Dynamic properties of deep rocks under different seepage gradients: Experimental investigation and theoretical modeling

Deep rock engineering projects are frequently conducted in water-rich regions characterized by elevated geo-stress, differential pore water pressure, and frequent dynamic disturbance. Elucidating the dynamic behavior of rocks under hydraulic-mechanical coupling is critical for evaluating the stability of engineering structures. In this study, a modified triaxial split Hopkinson pressure bar (SHPB) system integrated with hydraulic loading technique was utilized to apply simultaneous differential water pressure and confining pressure. Dynamic loading experiments were performed on white sandstone under varying strain rates and hydraulic pressures to simulate three distinct seepage gradients. The results demonstrated that increasing the water pressure difference between the two ends of the specimen accelerated the development of internal fractures, enhancing intrinsic permeability and exacerbating fragmentation. Both dynamic compressive strength and energy consumption exhibited rate dependency. As the seepage gradient increased, the dynamic compressive strength declined, while energy dissipation capacity remained constant. Building on the principles of element combination theory in rheological modeling, a dynamic constitutive model of rocks was developed under coupled pore and confining pressures by incorporating the hydraulic pressure gradient. Assuming a linear correlation between the hydraulic effects and pore water pressure, the mathematical framework of the model was derived and then validated against experimental results. Finally, the influence of seepage flow, quantified through model parameters, was analyzed in detail. • A modified SHPB system is used to realize coupled hydraulic-mechanical loading. • Active implementation of seepage gradients in dynamic experiments. • Effects of differential water pressure on rock dynamic properties are investigated. • A dynamic constitutive model incorporating seepage gradient coupling is proposed. • Impacts of seepage are quantified and discussed.