Study On Decompression Mechanism Of The Pervious Slabs In Plunge Pool

The safety of protecting structure in plunge pool is the key to success or failure of energy dissipation. In recent years, a batch of high dams is under construction in China. So the stability of lining structure in the plunge pool is one problem that needs to be solved in practice and also one of the subjects that many researchers have studied for years. Protecting structure in plunge pool includes two types, which are trapezoid section and counter-arch. Compared to trapezoid section, counter-arch slab is more safety. And the results show that the load reduces obviously acting on the pervious slab. From the concept of initiative protection, pervious slab can initiatively decrease the load acting on the pervious slab in plunge pool and improve the stability of protection structure. So the decompression mechanism of pervious protecting structure is one problem that needs to be solved in practice. In this dissertation, based on large-scale model test, the characteristics of pressure fluctuations propagation in joints and the characteristics of the load acting on both the pervious slab and impervious in plunge pool are proposed by the synchronous measure of hydraulic parameters. Fore more the decompression mechanism of pervious protecting structure is studied. The main harvests of this dissertation include as follows:(1) According to that the change condition for pressure fluctuations in joints, destroy process for plunge pool slabs is divided into two stages, that is transient flow stage and slabs-water vibrating stage, inherent relationship among them is analyzed.(2) The characteristics of amplitude, frequency, relation and scale for pressure fluctuations in joints on both the pervious slab and impervious are analyzed.(3) Compared to impervious slab, corresponding pressure fluctuations spectral density of pervious slab is reductive. And spectral density of pressure fluctuations indicated energy intensity is obvious reduced. The results show that, to some extent, pressure fluctuations are released when pressure fluctuations spread along joints and encounter pervious holes. Simultaneously, the results show that the phasic relation of pervious slab is lower than impervious. When the phasic relation is weaken, it is possible for uplifting force to decrease.(4)In same discharge hydraulic conditions, at first pressure fluctuations coefficient of both pervious and impervious slab increase with the increasing of Lx L ; maximum when Lx L equal to 0.73; on the contrary, decrease with the increasing of Lx L . Based on testing the relation between pressure fluctuations coefficient and Lx L , validates the conclusion that the function of pervious holes are equivalent to reducing the effectively scale of slab.