Wyee colliery, located on the Central Coast of NSW, is about to commence extraction of Longwall 22. Prior to recent geological anomalies presenting themselves the mine had an expected life span of a further 10 years mining under Lake Munmorah. The mine extracts coal from the Fassifern seam. It has in the past extracted coal from the Great Northern seam but this seam has been extensively worked and is currently used as a main return for the mine.
The mine is ventilated by two 530kw Fox “Hi-Flow” centrifugal fans ventilating in a parallel “Richardson” arrangement. The ventilation system incorporates 2 intake drifts, a down cast shaft and one upcast shaft.
The mine is ventilated with three intake roadways in the Fassifern Seam approximately 7km in length. Intakes drop down to two for the last 500m, which allows for a single return back to a staple shaft. The return from the staple shaft is through the Great Northern seam back to the upcast shaft. Being mostly goaf the Great Northern seam is equivalent to eight parallel roadways.
The two main mine fans both operate 5% higher than rated maximum operating running speeds but still struggle to ventilate the mine.
The need for a new staple shaft arose when planning for longwall 22 found that the currently used single return roadway absorbed over half of the pressure produced by the main mine fans. This in turn showed that ventilation quantities desired would not be achievable.
In recent times, the NSW coal industry has seen a major shift in moving away from using large amounts of explosives in work like staple shafts. The rules and conditions that need to be imposed for this work become very demanding. The rising cost of sometimes unobtainable explosives permitted for use around coal lead Wyee’s technical services team to examine raise bore technology.
In conjunction with company Raisebore Australia, Wyee initially planned to uphole ream or push bore to a diameter of 1.44m and install multiple shafts. Using Ventsim and standard ventilation equations, four shafts would be required given the 1.44m diameter. The uphole reaming contained a fair amount of R&D for both Raisbore Australia and Wyee Colliery. The access to the shaft sites in the Great Northern seam was only accessible by traversing a 30m ladder up an existing staple shaft and walking 2km to the planned hole through site. Any equipment required on top of the shafts prior to punching through would have to be transported the 2km in a wheel barrow.
Raisebore Australia used a rig able to deliver a pilot thrust of 235kN, a reaming thrust of 1335kN at a torque of 60kNm and requiring 4.5m of height in the Fassifern seam. This was prepared prior to the project commencing and a concrete floor was put down for rig stability. It utilised drill rods of 203mm diameter.
Uphole hole reaming the first pilot hole of 600mm diameter proved slower than expected due to the nature of some very hard strata intersected in the hole and due to this it was determined that only the pilot holes would be uphole reamed and the 1.44m diameter work would be done by back reaming.
Due to the lack of vehicle access to the top of the shaft sites and the fact that the 1.44m reaming head weighed close to 3 tonnes, the head had to broken into pieces that would be light enough and small enough to hoist up one of the 600mm pilot holes.
A mono rail system was set up in the Great Northern seam above the pilot holes so that moving the reaming bit, once assembled could be achieved. The holes were successfully back reamed using this method.
* Jason Wagstaffe – regional ventilation officer, Powercoal, and secretary, Ventilation Officers Society of Australasia (VOSA) Inc.
