Numerical analysis of loess and weak intercalated layer failure behavior under direct shearing and cyclic loading
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Numerical analysis of loess and weak intercalated layer failure behavior under direct shearing and cyclic loading ZHANG Ze-lin1* WANG Tao2
https://orcid.org/0000-0001-8180-0787;
e-mail: [email protected]
https://orcid.org/0000-0003-0075-3398; e-mail: [email protected]
*Corresponding author 1 College of Water Resources and Civil Engineering, China Agricultural University, Beijing 100083, China 2 Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China Citation: Zhang ZL, Wang T (2020) Numerical analysis of loess and weak intercalated layer failure behavior under direct shearing and cyclic loading. Journal of Mountain Science 17(11). https://doi.org/10.1007/s11629-020-6178-0 © Science Press, Institute of Mountain Hazards and Environment, CAS and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract: The mechanical behavior of the joints inside a loess layer is greatly important in weak intercalation studies owing to its involvement in a wide range of landslides in the loess region in China. The shear behavior of the joints in the loess stratum during direct shear and cyclic loadings was investigated using the PFC2D discrete element software. Loess mudstone and mudstone with weak intercalated layer materials were subjected to direct testing, and cyclic shear tests were conducted with consideration to the influence of normal stress and shear velocity. The macroscopic properties and damage patterns were obtained for six numerical configurations; namely, loess-weathered mudstone with 0°, 10°, and -10° joints and weathered mudstone with 0°, 10°, and -10° weak intercalated layers. The numerical test results revealed that, in the direct shear tests, the shear stress and shear displacement of the samples increased with the normal stress. In the cyclic shear tests with a total cycle number N=20, the shear stress-shear strain curve of the six different configurations exhibited a hysteresis loop. The numerical tests also revealed that, under cyclic shear, the normal stress and shear velocity affected the shear strength. The degree of damage increased as the shear velocity decreased from 0.1 mm/s to 0.005 mm/s for all six numerical configurations. Compared with the damage pattern of the direct shear tests, the damage Received: 30-Apr-2020 Revised: 24-Jun-2020 Accepted: 11-Oct-2020
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of the cyclic shear tests mainly comprised shear cracks and fractures, some shaking consolidation settlement and fewer shear strain occurred around the joints. In the direct shear tests, more compression cracks and fractures occurred in the samples. The damage mainly developed along the joints, and shearing-off damage occurred. The results obtained by this study further elucidate the failure mechanism and microscopic damage response of the joints in the loess stratum in Northwest China. Keywords: Loess; Mudstone; Weak intercalated layer; Direct shear test; Cyclic shear test; PFC2D
Introduction Interfaces such as faults, bedding planes, weak intercalat
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