FUNDAMENTALS

longwall mining
 

advancing and retreating longwalls
   

retreating longwalls
 

Advancing and Retreating Longwalls

Retreating Longwalls

In this method, the gate roads are first driven from the main headings to the block limits and then connected with a roadway to install the face equipment. The gate roads may be connected to another set of roadways at that point for ventilation/gas control purposes. Once the face equipment is installed, production commences with the face retreating from the limit back towards the main headings, usually to finish at a position so that a barrier pillar is left to protect the latter headings.



Principle of retreating longwall

Because the gate roads are long, it is normally necessary to drive at least two (sometimes more) at each side of the block. That set of roadways which will be used for access onto the longwall and for coal clearance off the longwall are typically called the "maingate roadways" whilst the other roadway or set of roadways is typically referred to as the "tailgate roadways". The latter are used for primary access on occasions, but this is not generally the case.

As the face retreats, the roadways forming the face ends are destroyed and become part of the goaf. The other roadways will remain open if adequately supported and it is common practice for one of the remaining roads at the maingate end (usually only one in any case) to become the tailgate of the next block. The gate road first working pillars then become the chain pillars between the blocks.