Background: Research performed under NCHRP Project 1-34, "Performance of Subsurface Pavement Drainage," produced unexpected findings. These findings are based principally on analyses of visual distress survey data and on external inspection of the condition and operation of the subsurface drainage features; more comprehensive inspections were not possible within the constraint of available project funds. Thus, the unexpected findings might have been at least partially influenced by the operational performance of the various types of subsurface drainage features rather than by limitations inherent in their design. The NCHRP panel established subsequent Projects 1-34B, 1-34C, and 1-34D to further evaluate these findings with data on the performance and functionality of field projects with subsurface pavement drainage features in the LTPP program.

Objectives: The objectives of this project are to (1) quantitatively test the functionality of the subsurface drainage features in the LTPP SPS-1 and SPS-2 field sections and (2) refine the relationships between subsurface drainage features and pavement performance developed in Projects 1-34 and 1-34C.

Tasks: Accomplishment of these objectives will require, as a minimum, completion of the following tasks.

(1) Resolve discrepancies in as-designed versus as-constructed drainage features in SPS-1 and SPS-2 experiments identified in NCHRP Project 1-34C. (2) Resolve other discrepancies in the as-designed versus as-constructed conditions identified in NCHRP Project 1-34C. (3) Develop a method for quantitative testing of the functioning of subdrains in SPS-1 and SPS-2 test sections. (4) Conduct testing of subdrainage functioning in SPS-1 and SPS-2 test sections. (5) Review and analyze the field data from Task 4. (6) Analyze deflection data from the SPS-1 and SPS-2 sections to determine their current structural capacity and assess how much of the observed differences in performance is attributable to differences in structural contribution of the three base types compared with differences in the subsurface drainage features. (7) Incorporate available data from MnRoad and Wisconsin DOT field studies into the analysis of the effect of subsurface drainage on pavement performance. (8) Refine and amplify the analysis from Project 1-34C to better define the effect of subsurface drainage on pavement performance. (9) Submit a final report that documents the entire research effort and includes any revisions required to the conclusions and guidelines presented in the final reports for Projects 1-34 and 1-34C.

Status: The project is complete.

Product Availability: The final report has been published as NCHRP Report 583: Effects of Subsurface Drainage on Pavement Performance: Analysis of the SPS-1 and SPS-2 Field Sections.