Discovery Of The Mines Instability

Discovery Of The Mines Instability

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Collapse
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Thickness Contours
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Unstable Pillar

Discovery of instability

Concerns were heightened in the late 1980s after a roadwork contractor hacked through a section of the mines with a backhoe while excavating a trench. The then Bath City Council appointed a team, led by Dr Brian Hawkins, to investigate and map the mines following repeated accidents by utilities contractors and the increasing traffic over the mines area.

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Dr Hawkins' study

The team also identified especially hazardous areas. The condition of the supporting pillars was examined and Dr Hawkins classified them 1 to 5 where 1 meant the lowest level of deformation and 5 represented the highest levels of deformation and deterioration. In essence, a classification of 5 meant that the pillar had failed and that it had minimal capacity to support the roof.

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Results of the study

A total of 3,737 pillars were surveyed with over 20% of pillars graded 3 to 5 which meant that they were deemed unstable with the remaining pillars considered unstable in the long-term. Nevertheless, given the potential domino effect which was likely to take place if one pillar collapsed, transferring the weight onto nearby pillars, even short-term stability of the mine could not be guaranteed for those pillars classified as 1 and 2. The conclusion was that the stability of the mines could not be guaranteed and a widespread progressive collapse could occur over a short time with extensive impact on life and property.

In 1994 Dr Hawkins completed a series of studies which identified the nature of the problem more fully. Only 1% of the solid floor was visible and roof collapses to within 3 metres of ground surface had taken place, some of which manifested themselves on the surface including collapses in the nearby golf course and rugby field and in people's driveways.

Following a visit in 2000, Her Majesty's Inspector of Mines (HMIM) recommended a series of safe access ways to be driven through the mines complex to determine the extent of remedial works required.

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