• 作者： 徐鐵良
• 作者服務機構： 臺灣省地質調查所
• 中文摘要： 北部橫貫公路主要部份乃沿大漢溪修築，聯結西部大溪鎮及東部之宜蘭。沿溪最發達之地形計有峽谷、河階、及切蝕河灣等。從地形之表現，可知此區尚在幼年侵蝕期階段，反映此區地盤自更新世以來一直強烈的上升。 由於地形因素的支配，公路經過之處多屬陡峭坡麓，對於公路基礎之穩定，頗受影響。地質方面，除小部地區為中新世外，餘多屬於漸新世與始新世之地層。漸新世與始新世之地層，均多為曾經輕度變質之沙岩及頁岩所組成，大桶山層及澳底層，即為其主要代表。除氣候因素之外，地形與岩層之性質實為影響公路安定之重要原因。較嚴重之公路崩坡集中於榮華至萱原間長約二十公里之路段內(34－54K)。分佈於此地區內之地層為大桶山層及澳底層。兩地層內皆含有多量之板岩或硬頁岩，最易風化崩落。每遇豪雨，更常有公路崩坡之發生。 山崩之方式以岩石或岩屑之滑落二者為主。坡麓陡立之處亦常有岩屑或岩石之崩落。 穩定邊坡之道，在通用之各種方法中，以檔土牆及植生保護方式，較為簡便易行。河岸為流水侵蝕更為此區崩坡發生之基本原因之一。石門水庫攔沙壩之興建，可以減緩河流侵蝕，對於道路邊坡穩定，亦有助益。
• 英文摘要： The Northern Cross-island Highway located between Tachi and Ilan isbuilt along the Tahanchi valley where gorgeous valleys, river terraces, andincised meanders are well developed. This type of landform reveals thatthe region has been youthly dissected and vigorously uplifted since Pleisto-cene. As a characteristic of the youth landform, steep slopes are extensive inthe region. The highway which goes through the area inevitably faces theproblem of slope stability. The rock formations distributed in the region are composed of a con-siderable amount of slate or argillite. Besides the climatic factor the geo-morphic feature and the lithology of the formations in this region are ofsignificance to the stability of the highway. Most of the serious landslidesare distributed in the area about 20 km long from Yunghwa to Hsuanyuan(34 k to 54 k). Both the Tatungshan Formation and the Aoti Formationconsist of slate or argillite. They are friable and fragmentary and areunfavorable as foundation rock for engineering works. Though heavyrainfall is the immediate cause of landslide, however, the occurrence of land-slide is usually where the valley is steep and the rock material is weak. Landslides occur in the Northern Cross-island Highway may be simplydistinguished into types of debris slide and rock slide. Rock or debris falloccurs in places where the slope is steeper. For stabilizing the side slope, the building of retaining wall with vegeta-tion cover seems the best to improve the stability in addition to the con-ventional ways. Since the valley wall is usually steepened by river mean-dering the stabilization of river banks by building check dams or othermeans of protection is helpful.
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