Mechanism and control strategy of asymmetrical floor heave of coal pillar roadway in fully mechanized caving face

To study the problems such as dramatic asymmetrical floor heave deformation of coal pillar roadway in fully mechanized caving face,difficulty in support and maintenance,theoretical analysis,numerical simulation and field test were adopted. The stress environment,deformation and failure characteristics of the coal pillar roadway in the fully mechanized caving face at Dananhu No. 1 coal mine in China were analyzed. The results demonstrate that the asym- metrical phenomenon of surrounding rock stress environment caused by mining is the intrinsic reason for the asymmet- rical floor heave in the coal pillar roadway. It also leads to a non-uniform distribution of the plastic zone of floor in coal pillar roadway. The degree of asymmetrical floor heave has internal relations with the thickness of caving coal. When the thickness of caving coal is in the range of 5. 9 m,the greater the parameters,such as the thickness of the caving coal,the breaking deflection angle of the strata of main roof,the principal stress ratio and the rotation angle of the prin- cipal stress direction in the stress environment of the roadway, the more obvious deformation of asymmetrical floor heave caused by plastic failure in floor. The maximum plastic failure depth position of the floor gradually moves toward the middle of the roadway as the rotation angle of the principal stress direction increases. It causes a different distribu- tion of the maximum deformation position of floor heave. At the same time,the deformation of the floor heave of the coal pillar roadway is poorly controllable. It is not feasible to attempt to use high-strength support under the current technical condition. The control should mainly be adapted to the floor heave deformation. When the thickness of caving coal more than 5. 9 m,the strata of main roof have the possibility of instability and being cut along the edge of the coal pillar,and the surrounding rock stress environment of the roadway tends to the original rock stress state. Consequently, the distribution range of the surrounding rock plastic zone is greatly reduced in the roadway. The deformation of floor heave is small. Based on the results above,the strategy of floor heave control based on adjusting the relationship of mining and driving,and optimizing the roadway floor heave treatment plan was proposed and good results were ob- tained. With the decrease of deformation of the floor heave,the working volume of floor heave was also greatly re- duced.