Numerical Analyses of the Karnaphuli River Tunnel

Abstract

Effects on ground during tunnel construction phases especially during excavation process, has been a complicated topic for the researchers for many years. Tunneling in soft soil requires proper investigation and accurate calculation before starting the main construction sequences. This study deals with tunnel project under the river Karnaphuli, Bangladesh. As it is going to be constructed underwater, lots of challenges have to be considered during the construction of the tunnel including water pressure, erosion of the river bed above the tunnel, and interaction between tunnel and the surrounding soils. To determine the ground deformations and stress occurred during the construction sequences of the tunnel, numerical analysis can be considered as an important tools in this prospect. In this research, FEMtij-2D, a finite element programme has been used for finite element analysis. In the simulation subloading-tij model has been used as a constitutive model of the soil. Soil parameters defining physical and strength properties were determined from laboratory tests. Model parameters were obtained from triaxial test and consolidation tests. It requires only a few unified material parameters and can consider influence of intermediate principal stress on the deformation and strength of soils, surface settlement, displacement vector, influence of stress path on the direction of plastic flow and influence of density and/or confining pressure. P a g e | vii Experimental model was performed on the basis of field scale to evaluate the model. A comparison was made between results obtained from experimental model and numerical analysis for shield tunneling. It was observed that in FEM-tij model, simulation of soil-structure interaction and behavior as per practical situation enables higher safety factor comparing the result of experimental model. Hence, an optimized underwater tunnel system can be constructed for Chittagong city after proper prediction of ground movements and influence of tunneling with a sophisticated simulation tool FEM-ti