Investigation of karst cavities under the railway basement by GPR: Application to some artificially trenched sections of the Yichang-Wanzhou Railway in China

Yichang-Wanzhou railway with total length of 377 km was constructed in the mountain region presenting the most complex karst geological conditions in the world. Several collapses happened in its artificially trenched sections since this railway opened in the December of 2010. We proposed GPR technique for accurate location of karst cavities and tubes beneath the railway basement for grouting reinforcement. We used EKKO PRO with 100 MHz antenna equipment to detect totally 5.1 km long artificially trenched sections along this railway. Five rail-parallel GPR survey lines were deployed along the railway. We used spatial difference filtering and background removal to suppress flat-lying features and enhance dipping and hyperbolic diffraction features. The processed GPR profiles with effective exploring depth to 20 more meters revealed karst cavities and tubes very clearly. For data interpretation we used FDTD modeling for typical cluster of karst cavities, and the simulated GPR profile is similar to the one collected in field in both dynamic and kinematic characteristics. Next, a novel drilling technique, which do not require water while drilling, combined with borehole-televiewer measurement was used to test and verify GPR interpretation results, and thus proving the accuracy and correctness of GPR profile interpretations.