School of Mechanics and Civil Engineering, China University of Mining & Technology-Beijing
State Key Laboratory of CoalResources and Safe Mining, China University of Mining & Technology−Beijing

The deformation, fracture, and movement mode of rock strata are greatly related to underground pressure, surfacesubsidence, etc. The fracture modes of the thin rock stratum and thick rock stratum are significantly different. How touniformly describe the fracture modes of rock strata with different thicknesses and establish a mechanical model is a difficulttheoretical problem in rock movement. In this paper, the fracture structures of mining strata in 23 typical working faces are investigated. In addition, the fracture mechanical factors and movement modes of the rock stratum are classifiedbased on fracture mechanics, and the relationship between fracture structure and rock stratum thickness is analyzed. Basedon the medium-thick plate theory, the fracture mechanical model of rock strata with different thicknesses is established.The fracture mechanical mechanism and fracture mode of rock strata with different thicknesses are revealed, and the correspondingcriteria are given. The breakage and movement laws of rock strata with different thicknesses and fracturemodes in the mining process are analyzed by numerical simulation. The research shows that when different mining conditionsand different stress boundary conditions act on rock strata with different thicknesses, different fracture modes willoccur. With the increase of the rock strata thickness, the shear stress of rock strata increases continuously, and the fracturemechanical mechanism of rock stratum presents the evolution law of tensile fracture, tensile shear fracture, and shear fracture.Also, the corresponding rock mass structures are masonry beam structure, layered fracture, and step voussoir beamrespectively. Moreover, the statistical data show that the rock layers with a thickness span ratio greater than 0.5 are moreprone to occur shear fractures and form step voussoir beams. Based on the above analysis, a mixed fracture model is proposedaiming at the possible tension shear failure of thick rock strata, and the rock fracture mechanical factors are furthersubdivided into three types: tensile fracture, tensile shear fracture, and shear fracture. There are seven types of fracturemodes in rock strata in total. Tensile fracture often occurs in a thin layer, which will change to a shear fracture when thefault appears. Tensile fracture, tensile shear fracture, and shear fracture are typically fracture modes in a thick layer, inwhich tensile shear mixed fracture is divided into end tensile shear mixed fracture, layered linkage movement, and layereduncoordinated movement. Further research on the fracture modes of rock strata can provide valuable theoretical supportfor the control of ground pressure and the prevention of surface subsidence hazards in mining.

国家杰出青年科学基金资助项目(52225404)；北京市卓越青年科学家资助项目(BJJWZYJH01201911413037)；中央高校优秀青年团队资助项目(2023YQTD01)

左建平，于美鲁，孙运江，等. 不同厚度岩层破断模式转变机理及力学模型分析[J]. 煤炭学报，2023，48（4）：1449−1463.
ZUO Jianping， YU Meilu， SUN Yunjiang， et al. Analysis of fracture mode transformation mechanism and mechanical model of rock strata with different thicknesses[J]. Journal of China Coal Society， 2023， 48（ 4）：1449−1463.

ZUO Jianping，YU Meilu，SUN Yunjiang，et al. Analysis of fracture mode transformation mechanism and mechanical model of rock strata with different thicknesses[J]. Journal of China Coal Society，2023，48(4)：1449−1463