ANALYSIS OF BEHAVIOUR OF SOIL SURROUNDING AROUND BAGHDAD METRO AT BAGHDAD CITY CENTER DURING AND AFTER TUNNEL EXCAVATION USING THE FINITE ELEMENT METHOD

Tunnel excavation disturbs the initial stresses balance and causes stresses redistribution in soil around it. It is significant to study the characteristic of displacements of soil surrounding around tunnel with and without lining. The finite element analysis is used world widely in tunnelling to obtain the soil displacements caused by tunnel excavation. Based on numerical simulation method, the vertical displacements of soil surrounding around Baghdad metro at Baghdad city center, under Al-Tairan Square, are predicted in this paper using the commercially available finite element package, Abaqus 2016. Aseries of actual tunnelling processare simulated by using a fully coupled three dimensional stress-pore pressure finite element model to realistically capture the mechanical and hydrological interaction between the tunnelling and ground water. The vertical displacements of soil surrounding around Baghdad metro passing under Al-Tairan Square are computed through the time periods of three sequential simulation steps. These steps are named as the excavation, linings installation, and consolidation steps. It is found that maximum vertical displacement occurs at the crown to the downward with value equal to 28.5 m approximately after linings installation immediately. Also highlighted is the importance of the stress-pore pressure coupled analysis in the numerical prediction tunnel behaviour.