Quantifying the impact of loads on connections between segments of an immersed tunnel

Abstract

Immersed tunnels have become an integral part of the modern day society. Their serviceability and maintenance are of prime importance. In recent years, monitoring of immersed tunnels for deformations showed the necessity for the analysis of certain tunnels due to an unexpected and local increase of settlements and rotations. With the Kiltunnel in the Netherlands, settlements observed at a segment joint of the tunnel were higher than expected. This master thesis focuses on the structural behavior of the segment joint of this immersed tunnel. Developing a 3-D FEM model consisting of the two segments of the tunnel coming together at the connection/joint is described in this thesis. The model is fixed on one end and forces are applied at the other end. The forces which are expected to occur are calculated with the available values of settlement and rotation on site. Various schemes of the combination of forces are studied in this work. First, the behavior of the joint is observed when the connection is subjected to a shear force only. It is found that the shear force at the joint is concentrated in the walls and almost equal percentages of force flows through each wall. The shear stress values are highest at the middle wall. The middle wall is less thick than the outer walls making it more vulnerable to damage and cracking. It is also found that in a linear analysis, the tunnel joint is capable of carrying the estimated shear force without the activation of reinforcement. This is applicable to both the top tooth and the bottom tooth of the tunnel. The concrete tensile stresses are far below the concrete tensile strength. It is expected that the actual capacity would be much higher if detailed non-linear analysis is carried out. When a combination of shear force and bending moment is applied, it was noticed that the DIANA model becomes unstable and there is loss of equilibrium. This implies that soil should be modeled as elastic foundation in order to come to a conclusion about the capacity of the tunnel connection.