Numerical modeling on brittle failure of coal wall in longwall face-a case study

摘要

In China, as the shearer cutting height increases in longwall face, serious coal wall failure and spallings occur often, especially for brittle coal seam, which leads to large block spallings, equipment damage, and casualties. In this paper, 2D finite difference models are constructed, aiming to exam the brittle failure of coal wall during longwall mining in Majialiang coal mine, Shuozhou, China. The strain-softening constitutive model is used to reveal the brittle failure characteristics of the coal wall. A numerical algorithm is developed to simulate the longwall goaf compaction process, and obtain the proper mining-induced stress around the longwall face. Based on extensive field surveys, three numerical models, i.e., intact coal wall, coal wall including vertical discontinuities and criss-cross discontinuities, are presented for investigating the brittle failure mode and spalling mechanism of the coal wall. The numerical results show that both coal wall failure modes and the failure (spalling) depths are in good agreement with the field observations. The simulations reveal that the sizes of the spalling blocks are closely related to the failure mode. For intact coal wall or coal wall including large space vertical discontinuities, occurrences of the large block spallings are favorable. For coal wall including small space vertical discontinuities and criss-cross discontinuities, small segment spallings play a dominant role. In light of this, analyses are conducted to investigate the effects of the face stoppage time and face guard on the failure mode and spallings of the coal wall. The result of this study indicates that the mining operation should accelerate and the length and pressure of the face guard should increase in this longwall face.