SWA000022__09 Geotech 2013-11-27 Lawyers Rd Subsurface_20201001

S4)-
Land Development Services
November 27, 2013
Mr. Todd Pomorski
Epcon Communities
500 Stonehenge Parkway
Dublin, Ohio 43017
Reference: Geotechnical Engineering Evaluation
Epcon Communities - Lawyers Road Project
Union County, North Carolina
CESI Project Number 131134.000
Mr. Pomorski:
CESI has performed a geotechnical engineering test pit evaluation in accordance with our Proposal
P131113 dated November 13, 2013.
On November 21, 2013, CESI's Geotechnical Engineer, Edward S. Cummings III, PE observed 15
test pits excavated according to the attached Test Pit Location Plan. The test pits were performed to
evaluate subsurface soil conditions in order to determine the presence of topsoil, unsuitable soils and
shallow rock.
FINDINGS
The site is bordered by Lawyers Road on the southwest, Emerald Lake Subdivision on the east and
undeveloped land on the north. The site is wooded.
Test pits were excavated by a CAT 315 CL track hoe at the locations shown on the enclosed Test Pit
Location Plan. Soil strata in each test pit was observed, identified and recorded by our geotechnical
engineer.
Topsoil was present at the test pit locations. The average topsoil / anticipated stripping depth was
6.5 inches. At the evaluated locations, tree roots are prevalent in the topsoil and extend into the
underlying residual soils.
Washed in or alluvial soils were not present at the test pits. Alluvial soils are compressible strata that
typically have never been subject to an overburden consolidation load and are considered
nonstructural. Even though alluvial soils were not present at the soil test borings, alluvial soils may
be present in any drainage feature which crosses the site. If encountered, alluvial soils will need to
be removed prior to structural fill placement.
Weathered in place, residual soils were encountered beneath the topsoil. The residual soils
consisted of SILT (ML) and slate at various stages of weathering. These silts are fine grained soils
and are moisture sensitive. The Natural Resources Conservation Service (NRCS) has listed the site
45 Spring Street, SW P.O. Box 268 Concord, N.C. 28026-0268 704-786-5404
www.cesilds.com N.C. License Number C-0263

as having the following primary soils series: Badin, Secrest-Cid, and Tatum. The Badin soil series
can have fat CLAY (CH) strata between 7" and 28" below existing grade. The Secrest-Cid soil series
can have fat CLAY (CH) or elastic SILT (MH) strata between 43" and 54" below existing grade. The
Tatum Series can have elastic SILT (MH) between 7" and 42" below existing grade. Fat CLAY (CH)
and elastic SILT (MH) were not observed in the test pits but may be present in unexplored areas of
the site. Fat CLAY (CH) and elastic SILT (MH) have a high shrink/swell potential and are unsuitable
for direct building and pavement support. If encountered, these soils will have to be undercut and
repaired with structural fill.
The Badin, Secrest-Cid, and Tatum soil series have weathered from the volcanic slate of the Carolina
Slate Belt. Our Record of Test Pit Excavation depicts depths and excavation difficulties encountered
at each test location. The parent material of the slate was deposited in horizontal layers, but has
been turned vertical by geologic forces and trends northeast to southwest. As a result of the
orientation of the slate, weathering will be highly variable in short horizontal and vertical distances.
Groundwater was not encountered in the test pits. The elevation of the groundwater may vary
depending upon seasonal factors such as precipitation.
RECOMMENDATIONS
Topsoil, root zones, stumps, organics, strippings, and other unsuitable materials should be
stripped to at least 5 feet plus the plan fill depth beyond the outline of the proposed structural and
pavement areas. The entire cut/fill area should be root raked in multiple directions in order to
remove the root system created by the mature trees that were logged.
After stripping and undercutting, we recommend that the areas to provide support be carefully
evaluated for the presence of soft surficial soils by proofrolling with a 25-ton, four -wheeled, rubber -
tired roller, a loaded dumptruck, or similar approved equipment. The proofroll operation should be
carefully monitored by our Engineer. Areas that wave, rut, or deflect excessively and continue to
do so after several passes of the proofroller may need to be undercut to stiffer soils, based on site
conditions at the time of grading. The undercut areas should be backfilled in thin lifts with
approved, compacted fill materials.
Due to the presence of fine grained soils on the site, it is imperative that positive surface drainage
be maintained during grading operations to prevent water from ponding on the surface. The
surface should be rolled smooth to enhance drainage if precipitation is expected. Subgrades
damaged by construction equipment should be immediately repaired to avoid further degradation
in adjacent areas and to help prevent water ponding.
Fill Material and Placement
Recommended criteria for soil fill characteristics
The project design documents should include the
placement and compaction of project fill materials.
soils with a PI greater than 25 as structural fill.
representative borrow soil samples are collected ;
testing).
Earth Fill Materials
and compaction procedures are listed below.
following recommendations to address proper
We do not recommend the use of highly plastic
Earthwork operations should not begin until
ind tested (allow 3 to 4 days for sampling and
❑ General guidelines for project fill should control properties such as Plasticity Index (PI),
gradation, and organic content. The use of the following USCS soil types, as defined by
ASTM D 2487, should be satisfactory for use as project fill: GW, GP, GM, GC, SW, SP,
Epcon Lawyers Road Geotechnical Engineering Evaluation November 27, 2013
CESI Project Number 131134.000 Page 2

SM, SC, ML, MH (provided the PI is 25 percent or less for MH soils), or combinations
thereof.
❑ Organic content should be no greater than 5 percent by weight, and no large roots
should be allowed.
❑ Maximum particle sizes should be limited to 4 inches or less. A large sheepsfoot
roller such as a CAT 815 is recommended to crush the weathered slate fragments.
It is important to note that unweathered slate that cannot be broken under dozer
and sheepsfoot traffic will need to be reduced by a rock crusher prior to fill
placement or use as utility trench backfill. As a result, CESI would like the
opportunity to review the site grading plans once available and participate in pre -
bid and pre -construction site construction planning.
Compaction Recommendations
❑ One standard Proctor compaction test and one Atterberg limits test for each soil type
used as project fill. Gradation tests may be necessary and should be performed at the
Project Geotechnical Engineer's discretion.
❑ Maximum loose lift thickness — 8 inches.
❑ Compaction requirements — 95 percent of the maximum dry density to a depth of 2 feet
below subgrade, and 100 percent within the upper 2 feet as determined by the standard
Proctor compaction test.
❑ Soil moisture content at time of compaction — within plus 3 percent to minus 3 percent of
the optimum moisture content.
❑ One density test every 2,500 square feet for each lift or two tests per lift, whichever is
greater (for preliminary planning only; the test frequency should be determined by our
geotechnical engineering staff).
❑ Trench fill areas — one density test every 75 linear feet at vertical intervals of 2 feet or
less.
The construction should be monitored by our Construction Materials Testing Engineer. Our
Construction Materials Testing Engineer's (or technician) duties should include observation of
proofrolling activities, density testing of the soil backfill, density testing of the base course, field
sampling and testing of fresh concrete and laboratory compressive strength testing of the
concrete. Field observations, monitoring, and quality assurance testing during earthwork and
pavement construction are an extension of this analysis.
The building foundations should be sized for a maximum net allowable bearing pressure not to
exceed 2,500 pounds per square foot. The exploration findings indicate the building may be
supported by shallow spread footings bearing on residual soil or newly placed structural fill soil.
All footings should bear at a minimum depth of 12 inches below exterior grades for frost
protection. Properly reinforced building footings and adequate slab control joints are
recommended to handle differential settlements, if they occur.
CESI recommends that the residential slab be constructed of 4 inches of 3,000 psi concrete over
6 mil. polyethylene vapor barrier over 4 inches of compacted aggregate base course stone over
stiff residual soil or newly placed structural fill soil. Utility excavations within the structural area
should be properly compacted prior to stone installation.
Per Table 1613.5.2 of the 2009 International Building Code (IBC) as adopted by North Carolina, a
Site Class "C" should be assigned to the site for seismic design purposes.
Based on our site observations and geotechnical findings, difficult excavation due to rock will be
encountered during grading and utility installation operations. CESI recommends that Rock be
defined as the following:
Epcon Lawyers Road Geotechnical Engineering Evaluation November 27, 2013
CESI Project Number 131134.000 Page 3

General Mass Rock Excavation:
Any material which cannot be excavated with a single -tooth ripper drawn by a crawler tractor
having a draw bar pull rated at not less than 56,000 pounds (Caterpillar D8K or equivalent) or
excavated by a trackhoe having a bucket curling force rated at not less than 33,000 pounds
(Caterpillar 315C or equivalent).
Trench Rock Excavation:
Any material which cannot be excavated with a backhoe having a bucket curling force rated at not
less than 33,000 pounds (Caterpillar 315C or equivalent). If these rock excavation conditions are
encountered, CESI should be notified for verification and quantification. Excavation of encountered
trench rock will then require fracturing using jack hammering or blasting.
Pavement Design and Construction Considerations
Based on final site grades and soil subgrade proofroll observations, the proposed pavement areas
maybe supported on stiff residual soil and new structural fill soil.
Prevention of infiltration of water into the subgrade is essential to the successful performance of
any pavement. To prevent the subgrade from becoming saturated and reducing its support
capabilities, we recommend that the soil subgrade be graded to provide positive drainage away
from the pavement areas.
Presented in the tables below are our pavement thickness recommendations for flexible
pavement sections for the proposed subdivision streets. The recommended pavement thickness
below consists of minimum compacted thicknesses rather than nominal thicknesses. The
aggregate base course, asphalt surface course and concrete sections should meet the
requirements of and be placed in general accordance with the applicable sections of the latest
edition of North Carolina Department of Transportation (NCDOT) "Standard Specifications for
Roads and Structures".
Flexible Pavement Section
Recommended
Thickness
Recommended
Pavement Section
1.5 inches
Asphalt Surface Course — Type S 9.513 (NCDOT Section 610)
1.5 inches
Asphalt Surface Course — Type S 9.513 (NCDOT Section 610)
8.0 inches
Aggregate Base Course (ABC) — (NCDOT Section 520)
11 inches
To tal Recommended Section
The pavement sections are recommended under the assumption that the residual and new
structural fill subgrade soils are thoroughly proofrolled and stable immediately prior to construction
of the aggregate base course. Schedule CESI's Engineer to witness the proofroll.
Immediately prior to the installation of the asphalt surface course, aggregate subgrade should be
proofrolled under the supervision of the Engineer. The Engineering Technician's duties should
include in -place density testing of the soil backfill, in -place density testing of the base course, and
testing of the asphalt. Field observations, monitoring, and quality assurance testing during
earthwork and pavement construction are an extension of the pavement design.
Epcon Lawyers Road Geotechnical Engineering Evaluation November 27, 2013
CESI Project Number 131134.000 Page 4

FOLLOW-UP SERVICES
Field observations, monitoring, and quality assurance testing during earthwork, foundation
installation and pavement construction are an extension of the geotechnical design. As a result
we recommend the following:
• Proofroll observations of areas to receive fill soils;
• Density testing during fill soil placement;
• Density testing for utility trench backfill;
• Engineer observation of fill placement;
• Proofroll observations within the pavement areas prior to aggregate and asphalt
placement.
SUMMARY
Based on our site observations and findings, the site grading contractor will encounter SILT (ML),
unweathered and weathered slate. Excavation difficulty should be anticipated during grading and
utility installation operations. As a result, thorough planning and coordination on the part of the
Owner, Contractor and Geotechnical Engineer will be required.
We appreciate the opportunity to be of service to Epcon Communities and we look forward to helping
you through project completion. If you have any questions, please feel free to call.
Respectfully
CESI -4
Edward S. C
Geotec,onicalic -3L0roof"
N.C. Rbof§tration Number 24963
ATTACHED:
TEST PIT LOCATION PLAN
RECORD OF TEST PIT EXCAVATION
VAPOR BARRIER INFORMATION
James G. (Jay) Eaves III P.E.
Division Manager
N.C. Registration Number 27837
Epcon Lawyers Road Geotechnical Engineering Evaluation November 27, 2013
CESI Project Number 131134.000 Page 5

45 Spring Street SW
PO Box 268
Concord, North Carolina, 28026-0268
Phone: [phone]
Fax: [phone]
www.cesilds.com License C-0263
DATE:
TEST PIT LOCATION PLAN
EPCON - LAWYERS ROAD PROJECT DRAWN BY:
PROJ. NO
11-27-13
JGE
131134.000
LAWYERS ROAD SCALE: NTS
UNION COUNTY, NORTH CAROLINA
DRAWING NO.: 1

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An ACI warning:
Vapor Retarder Location
ACI committee 302, "Guide for Concrete Floor and Slab Construction: (ACI 302, 1 R-96) states in
section 4.1.5 that "if a vapor barrier or retarder is required due to local conditions, these products
should be placed under a minimum of 4 in. (100 mm) of trimable, compactible, granular fill (not
sand)." The Moisture Task Group of ACI Committees 302 & 360 has found examples where this
approach has directly contributed to floor covering problems and failures.
As a result of reviewing the details of problem installations, it became clear that the fill course
above the vapor retarder had taken on water from rain, wet -curing, wet -grinding or cutting, and
cleaning. Unable to drain, the wet or saturated fill provides and additional source of water that
contributes to moisture -vapor emission rates from the slab well in excess of the 3 to 5 lb/ 1000sf
/24 hr. recommendation of the floor covering manufacturers.
As a result of these experiences, and the difficulties involved with adequately protecting the fill
course from water during the construction process, caution is advised as to the use of the granular
fill layer when moisture -sensitive finishes are to be applied to the slab surface.
The task group believes that when the use of a vapor retarder or barrier is required, the decision
whether to locate the material in direct contact with the slab or beneath a layer of granular fill
should be made on a case -by -case basis.
Each proposed installation should be independently evaluated as to the moisture sensitivity of
subsequent floor finishes, anticipated project conditions, and the potential effects of slab curling
and cracking.
The following chart can be used to assist in the evaluation process. The anticipated benefits and
risks associated with the specified location of the vapor retarder should be reviewed with all
appropriate parties prior construction.

Flow Chart for Location of Vapor Retarder/Barrier
Does the project have a vapor -sensitive No
covering or a humidity -controlled area?
Yes
Fig. 1
Vapor retarder/barrier is required
if if
Slabs with vapor- Slabs in humidity -controlled areas
sensitive coverings
Will the slabs be placed with
Fig. 2 waterproof roof membrane in place?*
ZR
Yes
Fig. 2 Fig. 3
sb sb s'b'
Dry, granular material Dry, granular material Dry, granular material
Figure 1 Figure 2 Figure 3
*If granular material is subject to future moisture infiltration, use Fig. 2