Effects of Subsurface Drainage on Performance of Asphalt and Concrete Pavements (2003)

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1CHAPTER 1 INTRODUCTION PROBLEM STATEMENT Subsurface drainage is commonly believed to be beneficial to the performance of both asphalt and concrete pavements. However, research to date has neither clearly demonstrated nor quantified the effects of subsurface drainage on asphalt and concrete pavement performance for different climates, soils, and traffic conditions. Past research on this topic has also failed to clarify whether nonfunctioning drainage (due to inadequate design, improper construction, or maintenance) results in pavements performing the same as, or worse than, pavements without any subdrainage installation at all. Without guidance on these matters, the practicing engineer faces a dif- ficult task in judging whether or not subsurface drainage is a cost-effective pavement design component for a given project with a given set of climatic, soil, and traffic conditions. RESEARCH OBJECTIVES The SPS-1 experiment (Strategic Study of Structural Fac- tors for Flexible Pavements) and SPS-2 experiment (Strategic Study of Structural Factors for Rigid Pavements) in the Long- Term Pavement Performance (LTPP) studies were designed to study, among other things, the effects of subsurface drain- age on performance. The objectives of NCHRP Project 1-34C were to: 1. Assess the feasibility of using data available from the LTPP SPS-1 and SPS-2 experiments to evaluate the effects of subsurface drainage on the performance of asphalt and concrete pavements, 2. Recommend additional field data collection (e.g., inspec- tion of subdrainage functioning) needed to complement the available SPS-1 and SPS-2 data in support of the first objective, 3. Develop a plan for analysis of SPS-1 and SPS-2 data for the purpose of quantifying the effects of subsurface drainage on the performance of asphalt and concrete pavements, and 4. Conduct a pilot analysis of the effects of subsurface drainage on performance of asphalt and concrete pave- ments in the SPS-1 and SPS-2 experiments, using the data available in the LTPP database and field inspection results. RESEARCH APPROACH This report presents the results of the assessment of the feasibility of using the SPS-1 and SPS-2 experiments to eval- uate the effects of subsurface pavement drainage on pave- ment performance, and the results of the pilot analyses con- ducted. Based on these results, recommendations are given for additional field data collection and analysis work to be conducted in a subsequent study. Most of the data used in this study were obtained from LTPP data release 11.5, dated 13 June 2001. The as-constructed layer thickness and material type data were updated in June 2002, using data extracted from release 12.0. Layer thickness and material type data for one site (Arkansas SPS-2) were obtained from the Southern LTPP Regional Center’s Regional Infor- mation Management System (RIMS) database. Although drainage is one of the main experimental design factors for both SPS-1 and SPS-2, inspection of the function- ing of the drainage systems was not incorporated into the field monitoring program for these experiments. During the course of NCHRP Project 1-34C, the Federal Highway Administra- tion, with NCHRP support, contracted for the video inspection of edgedrains for the SPS-1 and SPS-2 sites. The results of these inspections were used by the 1-34C research team in this study. However, as discussed later in this report, it is difficult to assess the functioning of the edgedrain systems definitively on the basis of video inspections alone. ORGANIZATION OF THIS REPORT The research conducted for NCHRP Project 1-34C is described in this report in the following sequence: • Chapter 1—Introduction and research approach. • Chapter 2—Effects of subsurface drainage on the per- formance of asphalt pavements in the LTPP SPS-1 experiment. • Chapter 3—Effects of subsurface drainage on the per- formance of concrete pavements in the LTPP SPS-2 experiment. • Chapter 4—Conclusions. • Appendix A—Details of SPS-1 layouts, accumulated traffic, and video inspections. • Appendix B—Details of SPS-2 layouts, accumulated traffic, and video inspections.