Identification and zonation of deep-seated toppling deformation in a metamorphic rock slope
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ORIGINAL PAPER
Identification and zonation of deep-seated toppling deformation in a metamorphic rock slope Weihua Zhao 1 & Chengqiang Zhang 1 & Nengpan Ju 1 Received: 5 February 2020 / Accepted: 26 October 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Identifying deep-seated toppling failure presents unique challenges for the study of natural slope deformation in mountainous regions. In the absence of an effective quantitative approach, this study aims to provide a comprehensive grading system in order to establish a slope engineering geological model that can evaluate the deformation of a deep-seated metamorphic toppling slope. The toppling slope used in this study, located in Zhala, southwest China, affects a large area with a deformed rock mass of over 2.5 million m3. In order to objectively reflect the intensity of rock mass toppling, the deformation phenomena of this deep-seated toppling slope are first described in detail. Then, a grading index system is proposed to evaluate the degree of toppling deformation. This comprehensive index system includes the dip angle change of the rock strata, tensile cracks, rock mass structure, weathering grade, and longitudinal wave velocity. The toppling slope is divided into four toppling intensity zones: a completely toppled zone, a highly toppled zone, a moderately toppled zone, and an un-toppled zone. The detailed description and subdivision of the degree of deep-seated toppling deformation is the basis of establishing a fine engineering geological model. Different from the previous when the bottom boundary of toppling was considered as the only potential control boundary, this paper reveals that there may be multiple potential control slip zones in the deep-seated toppling slope, and different deformation degree zones correspond to different stability. As an engineering slope, engineering treatment measures can be formulated according to the degree of toppling deformation. Keywords Deep-seated toppling slope . Deformation characteristics . Toppling intensity zoning . Grading index system
Introduction Toppling failure is one of the most serious and hazardous types of rock slope instability or underground opening (De Freitas and Watters 1973; Goodman and Bray 1976; Wang 1981; Ishida et al. 1987; Goodman 1989; Aydan and Kawamoto 1987, 1992; Adhikary et al. 1996, 1997; Adhikary and Dyskin 2007). Previous research has shown that toppling is predominantly confined to the shallow part of an anti-dip slope close to the slope surface (Table 1, Evans and De Graff 2002; Leandro et al. 2010; Zhou et al. 2012 and Zhang et al. 2015). In the last 20 years, however, toppling
* Weihua Zhao [email protected] 1
State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, Chengdu 610059, Sichuan, China
failures at even more than 200 m depth have been recorded in southwest China, resulting in deep-seated, deep-seated landslides (Table 2; Huang 2013; Liu et al. 2016; Huang et al. 2017), which deviate f
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