The Broadmeadows Mine coal mine in Australia is being upgraded. The location of the mine site is situated in QLD’s Bowen Basin, 34 km north of a town named Moranbah.

 

The raise-bore shaft, which was completed by the client, required support above the rock encountered at a depth of approximately 32 m to ensure that the raise-bore machine could safely reach the surface.

 

Bauer Foundations Australia (BFA) were engaged to complete a ring-shaped secant piled wall.

This coal mining ventilation shaft ensures that clean/fresh air can be supplied to the underground mine workers.

 

 

Scope of Works

 

 

Secant ring-shaped wall with Ø 1,200 mm piles. Using segmental casing over the top 25 m for both soil material conditions and verticality control. BFA utilized a hydraulic extractor unit to remove the casings from the ground after the pile had been concreted. Both hard and soft (18 nos piles in total) secant piles drilled to a depth of 32 m below ground level (bgl). BFA also drilled a central pilot hole for the raise-boring machine, also with Ø 1,200 mm.

 

 

 

Geology

The site consisted of clayey/sandy soils to approx. 13 m bgl. From 13 m down to 22 m, low strength interbedded mudstone/sandstone layers. Medium strength mudstone/sandstone layers from 22 m to 32 m depth, with rock strength UCS values generally up to 20 MPa in strength.

 

 

Miscellaneous

 

The verticality of the drilled secant piles had to be completed to a 1:150 tolerance. As a contingency, the Client requested that also any hard piles that were potentially deviating out of tolerance and heading in the direction of the shaft, needed to have a fiber-glass cage installed from the intersection height of where the deviation came into the shaft. This situation did not occur on this project with any of the hard piles as Bauer’s tolerances were well within the Specification Requirements.

 

To monitor the actual verticality of the hole as it progressed with depth, a special 3D laser surveyor was used on each hard and soft pile drilled. This process was carried out prior to cage installation and concrete pouring.

 

BFA were under strict safety measures with the site being on a coal mine and had to meet any current and ongoing Covid 19 protocols that the mine enforced during the scope of works.

 

INFO

Construction Methods:           Secant pile wall

Construction Materials:          Concrete, steel

Main Equipment:                    BAUER BG 30

Construction period:              July 2022 – August 2022