Experimental study on flow and diffusion law of gangue filling slurry in caving zone

In view of the demand of green and low⁃interference gangue discharge at Dahaize Ten⁃million⁃ton coal mine，the filling technology of gangue slurry in the caving zone has been put forward in order to achieve the safe， efficient and green disposal of coal gangue without affecting the normal production of the mine. In order to ensure the feasibility of the technology and the basis of filling parameters，a model of gangue accumulation in the caving zone has been established in the ground gangue dump of Dahaize coal mine to study the flow and diffusion law of two kinds of gangue slurry in the gap between caving rock blocks in the goaf. The results show that 1 The flow of gangue slurry in the gap of caving rock blocks in the goaf can be divided into three periods，i.e.，flowing period，gushing period and seepage period. The three periods are interrelated and inseparable. 2 With the increase of gangue slurry filling amount， the dynamic flow gradient first decreases and then increases， and finally presents a stepped distribution. When the slurry filling amount reaches 176 m3 ，for 71.8% gangue slurry，the first step dynamic flow gradi⁃ ent is 7.5% and the second step dynamic flow gradient is 1.8%，and for 75.3% gangue slurry，the first step dynamic flow gradient is 7.8% and the second step dynamic flow gradient is 2.1%. 3 The flow of gangue slurry in the caving zone is stage selective. The slurry from the gushing point first flows within the first step along the flow gradient， and then the slurry in the first step flows toward the second step along the dip direction. When the mass concentration of slurry is 75.3%， the minimum width of the slurry entering into the gaps between rock blocks is about 10 mm. When the mass concentration of the slurry is 71.8%，the minimum width of the slurry entering into the gaps between rock blocks is about 7 mm. In the second step，the slurry，liking branching，successively fills the cavities and interstices between rock blocks，and forms some slurry accumulation points at the dip and strike boundaries. The slurry flowing from the first step to the second step can reach more than 37. 8% of the total amount of the slurry. 4 The vertical height distribution characteristics of slurry in Model 1 and Model 2 are basically the same. The vertical height of slurry decreases as it is far away from the outlet of low grouting pipe. The maximum vertical height of slurry is 2.11 m(1.77 m)，which is located in the first step of 6.5 m(6.3 m) inclined section，and the horizontal distance from the outlet of low grouting pipe is 0.5 m(0.3 m). The minimum vertical height of the slurry is 0.797 m (0.669 m)，which is located in the middle of the second step of the inclined section 29.2 m(29.0 m)，and the hori⁃ zontal distance from the outlet of the low grouting pipe is 25.595 m(25.364 m). 5Along the flow direction of the gangue slurry，the proportion of coarse particles in the gangue slurry decreases，the proportion of fine particles in⁃ creases，and the mass concentration of the gangue slurry decreases. The simulation test shows that the filling scale is related to the size of caving rock，the concentration of gangue slurry and the composition of gangue particle size.