Barrel Vault Method

The Barrel Vault Method allows safe excavation of tunnels, especially in soft ground conditions through railway or highway embankments without disrupting traffic or imposing speed restrictions. To eliminate level crossings, the Barrel Vault Method can be advanced from an open cut portal established below ground level. The Method has also been used successfully to support buildings while tunneling directly beneath their foundations.

CONSTRUCTION SEQUENCE

1. INSTALLATION OF CONCRETE PILES

2. EXCAVATION OF THE PORTAL AREA IN HORIZONTAL LAYERS

of a maximum thickness of 1.5m with immediate support of the curved starter wall using

• welded wire mesh
• shotcrete
• grouted steel pipe anchors

3. TIEBACK OF THE PILED WALL

4. INSTALLATION OF THE BARREL VAULT

• to ground level using 
• horizontal boreholes of up to 45m long and 
• crack grouting

5. CONTINUATION OF PORTAL AREA EXCAVATION AND SUPPORT

according to Stage 2 of the sequence

6. INSTALLATION OF FURTHER HORIZONTAL BOREHOLES

according to Stage 4 of the sequence

7. EXCAVATION AND IMMEDIATE SUPPORT OF THE TUNNEL

including excavation of an invert section in order to close the ring of immediate support no later than one tunnel diameter distance from the face

Please follow this link for an article describing the application of this method at a railroad crossing.