Application of Convergence-Confinement Method in the Design and Construction of Large-Diameter Tunnels in Soft Ground

Book excerpt: This dissertation focuses on a large-diameter and shallow-depth tunnel project for passenger cars and rail trains. Monitoring equipment (string gauge, ground settlement points, etc.) were installed from the outset of the project to gather pertinent data. With this large data set, used to monitor and analyze the surrounding soil and support structure of the tunnel, Convergence-Confinement Method (CCM) was systematically developed, including the Support Confinement Curve (SCC), Ground Reaction Curve (GRC), and Longitudinal Displacement Profile (LDP). First, this research initially aimed to identify the optimal approach for constructing these three CCM graphs: For SCC, the spatial distribution of axial force, bending moment, and radial displacement within the tunnel structure will be illustrated and compared with the other two models. Subsequently, essential field data will be utilized to establish the SCC. The GRC was formulated using a hardening soil model, selected after comparing indoor soil tests across various models. LDP were derived from monitoring the embankment's settlement as the tunnel was constructed. A numerical model was constructed and verified using monitoring results. This includes presenting and comparing the cross-section settlement curve with Peck's findings. Through these methods, the study sought to establish best practices for generating these key CCM graphs. The second thrust of this dissertation assembles these three curves and verification CCM from the construction process in a real large-diameter and shallow-depth tunnel project, validating the CCM equilibrium stress against monitoring data and corroborating the CCM results with data from strain gauge monitoring underscore the methodology's validity and reliability, establishing guidelines for tunnel project designs. Finally, to assess the applicability of CCM, the various findings resulting from this research are presented. This study finds that Terzaghi in-situ earth pressure is closer to CCM equilibrium earth pressure, which represents the soil stress after release. Therefore, Terzaghi loose earth pressure is deemed more suitable for application in the design in the Yellow River area. This study also extends to Wood's work to derive the compression factor when the tunnel is in the 'elliptical' mode of deformation and subsequently determined stress and displacement fields around a supported tunnel.