AI SearchAnalysis of scour hole formation in a plunge pool using a physical model
Heng Sokchhay
Analysis of scour hole formation in a plunge pool using a physical model - Pathum Thani, Thailand : Asian Institute of Technology, 2009 - 89, [3] leaves : ill. - Thesis ; no. WM-08-04 . - Asian Institute of Technology. Thesis ; no. WM-08-04 .
A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Water Engineering and Management
Thesis (M.Eng.) - Asian Institute of Technology, 2008
Plunge pool scour due to water jet impingement from flip bucket spillways is a major concern for stabilization of the hydraulic structures. Scour hole prediction using physical model is a potential tool to foresee its characteristic during the design stage. This study is aimed at predicting scour hole characteristic performed in the plunge pool bed of Nam Ngum 3 (NN3) Spillway in Lao PDR. The whole tasks were carried out using NN3 Spillway Physical Model constructed in the hydraulic laboratory of Water Engineering and Management department, Asian Institute of Technology, Thailand, with an undistorted scale of I :75 and the chute spillway composes of 4 radial gates. Both cohesive (cement mortar) and non-cohesive (gravel) material were used as trial bed materials. After several tests, cement mortar was selected as an ideal material for producing scour because the scour hole result was steep (front slope = 320%) and its maximum scour depth and impact location matched with some empirical formulas. The ideal mixing ratio by volume of cement mortar is Sand(40):Cement(1):Water(5), unit is bucket. The equilibrium phase of scour process was considered to occur at 1 hour (model dimension) after starting experiment because the energy of falling water was dissipated enough in the scour hole and the change in scour depth was not so significant after that period. Scour hole mainly depends on spillway's operation and natural topography of the river downstream. In this case, scour erosion developed toward the left bank because water impinged on the right bank and changed its direction to the left bank. The test showed that the ultimate scour depth measured from tailwater surface is around 93.77 m at maximum discharge (8,182 m³). The energy dissipated by both tailwater and scour hole were computed and the corresponding erosion volumes were also determined. The design spillway can dissipate energy about 33.32% of the total energy at maximum discharge. There are 28 empirical formulas which were used to estimate the ultimate scour depth. Their statistic performances showed that the combination formula of Mason-B (1979), Taraimovich (1978) and Mason-A (1985) yielded the most proper result. Additionally, the combined formula, Kawakami (1973)-Taraimovich (1978) was the most appropriate formula for impact location computation. Finally, based on the experimental data, a new empirical equation for maximum scour depth prediction was proposed. It is proportional to unit discharge and falling head (difference between reservoir water level and bucket lip) and inverse proportional to tail water depth. The new formula provided the satisfactory result in comparing with the existing formulas
Scour (Hydraulic engineering)--Laos
Spillways--Laos
Analysis of scour hole formation in a plunge pool using a physical model - Pathum Thani, Thailand : Asian Institute of Technology, 2009 - 89, [3] leaves : ill. - Thesis ; no. WM-08-04 . - Asian Institute of Technology. Thesis ; no. WM-08-04 .
A thesis submitted in partial fulfillment of the requirements for the degree of Master of Engineering in Water Engineering and Management
Thesis (M.Eng.) - Asian Institute of Technology, 2008
Plunge pool scour due to water jet impingement from flip bucket spillways is a major concern for stabilization of the hydraulic structures. Scour hole prediction using physical model is a potential tool to foresee its characteristic during the design stage. This study is aimed at predicting scour hole characteristic performed in the plunge pool bed of Nam Ngum 3 (NN3) Spillway in Lao PDR. The whole tasks were carried out using NN3 Spillway Physical Model constructed in the hydraulic laboratory of Water Engineering and Management department, Asian Institute of Technology, Thailand, with an undistorted scale of I :75 and the chute spillway composes of 4 radial gates. Both cohesive (cement mortar) and non-cohesive (gravel) material were used as trial bed materials. After several tests, cement mortar was selected as an ideal material for producing scour because the scour hole result was steep (front slope = 320%) and its maximum scour depth and impact location matched with some empirical formulas. The ideal mixing ratio by volume of cement mortar is Sand(40):Cement(1):Water(5), unit is bucket. The equilibrium phase of scour process was considered to occur at 1 hour (model dimension) after starting experiment because the energy of falling water was dissipated enough in the scour hole and the change in scour depth was not so significant after that period. Scour hole mainly depends on spillway's operation and natural topography of the river downstream. In this case, scour erosion developed toward the left bank because water impinged on the right bank and changed its direction to the left bank. The test showed that the ultimate scour depth measured from tailwater surface is around 93.77 m at maximum discharge (8,182 m³). The energy dissipated by both tailwater and scour hole were computed and the corresponding erosion volumes were also determined. The design spillway can dissipate energy about 33.32% of the total energy at maximum discharge. There are 28 empirical formulas which were used to estimate the ultimate scour depth. Their statistic performances showed that the combination formula of Mason-B (1979), Taraimovich (1978) and Mason-A (1985) yielded the most proper result. Additionally, the combined formula, Kawakami (1973)-Taraimovich (1978) was the most appropriate formula for impact location computation. Finally, based on the experimental data, a new empirical equation for maximum scour depth prediction was proposed. It is proportional to unit discharge and falling head (difference between reservoir water level and bucket lip) and inverse proportional to tail water depth. The new formula provided the satisfactory result in comparing with the existing formulas
Scour (Hydraulic engineering)--Laos
Spillways--Laos