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Scour of rock due to the impact of plunging high velocity jets Part II: Experimental results of dynamic pressures at pool bottoms and in one- and two-dimensional closed end rock joints

This paper presents the experimental results of dynamic pressure measurements at simulated plunge pool bottoms and underlying rock joints, due to plunging high velocity jet impact. Emphasis is given on the mean and the fluctuating part of the dynamic pressures, to the extreme pressure values, and to the spectral content of the fluctuations. Particular attention is also paid to the relationship between pool bottom pressures and the pressures they generate inside underlying rock joints. Based on data analysis in one- and two-dimensional rock joints, it was found that high velocity plunging jets are able to generate oscillatory and resonance pressure waves inside the joints. These non-linear transient phenomena propagate at wave celerities that depend on the air content of the air-water mixture inside the joint. This air content is directly related to the plunge pool air content and to instantaneous pressure fluctuations inside the joint. The resulting amplification of pool bottom pressures inside rock joints is believed to be a key for a better assessment of scour formation in rock.