台灣東北部基隆山地區落石災害之研究

本研究以台灣東北部基隆山地區的落石案例為探討的主題，利用現地的地貌表徵，地質材料的分佈，以及不連續面的延伸狀況，來探討當落石向下墜落時，所形成自由落體、彈跳及滾動等三種不同的運動軌跡，以及不同的地質環境特性所可能影響落石的範圍。從研究的結果中發現，落石的「恢復係數」和「摩擦係數」將會是影響其彈跳及滾動等運動軌跡中，最重要的兩個因子。落石的恢復係數主要是會受到坡面的材料強度、入射角、碰撞速度等三項因素的影響。當落石從3 公尺的高度向下墜落時，如果其入射角分別為30°、45°、60°時，其法線方向的恢復係數可以獲得0.18、0.12、0.10。這個意義告知，落石的法線方向的恢復係數，將會隨著入射角的增大而減小。當入射角固定為90°時，落石的高度分別從位於1公尺、2 公尺、3 公尺處向下墜落，其恢復係數分別為0.41、0.35、0.31，由此可見，落石的碰撞速度越大，恢復係數越小。落石的塊體大小相對於斜坡上的堆積石塊大小，也會對落石的運動方式造成影響，當落石的大小尺寸比坡底已經堆積的石塊體積更小時，其運動軌跡易受斜坡起伏的影響，這種影響的類型主要是以彈跳方式的運動軌跡為主。當落石的大小尺寸比坡底已經堆積的石塊體積更大時，則不容易受到坡面起伏的影響，將會持續保持滾動的狀態運動，此時落石的運動主要是會受到摩擦係數的影響，碰撞恢復係數的影響較小。當落石體積增大到一定程度時，則將不會再影響其碰撞恢復係數。研究使用RocFall 軟體，對AA`、BB`、CC`三處剖面進行模擬分析，記錄其自由落體、彈跳及滾動等三種不同的運動軌跡，及落石在運動過程中的能量，這些資料可以作為防治落石災害之重要參考依據。

關鍵字

落石；恢復係數；摩擦係數；自由落體；彈跳及滾動

並列摘要

This study focued on the case of rockfall in the Keelung Mountain Area in the northeastern part of Taiwan. To explore the different trajectories and range including free fall, bouncing and rolling when the rocks fall down, this research tried to analyze the local geomorphological characteristics, distribution of geological materials, and the extension of the discontinuities. In the results, "coefficient of restitution " and "coefficient of friction" are the most important factors which affect the movement trajectory of bouncing and rolling. The coefficient of restitution is mainly affected by the three factors, such as the strength of slope surface’s material, incident angle, and collision speed. In the situation when falling rocks descend from 2m height, and setting the incident angles as 30°, 45°and 60°, we observed the coefficient of normal restitution as 0.18, 0.12, and 0.10. These results showed that, the coefficient of normal restitution of the rockfall inversely decreased with the incident angle. When fixing the incident angle at 90°, the coefficients of restitution were observed as 0.41, 0.35, and 0.31 when the rockfall from 1 m, 2 m, 3 m. This research found that the coefficient of restitution inversely decreased with the collision speed of rockfall. The size of the falling rocks which was related to the size of the block on the slope, also affected the path of the rockfall based on the bouncing movement. When the size of the rock was smaller than the size of the block at the bottom of the slope, the trajectories were influenced by undulation. When the size of the rock was larger than deposited one, the rock was hard to be affected by slope fluctuation, and continue to keep scrolling. At this situation, the movement of the rockfall was mainly affected by the coefficient of friction rather than the coefficient of restitution’s impact. The simulation is carried out using the Rocscience Rocfall program, which depicts the path and energy of rockfall, these data can be used as important reference basis of prevention of rockfall hazards.