摘要
　　近年來南部國道陸續興建完成，然而沿線所大規模削切的邊坡大多屬於軟弱岩層如軟弱砂岩及泥岩，且我國因屬島嶼型氣候故常有豪大雨產生。基於岩性、氣候、設計不當等影響下，常造成南部國道軟岩邊坡的破壞，進而影響行乘安全。為了進一步研究邊坡的破壞機制，須了解軟岩在大變形後的力學特性，因此本研究中擬設計環形剪力試驗儀探討軟弱岩石材料在大變形後的真實殘餘剪力強度以提供設計者作為參考。文中並對環形剪力試驗儀做一詳細介紹。
　　在試驗部分首先針對台灣西南部地區的關廟層砂岩、古亭坑層泥岩及砂泥岩互層進行基本物理性質、電子顯微鏡分析(SEM)、元素分析(EDS)、崩解耐久性試驗、超音波試驗、單軸壓縮試驗、直接剪力試驗、環形剪力試驗等，以求得其物性、微觀構造及完整的力學特性及參數。
　　由試驗結果顯示此兩種岩石材料皆符合I.S.R.M.所建議的軟弱岩石的定義，且因成岩時間較短、材料孔隙比高、膠結性差，屬於極低到低崩解耐久性材料。此外，在殘餘剪力強度的探討中得其大小順序為砂岩>泥岩>砂泥岩互層，可知在軟岩邊坡中以互層界面的滑動潛能最大。而在環形剪力試驗與直接剪力試驗的比較中，因直接剪力試驗無法維持固定的剪動面積且剪斷變位不大，因此所得的殘餘剪力強度有偏高的現象。另外，含水量亦是影響殘餘剪力強度之一大重點，試驗結果知飽和試體的殘餘剪力強度明顯較氣乾試體減少30~40 %。
　　綜合以上的試驗結果知環形剪力試驗儀是獲得軟岩在大變形剪斷下之殘餘剪力強度的適當儀器，在未來的研究中將帶來更多的幫助。

Abstract
　　In the past few years, with the completed highways and their branches in southern Taiwan, there was extensive slope-cutting and unsuitable slope-protection along the highway. Thus, most of the slope failure happened during the oceanic climate rainfall. Moreover, in this area, the special layers mainly composed of crushed Tertiary sediments, including sandstone, sandy-shale, mudstone and a part of grindstone. Owing to the short diagenesis time of layers, the property of rock is soft and easy-collapsed by water. It affects the strength of rock extremely and results in many problems in engineering. Because of the properties of rock, climate, and unsuitable design, it results in the damages of slope of soft rock along southern highways; moreover, affects the safety of transport. In order to analyze and solve the problems in engineering, realizing physical properties, mechanical characters, and residual shear strength of the rock is necessary for the basis of slope stability analysis and design.
　　In this study, a new ring shear test is performed for Sandstone、Mudstone and the interface, to measure the residual shear strength and simulate the landslide along slip surface. Since direct shear tests are unable to supply constant shear area and large shear displacement, the study tries to develop a ring shear test to measure the residual shear strength of the smooth specimen after deforming greatly. According to the test, the residual shear strength parameters on sandstone of direct shear test and ring shear test are 36∘and 30∘in dried while 31∘and 28∘in saturation. On the other hand, from the images of Scanning Electron Microscopy, grains of sandstone were broken after shearing and formed a shear zone. With progress of shear displacement, extreme grain crushing occurred within the shear zone and shear strength reached residual condition. As a result, ring shear test will be performed to measure the residual shear strength parameters after deforming greatly

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