A major mining company situated in Australia has recently re-opened a previously worked mine, which was in the Bo-wen Basin mining area in central Queensland, approximately 900 km north of Brisbane. In line with expansion plans for this seam, a new ventilation shaft was required. This vent shaft ensures clean/fresh air can be supplied to the under-ground mine workers.

 

Geology:

Tertiary clayey/sandy material from construction level down to 13 m. From 13 m down to 68 m, Permian coal measures consisting of sandstone/siltstone material were encountered.

The Sandstone / Siltstone UCS strength ranged from 30 MPa up to 90 MPa.

 

Scope of works:

• Install concrete collar slab for position and pressure tolerance
• 5 m dia drilled down to 13 m bgl
• 4 m dia tertiary liner installed in with rig to 13 m bgl
• 2 m dia drilled down using 6 m long core barrel to 68 m depth
• Installation of 2.1 m OD liner to 68 m depth. Installed as 12 m sections and bolted together
• Drilling of 2 m dia through concrete plug and into top of working coal seam roof at 71 m

 

Miscellaneous:

 

The site has a number of challenges required to be overcome. The verticality of the drilled hole had to be nearly perfect (i.e. 1:200) verticality – to ensure the full length liner was fully installed. To assist with ensuring this was achieved, Bauer Foundations Australia (BFA) utilised the specially adapted 6 m long core barrel tooling. To monitor the actual verticality of the hole as it progressed with depth, a special 3D laser surveyor was used. Sources of ignition are a major item when working with mines and as BFA were holing into a working coal seam with inherent, potential flammable gases present, therefore there could be no hot works carried out with the liners. So to join the liner sections (12 m) together BFA designed the connection points using the Bauer double wall casing locks.

 

 

 

 

INFO

Construction Method:             Large dia vertical shaft

Construction Materials:          Concrete, steel liner, grout

Main Equipment:                    BAUER BG 40

Construction Period:              January 2020 - February 2020