Analysis and prediction of ground settlement considering support mechanism and groundwater inflow during shield tunneling

Abstract

Using underground space has been an attractive option, especially for urban areas. Construction of underground structures in cities is bound to have existing structures adjacent. Therefore, predicting and mitigating damage caused by tunneling-induced ground movements is an important goal for designing underground facilities. On the other hand, the shield TBM (Tunnel Boring Machine) is a tunnel construction method that simultaneously advances and supports the face and excavated wall. It mechanically excavates, generating less vibration, noise, and dust than the conventional blasting method, so the application of shield tunneling is gradually expanding in urban areas. However, the ground settlement caused by shield tunneling has been evaluated by performing numerical analysis on the site before construction and applying a simple empirical formula. Thus, developing an algorithm that can predict the ground settlement induced by shield tunneling variables during construction is necessary. In this dissertation, the ground settlement induced by tunneling is considered to be caused by excavation and controlled by supporting, so it is tried to investigate how the support system of shield tunneling affects the surrounding ground, how much the surrounding ground transfers the ground loss to the surface, and how much ground settlement occurs in what form. For this purpose, the ground movements for a circular tunnel excavation with supporting pressure were first understood by deriving an analytical closed-form exact solution in a two-dimensional linear elastic half-plane. As a result, it was found that the analytical solution with the internal support pressure is more suitable for simulating the settlement troughs than the solution with the conventional gap parameters, and it required to analyze both the support pressure and deformation of supporting material for the settlement induced by construction variables of shield tunneling. Then, the three-dimensional elasto-plastic behavior of the ground and shield tunneling sequence were numerically simulated to develop a field-applicable surface settlement prediction algorithm. For the shield TBM support system consisting of face pressure, slurry injection for over-excavation, and grout injection for tail voids, the settlement affected by pressure and stiffness of support materials were quantitatively analyzed by numerical parametric studies. The ground-support loss was introduced based on the results, which is the weighted ground loss by the investigated support mechanism of shield tunneling. In addition, ground correction coefficients were introduced to the ground-support loss for each stage to derive the maximum surface settlement according to construction variables, and a settlement prediction program was developed and applied to the construction fields. Furthermore, the ground settlement evaluation method using centrifuge testing was proposed to predict and control ground settlement induced by groundwater inflow and particle loss, which are governed by complex and independent geological factors and geotechnical factors.