Evolution law study of pore and fracture of coal gangue cemented filling body under axial compression using PFC2D

Abstract

Filling body is an important structure to support the safety of coal mine goaf. The cemented gangue backfill (CGB) is a multiphase heterogeneous brittle material composed of coal gangue, hydration reactants, pores and microcracks. According to Micromechanics studies, the accumulation and development of meso-structural damage in heterogeneous brittle materials is the direct cause of macroscopic failure. In this paper, particle flow numerical software PFC2D is used to simulate the meso-structure evolution of CGB. Considering the particle size of filling material, the coal gangue particles are drawn according to the real shape by vector software, then import it into PFC2D by FISH language and constructed as Clump unit. The relationship between micro-characteristics such as particle force chain distribution, cracks and pores and mechanical properties of CGB is analyzed. The results show that the stress-strain and crushing mode of the numerical simulation model have a good correspondence with the laboratory test results. The internal force chain distribution and fracture-pore evolution law of the model particles are analyzed. It is found that most of the force chains are concentrated near the larger particle units, forming the 'skeleton force chain' phenomenon. The initial cracks are mainly produced around the coal gangue particle unit. With the increase of axial pressure, the cracks grow obliquely from 30° to 45°, and finally macroscopic cracks are generated. Due to the hydration product generated, the internal porosity is gradual decrease. Other than that, during the uniaxial compression process，the porosity of the same curing age decreases first and then increases, and the pores are sudden increase after the complete crushing stage.