As we say in Yorkshire, "where there’s muck there’s brass"
Many parts of the United Kingdom have been affected by past mining activities at various times throughout our history. These have left a legacy of potential geotechnical & geo-environmental issues across Yorkshire, its surrounding counties, as well as many other parts of the UK as a whole.
How do we look at the risks?
The associated risks to a site or a proposed development vary just as much as the geology across the United Kingdom does. In basic terms, the risks are tied strongly to the underlying geology and when mining was carried out.
What was actually mined?
Although most mining was centred around the Industrial Revolution and extracting the coal that powered it, many other minerals such as iron, sandstone and other metals were also mined, often long before coal was sought on an industrial scale.
Understanding mining risks: how can we help?
At Abbeydale Geoscience we help our clients to understand what mineral seams are expected below a site and how any recorded or unrecorded shallow mine workings could affect what they want to do. This is why it’s important that we get to know as much as possible about what you want to do.
A Mining Risk Assessment is the first step in understanding the potential impacts of past mining activity and can be supplemented by an intrusive Shallow Mining Investigation if needs be.
As geoscience consultants we use a range of different data sources; from geological maps, memoirs and cross sections, to archive borehole records and ground investigation information, to really get a picture of what we think is happening under the site. More often than not the topography also plays an important part in the potential risks from underground mining. We bring together as much information as we possibly can about the geology and geomorphology of every site that we look at for our clients.
Understanding the legacy issues
Because mining occurred at various times throughout history, all using different technologies and techniques, the risks can be as much based on when mining is recorded or interpreted to have occurred, as well as the geology beneath a site. When technologies were more limited it wasn’t possible to dig as deep and keeping mines dry was a big problem until steam engine pumps were brought into use.
By looking at the historical setting of a site and the area that the site is in, Abbeydale Geoscience can look at when and where mining might have occurred, and what this might mean to a development. Earlier workings tended to be by bell pits, with pillar and stall and eventually long well mining and opencast mining techniques used more recently.
Sometimes when mining occurred in an area extraction might only have been possible in certain locations because of favourable conditions there. If you couldn’t keep a mine dry you wouldn’t be able to dig there would you?!
Although abandonment plan records were sometimes submitted to record where mining had taken place across the UK, it wasn’t until 1872 that this was a statutory requirement once mining had finished. Lots of mining had already occurred by then, particularly small localised workings by bell pits. That means that there are still lots of potentially unrecorded mine workings that aren’t documented anywhere. Often historical maps are good indicators of past mining activity, which is why we like to check them when we undertake a Mining Risk Assessment to provide a robust review of all available data sources.
How do we evaluate the potential risks?
The answer is quite simple, but also not simple at the same time! Overall the risks depend on how deep any coal or mineral seams are, how thick they are (or any workings to extract them) and how much rock cover is anticipated above them. We look for a certain ratio of rock cover above any potential or known mine workings.
If there’s enough rock cover then it might be that a collapse wouldn’t be expected to affect the surface stability of a site, or it may not affect down to foundation level for any proposed structures. The risk is really a blend of what’s in the ground (or been mined out of it!) and what is being proposed to put into it now.
