Sudbury sinkhole chaos directly linked to unrecorded historical mining

The people of Sudbury, a town in Suffolk, have had to endure traffic chaos for more than a month due to a gaping sinkhole that has occurred in the centre of the town. Tom Backhouse founder and lead geologist at mining specialist Terrafirma has revealed that this is not just an isolated incident and there could be many other areas across the region and the UK that are likely to be at risk from the often-destructive environmental phenomena.

Tom explained his findings further:

What is your theory around the cause of the sinkhole in Sudbury?

The recent ground collapse at Newton Road, Sudbury was very likely indirectly linked to historical underground chalk extraction from the mid to late 19th Century. Chalk mining is recorded to exist within 250 metres of the ground collapse and has historically caused subsidence in the local area, notably at Pot Kilns School and Maldon Court.

Taken into context, geological conditions are considered highly suitable for the subsurface extraction of high purity chalk and are analogous to known mining sites within Sudbury. Chalk mining in Sudbury is a result of extensive brick making in the town that occurred during the 18th and 19th Centuries, where chalk was an essential ingredient in the industry locally and nationally.

How can you be sure it is chalk mining that is the root cause?

Chalk was often quarried at the surface until overburden or land boundaries were reached, from which point, it was mined. In Sudbury, the chalk disappears beneath the Thanet Sand and it is from here that the known chalk mining occurs and is suspected to occur beneath Newton Road. Underground chalk mining was almost entirely unrecorded and was extracted by small galleries that are known locally to extend tens of metres from quarry faces and/or mine shafts. Interpretation of historical land use immediately adjacent to modern day Newton Road identifies several features of interest that infer underground mining, such as a shaft, mine infrastructure and spoil tip.

Is this just particular to Sudbury?

No, not at all. Where geological and land use conditions are suitable across the south and east of England and in numerous other urban locations, ageing utilities infrastructure is commonly triggering the collapse of shallowly mined mineral workings. In the case of chalk bedrock, even slightly acidic water can significantly increase the dissolution rate of the roof of a mine or pillars supporting the workings, eventually triggering collapse after a period of continuous water inundation, such as a faulty water main running beneath Newton Road.

Has this happened elsewhere in the UK?

This is known to have occurred in several other locations across the UK in the past 12 months alone, such as at Fontmell Close, St Albans and in Woolwich, South East London.

Where geological conditions are suitable and a historical demand for chalk exists, for example where there is a local brick making industry, a threat of mining-related subsidence/collapse exists. A large percentage of south and east England hosts these conditions and it is often within the outskirts of historical urban centres which have been developed in the last century, such as Sudbury, Norwich, Thetford, Bury St Edmonds and further afield at Reading, Hatfield, South East London, Rochester, Watford, High Wycombe and many more.

Could the Sudbury sinkhole have been prevented?

In short yes, a professional mining search would have revealed ground instability issues at this site. Mining search enquiries are necessary even when there are no obvious signs of mines existing in the area: when mines are closed, they leave little or no residual evidence on the surface, but can still cause major problems for land and property owners.

Just as in the case at Sudbury when looking back through history, much of the mining was undertaken in the 19th Century, upon which the Victorians subsequently built towns, using the very same minerals, for example, clay and chalk, to create bricks and cement.

What is a mining search and what should it include?

When asked what a mining search covers, most people refer to Coal, Cheshire Brine or Tin and consider the risk to be very specific to certain regions. There are over 60 different types of mineral extraction that have been carried out over thousands of years, across all regions of England and Wales.

A mining search should look beyond coal to consider the risks posed by other types of mining activity, such as clay, lead or chalk, all of which are significant factors in the ever-increasing number of sinkholes and mining collapses such as the case in Sudbury.

Terrafirma, a specialist provider of mining-instability risk assessment solutions to the UK’s Built Environment Sector.

This article was submitted to be published by Terrafirma as part of their advertising agreement with Today’s Conveyancer. The views expressed in this article are those of the submitter and not those of Today’s Conveyancer.

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