Investigation the interaction of twin tunnel and adjacent pillars

The effect of twin tunnels excavation on ground settlement and adjacent piles is investigated using numerical analysis and comparison to field monitoring records. Shiraz metro twin tunnels in vicinity of southern ring road bridge are selected as a case study. The result shows the surface settlement is started about three times the tunnel diameter in front of tunnel excavation head and it reaches to a steady state, gently. Vertical displacement of piles is constant due to its stiffness and they can control the ground settlement. Pile axial force and bending moment increases gradually and reaches to maximum amount at tunnel adjacent. The nearest pile has the most force and moment.
Summary : The interaction of twin tunnels and adjacent bridge foundation are modeled numerically using Flac3D software. The ground surface subsidence, adjacent piles axial force and bending moment variation are investigated.
Tunneling in weak grounds causes stress and strain variation, which may have a considerable effect on near structures such as pile foundations. The movements of the piles caused by the ground movements and the additional forces and bending moments induced in the piles should be considered by the designers to ensure structural serviceability. In order to analyze the interaction of twin tunnels and near foundation, a pile group has been investigated using the finite difference program FLAC3D. The deformations, loads, and moments induced on existing pile foundations during the tunneling process are discussed.
Methodology and Approaches : In this paper, the tunnel, adjacent piles and surrounding rock mass have been numerically simulated using 3D finite difference method. The results of obtained displacement are compared with real recorded settlement at Shiraz metro twin tunnel project.

Results and It is necessary to simulate and monitor the building displacement in vicinity of tunneling projects. Suitable location, placement and property of pillars can control the ground settlement. The surface settlement is started about three times the tunnel diameter in front of tunnel excavation head. Axial force and bending moment variation due to various overburden height to tunnel diameter ratio are investigated. The pile axial force and bending moment is increased at lower and higher ratio, respectively.