A Study on Seismic Analysis of Underground Tunnels for Delhi Metro

Due to fast urbanization, there is a shortage of above-ground surfaces. Thus to reduce this shortage of above-ground surface, underground tunnels are constructed beneath the structure for transportation purposes. As a result, it is critical to understand how earthquakes affect underground tunnels, so that people's lives can be saved and service levels can be maintained. Underground constructions cannot be considered entirely immune to the impacts of ground shaking, as evidenced by the Kobe earthquake (1995), the Chi-Chi earthquake (1999), and the Niigata earthquake (2004), when some underground structures were severely damaged. A typical section at Chandani Chowk of DMRC (Delhi Metro Rail Corporation) tunnels, New Delhi, India, has been analyzed by using the finite element method. Response of the soil tunnel system for the Uttarkashi earthquake (1991) has been found out in the form of maximum forces induced in the RC liner of the tunnel, displacement, induced acceleration and stresses. The results have been compared with the available closed -form solutions. Parametric studies by considering different parameters such as effect of contraction (volume loss), influence of boundary conditions and damping, effect of interface condition between soil and tunnel, effect of displacement time history and effect of a nearby building have also been conducted. Forces in RC liners and stress concentration obtained in the present study are well-matched to those obtained by available closed formed solutions. The vertical stress concentration and volume loss depend upon the soil medium's constitutive behavior. The section under consideration was safe against the 1991 Uttarkashi earthquake. It can also be observed that, due to the presence of the building, the axial force and bending moment increased in tunnel's liner, and the value of all three forces reduced as the position of the building was away from the tunnel. Shear force and bending moment were maximum for full slip condition between soil and tunnel lining however the effect of the interface condition on the displacement was negligible after a certain value of the interface condition.