Soil-carrying effect induced by super-large-diameter shallow-buried shield tunneling and treatment measures: A case study in Zhuhai, China

With the rapid urbanization and infrastructure development, there is a growing demand for the construction of super-large-diameter tunnels in China. As a result, understanding the impact of tunneling on soil behavior is becoming increasingly important. This paper provides a detailed case study on the construction of a super-large-diameter shallow-buried shield tunnel in Zhuhai, China, with a special focus on the soil-carrying effect. This phenomenon, identified for the first time in shield tunneling, is triggered by the covering of solidified grouting on the shield shell during tunneling and results in a distinct pattern of soil deformation. The study explores the mechanism and disturbance characteristics of the soil-carrying effect in shield tunneling. It also examines the causes of the mortar covering that triggers this effect. Through soil monitoring data, the disturbance characteristics of the soil-carrying effect in this project are demonstrated from three aspects: longitudinal ground displacement, settlement trough, and deep horizontal displacement. The study found that when the excavation width becomes insufficient to support the departure of the shield shell and mortar covering, the overlying soil gets pushed forward with the shield tunneling progression. This leads to two distinct failure faces in the overlying soil along the longitudinal axis and poses significant challenges in controlling the volume of synchronous grouting. The monitored data from the project revealed a “wave” disturbance on the ground during shield tunneling, accompanied by passive uplift and horizontal spreading and collapse of the surrounding soil during the shield passage. To address the soil-carrying effect, the primary treatment proposed involved the installation of multiple rows of vibrating steel sheet piles. These piles help loosen and block the solidified mortar, facilitating its removal from the shield shell. Furthermore, a new type of single-liquid slurry that extends the initial setting time was introduced to prevent the reappearance of mortar covering. The effectiveness of the proposed measures was verified through subsequent monitored ground displacement. The case presented can provide warning and reference for subsequent super-large-diameter shallow-buried shield tunneling projects.