Evolution law and engineering application of surrounding rock force chain in shallow coal seam working face

In the process of shallow seam mining,the rock pressure in mine appears intense,and the collapse accidents of support occur from time to time,which seriously restricts the safe and efficient mining of coal resources. In view of the sudden and violent rock pressure in the process of coal seam mining,the mechanical characteristics of surrounding rock and the stress characteristics of support structure are systematically studied. Firstly,the evolution characteristics of the surrounding rock force chain in working face are simulated by the particle element calculation software. Then,the mechanical models before and after the instability of the overburden strong force chain arch,and the support force model are established respectively. The track equation of the strong force chain arch is deduced,and the formulas for calculating the support load before and after the instability of the strong chain arch are obtained. On this basis,the sup- port load of working face is studied,combined with field measurement. The results show that before the excavation of coal seam,the mechanical structure of coal and rock mass is composed of force chain network,and the bearing capacity of surrounding rock mainly comes from the strong force chain,while the widely distributed weak force chain only plays an auxiliary bearing role on surrounding rock. After the excavation of coal seam,the strong force chain forms a force chain arch,which is the main load bearing capacity of coal and rock mass above the stope. The support of working face only bears the weight of coal and rock under the strong force chain arch. With the advance of working face,the strong force chain arch is constantly adjusted,it has a dynamic evolution process of “ formation-expansion-stability-break- age”. The strong force chain arch development will lose stability and break,when its load exceeds its own strength lim- it,resulting in severe rock pressure phenomenon. The support load of the working face increases greatly. The unstable fracture of the strong force chain arch is the essential reason for the strong dynamic load in the working face. The re- search results reasonably explain the sudden severe rock pressure in shallow seam working face,which has theoretical significance and engineering application value for the safe and efficient mining of coal seam.