ATC Report of Geotechnical Investigation - Lindsay Meadows Subdivision W....pdf

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ENVIRONMENTAL• GEOTECHNICAL
BUILDING SCIENCES • MATERIALS TESTING
7606 Whitehall Executive Center Drive. Suite 800
Charlotte, NC 28273
Tel: [phone]
Fax:[phone]
www.atcassociates.com
REPORT OF GEOTECHNICAL EXPLORATION
Lindsay Meadows Subdivision
Waxhaw, North Carolina
ATC Project No. 199CAR1808
Prepared For:
Mr. Hamilton Stolpen
American Homes 4 Rent
18805 W. Catawba Avenue, Suite 102
Cornelius, NC 28031
Prepared By:
ATC Associates of North Carolina, P.C.
7606 Whitehall Executive Center Drive, Suite 800
Charlotte, North Carolina 28273
July 3, 2018

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ENVIRONMENTAL• GEOTECHNICAL
BUILDING SCIENCES • MATERIALS TESTING
July 3, 2017
Mr. Hamilton Stolpen
American Homes 4 Rent
18805 W. Catawba Avenue, Suite 102
Cornelius, NC 28031
Subject: Report of Geotechnical Exploration
Lindsay Meadows Subdivision
Waxhaw, North Carolina
Project No. 199CAR1808
Dear Mr. Stolpen:
7606 Whitehall Executive Center Drive, Suite 800
Charlotte, NC 28273
Telephone [phone]
Fax [phone]
www.atceroupservices.com
ATC Associates (ATC) is pleased to submit this report providing engineering analysis for the proposed
single family development in Waxhaw, North Carolina. This report, which details the results of our
geotechnical exploration for the referenced project, summarizes the project information provided to us,
describes the site and subsurface conditions encountered, and details our geotechnical recommendations
for the project. The Appendix contains a Boring Location Plan and Soil Boring Logs.
We appreciate the opportunity to be of service to you for this phase of the project. If you have any
questions concerning this report, please call us.
Respectfully Submitted,
ATC SSOCIATES OF NORTH CAROLINA, P.C.
Brian Carpenter, P.E.
Project Engineer
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Joseph G. Schold, P.E.
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Reg. NC No. 21736
Principal Geotechnical Engineer
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Report of Geotechnical Exploration July 3, 2017
Lindsay Meadows Subdivision
TABLE OF CONTENTS
1.0 INTR OD UC TION.................................................................................................................... 2
1.1 Project Information...................................................................................................................2
1.2 Purpose and Scope of Exploration...........................................................................................2
2.0 EXPLORATION PROCEDURES AND FINDINGS............................................................. 4
2.1 Exploration Procedures............................................................................................................4
2.2 Site Geology................................................................................................................................4
2.3.3 Groundwater Conditions............................................................................................................7
2.4 Laboratory Testing....................................................................................................................7
2.4.1 Soil Classification.......................................................................................................................7
2.4.2 Moisture Contents.......................................................................................................................7
3.0 FOUNDATION SUPPORT AND RECOMMENDATIONS................................................. 8
3.1 Site Development Considerations and Recommendations.....................................................8
3.2 Shallow Foundation Design Recommendations......................................................................9
3.3 Floor Slabs..................................................................................................................................9
3.4 Slope Stability..........................................................................................................................10
3.5 Groundwater Conditions and Control..................................................................................10
3.6 Retaining/Below Grade Walls................................................................................................10
4.0 SITE PREPARATION...........................................................................................................
14
4.2 Wet Weather Construction.....................................................................................................16
5.0 CONSTRUCTION CONSIDERATIONS.............................................................................
18
6.0 GENERAL AND LIMITATIONS.........................................................................................
19
APPENDIX..................................................................................................................................
20
APPENDIX
Important Information About Your Geotechnical Report
Soil Test Boring Location Plan
Test Boring Logs
Reference Notes for Boring Logs
ATC Project No. 199CAR1808 i

Report of Geotechnical Exploration
Lindsay Meadows Subdivision
1.0 INTRODUCTION
1.1 Project Information
July 3, 2017
The property consists of one parcel totaling 17.385 acres located on the south side of Kensington Drive,
east of Waxhaw-Marvin Road in the northern part of Waxhaw, North Carolina. The property is located
along Kensington Drive in Waxhaw, Union County, North Carolina. According to information obtained
from the Union County Geographic Information System (GIS), the property is comprised of one parcel
identified as Parcel Number 06192007.
The surrounding area is mostly residential with vacant wooded areas. The vicinity of the subject property
is characterized by residential use to the north and south, with undeveloped land to the west and east
and part of the Union County Waste Water Treatment Plant to the east. Local topography slopes to the
south towards Twelve Mile Creek, which runs along the southern property boundary. The property is
currently mainly vacant heavily wooded land, with cleared areas in the northern part along Kensington
Drive.
It is our understanding construction at the site will consist of numerous single and two-story residential
structures, MSE retaining walls, utility infrastructure, and parking facilities and drives. A summary of the
anticipated site construction is provided below.
Project Details
Single and Two Story Above -Grade Residential Structures Wood Framing and Masonry Block
Estimated Design Column Loads Less than 20 - 40 Kips
Estimated Wall Loads 2 to 6 kips per foot
Approximate Maximum Mass Excavation Cut and Fill Depths Less than 10 feet
Design Traffic Loads Light to Medium Duty
1.2 Purpose and Scope of Exploration
The purpose of this exploration was to obtain subsurface data at the project site to provide geotechnical
engineering recommendations for the project. Services performed under this agreement included the
drilling of the soil test boring and preparation of a geotechnical engineering report. The subsurface
investigation data obtained for this study and related plans are presented for the proposed single family
residential structures, associated utilities, and parking facilities and drives.
Scope of Services Summary
Description of the site and presentation of subsurface test boring data, including Boring Location Plan
and Soil test Boring Logs.
Depths, thicknesses, and composition of soil strata that will be impacted by the planned site
construction.
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Report of Geotechnical Exploration July 3, 2017
Lindsay Meadows Subdivision
Depth of topsoil encountered at the site.
Recommendations pertaining to site development including site preparation, earthwork construction,
unsuitable soils, groundwater control, excavation slopes, and difficult excavation.
Depth and presence of rock on -site and recommendations regarding rip -ability and blast -ability of the
rock. Recommendations regarding the on -site use of any rock encountered on site.
Depths to encountered groundwater and soil strata that could affect the proposed construction.
Recommendations for control of groundwater in design and during construction.
Recommendations for foundation support of the proposed structures, including allowable bearing
pressures, and design parameters for use by other design professionals. Soil design parameters are
included for design to resist lateral loads and overturning.
Recommendations for floor slab support.
Recommendations regarding the suitability of the on -site cut soils with regard to use on site for general
grading, retaining wall backfill, pavement construction, utility backfill, etc.
Laboratory testing of on -site including in -situ moisture contents, gradations, and Atterberg Limit tests.
Recommendation for the design and construction of light and heavy duty pavements.
Recommendations regarding the suitability of the on -site cut soils with regard to use on site for general
grading, retaining wall backfill, pavement construction, and utility backfill.
Comments and recommendations regarding geotechnical construction considerations related to
preparation of the construction plans and specifications.
Our scope of services did not include recommendations for unsupported excavation slopes, stormwater
management, erosion control, detailed cost or quantity estimates, final plan and specification documents,
and construction observations and testing. Any statements in this report regarding odors, colors, or
unusual or suspicious items or conditions are strictly for the information of the client.
ATC Project No. 199CAR1808 3

Report of Geotechnical Exploration July 3, 2017
Lindsay Meadows Subdivision
2.0 EXPLORATION PROCEDURES AND FINDINGS
2.1 Exploration Procedures
ATC performed eighteen soil test borings, designated B-01 through B-21. The Standard Penetration
Testing (SPT) borings extended to depths of 20 feet below the existing ground surface. The referenced
boring locations were established in the field by an ATC engineer by measuring distances and estimating
right angles from existing site features shown on a conceptual site plan provided by your office.
All soil sampling and standard penetration testing (SPT) were in general accordance with ASTM standard
D 1586. The borings were advanced by hollow -stem rotary drilling techniques. At regular intervals, soil
samples were obtained with a standard 1.4-inch I.D., 2.0-inch O.D., split -barrel sampler. The sampler was
first seated 6 inches and then driven an additional foot with blows of a 140-pound hammer falling 30
inches. The number of blows required to drive the sampler the final foot was recorded and is designated
the "standard penetration resistance." Because the sampler may be damaged by driving it a foot into very
dense soils, it is driven a few inches into such materials and the penetration resistance is expressed as the
number of hammer blows versus the depth of penetration, e.g. 100/3", 50/1", etc. Penetration resistance,
when properly evaluated, is an index of the soil's strength, density, and foundation support capability.
Representative portions of the soil samples obtained with the split -barrel sampler were sealed in plastic
bags and transported to our laboratory. In the laboratory, they were examined by a geotechnical engineer,
classified in general accordance with the Unified Soil Classification System (USCS), and assigned laboratory
testing. The soil descriptions and classifications are based on visual examination and should be considered
approximate. Test Boring Records that present soil descriptions and graphically depict penetration
resistance and observed groundwater levels are included in the report Appendix. Occasionally, boreholes
will collapse preventing water level measurements. Groundwater levels were measured in the boreholes
at the completion of drilling operations. The groundwater elevations are indicated herein and on the
Boring Logs in the Appendix.
2.2 Site Geology
According to the USGS Topographic 7.5-Minute Series Catawba NE, South Carolina quadrangle map, dated
2014, and the Waxhaw, North Carolina quadrangle map, dated 2013, the property is located in an area
with an approximate elevation range from 490 feet above mean sea level (MSL) along the creek in the
southern part of the property to 550 feet above MSL in the northern part of the property. The property
slopes to the south towards Twelve Mile Creek, which runs along the southern property boundary.
According to the Geologic Map of North Carolina, the property is located in the Piedmont Physiographic
Province, and the rock type beneath the site consists of metavolcanic tuffs and flow rock. The shallow
subsurface in most areas of the Piedmont contains residual soil overburden, including structure -free
residuum, saprolite, and partially weathered rock (PWR) that derive from in -place weathering of the
crystalline bedrock. In areas near creeks and rivers, alluvium derived from weathered residual soil is often
present and such material may be present near drainages at the property. Saprolite and PWR typically
contain some relict structures from the original rock material. Depth to rock ranges from ground surface
at occasional outcrops to depths of up to 100 feet in areas of easily weathered rock.
ATC Project No. 199CAR1808 4

Report of Geotechnical Exploration July 3, 2017
Lindsay Meadows Subdivision
According to information obtained from the United States Department of Agriculture (USDA) Soil
Conservation Service (SCS) Web -Based Soil Survey, the property is primarily underlain by Tarrus gravelly
silty clay loam and Chewacla silt loam. Tarrus gravelly silty clay is well drained and located on hillslopes
on ridges. A typical soil profile consists of gravelly silty clay loam to 6 inches below ground surface (bgs),
silty clay from 6 to 45 inches bgs, and weathered bedrock from 45 to 80 inches bgs. Permeability is very
low to high, and the available water capacity is low. Chewacla silt loam is somewhat poorly drained and
located on floodplains. A typical soil profile consists of silt loam to 4 inches bgs, silty clay loam from 4 to
26 inches bgs, loam from 26 to 38 inches bgs, clay loam from 38 to 60 inches bgs, and loam from 60 to 80
inches bgs. Permeability is moderately high to high, and the available water capacity is high.
2.3 Subsurface Conditions
The procedures used for boring advancement and sample classification are included in the Appendix. The
subsurface materials encountered were classified using the USCS. The soil test boring logs, which detail
the subsurface conditions encountered in the borings, are included in the Appendix.
The field portion of ATC's geotechnical exploration consisted of fifteen soil test borings to depths of 5.5
to 15 feet below the existing ground surface elevations. Three generalized subsurface strata were
encountered within the termination depths and the soil strata are summarized as follows:
Approximate Maximum Depth to
Materials Encountered
Consistency / Relative
Description
Bottom of Stratum (ft.)
Density
Stratum A —
0 to 13.5 feet
Reddish brown and brown lean
SPT Blow counts of 12 to 73
Residuum Soils
CLAY and elastic SILT (CL and
bpf
MH)
Stratum B —
0 to 15+ feet
White, brown, and silty SAND
SPT Blow counts of 22 bpf to
Residuum Soils
(SM)
50 blows for 6-inches of
penetration
Stratum C —
4.5 to 20+ feet
Sampled as white brown,
SPT Blow counts of 50/6" to
Partially Weathered
brown, and tan silty sand
50/0"
Rock
2.3.1 Topsoil
Topsoil depths encountered at the site ranged from approximately 6 to 12 inches in depths. Due to the
heavy vegetation and potential water features on site, we expect topsoil depths to be higher in some
areas of the site.
2.3.2 Residual Soils
The residual soils encountered at the site consisted of stiff to hard sandy low and high plasticity SILTS (ML
and MH) and lean CLAYS (CL) in the near surface soils. Underlying the fat clays, the borings encountered
medium dense to very dense silty SANDS (SM).
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Report of Geotechnical Exploration July 3, 2017
Lindsay Meadows Subdivision
2.3.3 Partially Weathered Rock (PWR)
Weathered bedrock materials encountered during the drilling operations are summarized in the Table
below.
Boring No.
Approximate Depth to
Surface of PWR (ft.)
Auger Refusal Depth, ft.
B-01
5.5+
5.5
B-01A
6+
6
B-02
6 — 11
11
B-02A
9+
9
B-03
10 - 14
14
B-04
3.5 — 10.5
10.5
B-04A
13+
13
B-05
2.5 — 7.5
7.5
B-05A
7+
7
B-06
13.5 — 15
Terminated at 15 feet
B-07
4-15
Terminated at 15 feet
B-08
2.5 —10
10
B-08A
9+
9
B-09
13.5+
13.5
B-10
2.5 — 13.7
13.7
B-11
Not Encountered
NA
B-12
7.5 —12
12
B-13
1-6
6
B-13A
5+
5
B-14
2.5-5
5
B-14A
6-9
9
B-15
3-7
7
B-15A
7+
7
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Report of Geotechnical Exploration July 3, 2017
Lindsay Meadows Subdivision
2.3.3 Groundwater Conditions
Groundwater was not encountered during drilling operations. Generally, seasonal and yearly fluctuations of
the water table should be expected with variations in precipitation, surface runoff, evaporation, pumping,
and other similar factors.
2.4 Laboratory Testing
2.4.1 Soil Classification
Soil classifications provide a general guide to the engineering properties of various soil types and enable the
engineer to apply past experience to current problems. In our explorations, samples obtained during drilling
operations are observed in our laboratory and visually classified by an engineer. The soils are classified
according to consistency (based on number of blows from standard penetration tests), color and texture.
These classification descriptions are included on our Test Boring Records. The classification system discussed
above is primarily qualitative; laboratory testing is generally performed for detailed soil classification. Using
the test results, the soils were visually classified according to the USCS (ASTM D 2487). This classification
system and the in -place physical soil properties provide an index for estimating the soil's behavior. The soil
classification and physical properties obtained are presented in this report. The results of the Atterberg Limit
testing is provided below.
Laboratory Test Results
2.4.2 Moisture Contents
The moisture content is the ratio expressed as a percentage of the weight of water in a given mass of soil to
the weight of the solid particles. This test was conducted in general accordance with ASTM D 2216. The test
results are presented on the Boring Logs in the Appendix.
ATC Project No. 199CAR1808

Report of Geotechnical Exploration July 3, 2017
Lindsay Meadows Subdivision
3.0 FOUNDATION SUPPORT AND RECOMMENDATIONS
Soil data obtained during this subsurface exploration have been used to estimate the shearing strength and
deformation characteristics for the subsurface soils encountered at the site. These parameters have been
used as guidelines for foundation system design and to estimate potential settlement due to the anticipated
site construction and foundation loading. The engineering analysis based on these parameters was performed
in accordance with generally accepted engineering principles and practices.
3.1 Site Development Considerations and Recommendations
A grading plan was not available for review during preparation of this report, therefore we have assumed cuts
at the site to be less than 5 feet in depth. Additional evaluation of the site may be performed by ATC after
review of the site grading plans.
Based on the laboratory testing performed, the site contains some near surface high plasticity "elastic" SILTS
and lean CLAYS (CL). These soils were generally encountered in the upper 4 to 6 feet of the subsurface profile.
The plasticity of the elastic SILT soils was moderately high (PI's above 50 percent) making the near surface
elastic SILT's marginally suitable for use with the upper 3 feet below the proposed building foundations. These
soils may be very difficult to work with in wet and cool periods and these soils will also become unstable when
exposed to wet weather and/or heavy construction traffic like that associated with mass clearing and grading
operations. Therefore, undercut excavation, mechanical drying, and/or chemical stabilization should be
expected during and at the completion of the grading operations.
If the soils are stable, as determined by the geotechnical staff based on evaluation by proofrolling and DCP
testing, they may remain in -place as bearing materials for fill placement. However, again the use of these soils
within two feet of the foundation bearing elements is not recommended due to the potential for shrink/swell
and/or excessive foundation settlement due to soil softening.
Given the results of the soil test borings as noted in the Table on page 6 of this report and the general geology
of the site, weathered rock is expected across the site at relatively shallow depths. It is also expected that the
rock surface maybe highly variable in depth. For the weathered rock materials encountered, we expect these
materials to be excavatable in mass cutting and filling operations using standard to large sized construction
equipment. For trench rock excavations, rock hammers may be required above the noted "Auger Refusal"
depths. For excavations below the "Auger Refusal" depths, blasting may be required.
We recommend performing a series of Test Pit excavations at the site, in projected "deep cut" areas of the
site prior to the commencement of the site construction in order to help determine the "excavatability" of
the weathered rock materials.
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Report of Geotechnical Exploration
Lindsay Meadows Subdivision
3.2 Shallow Foundation Design Recommendations
July 3, 2017
Based on the anticipated site conditions, it appears the planned residential structures may be constructed
using shallow foundation systems. Based on the site findings, the proposed structures may be supported
on shallow foundations bearing on competent soils and may be proportioned based on an allowable net
soil bearing pressure of 2,000 pounds per square foot (psf). The presented allowable bearing capacity
includes a factor of safety of at least 3.0.
Description
Columns
Walls
Net allowable soil bearing pressure'
2,000 psf
2,000 psf
Minimum dimensions
30 inches
18 inches
Minimum protective embedment
18 inches
18 inches
Approximate total settlement
<1 inches
<1/2 inches over 50 feet
The recommended net allowable soil bearing pressure is the pressure in excess of the minimum surrounding
overburden pressure at the footing base elevation. This bearing capacity assumes that any fill or soft soils, as
noted herein and as encountered, will be undercut and replaced with compacted engineered fill in
accordance with the recommendations provided herein. The extent of any required site undercutting should
be determined in the field by experienced geotechnical personnel based on site conditions at the time of
construction.
Resistance to lateral loads for shallow foundations will likely be provided by frictional resistance between
the base of the concrete footings and the underlying structural fill. We recommend that an ultimate
friction factor of 0.45 be used for the design. Additional resistance to lateral loads will be provided by
passive pressure of the granular backfill adjacent to the perimeter of the footings. A passive resistance
modeled by an equivalent fluid unit pressure unit weight of 300 pcf may be used for soil against the edge
of the footing. This is an ultimate value. All backfill placed against the edge of the footings must be
properly compacted as indicted herein and the upper 18 inches of soils be not be included in the passive
pressure calculations.
3.3 Floor Slabs
For ground -level floor slabs placed at the site, we recommend the floor slabs be supported on low
plasticity residual soils or engineered fill with a minimum of a 6-inch layer of compacted Aggregate Base
Course material (ABC) or a 4-inch layer of washed stone (NC DOT No. 57 or 67 gradation), as well as a
vapor barrier, should be provided beneath all building floor slabs to provide a capillary break and to help
prevent a damp slab condition.
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Report of Geotechnical Exploration
Lindsay Meadows Subdivision
3.4 Slope Stability
July 3, 2017
Our exploration did not include a detailed analysis of slope stability for any temporary or permanent
condition. We recommend temporary slopes no steeper than 1.0(H):1.0(V) and permanent slopes no
steeper than 2.0(H):1.0(V) for construction in existing natural soils or new structural fill placed in
accordance with our recommendations. In building areas, minimum top of slope setbacks of 10 feet and
5 feet are recommended, respectively.
Slopes should be protected from erosion, and surface runoff should be diverted away from slopes. For
erosion protection, a protective cover of grass or other vegetation should be established on permanent
soil slopes as soon as possible.
3.5 Groundwater Conditions and Control
Based on the site conditions, we do not anticipate that groundwater will be encountered during
construction operations in low areas of the site, deep utility cuts, or in the area of the encountered water
features. The seasonal conditions will also influence the groundwater conditions at the site. The
contractor is responsible to assure adequate groundwater control is in -place and functioning prior to the
start of any work then allowing all work to be performed in a dry (free from flowing or standing water)
condition. The contractor is responsible to establish the means and methods of groundwater control and
to include all such items in his bid and scope of work. In order to prevent adverse effects of groundwater
to exposed subgrade materials, it has been our experience that groundwater levels when lowered and
maintained at a depth of at least 3 feet below the limits of subgrade excavation and undercutting elevation
typically provide a stable working platform.
Additionally, the dewatering system should be in -place and functioning sufficiently prior to beginning
earthwork construction within the area. Inadequate dewatering may cause the subgrade to destabilize
under loads from earthwork equipment and be problematic in placement and compaction of fill soils.
Rainwater and runoff that accumulate in footing excavations can be pumped out of small dug sumps.
Groundwater levels are subject to seasonal, climatic and other variations and may be different at other
times and locations than those stated in this report. A site drainage scheme should be implemented and
maintained at all times by the contractor to redirect all off site drainage away from the limits of
construction. Ponding or standing water may result in softening of soils that will require additional
remedial work to facilitate construction.
Installation of utilities below the water table will be problematic, requiring dewatering, if it is
encountered. The contractor should be required to control this water such that the utilities can be
constructed in the "dry". The utility joints should be covered with a drainage fabric such as Mirafi 180N,
or equivalent, which should extend at least 12 inches beyond each side of the joint.
3.6 Seasonal High Groundwater Table
Based on the results of the borings performed on site and the groundwater conditions encountered and
the review of the site topographical data, we estimate a Seasonal High Groundwater Table Elevation of
495 to 500 feet MSL.
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Report of Geotechnical Exploration
Lindsay Meadows Subdivision
3.7 Retaining/Below Grade Walls
July 3, 2017
Earth pressures on walls below grade are influenced by structural design of the walls, conditions of wall
restraint, methods of construction and/or compaction, and the strength of the materials being restrained.
The most common conditions assumed for earth retaining wall design are the active and at -rest
conditions.
Active conditions apply to relatively flexible earth retention structures, such as freestanding walls, where
some movement and rotation may occur to mobilize soil shear strength. Walls which are rigidly restrained,
such as basement, tunnel, or loading dock walls, should be designed for the at -rest condition. A third
condition, the passive state, represents the maximum possible pressure when a structure is pushed
against the soil, and is used in wall foundation design to help resist active or at -rest pressures. Because
significant wall movements are required to develop the passive pressure, the total calculated passive
pressure should be reduced by one-half for design purposes.
Based on previous experience with similar soils and construction, we recommend the following earth
pressure coefficients and equivalent fluid pressures for design of reinforced concrete retaining or below
grade walls on this project:
Earth Pressure Conditions Coefficient Recommended Equivalent Fluid Pressure,
(Pcf)
Active (Ka) 0.36 43
At -Rest (Ka) 0.53 64
Passive (Kp) 2.77 166
A moist soil unit weight of 120 pounds per cubic foot (pcf) should be used for design calculations. Our
recommendations assume that the ground surface above the wall is level. A coefficient of friction value
between soil and concrete of 0.35 is recommended. An allowable bearing pressure of 2,000 psf may be
used for footings designed to bear on competent existing fill materials, residual soils, or new structural
fills.
The recommended equivalent fluid pressures assume that constantly functioning drainage systems are
installed between walls and soil backfill to prevent the accidental buildup of hydrostatic pressures and
lateral stresses in excess of those stated. If a functioning drainage system is not installed, then lateral
earth pressures should be determined using the buoyant weight of the soil (approximately 58 pcf).
Hydrostatic pressures calculated with the unit weight of water (62.4 pcf) should be added to these earth
pressures to obtain the total stresses for design.
Tractors and other heavy equipment should not operate within 10 feet of below grade walls to prevent
lateral pressures in excess of those cited. If foundations or other surcharge loadings are located a short
distance outside below grade walls, they may also exert appreciable additional lateral pressures that must
be considered in design.
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Report of Geotechnical Exploration July 3, 2017
Lindsay Meadows Subdivision
These retaining wall/below grade wall recommendations should not be correlated with soil parameters
for use in mechanically stabilized earth (MSE) wall design. We recommend that soil parameters for any
MSE retaining wall design be established through appropriate laboratory testing by the wall designer.
3.8 Pavement Design and Construction
Based upon our evaluation and analyses, the on -site soils should be acceptable for construction and
support of a flexible (crushed gravel base) type pavement section after proper subgrade preparation as
discussed in the Site and Subgrade Preparation section of this report, provided that adequate drainage
controls are implemented. The subgrade should be compacted to a minimum depth of 12 inches to at
least 95 percent of the Standard Proctor maximum dry density (ASTM D-698). Any fill utilized to establish
the desired subgrade elevation should consist of approved structural fill uniformly compacted to a
minimum density of 95 percent of the soil Standard Proctor maximum dry density (ASTM D-698).
Base material should meet NCDOT requirements, including compaction to 100 percent of its maximum
dry density as determined by the Modified Proctor Test (ASTM D-1557). To avoid rutting, traffic should
not be allowed on the subgrade before the base is placed. As a guideline for pavement design, we
recommend that the Aggregate Base Course (ABC) and crushed concrete base materials be a minimum of
8-inches in thickness. The following flexible pavement recommendations are based on an assumed
California Bearing Ratio (CBR) value of 3 to 5. This value assumes the subgrade is prepared as discussed in
this report.
Flexible Pavement Structural Sections
The following pavement designs are based upon the design methods described in the "AASHTO Guide for
Design of Pavement Structures 1993" published by the American Association of State Highway and
Transportation Officials (AASHTO). These designs present the recommended range of 18-kip-equivalent
single axle loads for the "standard duty" and "heavy duty" pavement sections presented.
Pavement Flexible Pavement Structural Sections
Duty (15-year Design)
Standard 1.5-inches Surface Course 8-inches of Compacted Aggregate Base
2.0-inches Intermediate Course Course (ABC)
Heavy 1.5-inches Surface Course 8-inches of Compacted Aggregate Base
3.5-inches Intermediate Course Course (ABC)
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Report of Geotechnical Exploration July 3, 2017
Lindsay Meadows Subdivision
Concrete Pavement Structural Sections
As an alternate to the above flexible pavement design, a rigid concrete pavement design could be used.
It is recommended that the concrete pavement incorporate the following design criteria.
Design Parameters
Value
Minimum Concrete Compressive Strength (psi)
4,000 psi at 28-days
Minimum Concrete Modulus of Elasticity (psi)
3,600,000
Effective Modulus of Subgrade Reaction (pci)
150
Load Transfer Coefficient
3.8
Drainage Coefficient
1.0
Soil Subgrade CBR
3 to 5
The subgrade should be prepared to achieve a minimum California Bearing Ratio (CBR) of 3 to 5 to a depth
of at least 12 inches below the concrete base elevation. The subgrade soils should be compacted to at
least 95 percent of the Standard Proctor maximum dry density (ASTM D-698).
The following pavement designs are based upon the design methods described in the "AASHTO Guide for
Design of Pavement Structures 1993" published by the American Association of State Highway and
Transportation Officials (AASHTO). These designs present the recommended range of 18-kip-equivalent
single axle loads (ESALs) for the "standard duty" and "heavy duty" pavement sections presented below.
Pavement Duty Rigid Pavement Structural Sections
(15-year Design)
Standard 6-inches Concrete 6-inches Crushed Aggregate Base Course (ABC)
4,000 psi (28 days)
Heavy 7-inches Concrete 6-inches Crushed Aggregate Base Course (ABC)
4,000 psi (28 days)
Dumpster Pads 8-inches Concrete 6-inches Crushed Aggregate Base Course (ABC)
4,000 psi (28 days)
The above designs are based on assumed traffic volumes. If actual traffic volume and loading
characteristics are provided at a later date, some modification to these designs may be required.
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Report of Geotechnical Exploration July 3, 2017
Lindsay Meadows Subdivision
The ABC should be compacted to at least 100% of the Modified Proctor (D-1557) maximum dry density.
Based on our review of the minimum pavement design criteria and the pavement design procedures, the
pavement structural sections presented appear to satisfy the minimum pavement design criteria. It is
suggested that a rigid pavement be utilized in such areas as the dumpster locations, and in any other areas
where dumpster trucks or other large vehicles load, back up, and turn around.
4.0 SITE PREPARATION
4.1 Compacted Fill Recommendations
If organic laden soils are encountered at the site, the soils are general unsuitable for use in structural areas
of the site. These soils also contains moderate to high plasticity SILTs (MH) that are marginally suitable for
use as engineered fill on site. These soils are suitable for use in the planned parking areas and drives, if
the soils are at moisture contents which will allow the soils to be compacted to at least 95 percent of the
maximum dry density.
Fill materials used to replace potential undercut areas, pipe backfill, or establish finished grades should
meet the following criteria and should be generally free of deleterious materials and rock fragments larger
than 6 inches in diameter. Fill materials should also be at moisture content that allows for the proper
placement and compaction of the materials per the requirements provided herein. Fill materials to be
used as backfill materials should be tested, prior to use, in order to determine the soils suitability and
compaction characteristics.
Fill Type USCS Classification Acceptable Locations for Placement
On -site soils and residual low
plasticity soils including silts,
clays, and sands
On -site soils and residual
moderate to high plasticity soils
including silts and clays
M L, C L, SC, S P
CH and MH with LL>60 and 13I<30
Acceptable fill material at all locations
and elevations
Acceptable as fill in pavement areas
at least 2 feet below subgrade
Imported Soils ML, CL, SM, SP, GW with LL<50 and Acceptable in all locations and uses
PI<20
Fill materials should be free of large rock (greater than 6 inches in largest dimension) and organic materials
(less than 3 percent by weight). The use of larger rock or asphalt fragments in structural fill must be
carefully monitored and tested by the Geotechnical Engineer and/or his authorized representative.
We recommend that the grading contractor have equipment on site during earthwork for both drying and
wetting of fill soils. We expect that the on -site residual soils and some of the existing fill soils will be
suitable for use as structural fill on the project. Fill materials should be tested to verify their suitability.
We recommend that all fill materials have a dry unit weight of at least 95 pcf.
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Lindsay Meadows Subdivision
Compacted fill should be placed in lifts of 8 inches or less loose measure. In confined areas such as utility
trenches, portable compaction equipment and thin lifts of 3 to 4 inches may be required to achieve
specified degrees of compaction. We recommend that structural fill be compacted to at least 95 percent
of the Standard Proctor (ASTM D-698) maximum dry density.
The upper 12 inches beneath slabs and pavements should be compacted to at least 98 percent of the
same criteria. Moisture content of the fill at the time of compaction should be maintained within a range
of +\- 3% of the optimum moisture as determined by the Proctor test.
In excavated areas, the upper 12 inches of soils intended to support pavements should be scarified and
recompacted to at least 98 percent of the Standard Proctor maximum dry density. All fill material should
be placed in horizontal lifts and adequately keyed into stripped and scarified subgrade soils. All new fills
should also be benched into any existing slopes.
During fill placement, an ATC soils technician should determine the degree of compaction and compliance
with the project specifications by performing field density tests. At least one field density test should be
made per 5,000 square feet of pavement area for each one -foot thickness of compacted soil. The testing
frequency should be increased in confined areas. Any areas that do not meet the compaction
specifications for density and moisture should be reworked to achieve compliance.
The suitability of the on -site soils for reuse as structural fill must be confirmed by careful visual
examination by the Geotechnical Engineer and/or his authorized representative and by the results of
laboratory tests performed on proposed soil samples.
We recommend that all materials be placed and compacted using the following criteria:
• Soil fill should be placed in lifts of uniform thickness. The lift thickness should not exceed that
which can be properly compacted throughout its entire depth with the equipment available,
usually not more than 8 inches for clay soils and not more than 10 inches for granular soils for
area fills. In confined areas such as utility trenches where only small and light compaction
equipment can be used, lifts of 3 to 4 inches may be required to achieve the specified degree of
compaction.
• All fill should be properly keyed into stripped and scarified subgrades. The upper 1 foot of
materials in planned cut areas or in areas which do not receive more than one foot of new fill
should be scarified and recompacted using the guidelines outlined in this report section.
• Fill should not be placed on frozen or saturated subgrades.
• Fills should be placed and compacted to at least 95 percent of the Standard Proctor maximum dry
density (ASTM Method D-698). Fills placed within 12 inches of slab or pavement levels should be
placed and compacted to at least 95 percent of Standard Proctor maximum dry density.
• A minimum of at least 2 tests per lift is recommended in the planned building area. For utility
trenches, density tests should be taken every 50 linear feet for each fill layer placed. Any areas
not meeting the compaction specifications should be recompacted to achieve compliance.
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Report of Geotechnical Exploration
Lindsay Meadows Subdivision
July 3, 2017
• The soils should be placed within 3 percent of the optimum moisture content as determined by
the Standard Proctor test. Aeration is often necessary to bring fill materials to the required
moisture condition during wet and rainy periods. During dry periods, water may need to be added
to bring the soils, especially granular soils, up to the proper moisture content to achieve proper
compaction. Clay soils may require aeration prior to compaction even during dry periods.
• Compacted fills should extend horizontally outside of planned paved areas at least 5 feet before
sloping.
• Temporary slopes should be regularly evaluated for indications of movements during the
construction.
4.2 Wet Weather Construction
Site grading that occurs during traditional wet weather periods will be problematic at this site. Extensive
undercutting of saturated soils and chemical drying may be required if unfavorable weather conditions occur
during fill placement operations at the site. Although specific recommendations would be made at the time
of construction, the following guidelines are provided.
• Saturated surface soils are difficult to dry by mechanical and/or chemical methods depending on
the season and the soil type. Consequently, consideration should be given to removal and wasting
of saturated surface soils at the site.
• Lime or cement can be an effective in drying of soils that are typically about 4 to 8 percent wet of
their optimum moisture content. We expect chemical drying will be required during periods of
wet weather construction.
• The on -site soils are sensitive to excessive moisture. These soils types may require undercutting
and chemical drying if subjected to inclement weather conditions.
• Disturbed or uncompacted soils will more readily absorb and hold water. Disturbed or
uncompacted soils should be kept to a minimum area. Special attention and detail should be
given to "sealing -off" or compaction with a sooth drummed roller of disturbed areas prior to wet
weather periods. The contractor should also provide cut ditches to channel surface water runoff
from the construction areas. The site should also be graded to prevent ponding of water on the
site. Pumping should be performed in a timely manner in areas where water has collected.
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Report of Geotechnical Exploration
Lindsay Meadows Subdivision
4.3 Rock Excavation
July 3, 2017
The site grading plan was not reviewed as part of this investigation. Assuming significant cuts are not
planned for the site, we anticipate rock excavations will be required based on the borings performed. In
addition, for "deeper" utility or stormwater excavations planned for the site, some rock materials may be
encountered. ATC should review site grading plans prior to the site bidding to perform an additional
evaluation of the anticipated site conditions and the potential for encountering rock.
If rock is encountered, difficult excavation criteria are discussed below for your reference. In mass
excavations for general site work, dense soils and partially weathered rock can usually be removed by
ripping with a single -tooth ripper attached to a large crawler tractor or by breaking it out with a large
front-end loader. In confined excavations such as foundations, utility trenches, removal of partially
weathered rock typically requires use of large backhoes, pneumatic spades, or light blasting. Excavated
rock and partially weathered rock is generally unsuitable for use as structural fill.
The definition of rock can be a source of conflict during construction. The following definitions have been
incorporated into specifications on other projects and are provided for your general guidance:
General Excavation
Rip Rock - Any material that cannot be removed by scrapers, loaders, pans, bulldozers, or graders; and
requires the use of a single -tooth ripper mounted on a crawler tractor having a minimum draw bar pull
rated at not less than 56,000 pounds (Caterpillar D-8T or equivalent).
Blast Rock - Any material which cannot be excavated with a single -tooth ripper mounted on a crawler
tractor having a minimum draw bar pull rated at not less than 56,000 pounds (Caterpillar D-8T or
equivalent) or by a Caterpillar 977 front-end loader or equivalent; and occupying an original volume of at
least one (1) cubic yard.
Trench Excavation
Blast Rock - Any material which cannot be excavated with a backhoe having a bucket curling force rated
at not less than 25,700 pounds (Caterpillar Model 320D or equivalent) and occupying an original volume
of at least one-half (1/2) cubic yard.
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Report of Geotechnical Exploration July 3, 2017
Lindsay Meadows Subdivision
5.0 CONSTRUCTION CONSIDERATIONS
If encountered, groundwater should be maintained at least about 3 feet below the final bottom of footing
subgrade for the final subgrade observations and during placement of the foundation concrete. Should
significant groundwater be encountered during construction, the geotechnical engineer should be contacted
immediately to determine its effect on the design of the foundation.
Where reinforcing steel is to be placed in the foundation, observations should be provided to ascertain that
proper chairs or supports are provided and the reinforcing is properly positioned. Field observations and
testing should also be provided for the earthwork construction for this project. As applicable, appropriate
laboratory tests should be conducted on samples of the compacted backfill material, and field density tests
should be conducted during the earthwork construction to ascertain that fill material and compaction
requirements are being satisfied.
Field observations and testing should also be provided by our field engineer and/or technician personnel
under supervision of our geotechnical engineer assigned to this project. We cannot be responsible for the
interpretation or implementation, by others, of recommendations given herein.
Before beginning construction, the owner and contractor should become familiar with applicable local, state,
and federal regulations, including the current OSHA Excavation and Trench Safety Standards. Construction
site safety generally is the sole responsibility of the contractor, who should also be solely responsible for the
means, methods, and sequencing of construction operations. We are providing this information solely as a
service to our clients. Under no circumstances should the information provided herein be interpreted to
mean that ATC Associates is assuming responsibility for construction site safety or the contractor's activities.
This responsibility is not being implied and should not be inferred.
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6.0 GENERAL AND LIMITATIONS
July 3, 2017
Recommendations contained in this report are based on data obtained from the test boring performed at the
locations shown on the Boring Location Plan in the Appendix. This report does not reflect any variations,
which may occur beyond the test boring.
This report has been prepared for the exclusive use of American Homes 4 Rent, to aid in the evaluation of
this site and to assist their office and other design professionals in the design of this project. It is intended
for use with regard to the specific project described herein. Any substantial changes in the design loading,
site grading and estimated foundation depths, or location of the proposed structure, should be brought to
our attention so that we may determine any effect on our recommendations given herein.
This report should be made available to bidders prior to submitting their proposals and to the successful
contractor and subcontractors for their information only, and to supply them with information relative to the
subsurface investigation, and laboratory tests, etc. The opinions and conclusions expressed in this report are
those of the geotechnical engineer and represent his interpretation of the subsurface conditions based on
tests and results of analysis and studies he has conducted for design.
This report has been prepared in accordance with generally accepted principles of geotechnical engineering
practice and no other warranties are included, either expressed or implied, as to the professional services
provided under the terms of our agreement.
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Report of Geotechnical Exploration
Brookhaven Subdivision
November 8 2016
APPENDIX
Important Information About Your Geotechnical Report
Test Boring Location Plan
Soil Test Boring Logs
Reference Notes for Boring Logs
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