Abstract

The stress-strain state of the rock mass in the neighbourhood of the mining galleries is absolutely critical considering their behaviour particularly load and deformation. The stress-strain state can be affected by numerous geological and mining factors i.e. depth, mechanical parameters of the rock mass, the presence of faults, previous mining operations in case of multiple seam extraction and by the influence of the current longwall mining process.

Considering this fact the advanced measurement plan was developed. The measurements were conducted in one longwall maingate of the Czech coal mines. The holistic investigation program consisted identification of initial rock mass stress tensor and monitoring of its changing during the approach of the longwall face. Two CCBO (modified overcoring) probes were installed to obtain pre-mining full stress tensor and afterwards three CCBM probes were installed to continuous monitoring stress state in rock mass ahead of advancing longwall. The triple height telltales and endoscopic methods were applied to monitor the behaviour of rockmass in close proximity of the gateroad. Hydraulic dynamometers and strain gauged rockbolts were used to determine the support load. Also the gateroad deformation observations were performed. The results of aforementioned measurements allowed to determine the potential relation between stress-strain rock mass state and behaviour of the investigated gateroad in coarse of longwall face approaching.

1. Introduction

When applying a longwall extraction system in hard coal seams, it is essential to ensure that the gateroads are stable and of proper size during the whole mining process. In majority of European hard coal mining industry, there is a single gateroad system that prevails, consisting of steel arch yielding support. To ensure the proper maintenance of the roadway the mine managers have to efficiently cope with the rock mass movements of various intensity (e.g. roof sag, floor heave, and horizontal convergence) as a result of the extraction pressure impact [1].

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