Experimental Investigation of the Deformation Characteristics of Natural Loess under the Stress Paths in Shield Tunnel Excavation
Publication: International Journal of Geomechanics
Volume 17, Issue 9
Abstract
Natural loess with large voids and weakly bonded structures is widespread in the arid areas of the world, particularly northwestern China. Recent experimental studies have shown that the mechanical behavior of natural loess is stress path dependent. In practice, soils influenced by the construction of earthen structures may undergo various complex stress paths that are very different from the conventional stress paths commonly considered in geolaboratory experiments. Because of the limitations of current technologies, real stress paths are difficult to obtain from field tests or physical modeling. This study focused on the deformation behavior of natural loess from Jingyang, China, under the stress paths around a shield tunnel. First, the stress paths around a shield tunnel were determined from the numerical data obtained at different positions in a distinct-element simulation of shield tunnel excavation in sand (for simplicity) and by using a novel method referred to as the equivalent stress ratio method. Second, a set of undrained triaxial tests were conducted using the conventional and complex stress paths. The experimental results demonstrate that the deformation characteristics of the loess are different at different positions around the shield tunnel, and the largest deformation appears in the lateral zone (0°). This indicates that the lateral zone is the key zone to be controlled during shield tunneling. In addition, the relationship between the stress increments and the strain increments varies with the stress path. In a complete unloading path, the behavior of natural loess is largely elastic and linear. On the contrary, in a complete loading path or semiloading path, the behavior is largely inelastic and nonlinear, and this behavior is associated with the stress state and recent stress history. These results are valuable in establishing the constitutive relationships for natural loess under complex stress paths and may be useful for the construction of shield tunnels in loess areas.
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Acknowledgments
This work was financially supported by the China National Foundation for Distinguished Young Scientists (Grant 51025932), the National Natural Science Foundation of China (Grant 10972158), and the China Postdoctoral Science Foundation (Grant 2012M511669). All support is greatly appreciated.
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Published In
International Journal of Geomechanics
Volume 17 • Issue 9 • September 2017
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© 2017 American Society of Civil Engineers.
History
Received: Mar 31, 2016
Accepted: Mar 28, 2017
Published online: Jul 7, 2017
Published in print: Sep 1, 2017
Discussion open until: Dec 7, 2017
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