Effects of pore pressure on mechanical behavior of Xiyu conglomerate subjected to loading-unloading cycles with varied amplitude

The deteriorated bearing capacity and nonlinear expansion deformation of weakly cemented Xiyu conglomerate under complex water environments and stress disturbances pose significant risks to the safety of stratum engineering construction. In this study, to precisely comprehend the influences of pore pressure ( P w ) and stress path on the deformation characteristics, dilation behavior, and damage evolution of Xiyu conglomerate, a series of triaxial monotonic loading and cyclic loading-unloading tests were conducted on saturated Xiyu conglomerate with varied confining pressures ( σ 3 ) and pore pressures. The results indicate that as P w increases, the secant modulus, unloading modulus, and loading modulus decrease, but increase with rising σ 3 . Additionally, P w accelerates the onset of dilatancy, whereas σ 3 delays it. As σ 3 increases, the peak stress, crack damage stress, and residual strength increase, while these parameters decrease with increasing P w . A positive correlation exists between the effective confining pressure and the effective axial stress. Furthermore, an increase in P w results in a greater maximum dilation angle, which decreases with increasing σ 3 . The failure mode is mainly a tensile-shear mixed failure mode. The high pore pressure and cyclic loading stress path aggravate the deterioration of strength and failure mode of the weakly cemented Xiyu conglomerate. Finally, a new damage variable and conceptual model are proposed and discussed. The findings provide insight into the damage and failure mechanism of the Xiyu conglomerate under pore pressure and cyclic disturbance, offering a crucial experimental foundation for the design and construction of hydropower projects in the Xiyu conglomerate layer.