Study on control of ground subsidence cracks in coal mine based onextrusion blasting technology

The surface fractures caused by underground coal mining are the intuitive manifestation of mining subsidence damage，causing serious damage to buildings and land. At the same time，the penetration fractures cause surface ventilation system disorder，which seriously affects the normal and orderly production of mines，so it is of practical significance to propose a feasible surface subsidence fractures management system for the study of surface mining subsidence and high-yield and high-efficiency production of mines. To solve the problem of ground subsidence fracture，even local connection with gob in coalfield，taking the ground subsidence fracture of No.30509 working face in Tashan Coal Mine as the engineering background，through the analysis of fracture characteristics in the target area，the extrusion blasting and fracture blasting filling principle are discussed，the fracture blasting filling scheme is formulated，and the reasonable blasting parameters are determined，and the field application is carried out. The results show that the ground subsidence fractures are mainly divided into two types:rock fractures in the eastern part of the valley and soil fractures in the western part of the valley，with the maximum width of the fractures exceeding 2 m and the maximum subsidence depth of 6 m in the subsidence area. When the width of fracture fracture is greater than 100 cm，the double side blasting method is adopted; when the width is 30～100 cm，the single side blasting point extrusion blasting method is adopted; when the width is 20～30 cm，the blasting point extrusion blasting method is used inside the fracture. The loose blasting filling scheme is adopted for the soil fractures. When the width of the fractures is greater than 70 cm，the blasting method of arranging blasting points on both sides of the fractures is adopted，and when the width is less than 70 cm，the blasting method of arranging blasting points on one side in the fractures is adopted. By using the technology of laying metal mesh and upper compacted soil layer backfill，due to the wire mesh has a greater tensile strength than the soil or rock layer，the fractures can be ensured to move from the bottom to both sides along the metal mesh and avoid upward transmission. At the same time，the metal mesh and the upper compacted soil layer have certain bearing capacity，which can ensure the integrity and safety of the surface. After the implementation of extrusion blasting，combined with ground settlement monitoring data，the surface subsidence fractures have been effectively improved to meet normal production of mine.