Quantitative assessment for the rockfall hazard in a post-earthquake high rock slope using terrestrial laser scanning

Geometric information and discontinuity characterization of rock masses are the key aspects of the analysis of the evolution and failure mechanisms of rockfalls. With the advantageous use of terrestrial laser scanning (TLS), the accurate three-dimensional (3D) spatial information of rock slopes can be obtained without contact. By conducting a fuzzy K-means algorithm in this study, the automatic identification of discontinuity sets is achieved, and dominant occurrences of rock mass discontinuities in each local region can be acquired in great detail. This automatic identification method permits the user to visually identify the discontinuity sets and acquire their spacial distribution features, e.g. occurrences, spacings, trace lengths and their geometric compounding relationships. At the same time, based on the shortest distance (SD) algorithm and the surface-to-plane volume calculation algorithm, the distributions, shapes, volumes and scars of the rockfalls can be accurately detected over the monitored time interval. These methods are able to provide adequate investigations and quantitative assessment for the rockfall failure mechanisms and evolutions of the Hongshiyan post failure rock slope after the 2014 Ludian earthquake. The topography of the landslide surface, mechanical properties, scales and the structural features of the discontinuities have a significant effect on the failure mechanisms, distributions and volumes of rockfalls. The main failure mechanisms of the rockfall investigated in this rock slope can be divided into plane failure, wedge failure and toppling failure. The plane and wedge failures mainly occurred in the landslide surface while the toppling failures are mainly observed along the edge of the post failure slope, which is obviously responded by preferred discontinuities. The reverse-dip stratified structure characteristics and the excavation disturbances during the recovering and slope treatment stage induce numerous progressive and continuous failures of rockfalls. The results are beneficial for the design and optimization of rockfall treatments.