Rib and Lagging Shafts
These shafts are essentially a barrel that is sunk in reasonably good ground conditions that allow the excavation of 1.2 metres of ground at a time before installing support. A steel rib is placed in the bottom of the excavation and timber lagging is set within the flanges of the new rib and the one already in place above.
When the complete circumference of the shaft is lined, the annular space between the lagging and the excavated ground is grouted. Rib and lagging is a perfect partner with ground freezing where the stability of the soil can be guaranteed as long as the freeze is in place.