Mine Rehabilitation Handbook - Mining and Blasting

6.11 Abandoned Adits and Shafts
As with final voids, shafts and adits must be left in a safe condition and
will need to comply with the mine safety regulations. Potential problems
and hazards include subsidence, illegal access, fires, gas emissions,
pollution of surface or groundwater and a tendency to become illegal
rubbish dumps.
• Before closing off a shaft or adit, consideration should be given to
the possible need for future underground access, particularly when
no other workings exist in the area.
• Whenever possible, obtain information on the extent and design of
the workings and the geological conditions. Where there is a high
possibility of mine gas, seismic activity etc, ensure all structures
intended to seal the shaft are adequately designed. Seek advice.
• Check quality of mine water, it may be a useful water supply or a
potential pollution hazard.
• Remove all disused equipment and identify any waste ore or a
potential pollution hazard.
• Dispose of toxic wastes safely (not as fill in abandoned shafts) and
rehabilitate the area in accordance with relevant sections of these
guidelines.
6.11.1 Sealing and Closing
Selection of closure and sealing method will depend on site conditions.
Possible options include:
• Enclosure with safety fence or wall etc.
- encompass sufficient area to allow for subsidence;
- extend fence along line of adit excavation until rock cover is
sufficient to ensure protection;
- maintain enclosure while the adit or shaft remains unsafe; and
- do not rely on enclosure alone; cover the entrance to the shaft or
adit.
• Surface covers and caps.
- covers will help prevent accidental access, illegal dumping etc
when used in conjunction with enclosures but will not protect
against subsidence or support heavy loads;
- use concrete, steel plates etc to raise cover above the ground
level to avoid accidental loading;
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- make sure covers are sufficiently large to prevent burrowing
around the side by vandals etc;
- concrete caps (for shafts) should be made of reinforced concrete
supported around the periphery of the shaft by solid bedrock; and
- shaft caps should be sufficiently thick to prevent subsidence and
support normal loads, including suction or pressure from
collapsing fill or mine gas.
• Shaft plugs constructed at depth in order to retain access to the
upper levels.
- Plugs should be watertight and designed to accommodate
permeability, elasticity and compressive forces adjoining strata or
accumulated water. Seek specialised assistance.
• Backfilling with selected material.
- do not use abandoned shafts as disposal sites for rubbish,
chemical residues etc;
- where mine gas is present, avoid tipping quartzite, concrete rubble
with metal reinforcing or other material liable to cause sparking;
- the base of shafts should be stabilised with clean, hard, free
draining rock fill to a depth at least five times the diameter of the
shaft; and
- general fill suitable for filling a shaft (other than at critical points)
should be stable and able to fill voids and support the shaft linings
e.g. broken stone, brick and concrete rubble etc.
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