Plane-Strain Modeling of Progressive Goaf Compaction in a Depillaring Working

Abstract

The knowledge of the compaction behavior of goaf is critical for the stability and rational design of depillaring workings in a given geomining condition, particularly in conditions where part of the overburden is distressed in the presence of softcover comprising of dump material. In this study, a Bord and Pillar working from Jharia coalfield has been considered for the study of progressive caving behavior and goaf compaction under a similar geomining condition. An algorithm was developed and implemented with the help of FISH subroutines for plane-strain simulation of progressive caving of strata, filling of goaf and its compaction in a depillaring working using finite difference software—FLAC. The compaction and stress recovery of different goaf filled zones have also been evaluated with the progressive depillaring till the extent of working becomes extensive enough to offset the effect of cover depth. The findings show that the magnitude of the stress accommodated at the bottom of the goaf material is governed by the span of fractured strata and the distance between the face and the point of maximum stress in the goaf. The caved goaf material recovers almost 15% of the in situ stress after the main fall, whereas 89% of the stress recovery is observed at 200 m of face advance, which is almost twice the depth of cover. The goaf material spanning up to 40 m from the goaf edge achieves 50% of the maximum stress recovery at this stage. The modeling approach developed in this paper with the help of various subroutines amply explains the mechanism of compaction and settlement of the goaf material filled cyclically following progressive caving of roof in the depillaring working.