Combe Down and Bathampton Down Mines

Combe Down and Bathampton Down Mines is a 6.22 hectare (15.37 acre) Site of Special Scientific Interest (SSSI) in Bath and North East Somerset, notified in 1991, because of the Greater and Lesser Horseshoe bat population.

The mines dates from the 17th and 18th Century and were used to extract Bath stone for the city of Bath, and have since been disused.

A project which started in the 1990s is underway to stabilise the mine workings which are very close to the surface and present a risk of collapse.

Geology

Combe Down forms a plateau capped by Great Oolite limestones between the valley of the River Avon and Horsecombe Vale. The geology of the region is dominated by rocks of Middle and Early Jurassic ages. The Great Oolite is the uppermost lithology. This is underlain by the clays of the Fuller’s Earth Formation, which in turn is underlain by limestones of the Inferior Oolite and the Midford Sands of the Lias. The Great and Inferior Oolite formations provide effective aquifers (rock in which water can be stored and pass through) for public and private water supplies.

History

The Great Oolite stone, used for building purposes, formed over 146 million years ago when the area was underneath a deep tropical sea on which the shells of ooliths were deposited. The ooliths bonded together to form the distinctive rock known as oolitic limestone or locally as ‘Bath stone’. The Romans found that it was easily worked and used it for important fortifications. During the 17th Century, small quarries were opened, with major quarries being developed in the 18th Century to produce the Bath stone used for most of the buildings in Bath. Stone was extracted by the "room and pillar" method, by which chambers were mined, leaving pillars of stone between them to support the roof. These mines were once owned by Ralph Allen (1694–1764).

The mine contains a range of mine features including well preserved tramways, cart-roads and crane bases. The walls and pillars of the mine are studded with pick and tool marks and show evidence of the use of huge stone saws, all of which bear testimony to the variety of techniques used to extract the stone over the mine's three hundred year history.

No mine abandonment plans of - either the tunnels or the caverns, known as voids - were made prior to the 1872 Mining Act. Following their closure were used for a variety of purposes, including a mushroom farm and as an Air-raid shelter during the World War II Baedeker raids on Bath.

During 1989 a utilities contractor unexpectedly broke through into part of the mines complex whilst excavating a trench, which raised concerns locally which resulted in the then Bath City Council commissioning studies to survey the condition of the mines. It was clear that the mines were in a very unstable state and some experts considered them to be the largest shallowest and most unstable of their kind in Europe.

Mine and environmental survey

An underground survey of the Firs and Byfield mine areas was carried out in 1994, commissioned by the then Bath City Council. It was found that approximately 80% of the mines had less than 6 m cover and as little as 2 m in some places. Irregular mining and robbing stone from supporting pillars had left the mines unstable.

Approximately 80% of the mines, which are up to 9 m high and cover a total area of about 18 ha, had less than 6 m cover and as little as 2 m in some places.

An Environmental Impact Assessment was completed for the stabilisation scheme and submitted to the Local Planning Authority in December 2002. This highlighted that the mine is; within the World Heritage Site of the City of Bath; adjacent to the Cotswold Area of Outstanding Natural Beauty (AONB), within a conservation area, containing a number of Listed buildings; a Site of Special Scientific Interest; a candidate Special Area of Conservation; of international importance for Greater and Lesser Horseshoe bats; and of international geological importance partly due to the work of William Smith. Ritchies contract to create bat tunnels

During the access and emergency works Oxford Archaeology produced large scale plans of visible areas and substantial photography was carried out as the modern roadways allowed access. There were also trials of video photography and laser scanning, so that a substantial record has been produced of some 20% of the known workings.

The mine also lies above a Grade 1 aquifer from which water for public and private use is extracted via the springs that issue at the base of these units, in particular at the Prior Park, Whittaker and Tucking Mill springs.

Mine stabilisation project

In March 1999, the then Department of Environment, Transport and Regions (DETR), now known as the Department for Communities and Local Government, announced a Land Stabilisation Programme, based on the Derelict Land Act 1982. This programme was designed to “deal with abandoned non-coal mine workings which are likely to collapse and threaten life and property”. A Bath and North East Somerset Council outline bid for a two-phase stabilisation project was accepted in August 1999, by English Partnerships who administer the programme for the Office of the Deputy Prime Minister. A parliamentary Statutory Instrument (2002 No. 2053) was needed before the work could be undertaken.

Approximately 760 properties were included in the planning application boundary - we estimate that ca. 1660 people live within this area, which also includes a primary school, a nursery and 3 churches. Currently there are weight restrictions on the local roads, and width restrictions have been fitted to stop lorries passing through the area. As of mid-June 2006 there are also traffic lights along North Road. In September 2006 subsidence was noticed along Combe Road, at its junction with Westerleigh Road, and this road has therefore been closed for the foreseeable future. It is hoped that the road will open sometime in 2007 depending on the progress of work underneath.

Foamed concrete has been selected as the solution for the large scale infilling of the old mine works. It is planned that over 400,000 m3 of foamed concrete will be placed in the shallow underground mines, which potentially cover more than 25 hectares. This is the single largest application of foamed concrete on a project in the UK.

References

External links

• Photos of the inside of the mine