Fluidization Behavior of Soft Soil Induced by Shield Construction

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.