Fabric anisotropy; Micro-scale; Triaxial test; Unsaturated soil; Water distribution; X-ray CT; Geotechnical Engineering and Engineering Geology; Earth and Planetary Sciences (miscellaneous)
Abstract :
[en] The mechanical behaviours of unsaturated soils are highly related to the water content and pore water and air distributions. Under the context of climate change, geo-disasters related to soil moisture change attract more and more research attentions. Due to the heterogeneity of soil textures and the complicated morphology of liquid phases, it is crucial to understand the microstructural features of unsaturated soils. This work presents a study based on a miniaturized suction controlled triaxial device which is suitable for micro-CT image analysis. A fine sand is sheared in this device under different suction levels while CT scans are taken at different strain stages. After image 3D reconstruction, image trinarization, label analysis, contact detection and other customized image analysis and calculations, the micro-mechanisms of unsaturated granular soils upon triaxial shearing are investigated. It is observed that the inter-particle contact coordination number is reduced after shearing due to the dilation behaviour and the sample with the highest capillary strength has the highest coordination number. Although there is an initial fabric anisotropy due to gravity and sample compaction, triaxial loading will further enlarge the fabric anisotropy of the solid phase and the solid fabric anisotropy is also associated with shear strength. With the development of shear band, water drains out and the quantity of small-volume liquid clusters in the liquid bridge increases. This shifts the distributions of inter-facial areas. The effective stress tensor is interpreted microscopically based on small RVEs. Based on the CT image analysis, the suction-induced stress component is not an isotropic term and the anisotropy of the water phase is increased with triaxial deformation as well as decrease in degree of saturation when there are more isolated water bridges formed around solid contacts.
Disciplines :
Civil engineering
Author, co-author :
Wang, Ji-Peng ; School of Civil Engineering, Shandong University, Jinan, China
Luan, Ji-Yuan; School of Civil Engineering, Shandong University, Jinan, China
Gao, Xu-Guang; School of Civil Engineering, Shandong University, Jinan, China
Liu, Tai-Heng; School of Civil Engineering, Shandong University, Jinan, China
Andò, Edward; Laboratoire 3SR, Université Grenoble Alpes, Grenoble, France ; EPFL Center for Imaging, École Polytechnique Fédérale de Lausanne (EPFL), Lausanne, Switzerland
François, Bertrand ; Université de Liège - ULiège > Urban and Environmental Engineering ; Building Architecture and Town Planning Department (BATir), Université Libre de Bruxelles, Brussels, Belgium
Language :
English
Title :
A micro-investigation of unsaturated sand in mini-triaxial compression based on micro-CT image analysis
Publication date :
November 2022
Journal title :
Acta Geotechnica
ISSN :
1861-1125
eISSN :
1861-1133
Publisher :
Springer Science and Business Media Deutschland GmbH
F.R.S.-FNRS - Fonds de la Recherche Scientifique NSCF - National Natural Science Foundation of China
Funding text :
This work was funded by F.R.S-FNRS of Belgium (PDR.T.1002.14) and NFSC of China (Nos: 51909139, 52011530458). The first author also acknowledges the support of Taishan Scholar Project of Shandong Province of China.
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