Stability and Force Chain Characteristics of “Inclined Step Cutting Body” in Stope

Abstract

In the mining stage of shallow thick coal seam in the western mining area of China, there is often severe mine pressure and serious surface subsidence and damage. In this paper, theoretical analysis and PFC (Particle Flow Code) numerical simulation are combined to study the caving characteristics and force chain evolution characteristics of the overlying strata of stope. We analyze the stability of the structure of the “inclined step cutting body” on the overlying strata and obtain the calculation formula of the support force of the working face based on the instability of the structure. The force chain arch curve equation is modified according to the evolution law of force chains, from which the force chain can be the basis for judging the large area damage of the surface. The results demonstrate that the rock mass i1 ≤ 0.86, the structure of “inclined step cutting body,” is not prone to sliding and instability. Considering that i = 1.0~1.4 under the condition of shallow buried thick coal seam, the structure of the “inclined step cutting body” is prone to being destroyed leading to instability, resulting in severe rock pressure.The minimum supporting force to maintain structural stability is 0.2Fn, which is in line with the actual support force in the mining process of the working face. Taking the mining technical parameters of the nearby working face into the force chain arch formula, it can be concluded that, when the working face advances to 175 m, large-scale subsidence damage begins to appear on the surface, which agrees with the survey results. Therefore, the force chain is the main force system to bear the load of the overlying strata. PFC has unique advantages in simulating discontinuous deformation of overburden rock. The results of the study reasonably explain the phenomena of severe mine pressure and serious surface damage caused by the mining of the shallow thick coal seam working face, which has a certain reference value for preventing ground disasters caused by underground mining and land ecological restoration.

Keywords

• shallow depth
• force chain
• particle flow
• structural stability
• inclined step cutting body