南橫公路為連絡南台灣東西部的交通要道，兼具觀光旅遊及國防等功能。2004年7月2日敏督莉颱風帶來豪雨，造成南橫荖濃到埡口至少120處山崩，交通中斷36天。野外工作發現大半山崩屬於淺層碎屑崩塌，碎屑來源與崩塌機制值得深入研究。 南橫公路西段從荖濃到埡口，大部分路段穿過梅山層硬頁岩，風化碎屑主要來自硬頁岩，快速風化的硬頁岩是影響南橫山崩的重要因子。本研究利用岩石單壓強度會隨著風化進行而降低，嘗試測量岩石的風化速率，以瞭解岩石風化因子與山崩之關聯性。 測量岩石單壓強度有許多方法，例如超音波試驗、點荷重試驗、單壓試驗、岩石消散耐久試驗等。施密特（Schmidt）硬度錘試驗不須採樣，不會破壞試體，岩石留在現地逐月風化，每月去測量，可得到岩樣單壓強度的改變而求得風化速率。 本研究以南橫岩石樣本，於現地利用施密特硬度錘，每月測量其單壓強度，連續測量4個月。結果發現南橫出露岩石，風化最快的是硬頁岩，其風化速率78.8百萬帕/年；風化最慢的是板岩，其風化速率是13.5百萬帕/年。單壓強度超過80 MPa的新鮮硬頁岩，經4個月的風化後，單壓強度降為約8 MPa，同時，鉛筆構造出現。根據現地調查發現許多硬頁岩組成之山坡發生山崩，多導因於硬頁岩風化碎屑受重力或因下雨沖刷，形成淺層碎屑崩塌。另根據山崩統計結果發現，風化速率與山崩之崩塌比有高度之相關性。 The South Cross-Island Highway connects the east and west of southern Taiwan. Mindulle Typhoon brought about 2200mm precipitation from June 30 to July 5, 2004, and induced over 120 landslides along the road. As a result of the investigation, many landslides belong to debris slide. The source of debris and the mechanism of landslides were studied in this research. Western part of the highway from Laonong to Yakou passed through Miocene Meishan Formation（about 12-16 Ma）. Field study indicates that the debris came from weathering of dark gray argillite. The weathering rate of argillite is very quick. It is the main cause of the landslides. Determining the rate of weathering is not an easy task. Schmidt Hammer Test was used in this study. Because of the hammer is light for the field work as well as no core is required. The Uniaxial Compressive Strengths（UCS）of argillite were tested every month on site for four months from 2004.11.5 to 2005.3.13. After four months, the UCS of fresh argillite dropped to 8 MPa and pencil structures were produced. The average weathering rate of four argillite samples tested is 78.8 MPa/y. On the other hand, the average weathering rate of slate is only 13.5 MPa/y. Field observation also confirmed that the number of landslides is proportional to the rate of weathering. Therefore, the landslides on the South Cross-Island Highway is concluded to be attributed to the weathering of rock, especially argillite.
