Longwall Roof Support

Site Name:	Longwall Roof Support
Address:	Princes Highway Russell Vale NSW
GPS Coordinates:	H 306861, E 6196305, HSL 25.0 Metres.
Site Access:	Public Access Hicks St.

From Picks and Shovels

The coal mining industry in the Illawarra witnessed the evolution of mining technology from men using picks and shovels through to the broadly mechanised, high volume production operations in use today. This evolution has been reflected in all aspects of mine operations, but none more so than in the central process of cutting and transporting coal.

Following the introduction of mechanised the mining in the 1940s, mining machinery developments progressed with continuous miners and shuttle cars replacing coal cutting and coal loading machines in the 1950s. However as the depth of cover overlying the Bulli Seam increased roof conditions deteriorated and production from the Continuous miner units decreased. This led mine operators to look for an alternative mining system and the retreat longwall system of mining was chosen.

Two principal approaches for mining are available today – the bord (room) and pillar approach, and that of longwall mining. The latter has been of particular importance in the Illawarra, with mines here having been associated with significant technology development. For example, in 1965 the first successful fully mechanised retreat longwall mining system in Australia was installed at the Kemira colliery at Mt Keira.

Bord and Pillar, and Longwall

A central part of mining technology development has been around the means by which a safe working environment may be maintained while mechanically removing coal at high rates from a working face. The longwall chock (or powered roof support) on display at this site is an example of how this has been achieved, compared to the alternative approach.The bord and pillar method of mining employs an approach where a coal seam is divided into a pattern of coal pillars and roadways with the pillars in that pattern either extracted later by a chosen pillar extraction method or left standing with the roadways supported by chemically anchored roof bolts drilled into the roof. Mining is carried out in the bords (‘rooms’) between the pillars commonly using continuous miners – large mobile cutting machines which feed coal to a shuttle car for transport away from the bord and pillar face.

While the development roadways driven to create a longwall mining block follow the principles of the bord and pillar method of mining, that system has been largely supplanted as the primary method of producing coal by the retreat longwall mining system as described here and here. Once these very large rectangular longwall blocks of coal are defined the coal is progressively removed by taking slices across the face of the block with mechanised coal cutting and transport equipment. As the mined face retreats and the block diminishes in length, the exposed roof is supported by hydraulically powered roof supports that follow the retreating face of the block along with the longwall cutting machine and supporting armoured face conveyor. The roof is allowed to collapse behind the roof supports as they follow and provide support to the exposed roof at the coal face. The longwall system of mining now accounts for most of the coal mined underground in  Australia. Powered roof supports are an essential part of a safe and efficient longwall mining system.

The Dowty Roof Support (Chock)

The roof support on display at Russell Vale was one of a number of identical supports supplied by the Dowty Engineering Company (UK) as one part of a longwall retreat mining system package. This chock was installed in the Balgownie Seam by the Bellambi Coal Company at the nearby South Bulli Colliery (now known as Russell Vale Colliery). Longwall mining of the Balgownie Seam commenced in 1970 with roof supports supplied by Gullick Dobson (UK) .These supports proved to be inadequate and in 1978 were replaced by the chock shield design support, displayed here and manufactured by Dowty Engineering. Longwall mining of the Balgownie Seam continued for several years beyond 1978. However high ash levels in the coal mined and longwall panel development costs eventually forced the abandonment of mining of this seam.In use, a total of 118 of these 450 ton capacity roof supports were installed side by side along the longwall face, having a width of approximately 180 metres.

History of Development

The Timeline here provides a snapshot of the first steps taken by a number of mines in Illawarra to harness the potential of the longwall system to successfully mine the Bulli Seam. A review of these first installations reveals that the roof supports supplied in the early equipment packages and manufactured in the UK, were structurally weak and completely inadequate for the duty, not having the capacity and structural strength required to support and control the sandstone roof overlaying the Bulli Seam. This led to damage of the roof supports, roof falls on the face and damage to other equipment in the package in the immediate coal face area.

These issues were addressed and progressively solved over time by the persistent efforts and tolerance of the mineworkers, mine engineers and longwall equipment manufacturers from the UK and later on Germany. Other issues that had to be addressed and resolved included airborne dust control, the operation of the face shearing machine, and control of gas make on the face and in the goaf, adjustments to the working hours of the longwall and longwall development panels and mineworkers.

The mines listed in the Timeline table pioneered the introduction and use of the Longwall Retreat System in this country at great expense, time and effort with a great deal of ”watching on” by other mine operators.

As time went on more bigger and better longwall installations followed. One of some interest and success was the Miniwall (short face length) unit installed in 1990 at the Brimstone No1 Colliery in the Burragorang Valley, supplied by a Chinese manufacturer.

The longwall system is now widely accepted as the preferred system of mining with each major item of the equipment package linked to a sophisticated system of automation and control with on line access at the mine site and beyond. Underground mines using the Longwall Retreat system of mining are capable of achieving annual production rates exceeding 3 million tons per annum.

A detailed early history of mechanised retreat longwall mining in south coast mines can be viewed here

TIMELINE

A Timeline – Longwall Roof Support

1963 (Feb)
Coalcliff 1 Westphalia Germany -Coal Plough, 2 Leg Roof Supports, Armoured Face Conveyor (AFC)
1963 (Dec)
Equipment removed & returned to Westphalia. Support density 80/115 tons/metre of face(tmf)
1964 (Nov)
Coalcliff 2 Gullick 6x50ton/ leg roof supports, AFC, Powered Shearer. Support density 250 (tmf).Ranging Drum Coal Face Shearing machine installed
1965(Aug)
All: Ranging Drum Shearers were supplied as part of all LW packages from this time onwards
1965
Kemira Gullick 6x50ton/leg roof supports, balance of LW Package similar Coalcliff 2
1965
South Bulli Ditto equipment package
1967
Kemira and South Bulli Coal Industry Tribunal (CIT) permits 24 hr continuous operation of LW faces
1967 +
Research modelling of roof support behaviour (ACIRL). Overseas study visits
1968
Kemira Roof Support legs modified from single to double acting. As supplied, legs hydraulically raised, and lowered by sandstone roof above.
1969
Appin LW package installed Dowty E type six leg roof supports 600 ton yield and setting load
1969-70
Appin Additional Roof Supports added at centre of face
1970
Coal Industry Tribunal (CIT) grants permission for 24 hours per day production on all mining units 5 days per week.
1970
South Bulli New LW Equipment package. Gullick Dobson 7 leg supports 500 ton yield & setting load 193(tfm)
1970
South Bulli Longwall installed in the No2 Balgownie Seam
1972
Kemira Longwall operations ceased.
1973
South Bulli Additional face supports added & support density increased to 323(tmf)
1975
South Bulli Japanese Taiheyo LW Package Purchased. First appearance of the Chock/Shield roof support with a non- flexible floor base
1979
South Bulli Nine LW panels completed
1980
Appin Westphalia LW package installed & included 4 leg Chock Shield roof supports.
1982
Westcliff LW package purchased & included Gullick Dobson 4 leg Chock Shields of 900 tons support capacity
1984
Corrimal Face width of 1984 installation increased from 50 to 100 metres. New Shearer installed