Abstract
Shield construction will cause the fluidization of soft soil which is characterized by flow plasticity. This paper presents two theoretical models of soil flow behavior based on a fluid mechanics framework to understand the behavior of soft soil during shield tunneling, especially under the shearing action of the shield skin and the cutting wheel. The characteristics of the flow field are discussed, and their relationships with shield construction parameters such as advancing speed, cutting wheel rotation, applied thrust and torque, and water content are analyzed, while the proposed theory is verified by the results of a numerical simulation. Considering the shear-thinning effect of the soil, a closed four-stage shear path to describe the complete process of the soil behavior during shield tunneling is further interpreted. The results indicate that the sheared region produced by the rotating cutting wheel was larger than that produced by the shield shell shearing and that it was significantly affected by soil properties and tunneling parameters. In addition, it is concluded that the sheared region was significantly expanded due to the shear-thinning effect.
Highlights
Soft soil, such as mucky, silty clay, is widely distributed in Shanghai, Ningbo and Suzhou
The thrust required for soil flow decreased with the increase of water content, with the reason being that the soil with high water content had a smaller yield stress and viscosity coefficient, so the ability to resist deformation was smaller
Two theoretical models of soil fluidization behavior induced by shield tunneling parameters based on the fluid mechanics framework are proposed
Summary
Soft soil, such as mucky, silty clay, is widely distributed in Shanghai, Ningbo and Suzhou. This mucky, silty soil is characterized by a high water content, high compressibility, low permeability, and a high thixotropy with both fluid and solid properties [1,2]. During the process of shield tunneling, the shield skin and cutting wheel will inevitably cause a shearing effect on the surrounding soil and induce the proposed fluidization behavior of the soil. There is an obvious decrease in the strength and bearing capacity of the sheared soils around the shield, which further increases the range of disturbance to the soil and causes additional downward movement of the shield, increasing the difficulty of the deviation control. It is critical to study soil fluidization behavior and its relationship with shield tunneling parameters
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