Shear Behaviour of Rock Joints

Asadul Haque, Buddhima Indrarata

• Publisher: CRC Press
• Year: 2021
• ISBN:
  9781000445848
• Edition: 1
• Topic: Tecnología e ingeniería
• Subtopic: Ingeniería civil

This title covers the fundamental properties of rock joints, the method of laboratory testing of rock joints, and shear strength assessment under different loading conditions. This work is intended as a reference text for students and practitioners in mining and rock engineering.

CHAPTER 1

Characterization of joint surface roughness

1.1 INTRODUCTION

The majority of current rock joint models are capable of predicting the shear behaviour of relatively simplified joint surfaces. Many of these models do not include the complex joint surface characteristics, the effects of infill properties, and the degradation behaviour of asperities. In the field, joints are often infilled with clay and silt, which can be fully or partially saturated. A shear strength model should also address the role of Constant Normal Stiffness (CNS) boundary condition, which is commonly encountered in the field, for instance in underground mining situations. Current numerical techniques mainly rely on the conventional Constant Normal Load (CNL) strength parameters which are often inappropriate for:

– Evaluating the stability analysis of bedded mine roofs,

– Estimation of side shear resistance of rock-socketed piles, and

– Stability analysis of jointed strata subject to potential toppling failures.

The shear behaviour of non-planar joints is significantly influenced by the surface properties of the joints, or in other words, by the joint surface roughness. The rougher the joint, the greater the shear strength. Therefore, a numerical description of the roughness of a rock fracture surface is essential to the estimation of its shear strength, dilatancy, and stiffness. There are several methods of estimation of joint surface roughness. It is beyond the scope of this book to describe all of them. However, to have an understanding of the wide variety of methods dedicated to correctly represent the joint surface characteristics, the published literature can be categorised into the following four major techniques:

1. Joint Roughness Coefficient (JRC) measurement,

2. Self-similar and self-affine fractal method,

3. Spectral and line scaling method, and

4. Continuous mathematical functions such as Fourier transforms.

1.2 ROUGHNESS MEASUREMENT TECHNIQUES

1.2.1 JRC measurement

The degree of roughness is a measure of the inherent surface unevenness or waviness of the discontinuity relative to its mean plane. Barton (1973) proposed a joint roughness coefficient (JRC) to describe the surface roughness, using a scale from zero to 20. Typical roughness profiles for the entire JRC range are shown in Figure 1.1. This index is measured by the direct profiling method for the joint, or by an indirect method of performing a tilt test on a rough joint, together with a Schmidt Hammer Index test and the tilt t...