Mechanical characteristics and time and space evolvement of stress shell in stope floor stratum

Selecting 1232(1) working face in Xieqiao Coal Mine as the research object,by employing of numerical simulation,physical modeling and in-situ measurement,the mechanical characteristics and time and space evolvement of stress shell in stope floor stratum were studied. The results show that there is high stress bunch in the floor stratum, and high stress bunch high forms the stress shell. The principal stress inside and outside the stress shell are lower than in the stress shell. The vertical stress and horizontal stress will decrease from above to below over the inner boundary of stress shell,and compressive stress become to tensile stress in local area. Meanwhile,the degree of horizontal stress re- lief is lower,and there are horizontal stress concentration areas in stress shell and outer boundary of stress shell. The selectivity of three dimensional stresses is the intrinsic mechanics essence forming the stress shell in stope floor stra- tum. The form of stress shell will adjust with the change of stope structure. The short side of working face length and forward distance affects the depth of stress shell. The destroyed area and maximal displacement region are in the low stress areas above the internal boundary of stress shell. The stress shell is the principal concentrated force system to prevent the rock deformation and damage. If the stress shell in stope floor stratum loses balance,high dynamic phenom- ena will happen.