Characterization of rupture and failure of weakly cemented sandstone under uniaxial and triaxial compression: An experimental and DEM study

An in-depth understanding of deformation and failure of rocks at the macro- and meso-scale strongly contributes to stability analysis and construction safety in rock engineering. This paper performs a series of laboratory uniaxial and triaxial compression tests at a loading rate of 0.02 mm/min and multi-phase numerical simulations considering the variability in the strength of mineral particles based on the particle flow code (PFC2D) to investigate the macro- and meso-scale deformation and failure modes of weakly cemented sandstone (WCS) specimens under different confining pressures. The results reveal that the elastic moduli and peak strengths of WCS specimens at six confining pressure levels are between 1.74 GPa and 5.85 GPa and between 10.14 MPa and 62.53 MPa, respectively. Failure modes of WCS specimens exhibit obvious confining pressure dependence, and increasing confining pressure from 0 MPa to 15 MPa enables the failure modes of WCS specimens to change from splitting-shear failure to single-shear failure. The rupture plane of WCS specimen hindering particles displacements along the loading direction facilitates the specimen to undergo dilatancy. A meso-scale composite failure of "crack concentration zone - rupture concentration zone - displacement vector drastic change zone" is identified for WCS specimen. The development of tensile and shear cracks in specimen experiences four stages of "initiation - slowly linear growth - rapidly nonlinear growth - linear stabilization" with the increasing axial strain. The growth rate of shear cracks is slightly greater than that of tensile cracks in the pre-peak stage, while this situation is opposite in the post-peak stage. The confining compression contributes to a more stable crack development for specimens. The proportion of tensile cracks varies drastically until the pre-peak stage, with a very small change in the post-peak stage, and the failure of specimen is dominated by tensile cracks. The number of tensile cracks at peak stress is mainly characterized by a stable growth stage under low confining pressures and a stepwise growth under moderate to high confining pressures, while that of shear cracks at peak stress experiences an obvious stepwise growth for all for all confining pressure levels. The contact force chains gradually change from a closed-type ring feature before loading to an open-type column feature as the axial load increases. The average normal and tangential contact forces decrease dramatically after the peak, which lead to a sharp decrease in the load-bearing capacity and the final failure of specimens. The research results can provide a reference for the interpretation of macro- and meso-scale mechanical behaviors and failure mechanism of the WCS.