Experimental and numerical study on crack propagation characteristics of filled fractured sandstone under different lateral pressures

In order to investigate the influence of lateral pressure on the fracturing processes of fractured sandstone,the fracture mechanism of micro-cracks under different lateral pressures was studied by using acoustic emission (AE) monitoring technology and discrete element model. A discrete element meso-scale numerical model considering mineral composition was established to quantify the mechanical behavior of micro-crack fracture during loading,and the multi-fractal characteristics of AE signals of fractured sandstone under three kinds of lateral pressure were analyzed. The results show that the deformation and fracture process can be divided into microcrack closure stage, crack initiation stage, crack slow growth stage, crack uniform growth stage and crack accelerated growth stage. With the increase of the lateral pressure, the through failure mode of the sandstone specimens changes from macroscopic crack to local spalling failure, and the spalling range gradually increases. In addition,the level of initiation stress corresponding to tensile crack and shear crack increases gradually. The proportion of tensile crack is smaller than that of shear crack. With the increase of stress level,the average frequency width (Δα) shows a trend of first decreasing and then increasing. The average bandwidth difference (Δα₀) and the spectrum measure subset (Δf) show an opposite evolutionary trend. When the stress level is less than 0. 8σ_c,Δα₀ is greater than zero,indicating that the small fracture scale signal occurs in sandstone specimens. When the stress level is greater than 0. 8σ_c,Δα₀ gradually changes from a positive value to a negative one,and the large fracture scale signal is dominant in sandstone specimens.