“Tunnel Hoods” in Mumbai–Ahmedabad High-Speed Rail (MAHSR) Project

Why in News?

The Mumbai–Ahmedabad High-Speed Rail (MAHSR) Project has entered the next phase of tunnel construction with the introduction of tunnel hoods, a technology being used for the first time in Indian Railways.

About the Project

• The 508-km Mumbai–Ahmedabad High-Speed Rail corridor is India’s first bullet train project.
• It includes eight mountain tunnels:
  • Seven in Palghar, where the alignment passes through the Sahyadri Mountains.
  • One in Valsad.
• Each tunnel will have tunnel hoods at both the entrance and exit.

What are Tunnel Hoods?

• Tunnel hoods are cylindrical structures constructed at the entrances and exits of railway tunnels. They contain pressure-relief vents or windows that allow air pressure to dissipate gradually. They are widely used in high-speed rail networks where trains travel at speeds of over 300 km/h.

• When a high-speed train enters a tunnel, it behaves like a piston moving inside a cylinder, pushing a large volume of air ahead of it.

• This causes sudden compression of air inside the tunnel, formation of pressure waves that travel through the tunnel, and a “tunnel boom” or loud explosive noise when the train exits the tunnel if the pressure is not controlled.

• Tunnel hoods serve as a transition zone between the open atmosphere and the enclosed tunnel.

• Their pressure-relief vents; release compressed air gradually, reduce sudden pressure fluctuations, minimise the tunnel boom effect, improve the aerodynamic performance of high-speed trains and enhance passenger comfort and reduce environmental noise.

Source: IE