模擬岩塊受震滑動之動態摩擦行為初探

Abstract

岩石邊坡與土壤邊坡最大的差異在於岩石邊坡發生破壞往往沿著弱面破壞，此種有主要滑動面之邊坡破壞的行為，於1965年Newmark提出了滑動塊體法，為這類邊坡穩定性分析注入了新的分析方式。 在滑動塊體法中，提出了臨界加速度的觀點，當可能滑動之塊體所受的地震加速度超過其所能承受之臨界加速度時，塊體便會滑動產生永久位移。此方法假設塊體之臨界加速度為一定值，滑動面間的摩擦行為造成之影響暫不考慮，且臨界加速度係以靜態力平衡的狀態下得到。在前人的研究中，透過尖峰摩擦角所定義的臨界加速度，計算得到之累積位移量會有低估的現象，而以殘餘摩擦角定義之臨界加速度則是會有高估現象，因此也有學者提出了臨界加速度衰減的概念或塊體滑動後即採用殘餘摩擦角進行計算。 因此本研究便是基於滑動塊體法的基本概念，利用模擬岩塊於小型震動台進行一系列之實驗，首先探討震動條件下，塊體滑動時的即時靜摩擦角 是否與靜態條件所得到之靜摩擦角 相同，更進一步的探討受震滑動歷程中滑動面間的摩擦行為，並且探討震動頻率、滑動塊體正向應力及材料特性對即時靜摩擦角 、滑動歷程之摩擦行為的影響。 本研究中發現震動頻率及正向應力皆會對震動條件下，塊體的即時靜摩擦角 造成影響，當基盤的震動頻率提高，塊體的即時靜摩擦角 會有提高的趨勢；塊體的正向應力增加時，反而塊體的即時靜摩擦角 會有降低之趨勢。

Different from soil slope, the failure of rock slope destroyed along weak plane. Accordantly, block sliding method for these slope stable analysis was be devised by Newmark in 1965. A new point “critical acceleration” was devised in block sliding method; when block acceleration induced by earthquake exceed the “critical acceleration” of the sliding interface, the permanent displacement of sliding block was happened. However, in the method, “critical acceleration” derived from static force equilibrium was assumed to be a constant. The “critical acceleration” determined by peak friction angle could resulted the underestimate of permanent block sliding displacement; the “critical acceleration” determined by residual friction angle could resulted the overestimate of permanent displacement. Base on block sliding method, in this study, there were series experiments by using shake table. At first, to compare the instantaneous static friction angle of block obtained from shake table experiment and static friction angle obtained from tilt test, and then to investigate the influence of block frictional behavior by following factor: frequency of base vibration, normal stress of block, material of block. In this study, the instantaneous static friction angle of block was affected by frequency of base vibration and normal stress of block under dynamic shaking condition. When the frequency of base vibration was higher, the instantaneous static friction angle of block was higher; the instantaneous static friction angle of block reduced when the normal stress of block increased.