Construction and prospect of the technical system for the resource utilization of pressure-relieved floor rock strata in mine goafs

So far, relevant studies on achieving surface subsidence control and reducing the development height of the water-conducting fissure zone through backfill mining have all been carried out from the perspective of the roof rock strata. The backfill spaces mainly focus on the uncollapsed roof region behind the working face and the separated layer area of the overlying rock strata. However, it has not been noticed that the pressure-relieved area of the mining-induced floor can also serve as a potential backfill area. Therefore, the floor of the goaf is regarded as a useful resource for development and utilization, that is, to obtain space, find resources and borrow strength from the floor. The author has creatively proposed three new green mining concepts and technical methods covering “grouting filling in the pressure-relieved floor of the goaf, water injection and expansion forming arch bridge structure in the pressure-relieved floor of the goaf, and blasting-induced cracking and expansion in the pressure-relieved floor of the goaf”, and has made a deep outlook on the comprehensive utilization of the space resources of the floor. The strata control technology of grouting and filling in the pressure-relieved floor. Grouting and filling in pressure-relieved floor, that is, fully utilize the pressure-relieved effect of the floor after coal mining, and drill from the ground to the target grouting layer of the pressure-relieved floor, and then carry out high-pressure grouting to the target layer of the pressure-relieved floor. Under the action of grouting pressure, the target layer and the overlying rock strata will bulge upward, thereby significantly reducing the space below the roof rock strata of the goaf to reduce the development height of mining-induced fractures and reduce mining subsidence. The strata control technology of water injection and expansion forming arch bridge structure in pressure-relieved floor, that is, for the situation where the proportion of hygroscopic minerals such as bentonite, montmorillonite and illite in the pressure-relieved floor rock strata is relatively high, fully utilize their water expansion characteristics, and after water injection and fracturing to form a high-density fracture network in the floor, a large amount of liquid is injected to activate the deep interaction between water and rock, inducing the volume of the water-injected floor to expand significantly, promoting the uniform fracture zone and the destruction zone of the floor to bulge upward, forming arch bridge structure to support the overlying rock strata of the goaf, achieving the effect of reducing the guide height and slowing down the subsidence. The strata control technology of blasting-induced cracking and expansion in floor, that is, fully utilize the blasting-induced cracking and expansion effect and the bulging characteristics of the unloading floor, and precisely crack and break the coal seam floor through directional blasting, thereby increasing the degree of fragmentation of the floor to eliminate part of the extracted space of the coal seam, and equivalently increase the comprehensive expansion coefficient of the rock strata in the collapse zone after coal mining, reducing the space for the downward movement of the roof. In addition, as an important extension, the technology of self-weight-induced groundwater diversion and aquifer reconstruction is proposed, which can transfer the roof aquifer that is prone to communication with mining-induced fractures and water loss to the target water storage layer of the floor. The research results are of great significance to further stimulate the scientific thinking of the resource utilization of the depressurized floor and guide the implementation of the leading technology of the resource utilization of the floor.