運用分離元素法模擬落石撞擊明隧道之破壞模式

DEM Simulation of Rock Shed Failure due to Rockfall Impact

陳建安(Jian-An Chen)

指導教授 ： 林銘郎

國立臺灣大學/工學院/土木工程學研究所/碩士(2013年)

https://doi.org/10.6342/NTU.2013.00120

摘要

常用來抵擋落石威脅的人造設施為明隧道(Rock Shed)，其功能為讓道路上邊坡的落石從棚頂通過，直接往道路下邊坡滾落。當落石擊中明隧道造成損害，其可能之破壞型態包括明隧道全毀、頂版貫穿、版樑撓曲、柱挫屈、地梁基礎毀壞等五種破壞型態，為了避免明隧道遭到破壞並可令其在邊坡災害敏感區內具有臨時避難場所之功能，以減少人員傷亡及財產損失，故探討落石造成明隧道破壞之主控因子有其必要性。
有鑑於此，本研究以分離元素法之顆粒力學軟體Particle Flow Code 2D (PFC 2D)，進行明隧道破壞行為之數值模擬。首先，以模擬單壓試驗方式校核輸入之微觀參數的正確性，進而以衝擊力及塊體撞擊等方式探討落石造成明隧道破壞及對下邊坡之影響，並以阿里山台18線道路之明隧道作為案例探討。
依據數值模擬結果，落石墜落位置、落石量體、垂直落距以及明隧道結構主控了明隧道之破壞形式，其中，明隧道結構則分為梁柱接頭及地梁基礎進行討論。模擬結果顯示，貫穿破壞及撓曲破壞常主控於量體及落距，差異沉陷破壞則主控於撞擊位置及地梁基礎設置之有無，而梁柱接頭之設置使明隧道之梁較易沿著接頭處損壞，具有避免落石直接貫穿的效果。此外，地梁基礎形成閉合結構除了避免差異沉陷，並可保護道路路基以降低下邊坡之危害，而梁柱接頭設置符合強柱弱梁(strong column and weak beam)之精神，避免落石貫穿直接影響明隧道內之人車安全，應於明隧道設計時納入考量，以確保用路人之安全。

關鍵字

落石災害 ； 現地調查 ； 明隧道 ； 分離元素法 ； 台18線

並列摘要

The rock shed is a more costly but effective traffic facility used to keep out falling rocks in Taiwan. The main function of rock shed is to let the falling rock passing through via the top slab without hitting the road users. The failure mode of the rock shed due to rockfall impact generally includes punching of top slab, flexural cracks of beam, buckling of column, and damage of foundation, etc. Even so, the failure behavior of the rock shed is still complicated and difficult to predict.
Accordingly, this study adopts the discrete element program (PFC2D) to simulate the failure behavior of rock shed. A comparison with uniaxial compression test was carried out firstly to determine the micro parameters of structure elements. Th e model was utilized to simulate the behavior of rock shed with impact load or hitting of falling block separately. Then, a case study of present rock shed of highway NO.18 in middle Taiwan was analyzed.
The result indicates that: the primary causes of rock shed failure mode include block size, falling height, impact position, and structure system. The failure mode of punching shear failure or flexural cracks is dominated by block size and falling height. The occurrence of differential settlement is related to impact position and absence of combined footing. Considering the connection of beam and column, the structure is more likely to break at the joints rather than punching of the top slab. As a result, combined footing and beam-to-column joint should be to take into account to obtain safer protection of rock shed.

並列關鍵字

rockfall disaster ； PFC ； rock shed ； discrete element method ； highway NO.18

參考文獻

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