Analysis and Application of Toppling Failure of Anaclinal Rock Slope

• Main Authors: Chen, Kuan-Chih, 陳冠志
• Other Authors: Ke, Te-Chih
• Format: Others
• Language: zh-TW
• Published: 2000
• Online Access: http://ndltd.ncl.edu.tw/handle/13156714035242749895

碩士 === 中原大學 === 土木工程學系 === 88 === Because of steep topography, inferior geological condition and severe climate, slope instability is always a serious problem in Taiwan. Common failure modes of natural slopes are composed of sliding (planar, wedge and circular), toppling, rock-falling and flow. Toppling failure always occurs in anaclinal slopes of layered rock masses, such as thin-bedded sedimentary rocks, foliated metamorphic rocks, and those of one single joint set or hexagonal joint pattern. Such a failure is initiated from the toe region of slope due to undermining of erosion or excavation, leading to the progressive down-slope movement of slope mass above. Because its failure process is quite long, toppling has not been well noticeable in Taiwan. The objective of this thesis is to study the toppling behavior of two-dimensional rock slopes with "block toppling mode". The main analysis tool used is the limit equilibrium method-based "TOP" code, which was derived from the works of Goodman and Bray, and was then extended by Ke. In the parametric study of a regular slope profile, the influence factors under investigation include the slope angle, the base angle of failure surface, the width of rock block, joint dip, and the joint friction angle. The base friction machine first manufactured in Taiwan was also used to perform model tests of a series of toppling slope profiles, with test results being compared with the outcomes of TOP and DDA codes. Finally, two rock slopes along the Northern Cross-Island Road were selected for case study. The results of parametric study indicate that: 1) the required (limiting) friction angle for slope stability and the required support force at the toe of slope both increase with the slope angle; 2) the influence of the base angle of failure surface on support force becomes higher at the larger joint dip; the population of toppling (sliding) blocks decreases (increases) with the base angle of failure surface; 3) the required friction angle and the required support force both decrease with block width (0.5~2.5m); and the population of toppling blocks reduces with block width; 4) the required support force varies inversely with joint friction angle; the population of toppling (sliding) blocks increases (decreases) with the joint friction angle (greater than a certain value). The results of case study using TOP code indicated that the safety factors of the two slopes investigated are both slightly greater than 1.0, and some slope reinforcement should be employed.