## 5 Discussion  
Based on the above research results, the cutting height and breaking position of the main roof were found to significantly affect the rib spalling of coal walls, while the support strength and sidewall-protecting force only slightly influence rib spalling. With the increase in the cutting height, the thickness of the top coal decreases, and the cushioning effects of the weak top coal are reduced. The mine pressure directly acts on the coal wall, thus aggravating the instability of the coal wall. Additionally, the larger the cutting height, the greater the range of influence of the abutment pressure in front of the coal wall, leading to the development of fractures in the coal mass and increases in the extent of the plastic failure zone. Therefore, the cutting height plays a leading role in affecting the volume of the plastic zone. As the breaking position of the main roof gradually approaches the coal wall, the pressure on the coal wall increases, resulting in the extrusion of the coal wall and the continuous accumulation of horizontal displacement, so the breaking position of the main roof plays an important role in influencing the horizontal displacement. The support strength and sidewall-protecting force have limited effects on the rib spalling of coal walls; however, the hydraulic support directly acts on the coal-mining space; and, in particular, the sidewall protecting force directly acts on the coal wall, so the influences on the horizontal displacement are moderately strong. Based on the above analysis, considering the engineering conditions around the 31,204 working face, the key parameters for controlling and measures for preventing the rib spalling of the coal wall are proposed:  
1. The cutting height should be reasonably controlled. When considering the ratio of the cutting height to the caving height and mining speed, an appropriate cutting height should be selected. An increase in the cutting height aggravates the occurrence of mine pressure and reduces the inherent stability of the coal wall, greatly increasing the probability of the rib spalling of the coal wall. A small cutting height increases the height of coal caving and slows the advance of the working face, and an overly small cutting height does not meet the requirement for the ratio of the cutting height to the caving height. Therefore, the cutting height of the working face should be kept to below 3.5 m and should be properly reduced in the case of severe rib spalling of the coal wall. 2. The working resistance and sidewall-protecting force of the support should be improved. The selection of appropriate support equipment and processes can reduce the degree of rib spalling of the coal wall to some extent; therefore, the support parameters should be selected as follows: the support strength and sidewall-protecting strength should be 1.5 MPa and 0.75 MPa, respectively. Furthermore, considering that the #31 coal seam is independently mined in the rear section of the working face, the support height should not be too small, so a ZFY18000/25/39D two-column shield hydraulic support for coal caving should be selected. (3) The management of the coal wall should be strengthened during weighting. The breaking of the main roof significantly affects the failure of the coal wall. Therefore, coal walls are extremely prone to rib spalling and roof caving during weighting. It is necessary to standardize the operational processes and the use of equipment at the working face to ensure the requisite initial support force and working resistance. Moreover, the roof and the coal wall (after coal cutting) are quickly supported to reduce the exposure time, and the hydraulic support of roof wiping should be advanced with the appropriate pressures applied. By implementing the aforementioned measures, the rib spalling of the coal wall in the working face can be effectively controlled, reducing the risk of rib-spalling accidents and realizing safe, high-efficiency production at the 31,204 fully mechanized caving face over its large mining height.