Forensic Investigations of Roadway Pavement Failures

Abstract

This paper presents three field projects to illustrate the integrated approach to forensic investigations of roadway pavement failures used widely in Texas. In each case, the combined ground-penetrating radar (GPR) and falling weight deflectometer (FWD) data were extremely useful for identifying contributing factors, such as stripping in the hot mix or localized areas of wet or weak base. Dynamic cone penetration (DCP) is used for validating problems with base and subbase layers. Laboratory tests are often required to complete the investigation, especially if the repair strategy calls for in-place recycling of the existing structure. The extent of stripping and high porosity that caused delamination for Projects 1 and 2 was detected by GPR and verified by core samples. GPR, FWD, DCP, and field soil samples all showed indications that the existing base on Project 1 was wet and the stiffness was only about one-third that of a typical flexible base in Texas. FWD data demonstrate that the pavement structures for Projects 1 and 2 were inadequate, so a rehabilitation strategy was selected that included structural strengthening. In Project 3, GPR, lab density, and permeability tests indicate that the dramatic pavement failures were attributable to moisture entering the base through a poorly compacted asphalt concrete layer and poor longitudinal joints. The base material was found to be highly susceptible to moisture and did not meet the Texas Department of Transportation’s compressive strength requirements when subjected to capillary soaking. The repetitive triaxial test results revealed that the stiffness and load-carrying capability became inadequate when the base materials were exposed to moisture. The pavement structure had been totally replaced in 2004.