Nonlinear Mechanical and 3D Rupture Morphology of Saturated Porous Sandstone Under True Triaxial Stress

In deep underground geotechnical engineering, water-rock interaction emerges as a critical factor influencing the stability of engineering rock masses. This study delves into the macroscopic nonlinear mechanical behavior and fracture characteristics of natural water-bearing and saturated sandstone samples under various true triaxial stress states. The objective is to systematically elucidate the impact of actual three-dimensional stress conditions and water content on the mechanical behavior and fracture mechanisms of sandstone formations. The findings reveal significant anisotropic deformation in sandstone under 3D stress, while saturated sandstone exhibits robust plastic deformation capacity. Moreover, changes in the strain ratio coefficient are identified as precursors to rock fracture. The dilatation behavior of sandstone weakens progressively with increasing sigma 2, indicating reduced expansion in saturated sandstone. To account for the influence of sigma 2, a novel dilation index is proposed. The true triaxial strength of sandstone demonstrates a close relationship with both sigma 2 and water content, with strength initially increasing before declining as sigma 2 rises. In addition, water significantly undermines sandstone strength, although this weakening trend moderates with increasing sigma 2. Morphological analysis and SEM observations unveil three-dimensional volume fracturing characteristics in rock fractures, primarily characterized by shear accompanied by tensile fractures. Saturated sandstone samples, in contrast, exhibit numerous tensile and intergranular fractures. Overall, this study holds paramount practical significance for the evaluation of rock stability and the design of water-bearing engineering rock masses, encompassing domains, such as geology, water conservancy, and mining. The influence of the 2 and water on the nonlinear mechanical behavior of sedimentary sandstone was studied.A new dilatation index and strength criterion considering the effect of the 2 was proposed.The 3D fracture morphology and failure network characteristics of sandstone was analyzed.Mesoscopic fracture mechanism of the 2 and water on sandstone was revealed.