International Research Journal of Engineering and Technology (IRJET) e-ISSN: 2395-0056 Volume: 11 Issue: 05 | May 2024
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p-ISSN: 2395-0072
Static and seismic assessment of an existing tunnel due to a new tunnel placed vertically below at different spacing S.T.Amin1, S.M.Abbas2, A.Usmani3 1Research Scholar, Corresponding Author, Department of Civil Engineering,
JMI, New Delhi 2Professor, Department of Civil Engineering, JMI, New Delhi, India 3 DGM, ETDD, EIL, New Delhi ---------------------------------------------------------------------***---------------------------------------------------------------------
Abstract - The significance of tunnel construction has
to cater to various developmental requirements. Over the years, there has been a prevailing assumption that the underground structures offer greater seismic safety compared to their aboveground counterparts, attributed to the inherent restraint provided by the surrounding soil or rock. However, a multitude of incidents has demonstrated significant tunnel damage resulting from seismic events. Hashash [1] has cited several case studies which highlight the need for enhanced seismic design and mitigation strategies to bolster the structural integrity of tunnels in earthquake-prone regions.
elevated manifold owing to its diverse applications in contemporary transportation and communication infrastructures. Nonetheless, the seismic susceptibility of these underground structures is of utmost concern due to their vulnerability to different forms of damage. Consequently, this article undertakes a static and seismic analysis of an existing tunnel, both in the absence and presence of an additional new tunnel of same diameter, positioned vertically below the existing tunnel at different spacing. A 2D plain strain soil-tunnel model is created using Finite element analysis software GTS NX Midas. The characteristics of the soil are similar to the alluvial silts found in Delhi and the earthquake selected for seismic analysis is the Loma Preita earthquake. Response-spectra compatible earthquake data is produced using SeismoMatch software. The response parameters obtained from the results are in the form of forces generated in the existing tunnel lining such as axial force, bending moment, shear force, and contours depicting ground displacement. From static analysis, it is observed that due to a new tunnel, the lining forces in the existing tunnel decrease, whereas with increase in distance between the two tunnels, the existing tunnel of the twin tunnel system behaves similar to the single tunnel. However, during seismic analysis, there is negligible difference between the single tunnel and the existing tunnel of the twin tunnel system after a certain distance. Therefore, it can be understood that the seismic stability of the existing tunnel is independent of the vertical spacing of the new tunnel.
Seismic waves can induce significant structural impacts beyond those anticipated for an isolated tunnel due to a new adjacent opening. Research has been performed to anticipate the induced stresses in pre-existing tunnel structures during seismic events, especially accounting for the excavation of a neighbouring tunnel [2]. However, simpler approaches by Corigliano [3] have been found to yield good results for seismic analysis of deep tunnels, but an extensive assessment of the dynamic growth of internal stresses on the lining is essential for stable design in seismically active locations. The study looks at a variety of analytical methodologies, including simple procedures and advanced numerical simulations, to estimate the seismic stress increment and the reliability of pseudo-static solutions Also, Bobet performed a research [4] that introduced new mathematical methodologies for evaluating the effect of pore water pressure on tunnel stability under static and seismic loading. The research investigates the drainage conditions at the ground-liner interface, as well as the impact of groundwater pressure on ground and support reactions. Similarly, the study carried out in [5] focuses on seismic analysis of deep twin tunnels in Indian cities such as Delhi, taking into account specific soil properties and using a pseudo-static approach. The study quantifies the additional moments, thrusts, shear, and surface displacements caused by earthquake stresses on the tunnel liner, highlighting the need of including seismic loading into twin tunnel designs. Wang [6] determined the maximum bending moments using the full-slip closed form solution and compared to those obtained by no-slip finite difference analysis. The full-slip assumption resulted in higher bending moments than the no-slip assumption. The full-slip assumption
Key Words: plane strain, twin tunnel, alluvial silts, static and seismic analysis.
1. INTRODUCTION The beginning of underground tunnels traces back to 2200 B.C. Since their inception, these tunnels have served different purposes in transportation and communication. The ever increasing urbanization has led to a scarcity of available aboveground space for further expansion of communication networks and utility services. Consequently, in the contemporary era, there is a growing demand for underground structures, particularly tunnels,
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