The location of the site is in the center of the Tanami desert in the Northern Territory of Australia.

The raisebore shaft that the client was completing required a restraint over the top approx. 52m depth with the ground conditions to ensure the raisebore machine could reach the surface effectively.

 

Bauer Foundations Australia (BFA) were engaged to complete a ringed secant piled wall.

This gold mining vent shaft ensures clean/fresh air can be supplied to the underground mine workers.

 

Geology:

The site consisted of heavily weathered material from construction level down to 10-15m.  From 15m down to 20-25m, Coora Dolerite material, which was highly to moderately weathered.  From 25m to 52m the dolerite was moderately to slightly weathered. Some dolerite layers were over 100 MPa in strength and also inclined.

 

Scope of Works:

Secant ringed wall with 750mm dia piles. Using 880mm OD segmental casing over the top 15m for both soil material conditions and verticality control. Both hard and soft (30 no piles total) secant piles drilled to a depth of 52m bgl.

 

Miscellaneous:

The verticality of the drilled secant piles had to be completed to a 1:150 tolerance. Also any piles that were deviating out of tolerance and heading in the direction of the shaft, needed to have a fibreglass cage installed from the intersection height of where the deviation came into the shaft. The situation only occurred once on the project where we were required to use a fibreglass cage from approx. 30m depth to 52m.

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.

BFA were under strict security measures with the site being on a gold mine and also had to contend with the local wildlife encroaching for food!

 

INFO

Construction Methods:           Secant pile wall

Construction Materials:          Concrete, steel

Main Equipment:                    BAUER BG 30

Construction period:               August 2020 – December 2020