Formation and chemo-mechanical characteristics of weak clay interlayers between alternative mudstone and sandstone seque
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ORIGINAL PAPER
Formation and chemo-mechanical characteristics of weak clay interlayers between alternative mudstone and sandstone sequence of gently inclined landslides in Nanjiang, SW China Jie Liu 1 & Qiang Xu 1 & Sen Wang 1,2 & Srikrishnan Siva Subramanian 1 & Liang Wang 1,3 & Xing Qi 4 Received: 31 December 2019 / Accepted: 20 May 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Sedimentary rocks with alternating mudstone and sandstone sequence are susceptible to landslides even under very gentle slope inclinations. Continued occurrences of such landslides in Nanjiang, South Western part of China, bring out the necessity for more understanding of their failure mechanism. In this study, we present a series of investigations on the physical, chemical, and mechanical characteristics of weak interlayers during their formation at landslide slip surfaces, both in macro- and microscales. Our field investigations at these deep-seated landslides revealed the presence of extensive weak interlayers of clay in between alternating sandstone mudstone formations. Tectonic processes combined with loading and unloading effects and strain incompatibility might lead to the argillization of rock by easing water intake, which leads to the formation of these weak layers. We studied how changes in material microstructures, mineral composition, and ionic concentrations during the formation process (argillization) might cause a fall in mechanical strength. We found that degradation of mechanical resistance takes place even at the initial stages of argillization and shear strength of the weak layers decreases proportionally to the time of saturation and argillization. Keywords Landslides . Red layers . Argillization process . Weak interlayer . Micro-characteristics
Introduction Layered and interbedded sandstone and mudstone formations, known as “red layers” or “red beds,” are widespread in the Sichuan basin, the Three Gorges Reservoir area, and in North Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10064-020-01859-y) contains supplementary material, which is available to authorized users. * Qiang Xu [email protected]; [email protected] 1
State Key Laboratory of Geohazard Prevention and Geoenvironment Protection, Chengdu University of Technology, Chengdu 610059, Sichuan, China
2
China Railway Eryuan Engineering Group Co., Ltd., Chengdu 610059, China
3
College of Architectural Technology, Chengdu 610399, Sichuan, China
4
Opening Project of Sichuan Province University Key Laboratory of Bridge Non-destruction Detecting and Engineering Computing, Zigong 643000, China
Western regions of China. These geological structures are widely recognized as landslide prone, with catastrophic consequences (Fan et al. 2009; Xu et al. 2016) (Zhang et al. 2016). Remarkably, landslide occurrences were observed even at slope angles between 3° and 20°, a value that is noticeably lower than conservative estimates of the internal friction angle of both the materials necessitating fu
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