GS Littlejohn, BSc(Eng), PhD, CEng, MICE, MIStructE, FGS. This paper was first published in GE’s May 1979 edition.
Bearing in mind the variety of coal mining methods and extraction patterns developed in Britain over the centuries, together with the present-day situation of these same workings in various states of deterioration or collapse, no one method of treatment can be recommended to satisfy all conditions.
The workings may be single or multi-seam, horizontal or inclined, open or collapsed, dry or waterlogged, or underlying unconsolidated deposits or fractured rock strata as a result of partial subsidence. Old mine shafts with their range of diameters and depths may be empty, backfilled completely from the bottom, or the infill may be supported on a natural obstruction or platform at a shallower depth.
All these variations lead inevitably to varying solutions, and in practice the correct diagnosis of the problem and choice of the most suitable remedial treatment is a reflection primarily of the qu’ality end quantity of site information coupled with specialist experience.
Since a thorough and detailed site investigation is vital if an economical and safe solution is to be logically determined, basic guidelines are first presented on general site assessment and ground investigation, followed by a detailed description of grout consolidation techniques which are applicable to certain common categories of old workings including mine shafts.