![]() The direct or vane shear test can’t effectively model this type of stress environment. Under the influence of a dynamic load from the working chamber pressure and rotation of the shield screw conveyor, the conditioned soil in the spiral groove is subjected to additional stress in the pure shear state and in the spiral rotation of the principal stress axis. ![]() For example, the main factors affecting the mechanical properties of the contact surface and basic laws have been obtained via experimental studies, and a constitutive model describing the mechanical properties of the contact surface has been established by Zhang and Min. The model machine test is a basic method that studies the mechanical properties of the interface between muck and the EPB structure. It is currently one of the key research subjects related to the physical and mechanical properties of conditioned soil. Research on the static and dynamic characteristics of the interface between muck and an earth pressure balance (EPB) shield screw conveyor structure is concerned with frontier issues, such as nonlinearity, large creep and discontinuity. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Ĭompeting interests: The authors have declared that no competing interests exist. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.ĭata Availability: All relevant data are within the manuscript and its Supporting Information files.įunding: This research was funded by the National Basic Research Program of China under Grant 2015CB057802 and the Jiangmen City Foundation and Theoretical Science Research Science and Technology Project, NO. Received: SeptemAccepted: FebruPublished: March 13, 2019Ĭopyright: © 2019 Li, Tan. PLoS ONE 14(3):Įditor: Jianguo Wang, China University of Mining and Technology, CHINA The model provides an important theoretical basis and references for the design and optimization of soil conditioning during shield tunneling.Ĭitation: Li X, Tan N (2019) Calculation model of the equivalent spiral shear stress of conditioned sand. The results of the indoor test of the model machine verified the rationality and effectiveness of the theoretical model. The conditioned standard sand was used in the indoor tests. ![]() Based on the analysis of the stress conditions and the movement of the conditioned soil plug, the theoretical calculation model of the equivalent helical shear stress of the EPB shield screw conveyor was deduced based on the steady-state equilibrium conditions of moment of momentum. To better investigate the shear properties between the soil and the shield conveyor casing, a model screw conveyor was developed. The direct or vane shear test is now widely used to evaluate soil flow plasticity. During the progress of the EPB shield screw conveyor normal operation, the shear effects between the muck in the spiral tube and the screw shaft, as well as the flight, are different from the shear action, such as the direct shear or the vane shear. The spiral shear stress is the main determinant of the soil flow plasticity. Soil is the medium that balances the soil and water pressure on the excavation surface of an earth pressure balance (EPB) shield machine, and the soil flow plasticity directly affects the working performance of the shield machine.
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