土石壩受震之安全評估

摘要民國88年9月21日凌晨1時47分，台灣中部地區發生芮氏規模7.3的強烈地震，對不少水壩產生了極大的損害，而社會大眾對水庫安全極度關切，所以水庫受震安全評估的研究與改善更是刻不容緩。目前的水庫安全評估規範中關於地震安全評估，主要採用擬靜態分析法，求一安全係數表示壩體的安全程度。然而此法並未考量到工程之不確定性。事實上，工程上的風險與不確定性是無法避免的。因此，在本文中，即打算以風險分析來評估水庫受震的安全性，以得到更佳的水庫受震安全性評估方法。本文以石門水庫為例，採用事件樹觀念以地震危害度分析考量地震的不確定性，又取多個壩址附近的實測地震紀錄進行滑動量分析並以對數常態機率分佈來計算不同滑動量區間的機率，最後，考量滑動量對應破壞程度的機率，可求得壩體破壞的年發生率。經研究後得知壩體各種破壞程度的年發生率，此法較只求出安全係數來得有意義，且可作為政府進行風險決策的或水庫地震險的重要參考。

關鍵字

土石壩；水庫安全評估；石門水庫；事件樹；地震危害度分析

並列摘要

Summery On 21 september 1999,Ji-ji occur an earthquake,measured 7.2 on the moment magnitude scale,which cause severe damage on many dams.People concern Dam's safety a lot,so the research about seismic safety evaluation of a reservoir is urgent. In recent seismic safety evaluation of a reservoir,we mainly use pseudo-static analysis,which use a safety factor to represent a dam's safety.But actually,the risk and uncertainty in any construction is inevitable.So,in the paper,we plan to use risk analysis to evaluate seismic safety of a reservoir and try to get better method of seismic safety evaluation of a reservoir. In the paper,we take Shi-Men dam as a example,and use concept of event tree.To consider the uncertainty of earthquake,we use seismic risk analysis;to consider destruction,we calculate slide quantity.Finally,we can use the relation between slide quantity and probability of detroyed degree to calculate the year-probability of different detroyed degree of a dam. After the research,we know the year-probability of different detroyed degree of a dam.This method is more meaningfal than pseudo-static analysis,and can be a major consultation when government want to make a risk policy or insurance company want to consider the seismic risk of reservoir.