中橫公路大沙溪路段工程地質特性對公路養護之影響

山區道路交通量低，卻常因具有社會發展、國土保育與災害防治的需求，而需投入大量的養護資源。掌握山區道路易致災路段並釐清其影響因素，有利於研擬適當養護策略與工法。本研究針對台8線中部橫貫公路大沙溪路段，蒐集逾60年的歷史遙測影像，套疊影像、糾正變形、產製數值地表模型，繼而描繪公路路線以及崩塌、蝕溝等發育位置，據以選擇公路線形及結構型式變化較大區段，探討公路養護受環境與工程地質因素的影響。研究範圍約9.4公里路線長度，自1960年公路建成迄今，共有4個路段路線向山側偏移或改採隧道穿越，1處路工邊坡改建為明隧道型式，抑低邊坡崩塌或河岸側蝕的影響。與公路線形或結構型式調整有關的邊坡崩塌、蝕溝發育位置，皆位於大沙溪河道急彎處，且鄰近地層界面。地層界面附近因岩質不同造成差異侵蝕，以及岩層工程地質特性差異大，應為研究範圍大沙溪河岸側蝕、公路邊坡蝕溝在流水作用下相對快速風化，以至於在長期降雨、地震等因素作用下導致邊坡崩塌，成為造成公路改線及改建明隧道的重要影響因素。

關鍵字

山區公路；改線；邊坡崩塌；河岸側蝕；差異侵蝕；地層界面

並列摘要

Mountain highways have low traffic volume. However, their maintenances that require huge resources and cost are typically necessary due to the needs of social development, land conservation and natural disaster prevention and response. Recognizing the vulnerable sections of a mountainous highway and associate factors that influence their usual operation is conducive in the development of appropriate maintenances strategies and related measures. Taking the Dasha River section of the Central Cross-island Highway (Tai-8 line) as an example, this study collects historical remote sensing images for more than 60 years, processing images and interpreting highway routes, landslides and gullies at different times to identify the sections that have been rerouted or have highway structural type modifications, in order to investigate the environmental and engineering geological factors that affect the highway maintenance. Results of images interpretation reveal that, in the 9.4 km long mountainous highway studied and since the completion of the highway in 1960, four local sections have been rerouted toward hillside, even went through by tunnels, and one section has structural type modification to mitigate the influence of landslides and/or lateral erosion of the river. The locations of landslides and gullies development that are related to roads rerouted and structural type modification are all neighboring to some sharp turns of the Dasha River and adjacent to boundaries of geological strata. The differential erosion rate caused by various lithological properties and significant changes in engineering characteristics of rock masses in the vicinity of strata boundaries account for the relatively intense lateral erosion along the river and rapid development of gullies under the impact of runoff, which are also important geological factors related with the reroutes and structural modification of highway, in association with the long-term influences of rainfalls and earthquakes.

並列關鍵字

Mountainous highway ； reroute ； landslide ； bank lateral erosion ； differential erosion ； geological strata boundary

國際替代計量

中橫公路大沙溪路段工程地質特性對公路養護之影響

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