A Model for the Mechanics of Jointed Rock

TLDR

The paper discusses how discontinuities in blocky rock are represented, emphasizing the need for detailed descriptions of both rock blocks and joints, analogous to reinforced concrete analysis. The study introduces a new joint classification system derived from applying a joint element in finite element analysis of jointed rock structures. A linkage‑type element is developed to incorporate joint stiffness into the structural stiffness matrix, using normal, tangential, and shear parameters, enabling the rock mass to be modeled as a system of blocks and links. Illustrative examples show that joints significantly affect stress distribution, displacements, and failure patterns in underground openings and other jointed‑rock structures.

Abstract

The representation of discontinuities in analysis of blocky rock is discussed. A linkage type element is developed for addition of rock joint stiffness to the structural stiffness matrix describing the behavior of a system of rock blocks and joints. Several basic problems of jointed rock are studied. These examples demonstrate the marked influence joints may have on the stress distribution, displacements, and failure pattern of an underground opening or other structures in jointed rock. A new classification of joints is introduced, based on the application of the joint element to finite element analysis of structures in jointed rock. Normal stiffness, tangential stiffness, and shear strength are used as parameters in the classification system. The methods discussed in this paper allow a jointed rock mass to be treated as a system of blocks and links. Just as analysis of a reinforced concrete building requires detailed knowledge of the behavior of concrete alone and steel alone, the joint stiffness approach calls for and uses detailed description of the behavior of rock blocks and rock joints independently.