| Summary: | 碩士 === 國立交通大學 === 土木工程學系 === 99 === The western foothill is the mainly development area in Taiwan. Weirs were often built across rivers to elevate river water level for providing public water supply in Taiwan. Due to low rock strength and the head difference caused by the weirs, rapid scour downstream of weirs is often observed. There is no deep foundation in most weirs, so this type of scour may induce weir instability and accelerate river-bed scour. Moreover, channel would become trench by this type of scour.
This research aims to propose an approach for estimating the shape and depth of the scour hole downstream weirs built on weak rocks.
Intergarting the formula for calculating the stream power of water jet (Annandale, 2006), for estimating the dissipation energy in tailwater (Bollaert, 2003), and for determining the dissipation hydrodynamic pressures (Melo, 2006), the new method for estimating the shape and depth of the scour hole is presented. Then, the ultimate scour hole and shape for several real cases is calculated using the proposed method. Since the constant ke depending on rock properties in the formulation for determining the scour depth proposed by Liu(2005) is not easy to determine from rock putcrop, the erodibility index(Kh) is proposed to replace it. The relationship of Kh and ke is proposed based on the regression of the data of Liu’s cases. Using the modified Liu formulation, the ultimate scour hole is also calculated. The calculated scour depths from both methods are similar.
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