Elaborate numerical analysis and new fibre Bragg grating monitoring methods for the ground pressure in shallow large-diameter shield tunnels: a case study of the yellow crane tower tunnel project

The determination of ground pressure is an important prerequisite for the design load of tunnel. Currently, in the emerging field of shallow rock large diameter shield tunnels, the study of ground pressure is limited by the lack of comprehensive engineering case studies and experimental data. This study provides a comparison of elaborate numerical analysis method and Fibre Bragg Grating (FBG) monitoring method for the ground pressure in a shallow rock large-diameter shield tunnel based on a case study. Firstly, the elaborate 3D numerical model is developed by finite difference software to simulate the process of shield tunnelling. Construction details such as the force distribution, liner application, over-excavation gap and shield tail gap are considered in the simulation process. The elaborate numerical analysis method for the ground pressure in shallow rock large-diameter shield tunnels is presented. Then, using the elaborate numerical analysis method, the impact of key parameters such as support force at the tunnel face, grouting pressure, tunnel diameter, and tunnel depth on ground pressure are assessed. The new FBG monitoring method is developed to measure ground pressure in shallow rock large-diameter tunnel. Finally, the ground pressure obtained by the elaborate numerical analysis method is compared with that obtained by the new FBG monitoring method. The result shows that the elaborate numerical analysis method is generally larger than the new FBG monitoring method, with a reasonable 15% difference. The ground pressure that obtained by FBG monitoring shows the initial rapid increase, followed by gradual increase, eventually stabilising.