Energy Evolution and Mechanical Features of Granite Subjected to Triaxial Loading-Unloading Cycles

Feng Pei,Tongzhao Zhang,Hongguang Ji

doi:10.1155/2019/9871424

Abstract

Energy evolution varies during the whole process of rock deformation, and mechanical parameters are markedly altered under cyclic loading and unloading. In order to investigate the effects of confining pressure on energy evolution and mechanical parameters, cyclic loading and unloading experiments were performed for granite under six different confining pressures. The experiment revealed the confining pressure effect on variation and allocation pattern of energy and mechanical characteristics. Four characteristic energy parameters, namely, storage energy rock, storage energy limit, energy storage ratio, and energy dissipation ratio, were proposed to describe energy storage and dissipation properties of rock. Elastic modulus and dissipation ratio presented a downward “U” and “U”-shaped trends, respectively, with loading and unloading cycles, while Poisson’s ratio increased linearly at the same time. Elastic energy was accumulated mainly before peak stress, while the energy dissipation and release were dominant after the peak strength. As the confining pressure increased, efficiency of energy accumulation and storage limit improved. An exponential function was proposed to express the relationship between the energy storage limit and confining pressure. Dissipation energy increased nonlinearly with the strain, and the volume dilatancy point defined the turning point from a relatively slow growth to an accelerated growth of dissipation energy. The dilatancy point can be used as an important indication for the rapid development of dissipation energy.

Highlights

Many engineering projects have shown that rock is not in a stable stress environment but is subjected to a cyclic loadingunloading stress environment
(1) e outer envelopes of cyclic loading and unloading under different confining pressures are similar to conventional loading, and samples have undergone four distinct stages: compaction stage, elastic deformation stage, unsteady fracture development stage, and postpeak failure stage
Confining pressure effects on variation and allocation of energy were revealed based on the triaxial cyclic loading and unloading testing of granite under six different confining pressures. e correlation between mechanical parameters variation and energy characteristics was discussed

Summary

Introduction

Many engineering projects have shown that rock is not in a stable stress environment but is subjected to a cyclic loadingunloading stress environment. Deformation and failure of granite under engineering disturbance is a very complicated damage evolution process, and failure is governed by energy storing and dissipation phenomenon [1]. Rock is in a dynamic evolution process of input energy, accumulation energy, dissipation energy, and release energy. Rock burst and other dynamic disasters occur frequently, in China. Accumulation of energy and rapid release are the key control factors of rock burst [2,3,4,5,6]. Erefore, it is imperative to study the dynamic disasters such as rock burst from the aspect of energy Accumulation of energy and rapid release are the key control factors of rock burst [2,3,4,5,6]. erefore, it is imperative to study the dynamic disasters such as rock burst from the aspect of energy

Methods

Results

Conclusion