Geotechnical Engineering Report - Union County

Geotechnical Engineering Report Union County Landfill Retaining Wall

Wingate, North Carolina

October 22, 2015

Project No. 71155054

Prepared for:

CDM Smith

Charlotte, North Carolina

Prepared by:

Terracon Consultants, Inc.

Charlotte, North Carolina

Responsive ■ Resourceful ■ Reliable

TABLE OF CONTENTS

Page EXECUTIVE SUMMARY ............................................................................................................. i 1.0 INTRODUCTION ............................................................................................................. 1 2.0 PROJECT INFORMATION ............................................................................................. 1

2.1 Project Description ............................................................................................ 1

2.2 Site Location and Description ........................................................................... 1 3.0 SUBSURFACE CONDITIONS ........................................................................................ 2

3.1 Geology .............................................................................................................. 2

3.2 Typical Profile .................................................................................................... 2

3.3 Groundwater ...................................................................................................... 3 4.0 RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION ...................................... 3

4.1 Geotechnical Considerations ............................................................................ 3

4.2 Earthwork ........................................................................................................... 4

4.2.1 Site Preparation ....................................................................................... 4

4.2.2 Compaction Requirements ....................................................................... 5

4.2.3 Grading and Drainage .............................................................................. 6

4.2.4 Earthwork Construction Considerations .................................................... 6

4.2.5 Excavations .............................................................................................. 6

4.3 Foundations ....................................................................................................... 8

4.3.1 Foundation Design Recommendations ..................................................... 8

4.3.2 Foundation Construction Considerations .................................................. 8

4.4 Lateral Earth Pressures ..................................................................................... 9

4.5 Global Slope Stability ...................................................................................... 11 5.0 GENERAL COMMENTS ............................................................................................... 12

APPENDIX A – FIELD EXPLORATION

Exhibits A-1a & A-1b Site Location Map

Exhibit A-2 Boring Location Plan

Exhibit A-3 Field Exploration Description

Exhibits A-4 to A-7 Boring Logs

APPENDIX B – SUPPORTING INFORMATION

Exhibits B-1 Laboratory Testing

APPENDIX C – SUPPORTING DOCUMENTS

Exhibit C-1 General Notes

Exhibit C-2 Unified Soil Classification System

APPENDIX D – SLOPE STABILITY ANALYSIS

Exhibit D-1 Slope Stability Section Plan

Exhibit D-2 Slope Stability Section A-A’

Geotechnical Engineering Report Union County Landfill Retaining Wall ■ Wingate, North Carolina October 22, 2015 ■ Terracon Project No. 71155054

Responsive ■ Resourceful ■ Reliable i

EXECUTIVE SUMMARY

A geotechnical investigation has been performed for the proposed retaining wall, located at the

Union County Landfill in Wingate, North Carolina. Four (4) borings, designated B-1 through B-4

were performed to depths of approximately 15 to 28 feet below the existing ground surface in the

proposed retaining wall area.

Based on the information obtained from our subsurface exploration, the site can be developed for

the proposed project. The following geotechnical considerations were identified:

The residual soils and PWR as encountered in our borings at the site appear suitable to

support the proposed retaining wall on shallow foundations provided the subgrade is

prepared as outlined in this report.

The proposed retaining wall may be supported on conventional strip footings with a net

allowable bearing pressure of 3,000 psf for footings in residual soil. If footings are bearing

on or extended further below existing grades to PWR, a higher bearing pressure of 6,000 psf

may be used. Total and differential settlements of less than 1 inch and less than ½ inch over

40 feet or less are anticipated at these bearing pressures. Further details and

recommendations are provided herein.

The residual soils encountered at the boring locations may be excavated with conventional

construction equipment, such as bulldozers, backhoes, and trackhoes. However, difficult

excavation of very stiff to hard residual soils and partially weathered rock (PWR) may be

encountered.

We have performed a slope stability analysis at the critical section of the proposed retaining

wall alignment. Based on our analysis, the section satisfies the minimum factor of safety.

Additional details are included herein.

There are two culverts on-site that drain into the vicinity of the proposed retaining wall. These

culverts may impact design and should be accounted for by the engineer or addressed during

construction.

This summary should be used in conjunction with the entire report for design purposes. It should

be recognized that details were not included or fully developed in this section, and the report must

be read in its entirety for a comprehensive understanding of the items contained herein. The

section titled GENERAL COMMENTS should be read for an understanding of the report

limitations.

Responsive ■ Resourceful ■ Reliable 1

GEOTECHNICAL ENGINEERING REPORT

UNION COUNTY LANDFILL RETAINING WALL

WINGATE, NORTH CAROLINA Project No. 71155054

October 22, 2015

1.0 INTRODUCTION

A geotechnical engineering report has been completed for the proposed retaining wall, located at

the Union County Landfill in Wingate, North Carolina. Four (4) borings, designated B-1 through B-4

were performed to depths of approximately 15 to 28 feet below the existing ground surface in the

proposed retaining wall area. Logs of the borings and a description of the field exploration, along

with a Site Location Map and Boring Location Plan are included in Appendix A of this report.

The purpose of these services is to provide information and geotechnical engineering

recommendations relative to:

subsurface soil conditions foundation design and construction

groundwater conditions lateral earth pressures

earthwork and excavations global slope stability

2.0 PROJECT INFORMATION

2.1 Project Description

ITEM DESCRIPTION

Structures New concrete retaining wall and asphalt pavement.

Surcharge loads (assumed) Traffic: 300 psf

General Site Grading Not provided, but anticipated to be close to existing grades.

Cut and fill slopes None anticipated. Temporary slopes anticipated to be maximum

3:1 (Horizontal to Vertical).

Free-standing retaining walls Concrete retaining wall. Wall estimated to be 9.3 feet high and

approximately 170-feet long.

Below Grade Areas None anticipated.

2.2 Site Location and Description

ITEM DESCRIPTION

Location This project is located at the Union County Landfill located at 2125

Austin Chaney Road in Wingate, NC.



ITEM DESCRIPTION

Existing development The property includes an existing parking area, multiple buildings,

and waste disposal areas adjacent to an existing retaining wall.

Current ground cover Manicured grass areas, trees, and asphalt parking and drive areas.

Existing topography

The site is relatively flat in the vicinity of the asphalt parking and

access drive areas. The site appears to slope down approximately

8-feet for the waste disposal containers adjacent to the existing

retaining wall.

3.0 SUBSURFACE CONDITIONS

3.1 Geology

The project site is located in the Piedmont Physiographic Province, an area underlain by ancient

igneous and metamorphic rocks. The residual soils in this area are the product of in-place

chemical weathering of rock. The typical residual soil profile consists of clayey soils near the

surface where soil weathering is more advanced, underlain by sandy silts and silty sands that

generally become harder with depth to the top of parent bedrock. Alluvial soils are typically present

within floodplain areas along creeks and rivers in the Piedmont. According to the 1985 Geologic

Map of North Carolina, the site is within the Carolina Slate Belt. The bedrock underlying the site

generally consists of Cid Formation Metamudstone and Meta-Argillite, which is described as thin to

thick bedded; bedding plane and axial-planar cleavage common; interbedded with metasandstone,

metaconglomerate, and metavolcanic rock.

The boundary between soil and rock in the Piedmont is not sharply defined. A transitional zone

termed “partially weathered rock” is normally found overlying the parent bedrock. Partially

weathered rock is defined for engineering purposes as residual material with a standard

penetration test resistance exceeding 100 blows per foot. The transition between hard/dense

residual soils and partially weathered rock occurs at irregular depths due to variations in degree of

weathering. Groundwater is typically present in fractures within the partially weathered rock or

underlying bedrock in upland areas of the Piedmont. Fluctuations in groundwater levels on the

order of 2 to 4 feet are typical in residual soils and partially weathered rock in the Piedmont,

depending on variations in precipitation, evaporation, and surface water runoff. Seasonal high

groundwater levels are expected to occur during or just after the typically cooler months of the year

(November through April).

3.2 Typical Profile

Based on the results of the borings, subsurface conditions on the project site can be generalized

as follows:



Surficial materials encountered in the borings included approximately 3 to 5 inches of topsoil or

stone. Below the surficial materials, residual soils were encountered in each of our borings,

except B-4, to depths ranging from approximately 3 to 5.5 feet below existing grades. Residual

soils encountered consisted of sandy silt. This soil visually classifies as ML in accordance with

the Unified Soil Classification System (USCS). Standard penetration test values (N-values) in

the sandy silt ranged from 29 to 73 blows per foot (bpf), indicating a very stiff to hard

consistency.

Partially weathered rock (PWR) was encountered in borings B-1 to B-3 below the residual soils,

and below the surficial materials in boring B-4. The PWR was sampled and visually classified as

sandy silt. Auger refusal was encountered in each boring at depths ranging from approximately 15

to 28 feet below existing grades.

Conditions encountered at each boring location are indicated on the individual boring logs.

Stratification boundaries on the boring logs represent the approximate location of changes in soil

types; in-situ, the transition between materials may be gradual. Details for each of the borings can

be found on the boring logs in Appendix A of this report.

3.3 Groundwater

The boreholes were observed during and after completion of drilling for the presence and level of

groundwater. Groundwater was not encountered in any of the borings. Each borehole was

immediately backfilled after drilling, making subsequent groundwater measurements

unobtainable.

It should be recognized that fluctuations of the groundwater table will occur due to seasonal

variations in the amount of rainfall, runoff and other factors not evident at the time the borings were

performed. Therefore, groundwater levels during construction or at other times in the life of the

structure may be higher or lower than the levels indicated on the boring logs. The possibility of

groundwater level fluctuations should be considered when developing the design and construction

plans for the project.

4.0 RECOMMENDATIONS FOR DESIGN AND CONSTRUCTION

4.1 Geotechnical Considerations

In our opinion, the residual soils and PWR as encountered in our borings at the site are suitable

to support the proposed retaining wall on shallow foundations provided the subgrade is

prepared as outlined in this report. We recommend close examination of the bearing materials be

performed during construction to confirm stable soil conditions.



The residual soils encountered at the boring locations may be excavated with conventional

construction equipment, such as bulldozers, backhoes, and trackhoes. However, difficult

excavation of very stiff to hard residual soils and partially weathered rock (PWR) may be

encountered. We recommend that the contractor submit unit rates for difficult excavations in their

bid. Additional information regarding difficult excavation is included herein.

The proposed site retaining wall was evaluated for global slope stability. The slope stability

analysis was performed at a critical section of the proposed retaining wall alignment. Based on our

analysis, the section satisfies the minimum factor of safety. Additional details are included herein.

It should be noted that during site drilling operations, it was observed that there are two culverts

that drain into the vicinity of the proposed retaining wall. While not part of our scope of

services, these culverts may impact design and should be accounted for by the engineer or

addressed during construction.

4.2 Earthwork

4.2.1 Site Preparation

Existing vegetation, topsoil and any otherwise unsuitable material should be removed from the

construction areas prior to placing fill. Existing utilities should be removed and relocated, or

abandoned in place and filled with concrete or grout. The exposed subgrade soils in areas to

receive fill or at the subgrade elevation in cut areas should be proofrolled to detect soft or loose

soils and other unsuitable materials that may be present. Proofrolling should be performed with

a moderately loaded, tandem axle dump truck or similar pneumatic-tired construction equipment

weighing approximately 10 to 15 tons in the proposed building areas. A Terracon representative

should observe this operation to aid in delineating unstable soil areas. Proofrolling should be

performed after a suitable period of dry weather to avoid degrading an otherwise acceptable

subgrade. Soils which continue to rut or deflect excessively under the proofrolling operations

should be remediated as recommended by the geotechnical engineer.

If subgrade soils are unsuitable, they will require removal and replacement; however, if they are

unstable due to excessive moisture, the most economical solution for remediation may be to

scarify, dry and recompact the material. This remediation is most effective during the typically

hotter months of the year (May to October). If construction is performed during the cooler period

Based on the results of our subsurface exploration, it is our opinion that the proposed retaining

wall may be supported on conventional strip footings with net allowable bearing pressures of

3,000 psf in residual soils. If footings are bearing on or extended further below existing grades to

PWR, a higher bearing pressure of 6,000 psf may be used. Total and differential settlements of

less than 1 inch and less than ½ inch over 40 feet or less are anticipated at these bearing pres-

sures, if subgrade soils are prepared as described in this report. Further details and recommen-

dations are provided herein.



of the year, the timeline for scarifying, drying, and recompacting typically increases considerably

and may lead to alternative remediation solutions. These solutions can include overexcavation

of some or all of the unstable material to be backfilled with either approved engineered fill or

ABC Stone. Potential undercutting can be reduced if the site preparation work is performed

during a period of dry weather and if construction traffic is kept to a minimum on prepared

subgrades. We recommend that the contractor submit a unit rate cost for undercutting as part of

the bidding process.

The existing soils encountered in our borings appear to be suitable for re-use as engineered fill.

Engineered fill should meet the following material property requirements:

Fill Type 1 USCS Classification Acceptable Location for Placement

On-site Soils ML

(LL < 50 & PI < 30) All locations and elevations

Imported Low-Plasticity

Soils

ML, CL, SC, SM

(LL < 50 & PI < 20 with a

minimum 15% passing No.

200 sieve)

All locations and elevations

1. Controlled, compacted fill should consist of approved materials that are free of organic matter and

debris. Frozen material should not be used, and fill should not be placed on a frozen subgrade. A

sample of each material type should be submitted to the geotechnical engineer for evaluation.

4.2.2 Compaction Requirements

We recommend that engineered fill be tested for moisture content and compaction during

placement. Should the results of the in-place density tests indicate the specified moisture or

compaction limits have not been met, the area represented by the test should be reworked and

retested as required until the specified moisture and compaction requirements are achieved.

Engineered fill should meet the following compaction requirements:

ITEM DESCRIPTION

Fill Lift Thickness

8 to 10 inches or less in loose thickness when

heavy, self-propelled compaction equipment is

used

4 to 6 inches in loose thickness when hand-

guided equipment (e.g. jumping jack or plate

compactor) is used



ITEM DESCRIPTION

Minimum Compaction Requirements

95% of the materials maximum standard Proctor

dry density (ASTM D 698)

The upper 12 inches in pavement and building

areas should be compacted to at least 100% of

the materials maximum standard Proctor dry

density (ASTM D 698)

Moisture Content Requirements

Within 3% of the optimum moisture content value

as determined by the standard Proctor test at the

time of placement and compaction

4.2.3 Grading and Drainage

Final surrounding grades should be sloped away from the retaining wall on all sides to prevent

ponding of water. It should be noted that during site drilling operations, it was observed that

there are two culverts that drain into the vicinity of the proposed retaining wall. While not part of

our scope of services, these culverts may impact design and should be accounted for by the

engineer or addressed during construction.

4.2.4 Earthwork Construction Considerations

Unstable subgrade conditions could develop during general construction operations, particularly if

the soils are wetted and/or subjected to repetitive construction traffic. The use of light construction

equipment would aid in reducing subgrade disturbance. Should unstable subgrade conditions

develop, stabilization measures will need to be employed.

Upon completion of filling and grading, care should be taken to maintain the subgrade moisture

content prior to construction of on-grade slab and pavements. Construction traffic over the

completed subgrade should be avoided to the extent practical. The site should also be graded

to prevent ponding of surface water on the prepared subgrades or in excavations. If the

subgrade should become frozen, desiccated, saturated, or disturbed, the affected material

should be removed or these materials should be scarified, moisture conditioned, and

recompacted prior to on-grade slab and pavement construction.

The geotechnical engineer should be retained during the construction phase of the project to

observe earthwork and to perform necessary tests and observations during subgrade

preparation and just prior to construction of building slabs and pavements.

4.2.5 Excavations

The residual and fill soils encountered at the boring locations may be excavated with

conventional construction equipment, such as bulldozers, backhoes, and trackhoes; however,

very dense/hard residual soils and PWR were encountered at relatively shallow depths in each

of the borings. Additionally, auger refusal was encountered in each of the borings at depths



ranging from approximately 15 to 28 feet below existing grades. Shallow PWR and bedrock

material may also be encountered between boring locations. Smaller equipment may have

difficulty excavating PWR. A larger trackhoe or bulldozer equipped with a single-tooth ripper

may be required to excavate these materials. Some PWR, especially in confined excavations,

and rock will require blasting or impact hammering to efficiently excavate. We recommend that

unit rates for mass rock and trench rock be included in the bid package to limit disputes, in the

case that rock-like materials are encountered.

PWR may be encountered during site development. The depth and thickness of PWR,

boulders, and rock lenses or seams can vary dramatically in short distances and between the

testing locations.

It is our opinion that a clear and appropriate definition of rock be included in the project

specifications to reduce the potential for misunderstandings. A sample definition of rock for

excavation specifications is provided below:

Mass Rock is defined as any material that cannot be dislodged by a Caterpillar

D-8 Bulldozer, or equivalent, equipped with a single tooth ripper, without the use

of impact hammers or drilling and blasting. Trench Rock is defined as any

material that cannot be dislodged by a Caterpillar 312 hydraulic backhoe, or

equivalent, without the use of impact hammers or drilling and blasting. Boulders

or masses of rock exceeding ½ or ¼ cubic yard in volume shall also be

considered mass or trench rock, respectively, during excavation. These

classifications do not include materials such as loose rock, concrete, or other

materials that can be removed by means other than impact hammering, but

which for any reason, such as economic reasons, the Contractor chooses to

remove by impact hammering.

As a minimum, all temporary excavations should be sloped or braced as required by

Occupational Safety and Health Administration (OSHA) regulations to provide stability and safe

working conditions. Temporary excavations may be required during grading operations. The

grading contractor should be responsible for designing and constructing stable, temporary

excavations and should shore, slope or bench the sides of the excavations as required, to

maintain stability of both the excavation sides and bottom. All excavations should comply with

applicable local, state and federal safety regulations, including the current OSHA Excavation

and Trench Safety Standards.

Construction site safety is the sole responsibility of the contractor who controls the means,

methods and sequencing of construction operations. Under no circumstances shall the

information provided herein be interpreted to mean that Terracon is assuming any responsibility



for construction site safety or the contractor's activities; such responsibility shall neither be implied

nor inferred.

4.3 Foundations

In our opinion, the proposed retaining wall can be supported by shallow, strip footing foundation

systems bearing within suitable residual soils and PWR or new properly compacted fill. Design

recommendations for shallow foundations for the proposed structure are presented in the

following sections.

4.3.1 Foundation Design Recommendations

DESCRIPTION Wall

Net allowable bearing pressure 1 3,000 psf (residual soil) / 6,000 psf (PWR)

Minimum dimensions 24 inches

Minimum embedment below finished grade 18 inches

Approximate total settlement < 1 inch

Approximate differential settlement < 1/2 inch over 40 feet

1. The recommended net allowable bearing pressure is the pressure in excess of the minimum

surrounding overburden pressure at the footing base elevation. Assumes any fill or soft soils, if

encountered, will be undercut and replaced with engineered fill.

4.3.2 Foundation Construction Considerations

The foundation bearing materials should be evaluated at the time of the foundation excavation.

A representative of Terracon should use a combination of hand auger borings and dynamic

cone penetrometer (DCP) testing in conjunction with visual observations to determine the

suitability of the bearing materials for the design bearing pressure.

The base of all foundation excavations should be free of water and loose soil and rock prior to

placing concrete. Concrete should be placed soon after excavating to reduce bearing soil

disturbance. Should the soils at bearing level become disturbed, saturated, or frozen, the

affected soil should be removed prior to placing concrete. Exposure to inclement weather can

introduce unwanted moisture into the footing subgrade. If construction occurs during inclement

weather, and concreting of foundations is not possible at the time they are excavated, a layer of

lean concrete should be placed on exposed bearing surfaces for protection. Where high

moisture conditions are encountered at footing bearing elevations, the bottom of the

excavations could be stabilized with a relatively clean, well-graded crushed stone or gravel, or a

lean concrete mud mat to provide a working base for construction.

If unsuitable bearing soils are encountered in footing excavations, the excavations should be

extended deeper to suitable soils. The footings could bear directly on the soils at the lower level



or on lean concrete backfill placed in the excavations. The footings could also bear on properly

compacted structural fill extending down to the suitable soils. Overexcavation for compacted

structural fill placement below footings should extend laterally beyond all edges of the footings

at least 8 inches per foot of overexcavation depth below footing base elevation. The

overexcavation should then be backfilled up to the footing base elevation with well-graded

granular material placed in lifts of 10 inches or less in loose thickness and compacted to at least

98 percent of the material's maximum standard Proctor dry density (ASTM D-698). The

overexcavation and backfill procedures are described in the following figure.

4.4 Lateral Earth Pressures

Reinforced concrete walls with unbalanced backfill levels on opposite sides should be designed

for earth pressures at least equal to those indicated in the following table. Earth pressures will

be 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. Two wall

restraint conditions are shown. Active earth pressure is commonly used for design of

free-standing cantilever retaining walls and assumes wall movement. The "at-rest" condition

assumes no wall movement. The recommended design lateral earth pressures do not include a

factor of safety and do not provide for possible hydrostatic pressure on the walls.

D = Depth of overexcavation to suitable soils, as determined by a Terracon representative during construction.



Earth Pressure Coefficients

Earth

Pressure

Conditions

Earth Pressure Coefficient for

Backfill Type

Equivalent

Fluid Density

(pcf)

Surcharge

Pressure,

p1 (psf)

Earth

Pressure,

p2 (psf)

Active

(Ka)

On-site soils – 0.36

Imported granular soils – 0.33

43

40

(0.36)S

(0.33)S

(43)H

(40)H

At-Rest

(Ko)



64

60

(0.53)S

(0.50)S

(64)H

(60)H

Passive

(Kp)



360

360 --- ---

Applicable conditions to the above include:

For active earth pressure, wall must rotate about base, with top lateral movements of

about 0.002 H to 0.004 H, where H is wall height

For passive earth pressure to develop, wall must move horizontally to mobilize

resistance

Uniform surcharge, where S is surcharge pressure

In-situ soil backfill weight a maximum of 120 pcf

Horizontal backfill, compacted to 95 percent of standard Proctor maximum dry density

Unit weight of water (ɣw) is 62.4 pcf

Loading from heavy compaction equipment not included

No hydrostatic pressures acting on wall

No dynamic loading

No safety factor included in soil parameters

Ignore passive pressure in the upper 24 inches



Backfill placed against structures should consist of granular soils or low plasticity cohesive soils.

For the granular values to be valid, the granular backfill must extend out from the base of the

wall at an angle of at least 45 and 60 degrees from vertical for the active/at-rest and passive

cases, respectively. High plasticity clay (CH) and elastic silt (MH) should not be used as

backfill.

To minimize the build-up of lateral soil pressures in excess of the recommended design

pressures, over-compaction of the fill behind the wall should be avoided; however, a lesser

degree of compaction may permit excessive post-construction settlements. In order to limit wall

pressures resulting from over-compaction of wall backfill, we recommend that backfill within 5

feet of a wall be compacted by small, hand-operated compaction equipment to 95 percent of the

standard Proctor maximum dry density. Remaining backfill should be compacted in accordance

with the compaction recommendations provided in the Earthwork section of this report.

4.5 Global Slope Stability

A slope stability analysis for the proposed retaining wall was performed at the cross section of

the critical section of the retaining wall, i.e., the area along the wall alignment having the lowest

existing elevation and potential for the wall to be at its tallest. The location of the critical section

performed in our analysis is shown on Exhibit D-1 in Appendix D. The section selected for the

slope stability analysis is based on our understanding of the proposed retaining wall, the

existing topographic information provided by CDM Smith, and the borings that were completed

along the proposed retaining wall alignment.

The SLOPE/W computer program developed by Geo-Slope, Inc. was used for the slope stability

analysis. The design parameters used in the analysis were based on the findings during our

field exploration, laboratory testing results, literature research with regard to soil strength

conditions, and our experience with similar soils in the project area. Please refer to the following

table for the material strength parameters utilized for the slope stability analysis.

Soil Strength Parameters

Material

Effective Stress

Total Unit Weight (pcf) c’

(psf)

’

(Degrees)

Fill Soils 0 28 115

Residual Soils 100 26 115

PWR 0 45 135

The failure surface with the minimum factor of safety for the soil strength parameters tabulated

above is presented on Exhibit D-2 in Appendix D. The computer-generated outputs include the

cross-section analyzed along with the failure surface representing the minimum factor of safety,



the center of the circle of that failure surface, and the entry and exit points of the failure surfaces

that were analyzed. The minimum factor of safety for the section was determined to be greater

than 2.3. It is our opinion that this factor of safety is sufficient for the proposed retaining wall

under the conditions analyzed.

5.0 GENERAL COMMENTS

Terracon should be retained to review the final design plans and specifications so comments

can be made regarding interpretation and implementation of our geotechnical recommendations

in the design and specifications. Terracon also should be retained to provide observation and

testing services during grading, excavation, foundation construction and other earth-related

construction phases of the project.

The analysis and recommendations presented in this report are based upon the data obtained

from the borings performed at the indicated locations and from other information discussed in

this report. This report does not reflect variations that may occur between borings, across the

site, or due to the modifying effects of construction or weather. The nature and extent of such

variations may not become evident until during or after construction. If variations appear, we

should be immediately notified so that further evaluation and supplemental recommendations

can be provided.

The scope of services for this project does not include either specifically or by implication any

environmental or biological (e.g., mold, fungi, bacteria) assessment of the site or identification or

prevention of pollutants, hazardous materials or conditions. If the owner is concerned about the

potential for such contamination or pollution, other studies should be undertaken.

This report has been prepared for the exclusive use of our client for specific application to the

project discussed and has been prepared in accordance with generally accepted geotechnical

engineering practices. No warranties, either express or implied, are intended or made. Site

safety, excavation support, and dewatering requirements are the responsibility of others. In the

event that changes in the nature, design, or location of the project as outlined in this report are

planned, the conclusions and recommendations contained in this report shall not be considered

valid unless Terracon reviews the changes and either verifies or modifies the conclusions of this

report in writing.

APPENDIX A

FIELD EXPLORATION

TOPOGRAPHIC MAP IMAGE COURTESY OF THE U.S. GEOLOGICAL SURVEY

QUADRANGLES INCLUDE: WATSON, NC (1/1/1987).

SITE LOCATION MAP

Union County Landfill Retaining Wall 2125 Austin Chaney Road

Wingate, NC DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION

PURPOSES

KCM

CRB

CRB

CRB

A1 & A2

10/22/15

A-1a

Exhibit

2020-E Starita Road

Charlotte, NC 28206

71155054 Project Manager:

Drawn by:

Checked by: Approved by:

Project No.

File Name: Date:

1”=24,000 SF Scale:

PROVIDED BY MICROSOFT BING MAPS SITE LOCATION MAP


Wingate, NC

2020-E Starita Road

Charlotte, NC 28206

71155054

DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION

PURPOSES

Project Manager:

Drawn by:


KCM

CRB

CRB

CRB

A1 & A2

10/22/15

Project No.

File Name: Date:

A-1b

Exhibit

AS SHOWN Scale:

BORING LOCATION PLAN

10/22/15

2020-E Starita Road

Charlotte, NC 28206

71155054 AERIAL PHOTOGRAPHY PROVIDED BY MICROSOFT BING MAPS

LEGEND:

= Approximate Location of Borings


Wingate, NC DIAGRAM IS FOR GENERAL LOCATION ONLY, AND IS NOT INTENDED FOR CONSTRUCTION

PURPOSES

Project Manager:

Drawn by:


KCM

CRB

B-1

CRB

CRB

B-2

A1 & A2

B-3

B-4

Scale:

Project No.

File Name: Date:

AS SHOWN A-2

Exhibit


Exhibit A-3

Field Exploration Description

The boring locations were laid out on the site by Terracon personnel and were measured from

available site features. Right angles for the boring locations were estimated. The locations of the

borings should be considered accurate only to the degree implied by the means and methods used

to define them.

The borings were drilled with an ATV-mounted rotary drill rig using hollow stem augers to advance

the boreholes. Samples of the soil encountered in the borings were obtained using the split-barrel

sampling procedure.

In the split barrel sampling procedure, the number of blows required to advance a standard 2

inch O.D. split barrel sampler the last 12 inches of the typical total 18 inch penetration by means

of a 140 pound hammer with a free fall of 30 inches, is the standard penetration resistance

value (SPT-N). This value is used to estimate the in-situ relative density of cohesionless soils

and consistency of cohesive soils.

An automatic SPT hammer was used to advance the split-barrel sampler in the borings

performed on this site. A significantly greater efficiency is achieved with the automatic hammer

compared to the conventional safety hammer operated with a cathead and rope. This higher

efficiency has an appreciable effect on the SPT-N value. The effect of the automatic hammer's

efficiency has been considered in the interpretation and analysis of the subsurface information

for this report.

The samples were tagged for identification, sealed to reduce moisture loss, and taken to our

laboratory for further examination, testing, and classification. Information provided on the boring

logs attached to this report includes soil descriptions, consistency evaluations, boring depths,

sampling intervals, and groundwater conditions. The borings were backfilled with auger cuttings

prior to the drill crew leaving the site.

A field log of each boring was prepared by a staff professional. These logs included visual

classifications of the materials encountered during drilling as well as the driller’s interpretation of

the subsurface conditions between samples. Final boring logs included with this report represent

the engineer's interpretation of the field logs and include modifications based on laboratory

observation and tests of the samples.

6713 37-27-1016

8

12

2

4

00

13-30-43N=73

34-50/4"

35-50/6"

50/2"

50/4"

50/1"50/0"

0.3

3.0

18.519.0

4" TOPSOILSANDY SILT (ML), light brown to brown with tan, white, red, and black,hard, residuum

PARTIALLY WEATHERED ROCK, sampled as light brown to brown withtan, white, red, and black sandy silt with rock fragments

NO RECOVERYAuger Refusal at 19 Feet

Hammer Type: AutomaticStratification lines are approximate. In-situ, the transition may be gradual.

GR

AP

HIC

LO

G

TH

IS B

OR

ING

LO

G IS

NO

T V

ALI

D IF

SE

PA

RA

TE

D F

RO

M O

RIG

INA

L R

EP

OR

T.

G

EO

SM

AR

T L

OG

-NO

WE

LL 7

115

505

4 -

BO

RIN

G L

OG

S.G

PJ

TE

RR

AC

ON

2015

.GD

T 1

0/2

2/1

5

Union County Landfill Wingate, North CarolinaSITE:

Page 1 of 1

Advancement Method:Hollow Stem Augers

Abandonment Method:Borings backfilled with soil cuttings upon completion.

2020-E Starita RoadCharlotte, North Carolina

Notes:

Project No.: 71155054

Drill Rig: CME-550X

Boring Started: 9/30/2015

BORING LOG NO. B-1CDM SmithCLIENT:Charlotte, North Carolina

Driller: J. Cain

Boring Completed: 9/30/2015

Exhibit: A-4

See Exhibit A-3 for description of fieldprocedures.See Appendix B for description of laboratoryprocedures and additional data (if any).

See Appendix C for explanation of symbols andabbreviations.

PROJECT: Union County Landfill Retaining Wall

PE

RC

EN

T F

INE

S

WA

TE

RC

ON

TE

NT

(%

)

ATTERBERGLIMITS

LL-PL-PI

SA

MP

LE T

YP

E

WA

TE

R L

EV

EL

OB

SE

RV

AT

ION

S

DE

PT

H (

Ft.)

5

10

15

RE

CO

VE

RY

(In

.)

FIE

LD T

ES

TR

ES

ULT

S

DEPTH

LOCATION See Exhibit A-2

Dry Cave-In

No Free Water Observed

Dry Cave-In

WATER LEVEL OBSERVATIONSNo Free Water Observed

612

5

2

4

1

1

0

7-12-17N=29

50/5"

50/2"

50/4"

50/1"

50/1"

50/0"

0.4

3.0

17.5

20.5

5" TOPSOIL / STONESANDY SILT (ML), light brown to brown with tan, white, red, and black, verystiff, residuum

PARTIALLY WEATHERED ROCK, sampled as light brown to brown withtan, white, red, and black sandy silt with rock fragments

PARTIALLY WEATHERED ROCK, sampled as very light brown to very lightgray sandy silt with rock fragments

Auger Refusal at 20.5 Feet


GR

AP

HIC

LO

G

TH

IS B

OR

ING

LO

G IS

NO

T V

ALI

D IF

SE

PA

RA

TE

D F

RO

M O

RIG

INA

L R

EP

OR

T.

G

EO

SM

AR

T L

OG

-NO

WE

LL 7

115

505

4 -

BO

RIN

G L

OG

S.G

PJ

TE

RR

AC

ON

2015

.GD

T 1

0/2

2/1

5


Page 1 of 1




Notes:


Drill Rig: CME-550X



Driller: J. Cain


Exhibit: A-5




PE

RC

EN

T F

INE

S

WA

TE

RC

ON

TE

NT

(%

)

ATTERBERGLIMITS

LL-PL-PI

SA

MP

LE T

YP

E

WA

TE

R L

EV

EL

OB

SE

RV

AT

ION

S

DE

PT

H (

Ft.)

5

10

15

20

RE

CO

VE

RY

(In

.)

FIE

LD T

ES

TR

ES

ULT

S

DEPTH


Dry Cave-In


Dry Cave-In


548

23

35-27-88

18

8

4

3

1

1

1

11-13-16N=29

11-16-20N=36

30-50/2"

50/4"

50/3"

50/1"

50/1"

50/1"

0.3

5.5

22.0

27.0

28.1

3" TOPSOILSANDY SILT (ML), trace gravel, light brown to brown with red and tan, verystiff to hard, residuum

PARTIALLY WEATHERED ROCK, sampled as light brown to brown withtan, white, and red sandy silt

PARTIALLY WEATHERED ROCK, sampled as very light brown to very lightgray sandy silt with rock fragments

PARTIALLY WEATHERED ROCK, sampled as very light gray sandy siltwith rock fragmentsAuger Refusal at 28.1 Feet


GR

AP

HIC

LO

G

TH

IS B

OR

ING

LO

G IS

NO

T V

ALI

D IF

SE

PA

RA

TE

D F

RO

M O

RIG

INA

L R

EP

OR

T.

G

EO

SM

AR

T L

OG

-NO

WE

LL 7

115

505

4 -

BO

RIN

G L

OG

S.G

PJ

TE

RR

AC

ON

2015

.GD

T 1

0/2

2/1

5


Page 1 of 1




Notes:


Drill Rig: CME-550X



Driller: J. Cain


Exhibit: A-6




PE

RC

EN

T F

INE

S

WA

TE

RC

ON

TE

NT

(%

)

ATTERBERGLIMITS

LL-PL-PI

SA

MP

LE T

YP

E

WA

TE

R L

EV

EL

OB

SE

RV

AT

ION

S

DE

PT

H (

Ft.)

5

10

15

20

25

RE

CO

VE

RY

(In

.)

FIE

LD T

ES

TR

ES

ULT

S

DEPTH


Dry Cave-In


Dry Cave-In


3

2

2

5

1

0

50/3"

50/2"

50/2"

50/5"

50/1"

50/0"

0.3

15.0

4" STONEPARTIALLY WEATHERED ROCK, sampled as light brown and brown tovery light gray sandy silt with rock fragments

Auger Refusal at 15 Feet


GR

AP

HIC

LO

G

TH

IS B

OR

ING

LO

G IS

NO

T V

ALI

D IF

SE

PA

RA

TE

D F

RO

M O

RIG

INA

L R

EP

OR

T.

G

EO

SM

AR

T L

OG

-NO

WE

LL 7

115

505

4 -

BO

RIN

G L

OG

S.G

PJ

TE

RR

AC

ON

2015

.GD

T 1

0/2

2/1

5


Page 1 of 1




Notes:


Drill Rig: CME-550X



Driller: J. Cain


Exhibit: A-7




PE

RC

EN

T F

INE

S

WA

TE

RC

ON

TE

NT

(%

)

ATTERBERGLIMITS

LL-PL-PI

SA

MP

LE T

YP

E

WA

TE

R L

EV

EL

OB

SE

RV

AT

ION

S

DE

PT

H (

Ft.)

5

10

15

RE

CO

VE

RY

(In

.)

FIE

LD T

ES

TR

ES

ULT

S

DEPTH


Dry Cave-In


Dry Cave-In


APPENDIX B

LABORATORY TESTING


Exhibit B-1

Laboratory Testing

Samples retrieved during the field exploration were taken to the laboratory for further

observation by the project geotechnical engineer and were classified in accordance with the

Unified Soil Classification System (USCS) described in Appendix A. At that time, the field

descriptions were confirmed or modified as necessary. Moisture content, Atterberg Limits, and

wash no. 200 sieve tests were conducted in general accordance with the applicable ASTM

standards on selected soil samples and the test results are presented on the boring logs.

Laboratory tests were conducted on selected soil samples. The laboratory test results were

used for the geotechnical engineering analyses, and the development of earthwork and lateral

earth pressure recommendations. Laboratory tests were performed in general accordance with

the applicable ASTM, local or other accepted standards.

Selected soil samples obtained from the site were tested for the following engineering

properties:

In-situ Water Content

Sieve Analysis

Atterberg Limits

Descriptive classifications of the soils indicated on the boring logs are in accordance with the

enclosed General Notes and the Unified Soil Classification System. Also shown are estimated

Unified Soil Classification Symbols. A brief description of this classification system is included

in Appendix C of this report. All classification was by visual manual procedures. Selected

samples were further classified using the results of Material Finer than No. 200 Sieve and

Atterberg limits testing. The Water Content, Material Finer than No. 200 Sieve and Atterberg

limits test results are provided on the boring logs.

The following table summarizes the in-situ moisture content, wash No. 200 sieve tests, and

Atterberg Limits test results. These results are also shown on the boring logs in Appendix A.

Sample

Location

Depth,

(feet)

In-situ

Moisture

Content,

(%)

% Passing

the No. 200

Sieve

Liquid

Limit, (%)

Plastic

Limit, (%)

Plasticity

Index, (%)

B-1 1.0 – 2.5 13 67 37 27 10

B-2 1.0 – 2.5 6 - - - -

B-3 1.0 – 2.5 8 54 35 27 8

B-3 3.5 – 5.0 23 - - - -

APPENDIX C

SUPPORTING DOCUMENTS

Exhibit: C-1

Unconfined Compressive StrengthQu, (psf)

500 to 1,000

2,000 to 4,000

4,000 to 8,000

1,000 to 2,000

less than 500

> 8,000

Non-plasticLowMediumHigh

DESCRIPTION OF SYMBOLS AND ABBREVIATIONSS

AM

PL

ING

WA

TE

R L

EV

EL

FIE

LD

TE

ST

S

GENERAL NOTES

Over 12 in. (300 mm)12 in. to 3 in. (300mm to 75mm)3 in. to #4 sieve (75mm to 4.75 mm)#4 to #200 sieve (4.75mm to 0.075mmPassing #200 sieve (0.075mm)

Particle Size

< 55 - 12> 12

Percent ofDry Weight

Descriptive Term(s)of other constituents

RELATIVE PROPORTIONS OF FINES

01 - 1011 - 30

> 30

Plasticity Index

Soil classification is based on the Unified Soil Classification System. Coarse Grained Soils have more than 50% of their dryweight retained on a #200 sieve; their principal descriptors are: boulders, cobbles, gravel or sand. Fine Grained Soils haveless than 50% of their dry weight retained on a #200 sieve; they are principally described as clays if they are plastic, andsilts if they are slightly plastic or non-plastic. Major constituents may be added as modifiers and minor constituents may beadded according to the relative proportions based on grain size. In addition to gradation, coarse-grained soils are definedon the basis of their in-place relative density and fine-grained soils on the basis of their consistency.

LOCATION AND ELEVATION NOTES

Percent ofDry Weight

Major Componentof Sample

TraceWithModifier

RELATIVE PROPORTIONS OF SAND AND GRAVEL GRAIN SIZE TERMINOLOGY

TraceWithModifier

DESCRIPTIVE SOIL CLASSIFICATION

BouldersCobblesGravelSandSilt or Clay

Descriptive Term(s)of other constituents

N

(HP)

(T)

(DCP)

(PID)

(OVA)

< 1515 - 29> 30

Term

PLASTICITY DESCRIPTION

Water levels indicated on the soil boringlogs are the levels measured in theborehole at the times indicated.Groundwater level variations will occurover time. In low permeability soils,accurate determination of groundwaterlevels is not possible with short termwater level observations.

Water Level Aftera Specified Period of Time

Water Level After aSpecified Period of Time

Water InitiallyEncountered

StandardPenetrationTest

Unless otherwise noted, Latitude and Longitude are approximately determined using a hand-held GPS device. The accuracyof such devices is variable. Surface elevation data annotated with +/- indicates that no actual topographical survey wasconducted to confirm the surface elevation. Instead, the surface elevation was approximately determined from topographicmaps of the area.

Standard Penetration TestResistance (Blows/Ft.)

Hand Penetrometer

Torvane

Dynamic Cone Penetrometer

Photo-Ionization Detector

Organic Vapor Analyzer

ST

RE

NG

TH

TE

RM

S Standard Penetration orN-Value

Blows/Ft.

Descriptive Term(Consistency)

Descriptive Term(Density)

CONSISTENCY OF FINE-GRAINED SOILS

(50% or more passing the No. 200 sieve.)Consistency determined by laboratory shear strength testing, field

visual-manual procedures or standard penetration resistance

Standard Penetration orN-Value

Blows/Ft.

(More than 50% retained on No. 200 sieve.)Density determined by Standard Penetration Resistance

RELATIVE DENSITY OF COARSE-GRAINED SOILS

Hard > 30

> 50 15 - 30Very Stiff

Stiff

Medium Stiff

Very Soft 0 - 1

Medium Dense

SoftLoose

Very Dense

8 - 1530 - 50Dense

4 - 810 - 29

2 - 44 - 9

Very Loose 0 - 3

Exhibit C-2

UNIFIED SOIL CLASSIFICATION SYSTEM

Criteria for Assigning Group Symbols and Group Names Using Laboratory Tests A

Soil Classification

Group

Symbol Group Name B

Coarse Grained Soils:

More than 50% retained

on No. 200 sieve

Gravels:

More than 50% of

coarse fraction retained

on No. 4 sieve

Clean Gravels:

Less than 5% fines C

Cu 4 and 1 Cc 3 E GW Well-graded gravel F

Cu 4 and/or 1 Cc 3 E GP Poorly graded gravel F

Gravels with Fines:

More than 12% fines C

Fines classify as ML or MH GM Silty gravel F,G,H

Fines classify as CL or CH GC Clayey gravel F,G,H

Sands:

50% or more of coarse

fraction passes No. 4

sieve

Clean Sands:

Less than 5% fines D

Cu 6 and 1 Cc 3 E SW Well-graded sand I

Cu 6 and/or 1 Cc 3 E SP Poorly graded sand I

Sands with Fines:

More than 12% fines D

Fines classify as ML or MH SM Silty sand G,H,I

Fines classify as CL or CH SC Clayey sand G,H,I

Fine-Grained Soils:

50% or more passes the

No. 200 sieve

Silts and Clays:

Liquid limit less than 50

Inorganic: PI 7 and plots on or above “A” line J CL Lean clay K,L,M

PI 4 or plots below “A” line J ML Silt K,L,M

Organic: Liquid limit - oven dried

0.75 OL Organic clay K,L,M,N

Liquid limit - not dried Organic silt K,L,M,O

Silts and Clays:

Liquid limit 50 or more

Inorganic: PI plots on or above “A” line CH Fat clay K,L,M

PI plots below “A” line MH Elastic Silt K,L,M

Organic: Liquid limit - oven dried

0.75 OH Organic clay K,L,M,P

Liquid limit - not dried Organic silt K,L,M,Q

Highly organic soils: Primarily organic matter, dark in color, and organic odor PT Peat

A Based on the material passing the 3-inch (75-mm) sieve B If field sample contained cobbles or boulders, or both, add “with cobbles

or boulders, or both” to group name. C Gravels with 5 to 12% fines require dual symbols: GW-GM well-graded

gravel with silt, GW-GC well-graded gravel with clay, GP-GM poorly

graded gravel with silt, GP-GC poorly graded gravel with clay. D Sands with 5 to 12% fines require dual symbols: SW-SM well-graded

sand with silt, SW-SC well-graded sand with clay, SP-SM poorly graded

sand with silt, SP-SC poorly graded sand with clay

E Cu = D60/D10 Cc =

6010

2

30

DxD

)(D

F If soil contains 15% sand, add “with sand” to group name. G If fines classify as CL-ML, use dual symbol GC-GM, or SC-SM.

H If fines are organic, add “with organic fines” to group name. I If soil contains 15% gravel, add “with gravel” to group name. J If Atterberg limits plot in shaded area, soil is a CL-ML, silty clay. K If soil contains 15 to 29% plus No. 200, add “with sand” or “with gravel,”

whichever is predominant. L If soil contains 30% plus No. 200 predominantly sand, add “sandy” to

group name. M If soil contains 30% plus No. 200, predominantly gravel, add

“gravelly” to group name. N PI 4 and plots on or above “A” line. O PI 4 or plots below “A” line. P PI plots on or above “A” line. Q PI plots below “A” line.

APPENDIX D

SLOPE STABILITY ANALYSIS

LEGEND:

= Approximate Location of Slope Stability Analysis

= Approximate Location of Soil Test Borings

SLOPE STABILITY SECTION PLAN

Union County Landfill Retaining Wall

2125 Austin Chaney Road

Wingate, NCD-1

71155054

10/22/2015

CRB

KCM

CRB

DJC

AS SHOWN

Project Manager:

Drawn by:

Checked by:

Approved by:

Project No.

Scale:

File Name:

Date:

EXHIBIT

D-1 SSSPDIAGRAM IS FOR GENERAL LOCATION

ONLY, AND IS NOT INTENDED FOR

CONSTRUCTION PURPOSES2020 Starita Road, Suite E Charlotte, North Carolina 28206

PH. (704) 509-1777 FAX. (704) 509-1888

A’

A

B-2

B-4

B-3

B-1

D-2

71155054

10/22/2015

CRB

KCM

CRB

DJC

AS SHOWN

Project Manager:

Drawn by:

Checked by:

Approved by:

Project No.

Scale:

File Name:

Date:

EXHIBIT

D-2 A-A’DIAGRAM IS FOR GENERAL LOCATION

ONLY, AND IS NOT INTENDED FOR

CONSTRUCTION PURPOSES2020 Starita Road, Suite E Charlotte, North Carolina 28206

PH. (704) 509-1777 FAX. (704) 509-1888

SLOPE STABILITY SECTION A-A’

Union County Landfill Retaining Wall

2125 Austin Chaney Road

Wingate, NC

Center of Failure Surface

Minimum Factor of Safety

Traffic Surcharge = 300 psf

Note: Slope/W computer software

developed by GeoStudio was utilized in

our analysis.

crbriggs

Text Box

9.3 ft

crbriggs

Text Box

2.7 ft

Documents

Geotechnical Engineering Report - Union County