Pressure Prevention There are two types of pressure in a tunnel, the first is the pressure of the rock and dirt that is above and to each side of the tunnel.  This inward pressure can force water, dirt, and rock to fall upon the right of way and thus, must be prevented. Index of ... Pressure Grouting Avanti’s Injection Grouts High Pressure Grouting for Groundwater Ingress Control in Rock Tunnels and Caverns {*.PDF } Moving Vehicle Pressure The second is the pressure that builds up in front of a fast moving vehicle such as a High-Speed Train.  This pressure if not properly compensated for may harm passengers that are sensitive to pressure changes.  This in-tunnel pressure can also affect the operation of the rolling stock as it blocks forward motion and can produce wild side-to-side motion. Index of ... Aerodynamics and ventilation in rail tunnels High-speed rail tunnels are designed increasingly as twin-tube, single-track systems