In this method a succession of drives is made down the goaf side or sides of the pillar (picture).
Roof support for the drives is by rows of breaking-off propos placed along the goaf sideand with or without cross timber to support the immediate roof of the place. The method is only successful where;
- The strata are very strong and competent and give forewarning of a goaf collapse so men and machines can be withdrawn to safety, or
- The roof strata, while standing strong and competent across the breaking-off propos and falls regularly at the completion of each lift upon the progressive withdrawal of the timber.
This method of extraction had several deficiencies.
- With the exception of wooden props set along the goaf edge there was no protection for the machine crew
- The operators were exposed to goaf falls for a considerable length of time
- Changing stresses in the strata when the lift was holed at the back of the pillar gave rise to hazardous situations
- Strong roof that overhanged made operators nervous and significant time was wasted with the miners moving in and out of the lift
- Sequence moves were extensive and resulted in obvious loss of production time
- If the goaf flushed it either trapped the miner in the lift or prevents him from getting back in. It was this problem which forced alterations to the sequence of extraction and the subsequent loss of coal
This system is no longer a popular means of pillar extraction.