Elasto-Plastic Analysis of Delhi Metro Underground Tunnels Under Seismic Condition


Abstract eng:
Underground Structures are strategic elements in transportation and utility networks, like tunnels in metropolitan cities for mass rapid transit system, water conductor systems, roadway/ railway tunnels in hilly areas, large underground gas and petroleum storages, etc. The importance of these structures makes their vulnerability to earthquakes a very sensitive issue. A large earthquake would not only cause potential loss of human lives but can also damage lot of other infrastructures. This can result in severe economic losses, especially in view of the time required to restore the functionality of the network. Seismic analysis of underground structures involves the interaction with several disciplines including soil, rock and structural dynamics, structural geology, seismo-tectonics and engineering seismology. Underground structures cannot be treated as completely exempt damage during ground shaking, as demonstrated by 1995 Kobe earthquake, 1999 Chi-Chi (Taiwan) earthquake, and 2004 Niigata earthquake, where several underground structures suffered severe damages. Hence, the associated risk may be quite high. Seismic response of underground structures is basically controlled by the response of the surrounding ground and by the imposed ground deformation and not by the inertial characteristics of the structure itself. For these reasons, it is very important to study how metro tunnels suffer damage during earthquakes so as to protect human life and the service efficiency. A typical section between Rajiv Square and Patel Square of DMRC (Delhi Metro Rail Corporation) tunnels in Connaught Place, New Delhi, India has been considered for analysis. This section is situated on the Yellow line (line-B6) which was constructed in Phase-1 of the work of DMRC. Finite element analysis of soil-tunnel system has been performed for Uttarkashi 1991 and Chamoli 1999 earthquakes. Elasto-plastic behaviour of soil was simulated using Mohr-Coulomb yield criterion. The response of the system has been obtained in the form of horizontal displacement-time history and induced acceleration-time history. Similarly, maximum forces including axial force, shear force and bending moments induced in RC liners during shaking and also at the end of earthquake have been studied. Displacements in both soil medium and RC liners of the tunnel were found to increase significantly due to earthquake. Elasto-plastic behaviour of soil-tunnel system was compared with the corresponding elastic response. Nonlinear static analysis of the system has shown that forces in RC liners (axial force, shear force and bending moment) increase due to nonlinearity of the soil mass. Elasto-plastic seismic analysis suggests that – i) non-linearity of soil causes large deformations in soil-tunnel system, and ii) forces in RC liners reduce due to plasticity of soil when dissipation of seismic energy occurs through plastic zone mobilized around the tunnel periphery. If these forces exceed the permissible stresses in liners, the transportation network can suffer damage which can affect the serviceability of such infrastructures.

Contributors:
Conference Title:
Conference Title:
16th World Conference on Earthquake Engineering
Conference Venue:
Santiago (CL)
Conference Dates:
2017-01-09 / 2017-01-13
Rights:
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 Record created 2017-01-18, last modified 2017-01-18


Original version of the author's contribution as presented on USB, paper 4027.:
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