Numerical Analysis of the Gob Stress Distribution Using a Modified Elastic Model as the Gob Constitutive Model

Abstract

Numerical modelling-based design and stability analyses outcomes of longwall structures critically depend on a reliable simulation of the effect of the gob compaction process. The approaches available for modelling of the gob behaviour are either oversimplification of the actual phenomenon or too complicated. In this paper, a modified elastic model along with its algorithm was developed to simulate the strain hardening behaviour of the gob material. The proposed approach was implemented in the finite difference-based code—FLAC3D through single-element model, and its applicability was validated by comparing the model response with the laboratory-validated theoretical gob compaction model. The proposed approach can be implemented in any numerical modelling code using only three input parameters: initial modulus, density and maximum strain. Plane strain models of two longwall workings: one supercritical and the other subcritical, were constructed for its field-scale implementation to compare its findings with theoretical and field observations of the maximum surface subsidence. The modelling results of the gob stress redistribution were also verified against the findings in the literature. The study shows that the load transfer distance critically depends on the geological conditions of the overlying strata in addition to the depth of cover. The model observed profiles of abutment stress decay and the peak abutment stress of the two cases were in line with the field observations in typical geo-mining conditions in India.