Three-Dimensional Numerical Analysis of the Tunnel for Polyaxial State of Stress

Wenge Qiu,Chao Kong,Kai Liu

doi:10.1155/2015/301241

Abstract

The aim of this study is to have a comprehensive understanding of the mechanical behavior of rock masses around excavation under different value of intermediate principal stress. Numerical simulation was performed to investigate the influence of intermediate principal stress using a new polyaxial strength criterion which takes polyaxial state of stress into account. In order to equivalently substitute polyaxial failure criterion with Mohr-Coulomb failure criterion, a mathematical relationship was established between these two failure criteria. The influence of intermediate principal stress had been analyzed when Mohr-Coulomb strength criterion and polyaxial strength criterion were applied in the numerical simulation, respectively. Results indicate that intermediate principal stress has great influence on the mechanical behavior of rock masses; rock strength enhanced by intermediate principal stress is significant based on polyaxial strength criterion; the results of numerical simulation under Mohr-Coulomb failure criterion show that it does not exert a significant influence on rock strength. Results also indicate that when intermediate principal stress is relatively small, polyaxial strength criterion is not applicable.

Highlights

With respect to underground engineering, rock strength is one of the most important factors that affect stability of underground structure
Among the factors that affect rock strength, cohesion, internal friction angle, fissures, joints, and stress state of rock mass have a significant influence on rock strength [1]
MohrCoulomb failure criterion is presented that only cohesion and internal friction angle are considered to describe strength of rock mass

Summary

Introduction

With respect to underground engineering, rock strength is one of the most important factors that affect stability of underground structure. Senent et al [2] thought that enhancement of rock strength by intermediate principal stress σ2 was seriously affected by the defeats in the rock mass, rock mass could be modeled as homogeneous media with reduced strength property. Back analysis of the data obtained from field reveals that rock masses around the excavation have a strength enhancement owing to the effect of intermediate principle stress σ2. This paper begins with the effect of intermediate principal stress σ2 on the behavior of rock masses using MohrCoulomb failure criterion in Flac3D. Numerical simulation is conducted using polyaxial failure criterion to investigate the effect of intermediate principal stress σ2 on the behavior of rock masses. Comparisons of numerical results between these two failure criteria are made and applicability of these two failure criteria is discussed

Analysis of σ2 Using MOHR-Coulomb Failure Criterion

Analysis of σ2 Using Polyaxial Failure Criterion

15 Mpa ceq

Discussions

Conclusions