Study of Post-Peak Strain Softening Mechanical Behaviour of Rock Material Based on Hoek–Brown Criterion

Ping Cao,Qibin Lin,Peixin Wang

doi:10.1155/2018/6190376

Abstract

In order to build the post-peak strain softening model of rock, the evolution laws of rock parameters m,s were obtained by using the evolutionary mode of piecewise linear function regarding the maximum principle stress. Based on the nonlinear Hoek–Brown criterion, the analytical relationship of the rock strength parameters m,s, cohesion c, and friction angle φ has been developed by theoretical derivation. According to the analysis on the four different types of rock, it is found that, within the range from 0 to σ3min, the peak hardness of the rock becomes smaller as the confining pressure increases and the degree of rock fragmentation decreases as well. The post-peak stress-strain curves obtained from the developed softening model are in good agreement with the laboratory test results under different confining pressures. In conclusion, the analytical method is reasonable, and it can predict the post-peak mechanical behaviour of rock well, which provides a new thought for the rock-softening simulation.

Highlights

It is well known that the rock material is one type of heterogeneous brittle material with complex mechanical properties, which is significantly different from the metal material
By introducing the concept of generalized friction angle and generalized cohesion, Lu et al [14] constructed the post-peak computing model combined with FLAC code
According to several Mohr stress circles, the envelope can be drawn. us, the corresponding cohesion c and friction angle φ at the peak and the starting point of the residual stage under di erent con ning pressures can be obtained by analysis of the Mohr strength straight lines through the tangent points of envelopes

Summary

Introduction

It is well known that the rock material is one type of heterogeneous brittle material with complex mechanical properties, which is significantly different from the metal material. Many researchers have studied from different aspects regarding the post-peak strain softening behaviour. The confining pressure on the post-peak mechanical behaviour of rock was not considered. The laboratory tests [4,5,6,7,8] show that the confining pressure greatly affected the post-peak mechanical behaviour of rock. In order to study the post-peak strain softening mechanical properties of rock, the mechanical models described above are based on the Mohr–Coulomb criterion. Tan et al [17] considered degradation and expansion behaviour of the rock constructing the post-peak strain softening model based on the Hoek–Brown criterion. The analytical relationships among rock strength parameters (m, s), friction angle (φ), and cohesion (c) were developed, and a new post-peak strain softening model was proposed. E veri cation with laboratory test results shows that the analytical model is reasonable to predict the post-peak rock behaviour

Simplification of Strain Softening Process

Analytical Study of Hoek–Brown Parameters

Verification and Discussion

Conclusion