摘要:山區道路之興建與維護,在調查能力、施工技術及經費預算限制等因素影響下,往往疏於考慮道路邊坡之穩定性所可能造成的災害,以致在近幾年極端氣候高強度長延時之豪雨作用下,經常傳出災情。尤其在道路通過高陡岩坡下方或局部野溪山溝地形之處,很容易因上游源頭區之崩塌落石所造成之岩屑往下游運動,轉變成岩屑崩瀉(rock avalanche)、岩屑流(debris granular flow)、乃至於土石流(debris flow)現象,造成道路沖毀、中斷,若來往車輛正好通過於此,傷亡勢必難免。2007年辛樂克颱風所造成南投縣信義鄉豐丘明隧道南側出口崩塌案例,以及2010年10月梅姬颱風在蘇花公路造成的災害中,112k~116k段最為嚴重,其中116k+30及114k+500上邊坡處即為山溝地形,其道路均被土石流沖毀,而此二處也疑似為創意旅社遊覽車遇難處,車體至今尚未尋獲。
除上述岩屑崩瀉、岩屑流、乃至於土石流影響山區道路用路安全性,山區道路更常有防不勝防的落石災害。常用來抵擋落石威脅的人工設施主要為落石棚(明隧道),其功能為讓道路上邊坡的落石從棚頂無害通過,直接往道路下邊坡滾落,以保護人車之安全。當落石擊中明隧道時,如果量體過大或衝擊力過大常會造成明隧道損毀。如果能確保明隧道不損壞的話,明隧道可充當長距離山區道路之臨時避難區位,減少傷亡,故落石撞擊明隧道之力學模擬研究探討是非常重要的。
前人研究落石運動主要以單顆落石運動或落石群運動為主,有關岩體撞擊後破碎的研究甚少。有鑑於此,本計畫擬以兩年為期,基於已有的落石研究基礎,以分離元素法之顆粒力學軟體-PFC,與物理試驗成果作比對,用以校核PFC分析具節理強度岩體之撞擊破裂行為的能力以及落石對明隧道設施之作用及影響。同時至現地了解明隧道受損災害案例區進行調查,包含發源區的特徵、量體大小、運動坡度、節理特性等,再以PFC分析這些條件對人工構造物影響,同時進行案例之逆推反算分析,期能發展出一套公路線形選擇建議與明隧道受落石撞擊的分析流程。
Abstract: The construction and maintenance of the highway in mountain area, people usually neglect the slope stability in route selection due to the limitations of the following factors: investigation capability, construction technique and time limit for operation. So the disaster occurred frequently under the extreme climate including higher strength and longer duration rainfall induced landslide events in the recent years. Especially the highway which cross the steep and high rock slopes or local gully are usually destroyed by rock avalanche, debris granular flow and debris flow deriving from rockfall or landslide in source area. If just in the time, there was a vehicle passing through, then the harm was inevitable. In 2007, the Typhoon Sinlaku caused collapse of gravel tableland at south bound of Fengchiu Tunnel, Sinyi Town, Nantou County. In October, 2010, the Typhoon Megi caused disaster in the Suhua highway, the most serious sections were 112k~116k. The slopes within sections 116k+30 and 114k+500 are cross valley terrain, besides destroying by debris flow, one bus missed among the two places, and the vehicle had not found yet up to now.
Not only rock avalanche, debris granular flow and debris flow damage to the transportation, but also rock-fall does. The facilities which can divert rock-fall debris away is rock shed. Its main function is that let the rock fall blocks pass through above the shed, ensure the security of passenger. If immense mass body or impact force when the rockfall strike on the shed, that usually lead the shed to collapse. If we can make sure that the shed can stand stably and safely, then the shed can be a temporary shelter a long stretch of highway, and cut down the death toll during rainfall in mountain area. So the simulation and further investigation the behavior of rockfall and its impacting on rock shed are important.
Previous research all most focused on single rock-fall or a group of rock-fall, rarely discussed the breakage of the rock blocks during movement. So we will plan to spend two years on the project, using numerical software PFC(DEM method) calibrate with physical tests, to understand fracturing behavior of rock mass with joint strength during the movement of rockfall. Then we will obtain the characters which include mass amount, slope and joint properties in source area of landslide through field investigation. Finally, using PFC analyze how these condition affect the design of rock shed. Base on the result of these simulations, we will develop a set of analysis processes for rock shed design.