Experimental study of the microstructure of loess on its macroscopic geotechnical properties of the Baozhong railway sub
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ORIGINAL PAPER
Experimental study of the microstructure of loess on its macroscopic geotechnical properties of the Baozhong railway subgrade in Ningxia, China Zhao Meng 1 & Chen Liyi 1
&
Wang Shanyong 2 & Wu Honggang 3
Received: 26 December 2019 / Accepted: 24 April 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Loess is found all over the world, accounting for about 10 % of the world’s total land area. This soil exhibits a distinctive behavior that is related to their formation history, mineralogy, and microstructure, which can cause serious geotechnical engineering problems. This paper presents the microstructural evolution of the subgrade loess of the Baozhong railway in Guyuan. Particularly, the collapse potential, shear behavior, and the influence of microstructure on them are experimentally studied. The results reveal that the top loess contains more clay content, and the grains with a size of 1–20 μm are significantly more than those of the middle loess and the bottom loess. These particles usually have the effect of combining quartz, feldspar, and other particles. In addition, the macroscopic mechanical properties of top loess are more influenced by intergrains cementation bonds and are more sensitive to water. As a comparison, the middle and bottom loess are more influenced by its loose interstructure and are more sensitive to compression. Based on the analysis of microstructure, a cyclic process model which link the pore change and particle packing is proposed. It is demonstrated that the particle packing is closely related to the change of pores. While the pores decrease to a minimum, the particle packing changes to a bridged random close packing. This mechanism can be used to explain the uneven settlement of the Baozhong railway subgrade in Ningxia. Keywords Collapsible loess . Microstructure . Geotechnical properties . Pore change . Particle packing
Introduction Loess is found all over the world, accounting for about 10 % of the world’s total land area (Dudley 1970; Chen et al. * Chen Liyi [email protected] Zhao Meng [email protected]; [email protected] Wang Shanyong [email protected] Wu Honggang [email protected] 1
State Key Laboratory of Geo-Hazard Prevention and Geo-Protection, Chengdu University of Technology, Chengdu 610059, Sichuan, China
2
Priority Research Centre for Geotechnical Science & Engineering, The University of Newcastle, Callaghan, NSW 2308, Australia
3
China Northwest Research Institute Co. Ltd. of CREC, Lanzhou 730070, Gansu, China
2006; Gaver 2012; Li et al. 2016). It is widely recognized that loess has a metastable structure, the particles are randomly, loosely, and openly stacked, resulting in a high porosity and a low density, which is directly related to its airfall deposition(Liu 1985; Lommler and Bandini 2015; Zhang et al 2018). In addition, it is easy to suddenly reduce the total volume or collapse when wet (Gao 1980; Monroy et al 2010; Muñoz-Castelblanco et al 2012; Wen and Yan 2014). In the loess area, man
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