Abstract: As more and more high-dam hydropower and high head pumped storage projects have been constructed in China, the rock foundation of high dam and high pressure water diversion system generally sustain high water pressure and hydraulic gradient. In this circumstance, not only nonlinear flow is prone to occur in rock seepage; but also accompany with leakage, seepage failure and water-inrush risk. This study experimentally investigated the nonlinear flow characteristics of broken granite rock in Yangjiang subjected to a wide range of confining pressures (1-30 MPa) through triaxial cell test system. The characteristics of nonlinear flow in broken granite rock have been elucidated; and its representation methods have been investigated. The results show that nonlinear flow occurs in the broken granite with the increasing hydraulic gradient, while the flow nonlinearity decreases with the increasing confining pressures. Combined with the cracked morphology of broken granite and the magnitude of the permeability, three possible causes triggering the nonlinear flow have been elucidated, i.e. inertial effect, seepage failure and solid-water interaction. Further, the Forchheimer and Izbash equations have been adopted to characterize the nonlinear flow, respectively, which both provide excellent description for the nonlinear flow in broken granite. The nonlinear coefficient of Forchheimer equation experience positive and negative values during the loading process, which is possibly ascribed to the closure and extension of the cracks in the broken granite. The power-law function between the nonlinear coefficients of Izbash equation has been developed by relating them with confining pressures. The results may prove useful in proper understanding of fluid flow through fault zone and compressive zone under high water pressure and hydraulic gradient.

Key words: broken granite, high water pressure, non-linear flow, Forchheimer equation, Izbash equation