Evolution of macro-meso properties of intact loess under long-term seepage and its influence on irrigation-induced loess flowslides

• Published in: Journal of mountain science Vol. 19; no. 10; pp. 2935 - 2951
• Main Authors: Jian, Tao, Kong, Ling-wei, Bai, Wei, Liu, Bing-heng, Sun, Zhi-liang
• Format: Journal Article
• Language: English
• Published: Heidelberg Science Press 01.10.2022; Springer Nature B.V
• Subjects: Casualties; Earth and Environmental Science; Earth Sciences; Ecology; Economic impact; Environment; Evolution; Flowslides; Geography; Hydrostatic pressure; Ion concentration; Irrigation; Irrigation water; Liquefaction; Loess; Mechanical properties; Membrane permeability; Microstructure; Mineral composition; Original Article; Permeability; Plastic deformation; Pore pressure; Pore water; Pore water pressure; Porosity; Seepage; Shear properties; Shear strength; Shearing; Submarine springs; Triaxial tests; Water flow; Water pressure; Water seepage; Undrained shear behavior; Flowslides; Long-term seepage; Static liquefaction; Intact loess
• ISSN: 1672-6316; 1993-0321; 1008-2786
• DOI: 10.1007/s11629-022-7417-3

The loess tableland provides an excellent site for people to live and cultivate. However, flowslides occur frequently on the slope of loess tablelands due to agriculture irrigation, resulting in serious economic losses and casualties. The structure degradation effect of irrigation water seepage on intact loess leads to a weakening of its mechanical properties, which may be responsible for the recurrent occurrence of flowslides in irrigated loess tablelands. In this paper, seepage tests and triaxial tests were carried out to investigate the evolution of the microstructure and undrained shear properties of intact loess during seepage. The results show that water seepage leads to a significant decrease in pore water ion concentration and migration of fine particles with water flow, but no noticeably change in mineral composition. During seepage, the metastable structure of intact loess collapses, the fine particles disperse around the skeleton particle to fill the pores, and the total porosity decreases. The permeability coefficient gradually decreases with seepage time and then tends to a constant. The saturated intact loess shows strongly contractive behavior during undrained shear and has considerable liquefaction potential. After seepage, the intact loess is characterized by more rapid build-up of pore water pressure and more intense strain-softening during shearing and has lower shear strength (including peak strength and steady-state strength). In irrigated loess tablelands, long-term seepage could weaken the shear strength of intact loess and increases its liquefaction potential, which contributes to the initiation of loess flowslide failure and the movement with high-speeds and long run-outs.