Back-Analysis for the Elasto-Viscoplastic Parameters of Landslides Based on the Observed Displacements: A Case Study of the Wujiang Landslide, China

The Wujiang landslide is located on the right bank of Centianhe reservoir near the entrance of the Wujiang gorge, approximately 300 m upstream of the original dam. As a typical ancient landslide, this landslide’s total volume is approximately 1.327×107m3\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$1.327\times 10^{7}\hbox { m}^{3}$$\end{document}. The stability of the landslide affects the operation and safety of the dam and flood-release structures after the reservoir of the Expansion Project impounding. First, the observed internal landslide displacement is analyzed and shows that the Wujiang landslide is a long-term creep slope along the control shear plane, and the shear strength of the slip band has either approached or reached its long-term strength. Then, a typical cross section parallel to the sliding direction is selected for the calculation, and the strength parameters are back-analyzed based on the limit analysis method. Next, a finite element model of a typical cross section for the landslide is constructed, and the viscoplastic strain rate is calculated based on Mohr–Coulomb yield criterion and Perzyna’s assumption; therefore, the annual displacement creep rate calculated by the elasto-viscoplastic finite element program is obtained. Finally, the annual creep rate of the observed displacement and that of the calculated displacement are combined, and the elastic modulus and viscosity coefficient of the landslide are back-analyzed based on the orthogonal design method and simplex optimization algorithm. These parameters provide a basis for the analysis and control of the landslide and serve as a reference for similar projects.