Experimental Investigation of the Anomalously Low Friction Phenomena in Blocky Rock Systems

Yehui Shi,Helan Cheng,Shuxin Deng,Chenghua Xu,Hao Lu

doi:10.1155/2020/8893786

Abstract

Rock masses can be regarded as a blocky rock system. After a disturbance load is applied, the anomalously low friction phenomenon may take place and cause geological disasters. A series of impact experiments on granite blocks were conducted to investigate the anomalously low friction phenomena. Vertical vibration, Fourier frequency spectrum, and horizontal motions were investigated. It can be found that the tensile phases of vertical vibration can reduce the maximum static friction force, namely, the shear strength. The quasi-resonance operating mode of the rock blocks was observed. During the stress wave propagation, the vibration in the loading direction tends to transfer from high frequency to low frequency and the modes of stress wave propagation do not depend on disturbance energies. The observed translational and rotational motions were due to the initial shear force, which is less than the friction force with no disturbance load. Stability of the blocky rock system is very sensitive to the initial stress state. In the subcritical state, friction force reduction can easily break the equilibrium of forces along the contact surface and even a slight disturbance may make the horizontal motions happen, which may lead to geological disasters with great energy release.

Highlights

IntroductionWhen an external disturbance load is applied on rock masses, friction between adjacent rock blocks in the orthogonal direction to the disturbance load may be significantly reduced or even completely disappeared, which is known as an anomalously low friction phenomenon [1, 2].e phenomenon may lead to serious geological disasters, such as the large-scope tunnel deformations [3,4,5] and sliptype rock bursts [6,7,8] in the surrounding rock masses around tunnels. ese disturbance-induced geological disasters can pose considerable threats to construction safety and the stability of underground engineering.Natural rock masses can be considered as assemblies of rock blocks of different sizes [9,10,11]. e generalized faults between adjacent rock blocks can involve quite a wide range of scale levels from microscopic scale levels to macroscopic scale levels
We used an electrodynamic vibration exciter to provide the shock loading and a digital image correlation (DIC) method based on high-speed photography to perform quantitative in-plane deformation measurement
To investigate the anomalously low friction phenomena, a series of impact experiments on granite blocks were conducted by using an electrodynamic vibration exciter and a digital image correlation (DIC) method based on high-speed photography

Summary

Introduction

When an external disturbance load is applied on rock masses, friction between adjacent rock blocks in the orthogonal direction to the disturbance load may be significantly reduced or even completely disappeared, which is known as an anomalously low friction phenomenon [1, 2].e phenomenon may lead to serious geological disasters, such as the large-scope tunnel deformations [3,4,5] and sliptype rock bursts [6,7,8] in the surrounding rock masses around tunnels. ese disturbance-induced geological disasters can pose considerable threats to construction safety and the stability of underground engineering.Natural rock masses can be considered as assemblies of rock blocks of different sizes [9,10,11]. e generalized faults between adjacent rock blocks can involve quite a wide range of scale levels from microscopic scale levels to macroscopic scale levels. When an external disturbance load is applied on rock masses, friction between adjacent rock blocks in the orthogonal direction to the disturbance load may be significantly reduced or even completely disappeared, which is known as an anomalously low friction phenomenon [1, 2]. E generalized faults between adjacent rock blocks can involve quite a wide range of scale levels from microscopic scale levels to macroscopic scale levels. Effective strengths of these faults are much lower than the rock blocks, which makes the faults turn into slip surfaces.

Results

Discussion

Conclusion