不連續變形分析法應用於礫石型土石流運動之研究

The hazards of debris flow triggered by earthquake activities and heavy rainfalls occur frequently in Taiwan along the past decades. Especially after the 921 earthquake in 1999, considerable damages of debris flow hazards in hillside resident areas are increasing dramatically in which debris flow become a major obstacle for engineers to deal with. Accordingly, the study on the mitigation of debris flow hazards is the major concern in Taiwan. Based on the observation from colluviums of conglomerate formation in certral and east Taiwan, it is found that the granular debris flow is the major type in these areas. The Discontinuous Deformation Analysis (DDA) is therefore adopted to study the initiation and mechanism of the granular debris flow. To properly model the behaviour of the granular debris flow, several modifications including the consideration of water effects, linear distributed line load, and drag forces have been made. The methodology proposed in this study has been examined through the calculation of a number of numerical examples and comparison with available analytical results. Application examples were also provided to demonstrate the applicability of the revised DDA method. In addition, the influence of several important factors such as slope, friction angle, and water depth (or flow discharge) on the initiation of the granular debris flow were studied. The results obtained show that: (1) the DDA method can be a useful tool to model the initiation and mechanism of the granular debris flow under different situations, and (2) the hydrodynamic mechanism of mixed fluid and solid particles needs to be further studied.台灣地區因山坡地開發過度，導致地貌改變，加以九二一地震後地表土質鬆散，故每逢颱風豪雨來襲，各地土石流災情頻傳，近年來災害規模更是嚴重，所以土石流問題已成為現今國人所重視的課題，並不斷的投入調查及研究。 綜合災害案例顯示，台灣中部及東部地區多礫石層崩積土之分佈，因此多形成礫石型土石流之災害，故本研究針對礫石型土石流發生之機制，利用不連續變形分析法(DDA)建立模擬土石流運動之理論與程式架構，並進行初步之應用，以期使DDA能模擬更為複雜與實際之案例。 本研究考慮形成土石流的重要因子，利用DDA進行數值模擬分析，在分析過程中探討坡度、摩擦角及水位等不同的變因對土石流的影響，並進一步應用於研究土石流之啟動機制。分析結果顯示，DDA對於土石流運動之模擬有不錯之適用性，惟對於模擬土石流中水的影響方面，需再深入研究以獲得更接近現地狀況之力學行為。目 錄 頁次 中文摘要.................................................. Ⅰ Abstract..................................................... Ⅱ 目錄.................................................. Ⅲ 表目錄................................................Ⅴ 圖目錄................................................ Ⅶ 第一章 緒論.............................................1 1.1 前言............................................1 1.2 研究動機與目的........................................1 1.3 研究流程........................................2 1.4 研究內容..............................................3 第二章 文獻回顧..........................................5 2.1 土石流概述...........................................5 2.1.1 土石流之定義...................................5 2.1.2 土石流之特性...................................8 2.1.3 土石流之分類..................................10 2.1.4 發生土石流之因素..............................12 2.1.5 土石流數值模擬…………………………………18 2.2 不連續體分析方法....................................19 2.2.1 概述...........................................19 2.2.2 分離元素法與不連續變形分析法...................19 2.2.3 不連續變形分析法之發展.........................21 第三章 理論介紹.........................................25 3.1 不連續變形分析法之理論背景概述.......................25 3.2 不連續變形分析法之理論推導...........................26 3.2.1 DDA之基本假設.................................26 3.2.2 DDA之變形函數.................................27 3.2.3 平衡方程式....................................29 3.2.4 塊體運動理論..................................32 3.3 DDA結合水力機制之理論推導............................33 3.3.1 水壓力項之理論推導............................34 3.3.2 水流對塊石產生之作用力........................36 3.4 DDA之計算流程...................................38 3.5 不連續變形分析法之驗證...............................40 3.5.1 規則塊體於靜水中之驗證.......................40 3.5.2 不規則塊體於靜水中之驗證.....................41 3.5.3 不規則塊體於穩定流中之驗證...................43 3.5.4 塊體於坡面運動之驗證.........................45 3.5.4.1 規則形狀塊體...........................45 3.5.4.2 近圓形不規則形狀塊體...................51 3.5.5 不規則塊體於河床運動之驗證...................55 第四章 數值模擬.........................................59 4.1 幾何模型之建立.......................................59 4.2 土石物理參數之設定...................................60 4.3 土石流之數值模擬.....................................63 4.4 結果與討論...........................................63 4.4.1 坡度對土石移動之影響..........................63 4.4.2 不連續接觸面摩擦角對土石移動之影響............66 4.4.3 水位對土石移動之影響..........................69 4.4.4 影響因子探討..................................71 4.4.5 土石流啟動之模擬..............................72 第五章 結論與建議.......................................75 5.1 結論..................................................75 5.2 建議..................................................76 參考文獻.................................................78 附錄A 平面滑力LEM分析.................................................8