Previously called Ellalong, the Southland longwall mine is owned by Gympie Gold, and until earlier this year, was operated by contractor, Colrok. The mine is located near Cessnock in the NSW Hunter Valley. A new longwall is expected to be ordered next year, due for commissioning around April 2003. The probable cutting height will be around 4.5m

The ARM method divides the longwall block into two sub-panels, which are then developed and extracted sequentially. Each sub-panel is separated from the next one by a slanted roadway, driven across the longwall block to support ventilation requirements and coal clearance. The retreating longwall mines through the supported roadways.

The first block set up for the ARM method, SL2, is in the Bellbird section of the lease. By the time Thiess came onto site, the panel had been developed for the ARM method and one slanted roadway was already driven.

Subsequent to taking over operations at Southland, Thiess conducted a strategic review of the mine plan and came to the conclusion that conventional longwall extraction was the preferred option. For SL2, Thiess has decided to mine through the slanted roadway, as planned, and up to the second, yet to be developed, slanted roadway. The remainder of the SL2 block will be sterilised so that conventional longwall extraction can resume as soon as possible from the start of SL3.

In preparation for driving through the slanted roadway, the longwall stopped mining in late August and is expected to resume in mid-October. Routine convergence monitoring on the stopped face is showing only minimal and expected movement. Face spall has been reduced because of an aquacrete application.

Preparations are underway to backfill the slanted roadway for the longwall to mine through. While other methods were considered, including the use of cuttable cans or timber props, a risk assessment (conducted by Chris Taylor Mining), showed that backfilling was the safest option in terms of roof control.

A 5Mpa bulkhead will first be built in the tailgate end of the slanted roadway. Two 500m deep surface boreholes will then be used to pump around 4,400 cubic metres of fill into the roadway over a period of three weeks. Some shrinkage of the product is expected and the small void area will be filled to ensure there is no gap between the top of the cement and the roof, reducing the risk of bed separation.

An existing high area in the maingate roadway was also identified as a possible risk. The roof in this area is about 1.2m above the mining horizon and higher than the chocks can reach. A false roof is being constructed to bring the high roof level into alignment with the remainder of the block.

Mine manger, Bob Butcher, said operating standards at the mine had improved dramatically in recent months. Systems were being put in place based on monitoring, developing appropriate responses, and management systems.

Thiess has for example, begun developing an extensive roof control management plan to increase the understanding of the roof conditions. Tell-tales and extensometers have been installed, every 50m in standard drivages and every 25m in non-standard drivages. Pre-set trigger levels are the first indication that secondary support in the form of cables, need to be installed.

A computational geotechnical model of the mine is also being developed, to enable greater predictive analysis of stress regimes, as well as greater certainty of costs associated with development rates, etc.

Similarly, the mine’s spontaneous combustion plan has also been revamped and includes three-bag sampling per shift to check gas concentration levels behind the sealed goaf area. The tailgate stream, goaf stream and return airways are currently monitored. An inrush management plan has been developed because of the relative proximity of aquifers and old water-charged mine workings.

Minor problems with friction and belt tracking have been experienced on the mine’s 8km of conveyors. All conveyor belts are now monitored for belt wander and carbon monoxide.

Butcher said it would take around 12 months to implement all appropriate operating systems.