Unrecorded Shallow Coal Mining in Swansea
South Wales has a long complex history of coal mining. In the areas to the west of Swansea this has included a method of unrecorded shallow coal mining known as Bell Pits which is often overlooked when heavy reliance is placed on contemporary land searches.
A Bell Pit is a primitive method of mining coal that has been utilised since prehistoric times into the early 20th Century. A small shaft was sunk to reach the target seam which was then excavated by miners and transported to the surface via a crude bucket and winch system. The bottom of the shaft was then enlarged outward, and a curving feature created as the target mineral and surrounding rock is removed – forming a “bell” shape in cross section.
Typically, no support was used, and Bell Pits often flooded. This, together with the lack of support and the likelihood of collapse, meant they were dangerous to work and had a limited lifespan. As the next new Bell Pit was commenced, the arisings were sometimes used to backfill the previous pit. Bell Pits were not an efficient way of extracting minerals as they only partially exploited the resource.
The remains of Bell Pits can be identified by depressions left following settlement of infill materials or collapse of the features. In some places, they will follow a straight line as the seam of mineral is being followed.
In South Wales there is extensive evidence of this mining technique in the Penclawdd, Gowerton, Dunvant and Waunarlwydd areas. There is a particular risk posed by these features as they are often poorly recorded as they pre-date available Coal Authority and geological records and were also often utilised as non-commercial operations to supply individuals/families etc. who extracted shallow coal for personal use.
The physical risks associated with historic Bell Pits, stems from the subsidence and/or collapse of the shaft. Infilled pits may settle over time and sudden failure can occur.
Investigation and treatment of these features, generally comprises detailed Desk Studies of available information sources, essential site walkover (obvious depressions and adjacent spoil mounds can be common), followed by physical investigation that can comprise trial trenching/pitting and borehole investigation.