Monday, 25 July 2016

The eye in the sky: a new approach to monitoring abandoned mines...by Kieran Parker

The Phantom S900 UAV used by GSNI. 
Kieran Parker, environmental geologist with the Geological Survey of Northern Ireland continues to break new ground when it comes to locating collapsed mines. 

The Geological Survey of Northern Ireland (GSNI) work with the Department for the Economy (DfE) to monitor the many abandoned mines found in some parts of Northern Ireland. With over 2400 disused mine shafts and adits to survey, new techniques to improve coverage and safety are always explored.  

Parkmore mines are located just north of Cargan at the top of Glenariff, Co. Antrim and were worked for their iron and bauxite. Iron ore and bauxite were extracted from the Palaeogene interbasaltic formation, a layer of reddish-brown 'lithomarge', rich in clay, iron and aluminium oxides that developed from weathering of the underlying basalt. The area is one of extensive mining with the nearby Glenravel mines extracting the material and transporting it by narrow gauge railway lines to Waterfoot on the coast where it was shipped to market. The historic bridge, railway line and associated buildings are still evident on the landscape.

Aerial view of the Glenravel mines area. 
Parkmore mine is a large network of shallow mine pathways extending under the what is now Parkmore Forest and minor public roads. The system of mining used was the traditional room and pillar method where in situ ore rock is left as support pillars. Parkmore has previously been identified as having numerous surface collapses associated with the underlying mine but the area is now largely contained within a working forest, controlled and worked by the Forest Service of Northern Ireland with recent felling making it particularly difficult to access. The terrain is very uneven with high grass, a high density of tree stumps under grass cover and areas with previous subsidence now obscured.

Due to the number of adits and air shafts within the area as well as the rough terrain, surveying the land can be time consuming and hazardous. But GSNI's acquisition of an unmanned aerial vehicle (UAV) has meant that we can now use this to survey the area remotely with live aerial imagery fed back to a monitor at the base station. This method has proved so effective that during scheduled monitoring, two new collapses were identified within minutes of the survey; one was in an area that had undergone collapses previously with a retreating collapse of ground following the mine pathway, the other was in an area with no known previous collapse.

One of the mine collapses identified by the UAV.
The depression is approximately 10m wide.
Once the collapses were identified, the Forest Service of Northern Ireland were notified and the areas were fenced off to prevent members of the public and forestry working plant from entering the subsidence zones. The area is currently undergoing more extensive surveying to determine the full risk associated with the network of shallow mine pathways and plans are ongoing to implement long term remediation.

For more information on some of the other innovative techniques used by GSNI to monitor and assess abandoned mines then click here

No comments: