geotechnical investigation five points plaza … · 12/06/2018 · conditions and develop...

J O E L E . W O O D & A S S O C I A T E S P L A N N I N G • E N G I N E E R I N G • M A N A G E M E N T

GEOTECHNICAL INVESTIGATION FIVE POINTS PLAZA

CHARLOTTE, NORTH CAROLINA

For

AECOM

June 12, 2018

JWA File No.: 180509

P.O. Box 296 Clover, South Carolina 29710

2160 Filbert Highway York, South Carolina 29745

Tel. (803) 684-3390 Fax. (803) 628-2891 EMAIL: [email protected]

Main Office 2160 Filbert Highway York, SC 29745 P.O. Box 296 Clover, SC 29710 Tel.: (803) 684-3390 Fax.: (803) 628-2891 Kings Mountain, NC 104 N. Dilling St. Kings Mountain, NC 28086 P.O. Box 296 Clover, SC 29710 Tel.: (704) 739-2565 Fax.: (704) 739-2565


June 12, 2018 Mr. Chris Petterson, PE AECOM 6000 Fairview Rd, Suite 200 Charlotte, NC 28210 Re.: Geotechnical Report Five Points Plaza Improvements Charlotte, North Carolina Dear Mr. Petterson: Submitted herein is the report of our geotechnical evaluation for the above referenced project. Included is a summary of our field investigation, findings, and recommendations. It has been a pleasure working for you on this project and we appreciate the opportunity to be of service. Please notify us if there are any questions or if we may be of further assistance with the implementation of our recommendations. Sincerely, JOEL E. WOOD & ASSOCIATES Christopher E. Wood, P.E. President

Main Office 2160 Filbert Highway York, SC 29745 P.O. Box 296 Clover, SC 29710 Tel.: (803) 684-3390 Fax.: (803) 628-2891 Kings Mountain, NC 104 N. Dilling St. Kings Mountain, NC 28086 P.O. Box 296 Clover, SC 29710 Tel.: (704) 739-2565 Fax.: (704) 739-2565


Table of Contents 1.0 INTRODUCTION ..................................................................................................... 1

1.1 General ................................................................................................................... 1

1.2 Project Objectives .................................................................................................. 1

1.3 Project Description ................................................................................................. 1

2.0 FIELD INVESTIGATION ........................................................................................ 1

3.0 LABORATORY TESTING ....................................................................................... 2

4.0 SITE & SUBSURFACE CONDITIONS ................................................................... 2

4.1 Site Location and Description ................................................................................ 2

4.2 Area Geology ......................................................................................................... 2

4.3 Soil Stratigraphy .................................................................................................... 3

4.4 Groundwater ........................................................................................................... 3

5.0 RECOMMENDATIONS AND CONCLUSIONS .................................................... 3

5.1 Site Preparation ...................................................................................................... 4

5.2 Retaining Wall Design Parameters ........................................................................ 5

5.3 Foundations ............................................................................................................ 5

5.4 Seismic ................................................................................................................... 6

6.0 LIMITATIONS OF REPORT ................................................................................... 6

APPENDIX

Site Location Plan – Figure 1 Soil Test Boring Location Plan – Figures 2 Boring Logs – B-1 to B-5 Labwork

o Grain Size Distribution – GS-1 o Atterberg Limits – AL-1

of 6 JWA File NO.: 180509 June 12, 2018

1.0 INTRODUCTION

1.1 General A geotechnical investigation has been performed for the Five Points Plaza Improvement Project in Charlotte, North Carolina. The investigation was authorized by AECOM under Purchase Order 100584ACM.

1.2 Project Objectives The primary objectives of this investigation were to gather information on subsurface conditions and develop recommendations for site preparation, allowable soil bearing pressures, and retaining wall design parameters. The objectives were accomplished by executing the following: 1. Advancing soil test borings to provide data on soil stratigraphy and to obtain samples

for laboratory analysis; 2. Performing laboratory analyses on select samples to determine soil index properties

and design parameters; and 3. Performing engineering analyses to develop design guidelines and recommendations.

1.3 Project Description The project will consist of enhancements to the Five Points Plaza which will include pedestrian seating and expanded plaza areas, an interactive fountain, and amphitheater style steps/seats. To accommodate these improvements; ramps, steps, and retaining walls will be required for the grade changes. Based on the proposed layout, maximum wall heights/cuts on the order of 6 feet will be required. The general layouts of the plaza improvements are depicted on the Soil Test Boring Location Plan in the Appendix. Subsequent sections of this report contain descriptions of the field investigation, findings, and design recommendations.

2.0 FIELD INVESTIGATION On May 10, 2018, pavement cores were conducted in advance of the borings in order to ensure boring advancement through the pavement layers and to provide a clean core hole for patching. The pavement cores encountered up to 13 inches of asphalt and concrete. On May 11, 2018, five soil test borings (B-1 to B-5) were advanced to depths of 15 feet below existing grades. Additional borings were proposed but could not be accessed with the drill rig as a result of site features and above and below ground utilities. We believe that the borings that have been performed are sufficient for this evaluation as a result of


the consistency of the soils and the relatively small project areas. The soil test borings were advanced utilizing a Diebrich D50 track mounted drill rig and hollow stem augers. Standard split-spoon samples (SPT tests) were obtained at regular intervals throughout the depths of the borings in general accordance with ASTM D-1586 to determine the relative densities and consistencies of the subsurface soils. All of the collected soil samples were sealed in containers and transported to the laboratory for further examination. The soil samples were visually classified based upon the Unified Soil Classification System. The locations of the borings were determined in the field by Joel E. Wood & Associates personnel based upon the provided plan. The approximate locations of the soil test borings are provided on the Boring Location Plan in the Appendix.

3.0 LABORATORY TESTING Select samples were tested in the laboratory to determine applicable physical and engineering properties. The laboratory program included grain size distribution and Atterberg limits tests to evaluate the index properties of the soils and to verify classification of the soils in accordance with the Unified Soil Classification System (USCS). The results of the laboratory test program are presented in the Appendix.

4.0 SITE & SUBSURFACE CONDITIONS

4.1 Site Location and Description

ITEM DESCRIPTION

Location The site is located at the intersection of West Trade St., State St., Rozzelles Ferry Rd., and Beatties Ford Rd in Charlotte, NC.

Existing Development

The site currently consists of the intersection and existing Plaza areas in the northwest and southwest quadrants of the intersection. .

Current Ground Cover

The majority of the site is hard surfacing with some landscape areas adjacent to the existing plaza areas.

4.2 Area Geology The project is situated in the Piedmont Province of North Carolina. Geologic mapping indicates that the site is underlain by metamorphosed quartz diorite and tonalite rock. The Piedmont comprises the area from the foothills of the mountains to the “Fall Line.” This dissected peneplain surface slopes from elevations of about 2,000 feet in the northwest to about 400 feet along the southeast boundary. The Piedmont has a rolling to gently undulating land surface dissected by streams typically with dentritic patterns. The “Fall Line” represents the change from igneous and metamorphic rocks of the Piedmont to unconsolidated sediments of the Coastal Plain. Piedmont rocks range from low rank


metamorphosed sediments and volcanics to high rank metasedimentary and metaigneous rocks and intrusive acid to basic igneous rocks. These rocks are folded and faulted and are thought to be the late Precambrian to early Paleozoic in age. Mineral resources consist of granite, vermiculite, kyanite, barite, gold, silver, copper, sericite, manganese asbestos, topaz, pyrophyllite, and shale. Soils in the Piedmont have clayey to loamy surface layers and clay subsoils. These soils have undergone moderate to severe erosion. Alluvial soils have developed along the major stream courses. Most of the soils of the Piedmont have developed from the chemical weathering of crystalline bedrock, so that rock type and soil type are closely related.

4.3 Soil Stratigraphy In general, the soil test borings encountered up to 13 inches of asphalt and concrete below the ground surface. Below the surface materials, the soils generally consist of soft to very stiff fine-grained soils consisting of elastic silts (MH), silts (ML), and lean clays (CL) in general accordance with the Unified Soil Classification System (USCS). The standard penetration values (N-values) range from 2 to 11 blows per foot (bpf). Detailed descriptions of the soils encountered are provided on the boring logs in the Appendix. As with any geologic formation, the depth and thickness of the soil strata will vary across the site. Although we have designated strata changes at specific depths in our description of the soil stratigraphy on the boring logs in the Appendix, transitions between soil strata are generally gradual. Therefore, the outlined subsurface data should only be considered general on-site soil conditions and should not be utilized as an absolute indicator.

4.4 Groundwater Groundwater was not encountered within the depths of the soil test borings at the time of the field investigation. However, positive site drainage should be maintained at all times and contingencies should be made for dealing with perched groundwater within excavations if excavations are open during rain events.

5.0 RECOMMENDATIONS AND CONCLUSIONS The recommendations presented in this report are based upon the general soil conditions encountered in the soil test borings, our analyses of the site and subsurface conditions, and our experience on similar projects. The recommendations do not reflect variations in subsurface conditions or the presence of unsuitable soil conditions and obstructions. If subsurface conditions are discovered that would impact the assumptions developed in the design process, JOEL E. WOOD & ASSOCIATES should be contacted to evaluate the impact of the identified conditions.


5.1 Site Preparation As soon as possible after clearing, temporary and permanent site drainage should be established as needed to promote drainage away from the project area. Establishing good site drainage prior to construction and maintaining it thereafter can minimize the effects of shallow and/or fluctuating groundwater. Permanent site drainage should be established to prevent subgrade soils beneath slabs and foundation elements from becoming saturated and to minimize fluctuations in moisture contents. The shear strengths of soils typically decrease with increasing moisture contents and saturation. Therefore, site drainage is a critical factor impacting construction and the long-term performance of the structural foundations. The limits of construction and earthwork should be stripped of all surface vegetation, above and below ground obstructions, foundation elements, stumps, root systems, and organic surface soils. The upper near surface soils (topsoil), organic material, and root mat should be stripped to depths as required by the conditions encountered at the time of construction. All utilities and subsurface obstructions should be located and their potential impact on the proposed construction assessed. If utilities are to be removed, placed, or remain within the construction areas, care should be taken to properly backfill trenches and excavations and to ensure that all existing trenches have been properly backfilled and compacted. This will avoid future settlement and distress of pavements. Once all clearing activities have been completed and all required cuts have been made, the exposed subgrade should be proof-rolled with a loaded over-the-road tandem axle dump truck to identify areas of instability. Any areas of deficiency should be corrected at the direction of the geotechnical engineer. As a result of some soft/loose surface soils encountered in the test borings, localized undercutting and recompaction of these layers should be anticipated depending upon depths of cuts. The exposed subgrade soils should be scarified and compacted to ninety-eight percent (98%) of the soil’s standard Proctor maximum dry density before placing any fill or backfill. All structural fill and backfill should be placed in maximum eight (8.0) inch compacted lift thickness and compacted to ninety-eight percent (98%) of the soil’s standard Proctor maximum dry density. Fill and backfill in landscaped areas should be compacted to ninety percent (90%) of the soil’s standard proctor maximum dry density to guard against settlement of fill soils particularly over utility trenches. On-site non-organic soils encountered in the soil test borings should be suitable for re-use as structural fill as long as moisture contents are controlled. To verify adequate compaction of the soils and to ensure proper placement and selection of fill, JOEL E. WOOD & ASSOCIATES recommends that a representative of a geotechnical engineering firm be hired to monitor and evaluate all earthwork operations associated with the pavement areas and building.


5.2 Retaining Wall Design Parameters Based upon the proposed plans, retaining walls and steps will be required to accommodate the proposed grade changes. Maximum cuts/wall heights will be on the order of 6 feet. Parameters for design of the retaining walls have been developed based upon N-counts, soil types, laboratory data, and empirical relationships between N-counts and phi angle. Based upon the results of the field investigation and laboratory analysis, we recommend that retaining walls and/or temporary shoring be designed based upon the following design parameters.

KO (at rest earth pressure coefficient) = 0.53 Ka (active earth pressure coefficient) = 0.36 KP (passive earth pressure coefficient) = 2.77 Φ = (phi, internal angle of friction) = 28º γmoist (soil moist unit weight) = 120 pcf Net Allowable Bearing = 1,500 psf

All open excavations should adhere to OSHA regulations and guidelines for maintaining safe working conditions.

5.3 Foundations Shallow foundation elements can be utilized for support of the proposed structures. Based upon the variability in the soil conditions (i.e. zones of soft/loose soils), footings should be designed utilizing a net allowable soil bearing pressure of one thousand five hundred (1,500) pounds per square foot. Spread footings should be a minimum of twenty-four (24) inches wide to prevent local and/or punching shear failures. Based upon these recommendations, the soils encountered in the soil test borings, and anticipated depths of soil stress increase, total settlement on the order of one (1) inch can be anticipated. Since the soils are unsaturated, the settlements should be relatively immediate/elastic type settlements as loads are applied. There is no long term/consolidation type settlement anticipated. Each footing excavation should be thoroughly cleaned and compacted utilizing a mechanical tamper prior to placing any steel or concrete. Soft, loose soils were encountered within the borings and may need to be stabilized by compacting in-place or by removing such unsuitable soil and replacing with a compactable soil. In areas that are difficult to stabilize, a coarse crushed aggregate should be used to stabilize the excavations. We also recommend the placement of foundation concrete the same day the excavations are opened. If inclement weather prevents the placement of foundation concrete in a timely fashion, appropriate measures should be taken to protect exposed subgrade soils from both surface water and groundwater with either mud slabs or foundation drains. The on-site soils are suitable for support of the concrete slabs. We recommend that the slabs be designed utilizing a modulus of subgrade reaction (k1) of 140 pounds per cubic inch.


5.4 Seismic Based upon the results of the soil test borings and our experience with geologic conditions in the area, the site should be assumed to have a Site Class “D” classification per the International Building Code guidelines with design parameters of SDS=0.253g and SD1=0.163g. These recommendations are based upon the soils encountered and our experience with the geologic conditions in the area. A one hundred (100) foot boring was not performed in order to perform a site-specific classification.

6.0 LIMITATIONS OF REPORT This report has been prepared in accordance with generally accepted geotechnical engineering practice for specific application to this project. The conclusions and recommendations contained herein are based upon applicable standards in this geographic area at the time this report was prepared. No other warranty, expressed or implied, is made. The analyses and recommendations submitted herein are based, in part, upon the data obtained from the subsurface exploration. The nature and extent of variations between the borings will not become evident until construction begins. If variations appear evident, we request the opportunity to re-evaluate the recommendations in this report. In the event that any changes in nature or design of the project are planned, the recommendations contained in the report will not be considered valid unless the changes are reviewed and verified in writing.

AAPPPPEENNDDIIXX

SITE LOCATION PLAN Figure 1

600 ft

N

➤➤

N© 2018 Google

© 2018 Google

© 2018 Google

0.9

6.0

12.0

15.0

6.5" Asphalt, 4.5" Concrete

Firm to Stiff Red Elastic SILT with Sand (MH)

Firm Red and Tan Lean CLAY with Sand (CL)

Firm Tan, Red, and Gray SILT with Sand (ML)

Boring terminated at 15.0 feet

1.0

3.5

6.0

8.5

13.5

SS-1

SS-2

SS-3

SS-4

SS-5

2

1

2

2

2

4

2

2

2

3

4

2

3

3

4

8

4

5

5

7

Five Points PlazaCharlotte, NC

LOG OF BORING No. B-1

Station:Offset:

Notes:Date Drilled: 05/11/18 Supervisor: HAB Diedrich D50 Track Rig

Casing Length: N/A Ground Elevation:

Hammer Type: Gravity Automatic Other:

Water Level: N/A ATD, hours AD Drilling Method: HSA

LEGENDSAMPLER TYPE DRILLING METHOD

SS - Split Spoon NQ - Rock Core, 1-7/8" HSA - Hollow Stem Auger RW - Rotary WashST - Shelby Tube CU - Cuttings CFA - Continuous Flight Augers RC - Rock CoreAWG - Rock Core, 1-1/8" CT - Continuous Tube DC - Driving Casing

Ele

vatio

n(f

t.)

Dep

th(f

t.)

MATERIAL DESCRIPTION

Gra

phic

Log

Sam

ple

Dep

th(f

t.)

Sam

ple

No.

/Typ

e

1st 6

in.

2nd

6 in

.

3rd

6 in

.

N V

alue

STD. PENETRATION TEST DATA(blows/foot)

10 20 30 40 60 80

1.0

6.0

8.5

12.0

15.0

6.5" Asphalt, 5.5" Concrete

Firm to Soft Red Elastic SILT with Sand (MH)

Very Loose Brown and Red SIlty SAND (SM)

Soft Tan and Red Lean CLAY with Sand (CL)

Firm Gray, Tan, and Red SILT with Sand (ML)


1.0

3.5

6.0

8.5

13.5

SS-1

SS-2

SS-3

SS-4

SS-5

2

2

2

WOH

1

3

2

1

2

3

3

1

1

2

3

6

3

2

4

6



Station:Offset:







Ele

vatio

n(f

t.)

Dep

th(f

t.)


Gra

phic

Log

Sam

ple

Dep

th(f

t.)

Sam

ple

No.

/Typ

e

1st 6

in.

2nd

6 in

.

3rd

6 in

.

N V

alue


10 20 30 40 60 80

1.1

8.5

12.0

15.0

13" Asphalt

Red Firm to Soft Elastic SILT with Sand (MH)

Stiff Tan and Red Lean CLAY with Sand (CL)

Firm Gray, Tan, and REd SILT with Sand (ML)


1.1

3.5

6.0

8.5

13.5

SS-1

SS-2

SS-3

SS-4

SS-5

3

3

3

3

2

3

2

4

4

2

3

2

6

6

4

6

4

10

10

6



Station:Offset:







Ele

vatio

n(f

t.)

Dep

th(f

t.)


Gra

phic

Log

Sam

ple

Dep

th(f

t.)

Sam

ple

No.

/Typ

e

1st 6

in.

2nd

6 in

.

3rd

6 in

.

N V

alue


10 20 30 40 60 80

0.9

12.0

15.0

3.3" Asphalt, 7" Concrete

Soft to Stiff Reddish Tan Sandy Lean CLAY(CL)

Firm Red, Tan, and Black SILT with Sand(ML)


1.0

3.5

6.0

8.5

13.5

SS-1

SS-2

SS-3

SS-4

SS-5

1

3

4

3

3

1

5

5

4

4

2

6

6

6

6

3

11

11

10

10



Station:Offset:







Ele

vatio

n(f

t.)

Dep

th(f

t.)


Gra

phic

Log

Sam

ple

Dep

th(f

t.)

Sam

ple

No.

/Typ

e

1st 6

in.

2nd

6 in

.

3rd

6 in

.

N V

alue


10 20 30 40 60 80

1.1

12.0

15.0

6.5" Asphalt, 7" Concrete

Frim to Stiff Red Elastic SILT with Sand (MH)

Loose Tan, Red, and Black Silty SAND (SM)


1.1

3.5

6.0

8.5

13.5

SS-1

SS-2

SS-3

SS-4

SS-5

3

3

2

3

3

3

5

4

4

3

2

6

5

5

4

5

11

9

9

7



Station:Offset:







Ele

vatio

n(f

t.)

Dep

th(f

t.)


Gra

phic

Log

Sam

ple

Dep

th(f

t.)

Sam

ple

No.

/Typ

e

1st 6

in.

2nd

6 in

.

3rd

6 in

.

N V

alue


10 20 30 40 60 80

JOEL E. WOOD&

ASSOCIATES, L.L.C.

Client:

Project:

Project No.: Figure

AECOM


180509 GS-1

SYMBOL SOURCESAMPLE DEPTH

Material Description USCSNO. (ft.)

SOIL DATA

PE

RC

EN

T F

INE

R

0

10

20

30

40

50

60

70

80

90

100

PE

RC

EN

T C

OA

RS

ER

100

90

80

70

60

50

40

30

20

10

0

GRAIN SIZE - mm.

0.0010.010.1110100

% +3"Coarse

% GravelFine Coarse Medium

% SandFine Silt

% FinesClay

0.0 0.8 5.5 22.2 71.50.0 0.0 0.0 0.1 7.8 17.6 74.50.0 0.0 0.0 0.1 10.4 36.9 52.60.0 0.0 0.0 0.1 8.7 41.3 49.9

6 in

.

3 in

.

2 in

.1½

in.

1 in

.¾

in.

½ in

.

3/8

in.

#4 #10

#20

#30

#40

#60

#100

#140

#200

Particle Size Distribution Report

B-1 SS-5 13.5 SILT with Sand ML

B-3 SS-3 6.0 Elastic SILT with Sand MH

B-4 SS-2 3.5 Sandy Lean CLAY CL

B-5 SS-5 13.5 Silty SAND SM

LIQUID AND PLASTIC LIMITS TEST REPORTP

LAS

TIC

ITY

IND

EX

0

10

20

30

40

50

60

LIQUID LIMIT0 10 20 30 40 50 60 70 80 90 100 110

CL-ML

CL or O

L

CH or O

HML or OL MH or OH

Dashed line indicates the approximateupper limit boundary for natural soils

4

7

SOIL DATA

SYMBOL SOURCE

NATURAL

USCSSAMPLE DEPTH WATER PLASTIC LIQUID PLASTICITY

NO. CONTENT LIMIT LIMIT INDEX(%) (%) (%) (%)

JOEL E. WOOD&

ASSOCIATES, L.L.C.

Client:Project:

Project No.: Figure

AECOM


180509 AL-1

B-1 SS-5 13.5 NP 42.4 NP ML

B-3 SS-3 6.0 34.1 64.8 30.7 MH

B-4 SS-2 3.5 19.2 39.7 20.5 CL

B-5 SS-5 13.5 NP 49.5 NP SM

geotechnical investigation five points plaza … · 12/06/2018 · conditions and develop...

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