Dynamic mechanical characteristic and fracture evolution mechanism of deep roadway sandstone containing weakly filled joints with various angles

Abstract

To investigate the influence of weakly filled joint angles on the dynamic mechanical properties and fracture evolution mechanism of sandstone, dynamic uniaxial compression tests were performed on sandstone specimens with joint angles of 0°–90° under strain rates of 35–125 s−1 and an interval of 15° using a modified split Hopkinson pressure bar (SHPB) apparatus. The dynamic stress–strain relationship, dynamic strength, dynamic peak strain, energy characteristic, failure mode, typical failure progress, crack coalescence category, fracture micro-mechanism, and theoretical analysis were examined in this research. The test results indicated that both the dynamic compressive strength and peak strain of jointed sandstone first decreased and then increased with the increase in the joint angle. To maximise the energy reflection coefficient and minimise the absorbed energy density, a critical joint angle α(approximately 45°), was employed. The specimens with joint angles of 0°, 15°, and 30° exhibited considerable plastic deformation capacity, whereas the brittle failure feature of specimens with joint angles of 60°, 75°, and 90° was more typical than that of intact specimens. The stress bimodality phenomena of the specimen with a joint angle of 45° were more distinct than those of the specimen with a joint angle of 60°. Four types of crack coalescence behaviours were identified during the dynamic fracturing processes of the jointed specimens using a high-speed camera; subsequently, these were compared with the crack coalescence categories of jointed specimens under static loading. Moreover, the micro-fracture morphology well-revealed the macroscopic fracture behaviours of jointed sandstone specimens. It was further confirmed that the variable tendency of the dynamic compressive strength of jointed specimens based on experimental results agreed with the theoretical analysis.