Method for Unloading Zonation Based on Strain per Unit Crack: Case Study of a Large-Scale Rocky Slope on the Qinghai–Tibet Plateau

Abstract

Distribution of unloading zones determines stability of slopes, and the unloading of a large-scale rocky slope formed by rapid river erosion and surface uplift on the Qinghai–Tibet Plateau is particularly severe. Generally, unloading assessment relies on traditional methods, which are mainly related to phenomena. However, unloading is a process of deformation and failure regarding the rock mass. Based on deformation and failure, strain rate and crack rate established through theoretical analysis can measure the relationship between accumulative width of open cracks and unloading deformation and the relationship between accumulative number of cracks and unloading failure, respectively. Thus, a method that combines strain rate and crack rate, namely strain per unit crack (i.e., SPUC), is proposed. The SPUC was applied to assess the unloading zones of a large-scale rocky slope on the Qinghai–Tibet Plateau. The results show that the SPUC curve regularly varied and can be easily divided into three parts. Strong and weak unloading zones can be recognized from the SPUC curve. The reasonability of SPUC in the unloading zones assessment was confirmed by comparing and verifying with traditional methods. We found that SPUC has good universality and can compensate for the defect of using strain rate or crack rate to assess unloading zones.