暴雨誘發邊坡崩滑運動模擬與模擬方法改良

Abstract

台灣地質較為破碎，梅雨季與颱風季期間常降雨劇烈，暴雨往往誘發大規模地滑崩塌。若崩塌體運移而下堵塞河道形成天然壩，則可能使河道產生迴水而形成堰塞湖。根據堰塞湖案例的統計，壩體常在形成後之短時間內潰決，有可能造成相當大的災害，若能掌握更多天然壩與堰塞湖形成之相關資訊，當能提供有助於防災跟救災決策的相關資訊。然而快速潰決之天然壩體相關資訊往往不易事後獲得，因此有必要進行天然壩之模擬重建。本研究改良滲流力驅動崩滑的模擬機制，利用PFC3D軟體進行天然壩之模擬重建，改良的方式是將崩塌體劃分為不同的子分區，計算應施加於各子分區內之單位體積滲流力，期能更合理的模擬邊坡因暴雨誘發地滑的過程。此外也提出一套簡易的抗剪阻抗折減機制，藉由此折減機制可合理考慮降雨後地下水位上升之效應，亦能改善以往多依賴試誤法以估計抗剪阻抗之作法。經由太麻里包盛社堰塞湖的參數探討，可展示藉由本研究所提出之方法，確實可使啟動地滑的摩擦係數不至於過度降低，改善以往模擬時不合常理摩擦係數過低之假設，可驗證此方法之可行性。本論文進而運用此方法於其他堰塞湖案例之重建。

For unfavorable geological conditions, heavy rainfall may result in large scale landslide during a torrential or typhoon season. If the run out of the landslide mass blocks a river, a barrier lake may form and create additional hazard. According to the statistics of barrier lake cases, a landslide dam has a high chance to breach in a short time; its breach may cause serious problem to the downstream of the dam. More information about the behavior of landslide dams can help to plan the strategy and management of hazard prevention. However, the real data of a breached landslide dam may not be retrievable after the prompt failure of the dams. Under the situation, reconstruction of the formation process of a previous landslide dam hence can help to provide precious information for future hazard management. The goal of this thesis is to improve the simulation approach for modeling the trigger and run-out of a rainfall-induced landslide. The particle flow code PFC3D is used to simulate the formation process of landslide dams. The improved approach in the study considers seepage forces inside the landslide mass by zoning the slide mass into several sub-regions within the mass then calculate the seepage force per unit volume in each sub-region. By zoning the landslide mass, the distribution of seepage force can be better considered. Moreover, a simple approach for reducing frictional coefficient is proposed to consider the effect of pore water pressure inside the landslide mass due the rise of the ground water table. The proposed approach does not need to rely on a trial-and-error process to identify the appropriate friction coefficient for modeling the trigger and run-out of a landslide. A parametric study of the Tai-Ma-Lee landslide dam case demonstrates that the proposed approach can reasonably trigger the landslide without the need to overly reduce the frictional coefficient. Reconstructions of other landslide cases are also presented in this thesis.