Evaluation Of Roadway Subsurface Drainage On Rural Routes

Excess moisture has been identified as a cause for stripping, raveling, debonding, and rutting in flexible pavement [ODOT, 2016a]. The Ohio Department of Transportation (ODOT) has been getting substantially less than the expected 15 year service life after a resurfacing project, particularly on those routes without drainage. Providing drainage may help mitigate the premature failures ODOT is seeing on their rural routes. Section 205 of the 2016 Ohio DOT Pavement Design Manual (PDM) requires subsurface drainage on all new projects and recommends aggregate drains be used with bituminous surface treated and aggregate shoulders. Installing aggregate drains by contract during resurfacing has become costly for ODOT. This project was completed in two phases. The first phase focused on current practices of drainage installation on rural routes and on identifying available equipment for use by county crews. Phase 2 included a field evaluation to evaluate cost effective options for drainage incorporating the findings and recommendations from Phase 1. The Phase 1 evaluation identified aggregate drains as the appropriate drainage method and the rock saw as the most efficient equipment for aggregate drain installation. In Phase 2 aggregate drains were constructed by ODOT's Marion County personnel in forty test sections on State Route 529 using the rock saw and the backhoe. Drains were not installed in four sections which served as control sections, for a total of forty-four sections. Aggregate drains were installed using backfill meeting AASHTO #8, #57, and #4 gradations as well as a porous concrete backfill. Other factors evaluated included varied spacing between drains, trenches with and without fabric, compacted and un-compacted backfill, and narrow and wide trenches. Dynamic cone penetrometer testing was conducted before and after the monitoring period. The sections were monitored every four months for a one year period by testing with the falling weight deflectometer and measuring in-situ volumetric moisture.