Back analysis for stratigraphic structure of earthquake-induced soft-hard interbedded anti-dip Rannai Paleolandslides on the Southeastern Qinghai-Tibet Plateau

Abstract

Abstract Steep terrain and debris cover pose significant challenges to conventional investigation techniques for characterizing the pre-failure stratigraphic structure of soft-hard interbedded anti-dip rock slopes (SHIADRSs). To overcome this, this study develops a numerical back-analysis methodology to quantitatively determine the soft-hard interbedded thickness ratio (SHIR) for paleolandslides. The methodology integrates high-precision unmanned aerial vehicle remote sensing with the universal distinct element code (UDEC). The core of this approach involves simulating the seismic failure processes of numerical models with varying SHIR values and determining the optimal SHIR by maximizing the geometric fitness between the simulated failure surfaces and the actual landslide morphology. Applied to the Rannai Landslide (RNL) on the southeastern Qinghai-Tibet Plateau, the back-analysis yielded a pre-failure SHIR of 1:2.5 (hard rock dominant). This result shows a discrepancy of less than 5% compared to the local stratigraphic data, robustly validating the accuracy and reliability of the proposed back-analysis method. Furthermore, this study elucidated the failure pattern of the RNL under seismic loading, providing valuable insights into the dynamic instability mechanisms of such slopes.