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Draft Pavement Evaluation Report – Thornton Road Widening Project STA 23+00 to STA 105+50

City of Stockton Department of Public Works – County of San Joaquin, CA

Submitted by: Stantec Consulting Inc.

February 1, 2008

DRAFT PAVEMENT EVALUATION REPORT – THORNTON ROAD WIDENING PROJECT

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Executive Summary

The City of Stockton utilized the services of Stantec Consulting to conduct a comprehensive pavement evaluation of the Thornton Road pavement structure from station 23+00 to station 105+50. Thornton Road is located in the City of Stockton which is situated in the County of San Joaquin, California. Portions of Thornton Road consisted of both two and four lanes. Cores were extracted from each lane and direction to determine the condition of the asphalt concrete and to verify pavement layer types and thicknesses. A distress survey was also completed for each direction.

Deflection tests were performed in general at 250 ft intervals following the California Test Method (CT) 356 - Deflection Testing protocol. The pavement deflections measured with the FWD were used to determine the in-situ structural conditions of the pavement sections, including the subgrade soil conditions through a process known as “backcalculation.” The backcalculation analysis was performed according to the 1993 AASHTO Design Guide to calculate the in-situ pavement structural capacity and subgrade resilient modulus. In addition, the Caltrans Hot Mix Asphalt Pavement Rehabilitation Design Code was also used for analysis.

All field operations were conducted between November 12th and November 14th, 2007. The pavement structures consisted of an asphalt concrete surface layer underlain by a granular base. This pavement evaluation report presents the pavement evaluation results, analysis, and recommendations for Thornton Road. The evaluation, analysis, and recommendation details are provided in the main text of this report.

The pavement structures along all lanes of Thornton Road were in poor to fair condition with extensive areas of distress such as wheel and non-wheel path longitudinal cracking, transverse cracks, fatigue cracks, and patching. The pavement evaluation and FWD analysis showed that the existing pavement structural capacity is adequate to carry the future traffic loadings over the expected design period. However, due to the amount of surface distress, the potential for reflective cracking is apparent.

Consequently, a number of pavement rehabilitation strategies are recommended for Thornton Road which consist of an asphalt overlay with fabric or Stress Absorbing Membrane Interlayer (SAMI) and mill and overlay options.


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Table of Contents

EXECUTIVE SUMMARY E.1

1.0 INTRODUCTION ................................................................................................................1.1

2.0 PAVEMENT INVESTIGATION...........................................................................................2.1 2.1 FALLING WEIGHT DEFLECTOMETER (FWD) .................................................................2.1 2.2 GROUND PENETRATING RADAR (GPR).........................................................................2.2 2.3 CORING 2.2 2.4 CONDITION ASSESSMENT ..............................................................................................2.3

3.0 FWD ANALYSIS METHODOLOGY ...................................................................................3.1 3.1 AASHTO 1993 ANALYSIS METHODOLOGY ....................................................................3.1

3.1.1 Maximum Normalized Deflection .........................................................................3.1 3.1.2 Backcalculation & Evaluation of the In-situ Pavement Conditions.......................3.1

3.2 CALTRANS PAVEMENT DESIGN METHODOLOGY........................................................3.2 3.2.1 Mean and 80th Percentile Deflections ..................................................................3.2 3.2.2 Tolerable Deflection at the Surface (TDS) ...........................................................3.2

4.0 PAVEMENT EVALUATION AND RESULTS .....................................................................4.1 4.1 PAVEMENT PERFORMANCE AND EXISTING CONDITIONS .........................................4.1

4.1.1 Thornton Road - Northbound ...............................................................................4.1 4.1.2 Thornton Road - Southbound ..............................................................................4.2

4.2 CURB AND DRAINAGE .....................................................................................................4.3 4.3 GROUND PENETRATING RADAR AND PAVEMENT LAYER DATA ...............................4.3 4.4 PAVEMENTS......................................................................................................................4.6 4.5 FWD ANALYSIS RESULTS AND DISCUSSION................................................................4.7

4.5.1 Normalized FWD Deflections...............................................................................4.7 4.5.2 INSITU Pavement Conditions ............................................................................4.10

5.0 PAVEMENT REHABILITATION ANALYSIS .....................................................................5.1 5.1.1 Future Traffic Estimation......................................................................................5.1 5.1.2 Feasibility of Overlay as Rehabilitation Option ....................................................5.6 5.1.3 Rehabilitation Options..........................................................................................5.6

6.0 CLOSURE ..........................................................................................................................6.1

DRAFT PAVEMENT EVALUATION REPORT – THORNTON ROAD WIDENING PROJECT Table of Contents February 1, 2008

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List of Tables Table 2.1: FWD Sensor Configuration ......................................................................................................2.2 Table 4.1: Summary of GPR Layer Statistics ............................................................................................4.3 Table 4.2: Existing Northbound Lane Pavement Structure.......................................................................4.6 Table 4.3: Existing Southbound Lane Pavement Structure ......................................................................4.6 Table 4.4: Summary of Normalized Deflections........................................................................................4.7 Table 4.5: Summary of FWD Testing and Analysis Results ...................................................................4.18 Table 4.6: Average and 75th Percentile of FWD Results .......................................................................4.18 Table 5.8: Required AC Overlay Thickness Based on AASHTO 1993 Procedure...................................5.2 Table 5.9: Overlay Thicknesses based on Caltrans Design Method........................................................5.3 Table 5.10: Overlay Thicknesses based on Caltrans Design Method (cont’)...........................................5.5 List of Figures Figure 1.1: Approximate Project Limits and Testing Directions ................................................................1.1 Figure 2.1: CT-356 Method A ...................................................................................................................2.1 Figure 4.1: Fatigue Cracking (left) and Rutting and Bleeding (right) ........................................................4.1 Figure 4.2: Non Wheel Path Longitudinal Cracking (left) and Fatigue Cracking (right)............................4.2 Figure 4.3: Non-Wheel Path Longitudinal Cracking (left) and Raveling (right).........................................4.2 Figure 4.4: Non Wheel Path Longitudinal Cracking (left) and Fatigue Cracking (right)............................4.3 Figure 4.6: Thornton Road Northbound Lane 2 GPR Layer Profile..........................................................4.4 Figure 4.7: Thornton Road Southbound Lane 1 GPR Layer Profile .........................................................4.5 Figure 4.8: Thornton Road Northbound Lane 2 GPR Layer Profile..........................................................4.5 Figure 4.9: Maximum Normalized Deflection along the Northbound Direction (Lane 1) ..........................4.8 Figure 4.10: Maximum Normalized Deflection along the Northbound Direction (Lane 2) ........................4.9 Figure 4.11: Maximum Normalized Deflection along the Southbound Direction (Lane 1)........................4.9 Figure 4.12: Maximum Normalized Deflection along the South Bound Direction (Lane 2) ....................4.10 Figure 4.13: Subgrade Resilient Modulus along the Northbound Direction (Lane 1) .............................4.11 Figure 4.14: Subgrade Resilient Modulus along the Northbound Direction (Lane 2) .............................4.11 Figure 4.15: Subgrade Resilient Modulus along the Southbound Direction (Lane 1).............................4.12 Figure 4.16: Subgrade Resilient Modulus along the Southbound Direction (Lane 2).............................4.12 Figure 4.17: Effective Pavement Modulus along the Northbound Direction (Lane 1).............................4.13 Figure 4.19: Effective Pavement Modulus along the Southbound Direction (Lane 1) ............................4.14 Figure 4.20: Effective Pavement Modulus along the Southbound Direction (Lane 2) ............................4.15 Figure 4.21: Effective Structural Number along the Northbound Direction (Lane 1) ..............................4.16 Figure 4.22: Effective Structural Number along the Northbound Direction (Lane 2) ..............................4.16 Figure 4.23: Effective Structural Number along the Southbound Direction (Lane 1)..............................4.17 Figure 4.24: Effective Structural Number along the Southbound Direction (Lane 2)..............................4.17


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1.0 Introduction

The City of Stockton retained the services of Stantec Consulting to conduct a comprehensive in-situ pavement evaluation of Thornton Road from station 23+00 to station 105+50 (Figure 1.1). Testing in the northbound direction started at approximately station 105+50 (Pershing Ave) and ended at 23+00 (just before the bridge). For the southbound direction, testing started at approximately station 23+00 (just after the bridge) and ended at station 105+50 (Pershing Ave). Thornton Road is located in the City of Stockton which is situated in the County of San Joaquin, California. The in-situ pavement evaluation included the use of the Falling Weight Deflectometer (FWD) with backcalculation using the AASHTO 1993 methodology and Caltrans pavement design procedure, pavement coring, continuous Ground Penetrating Radar (GPR) thickness profile surveys and pavement condition assessments. All field operations were conducted between November 12th, 2007 and November 14th, 2007.

As a part of the pavement evaluation, this report was prepared to summarize the results of the FWD testing and data analysis, quantify the strength and condition of the existing pavement structures, and provide recommendations for maintenance, rehabilitation, or reconstruction strategies.

Figure 1.1: Approximate Project Limits and Testing Directions

Begin Project STA 23+00

End Project – STA 105+50

NB FWD Testing Station 0 ft

SB FWD Testing Station 0 ft

N



2.0 Pavement Investigation

This section provides an overview of the various field investigation activities performed as a part of the in-situ pavement evaluation. Testing included the use of the Falling Weight Deflectometer (FWD), Ground Penetrating Radar (GPR), Pavement Coring, and Pavement Condition Assessments.

2.1 FALLING WEIGHT DEFLECTOMETER (FWD)

FWD testing was performed using Stantec’s LTPP-SHRP calibrated Falling Wheel Deflectometer (FWD) to determine the in-situ structural capacity of the pavement structure (and subgrade soil conditions) located within the project limits.

Deflection testing was carried out in accordance with the California Test (CT) 356, Deflection of Test to Obtain Flexible Pavement Deflection Measurements for Determining Pavement Rehabilitation Requirements (June 2004). Method A of the CT-356 (Figure 2.1) test protocol recommends testing 21 test points per mile (or pavement section). In addition, FWD testing was staggered across all lanes to ensure maximum coverage. Tests were generally performed along each route at intervals of 250-ft or 21 points per section.

Figure 2.1: CT-356 Method A

At each test location, a series of four load applications were applied to the pavement surface. The first load application consists of a “seating” drop of 40 kN (9,000 lbf) to ensure that the FWD loading plate is firmly resting on the surface of the test location. The second load application consisted of three consecutive loads applied at approximately 40 kN (9,000 lbf) +/- 5% at each test location. Pavement deflections under each load were measured by nine sensors (geophones) placed at the following fixed distances (see Table 2.1.) from the center of the approximately 12 inch (300 mm) diameter load plate. Both pavement surface and air temperature readings were automatically and continuously recorded during FWD testing. A summary of the collected FWD data is presented in Appendix A.

DRAFT PAVEMENT EVALUATION REPORT – THORNTON ROAD WIDENING PROJECT Pavement Investigation February 1, 2008


Table 2.1: FWD Sensor Configuration

Sensor Number 1 2 3 4 5 6 7 8 9

Radial Offset from Center of the Load Plate (in inches) 0 12 18 24 36 48 60 72 -12

2.2 GROUND PENETRATING RADAR (GPR)

A GPR survey of all tested lanes was performed to determine the thickness profiles and changes in the pavement structure within the project limits. GPR testing was conducted using Stantec’s equipment manufactured by Geophysical Survey Systems Inc (GSSI). It consists of a SIR-20 data acquisition system with a Panasonic Toughbook Computer, a model 4105 2.2 GHz air-coupled horn antenna and wheel mounted distance measurement instrument. GPR data was collected along all lanes; GPR thickness profile scans were conducted in 1 ft increments, at a scan rate of 15 ns. Start and end locations of each pavement section along the lanes of all tested streets were marked by placing an identifier “flag” on the GPR data file, during data collection. In addition, each GPR scan was referenced linearly using a Distance Measurement Instrument (DMI) and GPS coordinates.

The processed GPR data provides high resolution pavement thickness profiles across the length of the project. The purpose of collecting GPR data is to assist in the selection of core locations and for enhancing FWD backcalculation analysis. The accuracy of the backcalculation analysis is dependent on accurate pavement layers thicknesses. GPR layer thickness profiles calibrated by field cores are one of the most accurate methods to determine the in-situ layer thickness and conditions.

2.3 CORING

Pavement coring operations were conducted using a trailer mounted coring rig to determine the pavement thickness and to verify the in-situ layer(s) profile and layer properties. Pavement cores were extracted at locations identified using the GPR thickness and the FWD deflection profiles in order to verify the in-situ asphalt layer thickness. A minimum of one core per lane mile or direction was extracted from each street. Additional cores were extracted in areas that exhibited significant changes in the GPR thickness profiles.

Each pavement core was assigned a unique core ID number, photographed and logged. Core data is summarized in Appendix B. The thicknesses of the different pavement layers were measured and recorded by a member of Stantec’s pavement engineering team.

DRAFT PAVEMENT EVALUATION REPORT – THORNTON ROAD WIDENING PROJECT Pavement Investigation February 1, 2008


2.4 CONDITION ASSESSMENT

A condition assessment of the pavement surface was performed to document the observed pavement distresses and document overall pavement performance along each lane and direction. At each FWD test point, a manual distress survey was carried out and digital images of the pavement surface were taken to document the existing pavement condition. A summary of this survey is presented in Appendix C.



3.0 FWD Analysis Methodology

Backcalculation analysis was performed using procedures provided and detailed in the AASHTO 1993 Guide for the design of pavement structures to determine the effective structural number (pavement structural capacity) and the in-situ subgrade soil resilient modulus along both directions of each street in Segment 1. In addition, the Hot Mixed Asphalt (HMA) Rehabilitation Design Code and Procedure from the California Department of Transportation (Caltrans) Office of Pavement Design was used. Both methodologies were used as a design analysis and evaluation checks to develop and recommend a rehabilitation strategy Thornton Road. The following subsections summarize and highlight both analysis methodologies.

3.1 AASHTO 1993 ANALYSIS METHODOLOGY

3.1.1 Maximum Normalized Deflection

The maximum normalized deflection (Do), measured at the center of the load plate, is a good indicator of the overall pavement stiffness (strength). The deflection at this location is a function of the pavement layer stiffnesses, including the support capacity of the subgrade soil beneath the pavement structure. The normalization of the deflection under the load plate is a process that is performed to normalize the effect of the load variation during FWD testing between different test locations and to normalize the deflection collected at different FWD load levels to a common “standard load level of 9000 lbf, at a standard temperature of 680F. The AASHTO 1993 temperature correction methodology was used to normalize the deflection to a standard temperature of 680F.

3.1.2 Backcalculation & Evaluation of the In-situ Pavement Conditions

The FWD measured deflections were used to determine the effective structural number and the in-situ subgrade resilient modulus. The structural number is a representation of the load carrying capacity of the pavement structure and the resilient modulus of the subgrade is a representation of the quality of the subgrade soil to resist permanent deformation under repeated traffic loading.

Backcalculation uses analytical pavement response models to predict deflections based on a set of given layer thickness values and moduli. With pavement thickness held constant, based on GPR thickness scans, coring results and/or as-built construction records review, the response models identify the set of subgrade and pavement layer moduli that produce deflections that are very similar to those measured during FWD field testing. The backcalculated moduli are examined to draw some conclusions about the degree of structural deterioration in the pavement layers and the expected remaining life of the pavement structure. In addition, the backcalculated moduli can be used for the design of future structural overlays for the existing pavement (i.e. for rehabilitation design).

DRAFT PAVEMENT EVALUATION REPORT – THORNTON ROAD WIDENING PROJECT FWD Analysis Methodology February 1, 2008


The outputs of the backcalculation and evaluation analysis are the modulus of elasticity of the pavement structure, known as the effective pavement modulus (EP), the effective Structural Number (SNeff) of the pavement layers, and the subgrade soil resilient modulus (Mr).

3.2 CALTRANS PAVEMENT DESIGN METHODOLOGY

The details of the Caltrans flexible pavement rehabilitation design methodology can be found in Chapter 630 (Flexible Pavement) of the California Highway Design Manual. The manual provides guidance on the specific/detailed engineering procedures for pavement and roadway rehabilitation. Rehabilitation strategies are divided into three main categories:

Overlay

Mill and Overlay

Remove and Replace

While the rehabilitation designs are governed by one or more of the following three major criteria:

Structural Adequacy

Reflective crack retardation

Ride Quality

On any resurfacing project, it is recommended to resurface (pave) the entire shoulder and mainline pavement (traveled roadway) using the same rehabilitation treatment.

3.2.1 Mean and 80th Percentile Deflections

The mean pavement deflection under the load plate - for a test section - is determined by dividing the sum of the individual deflection measurements by the number of deflection measurements, along this section. The 80th percentile deflection value (under the load plate) represents a deflection level at which approximately 80 percent of all measured deflections are less than the calculated deflection value and 20 percent are greater than the same value. As a result, a strategy based on the 80th percentile deflection provides more conservative rehabilitation approach compared to using only the mean deflection value. In addition, this California method allows the identification of the deflection outliers using upper and lower deflection limits.

3.2.2 Tolerable Deflection at the Surface (TDS)

The tolerable deflection (TDS) refers to the level beyond which repeated deflections of that magnitude produce fatigue prior to the planned Traffic Index (TI). TDS values are obtained from Table 635.1 A (Chapter 630, Caltrans Highway Design Manual) and are a function of the existing asphalt (HMA) thickness and the TI.

The TDS is then compared to the average D80 (80th percentile of the deflection under the load plate) to determine overlay requirements. If average D80 value of the roadway is smaller than the TDS, then the existing pavement is structurally adequate and no structural overlay is

DRAFT PAVEMENT EVALUATION REPORT – THORNTON ROAD WIDENING PROJECT FWD Analysis Methodology February 1, 2008


required. On the other hand, if the average D80 value is greater than the TDS, a required percent reduction in deflection at the surface (PRD), to restore roadway structural adequacy, must be calculated from the following equation:

PRD = Average D80 – TDS * 100 AverageD80

The additional required Gravel Efficiency (GE) is then determined using the calculated PRD and Table 635.1B (Chapter 630, Caltrans Highway Design Manual). The additional GE is the amount of aggregate base that will provide sufficient strength to reduce the surface deflections to less than the tolerable level.

For additional details of the Caltrans based method, please refer to Chapter 630 of the California Highway Design Manual.



4.0 Pavement Evaluation and Results

The following sections summarize the in-situ pavement condition for Thornton Road as determined from the field operations and the subsequent analyses detailed earlier in this report. Thornton Road was evaluated from station 23+00 to station 105+50. In addition, several rehabilitation alternatives are presented and discussed.

4.1 PAVEMENT PERFORMANCE AND EXISTING CONDITIONS

The existing pavement condition was evaluated along both directions of Thornton Road using a modified SHRP-LTPP manual pavement distress protocol. The following sections summarize the results of the distress survey for the north and southbound lanes. The detailed results of this survey are presented in Appendix C.

4.1.1 Thornton Road - Northbound

For the outer northbound lane (Lane 1) of Thornton Road, medium to high severity fatigue cracking was observed for approximately 80% of the entire section (Figure 4.1). High severity wheel path and non-wheel path longitudinal cracking was observed for approximately 60% of the length between stations 2,800 ft to 8,000 ft. Transverse cracks and block cracking were observed at a number of locations. A few localized areas of rutting and bleeding were observed at the start of the section (Figure 4.1).

Figure 4.1: Fatigue Cracking (left) and Rutting and Bleeding (right)

The inner northbound lane (Lane 2) of Thornton Road is approximately 1,300 feet in length. High severity fatigue cracking was observed for approximately 25% of the section, towards the end of the lane. Non-wheel path longitudinal cracking was observed for the entire length of the section (Figure 4.2). A few localized areas of rutting and bleeding were also observed.

DRAFT PAVEMENT EVALUATION REPORT – THORNTON ROAD WIDENING PROJECT Pavement Evaluation and Results February 1, 2008


Figure 4.2: Non Wheel Path Longitudinal Cracking (left) and Fatigue Cracking (right)

4.1.2 Thornton Road - Southbound

For the outer southbound lane (Lane 1) of Thornton Road, medium to high severity fatigue cracking was observed for approximately 80% of the entire length. High severity block cracking was observed for approximately 20% of the section towards the beginning of the project limits (Figure 4.3). Medium to high severity wheel path longitudinal cracking was observed for approximately 30% of the section. A few localized areas of transverse cracking, patches, rutting and bleeding were observed over the length of the section.

Figure 4.3: Non-Wheel Path Longitudinal Cracking (left) and Raveling (right)

For the inner south bound lane (Lane 2) of Thornton Road, medium to high severity fatigue cracking was observed throughout the entire length. A few localized areas of non-wheel path longitudinal cracking and transverse cracking was observed (Figure 4.4).



Figure 4.4: Non Wheel Path Longitudinal Cracking (left) and Fatigue Cracking (right)

4.2 CURB AND DRAINAGE The condition of the concrete curb along the north and south bound lanes of Thornton Road was observed to be in fair to good shape. Drainage along Thornton Road consisted primarily of catch basins and ditches in a few areas. Overall, the drainage condition on the site can be characterized as fair to good with no standing water observed during the time of inspection.

4.3 GROUND PENETRATING RADAR AND PAVEMENT LAYER DATA The GPR Thickness profiles from the north and southbound lanes are presented in Figures 4.5 to 4.8, respectively. For the northbound lanes, the thickness profile of the asphalt concrete varies from 2.5 inches to 18.0 inches across the length of the project, with an average thickness of 12.3 and 8.6 inches for lanes 1 and 2 respectively. The standard deviations of the asphalt concrete in the northbound lanes are 3.2 and 0.58 for lanes 1 and 2 respectively. The coefficient of variation in the northbound lanes is estimated at 26 % and 7 % for lanes 1 and 2 respectively. For the southbound lanes, the GPR thickness profiles of the asphalt concrete layer vary from 4.3 inches to 17.2 inches across the length of the project, with an average thickness of 11.8 and 9.8 inches in lanes 1 and 2 respectively. The standard deviations of the asphalt concrete in the southbound lanes are 2.3 and 2.97 inches for lanes 1 and 2 respectively. The coefficient of variation in the southbound lanes is estimated at 19.6 % and 30.3 % for lanes 1 and 2 respectively.

Table 4.1: Summary of GPR Layer Statistics

Direction Lane Minimum AC

Thickness [inches]

Maximum AC Thickness [inches]

Average AC Thickness [inches]

Standard Deviation

1 2.5 18.0 12.3 3.2 North

2 7.5 11 8.6 0.58

1 4.7 16.0 11.8 2.3 South

2 4.3 17.2 9.8 2.97



GPR Layer Profile - Thornton Road N1

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Figure 4.5: Thornton Road Northbound Lane 1 GPR Layer Profile

GPR Layer Profile - Thornton Road N2

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GPR Layer Profile - Thornton Road S1

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Figure 4.7: Thornton Road Southbound Lane 1 GPR Layer Profile

GPR Layer Profile - Thornton Road S2

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4.4 PAVEMENTS The pavements along Thornton Road consist primarily of asphalt concrete (AC) over a granular base layer on top of the subgrade soil. The Thornton Road structure can be characterized as a flexible pavement structure. Fifteen cores were advanced through the existing flexible pavement structure along the north and southbound lanes of Thornton Road. The results of the investigation are summarized below in Tables 5.2 to 5.5.

Overall, the existing asphalt concrete surface layer was found to be in good condition. The inner northbound lane (lane 1) showed that the minimum, maximum, and average asphalt thickness were found to be 5.5, 14.0, and 10.4 inches respectively. A single core was extracted from the outer northbound lane (lane 2) and found to be 8 inches. The inner southbound lane (lane 1) showed that the minimum, maximum, and average asphalt thickness were found to be 4.75, 13.75, and 10.8 inches respectively. The outer southbound lane (lane 2) showed that the minimum, maximum, and average asphalt thickness were found to be 6.5, 15.0, and 11.5 inches respectively.

Core results were used to calibrate and check the validity of the results of the GPR thickness profiles. The results of the GPR thickness profile were found to be accurate and were used for the subsequent FWD analysis.

Table 4.2: Existing Northbound Lane Pavement Structure

Lane Number

Layer Number

Material Type

Range of Thickness [inches]

Mean Thickness [inches]

Comments

N1 1 Asphalt 5.5 to 14.0 10.4 Overall fair condition 6 cores extracted

N1 2 Granular Base 6 6 Assumed Thickness of 0.5 ft

N2 1 Asphalt 8 8 Overall fair condition 1 core extracted

N2 2 Granular Base 6 6 Assumed Thickness of 0.5 ft

Table 4.3: Existing Southbound Lane Pavement Structure

Lane Number

Layer Number

Material Type

Range of Thickness [inches]

Mean Thickness [inches]

Comments

S1 1 Asphalt 4.75 to 13.75 10.8 Overall fair condition 5 cores extracted

S1 2 Granular Base 6 6 Assumed Thickness of 0.5 ft

S2 1 Asphalt 6.5 to 15.0 11.5 Overall fair condition 3 cores extracted

S2 2 Granular Base 6 6 Assumed Thickness of 0.5 ft



4.5 FWD ANALYSIS RESULTS AND DISCUSSION

The major findings of the AASHTO 1993 backcalculation and pavement evaluation analysis results for Thornton Road are presented in the next subsections. The results are presented in terms of the normalized pavement deflection (Do) under the load plate, the in-situ subgrade resilient modulus (MR), the effective pavement modulus (EP) and the effective structural number (SNeff), respectively. Detailed results of the FWD deflection testing for the north and southbound lanes are presented in Appendix A.

4.5.1 Normalized FWD Deflections

The measured deflections were normalized to a standard load of 9,000 lbf and corrected for a standard temperature of 680F. Table 4.4 summarizes the maximum, minimum, average, and 80th percentile normalized maximum deflections (used by Caltrans design procedure) for each direction and lane; while, Figures 4.9 to 4.12 present the variation of the normalized maximum deflection (Do) data along the north and southbound lanes of Thornton Road.

Table 4.4: Summary of Normalized Deflections

Direction Lane Max

Deflection [mils]

Minimum Deflection

[mils]

Average Deflection

[mils]

California 80th

Percentile Deflection

[mils]

1 23.17 1.38 4.05 9.01 North

2 14.15 6.38 9.08 13.44

1 110.88 1.49 7.50 8.81 South

2 31.07 1.64 7.16 16.80

A detailed review of Figures 4.9 and 4.10 indicates that most of the maximum normalized deflection (Do) of the northbound lanes range between 1.38 and 23.17 mils. On the other hand, a review of Figures 4.11 and 4.12 indicates that most of the (Do) along the southbound lanes range between 1.49 and 110.88 mils. The two figures reveal that the averages (Do) are consistent between the two southern lanes of the Thornton Road pavement structures (7.50 and 7.16), but the averages vary between the two northbound lanes of the Thornton Road pavement structures (4.05 and 9.08) indicating that the southern lanes is a homogenous pavement section while the northern lanes are a non-homogenous pavement section within the limits of this roadway.

According to the AASHTO 1993 design guide a coefficient of variation (COV) less or equal 15% for a pavement section deflection indicates a low variation and reflects uniform pavement conditions along the roadway pavement section. COV between 15 and 30% indicated moderate variation and reflects less uniformity of the pavement section along the roadway pavement section. While, COV values that are greater than 30% represents variable (non uniform)



pavement section; the high variability is most likely a reflection of the existing distress along the roadway. COV of normalized deflections were found to be 102 & 28% and 246 & 114% for the north (for lane 1 and lane 2) and southbound (for lane 1 and lane 2) lanes respectively, which indicate non-uniform performance across the four lanes which is an indication of significant pavement distress.

Thornton Road NB Lane 1 - Maximum Normalized Deflection [D1]

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Figure 4.9: Maximum Normalized Deflection along the Northbound Direction (Lane 1)



Thornton Road NB Lane 2 - Maximum Normalized Deflection [D1]

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Figure 4.10: Maximum Normalized Deflection along the Northbound Direction (Lane 2)

Thornton Road SB Lane 1 - Maximum Normalized Deflection [D1]

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Figure 4.11: Maximum Normalized Deflection along the Southbound Direction (Lane 1)



Thornton Road SB Lane 2 - Maximum Normalized Deflection [D1]

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40.00

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000

Stations [feet]

D1

[mils

]

Figure 4.12: Maximum Normalized Deflection along the South Bound Direction (Lane 2)

4.5.2 INSITU Pavement Conditions

4.5.2.1 Subgrade Resilient Moduli (MR) The calculated subgrade soil resilient modulus (MR) below the flexible pavement structure, for the north and southbound lanes of Thornton Road is graphically presented in Figures 4.13 to 4.16 respectively. A high subgrade resilient modulus is desirable to provide adequate support for the pavement structure and resist the permanent deformation under repeated traffic loading. Low subgrade resilient modulus is usually associated with weak and/or soft subgrade soil conditions that is usually the result of pavement deterioration, loss of support conditions, and reduced fatigue life of the pavement roadway.

The calculated MR values along both northbound lanes varied from 2,527 psi to 19,208 psi; while, the MR along both southbound lanes varies from 2,729 psi to 14,542 psi. For the northbound lanes, the average MR values are 9,582 psi and 4,218 psi for lanes 1 and 2 respectively. For the southbound lanes, the average MR values are 9,127 psi and 7,516 psi for lanes 1 and 2 respectively.

For typical sandy subgrade soils, the AASHTO 1993 Pavement Design Guide identifies MR values less than 3,500 psi to be low and attributed to the deterioration of the subgrade. Since some of the test locations were below this level and the average MR values are only marginally higher for Northbound Lane 2, the subgrade support along this section can be defined as partially adequate.



Thornton Road NB Lane 1 - Subgrade Resilient Modulus [MR]

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

20,000

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000

Stations [feet]

MR [p

si]

Figure 4.13: Subgrade Resilient Modulus along the Northbound Direction (Lane 1)

Thornton Road NB Lane 2 - Subgrade Resilient Modulus [MR]

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

20,000

0 200 400 600 800 1,000 1,200 1,400

Stations [feet]

MR [p

si]

Figure 4.14: Subgrade Resilient Modulus along the Northbound Direction (Lane 2)



Thornton Road SB Lane 1 - Subgrade Resilient Modulus [MR]

0

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

20,000

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000

Stations [feet]

MR [p

si]

Figure 4.15: Subgrade Resilient Modulus along the Southbound Direction (Lane 1)

Thornton Road SB Lane 2 - Subgrade Resilient Modulus [MR]

2,000

4,000

6,000

8,000

10,000

12,000

14,000

16,000

18,000

20,000

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000

Stations [feet]

MR [p

si]

Figure 4.16: Subgrade Resilient Modulus along the Southbound Direction (Lane 2)



4.5.2.2 Effective Pavement Modulus (EP) The backcalculation results for the Effective Pavement Modulus of Elasticity (Ep) are provided in Figures 4.17 to 4.20. Ep is a representation of the overall pavement stiffness (the combined stiffnesses of all pavement layers above the subgrade layer) and is used to calculate the effective structural number. Ep values of new flexible pavements usually range between 150,000 to 250,000 psi depending on the overall pavement thickness. High values of Ep indicate a stronger pavement structure.

The Ep values along the northbound direction varies from 74,250 psi to over 500,000 psi; while, the Ep along the southbound direction varies from 5,342 psi to over 500,000 psi. For the northbound lanes, the average EP values are 460,691 psi and 391,939 psi for lanes 1 and 2 respectively. For the southbound lanes, the average EP values are 434,506 psi and 410,011 psi for lanes 1 and 2 respectively.

Ep values are dependent on the overall pavement thickness and the integrity of the pavement layers. In general, the EP values found along the north and southbound lanes can be described as reasonable. At a few locations, the Ep was found to be poor (low) indicating pavement deterioration and low structural capacity. Low Ep and high COV of Ep values can also be strong indicator of the deterioration of the base layer or the pavement support layers.

Thornton Road NB Lane 1 - Effective Pavement Modulus [EP]

0

100,000

200,000

300,000

400,000

500,000

600,000

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000

Stations [feet]

E P [p

si]

Figure 4.17: Effective Pavement Modulus along the Northbound Direction (Lane 1)



Thornton Road NB Lane 2 - Effective Pavement Modulus [EP]

0

100,000

200,000

300,000

400,000

500,000

600,000

0 200 400 600 800 1,000 1,200 1,400

Stations [feet]

E P [p

si]

Figure 4.18: Effective Pavement Modulus along the Northbound Direction (Lane 2)

Thornton Road SB Lane 1 - Effective Pavement Modulus [EP]

0

100,000

200,000

300,000

400,000

500,000

600,000

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000

Stations [feet]

E P [p

si]

Figure 4.19: Effective Pavement Modulus along the Southbound Direction (Lane 1)



Thornton Road SB Lane 2 - Effective Pavement Modulus [EP]

0

100,000

200,000

300,000

400,000

500,000

600,000

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000

Stations [feet]

E P [p

si]

Figure 4.20: Effective Pavement Modulus along the Southbound Direction (Lane 2)

4.5.2.3 Effective Structural Number (SNeff) The effective strength or structural capacity of the existing pavement layers is traditionally represented by the effective structural number, SNeff. Low SNeff values indicate low structural capacity of the pavement structure; while, high SNeff values indicate high structural capacity of the pavement structure.

The backcalculated SNeff values are typically adjusted and are used to develop subsequent rehabilitation design strategies. The average SNeff values for the northbound lanes are 8.59 and 4.73, for lanes 1 and 2 respectively. The average SNeff values for the southbound lanes are 8.08 and 7.95, for lanes 1 and 2 respectively. The SNeff values for the north and southbound lanes of Thornton Road are presented in Figures 4.21 to 4.24.

For rehabilitation and overlay design, an 85th percentile of the backcalculated SNeff results is recommended for rehabilitation design. Since Stantec’s backcalculation methodology performs calculation at each test point; the methodology normalizes the SNeff at each point and uses the average value for all subsequent pavement designs.



Thornton Road NB Lane 1 - Effective Structural Number [SNeff]

0.00

4.00

8.00

12.00

16.00

20.00

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000

Stations [feet]

SNef

f

Figure 4.21: Effective Structural Number along the Northbound Direction (Lane 1)

Thornton Road NB Lane 2 - Effective Structural Number [SNeff]

0.00

4.00

8.00

12.00

16.00

20.00

0 200 400 600 800 1,000 1,200 1,400

Stations [feet]

SNef

f

Figure 4.22: Effective Structural Number along the Northbound Direction (Lane 2)



Thornton Road SB Lane 1 - Effective Structural Number [SNeff]

0.00

4.00

8.00

12.00

16.00

20.00

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000

Stations [feet]

SNef

f

Figure 4.23: Effective Structural Number along the Southbound Direction (Lane 1)

Thornton Road SB Lane 2 - Effective Structural Number [SNeff]

0.00

4.00

8.00

12.00

16.00

20.00

0 1,000 2,000 3,000 4,000 5,000 6,000 7,000 8,000 9,000

Stations [feet]

SNef

f

Figure 4.24: Effective Structural Number along the Southbound Direction (Lane 2)

The SNeff plots reveal that the residual structural capacity (effective structural capacity) of the existing pavement structures is very high and indicates a high structural capacity of the existing pavement sections. The maximum normalized deflection (Do) and the backcalculation results



(MR, EP, and SNeff) for the north and southbound lanes along Thornton Road are summarized below in Tables 4.5 and 4.6.

Table 4.5: Summary of FWD Testing and Analysis Results

Direction Lane Maximum

Normalized Deflection [mils]

Subgrade Resilient Modulus MR [psi]

Effective Pavement Modulus Ep [psi]

Effective Structural Number

SNeff

1 1.38 to 23.17 2,917 to 19,208 74,250 to 500,000 2.32 to 13.10North

2 6.38 to 14.15 2,527 to 5,360 221,941 to 500,000 3.81 to 5.39

1 1.49 to 110.88 2,729 to 14,542 5,342 to 500,000 1.06 to 13.64South

2 1.64 to 31.07 2,790 to 11,298 36,174 to 500,000 1.62 to 13.24

Table 4.6: Average and 75th Percentile of FWD Results

Direction Lane MRavg [psi]

EPavg [psi]

SNeff avg

MR 75%-ile

[psi]

EP 75%-ile

[psi]

SNeff 75%-

ile

1 9,582 460,691 8.59 11,684 500,000 10.26North

2 4,218 391,939 4.73 5,008 500,000 5.21

1 9,127 434,506 8.08 10,786 500,000 9.54 South

2 7,516 410,011 7.95 10,384 500,000 11.08



5.0 Pavement Rehabilitation Analysis

The results of the backcalculation analysis performed on the FWD data were used to determine the future rehabilitation needs of this roadway. In this analysis, a comparison was made between the adjusted effective SN (SNeff) and the required SN (SNreq). As previously mentioned in this report, both the AASHTO 1993 and the Caltrans Pavement Design procedure were used for the rehabilitation analysis.

The required AC overlay thickness based on the AASHTO 1993 analysis detailed earlier in Section 3.0 was calculated using the following relationship:

hOL = [SNreq-SNeff]/0.44

Where: hOL = the required AC* overlay thickness

*AC describes the asphalt concrete layer. This terminology is sometimes replaced by HMA (Hot Mix Asphalt) that describes a high quality asphaltic concrete layer (s)

SNeff = effective structural number (SNeff*0.85) of the existing pavement structure SNreq = required structural number to carry future traffic

5.1.1 Future Traffic Estimation

A number of traffic levels for the rehabilitation analysis were provided by the City of Stockton in terms of Traffic Indices (TIs). Based on our project experience and with other municipalities in the State of California, both 10 year and 20 year design periods were considered for the rehabilitation analysis.

For the AASHTO 1993 analysis procedure, traffic levels in terms of Equivalent Single Axle Loads (ESALs) are required. The traffic levels in terms of TIs and ESALs which were used for the analysis are presented below in Table 5.7.

Table 5.7: Traffic Levels

Traffic Level

Traffic Index (TI)

Equivalent Single Axle Loads (ESALs)

1 7.5 220,0002 8.0 370,0003 8.5 620,0004 9.0 1,000,0005 9.5 1,600,0006 10 2,400,000

7 10.5 3,700,000

DRAFT PAVEMENT EVALUATION REPORT – THORNTON ROAD WIDENING PROJECT Pavement Rehabilitation Analysis February 1, 2008


Based on the rehabilitation analysis, the required overlay thickness at each of the FWD test locations shows some variation in both directions for this segment of road. For the northbound lane, the required overlay thickness ranges from 0 to as high as 11.5 inches, depending on the level of traffic (TIs or ESALs). For the southbound lane, the required overlay thickness ranges from 0 to 13.2 inches, depending on the level of traffic (TIs or ESALs). The average required AASHTO overlay thickness (hOL) for the north and southbound lanes of Thornton Road are presented below in Table 5.8. As can be seen from Table 5.8, the performance and resulting required asphalt concrete overlay of the north and southbound lane is generally 0.0 for both lanes in the north and southbound direction respectively. However, a structural overlay is required for Lane 2 in the northbound direction as the level of traffic increases beyond a TI of 8.0. It is important to note that a structural overlay may be required at an isolated location that is not necessary representative of the overall requirement along the length of the section. In accessing the overall requirement, the overall performance of the section or homogeneous sub-sections must be considered and not a per-test-point approach.

Table 5.8: Required AC Overlay Thickness Based on AASHTO 1993 Procedure

Traffic Level

ESALs (TIs)

Lane

Average AC

Thickness [in]

Avg. Effective Structural Number (SNeff*85)

Avg. Required Structural Number (SNreq)

Avg. Required Overlay Thickness hOL = SNreq-SNeff/0.44

[inches]

N1 12.3 7.30 2.975 0.0

N2 8.6 4.02 3.0 0.0

S1 11.8 6.87 3.0 0.0 1 220,000

(7.5)

S2 9.8 6.76 3.0 0.0

N1 12.3 7.30 2.99 0.0

N2 8.6 4.02 3.0 0.0

S1 11.8 6.87 3.0 0.0 2 370,000

(8.0)

S2 9.8 6.76 3.0 0.0

N1 12.3 7.30 3.2 0.0

N2 8.6 4.02 4.17 0.34

S1 11.8 6.87 3.2 0.0 3 620,000

(8.5)

S2 9.8 6.76 3.5 0.0

N1 12.3 7.30 3.92 0.0

N2 8.6 4.02 5.4 3.09

S1 11.8 6.87 3.95 0.00 4 1,000,000

(9.0)

S2 9.8 6.76 4.43 0.00



In addition, the Caltrans Pavement Rehabilitation Design procedure based on California Test (CT) 356 was used to determine the required asphalt overlay thicknesses. The method is based on a percent tolerable and percent reduction in deflection and is a function of the 80th percentile deflection, existing asphalt (HMA) thickness, design period, and level of traffic (TI). The results of the Caltrans based design procedure is presented in Tables 5.9 and 5.10.

Table 5.9: Overlay Thicknesses based on Caltrans Design Method

Required Overlay [ft] Traffic Index (TI)

Lane Average

AC Thickness

[ft]

California 80th


[mils]

% Tolerable Deflection

% Reduction

in Deflection

Gravel Equiv. Structural

Adequacy Reflective Cracking

Ride Quality

N1 1.03 9.01 18 0 -- 0.0 0.35 0.25

N2 0.72 13.44 18 0 -- 0.0 0.35 0.25

S1 0.98 8.81 18 0 -- 0.0 0.35 0.25 7.5

S2 0.82 16.80 18 0 -- 0.0 0.35 0.25

Traffic Level ESALs

Lane

Average AC

Thickness [in]

Avg. Effective Structural Number (SNeff*85)

Avg. Required Structural Number (SNreq)

Avg. Required Overlay Thickness hOL = SNreq-SNeff/0.44

[inches]

N1 12.3 7.30 4.65 0.0

N2 8.6 4.02 5.92 4.31

S1 11.8 6.87 4.5 0.0 5 1,600,000

(9.5)

S2 9.8 6.76 5.0 0.0

N1 12.3 7.30 4.85 0.0

N2 8.6 4.02 6.41 5.4

S1 11.8 6.87 5.0 0.0 6 2,400,000

(10.0)

S2 9.8 6.76 5.44 0.0

N1 12.3 7.30 5.22 0.0

N2 8.6 4.02 6.81 6.34

S1 11.8 6.87 5.33 0.0 7 3,700,000

(10.5)

S2 9.8 6.76 5.82 0.0



Required Overlay [ft] Traffic Index (TI)

Lane Average

AC Thickness

[ft]

California 80th


[mils]

% Tolerable Deflection

% Reduction

in Deflection

Gravel Equiv. Structural

Adequacy Reflective Cracking

Ride Quality

N1 1.03 9.01 17 0 -- 0.0 0.35 0.25

N2 0.72 13.44 17 0 -- 0.0 0.35 0.25

S1 0.98 8.81 17 0 -- 0.0 0.35 0.25 8.0

S2 0.82 16.80 17 0 -- 0.0 0.35 0.25

N1 1.03 9.01 15 0 -- 0.0 0.35 0.25

N2 0.72 13.44 15 0 -- 0.0 0.35 0.25

S1 0.98 8.81 15 0 -- 0.0 0.35 0.25 8.5

S2 0.82 16.80 15 11 0.04 0.0 0.35 0.25

N1 1.03 9.01 14 0 -- 0.0 0.35 0.25

N2 0.72 13.44 14 0 -- 0.0 0.35 0.25

S1 0.98 8.81 14 0 -- 0.0 0.35 0.25 9.0

S2 0.82 16.80 14 17 0.08 0.05 0.35 0.25

N1 1.03 9.01 13 0 -- 0.0 0.35 0.25

N2 0.72 13.44 13 3 0.01 0.0 0.35 0.25

S1 0.98 8.81 13 0 -- 0.0 0.35 0.25 9.5

S2 0.82 16.80 13 23 0.14 0.1 0.35 0.25

N1 1.03 9.01 12 0 -- 0.0 0.35 0.25

N2 0.72 13.44 12 11 0.04 0.0 0.35 0.25

S1 0.98 8.81 12 0 -- 0.0 0.35 0.25

10.0

S2 0.82 16.80 12 29 0.22 0.1 0.35 0.25

N1 1.03 9.01 11 0 -- 0.0 0.35 0.25

N2 0.72 13.44 11 18 0.1 0.05 0.35 0.25

S1 0.98 8.81 11 0 -- 0.0 0.35 0.25 10.5

S2 0.82 16.80 11 35 0.32 0.15 0.35 0.25



Table 5.10: Overlay Thicknesses based on Caltrans Design Method (cont’)

Required HMA Overlay for Retardation

of Reflective Cracking [ft]

Rubberized Overlay Option [ft] Traffic

Index (TI)

Direction

HMA HMA + SAMI-R

HMA + SAMI-F RAC-G RAC-G+SAMI

N1 0.35 0.2 0.25 0.1 over 0.15 -- N2 0.35 0.2 0.25 0.1 over 0.15 -- S1 0.35 0.2 0.25 0.1 over 0.15 --

7.5

S2 0.35 0.2 0.25 0.1 over 0.15 --


8.0

S2 0.35 0.2 0.25 0.1 over 0.15 --


8.5

S2 0.35 0.2 0.25 0.1 over 0.15 --


9.0

S2 0.35 0.2 0.25 0.1 over 0.15 --


9.5

S2 0.35 0.2 0.25 0.1 over 0.15 --


10.0

S2 0.35 0.2 0.25 0.1 over 0.15 -- N1 0.35 0.2 0.25 0.1 over 0.15 -- N2 0.35 0.2 0.25 0.1 over 0.15 -- S1 0.35 0.2 0.25 0.1 over 0.15 --

10.5

S2 0.35 0.2 0.25 0.1 over 0.15 --



5.1.2 Feasibility of Overlay as Rehabilitation Option

The selection of an overlay as a rehabilitation option should be made in conjunction with a review of all pavement performance parameters and properties. In general, the use of an overlay is not a suitable rehabilitation treatment if one of the following conditions applies:

• The subgrade resilient modulus is less than a minimum value. This value is based on the predominant soil type. At a few locations, the subgrade resilient modulus was found to be less than the 3,500 psi level indicating potential “soft-spots” in the subgrade and consequently inadequate support for the projected traffic loadings.

• The existing asphalt concrete surface layer is severely distressed with load associated distresses such as high-severity fatigue cracking, potholes and rutting. As discussed in the section outlining the condition assessment, the pavement was observed to be severely distressed during the time of the pavement evaluation and field testing.

The rehabilitation options presented in the upcoming section are based on a number of traffic levels. The Traffic Index (TIs) used in the rehabilitation analysis ranged from 7.5 to 10.5 with corresponding ESALs ranging from 620,000 to 3,700,000. If traffic loads higher than 10.5 TIs or 3,700,000 ESALs are expected in the future, the rehabilitation analysis should be revised. It is also important to mention that these rehabilitation stragties were developed to offer the most economical solution for the city of Stockton based on the Stantec IMPE team.

5.1.3 Rehabilitation Options

The feasibility of using a specific rehabilitation treatment was evaluated considering the following constraints:

• No major geometric improvements (widening, horizontal or vertical alignment modifications, etc.) are expected along the right-of-way.

• Placing an additional asphalt concrete overlay on the existing pavement surface will not impact clearances and other height restrictions.

• Pavement shoulders, bike lanes, etc. typically receive the same mainline rehabilitation treatment.

Results of the backcalculation analysis indicate that the subgrade modulus (support) for the existing pavement test locations is adequate to support the projected traffic loadings on this roadway for the design period. A few subgrade “soft-spots” were identified along the project length and the computed effective pavement modulus of the overall pavement structure indicates that the overall pavement is structurally adequate. During the condition assessment, several areas of pavement distress were observed across both directions of Thornton Road. The following rehabilitation options are recommended.



Option 1: Asphalt Concrete Overlay

The first rehabilitation option involves repairing any localized areas of surface distress and overlaying the existing pavement with new high quality asphalt concrete material. Since the pavement surface had extensive moderate to high severity distresses such as longitudinal cracking and fatigue cracking, the use of an asphalt concrete overlay must considered with caution. Since overlaying a distressed pavement can lead to pre-mature reflective cracking in the newly placed asphalt concrete layer, a fabric or Stress Absorbing Membrane Interlayer (SAMI) must be considered with this rehabilitation strategy.

This option involves repairing any existing distress (routing and cleaning/sealing existing cracks, filling potholes, and patching areas of fatigue cracking), placing a fabric or Stress Absorbing Membrane Interlayer (SAMI) and overlaying the existing pavement with high quality Hot Mix Asphalt (HMA). To help mitigate and retard reflective cracking, based on the Caltrans pavement design procedure, an overlay consisting of 0.35-ft (4.25 inches) of HMA with RAC-G or a Stress Absorbing Interlayer (SAMI) is recommended.

For TIs below 9.0, the following is recommended:

Repair existing pavement distress. Rout, clean and seal any existing cracks with high quality material. Patch or repair any potholes or areas of fatigue cracking.

Place fabric or Stress Absorbing Membrane Interlayer (SAMI) over cleaned pavement surface

Overlay fabric or SAMI layer with 3.5 inches of high quality Hot Mix Asphalt (HMA)

For TIs of 9.5 or above, the following is recommended:

Repair existing pavement distress. Rout, clean and seal any existing cracks with high quality material. Patch or repair any potholes or areas of fatigue cracking.

Place fabric or Stress Absorbing Membrane Interlayer (SAMI) over cleaned pavement surface

Overlay fabric or SAMI layer with 3.5 inches of high quality Hot Mix Asphalt (HMA)

Since the required overlay thickness for Lane 2 in the northbound direction is 4.3, 5.4, and 6.3 inches for a TI of 9.5, 10.0, and 10.5 respectively, the following rehabilitation option is recommended to satisfy both design procedures;

Mill 2.0 inches of the existing asphalt surface, clean milled surface and apply proper tack coat and ;

Overlay milled surface with (or to match existing grade of northbound Lane 1);



- TI 9.5: 5.5 inches of high quality Hot Mix Asphalt (HMA)


- TI 10.5: Partial Reconstruction – Remove existing asphalt concrete and replace with high quality HMA to match existing pavement grade. It is important to re-establish the proper compaction levels of the underlying aggregate base and repair any contaminated or wet areas.

Option 2: Mill and AC Overlay

The second rehabilitation option involves milling a depth of the existing asphalt layer and overlaying the existing pavement with new high quality asphalt concrete material. This option offers a higher rate of success since the aged and areas of high pavement surface distress are removed, and re-establishes a good bond condition between the existing pavement structure and the new AC overlay. Since both directions of Thornton Road have significant pavement distress, milling would also mitigate and/or retard reflective cracking and improve the overall ride quality.

For TIs below 9.0, the following is recommended:

Mill 2.0 inches of the existing asphalt surface, clean milled surface and apply proper tack coat and;

Overlay milled surface with 4.5 inches of high quality Hot Mix Asphalt (HMA)

For TIs of 9.5 or above, the following is recommended:


Overlay milled surface with 4.5 inches of high quality Hot Mix Asphalt (HMA)

Since the required overlay thickness for Lane 2 in the northbound direction is 4.3, 5.4, and 6.3 inches for a TI of 9.5, 10.0, and 10.5 respectively, the following rehabilitation option is recommended:


Overlay milled surface with;






The Caltrans pavement design procedure recommends a 4.25 inch overlay of Hot Mix Asphalt (HMA) with the use of a fabric or Stress Absorbing Membrane Interlayer (SAMI). However, Stantec recommends a mill and overlay option which mitigates and/or retards reflective cracking and improves ride quality.

It is important to note that the recommended rehabilitation options for the various levels of traffic need to take into consideration preventative maintenance strategies over the course of the pavements design life. For example, cracks should be routed, cleaned and sealed with high quality sealant when they begin to propagate. In addition, areas of fatigue cracking should be repaired and patched with high quality Hot Mix Asphalt (HMA). Preventative maintenance is important in preserving pavements, maintaining a high level of service and delaying major rehabilitation and/or reconstruction. It is recommended to apply a seal coat of 0.5” to 0.75” between year 6 and 7. In addition, it is recommended to repeat the same strategy between year 12 to 14 to ensure the expected design life.



6.0 Closure

This report presents the results of a pavement evaluation completed by Stantec’s IMPE team for the City of Stockton. The analyses and recommendations submitted are based upon the pavement evaluation and field exploration performed at the test locations described in this report. This report does not reflect soil or pavement conditions that may become evident during future construction, at which time re-evaluation of the recommendations may be necessary.

This report was prepared by Stantec Consulting and the material in it reflects the best judgment in light of the information available to it at the time of preparation. Stantec assumes immediate implementation of the results and recommendations presented in this report. Should you have any questions or comments, please don’t hesitate to contact us.


ch w:\active\1841stockton\phase\report\appendix_a_fwd_data_020108.doc A.1

Appendix A: Summary of FWD Data

RouteID Direction Stn [ft]

Load [lbf]

CD1 [mils]

D1 [mils]

MR [psi]

EP [psi] SNEff

Thorn_N1 N 0 9,000 7.73 6.44 4,546 500,000 5.75 Thorn_N1 N 200 9,000 9.50 7.92 4,237 474,897 5.02 Thorn_N1 N 400 9,000 10.02 8.35 4,281 305,205 5.15 Thorn_N1 N 600 9,000 9.02 7.52 4,504 440,613 5.20 Thorn_N1 N 800 9,000 9.64 8.03 4,396 386,604 5.00 Thorn_N1 N 1000 9,000 25.68 21.40 2,917 76,450 2.90 Thorn_N1 N 1200 9,000 9.58 7.98 4,552 388,511 4.91 Thorn_N1 N 1400 9,000 18.90 15.75 3,740 138,951 2.95 Thorn_N1 N 1600 9,000 27.80 23.17 3,255 74,250 2.32 Thorn_N1 N 1800 9,000 23.22 19.35 3,718 79,520 2.74 Thorn_N1 N 2000 9,000 10.92 9.10 3,979 500,000 4.28 Thorn_N1 N 2200 9,000 3.88 3.23 12,786 500,000 5.72 Thorn_N1 N 2200 9,000 3.31 2.76 12,861 500,000 6.54 Thorn_N1 N 2200 9,000 3.69 3.08 13,038 500,000 5.91 Thorn_N1 N 2400 9,000 4.60 3.83 9,389 500,000 5.71 Thorn_N1 N 2400 9,000 4.68 3.90 9,311 500,000 5.64 Thorn_N1 N 2400 9,000 4.39 3.66 9,502 500,000 5.91 Thorn_N1 N 2600 9,000 9.34 7.79 4,177 252,873 6.27 Thorn_N1 N 2800 9,000 4.38 3.65 11,222 467,118 7.26 Thorn_N1 N 2800 9,000 3.31 2.76 12,124 500,000 8.49 Thorn_N1 N 3000 9,000 3.16 2.63 9,833 500,000 9.73 Thorn_N1 N 3200 9,000 3.35 2.79 9,056 500,000 9.66 Thorn_N1 N 3400 9,000 2.75 2.29 8,129 500,000 11.55 Thorn_N1 N 3400 9,000 3.04 2.54 8,125 500,000 10.68 Thorn_N1 N 3400 9,000 3.10 2.58 8,099 500,000 10.55 Thorn_N1 N 3600 9,000 3.28 2.73 10,401 500,000 9.17 Thorn_N1 N 3800 9,000 3.49 2.91 8,677 500,000 9.20 Thorn_N1 N 3800 9,000 3.14 2.62 8,414 500,000 10.08 Thorn_N1 N 3800 9,000 3.42 2.85 8,440 500,000 9.43 Thorn_N1 N 4000 9,000 5.50 4.58 7,827 395,870 7.23 Thorn_N1 N 4200 9,000 2.89 2.41 8,987 500,000 10.27 Thorn_N1 N 4200 9,000 2.93 2.44 8,851 500,000 10.24 Thorn_N1 N 4200 9,000 2.73 2.28 8,880 500,000 10.80 Thorn_N1 N 4400 9,000 2.50 2.08 8,702 500,000 11.58 Thorn_N1 N 4400 9,000 2.27 1.89 8,698 500,000 12.58 Thorn_N1 N 4400 9,000 2.43 2.02 8,853 500,000 11.75 Thorn_N1 N 4600 9,000 2.70 2.25 10,096 500,000 10.15 Thorn_N1 N 4600 9,000 2.72 2.27 10,133 500,000 10.08 Thorn_N1 N 4600 9,000 2.56 2.13 10,112 500,000 10.60 Thorn_N1 N 4800 9,000 4.19 3.49 8,543 500,000 8.20 Thorn_N1 N 5000 9,000 3.90 3.25 10,274 500,000 8.39 Thorn_N1 N 5200 9,000 2.39 1.99 9,914 500,000 11.19

DRAFT PAVEMENT EVALUATION REPORT – THORNTON ROAD WIDENING PROJECT Appendix A: Summary of FWD Data February 1, 2008



Load [lbf]

CD1 [mils]

D1 [mils]

MR [psi]

EP [psi] SNEff

Thorn_N1 N 5200 9,000 2.19 1.82 10,109 500,000 11.94 Thorn_N1 N 5200 9,000 2.21 1.84 10,214 500,000 11.78 Thorn_N1 N 5400 9,000 3.36 2.80 8,841 500,000 8.96 Thorn_N1 N 5600 9,000 1.84 1.54 16,677 500,000 10.64 Thorn_N1 N 5600 9,000 1.87 1.56 16,619 500,000 10.54 Thorn_N1 N 5600 9,000 1.66 1.38 16,597 500,000 11.58 Thorn_N1 N 5800 9,000 2.30 1.92 19,208 500,000 8.90 Thorn_N1 N 6000 9,000 2.59 2.16 12,747 500,000 9.51 Thorn_N1 N 6000 9,000 2.59 2.16 12,830 500,000 9.48 Thorn_N1 N 6000 9,000 2.57 2.14 13,286 500,000 9.39 Thorn_N1 N 6200 9,000 2.42 2.02 11,922 500,000 10.25 Thorn_N1 N 6200 9,000 2.62 2.19 11,998 500,000 9.61 Thorn_N1 N 6200 9,000 2.51 2.09 12,306 500,000 9.83 Thorn_N1 N 6400 9,000 2.51 2.09 11,750 500,000 10.04 Thorn_N1 N 6400 9,000 2.48 2.07 11,661 500,000 10.14 Thorn_N1 N 6401 9,000 3.86 3.21 11,891 500,000 7.36 Thorn_N1 N 6600 9,000 3.17 2.64 9,880 500,000 9.24 Thorn_N1 N 6800 9,000 5.00 4.17 9,893 404,017 6.97 Thorn_N1 N 6800 9,000 6.90 5.75 9,724 232,077 5.79 Thorn_N1 N 6800 9,000 5.81 4.84 9,989 306,257 6.35 Thorn_N1 N 7000 9,000 2.16 1.80 11,581 500,000 11.60 Thorn_N1 N 7000 9,000 2.08 1.73 11,515 500,000 11.99 Thorn_N1 N 7000 9,000 2.56 2.14 11,570 500,000 10.17 Thorn_N1 N 7200 9,000 1.76 1.47 12,420 500,000 13.10 Thorn_N1 N 7200 9,000 1.93 1.61 12,602 500,000 12.09 Thorn_N1 N 7200 9,000 2.31 1.93 12,589 500,000 10.49 Thorn_N1 N 7400 9,000 2.70 2.25 13,412 500,000 9.25 Thorn_N1 N 7600 9,000 3.52 2.94 7,709 500,000 9.36 Thorn_N1 N 7600 9,000 3.74 3.12 7,666 500,000 8.96 Thorn_N1 N 7600 9,000 3.94 3.28 7,902 500,000 8.50 Thorn_N1 N 7800 9,000 5.15 4.29 8,937 432,078 6.93 Thorn_N1 N 8000 9,000 3.39 2.83 10,231 500,000 8.41 Thorn_N1 N 8000 9,000 3.15 2.62 10,263 500,000 8.88 Thorn_N1 N 8000 9,000 3.27 2.72 10,396 500,000 8.60 Thorn_N1 N 8165 9,000 3.11 2.59 9,924 500,000 9.10 Thorn_N1 N 8400 9,000 3.88 3.23 7,387 500,000 8.38 Thorn_N1 N 8400 9,000 3.95 3.29 7,376 500,000 8.26 Thorn_N1 N 8400 9,000 3.93 3.27 7,363 500,000 8.31 Thorn_N2 N 100 9,000 9.37 7.81 4,915 447,819 4.63 Thorn_N2 N 100 9,000 9.45 7.87 4,887 442,518 4.61 Thorn_N2 N 300 9,000 7.65 6.38 5,287 500,000 5.39 Thorn_N2 N 300 9,000 7.96 6.63 5,360 500,000 5.19 Thorn_N2 N 300 9,000 7.81 6.50 5,350 500,000 5.27 Thorn_N2 N 500 9,000 10.30 8.58 3,670 453,016 5.09




Load [lbf]

CD1 [mils]

D1 [mils]

MR [psi]

EP [psi] SNEff

Thorn_N2 N 500 9,000 10.35 8.62 3,692 444,402 5.06 Thorn_N2 N 500 9,000 9.62 8.02 3,727 500,000 5.34 Thorn_N2 N 700 9,000 12.90 10.75 3,721 244,900 4.30 Thorn_N2 N 900 9,000 16.98 14.15 2,527 225,427 4.08 Thorn_N2 N 1100 9,000 15.22 12.68 3,152 223,250 4.00 Thorn_N2 N 1300 9,000 13.21 11.01 4,325 221,941 3.81 Thorn_S1 S 0 9,000 3.42 2.85 7,873 500,000 9.77 Thorn_S1 S 0 9,000 3.23 2.69 7,940 500,000 10.16 Thorn_S1 S 0 9,000 3.66 3.05 7,765 500,000 9.33 Thorn_S1 S 190 9,000 8.00 6.66 5,624 385,903 5.35 Thorn_S1 S 390 9,000 9.79 8.16 5,615 290,349 4.39 Thorn_S1 S 590 9,000 9.44 7.87 9,437 146,877 4.71 Thorn_S1 S 590 9,000 4.98 4.15 9,502 447,545 6.84 Thorn_S1 S 790 9,000 6.79 5.66 11,194 236,255 5.20 Thorn_S1 S 990 9,000 5.27 4.39 10,294 380,341 6.38 Thorn_S1 S 1190 9,000 10.88 9.07 9,089 122,190 4.29 Thorn_S1 S 1191 9,000 4.17 3.48 9,365 500,000 7.59 Thorn_S1 S 1191 9,000 4.09 3.41 9,403 500,000 7.69 Thorn_S1 S 1390 9,000 2.68 2.23 12,323 500,000 9.46 Thorn_S1 S 1390 9,000 2.22 1.85 12,176 500,000 10.97 Thorn_S1 S 1390 9,000 2.24 1.87 12,499 500,000 10.76 Thorn_S1 S 1590 9,000 4.56 3.80 7,767 500,000 7.59 Thorn_S1 S 1790 9,000 3.44 2.86 11,745 500,000 7.79 Thorn_S1 S 1790 9,000 3.00 2.50 11,869 500,000 8.58 Thorn_S1 S 1790 9,000 3.29 2.74 11,817 500,000 8.02 Thorn_S1 S 1990 9,000 3.40 2.83 12,170 500,000 7.93 Thorn_S1 S 1990 9,000 2.70 2.25 12,138 500,000 9.37 Thorn_S1 S 2190 9,000 2.47 2.06 11,884 500,000 10.20 Thorn_S1 S 2190 9,000 2.42 2.02 11,858 500,000 10.36 Thorn_S1 S 2191 9,000 2.51 2.09 11,678 500,000 10.21 Thorn_S1 S 2390 9,000 3.51 2.92 11,680 500,000 7.70 Thorn_S1 S 2590 9,000 2.49 2.07 14,542 500,000 9.43 Thorn_S1 S 2590 9,000 2.47 2.05 14,443 500,000 9.51 Thorn_S1 S 2590 9,000 2.49 2.07 14,281 500,000 9.48 Thorn_S1 S 2790 9,000 3.26 2.71 9,874 500,000 8.82 Thorn_S1 S 2790 9,000 3.20 2.67 9,996 500,000 8.89 Thorn_S1 S 2790 9,000 3.51 2.92 9,905 500,000 8.33 Thorn_S1 S 2990 9,000 3.16 2.63 8,991 500,000 9.72 Thorn_S1 S 2990 9,000 3.24 2.70 9,266 500,000 9.42 Thorn_S1 S 2990 9,000 3.33 2.77 8,948 500,000 9.37 Thorn_S1 S 3190 9,000 1.90 1.58 10,912 500,000 12.86 Thorn_S1 S 3190 9,000 1.79 1.49 10,754 500,000 13.64 Thorn_S1 S 3190 9,000 1.93 1.61 10,910 500,000 12.68 Thorn_S1 S 3390 9,000 3.08 2.56 10,050 500,000 9.51




Load [lbf]

CD1 [mils]

D1 [mils]

MR [psi]

EP [psi] SNEff

Thorn_S1 S 3390 9,000 3.07 2.56 9,944 500,000 9.56 Thorn_S1 S 3390 9,000 3.19 2.66 10,032 500,000 9.28 Thorn_S1 S 3590 9,000 4.23 3.52 9,247 500,000 7.60 Thorn_S1 S 3790 9,000 4.26 3.55 7,895 500,000 7.72 Thorn_S1 S 3790 9,000 4.18 3.49 7,864 500,000 7.85 Thorn_S1 S 3791 9,000 4.00 3.33 7,879 500,000 8.15 Thorn_S1 S 3791 9,000 4.06 3.39 7,700 500,000 8.13 Thorn_S1 S 3990 9,000 8.37 6.98 5,573 266,703 5.82 Thorn_S1 S 4190 9,000 3.24 2.70 8,112 500,000 9.88 Thorn_S1 S 4190 9,000 3.29 2.74 8,098 500,000 9.76 Thorn_S1 S 4190 9,000 3.71 3.09 8,293 500,000 8.83 Thorn_S1 S 4390 9,000 3.03 2.53 10,568 500,000 8.82 Thorn_S1 S 4390 9,000 2.85 2.37 10,466 500,000 9.32 Thorn_S1 S 4390 9,000 2.97 2.48 10,490 500,000 9.00 Thorn_S1 S 4590 9,000 1.91 1.60 10,638 500,000 13.33 Thorn_S1 S 4590 9,000 2.20 1.83 10,555 500,000 11.95 Thorn_S1 S 4591 9,000 7.42 6.19 10,646 199,580 5.28 Thorn_S1 S 4790 9,000 2.65 2.21 8,623 500,000 11.30 Thorn_S1 S 4790 9,000 2.43 2.02 8,926 500,000 11.94 Thorn_S1 S 4790 9,000 2.97 2.47 8,619 500,000 10.34 Thorn_S1 S 4990 9,000 2.88 2.40 10,751 500,000 9.41 Thorn_S1 S 4990 9,000 2.97 2.47 10,712 500,000 9.22 Thorn_S1 S 4990 9,000 2.84 2.37 10,735 500,000 9.52 Thorn_S1 S 5190 9,000 2.54 2.12 10,150 500,000 10.86 Thorn_S1 S 5190 9,000 2.50 2.08 10,349 500,000 10.91 Thorn_S1 S 5190 9,000 2.51 2.09 10,127 500,000 10.99 Thorn_S1 S 5390 9,000 3.31 2.75 10,975 500,000 8.99 Thorn_S1 S 5590 9,000 3.12 2.60 10,599 500,000 8.82 Thorn_S1 S 5590 9,000 3.14 2.62 10,500 500,000 8.81 Thorn_S1 S 5590 9,000 2.92 2.44 10,345 500,000 9.37 Thorn_S1 S 5790 9,000 3.79 3.15 10,295 500,000 7.71 Thorn_S1 S 5990 9,000 2.83 2.36 11,032 500,000 8.75 Thorn_S1 S 5990 9,000 2.86 2.38 10,819 500,000 8.77 Thorn_S1 S 5990 9,000 2.80 2.33 10,916 500,000 8.88 Thorn_S1 S 6190 9,000 133.05 110.88 4,150 5,342 1.06 Thorn_S1 S 6190 9,000 99.87 83.22 4,144 7,703 1.20 Thorn_S1 S 6190 9,000 133.03 110.86 4,128 5,350 1.06 Thorn_S1 S 6390 9,000 14.88 12.40 5,483 156,163 2.96 Thorn_S1 S 6590 9,000 17.48 14.56 3,076 229,988 3.37 Thorn_S1 S 6790 9,000 35.77 29.81 2,729 52,715 2.09 Thorn_S1 S 6990 9,000 12.21 10.18 4,658 228,460 3.99 Thorn_S1 S 7190 9,000 9.78 8.15 6,084 284,044 4.15 Thorn_S1 S 7390 9,000 8.27 6.89 6,272 358,478 4.79 Thorn_S1 S 7590 9,000 10.03 8.36 4,361 370,728 4.82




Load [lbf]

CD1 [mils]

D1 [mils]

MR [psi]

EP [psi] SNEff

Thorn_S1 S 7790 9,000 10.96 9.14 4,128 333,756 4.58 Thorn_S1 S 7990 9,000 7.50 6.25 5,028 500,000 5.86 Thorn_S1 S 7990 9,000 7.34 6.12 5,114 500,000 5.92 Thorn_S1 S 7990 9,000 7.60 6.33 5,143 491,445 5.75 Thorn_S1 S 8190 9,000 12.55 10.46 3,510 302,071 4.43 Thorn_S2 S 0 9,000 2.39 1.99 11,271 500,000 10.72 Thorn_S2 S 0 9,000 2.37 1.98 11,298 500,000 10.75 Thorn_S2 S 0 9,000 2.28 1.90 11,260 500,000 11.11 Thorn_S2 S 3550 9,000 1.97 1.64 10,359 500,000 13.24 Thorn_S2 S 3554 9,000 2.44 2.03 10,522 500,000 11.00 Thorn_S2 S 3554 9,000 2.41 2.01 10,440 500,000 11.14 Thorn_S2 S 3800 9,000 2.59 2.16 9,425 500,000 11.04 Thorn_S2 S 3800 9,000 2.56 2.13 9,245 500,000 11.26 Thorn_S2 S 3800 9,000 2.65 2.21 9,236 500,000 10.95 Thorn_S2 S 4000 9,000 3.16 2.63 8,792 500,000 9.54 Thorn_S2 S 4000 9,000 3.51 2.93 8,661 500,000 8.83 Thorn_S2 S 4001 9,000 2.97 2.47 9,133 500,000 9.87 Thorn_S2 S 4230 9,000 2.38 1.99 10,408 500,000 11.37 Thorn_S2 S 4230 9,000 2.37 1.98 10,600 500,000 11.31 Thorn_S2 S 4230 9,000 2.15 1.79 10,331 500,000 12.39 Thorn_S2 S 6200 9,000 34.65 28.87 3,461 40,754 2.18 Thorn_S2 S 6400 9,000 37.28 31.07 4,172 36,174 1.62 Thorn_S2 S 6600 9,000 21.12 17.60 3,374 159,285 2.63 Thorn_S2 S 6800 9,000 20.48 17.07 3,189 133,574 3.03 Thorn_S2 S 7000 9,000 15.29 12.74 3,476 253,582 3.58 Thorn_S2 S 7200 9,000 8.50 7.08 4,676 500,000 5.28 Thorn_S2 S 7400 9,000 6.07 5.06 6,446 500,000 5.99 Thorn_S2 S 7400 9,000 5.81 4.84 6,657 500,000 6.12 Thorn_S2 S 7400 9,000 6.05 5.04 6,472 500,000 5.99 Thorn_S2 S 7600 9,000 10.10 8.41 3,972 404,478 5.03 Thorn_S2 S 7800 9,000 14.39 11.99 2,790 298,414 4.42 Thorn_S2 S 7999 9,000 14.08 11.73 3,265 244,040 4.23


ch w:\active\1841stockton\phase\report\appendix_b_core_photos_010208.doc B.1

Appendix B: Core Photos

DRAFT PAVEMENT EVALUATION REPORT – THORNTON ROAD WIDENING PROJECT Appendix B: Core Photos February 1, 2008


Thornton Rd NBL Sta 526 Lane 1

Thornton Rd NBL Sta 1,742 Lane 1





Thornton Rd NBL Sta 5,323 Lane 1 Thornton Rd NBL Sta 7,711 Lane 1

Thornton Rd NBL Sta 1,300 Lane 2 Thornton Rd SBL Sta 6,582 Lane 1



Thornton Rd SBL Sta 9171 Lane 1 Thornton Rd SBL Sta 10,574 Lane 1

Thornton Rd SBL Sta 12,196 Lane 1 Thornton Rd SBL Sta 13,398 Lane 1



Thornton Rd SBL Sta 5,868 Lane 2 Thornton Rd SBL Sta 9,636 Lane 2

Thornton Rd SBL Sta 12,836 Lane 2


ch w:\active\1841stockton\phase\report\appendix_c_distress_survey_020108.doc C.1

Appendix C: Condition Survey

DRAFT PAVEMENT EVALUATION REPORT – THORNTON ROAD WIDENING PROJECT Appendix C: Condition Survey February 1, 2008


draft pavement evaluation report – thornton road widening ... pavement eval report … · draft...

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