1. INTRODUCTION

Longwall mining is one of the most widely used methods in underground coal extraction. One of the most important advantages of this method is the automated form of underground coal mining characterized by high recovery and extraction rates. The main objective of the coal mining is to economically extract coal and safely remove them from the ground. Hence, the mining efficiency solely depends on the coal seams’ overall conditions. In this method, due to the extraction of coal seams within a considerable panel width, after advancing the hydraulic jacks or powered roof supports, the immediate roof of the mined panel is unsupported and hence is allowed to collapse and cave in some distance behind the hydraulic jacks or in the goaf area. The downward movement of the roof strata then gradually extends upwards and will cause the disturbed roof strata to become fractured and destressed. Thus, the overburden pressure above the fractured zone will be redirected towards the front solid sections behind the face and the adjacent sections where the gate roads (access tunnels serving the coal face) intervening barrier pillar and unmined solid sections are located. The upward extension of the fractured zone mainly depends on a variety of parameters such as depth thickness of extracted coal seams, panel width, the number, relative thickness and strength of panel roof strata and the corresponding coefficient of expansion. Nowadays, the prime concerns of many coal mining researchers are to find the appropriate approaches to appraise the panel roof strata behavior during and after panel extraction. Whilst, the professional mining engineers who are dealing with longwall mining design are very much concerned with effectively determining the height of fractured zone above the panel roof that is induced due to longwall mining.

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