In longwall 7, the longwall traversed through areas where roof strength was as low as 3Mpa, causing 20 consecutive falls of ground prior to the final longwall take-off position. The use of steel and fibreglass dowels and PUR injection allowed mining to proceed under these conditions. Prior to takeoff the roof was resecured through consolidation with PUR and cementitious grout and the installation of long tendon support. The roof control problems have reduced Crinum’s full year production forecast by 1.3Mt.
Mine manager Shane Hansen said Crinum has a comprehensive strata management plan involving monitoring, trigger levels, action response plans and responsibilities which extend from the face workers to the senior site executive. Telltales are used as the primary roof monitoring instrumentation with GEL electronic extensometers used in critical areas. The longwall support pressures are also monitored continuously
Longwall equipment is now being set up for longwall 8, due to commence mining December 20 and wrap up in June 2002. While longwall 8 starts off in weak ground, conditions are expected to be much better than those experienced at the end of longwall 7.
Crinum recently purchased a second DBT Electra 1000 shearer, due to be commissioned in longwall 8. The refurbished shearer will include improvements such as upgraded hydraulic pump carts, hydraulic dump panel and filter sled. These improvements are expected to lead to more efficient roof support operation and improved strata control.
Hansen said the main reason for the purchase was to reduce changeover time from one panel to the next and reduce overhaul costs by extending the time allowed for overhaul.
The integrity of a cross sample of three of Crinum’s roof supports, undertaken during the recovery process, found them to be in very good condition.
Roadway development performance is currently above budget, and is well over a panel ahead of current mining with development of longwall 9, scheduled for mining by mid-2002, already finished.
While water inflows from the underground have stabilised at 6 million litres per day additional evaporation capacity is required to ensure there are no unplanned water releases from the mine under any circumstances.
On the equipment front a new, a bigger capacity AFC with more grunt and a bigger chain size remains an important requirement. The current DBT conveyor is rated at 3500t/h.
Regarding the mine’s approach to safety, Hansen added that management focus on the reduction of the total number of injuries on the job encouraged supervisors to look more widely at the underlying behavioural factors which contribute to all injuries, not just lost time injuries.
