| Summary: | 碩士 === 國立中央大學 === 應用地質研究所 === 94 === 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.
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