Abstract: The first weighting of main roof above confined water in deep longwall face is a severe phenomenon of underground pressure, which often causes the large-scale failure at the floor area and water inrush accidents. To study the linkage effect between the floor failure and first weighting of the main roof in deep longwall mining, the fracture and failure characteristics of roof and floor during the first weighting in deep mining were analyzed by the similar material simulation test. The breakage model of the main roof and the mechanical model of floor during the first weighting were established. From the perspective of stress increment, the linkage effect between the compression failure and unloading failure at the floor area and the first breakage of the main roof was obtained. Linkage changes of the stresses and deformation at the floor area during the first weighting in different mining depths were simulated by using the discrete element software. Then the weakened control technologies of roof and floor in deep mining were provided, which mainly include the pre-split main roof for eliminating the mid-span gangue contact effect, enhancing the working resistance of supports for reducing the dynamic loads of main roof breakage, and reducing the unloading starting point and unloading level of stresses at the floor area. The results show that there is a zone of the increased compressive stresses at the floor area of contacting gangues in the middle of main roof after the first breakage of main roof in deep mining. Its displacement direction changes to downward compression after the first weighting from the upward heave before first weighting. It is also found that the position of the back foot changes to the contacting zone from the floor area in front of coal rib, the pressure arch at floor area changes from one single arch structure with the width of the ultimate span to two arches structure whose width are both about half of the ultimate span. The deeper the mining depth, the higher the increment of horizontal stresses at floor area of contacting gangues zone are, and the influence depth of vertical stresses increment are higher than that of horizontal stresses. With the increase of the maximum stress variation, the maximum deformation at floor area approximately increases exponentially, and its non-linear increases are the most serious on the vertical direction.

Key words: floor failure, the beam of main roof, the first weighting, deep longwall mining, stress increment