Len Wright, 2011.

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.

Introduction

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.

Coalcliff Colliery

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The unit was withdrawn in December 1963 and returned to Westphalia after taking nine months to mine 6,300 tonnes of coal.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, the development of future longwall panels continued to be limited to 2 shifts per day.

ACIRL

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 hydraulically powered legs of the Coalcliff supports and had found that the hydraulic pistons in these legs had lowered by approximately 8cm before reaching their yield load set point.

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:

1. 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.

2. 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 along with equipment from other countries on display.

3. 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

Kemira Colliery supports installed in 1965 were of the single acting design, using the weight of the canopy to lower the legs, and this created 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.

Longwall operations at this colliery ceased in 1972 after mining in excess of 1 million tonnes involving 7 individual longwall panels.

South Bulli Colliery

In 1970 a second longwall unit was installed in the Bulli seam – Gullick Dobson 7 leg supports of 500 tonne yield and a setting load of 193 tonnes/m of face.  Some reasonable production was achieved – Westphalia supports were added to the centre of the face in 1973 having a setting load of 323 tonnes/m length of face.

A new Japanese Taiheyo designed and built equipment package arrived towards the end of 1975 and was of the chock shield design and a setting load of 313 tonnes/m of face.  After modifying the Mitsui shearer drum to allow pick point flushing for water sprays re dust suppression the unit was installed underground.

This unit, in my opinion, proved to be the first successful Longwall unit in the Southern District in terms roof control, reliability and production.  On the 9 Longwalls mined with the Taiheyo supports no bent legs or other major hydraulic failures occurred.

By the end of 1979 the longwall faces had produced in excess of 8,000 – 9,000 tonnes /day.  In 1980 Dowty 4 leg chock shields supports arrived.

Appin Colliery

Towards the end of 1968 Dowty six leg E type chocks of 600 tonne yield load, a setting load of 30 tonnes/leg and an Anderson Boyes double ranging drum shearer arrived at the colliery.  The unit was installed underground in February 1969.  The usual teething problems were encountered in using the equipment but these chocks survived the first two panels without modification.

The chocks were modified from 6 to 4 legs for longwall 3, including lengthening because of damage to back legs caused by goaf falls. The chock pressures were increased to compensate for modifications.  Problems on longwall 3 indicated stronger chocks were needed in the centre of the face and 15 Dowty 4 leg chocks with 120 tonne yield legs were installed in the centre of the face.  As production increased, many other modifications to equipment were required to handle the increased volume of coal and included the quality of maintenance. 

From 1969 to 1979 production increased from 1,000 to 3,000 tonnes/day.  In 1980 Westphalia 4 leg chock shield type supports arrived with an Eichoff shearer.

Corrimal Colliery

In 1980 Dowty 4 leg chock shields 630 tonne yield load supports arrived.  These chocks were the first to be equipped with electro hydraulics in Australia.  Unfortunately a second hand face conveyor from Appin was used and caused considerable problems and was replaced by another refurbished face conveyor from South Bulli for the next face.

In 1984 face width was increased by 50m to 150m.  A Mitsui shearer replaced the Anderson Strathclyde AB 16 and an upgraded face conveyor installed.  The fifth longwall block achieved tonnages exceeding 8,000 tonnes/day.

Westcliff Colliery

ACIRL recommended a support capacity of 800 tonnes/chock following model studies of Westcliff conditions.  Westcliff increased this to 900 tonnes and selected Gullick Dobson 4 leg chock shields, an AM 500 Anderson Strathclyde shearer. The latest monitoring equipment for the shearer and roof supports was incorporated in the system.  This equipment was installed underground in 1982.

Sumamry

Methods of producing coal underground have always been an evolving process and this is expected to be the case into the foreseeable future.  In the earlier years of the introduction of mechanized retreat longwall mining to South Coast mines there were major problems to be overcome including

1. The need for adequate strength and setting loads in the roof supports to control the roof under massive sandstone.

2. The roof supports had to be designed to provide early forward support, protect the legs from goaf falls and also prevent the rilling of goaf between the supports.

3. The face conveyors and associated transport system had to be increased in capacity and strength to carry increased production.

4. The shearers had to be modified – double drum instead of single.  Drum width was increased as roof control improved and pick point water sprays introduced to help suppress airborne dust.

5. Many other factors had to be taken into account to suit local circumstances at a mine including gas drainage, speed of development of roadways for future panels etc.

A further application was made in 1970 to the Coal Industry Tribunal for 24 hour per day production on all production units.  “In response to the Tribunal’s indication that the Joint Coal Board should present relevant factual information, statistical and otherwise, the Board sought and was granted leave to intervene.”  The Tribunal granted permission for 24 hours per day production on all production units 5 days per week and an award working week of 37.5 hours initially, later reducing to 35 hours.

The mines with longwall equipment subsequently adopted a system based on 4 shifts per day for development work in exchange for an award working week of initially 37.5 hours and later reducing to 35 hours.  This helped to increase production and enhanced the utilization of capital equipment.

Conclusion

Great credit must be given to the mining engineers and the mineworkers involved in the early introduction of mechanised retreat longwall mining in the Southern District who had to endure considerable and extreme difficulties at times – sometimes heartbreaking – but they persevered and won.  Credit must also be given to the equipment manufacturers prepared to modify the design of their equipment to satisfy the requirements and needs of the South Coast mines.

These mines pioneered the introduction of mechanised retreat longwall mining in Australia at great expense, in what was considered to be poor roof conditions and eventually obtained much higher production than could be obtained from continuous miners. It is also considered to be a safer method than pillar extraction with continuous miners.

Other mining companies throughout Australia (understandably) “sat on the fence” regarding the introduction of longwall mining operations into their mines to await the outcome in South Coast mines.  However, once the major problems were seen to be overcome in the South Coast mines and the great potential was seen in the benefits of longwall mining, this system has since spread into mining areas in NSW and Queensland considered to have good roof conditions as well as those with poor roof conditions.

In recent times, with continued evolution of mining systems and equipment, longer faces which have assisted goaf caving and better roof control, much higher production is being obtained locally with one mine achieving close to 3 million tonnes in 2006-7.  In the same period the top longwall producer in NSW and Queensland was 5 million tones from a NSW mine.

With further evolution likely who knows what future production may be?

References

1. AusIMM – Illawarra District Conference 1976

Longwall Extraction at South Bulli Colliery – K. Ross

Longwall Mining at Appin Colliery. – A.E.R. McCoy

2. AusIMM – Australian Coal Mining Practice – Monograph 12 – 1986

Chapter 1 – Historical – C.H. Martin

Chapter 21 – Longwall and Shortwall – A. McDonald

3. Joint Coal Board Annual Report 1970-71 P 51

4. Personal notes, photographs and observations.

Original author of this information Len Wright 23/8/2011

Rev 1 GK/RAC 28/10/2014