Abstract: Effects of non-cohesive sediment grain gradation on cavitation erosion in high velocity flows is studied experimentally in a small looped water tunnel. First, eight non-cohesive sediment samples of different gradations are prepared in the inner tank of the tunnel－weight percentages smaller than a certain grain size of P < 2%, 12%, 33%, 47%, 56%, 70%, 86%, 100%; Sediment concentration is measured using an infrared suspended solid analyzer. A dynamic pressure data acquisition system is adopted to measure real-time the pressure in the tunnel working section, including the cavitation zone and cavitation erosion zone in the condition of eight sediment gradations. Second, concrete specimens with different strengths are used for the tests of erosion of 4 hours long under the condition of the same concentration S and different sediment gradations. The results show that at S = 12 kg/m3 and throat flow velocity V = 38.6 m/s, an increase in weight percentage P lowers the pressure in the cavitation zone, promoting the occurrence of cavitation; but it raises the pressures in the erosion zone, enhancing cavitation erosion. At a fixed strength of concrete specimens, their cavitation erosion intensifies with an increase in P; at fixed values of S and P, a specimen with a higher strength (fcu = 17.8 MPa) presents a greater cavitation erosion resistance than that with a lower strength (fcu = 13.7 MPa).

Key words: hydraulics, non-cohesive sediment, grain gradation, cavitation erosion, high velocity flow