Three-Step Tunnel Excavation Overview
Three-step tunnel excavation involves dividing the tunnel excavation into three sections: upper (crown), middle, and lower parts. The process is done in stages to allow proper control of tunnel stability and minimize the risk of collapse. Wet shotcrete is used to support each section after it's excavated.
Excavation of the Crown (Upper Part)
First, the top section or crown of the tunnel is excavated.
The crown excavation provides initial access to the tunnel and allows shotcreting to be done before moving to the next section.
Excavation of the Middle Section
After stabilizing the crown, the middle portion of the tunnel is excavated.
Excavation of the Lower Section
Finally, the lower section (invert) of the tunnel is excavated once the upper sections are stabilized.
