Segmental adjustment of hydraulic support setting load in hard and thick coal wall weakening: a study of numerical simulation and field measurement

The purpose of this study was to introduce a novel technology named segmental adjustment of hydraulic support setting load (SAHSSL) for pre-splitting and weakening the coal wall of a fully mechanized working face in hard and thick coal seams (HTCSs). The efficiency of SAHSSL was explored in the relatively stable and significant movement stages. A numerical simulation method using fast Lagrangian analysis of continua in three dimensions was used to evaluate the instability characteristics of the coal wall under different support setting loads (SSLs) ranging from 2000 to 8000 kN. The numerical results were verified by industrial testing of coal wall weakening in HTCSs. The results revealed that with the implementation of SAHSSL, the average coal-cutting time of the shearer reduced by about 21.7% (or 1.8 h), and the increasing resistance state was 64.8% of the 115 working cycles in the working specialty measurement of the support. Reasonable SSLs in the relatively stable stage of the periodic weighting length were obtained between 4000 kN and 6000 kN. The ground pressure was found to be the primary factor influencing the hard coal wall weakening for thick coal seam mining. The findings of this study clearly indicate that the proposed SAHSSL technology greatly enhanced the coal-cutting efficiency and weakened the coal wall effectively, and it could be adjusted under an effective roof control principle to meet the segmental requirements of coal wall weakening for thick coal seam mining.