Earthblog

TEMPORARY STEEL SEGMENTAL SHAFTS

Tunnel Boring Australia has developed a design & fabrication system for deep shafts installation using steel segmental casing. The shafts are constructed utilising a set of four custom built hydraulic jacks (gallows) which provide for controlled advancement of the shaft segments into the ground, and for recovery of the same. The system consists of standard shaft rings and one initial shaft ring. The standard shaft ring is made of 4 segments, 1200mm high. The initial shaft ring has a different design which also includes a 200mm cutting edge. The shafts can be of various depths and diameter. Tunnel Boring Australia recently successfully installed a 6m diameter, 12m deep steel segmental shaft for Setlow Constructions as part of the Thiess John Holland Airport Link Project in Brisbane.

Once the initial ring is positioned in place, a concrete ring beam is poured, adequately designed to withstand the forces applied by the four or more hydraulic jacks (gallows). Excavation of layers of 200-300mm precedes each push until the full 1200mm height of the initial shaft ring is jacked into position. The hydraulic jacks are used to control the plumb of the shaft. Once the initial shaft ring is into position, then the first standard ring is placed on top of the initial shaft ring and the whole process of excavation and jacking is repeated.
Upon reaching it’s final destination, the shaft is secured and then pushed from the bottom in 300mm increments with the assistance of four jacking rams. Once the 300mm push is achieved, the jacking rams are withdrawn and the 300mm is backfilled. Once 1200mm of the shaft is been exposed above the surface level, the first ring of segments is dismantled. This process continues until the full depth of the segmental shaft is retrieved in a safe and controlled manner.