Application of remote ground-penetrating radar for condition assessment of wooden crossties

Abstract

Wooden crossties are an important component in railroad infrastructure as a load-bearing member connecting rail tracks and the ballast. Their internal failures (e.g., flexural cracks, delamination, and railroad crosstie-ballast failures) could be left undetected for years from routine inspection. Subsurface nondestructive testing/evaluation (NDT/E) techniques are required for effective routine inspections. In this paper, the feasibility of a 1.6 GHz ground-penetrating radar (GPR) was assessed for condition assessment of wooden crossties in both contact and remote setups. Two wooden crossties (one intact with length = 100 ", width = 7", depth = 9"), and one damaged with (length = 100", width = 6", depth = 9", with two symmetrical wedge-shaped cracks due to end-splitting on both sides) were considered. A height-adjustable Styrofoam slab was created and used for controlling the separation distance to different values (0, 1"/2.5 cm, 2.6"/6.6 cm, 4.2"/10.7 cm, and 5.8"/14.7 cm). The crossties were scanned along their length and multi-dimensional amplitude, and dielectric mapping analyses were performed to detect and map the locations of crack boundaries for each separation distance. From our results, it was found that GPR scan parameters such as dielectric analysis and A-scan comparison can detect and map defects in railroad crossties. Moreover, it was found that an increasing separation distance reduces the GPR signal amplitude as well as damage detectability for condition assessment of wooden crossties in railroad infrastructure.