FUNDAMENTALS

longwall mining
 

advancing and retreating longwalls
   

Comparison of Advancing and Retreating Longwalls
 

Advancing and Retreating Longwalls

Comparison of Advancing and Retreating Longwalls

The advantages of retreating longwalls compared to advancing are:

  • Gate road formation is remote from face operations (less congestion at face ends, less supplies into longwall face area, face not held up waiting for gate road preparation or vice versa, no problems of dust production from gate road workings affecting longwall personnel).

  • No gate or roadway side packs required, so less supplies overall

  • Longwall block is surrounded by roadways before the longwall starts so knowledge of strata conditions is much better

  • Gas drainage of adjacent blocks can be carried out starting during development; with longwall advancing the drilling can only be done behind the face after longwall extraction, allowing less drainage time before the next block commences production

  • With retreat longwall mining, additional gateroads or bleeder roadways behind the goaf area can be developed for ventilation by the development unit if required. Such additional roadways are much more difficult to mine with an advancing longwall

  • There are more options for ventilation/gas control using additional roadways at the limit of the block

  • Advancing longwall gateroads typically require extensive maintenance to maintain the roadway cross-section (roof and floor brushing) during the life of the longwall block, whereas retreat longwall gateroads are allowed to collapse behind the retreating face

The only real advantages of advancing longwalls are:

  • Production can begin earlier as the mine does not have to wait for the gate roads to be developed before longwall production can commence (provided development rates are adequate this should only apply for the first longwall in a mine)

  • It provides an opportunity for disposal of stone which has to be excavated into gate side packs (this benefit is probably more than offset by the costs involved in pack construction)

As far as the writer is aware, only one advancing longwall has been worked in Australia, a hand worked face at Stockton Borehole Colliery operated from the late 1890's to the mid 1950's.