Len Wright, 2008.
Mr Wright was a mine manager, and later District Mining Engineer for the Joint Coal Board when longwall mining was first being developed in South Coast mines and writes here of events of that time.
After being appointed to the position of District Mining Engineer, Southern District for the Joint Coal Board at the end of August 1964 I consider I was extremely fortunate to have had the opportunity to witness the dramatic changes that took place in the coal mining industry commencing at that time and for many years after.
My position required me to visit all the mines in the Southern District, including the Burragorang Valley, and to a lesser degree the Lithgow and Western Districts and report to the Board on developments in these areas. My comments will be limited to the Southern District and the development of longwall production.
Coastal mines at that time were using ripper type continuous miners as production units in bord and pillar operations. With increasing depth of cover, roof conditions were deteriorating, resulting in poor production from these units. Experiences in some of these mines are as follows.
Following overseas investigations, Coalcliff colliery installed a German Westphalia longwall face in February 1963, consisting of 2 leg supports and a coal plough that traversed the face on an armoured conveyor.
The unit was found to be vastly under strength for the massive sandstone roof conditions on the 137m face. Roof supports became ironbound and were damaged. Falling stone damaged the face conveyor, the goaf rilled into the roof supports, large slabbing of coal occurred from the coal face and conditions were very dusty.
The unit was withdrawn in December 1963 and returned to Westphalia after taking nine months to mine 6,300 tonnes of coal. Management concluded that the supports were designed to handle a more plastic nature of roof experienced in Europe. It is understood that support density of 80-115 tonnes/metre length of face was acceptable in Europe prior to 1963.
A second Longwall unit with increased support capacity, consisting of Gullick chocks 6×50 tonne legs, a Meco conveyor and an Anderson Boyes ranging drum shearer was installed in November 1964. Working height was approximately 3m and the face length 153m. The support density had been increased to 250 tonne/m length of face. These supports also proved to be inadequate for the roof conditions encountered.
The sandstone roof was breaking off approximately 1.2m ahead of the coal face causing large lumps of sandstone to fall on to the face conveyor causing damage to the conveyor and delaying loading on to the panel belt at the main gate.
Subsequently the roof supports could not reach the new roof and timber packing had to be built above the chocks so they could ram the conveyor forward and then lower to be advanced. It was a time consuming situation and with this delay, weight was experienced in the gate roads near the face which caused roof problems there as well. Conditions were also very dusty when cutting coal.
After approximately 45m of face advance (53,000 tonnes) the unit ceased production in August 1965.
KEMIRA AND SOUTH BULLI COLLIERIES
During 1965 mechanised retreat longwall mining also began at Kemira and South Bulli collieries, both using supports supplied by Gullick. Problems were encountered at both collieries in controlling the roof but more so at South Bulli because of the massive sandstone roof. Face conveyors were damaged and jammed by falling roof, difficulties were experienced at Tail Gate and Main Gate ends of the face, chock legs were damaged by goaf falls and conditions were very dusty at times. At South Bulli conditions became so bad on its first longwall face the roof above the face conveyor on the first half of the face had fallen to a height of approximately 8m or more. It was decided to abandon this part of the face and the longwall block was then split up the middle of the block and then extracted on a 73m wide face. Both collieries carried on under difficult conditions with South Bulli modifying some of Coalcliff supports and adding other manufacturer’s supports (H.G. Wild) in trials attempting to improve conditions.
Because of the difficulties encountered in longwall operations when the face was stopped, and the potential of the longwall system, an application to the Coal Industry Tribunal for the right of 24 hour production was made and granted on 14th April 1967. This permitted continuous operations of longwall faces, and this was achieved by the use of 4 crews per installation. However, development work continued to be limited to 2 shifts per day.
Australian Coal Industry Research Laboratories at Bellambi were carrying out modelling of underground mining conditions (following their studies of these methods used in Germany). Frank Jaggar was the mining engineer carrying out this work and I kept in regular contact with him. He considered the main problem the longwalls were having in controlling the roof was caused by the setting load being too low on the roof supports. He also advised that he had tested individual legs of the Coalcliff chocks and had found that the pistons had lowered approx 8cm before reaching yield load.
I had the opportunity to accompany a Board member of The Joint Coal Board (Mr. S. Flowers) on an overseas mining study tour in 1967 which included:
- The American Coal Show at Cleveland (Ohio) where mining equipment (including longwall faces) from around the world were on display in an underground area of approx. 2 hectares.
- Visits to underground mines in Virginia (USA), Germany, France, the U.K. and Russia. In Russia we attended the 5th world mining congress held at Moscow University, and the Mining Equipment exhibition in Gorky Park Moscow with equipment from other countries on display also.
- Mining research centres were visited in each of these countries.
In each country I enquired as to the setting load being used on longwall roof supports. With the exception of the UK, mines visited in other countries were using higher setting loads than here on the South Coast. The most important discussion I had was with a French mining engineer (who spoke very good English) who explained how they kept on increasing their setting load on their roof supports and achieved the required results. After describing South Coast conditions to him he was confident increased setting loads would cure the problem.
On return from overseas I passed this information on to Lloyd Pearce (Asst. Supt. AIS Collieries) and to others.
Kemira Colliery chocks had been single acting (had to allow the weight of the canopy to lower the legs) and this had meant delays in lowering the legs. When Kemira chocks were modified and reinstalled in 1968 they were made double acting and each leg set at 25 tonne. The result was that conditions improved, production improved (and in my opinion) this face gave the first glimpse of hope re the potential of longwall mining on the south coast. L. Pearce stated later to me that he considered that using a higher setting load on the roof supports had been the answer.