Zonal Disintegration Mechanism of Deep Rock Masses under Coupled High Axial Geostress and Blasting Load

Pu Yuan,Ying Xu

doi:10.1155/2018/4957917

Abstract

Zonal disintegration phenomenon with alternative distribution of fracture zones and nonfracture zones is a characteristic failure in deep rock masses, especially for deep tunnel excavated by drill and blast method. To investigate the mechanism of zonal disintegration under coupled high axial geostress and blasting load, elastic stress field distribution for a circular tunnel in deep isotropic rock masses is obtained. Furthermore, Hoek-Brown criterion is amended by considering blast-induced damage effect. Both radial blasting load and blast-induced damage effect are assumed to decay in a negative exponential function. Taking the deep tunnel of Dingji coal mine in China as engineering background, the number and width of fracture zones are determined by deduced elastic stress field and modified Hoek-Brown criterion. Then numerical computation is conducted. Numerical computation results indicate that both the number and width of fracture zones mainly depend on high axial geostress and mechanical parameters of deep rock masses, and peak radial blasting load plays an important role in determining the width of fracture zone near the excavation.

Highlights

With the ever-increasing demand of energy resources, deep mineral resources exploitation is inevitable and imperative due to the continuing consumption of shallow mineral resources [1], and deep mining has been identified as an important topic for research under China’s State Key Research and Development Program [2]
To study the formation mechanism of zonal disintegration under coupled high axial geostress and blasting load, the elastic stress field distribution for a circular tunnel in deep isotropic rock masses is deduced by assuming that radial blasting load decays in a negative exponential function
Hoek-Brown criterion is modified by assuming that blast-induced damage effect decays in a negative exponential function

Summary

Introduction

With the ever-increasing demand of energy resources, deep mineral resources exploitation is inevitable and imperative due to the continuing consumption of shallow mineral resources [1], and deep mining has been identified as an important topic for research under China’s State Key Research and Development Program [2]. Based on non-Euclidean model, zonal disintegration mechanism around a deep circular tunnel was investigated and elastic stress field of surrounding rock was derived under various conditions, such as nonhydrostatic pressure state and dynamic unloading. Blasting excavation applies a dynamic load on deep rock masses and induces blasting damage around an excavation [31, 32] By considering both high axial geostress and blasting load in deep rock masses, failure mechanism of zonal disintegration is investigated by elastic stress field analyses and modified Hoek-Brown criterion. The effects of high axial geostress, mechanical parameters of deep rock masses, and radial blasting load on zonal disintegration are analyzed

Elastic Stress Field under Coupled High Axial Geostress and Blasting Load

Hoek-Brown Criterion Considering Blast-Induced Damage Effect

Validation of Present Results

Numerical Computation Results

Conclusions