Author(s): Pedro Manso; Virgilio Fiorotto; Anton Schleiss
Linked Author(s): Anton J. Schleiss
Keywords: Plunging jets; Rock fissures; Opening dimensions; Air-water flows
Abstract: The transfer of plunging jet impact pressures to the underlying rock mass depends on the dimensions of fissure openings at the surface. Based on analytical and experimental results of jet pressure propagation inside closed-end fissures, the paper presents evidence of the relationship between pressure wave filtering and fissure opening characteristics (as observed at the rock surface). Analytical developments based on a local application of the Frozen Turbulence principle at stagnation, show that point pressure fluctuations can be averaged when integrated over a given time interval (or distance), due to bi-dimensional pressure diffusion. The energy at high frequencies is reduced the longer the fissure width. This is verified experimentally with impact pressures generated by plunging jets with velocities up to 30 m/s at emission, diffusing over a pool depth between 2. 8 to 12. 4 times the jet diameter, and sampled at 1 kHz. High frequency pressure waves are filtered at the transition from freesurface pool flow to pressurized fissure flow. These analytical and experimental developments show that fissure opening dimensions are a key parameter to consider in the rock scour processes of crack propagation and block displacement.