Experimental Study on Stress Wave Energy Attenuation Across Rough Joints

Hong, Shengnan (Institute of Rock and Soil Mechanics / University of Chinese Academy of Sciences) | Li, Jianchun (Institute of Rock and Soil Mechanics / Southeast University) | Li, Haibo (Institute of Rock and Soil Mechanics) | Rong, Lifan (Institute of Rock and Soil Mechanics / University of Chinese Academy of Sciences) | Li, Zhiwen (Institute of Rock and Soil Mechanics / University of Chinese Academy of Sciences)

OnePetro 

Abstract

The mechanical properties of rock masses are significantly affected by the additional mechanical compliance that result from joints, fractures or faults. The effects of these features, generally referred to as joints, can be so influential in many problems of geology, geophysics, mining engineering and so on that it is important to assess its influence on the mechanical properties of rock masses. As one of important rock masses’ seismic properties, the stress wave energy attenuation in jointed rock mass is studied in the paper in the aspect of its relationship with rough joints. Thus, a series of uniaxial compression experiments were conducted on a split Hopkinson pressure bar systems (SHPB). And specimen is made of two cylindrical rocks extracted from a same granite. Where two rocks contact makes a joint. And artificial joints with different roughness are made by notching one surface of the joint to a different degree. Here, the joint matching coefficient are introduced to estimate joint roughness, which equals the ratio of contact area of two cylindrical rocks to cross-section area of them. In tests, the incident, reflected and transmitted waves across the joints were recorded from the strain gauges stuck on the input and output bars of SHPB. Then, the seismic quality factor Qseismic can be calculated by the recorded data, which is adopted in the paper to describe the stress wave energy attenuation during travelling across jointed rock masses. Based on the experiment data, we can know how joints with different matching coefficient effect stress wave energy attenuation.

1. Introduction

The term rock joint is used to describe the mechanical discontinuities of geological origin, that intersect almost all near-surface rock masses (Barton and Choubey, 1977). And it is well known that the rock joints have a significant effect on the mechanical behavior of the rock masses, which is of great importance to evaluate the stability and the damage of rock structures under dynamic load, like earthquake, explosion and so on. As one of important rock seismic properties, the stress wave energy attenuation in jointed rock mass is worth to study.

In the past, lots of researches have been conducted on the mechanical properties of rock joints. To investigate the joint deformation, Bandis, Lumsden et al (Bandis et al., 1983) built static Bandis-Barton (B-B) model through a large number of static tests. The model described the hyperbolic relationship between stress and joint closure. Based on that, Zhao, Cai et al (Zhao et al., 2008) proposed the dynamic Bandis-Barton (B-B) model, which was applied to predict stress wave attenuation across factures, and it turned out that a fracture with higher values of dynamic fracture closure constant and dynamic fracture stiffness constant leads to lower attenuation.