土石壩滲流相關之破壞型態與參數探討

Abstract

本研究以兩座型態迥異的土石壩為模擬例進行土石壩數值模擬分析，以探討土石壩之壩體內一旦出現缺陷或裂縫時可能出現與滲流相關之異常問題。鯉魚潭壩與新山壩分別屬於對稱良好之分區型土石壩及非常不對稱土石壩的兩種典型，其滲流相關之異常問題與可能出現之問題特性相當不同，因此被選為本研究之模擬對象。 本研究首先以鯉魚潭壩作為典型對稱良好壩型之案例，模擬土石壩於各種不同滲流條件之反應。對比理想狀態行為，藉數值分析模擬土石壩幾種的潛在缺陷問題可能引致之異常滲流問題，探討之內容包括：(1)橫向裂縫、(2)縱向裂縫、(3)心層與基礎交界面水密性不足、(4)濾層失效、(5)隔幕灌漿失效等缺陷，分別歸納分析其滲流、孔隙水壓、水頭、與水力坡降之異常現象。 本研究復以新山壩加高後之壩體為例，探討典型極不對稱型土石壩體可能出現之特殊滲漏相關問題。新山水庫濾層呈「ㄑ」形，當水位高過加高前壩頂高度後，在新心層之下方易產生濕潤區。探討之重點有：(1)因壩心極不對稱與濾層曲折的可能影響、(2)曾經過加高的土石壩於新舊心層交界面上若有水密性較差的情況將有何影響、(3)當曲折的濾層一旦發生阻塞將有何影響。 經由詳細分析各考慮情況下之滲流、孔隙水壓、水頭、與水力坡降等模擬結果，釐清可能出現的特殊異常現象，期能有助於監測儀器之佈置選擇與監測結果合理詮釋之參考。

This project made use of numerical simulation to investigate abnormal earthdam response associated with internal seepage regarding defects occurred within or under the earthdam. Li-Yu-Tan Dam and Sin-San Dam, respectively, were taken as typical examples to represent a well symmetrical and a poorly symmetrical zoned earthdam. The features in the response of seepage problems for these two types of zoned earthdam are distinctive. For Li-Yu-Tan Dam, as a typical well symmetrical zoned earthdam, this project simulated the dam responses subjected to various defects or problems in the dam or the foundation. The considered defects or problems included (1) transverse crack, (2) vertical crack, (3) poor water-tightness of the interface between earthdam core and foundation, (4) clogging of filter drain, and (5) breakage of curtain grouting (cut-off wall). Sin-San Dam has a very unusual shapes of dam core and filter drain due to its history of dam construction. Both of its dam core and filter drain have sharp corners. This dam was taken as a typical example of poorly symmetrical zoned earthdam for studying problems associated with seepage due to the unusual shapes of dam section. The following problems were investigated: (1) possible influence of seepage due to the unusual shapes of dam section, (2) unfavorable influence of seepage due to poor water-tightness of the interface between old and new (elevated) cores, and (3) influence of seepage due to clogging of filter drain. Critical seepage flow, pore water pressure, water head, and hydraulic gradient, for each case were examined and deliberated to identify crucial signs that can be helpful for the planning of instrumentation locations and for the interpretation of monitored data.