Coal Investigations

Coal Investigations

Remove The Risks To Your Site & Render It Suitable

Many think that coal mining is a modern problem, after all there are still coal mines around, but don’t be fooled, we have been mining coal since pre-historical times.

Equally, whilst coal mining is generally associated with Yorkshire and South Wales, that is as much of a misconception as how long we’ve been mining it.  Historically, as a nation we have also mined coal in Nottinghamshire, Scotland, the Northwest, the Northeast and even Kent (late 20th century).

Coal mining represents two potential issues to our homes and development in general.  Firstly, and probably the one with the highest level of awareness is that of subsistence, where worked coal seams collapse underground and that collapse works its way up to the surface causing subsistence.  The most dramatic form of subsistence is that of sink holes, although it must be remembered that coal mining is not the only cause of a sink hole, other mining operations can cause them, and they can occur naturally by the erosion of rock.

Coal mining takes place in two forms, deep coal mines and surface/shallow mines, known as opencast mining.

Deep mining is not such a problem to developments as, typically, we are talking tens of metres below the surface, with generally a decent thickness of solid rock between the surface and the worked seam.  Having said that, we still can’t ignore deep mines.

Near surface mining is the type with the longest history, the most common form, dating from pre-history is that of bell pits, where a hole is dug into the ground and the coal removed creating a bell-like profile, the diameter being a function of when the sides become potentially unstable, at which point the bell pit is abandoned and a new one sunk nearby.

These bell pits were typically backfilled with anything available at the time and not in what we now consider an engineered manner.  However, we still come across bell pits today.  Adits are another form of near surface mining.  Adits are generally found in hillsides where the coal is accessed horizontally (or nearly horizontally).

The other risk we encounter from coal mining is that of mine gas. Mine gas (or in days gone by, Firedamp) is a combination of Methane and Carbon Dioxide. However, both Carbon Monoxide (white damp) and hydrogen Sulphide (Stink damp) can also be present.

Mine gas is dangerous as its both explosive (due to its Methane content) and an asphyxiant (due to its Carbon Dioxide content).  As such the potential for mine gas must be considered in any development proposal.

The Coal Authority is the source of information on coal mining in the UK and if your site lies within a Coal Mining Development High-Risk Area, planning applications are required to include a Coal Mining Risk Assessment (CMRA).

A CMRA analyses is a desk study of data provided by the Coal Authority and other sources such as the British Geological Survey, assesses the associated risks of coal mining related hazards within the proposed site area.

Following completion of a CMRA, it may be necessary to carry out an intrusive investigation, which would be needed to confirm or remove the risks identified in the CMRA.  This type of investigation would involve deep boreholes, typically 30 to 40 metres in depth to locate any underground coal seam or workings and the installation of monitoring standpipes to monitor for mine gas.

Confirming that mining does pose a risk to a development doesn’t mean you can’t development a site, there are several remedial options available, such as bentonite grouting the coal seam.

In addition to providing both of the above investigative services, our team of experienced engineers and geologists can advise on the most appropriate and cost-effective remedial options to remove the risks to your site and render it suitable for the proposed end-use.