Displacement Analyses for a Natural Slope Considering Post-Peak Strength of Soils

Chien-Li Lo,Ching-Chuan Huang

doi:10.3390/geohazards2020003

Abstract

A natural slope undergoing recurrent movements caused by rainfall-induced groundwater table rises is studied using a novel method. The strength and displacement parameters are back-calculated using a force-equilibrium-based finite displacement method (FFDM) based on the first event of slope movement recorded in the monitoring period. Slope displacements in response to subsequent rainfall-induced groundwater table rises are predicted using FFDM based on the back-calculated material parameters. Important factors that may influence the accuracy of slope displacement predictions, namely, the curvature of the Mohr-Coulomb (M-C) failure envelope and post-peak strength softening, are investigated. It is found that the accuracy of slope displacement predictions can be improved by taking into account post-peak stress-displacement relationship in the analysis. The accuracy of slope displacement predictions is not influenced by the curvature of the M-C failure envelope in the displacement analysis.

Highlights

Intensive rainfall causes geohazards in the form of slope failures and debris flows such as those reported by Huang et al [1,2,3,4,5]
Tatsuoka et al [14] showed the effectiveness of utilizing generalized hyperbolic equations and an exponential function for simulating the post-peak strength softening of sandy soils
To correctly reflect the displacement status of approach that uses force-equilibrium-based finite displacement method (FFDM) for slopes undergoing periodic slope movements induced by rainfall

Summary

Introduction

Intensive rainfall causes geohazards in the form of slope failures and debris flows such as those reported by Huang et al [1,2,3,4,5]. The calculated value of Fs reflects the safety margin of the slope against failure, providing no information on the deformation (or displacements) of the slopes Both strength- and displacement-related parameters back-calculated from the first event of slope displacement were found to be valid for predicting slope displacements that occurred in subsequent rainfall events (or groundwater table rises) In their studies, linear Mohr-Coulomb (M-C) envelopes an42d hyperbolic stress-displacement relationship were used; this may be insufficient to properly simulate the behavior of soils. The following hyperbolic equation is used for the normalized shear stress (τ/τf) vs. 2s.hMeaertdhiosdpolalocegmy ent (Δ) relationship along a potential failure surface (Figure 1): Observing the slope failure in natural slope and a series of rainfall tests, the mechanism of slope displacement of rainfall-induced groundwater table rises will be deserving of studying and discussing

Constitutive Law for Stress-Displacement Relationship

Internal Friction Angle of Soils

Displacement Compatibility Requirements

Force-Equilibrium-Based Finite Displacement Method

Results of Back-Analysis

Conclusions