開口變化梳子壩之力學分析

Abstract

The channel structures for retaining debris flow can be categorized as permeable dam and impermeable dam. Usually, slit dam (permeable dam) is more efficient than the check dam (impermeable dam). Despite of their advantages, slit dams are often blockaded by boulder. In this study, slit dam with varied slit width, i.e., slits of different heights, was proposed to achieve the safe and economical objectives. To ensure the stability of slit dam with varied slit width, four different conditions with two different heights were analyzed in this study: (1) filled dam with normal flow under maximum earthquake, (2) filled dam with maximum flow, (3) empty dam impacted by debris flow, and (4) nearly filled dam striken by giant boulder at the top of dam. For illustrative purpose, an 8 meters high slit dam with varied slit width under condition (4) was designed to illuminate the mechanics analysis, thickness of the dam at different elevation, and the reguired amounts of steel bar. Finally, this study indicates that slit dam with varied slit width can achieve the safety objective with lower cost than traditional slit dam does.

河道中攔阻土石流之構造物大致可分為透過性壩與非透過性壩兩種，其中梳子壩(透過性壩)在土石流攔阻上比防砂壩(非透過性壩)更有效率，但即使如此，梳子壩本身仍易被土石流所堵塞。故本研究提出一開口變化梳子壩之設計，藉由不同高度之斷面變化，俾使梳子壩在防治土石流上，能兼顧成效與經費，達到安全經濟的目的。 針對開口變化梳子壩應在面臨河道中不同狀況下壩體均能保持安定，本文提出了四種狀況來分析壩體之穩定性，分別為case 1 淤滿+普通流量+設計最大地震、case 2 淤滿+設計最大洪水、case 3 空壩+土石流平均推擊、case 4 近淤滿+巨石撞擊，並在每種情況又分不同高度來分析。同時舉一8m高之開口變化梳子壩面臨case 4 情況為例，將其力學分析、壩體各部份厚度檢算及鋼筋配置計算方法詳列而出，以期作為一設計之參考。最後在實際計算其所需經費時指出開口變化梳子壩比梳子壩在面臨同樣情形下，能達到節省經費之目的。