Mine Workings and Voided Ground

Geophysical survey enjoys widespread application within brownfield studies and over the years we have located many bellpits, costeaning / trial pits and shafts of various sizes and dates across both coal and the metalliferous mining areas of Cornwall, Devon and Wales. We work to assist invasive investigation and remediation, augmenting and providing context for the work of drilling and engineering contractors.

Detection of shallow mine workings, lost wells and other voids

Geophysical detection of former mine workings, followed by targeted truthing, provides a more reliable and comprehensive result than trenching alone and benefits include:

greater depth of investigation (3+ m);
high lateral resolution throughout (e.g. 1m);
can be used in sensitive areas e.g. SSSIs or over weak ground;
rapid investigation, faster than trenching;
better targeted drilling or pitting, minimising disturbance.

Targets that can be detected include subsidence (e.g. slumping of soils), voids, the masonry or brickwork of linings and collars, capping slabs and plugs, as well as more subtle indicators like buried rubbish and evidence for past landscaping.

Leeds Shaft Wheal Prosper - B. Jones — View into a recently collapsed shaft in Cornwall - B. Jones

Rapid magnetic and electromagnetic techniques can identify pithead structures, collars, caps and voids as well as indirect indicators like debris scatters, pipework and tramway remains. For deeper targets electromagnetic and radar methods can search to about 5m and for large voids, e.g. stopes, micro-gravity can be used.

Magnetic data across shaft collars — Rapid magnetic survey here revealed shaft collars and open shafts beneath (probably timber) caps within an 'ordinary' arable field in Cornwall

Investigation of subsidence

While drilling can identify a void, sometimes a non-invasive approach is more appropriate, e.g. to explore the context of subsidence. The use of radar can be invaluable for a 'first look' and / or to target subsequent drilling or excavation.

GPR section through subsidence near Mary Tavy, Devon showing typical distortion of sediments and successive fills within unstable ground

Why use TigerGeo?

We can bring key skills including geological assessment of strata to determine whether disturbed or natural and identification of rock fragments as surface or from depth. Many years experience of landscape survey across the UK, combined with detailed knowledge of surface mining structures from late medieval times onwards means we can effectively target methods and areas.

Electromagnetic survey underway in the mountains of the central Wales lead mining district

2D / 3D electrical resistivity tomography, electromagnetics, ground penetrating radar, micro-gravity, seismic reflection / refraction