Abstract

This study experimentally investigated the effects of fracture surface roughness, normal stiffness, and initial normal stress on the shear-flow behavior of rough-walled rock fractures. A series of shear-flow tests were performed on two rough fractures, under various constant normal stiffness (CNS) boundary conditions. The results showed that the CNS boundary conditions have a significant influence on the mechanical and hydraulic behaviors of fractures, during shearing. The peak shear stress shows an increasing trend with the increases in the initial normal stress and fracture roughness. The residual shear stress increases with increasing the surface roughness, normal stiffness, and initial normal stress. The dilation of fracture is restrained more significantly under high normal stiffness and initial normal stress conditions. The hydraulic tests show that the evolutions of transmissivity and hydraulic aperture exhibit a three-stage behavior, during the shear process—a slight decrease stage due to the shear contraction, a fast growth stage due to shear dilation, and a slow growth stage due to the reduction rate of the mechanical aperture increment. The transmissivity and hydraulic aperture decreased, gradually, as the normal stiffness and initial normal stress increase.

Highlights

  • Underground fracture rock masses consist of the intact rock matrix and various discontinuities.Discontinuities such as joints and fractures play a significant role in the hydro-mechanical behaviors of a host rock mass [1,2,3,4,5,6,7]

  • They suggested the Rec ranged from 1.5 to 13.0, as shear displacement increased from 0 to 10.9 mm. Most of these shear-flow tests were conducted under constant normal load (CNL) boundary conditions, in which the normal load applying on the fracture surface was constant, during shearing

  • The results showed that the hydraulic aperture under the CNL condition was larger than the constant normal stiffness (CNS) condition

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Summary

Introduction

Underground fracture rock masses consist of the intact rock matrix and various discontinuities. They suggested the Rec ranged from 1.5 to 13.0, as shear displacement increased from 0 to 10.9 mm Most of these shear-flow tests were conducted under constant normal load (CNL) boundary conditions, in which the normal load applying on the fracture surface was constant, during shearing. Investigated the effects of normal stiffness and initial normal stress on the hydraulic behavior of joint, during the shear process. Sato et al [32] studied the effect of roughness on the hydraulic behavior, under the CNS and the CNL condition They expressed that the permeability of joints was larger for rougher fractures. We conducted shear-flow tests on two types of fractures, with different surface roughness, under the CNS boundary conditions. The effects of shear displacement, joint surface roughness, normal stiffness, and initial normal stress on mechanical and hydraulic characteristics of fractures were analyzed

Specimen Preparation
Experimental Results
Effect
Evolution of Transmissivity during the Shear-Flow Tests
G1 andand
Evolutions of the Mechanical Aperture and the Hydraulic Aperture
Conclusions

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