Enhancing High-Speed Rail Tunnel Design: An Aerodynamic Methodology

Abstract

Since the Industrial Revolution, railways have played a crucial role in transporting goods, services, and people, wielding profound economic and social implications. However, today railways represent a diminishing portion of transportation. The decline of the railway's prominence can be attributed to inefficient integration with other transportation systems, slower speeds compared to alternative transportation methods, and escalating passenger prices (World Bank, 2024). Despite its diminishing appeal, railways remain a sustainable method of transportation in contrast to road and air travel, as they utilize renewable energy sources and generate minimal carbon emissions during operation. With the imperative for climate-friendly transportation becoming more urgent, the legacy of railways has a chance of redemption. The expansion of high-speed rail presents opportunities for rail travel to be more cost-efficient, time-efficient, and environmentally friendly. However, significant physical barriers such as bodies of water and mountain ranges pose challenges to rail expansion, necessitating the implementation of extensive tunnel systems. Rail tunnels, as large infrastructure projects, contribute significantly to carbon emissions during construction. This is known as their “embodied carbon footprint.” It is necessary to design rail tunnels efficiently to mitigate the potential adverse environmental effects caused by the embodied carbon and fulfill the larger sustainability objectives of the railway system. This thesis explores a methodology to optimize the design of high-speed rail tunnels by examining the implications the tunnel’s cross-sectional area has on the short-term and long-term costs and the environmental ramifications. The cross-sectional area of a tunnel has an inverse relationship with the drag force experienced by the train and the power required to overcome this force. Decreasing the cross-sectional area increases the drag force and the long-term operational power costs. However, it reduces the embodied carbon footprint. Conversely, increasing the cross-sectional area allows for operational cost savings which can mitigate the increased environmental costs caused by the increase in embodied carbon footprint. Determining the cross-sectional area that minimizes both the long-term operational costs and embodied carbon footprint leads to the most efficient design of the high-speed rail tunnel. This thesis produces a model that reflects the balance between functionality and sustainability and applies the model to several case studies of rail tunnels worldwide.