TABLE OF CONTENTS SECTION PAGE Background of Existing Facility 3 Proposed Work 4 Objective of this Report 4 Required Data 4 Pavement Design Procedure 5 Other Data Requirements 7 Pavement Structures 8 Pavement Drainage Analysis 10 Conclusion 10 Appendix A: Project Location Map 11 Appendix B: Existing Pavement Structure Typical Sections 13 Appendix C: TxDOT Rigid Pavement Policy 14 Appendix D: Annual Precipitation by Climatic Divisions 15 Appendix E: Pavement Management Information System Report and Base Maps 16 Appendix F: Traffic Analyses, from TP&P 17 Appendix G: The Existing Configuration of IH-635 18 Appendix H-1: Subgrade Soils Report for Pavement Design 19 Appendix H-2: Results of the Additional Subgrade Soils Investigation on the Extent of the Soluble sulfate Content 20 Appendix I: Dallas District Policy on Subgrade Potential Vertical Rise and On Required Minimum of 4 of HMAC base for Rigid Pavement 21 Appendix J: Results of DARWin Computations 22 Appendix K: Proposed Pavement Structure Typical Sections 23 2
Background of Existing Facility The reconstruction of IH-635 (LBJ Freeway) is approximately a twenty-mile roadway project that consists of two sections called the East section and the West Section. The overall location of the project is shown in Appendix A. The West section which is the subject of this report is approximately 8.81 miles, located in the cities of Dallas and Farmers Branch and consists of four CSJ s. This segment of LBJ Freeway was constructed in the late 1960 s to early 1970 s to serve as an outer loop freeway and provide mobility for the rapidly growing North Dallas and Farmers Branch areas. The existing facility within the limits of the West section consists of eight 12-foot mainlanes, two HOV lanes, two 10-ft outside shoulders as well as non-continuous frontage roads and a few auxiliary lanes. Table 1 and Table 2 summarize the existing pavement structures of the freeway. MAIN LANES FRONTAGE ROADS From Luna Rd To IH-35 Interchange Travel Lanes Pavement structure from top to bottom: - 10 Continuously Reinforced Concrete Pavement (CRCP) - 4 Asphalt Stabilized Base - 8 Lime Treated Subgrade Travel Lanes Pavement structure from top to bottom: - 9 Asphalt Concrete Pavement - 8 Lime Treated Subgrade Table 1 Pavement Structure of the Existing Facility From IH-35 Interchange To East of U-75 MAIN LANES FRONTAGE ROADS Travel Lanes Pavement structure from top to bottom: - 8 Continuously Reinforced Concrete Pavement (CRCP) - 6 Lime Treated Flexible Base - 6 Lime Treated Subgrade Travel Lanes Pavement structure from top to bottom: - 8 Uniform Concrete Pavement - 6 Lime Treated Flexible Base - 6 Lime Treated Subgrade Table 2 - Pavement Structure of the Existing Facility The existing typical sections of pavement structures for above segments are included in Appendix B. 3
Proposed Work The proposed roadway work for the West section of IH-635 that extends from West of Luna Rd to East of Park Central Drive (a segment of approximately 9 miles) consists of complete reconstruction of the existing facility. The proposed improvements include: Mainlane improvement; Addition of multiple HOV lanes in both directions from 0.5 miles East of Luna Rd to East of Josey Lane and from Hughes Lane to West of Coit Rd. Addition of two- and three-lane frontage roads to link the existing noncontinuous frontage roads in each direction; Reconstruction of the existing frontage roads to accommodate other corridor improvements; Removal of old ramps and construction of new ramps. Addition of two bored and cut-and-cover tunnels for managed HOV lanes from Midway Rd to Preston Rd. The pavement structure for use in these tunnels is beyond the scope of this study. The project generally follows the existing horizontal alignment of IH-635. The proposed vertical alignment will almost be completely modified in order to provide for current vertical curve design standards and vertical clearance standards. Objective of This Report The objective of this report is to present the rigid pavement design analysis used in developing the proposed pavement structure for the reconstruction of the West section of the LBJ freeway including its mainlanes, managed HOV lanes, frontage roads and ramps. Required Data The following inputs are required to determine the Design Thickness of the concrete pavement in inches: Effective Modules of Subgrade Reaction, k (pci) Concrete Elastic Modulus, E c (psi) Mean Concrete Modulus of Rupture, S'c (psi) Load Transfer Coefficient, J Drainage Coefficient, C d Initial Serviceability Index Terminal Serviceability Index Reliability, (%) Overall Standard Deviation, S o Estimated Future Traffic, Total 18-kip Equivalent Single Axle Load (ESAL) Applications for the Performance Period Pavement Design Procedure 4
The required thicknesses of the concrete pavement for carrying the proposed traffic loads were determined by the use of DARWin Pavement Design and Analysis System. This program is the automated version of the design procedure that is outlined in the AASHTO Guide for Design of Rigid Pavement Structures, 1993. The procedure is described in Part II, Chapter 3, Section 3.2 of the Guide. Selections of the pavement design parameters, required as input data for the DARWin program, were based on TxDOT Pavement Design Manual recommendations and rigid pavement policy. This information is shown in Appendix C. The following sections describe how various parameters were chosen: 1. Effective Modules of Subgrade Reaction, k (pci) A Modulus of Subgrade Reaction, k of 300 pci is selected for this project per TxDOT Pavement Design Manual recommendation. 2. Concrete Elastic Modulus, E c (psi) It is anticipated that the coarse aggregate used in the concrete for this project will be crushed limestone. The resulting concrete Elastic Modulus will be 4,000,000 psi. This is in accordance with the Pavement Design Manual for rigid pavement provided by Construction Division of TxDOT, March 2001. Although the actual Elastic Modulus concrete could be different from this value, however, the end result will not have a significant effect on the slab thickness. 3. Mean Concrete Modulus of Rupture, S'c (psi) The Modulus of Rupture is a measure of flexural strength of concrete as determined by breaking concrete beam specimens. Per TxDOT Pavement Design Manual a value of 650 psi is to be used with the current statewide specification for concrete pavement and standard detail drawings. 4. Load Transfer Coefficient, J This project will utilize load transfer devices at joints and will have more than two lanes in one direction; therefore based on Table 3-1, page 3-10 of TxDOT Pavement Design Manual the value of J will be 2.9. The table is included in Appendix C. 5. Drainage Coefficient, C d The guidelines suggested on Table 3-2, page 3-11 of the Pavement Design Manual are used to determine C d. Texas Almanac chart (presented in Appendix D) shows an annual rainfall of 36 inches in the project area. Therefore, the Drainage Coefficient, C d chosen is 1.02. 6. Serviceability Indices, SI Based on TxDOT Manual recommendation, an initial serviceability index of 4.5 and a terminal serviceability index of 2.5 is selected for this project. 7. Reliability, (%) 5
The reliability determination is made using Table 3-3, page 3-11 of the Pavement Design Manual. This project involves an urban interstate facility with controlled access and projected average daily traffic (ADT) per lane of more than 20,000. According to the table, a Reliability of 99.9% is recommended. However, considering the satisfactory condition of the existing pavement (Refer to Appendix E) a reliability of 95% would be justified. 8. Overall Standard Deviation A value of 0.39 is used for this project as recommended by TxDOT Pavement Design Manual for this type of roadway. 9. Traffic Analysis Report The traffic loading used to develop the pavement sections, for the mainlanes as well as the frontage roads, is based on the traffic analyses performed by TxDOT Transportation Planning and Programming Division. The traffic projections were determined according to a 30-year design period from 2010 to 2040, and were evaluated for 10-inch and 13-inch thick rigid pavement slabs. The traffic analyses report is presented in Appendix F. As described in the report, due to differences in traffic volumes, the project was divided into three sections namely 4, 5 and 6 for the West section. Table 3 shows the (average) total number of 18K Equivalent Single Axle Load (ESAL) applications expected, in one direction, for each section and in terms of the existing configuration within the limits of LBJ West section. The existing configuration of the West Section is presented in Appendix G. CSJ SECTION LIMITS TOTAL NUMBER OF 18K ESAL APPLICATIONS FROM - TO Mainlanes Frontage Rd s 2374-07-046 6-5/Q Luna Rd E. End of BNSF RR 201,190,000 6,040,000 2374-01-032 5/P E. End of BNSF RR 198,134,000 9,022,000 Webb Chapel Road 2374-01-068 4/N,M,L Webb Chapel Road E. of DNT 255,570,000 20,832,000 Including 2374-01-136 2374-01-068 Including 2374-01-136 4/K E. of DNT E. of Park Central 314,123,000 19,769,000 Table 3 - Total Number of 18K Equivalent Single Axle Load Applications The LBJ Freeway within this section will have more than eight mainlanes and 5-6 frontage road lanes. Therefore, according to Table 3-4 of the TxDOT Pavement Design Manual a Lane Distribution Factor (LDF) of 0.6 and 0.8 is selected for the mainlanes and frontage road lanes respectively. The corresponding adjusted 18K ESAL applications are shown in Table 4. ADJUSTED 18K ESAL CSJ SECTION LIMITS APPLICATIONS 6
FROM - TO Mainlanes Frontage Roads 2374-07-046 6-5/Q Luna Rd E. End of BNSF RR 120,714,000 4,832,000 2374-01-032 5/P E. End of BNSF RR 118,880,400 7,217,600 2374-01-068 Including 2374-01-136 2374-01-068 Including 2374-01-136 Webb Chapel Road 4/N,M,L Webb Chapel Road E. of DNT 153,342,000 16,665,600 4/K E. of DNT E. of Park Central 188,473,800 15,815,200 Table 4 Adjusted Number of 18k Equivalent Single Axle Load Applications In this study no provisions for stage-construction are considered for the design of the proposed rigid pavement. Other Data Requirements In addition to the above data the following reports were also obtained and used for determining the total thickness of the new pavement structure and the condition of the existing concrete pavement: 1. District Laboratory Subgrade Soils Report This report (see Appendix H-1) was prepared by the Dallas District Laboratory. Seventeen soil borings were drilled within the limits of the project and several samples were obtained and tested to determine the in-situ soil properties and estimate the required depth of cover above the subgrade to limit the Potential Vertical Rise (PVR) to one inch. Dallas District policy on restricting subgrade PVR is presented in Appendix I. According to visual description and laboratory tests the District Lab determined that there are two types of subgrade soils within the limits of LBJ West Section, namely Type 1 and Type 2. Table 5 presents the extent of Type 1 and Type 2 soils in terms of the existing configuration within the limits of the LBJ West Section. SUBGRADE SOILS LIMITS TYPE 1 TYPE 2 CSJ FROM - TO CSJ FROM - TO Luna Rd E. End of BNSF RR Luna Rd 2374-07-046 (E.B.) 2374-07- E. End of BNSF E. End of BNSF RR 046 RR 2374-01-032 Webb Chapel Road (W.B.) 2374-01-68 E. of DNT E. of Park Central Table 5 - Extent of Type 1 and Type 2 soils 7
According to the as built plans Type 1 soil, which exists at borings 1 and 3 (westbound between Luna Rd and IH35E interchange) is actually the embankment materials placed underneath the existing pavement and does not represent the in-situ subgrade soil. The soil has a Texas Triaxial Class of 4.75 with a median plasticity index (PI) of 17. Type 2 soils which exist at boring 2 and between borings 4 and 17, have a Texas Triaxial Class of 6 and consist predominantly of brown sandy clay to clay with calcareous nodules (CH). The clays have a median PI of 37. In this report these soils are considered to be the existing natural subgrade for the entire project. Evidence of sulfate materials was visually identified in boring 8 (approximately 600 feet to the east of Webb Chapel Rd), between the depths of 2-3 feet. The results of the laboratory tests on the samples from this boring indicate that the soluble sulfate concentrations at the location of this borehole is more than 10,000 ppm. To determine the extent of the soluble sulfate, further subsurface explorations were conducted by drilling two additional boreholes (about ¼ of a mile in each direction from boring 8, and to a depth of ten feet) and collecting samples for visual inspection. The results of the investigations indicated no significant presence of sulfate materials in either borehole (refer to Appendix H-2). Therefore, based on the information provided by the Dallas district laboratory, it is the opinion of this report that if, within the limits of the West section, sulfate materials do exist it would be only localized and found in small pockets. 2. Pavement Management Information System (PMIS) Data and Base Maps PMIS data and base maps were obtained from the Dallas District Pavement Section to evaluate the condition of the existing pavement. The information is included in Appendix E. The following conclusions have been drawn from the PMIS data and Base Maps: Distress Score- about 25% Very Poor to Fair and about 75% Good to Very Good Ride Score- about 20% Fair and about 80% Good Condition Score- about 25% Poor to Fair and about 75% Good to Very Good Based on the above information and the fact that the freeway was constructed more than 30 years ago, conclusions could be drawn that the condition and the performance of the existing concrete pavement within the West section of the LBJ freeway is satisfactory. Pavement Structures The results of the DARWin software program, using the above required data, are included in Appendix J. The required thickness of concrete slabs for the mainlanes and the frontage roads are summarized in Table 6. 8
CSJ SUBGRADE SOIL TYPE LIMITS FROM - TO CONCRETE THICKNESS (in) Main Frontage Lanes Roads 2374-07-046 (1=Fill), 2 Luna Rd E. End of BNSF RR 14.40 8.61 2374-01-032 2 E. End of BNSF RR Webb Chapel Road 14.36 9.21 2374-01-068 2 Webb Chapel Road E. of DNT 14.93 10.57 2374-01-068 2 E. of DNT E. of Park Central 15.40 10.48 Table 6 Required Thickness of Concrete for the mainlanes and the frontage roads Based on these results and TxDOT rigid pavement policy (Appendix C) requiring the use of a minimum of four inches of hot mix asphalt concrete (HMAC) under concrete pavement the following pavement structures are proposed: Main Lanes, HOV lanes and shoulders A 15-inch CRCP slab with 4 inches of HMAC base is proposed for pavement structures for the mainlanes, managed HOV lanes and shoulder. This project is located within a controlled access facility. The District policy, shown in Appendix I, requires the PVR to be restricted to 1.0 inch on this class of roadways. Based on the PMIS information the overall condition of the pavement structure within the segment that Type 1 soil exists is fair to good. Therefore, it is recommended that the top 6-12 inches of this material be lime stabilized with 4% lime (by weight) for further improving the condition of the soil, and also for providing a firm platform for facilitating construction. For Type 2 soils, according to the District Laboratory soil report, the total depth of cover must be at least 38 inches to restrict the PVR to one inch. Therefore, in the fill sections, whereas most contractors have machines that will mix lime 12 inches deep, a minimum of 7 inches of suitable fill materials must be provided to fulfill the minimum 38-inch cover and the PVR requirements. In the cut sections since, in most cases, stabilizing the existing subgrade with lime is less expensive than bringing in select borrows it is recommended temporarily removing the top 7 inches, lime stabilizing 12 inches of the existing subgrade, and then replacing and lime stabilizing the top 7 inches. As recommended by the soil report Type 2 soils shall be mixed with 6% lime (by weight). Also, although very localized, if any soluble sulfate concentrations of greater than 2000 ppm (the maximum permissible) is encountered during the construction the subgrade at that location must be removed and replaced with suitable fill materials. Ramps The ramps for controlled access facilities are typically designed to have the same sections as the mainlanes. Therefore, the ramps for this project will have the same pavement structure as the mainlanes. 9
Frontage Roads A 9-inch CRCP with 4 inches of HMAC base is proposed for the segment between Luna Road and Webb Chapel Road. For the segment between Webb Chapel Road and E. of Park Central an 11-inch CRCP with 4 inches of HMAC base is recommended. As indicated in the soil report for type 2 soils (that are the existing natural subgrade of the frontage roads) the required depth of better material must be 22 inches to limit the PVR to 1.5 inches. Therefore, a minimum depth of 6 inches of lime stabilization is recommended for fulfilling the minimum 22-inch cover and the PVR requirements. This would also serve as a firm platform for facilitating construction. Again, if any soluble sulfate concentrations of greater than 2000 ppm is encountered the subgrade at that location must be removed and replaced with suitable fill materials. For all embankments, associated with the pavement structures, suitable fill material with plasticity index between 8 and 40 should be specified. As suggested in the District laboratory report the backfill materials for bridge abutments should be restricted to select fill with plasticity index between 10 and 25. All embankments shall be compacted using moisture and density controlled method. To avoid destabilizing the existing subgrade it is recommended that the existing pavement remain in place and be overlaid with fill and pavement materials for the fill sections. This strategy will also contribute to cost benefits as far as removals and subgrade stabilization are concerned. The typical sections of pavement structures for the mainlanes, managed HOV lanes, shoulders, ramps and frontage roads (corresponding to the above cases) are shown in Appendix K. It should be noted that these sections are for pavement structure layers illustration only and they do not represent the proposed roadway typical sections. Pavement Drainage Analysis The pavement will be drained by a network of storm sewer systems, and within a few short stretches, by side ditches. Ramps and connectors will be drained over the sides of the embankments and along the side ditches into the storm sewer systems. Positive drainage, as a whole, is not expected to be a problem because the project will extensively render increased impervious surface, and it will be constructed in a controlled drainage environment. Conclusion This pavement design is based on the available data and the currently accepted practices which indicate that the methods employed are considered to be sound approaches to providing the performance required for the facility. 10
Appendix A PROJECT LOCATION MAP 11
DNT I.H. 635 (LBJ) Corridor Study na Road End at Valley View / SH 161 PGBT I.H. 635 (LBJ) I.H. 35E LUNA WEST SECTION BELT LINE U.S. 75 EAST SECTION S.H. 78 RD BELT LINE LOOP 12 GARLAND I.H. 30 I.H. 35E U.S. 75 / I.H. 635 Interchange (The Dallas High Five) Under Construction CBD I.H.30 I.H. 635 (LBJ) U.S. 80 12
Appendix B EXISTING PAVEMENT STRUCTURE TYPICAL SECTIONS 13
Appendix C TxDOT RIGID PAVEMENT POLICY 14
Appendix D ANNUAL PRECIPITATION BY CLIMATIC DIVISIONS 15
Appendix E PAVEMENT MANAGEMENT INFORMATION SYSTEM (PMIS) REPORT AND BASE MAPS 16
Appendix F TRAFFIC ANALYSES, FROM TP&P 17
Appendix G THE EXISTING CONFIGURATION OF IH-635 18
Appendix H-1 SUBGRADE SOILS REPORT FOR PAVEMENT DESIGN 19
Appendix H-2 RESULTS OF THE ADDITIONAL SUBGRADE SOILS INVESTIGATION ON THE EXTENT OF THE SOLUBLE SULFATE CONTENT 20
Appendix I DISTRICT POLICY ON RESTRICTING SOIL POTENTIAL VERTICAL RISE (PVR) AND ON REQUIRED MINIMUM OF 4 OF HMAC BASE FOR RIGID PAVEMENT 21
Appendix J RESULTS OF DARWin COMPUTATIONS 22
Appendix K PROPOSED PAVEMENT STRUCTURE TYPICAL SECTIONS 23