ABSTRACT

This paper introduces the instances and results of our analyzing studies concerning the various phenomena at longwall mining panels. In case of longwall mining with hydraulic self-advancing supports at coal mines, one important technical problem is the break down or collapse the roof rocks of goaves which is used to maintain the Working spaces including coal faces in safety.

Our analysis covers the intentional control of wall pressure around the working spaces at longwall faces, the property of calculation at every step of mining, various phenomena originated in mining multiseams of coal, the excavation of coal seams with faults under bottom of sea, etc.

For analyzing such problems by computer, we assume an elastic-collapse model with artificial plasticity and applied Prof. kawai's Rigid Body Spring Model (RBSM) (kawai 1980). In the RBSM coal seams or rock strata are considered as a discrete Physical model and the Limit Analysis is established.

Our results indicate that the stress distribution around the underground large spaces should be induced from the stepwise calculation in excavation process.

INTRODUCTION

In order to carry out the mining works safely and keep the stability of production, the analysis of earth or rock pressure is very important and can not be neglected.

One reliable method for such analysis is the Finite Element Method (FEM) (Zienkiewitz 1977), which is widely used. However, it is too costly to use this method for tracing the occurrences the daily work.

On the other hand, the ground media itself which consists of soil, rock etc. can be considered as a kind of discontinuous structural specimen. Therefore, we use the RBSM which is available for the contract problem by adopting a discrete model of the ground body.

The Displacement Discountinuity Methos (Crouch 1976) is used supplimentarily because it can handle with ease the input and output data.

The purpose of our analysis is to follow the various phenomena caused by every advance of mining faces day by day and to simulate them from a view point of mining operation.

DISCRETE MODEL WITH SUPPOSED SLIP ON ELEMENTS BOUNDARY PLANE

In case of FEM, the energy with constant strain element A and B is considered to be balanced through each node as shown in Fig. 1. To calculate some slips etc. on the boundary lines (planes) a Joint Element C is inserted between A and B as shown in Fig. 2. However, these join t element must be arranged prior to the calculation.

In the case of RBSM, each element is considered as a rigid body. Then the elements are jointed with lumping springs on the boundary line of each element and the stiffness of these springs is equivalent to the elasticity of each original element. Therefore, the slips between elements can be calculated at every spots of all boundary lines of the structure model by the stress given to each spring. Fig. 3 shows this model.

(Figure in full paper)

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