加勁護岸應用於土石流防治之模型試驗

Abstract

本研究透過室內物理模型試驗模擬土石流衝擊地工織物加勁土(Geosynthetic-Reinforced Soil, GRS)壁壘(護岸)之情形。試驗過程中，透過質點影像速度法(Particle Image Velocimetry, PIV)分析土石流前端流速，及顆粒追蹤速度法(Particle Tracking Velocimetry, PTV)觀察特定質點的位移，並於坡趾處架設衝擊力量測裝置量測衝擊力，觀察壁壘受衝擊後之力學行為，且比較不同型式壁壘間的差異，以利整治土石流的參考。 首先，土石流模擬試驗考慮不同的土石流量體，由試驗結果可知，無論量體大小，其前端速度無顯著改變，然而，量體大者初始流速慢，但表面流速最終趨於一致，且經換算與現地土石流流速範圍相符。在衝擊力方面，土石流量體增加，對衝擊力歷時曲線型式影響不大。但量體增加時，最大衝擊力發生時間會隨之延緩，並導致衝擊力上升，然因流深變化的不同，單位面積所受之力並不一定與衝擊力成正比。此外，衝擊力量測裝置架設位置也會影響衝擊力大小，裝設在側邊之衝擊力約為中間處的0.9倍，且衝擊力消散所需之時間較長。 其次，進行土石流衝擊壁壘試驗，考慮加勁層以黏接式及回包式牆面之兩種型式壁壘，土石流受壁壘阻擋改變其流動方式，致使黏接式壁壘所受之正向力較大、剪力較小，造成受衝擊段之受力側凹陷及背力側凸出變形皆大於回包式壁壘，水面交界處之角隅破壞、磨損情形較嚴重。回包式壁壘屬較柔性結構，其基礎背力側有明顯的側向變形，反之，黏接式壁壘卻導致整體側移，但兩壁壘皆無漏土或整體性破壞，驗證GRS壁壘確實能發揮其加勁功用。

In this study, a small-scale model test was conducted to simulate the impact of debris flow on reinforced-soil structures. Materials were selected according to similitude laws to simulate the particle size distribution of the material at a debris flow site (Fengchu) and the geosynthetics. During the test, the movement of the materials was recorded by three video cameras. The analyses of the front velocity and mean velocity for specific particles were performed by particle image velocimetry (PIV) and particle tracking velocimetry (PTV). Moreover, a device was set up at the toe of the slope for measuring the impact force from debris flow. The variations in velocity and impact force were studied in terms of different quantity of flow. The mechanic behavior of the barriers (revetments) and comparison between two types of barriers were discussed. In the debris flow simulation test, flows of different quantities were considered. According to the physical test result, the variation in front velocity was not obvious. However, the quantity of flow had influence on the mean velocity. Although the initial mean velocity of large quality flow was slower, the mean velocities of flows with different quantities were almost the same. Regarding for the impact force, the quantity of flow had little influence on the pattern of time history. As the quantity of flow was increased, the maximum impact force increased as well; nevertheless, the impact force per unit area was not increased proportionally to the impact force. It was found that the impact force at the middle was larger than that at the side of the flow. To measure the impact of debris flow on reinforced-soil structures, two types of barrier, wrap-around and glued facings, were taken into consideration. Based on the observation, the glued-facing barrier depressed more at the up-stream side and bulged more at the downstream side than the wrap-around barrier. After uncovering the embedded layer, the foundation of wrap-around barrier had significant lateral deformation at the downside; while the glued-facing barrier had small overall sideway movement. Both barriers did not have rupture of reinforcement or soil washed out, indicating the good function of the GRS barriers.