Soils_and_Foundation_Report.pdf

Eastern Federal Lands Highway Division Sterling, Virginia

SOILS AND FOUNDATION REPORT

BLUE RIDGE PARKWAY

MILEPOST 283.0 TO 291.9

Watauga County, NC

Project PRA-BLRI 2F24

Prepared for:

Department of the Interior

National Park Service

Federal Highway Administration

October 3, 2014

Memo Date: Tuesday, February 24, 2015

Project: BLRI‐2F24

To: Yanina Kirtley, PE

From: Claudia Walsh, PE; Ryan Tinsley, PG

Subject: Addendum #1 to Final Soils and Foundations Report

This memo is Addendum No.1 to the Final Geotechnical (Soils and Foundation) Report (GER) for project PRA-BLRI 2F24 dated October 3, 2014.

At the 70% and 95% review meetings, the following was agreed to by EFLHD, NPS, and HDR:

1. HDR will not include Full Depth Patch Type 4 (FDP‐4) locations in future plan sets. For EFLHD reference and information, the FDP‐4 locations are documented in the 70% plans and in the

Appendix J of the Final GER. The recommendations specified in the GER are based on the findings of HDR’s evaluation and analyses of existing pavement conditions and proposed FDR remediation.

2. Future plan sets will include details for FDP‐4 and subexcavation to be utilized at the direction of the CO during construction based on observed conditions. The field verification process will be developed by EFLHD to determine when the details should be applied during construction.

The FDP‐4 patches are intended to be completed prior to the FDR process. The subexcavation details are intended to be completed after existing pavement and subbase reclamation, and prior to cement stabilization based on performance of reclaimed base during construction.

Patches and subexcavation shall be completed in accordance with the details specified in the plans and should not be modified or combined. The minimum depth of subexcavation is based on backfill material type utilized to meet the structural capacity of the existing subbase/ subgrade surrounding the subexcavation.

3. FDP‐4 detail will be consistent with the 70% plan submission (Sheet S‐7). Subexcavation details utilizing both pavement milling backfill and aggregate base coarse backfill will be consistent with the 95% submission (Sheet S‐2). All details will include a Type II‐B geotextile at the base of the subexcavation.

4. FDP‐4 quantities will consist of 40% of quantity shown in the 70% plans per the following schedule breakdown:

FDP‐4

Sch. A was 2,500 SY, 40% = 1,000 SY

Sch. B was 2,500 SY, 40% = 1,000 SY

Sch. C was 1,600 SY, 40% = 640 SY

Total = 2,640sy

The subexcavation quantity will consist of 60% of the quantity shown in the 95% plans per the following schedule breakdown:

Subexcavation

Sch. A was 325 CY, 60% = 195 CY

Sch. B was 440 CY, 60% = 264 CY (round to 265 CY)

Sch. C was 15 CY, 60% = 9 CY (round to 10 CY)

Total = 470cy

5. FDP‐5 patches at the bridge approaches will remain on the plans and in the quantities as previously provided.

Soils and Foundation Report Blue Ridge Parkway Milepost 283.0 to 291.9

Watauga County, NC Project PRA-BLRI 2F24

HDR Project 223152 i

CONTENTS

1.0 INTRODUCTION

1.1 Authorization, Purpose, and Scope

1.2 Project Location and Description

1.3 General Geology

2.0 PROCEDURES

2.1 NDT Program

2.2 Pavement Condition Surveys

2.3 Test Boring Program

2.4 Laboratory Testing Program

2.5 Pavement Structural Analyses

2.6 HDR Evaluation of Distress, Repairs, and Rehabilitation Alternatives

3.0 RESULTS AND FINDINGS

3.1 NDT Results

3.2 Pavement Condition Survey Results

3.3 Test Boring Results

3.4 Laboratory Testing Program

3.5 Evaluations

3.5.1 Alternative 1: Repair and Overlay

3.5.2 Alternative 2: Repair, Mill and Overlay

3.5.3 Alternative 3: Repair, Recycle and Overlay

3.5.4 Alternative 4: Full Depth Reclamation

4.0 DISCUSSION

4.1 Traffic Data and ESAL Determination

4.2 Pavement Rehabilitation

4.2.1 Pavement Repairs

4.2.2 Pavement Overlay Strategies for Alternatives 1 through 4

4.2.3 Reconstruction Areas

4.3 Corrosion of Drainage Pipes

4.4 Drainage Improvements

4.5 General Observations during Field Review

5.0 RECOMMENDATIONS

5.1 Pavement Rehabilitation

5.1.1 Pavement Repairs

5.1.2 Pavement Overlays

5.1.3 Preliminary Cost Estimate

5.1.4 Further FDR Considerations

5.2 Reconstruction Areas

5.3 Drainage Improvements

5.4 General Pavement and Earthwork

5.5 General Considerations based on Field Review

6.0 LIMITATIONS

7.0 BIBLIOGRAPHY

Watauga County, NC Project PRA-BLRI 2F24 ii

APPENDICES

Appendix A Figures and Tables Appendix B Pavement Condition Survey Field Sheets Appendix C Subsurface Boring Logs Appendix D Laboratory Test Results Appendix E PTS Pavement Evaluation Report Appendix F Relevant Photographs Appendix G Summary of Pavement Repair and Distress Quantities Appendix H Asphalt Core Photographs Appendix I Typical Sections and Details Appendix J Summary of Full Depth Patch (Type 4 and 5) Locations and Quantities

Watauga County, NC Project PRA-BLRI 2F24

1.0 INTRODUCTION

1.1 Authorization, Purpose, and Scope

This Soils and Foundation Report has been prepared by HDR Engineering, Inc. (HDR) for Eastern Federal Lands Highway Division (EFLHD) to summarize the results of the pavement investigation authorized under Contract No. DTFH71-12-D-00003 and Task Order No. 14 (Phase II) for Project PRA-BLRI 2F24. HDR received Notice to Proceed for Phase II on January 6, 2014. This project is located between Mile Post (MP) 283 and 291.9 of the Blue Ridge Parkway in Watauga County, North Carolina. The purpose of the investigation was to evaluate the condition of the existing Parkway pavement and to develop recommendations for repair and rehabilitation for mainline, overlooks, and ramps. This report addresses the east entrance and exit ramp between the Parkway and U.S. Route 321 and four overlooks within section 2F24.

The original project limits were from MP 276.4 to MP 291.9 along Section 2F. Due to funding reallocations, the project limits were reduced by EFLHD per email correspondence on March 17, 2014, from MP 283.0 to MP 291.9 during Phase II of the project. The field investigation for the project was performed between March and May of 2014, and consisted of the following components and project limits:

• Field reconnaissance of the project (MP 283 – MP 291.9)

• Nondestructive testing (NDT) program (MP 276.4 – MP 291.9) – testing was completed prior to project limit reduction

• Pavement condition survey (MP 283 – MP 291.9)

• Test boring program to investigate pavement composition, distressed areas, and subgrade conditions (MP 283 – MP 291.9)

• Laboratory testing program (MP 283 – MP 291.9)

All work was performed in general conformance with Chapters 6 and 11 of the Federal Highway Administration Eastern Federal Lands Highway Division (FHWA-EFLHD) Project Development and Design Manual in English units of measurement. The Standard Specifications for Construction of Roads and Bridges on Federal Highway Projects (FP-03) will be the governing specification document for this project.

This report has been updated from our Draft Soils and Foundation Report dated June 25, 2014 to reflect comments, discussions, and decisions made at the 30% Review Meeting between the NPS, EFLHD and HDR. Revisions to the recommended pavement alternative for BLRI 2F24 were based on NPS and EFLHD experiences during construction and rideability concerns of the full depth reclaimed pavement.

1.2 Project Location and Description

The project is located north of Blowing Rock along the Blue Ridge Parkway in Watauga County, North Carolina. It consists of the mainline Parkway from milepost 283.0 to 291.9, the east entrance/exit ramp between the Parkway and Route 321 (MP 291.9), and the following overlooks and parking areas:

• Boone’s Trace Overlook (milepost 285.1)

• Raven’s Rock Overlook (milepost 289.6)

Watauga County, NC Project PRA-BLRI 2F24

• Yadkin Valley Overlook (milepost 289.9)

• Thunder Hill Overlook (milepost 290.4)

The Parkway is a low-volume, two-lane facility that serves both local commuter and seasonal tourist traffic. A Site Location Map showing the project limits is included as Figure 1 in Appendix A.

1.3 General Geology

The PRA-BLRI 2F24 is located in the Blue Ridge physiographic province consisting of mountainous terrain of steep ridges, inter-mountain basins and valleys intersecting at various angles creating a rugged topography. The elevation in the Blue Ridge topography can exceed 6,000 feet and separate it from the Piedmont province to the east. The rocks forming the Blue Ridge Mountains have been subjected to multiple rifting and collision events spanning almost two billions years.

Specifically, the project is primarily underlain by rocks of the Blowing Rock Formation of Middle Proterozoic era from approximate MP 286.4 to 291.9. This formation consists of a metamorphic gneiss having white feldspar megacrsts (crystals considerably larger than the matrix) in a matrix of banded biotite schist, phyllite, black slate, greenstone, and tuff. From approximate MP 284.6 to 286.4, the project is underlain by a Biotite Granitic Gneiss of the Middle Proterozoic era. This gneiss consists of pinkish gray to light gray, massive to well-foliated, granitic gneiss interlayered with amphibolite and marble. From MP 284.4 to 284.6, the project is underlain by the Ashe Metamorphic Suite and Tallulah Falls Formation, which primarily consists of an amphibolite.

The amphibolite consists of a massive to well foliated, interlayered metamorphosed intrusive to extrusive mafic rock and also includes metasedimentary rocks. The northern 1.4 miles of the project between MP 283.0 to 284.4 is also underlain by the Ashe Metamorphic Suite and Tallulah Falls Formation, but primarily consists of a muscovite-biotite gneiss at this location.

The gneiss is locally sulfidic, interlayered and gradational with mica schist with occasional occurrences of amphibolite and hornblende gneiss. A Geology Map of the project limits is included as Figure 2 in Appendix A.

According to the USDA Soil Survey, the surficial soils along majority of the project limits consists of the Unaka-Porters Complex, Saunook Loam, Porters Loam, Ash-Chestnut Complex, Chandler fine sandy loam, and Cullasaja loam with all soil types having variable percent slopes.

These soils tend to be very rocky/cobbly, well drained, strongly acidic, and derived from the parent bedrock (gneiss). Depth to rock is typically less than 7 feet below natural ground.

2.0 PROCEDURES

The field investigations for the project consisted of an NDT program, a pavement condition survey, a test boring program, and a laboratory testing program. The procedures utilized for each of these components are described in the following sections.

2.1 NDT Program

The NDT program was conducted by Pavement Technical Solutions, Inc. (PTS) of Colliers, WV.

The NDT program was performed to assess the load/deformation characteristics of the existing pavement sections. The deflection data was collected during the week of March 10, 2014 using a Dynatest Model 8000 Falling Weight Deflectometer (FWD). PTS’s FWD is capable of simulating a moving wheel load up to 34,000 lbs. The NDT program included a series of NDT

Watauga County, NC Project PRA-BLRI 2F24 tests generally performed at 500-foot intervals in each lane of the mainline Parkway (250 feet staggered) along the length of the project. The testing intervals were reduced at the overlooks and the Route 321 east entrance/exit ramp (Route 321 ramp) to 100 feet. The NDT tests were conducted in accordance with ASTM D4694-09 “Standard Test Method for Deflections with a Falling-Weight-Type Impulse Load Device” and ASTM D4695-03, “Standard Guide for General Pavement Deflection Measurements.”

The NDT data were subsequently reduced and evaluated by PTS to determine the elastic moduli of the pavement layers and the subgrade for use in pavement structural analyses for both rehabilitation (overlay/recycling) and reclamation. In accordance with the AASHTO Guide for Design of Pavement Structures (1993), the deflection data was normalized to a temperature of 68°F for back-calculation of layer elastic moduli. The deflection at a distance of 36 inches from the center of the load plate was utilized for determination of the subgrade resilient modulus (MR). Parametric analyses and pavement designs were performed using the normalized NDT data and in accordance with AASHTO.

2.2 Pavement Condition Surveys

One crew of HDR personnel conducted the pavement condition survey. The purpose of the survey was to identify areas of pavement distress and to quantify any necessary pavement repairs to be performed for the project.

The methodology utilized in the condition survey is consistent with the FHWA Distress Identification Manual for the Long-Term Pavement Performance Project (FHWA, 2003). For the Parkway and the Route 321 ramp, the survey was performed by walking the entire alignment of the roadways while identifying and documenting the distressed areas on standard condition survey forms. The condition survey of the overlooks was documented on sketches drawn at the time of the survey. Areas of low severity distress were generally not noted on the condition survey forms. The pavement condition survey forms are included in Appendix B.

2.3 Test Boring Program

Twelve pavement test borings (P-1, P-2, P-2A, P-3 to P-6, P-6A, and P-7 to P-10) were drilled for the mainline Parkway, five test borings (R-1, and OL-1 to OL-4) were drilled for the overlooks and the Route 321 ramp, and four test borings (GB-1 to GB-4) were drilled within the mainline Parkway for specific, isolated areas of geotechnical-related pavement distress. The borings were performed to determine the thickness and composition of the existing pavements for NDT evaluations, to aid in evaluation of pavement distresses, and to evaluate the subgrade material characteristics for pavement design. The data obtained from all borings, including the boring stations and offsets, are summarized and presented in the Table A-1 in Appendix A. As-drilled boring locations were not instrument-surveyed. Approximate boring locations are shown on Figures 3A to 3F in Appendix A. The gINT field logs are provided in Appendix C.

The test borings for the investigation were performed by Froeling & Robertson, Inc. (F&R) of Charlotte, NC. The borings were advanced using a truck-mounted drill rig. Asphalt pavement was cored at each boring location. After pavement was cored, the borings were advanced using hollow stem augers. SPTs (Standard Penetration Tests) with split-barrel spoon sampling of soils were conducted using an automatic hammer. SPT samples were collected continuously in the upper ten feet and at five-foot intervals below a depth of ten feet below the pavement structure.

Eighteen-inch SPT samples were collected for the four geotechnical borings; 24-inch SPT samples were collected for the remaining borings. Several of the borings encountered auger

Watauga County, NC Project PRA-BLRI 2F24 refusal prior to reaching the target depth. No rock coring was performed for this project. Several of the borings were offset to obtain bulk soil samples for laboratory moisture-density and California Bearing Ratio (CBR) tests in addition to classification testing. The borings were patched with asphalt cold patch. After drilling, the soil samples were transported to F&R’s laboratory in Charlotte, NC for testing. Driller’s field logs detailing the test boring program were provided by F&R.

HDR personnel laid out the planned boring locations in the field based on pre-laid stationing provided by surveyors.

2.4 Laboratory Testing Program

Laboratory testing services were performed by F&R in Charlotte, NC on soil samples collected from the test boring program. HDR personnel evaluated the field logs provided by F&R and assigned specific samples for testing. The soil testing program included natural moisture content, gradation, Atterberg Limits, moisture-density, CBR, pH, and electrical resistivity tests.

All tests were performed in accordance with applicable ASTM and AASHTO Methods per Chapter 6 of the FHWA-EFLHD Design Manual. The results of the laboratory testing program are included in Appendix D.

2.5 Pavement Structural Analyses

PTS performed structural analyses of the existing project pavements to identify their structural capacity and determine the structural requirements for each pavement rehabilitation alternative.

The analysis used pavement moduli (asphalt, subbase, and subgrade) developed from processed NDT data, pavement thicknesses developed from the pavement test borings, and traffic data that was provided to HDR by EFLHD. The analyses were performed in accordance with the AASHTO Guide for Design of Pavement Structures (AASHTO, 1993). PTS’s report is included in Appendix E.

2.6 HDR Evaluation of Distress, Repairs, and Rehabilitation Alternatives As discussed in Section 2.2, the pavement distresses were documented along mainline Parkway, overlooks, and the Route 321 ramp of Section 2F. HDR evaluated the type and frequency of distresses to develop a distress repair strategy for each pavement rehabilitation alternative. The pavement rehabilitation alternatives considered for Section 2F24 are as follows:

1. Repair and Overlay – The Repair and Overlay alternative consists of conventional partial and full depth repairs, crack sealing, and either a structural or functional asphalt overlay. A structural overlay is required to meet the structural capacity (SNf) for future traffic expected during the design. If structural deficiency of the existing pavement is not present (SNeff SNf), a functional overlay may be necessary to improve rideability and address surface roughness or friction.

2. Repair, Mill, and Overlay – The Repair, Mill, and Overlay alternative consists of conventional full depth patches, crack sealing, and a structural asphalt overlay

3. Repair, Recycle, and Overlay – The Repair, Recycle, and Overlay alternative consists of conventional full depth patches, partial depth cold in-place recycling (CIPR), and either a structural or functional asphalt overlay. This alternative was not considered for the overlooks and the Route 321 ramp.

4. Full Depth Reclamation (FDR) – The FDR alternative consists of conventional full depth patches, full depth recycling of the pavement layers and partial depth recycling of

Watauga County, NC Project PRA-BLRI 2F24 the existing subbase with cement stabilization to provide a new stabilized base course.

This alternative would include a structural asphalt overlay. This alternative was not considered for the overlooks and the Route 321 ramp.

The pavement rehabilitation alternatives and distress repair strategies are discussed in more detail in Sections 3.5 and 4.2 of this report. A pavement reconstruction alternative was not considered for the following reasons:

1. This alternative requires complete removal of the existing pavement structure and does not conserve existing pavement resources.

2. This alternative requires additional construction traffic on the mainline Parkway to accommodate removal of existing pavement.

3. Reconstruction is less cost effective compared to the pavement rehabilitation alternatives considered above.

3.0 RESULTS AND FINDINGS

3.1 NDT Results

The NDT data was used to develop ranges of elastic moduli of the various pavement layers, including the subgrade resilient moduli (Mr). PTS developed three (3) mainline design sections based on trends in the NDT data, and pavement section thicknesses encountered in the test borings. The representative elastic modulus (E) for each pavement layer and design subgrade resilient modulus (Design Mr) values were back-calculated from the NDT data for each mainline design section, overlook, and ramp, and used for design as summarized in Table 1.

Table 1: Elastic Moduli and Design Subgrade Resilient Modulus

Pavement Section/Design

Average Existing AC Thickness

( in)

Average Existing Granular Subbase

Thickness (in)

E AC

(psi)1

E Subbase

(psi)1

Design Subgrade Mr (psi)2

Mainline Parkway – Milepost 283 Station 00+00 to MP 285 Station

40+00 5 9 263,265 37,370 2,223

Mainline Parkway – Milepost 285 Station 40+00 to MP 290 Station

12+00 7 8 261,091 11,859 4,391

Mainline Parkway – Milepost 290 Station 12+00 to MP 291 Station

43+43 5 12 219,689 10,633 4,709

Boone’s Trace Overlook 4.5 7.0 128,880 36,717 2,372

Raven’s Rock Overlook 4.0 6.0 646,905 11,973 4,420

Yadkin’s Valley Overlook 5.5 4.5 384,639 40,657 6,291

Thunder Hill Overlook 5.0 4.0 336,992 23,817 6,695

US 321 Ramp (East side) 6.5 7.5 353,376 43,914 4,762

1. Backcalculations for AC and Subbase layers were computed using PCASE.

2. Design Subgrade Modulus was backcalculated per the equation presented in Part III, Chapter 5, page III-101 of the "AASHTO Design Guide for Design of Pavement Structures ", 1993

Watauga County, NC Project PRA-BLRI 2F24

The back-calculated elastic moduli, E, for the asphalt were relatively consistent along the Parkway mainline with a lower value estimated for Boone’s Trace Overlook. The lower value is likely due to the thinner pavement section. The back-calculated E for the granular subbase was found to be significantly higher in Design Section 1 compared to Design Sections 2 and 3, with values approximately 1/3 of Design Section 1. These data support the granular subbase in Design Sections 2 and 3 is likely more compromised (contaminated with fines) than the granular subbase in Design Section 1.

The uncorrected subgrade resilient modulus values for Design Sections 1 and 2 correlate to CBR values of approximately 6.5 and 8.9 using the following standard empirical correlation for fine-grained soils:

CBR = (Design Mr / 0.33) / 1,500

The uncorrected subgrade resilient modulus value for Design Section 3 correlates to a CBR value of approximately 11 using the following standard empirical correlation for coarse-grained soils:

CBR = ((Design Mr / 0.33) / 3000)(1/0.65)

Based on this, the correlated CBR values correspond reasonably well with the laboratory CBR test values of 4 to 8 for Design Sections 1 and 2 as reported in Section 3.4. The correlated CBR value was considerably less than the laboratory CBR test values of 20 for Design Section 3, likely due to the variations is grain size distribution and moisture content of the coarse grained material tested in the field and laboratory.

3.2 Pavement Condition Survey Results

Pavement distress types were observed and documented in the condition surveys and categorized using the FHWA manual (FHWA, 2003). For each type of distress observed, a severity rating of low, moderate, or high was determined. However, low severity distresses, while observed, were not noted on the survey sheets. The pavement condition survey field sheets are included in Appendix B.

The pavement distress areas observed in the section 2F24 mainline Parkway pavement include fatigue (alligator) cracking, block cracking, edge cracking, longitudinal cracking, transverse cracking, patch deterioration, potholes, and lane-to-shoulder drop-off. Distresses of low severity are common along much of mainline. Medium and high severity distresses predominantly consist of fatigue, block cracking, and longitudinal cracking along the wheel paths. In general, the primary distresses in Design Section 1 (MP 283-MP287, Station 40+00) are longitudinal and transverse cracking with approximately 4% of the pavement having medium fatigue cracking.

More frequent medium to high fatigue cracking (7 to 11%) and deeper rutting depths are present in Design Sections 2 and 3 (MP 287, Station 40+00 to MP 291, Station 45+33). Distresses (block and transverse cracking) were frequently observed in fill and open areas where the pavement is continually subjected to temperature changes (shrinkage stress), particularly in the southern 5 miles of the project (Design Sections 2 and 3). Photographs of common distresses observed are presented in Appendix F. The field condition survey sheets are included in Appendix B. Based on the distress noted on the condition survey sheets, repair types and quantities are tabulated in Appendix G. A discussion of mainline Parkway repair and rehabilitation methods is included in Section 4.2.

Watauga County, NC Project PRA-BLRI 2F24

The pavement distress areas observed in the four overlooks/parking areas in section 2F24 include fatigue cracking, longitudinal cracking, and transverse cracking. Minimal pavement distress was observed in the Route 321 ramp. The ramp appears to have been recently overlaid. The overlook and entrance/exit ramp field condition survey notes are included in Appendix B. Based on the distress noted on the condition survey sheets, repair types and quantities are tabulated in Appendix G. A discussion of overlook and entrance/exit ramp repair and rehabilitation methods is included in Section 4.2.

3.3 Test Boring Results

As discussed in Section 2.3, twelve pavement test borings were drilled for the mainline Parkway, five test borings were drilled for the Route 321 ramp and overlooks, and four test borings were drilled within the mainline Parkway for specific, isolated areas of geotechnical-related pavement distress. The borings were performed to determine the thickness and composition of the existing pavements for NDT evaluations, to aid in evaluation of pavement distresses, and to evaluate the subgrade material characteristics for pavement design. The data obtained from all borings, including the boring stations and offsets, pavement and granular subbase thicknesses, and auger refusal depths, if encountered, are summarized and presented in the Table A-1 in Appendix A. The gINT logs are provided in Appendix C.

The twelve pavement and four geotechnical borings drilled for the section 2F24 mainline Parkway encountered between 4.0 and 8.25 inches of asphalt concrete, with an average thickness of 5.7 inches. Asphalt core photographs are presented in Appendix H. The granular subbase was 6.0 to 12.0 inches thick, with an average thickness of 9.1 inches. Two of the mainline geotechnical borings (GB-3 and GB-4) encountered auger refusal at depths of between

8.3 and 12.3 feet below the pavement surface. Based on field observations, GB-4 likely refused within fill primarily containing boulders, placed during original construction.

The borings drilled for the four overlooks/parking areas in section 2F24 encountered 4.0 to 5.5 inches of asphalt overlying 4.0 to 7.0 inches of granular subbase. One of the borings (OL-3) encountered auger refusal at a depth of 4.3 feet below the pavement surface. The boring drilled for the US Route 321 ramp encountered 6.5 inches of asphalt concrete overlying 7.5 inches of granular subbase.

The pavement subgrade materials generally consist of soft to very hard cohesive soils (ML) and very loose to very dense granular soils (GM, GP, GP-GM, and SM). SPT N-values in the subgrade materials ranged from 2 to greater than 50 blows per foot (bpf). With the exception of two geotechnical borings (GB-1 and GB-2), SPT N-values typically exceeded 10 blows per foot.

All four geotechnical borings were located in areas of severe pavement distress supported by fill embankments. The moisture condition of the subgrade materials was generally described as moist. None of these borings encountered groundwater.

3.4 Laboratory Testing Program

The types and quantities of laboratory tests performed on soil samples collected from the test boring program are summarized in Table 2.

Watauga County, NC Project PRA-BLRI 2F24

Table 2: Laboratory Testing Program Test Quantity

In-situ moisture content 32

Gradation 8

Atterberg limits 8

Moisture-density 6

California Bearing Ratio 6

Minimum soil resistivity 6 pH 6

The soils tested generally classified as sandy silts (ML) and silty sands (SM). These samples generally contained between 25% and 74% finer than the #200 sieve (silt and clay). In-situ moisture contents ranged from 6% to 52%, with a majority ranging from 11% and 32%.

Additionally, moisture-density and CBR tests were performed on six bulk soil samples obtained during the test boring program. The results are summarized in Table 3.

Table 3: Bulk Soil Sample Laboratory Test Data

Boring No.

Sample Depth (feet)

Nat.

Moist

Fines (%) Class.

Max. Dry Density

(pcf)

Optimum Moisture Content

CBR1 pH Min.

Resistivity (ohm-cm)

P-01 1.0 – 7.0 22.5 46.3 SM 105.2 19.3 5 6.3 21,000

P-02A 1.3 – 7.3 20.7 52.8 ML 107.5 16.9 7 6.5 17,000

P-03 1.3 – 7.3 22.0 53.5 ML 108.2 17.1 8 6.9 61,000

P-07 1.3 – 7.3 16.4 25.2 SM 124.0 13.4 4 7.5 15,000

P-08 1.4 – 7.4 8.5 11.3 GP-GM 133.9 9.5 20 8.3 23,000

P-10 1.4 – 7.4 15.2 33.8 SM 120.3 12.7 20 6.8 26,000

1 Soaked value @ 0.1” penetration

Minimum soil resistivity and pH tests were performed bulk samples obtained from 6 pavement borings. The locations were spread over the length of the project to provide a reasonable representation of existing conditions. The soil resistivity ranged from 15,000 to 61,000 ohm-cm with the majority between 15,000 and 26,000 ohm-cm. The measured soil pH values ranged from 6.3 to 8.3. Based on these test results, the soils along the length of Section 2F24 are considered to be non-corrosive. Laboratory test results are included in Appendix D.

3.5 Evaluations

The PTS report summarizes the structural analyses of the existing mainline Parkway, overlooks, and ramps, and the resulting overlay required by AASHTO analysis methods with the design traffic for section 2F24. These analyses were performed for the four rehabilitation strategies (alternatives) described briefly in Section 2.6 of this report. The effective modulus (Ep), effective structural number (SNeff), and structural number for future traffic (SNf) for each alternative are summarized in Appendix B of PTS’s report (Appendix E of this report). The pavement designs are discussed further in Section 4.0. The results of PTS’s pavement analyses can generally be summarized in the following sections:

Watauga County, NC Project PRA-BLRI 2F24

3.5.1 Alternative 1: Repair and Overlay

The first strategy of “repair and overlay” includes the use of full depth (asphalt concrete and subbase) pavement patches where the levels of distress indicate the granular subbase and/or subgrade have been impacted (e.g. medium and high severity fatigue cracking and high severity block cracking), partial depth repairs for the distresses influenced by temperature changes and shrinking stresses in the asphalt concrete (e.g. medium severity block cracking), crack sealing of moderate and high longitudinal and transverse cracks, followed by a functional asphalt overlay thickness of 1.5 inches. This alternative will raise the existing grade approximately 1.5 inches along mainline.

3.5.2 Alternative 2: Repair, Mill and Overlay

The second strategy of “repair, mill, and overlay” includes the use of full depth pavement patches for the medium and high severity fatigue cracking and high severity block cracking, milling 1.5 inches, followed by a structural asphalt overlay replacement of 1.5 inches. This alternative will not raise the grade along mainline.

3.5.3 Alternative 3: Repair, Recycle and Overlay

The third strategy of “repair, recycle, and overlay” includes the use of full depth pavement patches for medium and high severity fatigue cracking and high severity block cracking. In-place cold recycling would be performed on the top 3.0 inches of existing pavement to repair lesser distress types that have impacted the asphalt concrete only. The recycling would be followed by a structural asphalt overlay thickness of 1.5 inches. This alternative will raise the existing grade approximately 1.5 inches along mainline.

3.5.4 Alternative 4: Full Depth Reclamation

The fourth strategy includes “full depth reclamation” (FDR) for the entire mainline project limits.

FDR includes the use of full depth pavement patches for medium and high severity fatigue cracking and high severity block cracking. FDR has a minimum depth of 8 inches to establish an base course consisting of the existing asphalt concrete pavement and granular subbase with cement stabilization. The existing asphalt pavement thickness typically varies between 4 and 8 inches with granular subbase thicknesses between 6 and 12 inches. The FDR asphalt and treated aggregate base would have a structural overlay thickness of 2.0 inches. This alternative will raise the existing grade approximately 2.0 inches along mainline.

4.0 DISCUSSION

The section of this report discusses the traffic data, pavement rehabilitation and repair strategy, corrosion potential, reconstruction areas, drainage improvements, and general observations for the mainline Parkway, the overlooks, and the Route 321 ramp.

4.1 Traffic Data and ESAL Determination

The Average Daily Traffic (ADT) data for the mainline Blue Ridge Parkway (Section 2F) was obtained from the EFHLD design scope report. The provided ADT was 470 (2013) vehicles with a design traffic of 727 and design year of 2035. A compound growth rate of 2.0% per year was specified in the analyses. The vehicle/truck percentage provided EFLHD design scope report and Equivalent Single Axle Load (ESAL) factors selected for ESAL determination are summarized in Table 4.

Watauga County, NC Project PRA-BLRI 2F24

Table 4: Traffic Percentage and ESAL Factors FHWA Class Description Traffic Percentage ESAL Factor

2 Passenger Cars 98.4 0.0008

4 Buses 0.23 0.75

5 RV 0.38 0.5

5 RV/Trucks with Trailers 0.75 0.5

The ESAL factors were selected based on Class and common ranges specified in Section

11.2.1.2 of the PDDM. The high range for Class 1 vehicles was selected based on a back-check utilizing the Table D-1 of the AASHTO Guide for Design of Pavement Structures Manual (1993). A low range factor for Class 4 vehicles was selected, because the commercial buses are not permitted on the parkway. A middle range factor was selected for Class 5 vehicles.

ESALs were estimated in accordance with AASHTO. The cumulative ESALs for 20 years in both directions were approximately 36,112. Per Section 11.2.1.2 of the PDDM, a minimum of 50,000 ESALs were selected for design of paved roadways.

The following parameters were specified for flexible pavement design for the mainline Parkway in accordance with the PDDM and utilized in PTS’s pavement designs:

Reliability = 75%

Overall Standard Deviation = 0.49 Initial Serviceability = 4.2 (flexible pavement)

Terminal Serviceability = 2.0 Lane Distribution Factor = 1 Direction Distribution = 60% Design Period = 20 years

4.2 Pavement Rehabilitation

As previously mentioned in Section 3.5, four alternate pavement rehabilitation strategies were evaluated for this project. They are the “repair and overlay” (Alternative 1); “repair, mill, and overlay” (Alternative 2); “repair, recycle, and overlay” (Alternative 3); and “full depth reclamation” (FDR) (Alternative 4) options. Repair, overlay, recycle, and reclamation strategies have been developed for the four rehabilitation alternatives on 2F24. The following sections discuss pavement repairs, overlay strategies, and reconstruction considerations for each alternative. In addition, corrosion potential, drainage improvements, and rockfall hazards are also discussed.

4.2.1 Pavement Repairs

Pavement distress types were examined in the condition survey and categorized using the FHWA Manual (FHWA, 2003). Although low severity distresses were observed, only the medium and high severity distresses were documented during the survey. A summary of all the distress types for flexible pavements are included in Table 5, General Pavement Repair Strategy. The table also includes the recommended repairs for the various types of distress for the four rehabilitation strategies. Distress types documented during the pavement condition survey include:

a. Fatigue Cracking, Distress Type 1. Medium and high severity fatigue cracking is prevalent throughout 2F24.

Watauga County, NC Project PRA-BLRI 2F24

b. Block Cracking, Distress Type 2. Medium and high severity block cracking are prevalent throughout 2F24.

c. Edge Cracking, Distress Type 3. Medium to high severity edge cracking is present in a few relatively small, isolated areas on 2F24.

d. Longitudinal Cracking (Wheel Path & Non-Wheel Path) Distress Type 4a/4b. Medium and high severity longitudinal cracking is prevalent throughout 2F24.

e. Reflection Cracking at Joints, Type 5. Reflection cracking is not applicable to this project since it is cause by cracks reflecting through the asphalt surface from joints in a concrete base.

f. Transverse Cracking, Distress Type 6. Medium and high severity transverse cracking is prevalent throughout 2F24.

g. Patch/Patch Deterioration, Distress Type 7. Medium severity patch deterioration is present in a few relatively small, isolated areas on 2F24.

h. Potholes, Distress Type 8. Medium and high severity potholes are present in a few relatively small, isolated areas on 2F24.

i. Rutting, Distress Type 9. Rutting was observed along wheel paths on 2F24.

j. Shoving, Type 10. Shoving was not observed on 2F24.

k. Bleeding, Distress Type 11. Bleeding was not observed on 2F24.

l. Polished Aggregate Type 12. Polished Aggregate was not observed on 2F24.

m. Raveling (Weathered), Distress Type 13. Raveling was not observed on 2F24.

n. Lane-to-Shoulder Drop-off, Distress Type 14. Lane-to-shoulder drop-offs is present in a few relatively small, isolated areas on 2F24.

o. Water Bleeding and Pumping, Type 15. Evidence of water bleeding and pumping was not observed on 2F24.

Photographs of common distresses observed along the mainline Parkway are provided in Appendix F.

Watauga County, NC Project PRA-BLRI 2F24

Table 5: General Pavement Repair Strategy

Rehabilitation Strategy Alternatives (Mainline)

Proposed Repair Partial and Full Depth Rehab

1 2 3 4

Distress Description Distress Type

Distress Severity

Repair &

OL

Repair/ Mill & OL

Repair/ 3” Recycle

& OL

8” FDR w/ Cement

Stabilization

& OL

Fatigue (Alligator) Cracking

L None1 Mill CIPR2 FDR

M FDP-4 FDP-4 FDP-4 FDP-4

H FDP-4 FDP-4 FDP-4 FDP-4

Block Cracking 2 L None1 Mill CIPR2 FDR M FDP-1 Mill CIPR2 FDR

H FDP-4 FDP-4 FDP-4 FDP-4

Edge Cracking 3 L None1 Mill CIPR2 FDR

M FDP-4 FDP-4 FDP-4 FDP-4

H FDP-4 FDP-4 FDP-4 FDP-4

Longitudinal Cracking ('a' wheel path/'b' non-wheel path)

4a/4b L None1 Mill CIPR2 FDR M Seal Mill CIPR2 FDR H Seal Mill CIPR2 FDR

Reflection Cracking at Joints ('T' transverse/'L' longitudinal)

5T/5L

L NA NA NA NA

M NA NA NA NA

H NA NA NA NA

Transverse Cracking 6 L None1 Mill CIPR2 FDR M Seal Mill CIPR2 FDR H Seal Mill CIPR2 FDR

Patch/Patch Deterioration 7 L None1 Mill CIPR2 FDR M Seal Mill CIPR2 FDR

H FDP-4 FDP-4 FDP-4 FDP-4

Potholes 8 L None1 Mill CIPR2 FDR

M FDP-4 FDP-4 FDP-4 FDP-4

H FDP-4 FDP-4 FDP-4 FDP-4

Rutting 9 NA FDP-4 Mill CIPR2 FDR Shoving 10 NA FDP-1 Mill CIPR2 FDR

Bleeding 11 L None1 Mill CIPR2 FDR M None1 Mill CIPR2 FDR H None1 Mill CIPR2 FDR

Polished Aggregate 12 NA None1 Mill CIPR2 FDR

Raveling (Weathering) 13 L None1 Mill CIPR2 FDR M None1 Mill CIPR2 FDR H FDP-1 Mill CIPR2 FDR

Lane-to-Shoulder Drop-off 14 NA Reb Shldr3 Reb Shldr3 Reb Shldr3 Reb Shldr3 Water Bleeding and Pumping 15 NA FDP-3 FDP-3 FDP-3 FDP-3 1 None - No repair is recommended other than the asphalt overlay 2 CIPR is an abbreviation for “cold-in-place recycling.”

3 Rehabilitation of the shoulder is necessary where there is lane-shoulder drop off. During construction, these areas should be graded to meet the pavement surface.

Watauga County, NC Project PRA-BLRI 2F24

The repair types shown in Table 5 include the following:

Partial Depth Patch, Type 1 (FDP-1) – Per Section 428, this repair type consists of partial removal of the asphalt up to 1.5 inches for removal of distressed pavement impacted by low temperature changes and shrinkage stress. FDP-1 is recommended for areas of medium severity block cracking (2M). If block cracking was observed within both wheel paths of a lane, the FDP-1 will extend the length of the distress over the full lane width. This patch type is proposed for Alternate 1 only.

Full Depth Patch, Type 4 (FDP-4) – This repair consists of removing the existing asphalt, undercutting 12 inches of the underlying material (granular subbase and soil subgrade), placing a geotextile at the base of the undercut, replacing the undercut with aggregate base backfill, and replacing the existing asphalt (4 to 8.25 inches) with asphalt and aggregate base of variable thickness depending on which pavement rehabilitation alternative is selected. This repair is recommended for areas of medium to high severity fatigue cracking (1M, 1H), high severity block cracking (2H), medium to high severity edge cracking (3M, 3H), high severity patch deterioration (7H), medium to high severity potholes (8M, 8H), severity rutting (9), and water bleeding and pumping (15). FDP-4 will extend the length of the distress over a minimum width of 4 feet. The minimum patch width is based on conversations with EFLHD Construction and their experience with local contractors to the project. If fatigue or block cracking was observed within both wheel paths of a lane, the FDP-4 will extend the length of the distress over the full lane width. The patch locations are based on the distress locations and are proposed for pavement rehabilitation alternatives 1-4.

Limits of the FDP-4s match the limits of the distresses in the pavement condition survey. Per Section 428, the contractor shall extend the limits of the patch 1-foot beyond the limits noted on the plans. A 1-foot contingency in the longitudinal direction (both sides of the patch) has been incorporated into the quantities.

Full Depth Patch, Type 5 (FDP-5) - This repair is utilized at bridge approaches to address existing or potential future differential settlement between the bridge and parkway approaches.

The patch consists of removing the existing asphalt, undercutting 48 inches of the underlying material (granular subbase and soil subgrade), placing a geotextile at the base of the undercut, and installing a toe collector drain on the bridge side of the undercut. The undercut is replaced with granular and aggregate base backfill, followed by asphalt of variable thickness depending on which pavement rehabilitation alternative is selected. FDP-5 will extend a minimum of 30 feet from the bridge and will span both travel lanes. These patch locations are proposed for pavement rehabilitation alternatives 1-4.

FDP-5s were requested by EFLHD at the bridge approaches as a preventative measure against future differential settlement. It is important to note that specific site investigation and analyses were not conducted to verify the patch effectiveness to reduce settlement at the bridge approaches. HDR understands the FDP-5 patches have performed well on other projects.

Therefore, HDR incorporated the EFL provided FDP-5 detail into this report and plans solely based on EFLHD’s request and past performance.

Crack Sealing – Medium to high severity longitudinal (4M, 4H) and transverse cracking (6M, 6H) will be crack sealed prior to the overlay with Alternative 1. Low severity cracks for this alternative will not be treated. The medium and high severity crack quantity is based on the

Watauga County, NC Project PRA-BLRI 2F24 crack lengths observed during the pavement condition survey. The crack sealing will be conducted in accordance with Section 414.

Low to high severity cracks longitudinal (4L, 4M, 4H) and transverse cracking (6L, 6M, 6H) will be addressed with milling in Alternative 2. However, a high severity crack may exist below the mill depth. In this case, the remaining crack will be sealed. For purposes of determining a crack seal quantity for Alternative 2, 25 percent of the crack seal quantity for the moderate to high longitudinal and transverse cracking across for the project was assumed. Crack sealing will not occur with Alternatives 3 and 4.

The crack seal quantity for moderate to high severity longitudinal and transverse cracks was estimated to be approximately 59,400 lineal feet for Alternative 1 and approximately 15,000 lineal feet of high severity cracks for Alternative 2. Although low severity distresses, particularly longitudinal and transverse cracks, fatigue, and block cracking, were observed along the entire mainline Parkway, these distresses were not documented during the pavement condition survey and quantified per our scope. These quantities are presented in more detail in Appendix G.

As previously mentioned, estimates of repair quantities have been developed for the four pavement rehabilitation strategies. The partial depth patches (FDP-1) are required for approximately 4.5% of the mainline pavement. Full depth patches (FDP-4) are required for approximately 7% of the mainline pavement and are included with all alternatives.

As discussed in Section 3.2, less pavement distresses were observed in Design Section 1 than in Design Sections 2 and 3. This pavement section has likely experienced less distress due to less commuter traffic exposure, and the granular subbase is generally more competent as supported by the FWD testing. For Alternative 4 (FDR), the FDPs may be minimized by only addressing the high severity fatigue and edge cracking distressed areas and eliminating the medium fatigue cracking.

In Design Sections 2 and 3, more pavement distresses were observed relative to medium and high fatigue cracking and deeper rutting in localized areas. The higher commuter traffic, combined with less competent granular subbase, have likely caused the higher frequency of distresses. Therefore, FDP-4 patches should be utilized to treat the likely compromised granular subbase below the FDR stabilization.

The extent and severity of pavement distresses and subsequent repair recommendations detailed in this report are based on the pavement conditions that existed at the time the report was prepared. Depending on the lag time between completion of the report and the start of construction, the extent and severity of the distresses could potentially increase substantially. If the lag time is more than one year, we recommend a supplemental condition survey be conducted and recommendations revised as necessary. Field judgment will be required based on conditions encountered during construction. Full-depth pavement repairs should be made prior to the application of any overlays.

4.2.2 Pavement Overlay Strategies for Alternatives 1 through 4 Pavement overlay recommendations are based principally on the results of analyses of the NDT data, the pavement borings, and the predicted traffic. Rehabilitation Alternatives 1-4 were designed by PTS to provide adequate long-term structural capacity based on predicted traffic volumes and types, and structural analyses of the existing pavement. Based on our past

Watauga County, NC Project PRA-BLRI 2F24 experience on EFLHD projects, the minimum overlay thickness has been 1.5 inches. In some areas where analyses indicate a structural overlay is not required, a functional overlay is recommended after the repairs have been completed. This functional overlay will provide a uniform smoothness and appearance consistent with the other portions of the project that require structural overlays. During the 30% review meeting, NPS and EFL were concerned about rideability of the FDR overlay and the differential swell of the FDR cement stabilized base.

NPS and ELF requested a minimum a 3.5-inch thick functional overlay for the FDR alternative during the 30% review meeting. In order to avoid more than a 2-inch grade change, a 1.5-inch mill of the existing pavement will be utilized prior to the FDR and overlay operations.

PTS’s rehabilitation analyses of structural conditions for the existing pavements was developed using three design sections on mainline Parkway. These sections were based on test boring information and grouping of similar NDT data. The average asphalt pavement thickness across the three design sections ranged from 5 to 7 inches and the average granular subbase thickness ranged from 8 to 12 inches based on conditions encountered in the pavement borings. The existing pavement was found to be structurally adequate based on the existing pavement structure thickness and the design traffic loading conditions along mainline Parkway for Alternatives 1 and 2, Design Sections 1 and 2. Structural overlays of 1.5 inches were required for Alternative 3, Design Section 1. For the remaining Design Sections for Alternatives 1-3, a functional overlay of 1.5 inches is recommended for reasons discussed above. A minimum overlay of 3.5 inches is recommended for Alternative 4 over the stabilized FDR base.

The effective modulus (Ep), effective structural number (SNeff), and structural number for future traffic (SNf) for each alternative are summarized in Appendix B of PTS’s report (Appendix E of this report). These resulting overlay requirements are summarized in Table 6 and the net pavement structure thickness (existing pavement asphalt + granular subbase + required structural or recommended functional overlay) are summarized in Table 7 for all alternatives.

Watauga County, NC Project PRA-BLRI 2F24

Table 6: Calculated Overlay Requirements for Section 2F24

Pavement/Design Section

Average Existing

AC

Thickness

( in)

Average Existing Granular Subbase

Thickness (in)

Alt. 1:

Repair

Overlay

Alt. 2:

Repair, 1.5” Mill

Overlay

Alt. 3:

Repair, 3” Recycle

Overlay

Alt. 4: 8”

FDR &

Overlay

Required Structural Overlay Thickness (Dol – in.)

Mainline Parkway – Milepost 283 Station 00+00 to MP

285 Station 40+00

5 9 N/R1 ONR2 1.5 3.5

Mainline Parkway – Milepost 285 Station 40+00 to MP

290 Station 12+00

7 8 N/R1 ONR2 N/R1 3.5

Mainline Parkway – Milepost 290 Station 12+00 to MP

291 Station 43+43

5 12 N/R1 ONR2 N/R1 3.5

Boone’s Trace Overlook 4.5 7.0 2.1 1.5 NA NA

Raven’s Rock Overlook 4.0 6.0 N/R1 ONR2 NA NA

Yadkin’s Valley Overlook 5.5 4.5 N/R1 ONR2 NA NA

Thunder Hill Overlook 5.0 4.0 N/R1 ONR2 NA NA

US 321 Ramp (East side) 6.5 7.5 N/R1 ONR2 NA NA

1. N/R – Structural asphalt overlay not required, however, a 1.5” asphalt overlay is recommended

2. ONR – Structural asphalt overlay not required beyond the 1.5” Mill and Replace included with Alt.

3. NA – Alts 3 and 4 were not considered for the overlooks and ramp

Watauga County, NC Project PRA-BLRI 2F24

Table 7: Net Pavement Structure Thicknesses for Section 2F24

Pavement/Design Section

Average Existing

AC

Thickness

( in)

Average Existing Granular Subbase

Thickness (in)

Alt. 1:

Repair

Overlay1

Alt. 2:

Repair, 1.5”…