Investigation and analysis of the rock burst mechanism induced within fault–pillars

• Two or more roof strata fracture simultaneously in the fault area.
• The main factors are the dynamic and static stresses in the pillar.
• Smaller pillar widths facilitate easier roof rotation.
• Larger roof thicknesses and smaller roof subsidence favor easier roof rotation.
• The average stress rises as the pillar width drops and roof fracture length rises.

An investigation is made of the characteristic strata movement and mechanism underlying fault–pillar induced rock bursts (FPIRBs) in order to mitigate rock burst damage in fault areas. A mechanical analysis of the fault–pillar model is established and roof rotation criteria is obtained. A formula is derived for the average static stress in the pillar through theoretical analysis, physical simulations, and engineering practice. The results show that when a coalface approaches a fault area, two or more roof strata simultaneously fracture in the fault area, leading to an increase in the dynamic and static stresses in the pillar. The most important factors affecting FPIRB are the static stress in the pillar and the dynamic stress induced by fault slides. The roof block rotates more easily when the pillar width is smaller, the roof thickness larger, and the roof subsidence smaller. The average static stress in the pillar increases with decreasing pillar width and/or increasing roof fracture length. The stress is greater if there is a voussoir beam structure, in which case the stress is directly proportional to the squared length of the fractured roof, and inversely proportional to the squared width of the pillar just before rotation occurs. After rotation, it is directly proportional to the roof fracture length and inversely proportional to the pillar width. Based on the FPIRB mechanism and analysis of the mechanical model, six methods of FPIRB prevention are proposed. Also, we find that FPIRB occurrence can be effectively reduced by the use of de-stress blasting and large diameter drilling.