厚且坚硬关键岩层的变形与破断影响着上覆岩层的运动，针对传统“梁”或“薄板”理论在分析厚且坚硬关键岩层受力与破断适应性差的问题，基于中厚板理论对存在厚且坚硬关键岩层的孤岛工作面在初次来压、周期来压时关键岩层的位移及应力分布情况进行了研究，讨论了关键岩层厚度对于切应力分布的影响，揭示了关键岩层的受力与破断特征，提出了关键岩层破断模式判据。结果表明:在覆岩条件一定的条件下，关键岩层厚度越小，越容易发生拉伸破断，随着关键岩层厚度的逐渐增大，破断形式逐渐转变为拉剪混合破断和剪切破断;关键岩层厚度较小时，在破坏时多发生的是拉伸破断，破断后的关键岩层沿支点旋转形成绞接结构，不会对工作面造成太大的载荷;坚硬厚关键岩层则多发生剪切破断，对工作面造成冲击，易发生剪切破断的坚硬厚关键岩层破断位置与传统薄板理论确定的破断位置不同;坚硬厚关键岩层内分布的切应力随着岩层厚度的增加而增大，来压前后，关键岩层内部的应变能峰值由中部向工作面两端转移;坚硬厚关键岩层内部的切应力分布更为集中，将切应力集中分布的这部分区域作为围岩控制的重点，实现工作面灾害分区域、分级防控。

The deformation and fracture characteristics of hard and thick key strata affect the movement of the overlying strata. In view of the poor adaptability when the traditional “beam” or “thin plate” theory is used to analyze the stress and fracture of thick and hard key strata,based on the theory of medium and thick plate,the displacement and stress distribution of the key strata of the isolated island face with thick and hard key strata are studied,the influence of the thickness of key strata on the distribution of shear stress is discussed,the stress and fracture characteristics of key strata are revealed,and the criterion of failure mode of key strata is proposed. The results show that under certain overburden conditions,the smaller the thickness of the key strata,the more prone to tensile rupture. With the increase of the thickness of the key strata,the failure mode gradually changes into tensile shear mixture failure and shear failure. When the thin key strata are damaged,it is often broken by stretching. After the key strata is broken,it rotates along the fulcrum to form an articulated structure,which will not cause too much load on the working face. The hard and thick key strata is often cut off and broken,causing impact on the working face. The thin key strata are more prone to tensile rupture,and the broken key strata rotates along the fulcrum to form a splice structure,which will not cause too much load on the working face. The hard and thick key strata tend to shear failure,causing impact on the working face. The failure location of the hard and thick key strata prone to shear fracture is different from that by the traditional“thin plate” theory,and the distribution of shear stress in the hard and thick key strata is more concentrated. Th shear stress distributed in the hard and thick key strata increases with the increase of the thickness of the key strata.Before and after the weighting,the strain energy peak inside the key strata are transferred from the middle to both ends of the working face. The distribution of shear stress in the hard and thick key strata is more concentrated. The focus of ground control is to focus on the area where shear stress is concentrated,so as to realize the prevention and control of coal and rock disasters in working face in different regions and grades.