ABSTRACT

In this paper, simulation analysis for shearing behavior of rock discontinuity by distinct element method is proposed. The purpose is behavior of surface of discontinuity in the shear process and destruction situation of the roughness are clarified by numerical simulation. By using this analysis method, it was possible that the behavior of the test-piece model, the shear strength and the dilation behavior are analyzed. And, distribution situation of the internal stress in the shear process was clarified by visualizing the stress which affects each particle.

INTRODUCTION

The mechanical properties of jointed rock masses depend on the characterization of rock joint. Therefore many researches in related with the mechanical properties of rock joint have been done. However the conventional researches are mostly focused on the shearing behavior based on experiments with the purpose of assuming the strength. Thus it has been difficult to correctly figure out the destruction situation and shearing behavior of rock discontinuity.

Considering these background, this research uses cement test-pieces as the experimental method and by modeling discontinuous rock consisting of the JRC as a standard discontinuous figure using the DEM in the analysis, tries to clarify the rock joint of rock discontinuity. DEM is said to have the high degree of availability for the discontinuity analysis and it draws an attention as a solution for problem of large deformation in particular. However since rock quality is continuum, it was impossible to describe it using the conventional DEM. So this research introduces concept of tension to DEM, making it a possible solving method to adapt to continuum. By conducting simulation using this method, we try to clarify the character of the shearing behavior of rock discontinuity.

METHOD OF ANALYSIS
DEM

Distinct Element Method is an analysis method established by P. Cundall and is aimed to cover a discontinuity such as rock and soil. It analyzes dynamic behavior of rock and others by considering particles of a simulation target an aggregation in a broad perspective. It assumes that there are virtual springs between each particle and by calculating acceleration, velocity and displacement from their action force, it can figure out the behavior of the particles. Fig. 1 shows the initial state of the particle model. This analysis defines that the natural strength of the springs is a contact distance (gap) and calculates the action force.

Bonding force

When adapting the granular models to solid substance such as a rock, not only repulsion will act between particles. Considering concretes and rocks,

(Equation in full paper)

neighboring particles are bonded in one way or another and tension acts between particles. Therefore, this research has described tension by introducing bonding forces.

As Fig. 2 shows, we have defined two kinds of radius, rb1 and rb2.The rb1 is a distance that the tension is led to yield, and rb2 is a distance that the bonding is to be destroyed. In other words, the tension temporarily increases from r that is bonding point to rb1, and after rb1, it temporarily decreases.

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