Structural mechanics model and its fracture mode of variable-thickness roof strata in large mining height stope

LU Yangbo; YAN Shaohong; ZHOU Kunyou; WANG Yuanjie; FU Peng; ZHANG Chenxi

doi:10.12438/cst.2024-1923

Abstract：Understanding the fracture movement laws of rock strata plays an important role in the control of mine pressure and the preven-tion and control of dynamic disasters such as strong mine seismic events in stope.The fracture modes of thin rock strata and thick rock strata are obviously different,and in the production practice,due to the complexity of geological conditions,rock strata thickness often dis-plays"variable-thickness"characteristics.To systematically analyze fracture modes under varying thickness conditions,this study estab-lished a structure mechanical model of variable-thickness roof strata in the stope based on the geological setting of 30202 longwall face in Muduchaideng Coal Mine,and the influence mechanism of factors such as strata thickness gradient,unsupported span length,and mechan-ical strength on fracture modes were investigated,revealing the mechanical principles governing different fracture behaviors.The results show that with the thickness gradient increase,the dominant stress acting on the strata transitions from tensile stress to shear stress,shift-ing the fracture mode from"tensile fracture"to"shear fracture",and the unsupported span length of rock strata shows an increase with the increase of tensile strength and shear strength of rock strata,and shows different growth trends under different thickness gradients.Com-bined with the numerical simulation test,it is obtained that under the geological conditions of 30202 longwall face,the critical thickness of the rock strata in which the fracture mode of the thick and hard rock strata evolves from"tensile fracture"to"shear fracture"is 16.5 m,which reveals the different of fracture mode of rock strata with different thickness under specific geological conditions.Based on the re-sponse law of the seismic source fracture mechanism and the structure formed by the fracture of thick and hard rock strata,it is verified that the fracture modes of rock strata with different thicknesses are different.At the same time,based on the correlation between the on-site microseismic monitoring data and the structure formed by the fracture of thick and hard rock strata,through the inversion analysis of the whole process of overburden structure evolution and mine earthquake activity under thick and hard rock strata,the relationship between different fracture modes of rock strata and energy release is clarified.The research results can provide theoretical and technical support for the prevention and control of dynamic disasters.