Experimental study on dynamic strength characteristics of fractured rocks under high water pressure and high stress

Numerous pre-existing fractures within deep engineered rock masses and the complex hydraulic environment，significantly affect the dynamic strength characteristics of these engineered rock masses. To investigate the effects of fractures and high water pressure on the dynamic strength characteristics of rocks，five types of red sandstone specimens with different fracture inclination angles were prepared. Impact tests were carried out under six water pressure gradients using a self-developed rock dynamics testing device capable of simulating high water pressure and high geo-stress conditions. The results indicate that with the increase of water pressure and fracture inclination angle，the dynamic stress-strain curve of the fractured rock is gradually transformed from plastic to elastic after-effects after the peak. The curve characteristics can be categorized into three stages. When the fracture inclination angle is fixed，the dynamic peak stress of the fractured rock initially increases with rising water pressure，followed by a slight decreases. The relationship between dynamic peak stress and water pressure follows a Gaussian distribution. As water pressure increases，the average strain rate first decreases and then increases. Under the same water pressure，the dynamic peak stress of fractured rock generally exhibits a trend of slow initial increase followed by a rapid rise as the fracture inclination angle increases，and this trend is influenced by the radial connectivity of the fractured rock and the oblique incidence of stress waves. Moreover，the average strain rate gradually decreases with the increase of fracture inclination angle. A clear negative linear relationship is observed between the dynamic peak stress of the fractured rock and the average strain rate.