| Summary: | 碩士 === 國立交通大學 === 土木工程學系 === 100 === In the Western Taiwan, most of major rivers flow through the geological region of Western foothill which is composed of young sedimentary rocks. Their engineering behaviors are tended to be like weak rocks, e.g. poor cementation, high deformability, and low strength. Weirs were often built across rivers to elevate river water level for providing public water supply in the area. Due to low rock strength and the head difference caused by the weirs, rapid scour downstream of weirs is often observed. This type of scour may induce weir instability and make river-bed erosion. Since the water flow quantity passing over a weir is varied with time, the impinging points of jet flows on downstream rock bed are different for different flow events. The depth and shape of scouring hole may be affected by the inclination angle of jet flow. This thesis aims to develop a jet erosion equipment for simulating the formation of scour hole on weal rocks river-bed down stream weirs, and investigating the effect of jet impinging angle on the scouring depth and scouring rate of the holes.
Based on the multi-function erosion equipment for weak rocks developed by Kuo(2010), this thesis develops a jet erosion equipment with variable impinging inclination angles for weak rocks in laboratory. Testing procedure, sample preparation, and measurement of the surface topography of the specimen are introduced in the thesis. Also, three sets of jet erosion tests with varied jet inclination on sandstone specimen are conducted. The testing inclination angles include 30°,50°, and 70°.
The testing results show that the eroded volume of the specimens increases with the decrease of the inclination angle, because the total applied energy on the specimen decreases with the increase of the inclination angle. The results of the pilot tests demonstrate that the equipment is suitable for performing the scouring tests on weak rocks in laboratory.
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