室內軟弱岩石射流沖刷設備建立

Abstract

我國西部麓山帶出露甚廣的上新世與更新世地層沈積地層，此類地層的組成岩石普遍具有膠結不良、遇水極易軟化且極易受沖蝕之特性。河道上攔河堰之設置改變河川坡度，造成上游泥砂淤積，下游護甲層流失，喪失對岩盤之保護作用，而攔河堰下游沖刷坑形成後，隨著深度發展會造成被動土壓力之減少，可能使堰體因滑動或傾覆破壞。因水流流況不同，經攔河堰後水流沖擊下游岩床角度將有所不同，因此形成的沖刷坑之深度及形狀亦應當有所差異，其差異狀況值得加以探討。本研究旨在建立適用於軟弱岩石之室內射流沖刷設備，以模擬攔河堰下游沖蝕坑之形成。 本研究以郭炳宏(2010)建立之多功能室內沖蝕儀為基礎，增設可變角度射流沖刷設備，並建立試驗程序、試體準備方法及量測分析方法，最後以軟弱砂岩塊進行儀器測試。 本研究針對沖刷角度為30°、50°、70°進行三組試驗，一樣的沖刷時間下，作用在角度較小試體的總能量（總功）較大，而較大的總功也造成較多的沖蝕量。而射流角度較大的試體（70°）表面產生大規模塊體脫落之時間較早(4hrs)，相對的，射流角度較小的試體（30°），大規模塊體脫落需經過較長的沖蝕時間才會產生(24hrs)。

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.