>4
LL -38
P1=21
1.25 inch diameter pvc irrigation
line ruptured at 1 foot BGS (not
SILTY SAND, (SM) light brown,
very dense, moist
pressurized)
e,
0
BG
20.6
23.5
2.5
♦ ..
°
1
Light to moderate calcium
•
:
carbonate cementation
{jl
observed from 1:3 to 4.5 feet
ee
BGS
SM
q'°
.� le
Significant to moderate
cementation observed from 4.5
o@
to 7 feet BGS
SILTY GRAVEL, With Sand, (GM)
!
1°
orange brown, dense to medium
dense, moist
GM
!1
s
75
�i
a
POORLY GRADED GRAVEL, With
Sand, (GP) orange brown, medium
dense, moist
p O
6 ,4
Percolation test performed at 9
o l�o
feet BGS. Infiltration rate =30
Inches per hour measured.
10.0
GP-�
o ^
v vim`
i.
-D
cJ(
Piezometer installed to 12.5
feet BGS
^ n'
Test Pit Terminated at 12.5 Feet.
Client: JAYO DEVELOPMENT
Test Pit Number: TP-1
EXPLORATORY
Project: B013258A
Date Excavated: 10_042013
STRaTcr
`"`""` " ` `"'
TEST PIT LOG
Backhoe: CASE 580
Bucket Width: 2'
Depth to Groundwater: N.E.
Logged By: AM
Sheet 1 Of 1
c
0 a
�o
'y
e'
m
REMARKS
USCS Description
F-,
w r
3w
g
m
a -n
W -
a❑ `
❑
ej
U
g
N
@
0
don
z
❑ a
Z
oro
`o
s
Note: BGS =Below Ground
H
e
o
Surface
7
❑
U
o_
SANDY LEAN CLAY, (native), (CL)
',
Moderate vegetation and
brown, stiff, moist
organics to about 8 inches BGS
ATTERBERG LIMITS
LL = 38
BG
68.0
17.7
PI=21
CL
2.5
Moderate cementation
observed from 4 to 5.5 feetBGS
SILTY GRAVEL, With Sand, (GM)
° a t
orange brown, dense to medium
dense, moist
ops
5.0
GM
ill
POORLY GRADED GRAVEL, With
Sand, (GP) orange brown, medium
dense, moist
7.5
9i—bi�
O V.
GP
J
U Q.
q h'.
;v.4.
7'
Piezometer installed to 12.5
feet BGS.
OSr�
Test Pit Terminated at 12.5 Feet. 19'
Client: dAYO DEVELOPMENT
Test Pit Number: TP -2
Irl—
EXPLORATORY
Project: B013258A
Date Excavated: 10-04-2013
5 T R 3T?_a
TEST PIT LOG
Backhoe: CASE 580
Bucket Width: 2'
Logged By: AM
Depth to Groundwater: N.E.
Sheet 1 Of 1
x
mrq
p
d
Jc
O m
yoo
E°
a,.
REMARKS
USCS Description
a
s
o
E E °;
¢ x w
�^
o g
Nc
w —'
vi
F
p h
a 6
'E
,
m v
Note: BGS = Below Ground
o
U
W
m
F
o z
a
o
o
Surface
SANDY LEAN CLAY, (native), (CL)
\Moderate
vage a ion an
light brown, hard, moist
\ \
organics to about 6 inches
BGS.
Note: Approximate 3 inch
CLQ\
diameter aluminum water line
(inactive) ruptured at 1 foot
BGS
2.5
SILTY SAND, (SM) light brown,
very dense, moist
SM
SILTY GRAVEL, With Sand, (GM)
orange brown, dense to medium
dense, moist
GM
s.o
l
}
POORLY GRADED GRAVEL, With
Sand, (GP) orange brown, medium
dense, moist
v D< :
a a.
ado.
GPD.°
\lam.
Jtirl ,
1a.o
P Qj\
Test Pit Terminated at 12.0 Feet.
Client: JAYO DEVELOPMENT
Test Pit Number: TP -3
EXPLORATORY
Project: B013258A
Date Excavated: 10-04-2013
STFta-r
TEST PIT LOG
Backhoe: CASE 580
Bucket Width: 2'
Depth to Groundwater: N.E.
Logged By: AM
Sheet1 Of 1
C
�om
ms
�'
ax
REMARK
S0
USCS Description
Ng
E
F
❑
o
'6`w
Note: BGS = Below Ground
❑
❑
r}n
N
on.
Z
2 o
Surfaceo
Umm
❑
SANDY LEAN CLAY, (native), (CL)
\N
Moder-ate vegetation an
light brown, firm, moist
CL
\\
organics to about 6 inches
BGS.
Two 2 inch pvc lines. and phone
SILTY SAND, (SM) light brown,-
very dense, moist
SM
line ruptured at approximate 1
foot BGS
SILTY GRAVEL, With Sand, (GM)
i++
orange brown, dense to medium
4
dense, moist
Moderate cementation
}
observed from 1.7 to 4 feet
BGS.
2.5
GM
I
?RI
SIR
}k
POORLY GRADED GRAVEL, With
-
Sand, (GP)orange brown, medium
dense, moist
5.0
Q,d
;o J"
Percolation test performed at
`
6.5 feet BGS. Infiltration rate =
b GC
30 inches per hour measured
"j
GP
0`
7.5
Q G
orq�
o 'n
l `.1 lel
10.0
JU.
Piezometer installed to 10.7
p
feet BGS.
Test Pit Terminated at 11.0 Feet.
Client: JAYO DEVELOPMENT
Test Pit Number: TP -4
EXPLORATORY
Project: B013258A
Date Excavated: 10-04-2013
STRr�T2►
TEST PIT LOG
Backhoe: CASE 580
Bucket Width: 2'
_ _
Sheet 1 Of 1
Depth to Groundwater: N.E.
Logged By: AM
x
mw
p
C
REMARKS
Description
x
°¢USCS
ME
E
¢
M60
o n
y
d
o
n
R
o
NoteBGS =Below Groundw
mZ
o
�U
Surface
U
ao
SANDY LEAN CLAY, (native), (CL)
Significant vegetation an
light brown, very stiff, moist
organics to about 6 inches
CL
BGS.
SILTY SAND, (SM) tan, very
dense, moist
Moderate to significant
cementation observed from 2 to
6.5 feet BGS.
2.5
BG
66.0
Tit
SM
5.0
SILTY GRAVEL, With Sand, (GM)
orange brown, dense to medium
dense, moist
GM
}
T5
V
POORLY GRADED GRAVEL, With
Sand, (GP) orange brown, medium
dense, moist
p
(�o
'
oto
a�
10.0
GP
b �,
J. v:
v
.y
Test Pit Terminated at 12.5 Feet.
Client: JAYO DEVELOPMENT
Test Pit Number: TP -5
EXPLORATORY
Project: B013258A
Date Excavated: 10-04-2013
s-rrRa-r21 TEST PIT LOG
Backhoe: CASE 580
Bucket Width: 2'
Sheet 1 Of 1
Depth to Groundwater: N.E.
Logged By: AM