Cavitation destruction of concrete and protective facings under natural conditions

Abstract

The first cases of cavitation erosion of concrete of hydraulic structures were noted at the end of the 1930's (Bonneville Dam, USA), but reports about this appeared much later in the literature [1. 2].Cavitation erosion of concrete of hydraulic structures after 1-2 years service has been described and partially analyzed in domestic literature. Such destruction has been noted at the V. I. Lenin Volga [3][4][5], Bukhtarma [6], and Bratsk hydroelectric stations [7], and Suphung station in the Chinese People's Republic [8].In 1963 a field inspection was made of the condition of the concrete in the lower pool of the dam of the V. I. Lenin Volga hydroelectric station.* Unlike previous years, besides the energy dispersion baffles an investigation was the made of condition of the concrete of the spillway face, piers, bottom of the stilling pool, and first subsidiary dam of the third section, which was dewatered for repair for the first time after 7 years of service.The concrete dam is divided by two massive abutment piers reaching to the first subsidiary dam, into three sections (the sections are numbered from the left bank to the right). The stilling device consists of two rows of energy dissipation baffles in the form of truncated pyramids located on the bottom of the stilling pool in staggered order and two subsidiary dams. Twelve deflecting baffles are located in each extreme section to eliminate convergence of the current near the bank abutments.The presence of destruction on such elements as the side faces of the baffles and bottom of the stilling pool in the wake of the piers precluded the assumption that destruction was caused by the impact of floating bodies or the dynamic action of the water flow. An analysis of the possible causes of destruction led to the conclusion that erosion in the examined cases was the result of cavitation. It was found in the inspection that the concrete of the energy dissipation baffles and the deflecting baffles had experienced maximum cavitation destruction. Out of 82 dissipating and deflecting baffles 57 were eroded to a depth of 10-60 cm. Destruction occurred mainly on the dissipation baffles looated in the middle of the span (Fig. 1). One deflecting baffle and 13 dissipation baffles of the first row were severely erorded. For some, up to 60% of the side surfaces were eroded and the exposed 25-cm-diam. reinforcement was deformed (Fig. 2). The presence of a large quantitity of gravel protruding from the concrete was characteristic for the cavitation zone on the inside faces (Fig. 3). This fact, and the results of laboratory tests [9] proved the assumption that cavitation erosion of concrete begins in the "binder-aggregate" contact zone and consists in destruction of the hardened binder, weakening of the bond of sand grains in the conglomerate, and washing out of the mortar component and then of the coarse aggregate particles.Destruction of the upper and front faces of the deflecting baffles and dissipation baffles of the first row was quite insignificant (Figs. 1, 2, and 4). The di...

Discharge Coefficient of Rectangular Short-Crested Weir with Varying Slope Coefficients

“…The broken-line short-crested weir is classified into rectangular profile and trapezoidal profile according to the longitudinal profile [2]. Moreover, the rectangular short-crested weir is insensitive to the downstream submergence, and in special situations the geometrical configuration could be flexibly modified so as to increase discharge capacity and avoid cavitation damage of weir flow structures [3].…”

Numerical and Physical Modeling of the Effect of Roughness Height on Cavitation Index in Chute Spillways

“…Three factors that contribute to the damage on spillway are flow velocity; material strength; 28 and operating time [3]. Inozemtsev (1969) [4] studied the possibility of the occurrence of 29 cavitation, particularly in high-velocity flows at the first part of spillway downstream, which 30 can contribute to severe damages or structural failure. Kells and Smith (1991) [5] proposed a method for preventing or reducing cavitation damage on spillways using spillway aerators and they presented design considerations and criteria for the spillway aerators using physical hydraulic models.…”