Monitoring of displacement evolution during the pre-failure stage of a rock block using ground-based radar interferometry

Abstract

As a typical abrupt geological hazard, rockfalls are widely distributed and occur frequently. It is often difficult to predict the occurrence, and therefore record and monitor the whole failure process of rockfalls. In this study, with the combined use of terrestrial laser scanning (TLS) and ground-based radar interferometry (GB-InSAR) technologies, a typical small collapse in the Hongshiyan post-earthquake rock slope was monitored. An accurate TLS three-dimensional (3D) rock slope model of the study area was established with high-resolution geometry and morphology information, the discontinuity sets and their orientations and distributions were visually identified and analyzed by means of an automatic discontinuity identification algorithm. A perspective view of the whole dynamic failure process of the small collapse was achieved; the displacement behavior during critical sliding stage was revealed by integrating the high-accuracy (millimetric) GB-InSAR monitoring results into the TLS 3D model. It can be used for a complete analysis of the failure behavior and stability assessment of the rock slope during a phase of emergency. The unstable rock block on the slope exhibited a rapid growth of displacement. The dynamic failure process of the rock block underwent three obvious accelerating periods. There was a correspondence between the spatial expansion of the moving area and the process of cracking propagation of rock bridges. The stability of the perilous rock above the tafoni was controlled by the connectivity of rock bridges. Thanks to monitoring, early warning and preventive measure were taken, which avoided a possible undesirable event. This typical case study can provide a reference for the monitoring of an unstable rock slope and the understanding of the evolution of rock block kinematics before collapse.