Rock characteristics and dynamic fragmentation process of the 2018 Daanshan rockslide in Beijing, China

This study investigated the failure mechanism associated with the rock mass structure and the dynamic fragmentation process of blocky rocks of the 2018 Daanshan rockslide that occurred on 11 August, 2018. It was found that the initially collapsed rock of this rockslide was partitioned along the unconformity and strata interfaces. We analyzed how the unique rock mass structure, coupled with the road cut and the antecedent rainfall, jointly resulted in its failure. Based on the rock types and geological structures, the initial stratified configuration of a discrete element model was setup to reveal the influences of the local structure. The numerical model was divided into three parts. Part 1 is the basalt of the Nandaling Formation, the normal and shear stiffnesses of the basalt particles are set as 80 MPa and 40 MPa. Parts 2 and 3 are the sandstones interbedded with mudstone and sandstone of the Shihezi Formation, and the normal and shear stiffnesses of these parts were set as 6 MPa and 10 MPa, respectively. The dynamic process of the rockslide, particularly the rock fragmentation process, was numerically analyzed using a 3D discrete element method. The numerical results were compared with real-time videos and field investigations. The results show that the rock fragmentation and the final deposition range match well with the real disaster phenomenon, and the calculation accuracy of the rockslide reaches 82.41%. Moreover, a parameter sensitivity analysis was conducted, and classical uniform models under different bonding forces were established; the stratified model can better restore the true state of the fragmentation, movement, and deposition processes of rockslides. Therefore, for complicated rocks with significant differences in lithology, clarifying the rock mass stratigraphy is essential for an accurate reconstruction of the dynamic process of rockslides.