Research On The Fracture Law Of Overlying Rock In Shallow Coal Seam Mining Under Karst Cave Landform

The shallowly buried coal seams in mines in the southwest region have a large number of shallowly buried coal seams and cavernous geomorphology,resulting in the mining of shallowly buried coal seams in cavernous geomorphology,resulting in abnormal overburden breakage patterns during coal mining face advancement,which has a particular impact on mine production.This paper takes a mine in the southwest region as the engineering background to gain a deeper understanding of the overburden breakage pattern during the mining of shallowly buried coal seams in cavernous terrain.It uses various research methods such as field research,theoretical analysis,numerical simulation,and similar simulation to conduct an in-depth study on the incoming pressure pattern of the working face,the overburden breakage and transport pattern,and the cavern instability and deformation process during the mining of shallowly buried coal seams in cavernous terrain in this mine.The mutual influence relationship between the cavern and the overburden was discussed and compared with the conventional shallow buried coal seam mining.The reasons for the abnormal overburden breakage pattern in shallowly buried coal seam mining under cavernous terrain were initially analyzed.The main research results are as follows:(1)The types of cavities and collapse situations studied in this paper are analyzed,the analytical model of "overburden-cavity" under the action of mining is constructed,the primary top initial and cycle breakage mechanical analysis model during mining of shallowly buried coal seams under cavernous terrain is established by using the solid support beam,simple support beam,and cantilever beam models in elastic mechanics,and the basic top initial and cycle breakage,mechanical analysis model,during working face advance is derived.The formulae for the initial and periodic breakage step of the essential roof during the advance of the working face were derived,the initial and periodic breakage step of the bare roof was calculated,and the influence of various parameters of the primary roof on the initial and periodic breakage step of the essential roof was analyzed.(2)A numerical analysis model and a physical analysis model for shallow buried coal seam mining in cavernous terrain were established,revealing the whole process of cavern instability and deformation in shallow buried coal seam mining in cavernous terrain,observing the change of cavern morphology and the development pattern of fractures undermining disturbance,obtaining the characteristics of fracture movement of the cavern and its surrounding rock strata,and exploring the interaction between cavern fractures and overlying rock fractures.(3)The numerical analysis model and physical analysis model of shallow buried coal seam mining under cavernous terrain were established,the whole process of overburden fracture movement of shallow buried coal seam mining under cavernous terrain was inferred,the influence of mining disturbance on the roof and overburden was studied,the initial and periodic pressure step of the working face and the development height of "three zones" of overburden were obtained.The main characteristics of the overburden breakage pattern when the working face passes through the cavern influence zone were obtained by comparing with conventional shallow buried coal mining.(4)Combined with the whole process of overburden breaking movement and cavern destabilization and deformation in shallow buried coal seam mining in cavernous terrain,the causes of the abnormal overburden breaking pattern and the mechanism of cavern destabilization and deformation in shallow buried coal seam mining in cavernous terrain were initially discussed.(5)Based on the overburden fracture pattern of shallow buried coal seam mining under cave terrain and combined with existing technical means,the safety protection technology of shallow buried coal seam mining over cave influence zone under cave terrain is proposed,which can provide some theoretical basis for the safety protection technology design of coal mines under similar conditions.