Shrigley 5 June 2014

Client shrigley photo   geotec4 thumb

The Challenge

Geotec Surveys were contacted by Down District Council to provide an underground mapping survey to search for and map any evidence of voiding and anomalies, that may be located in the ground below the grassed recreational area identified in the photographs above.

It was indicated that originally this area of land, measuring around 5,000 square metres, was the site of the mill houses, built around the 1820's and at present is being used as a general amenity area where children play.

The BBC has since discussed the problem as part of a news article ( whereby local councillor Billy Walker said: "It could have been a great danger, not just to kids, but also to council officials who cut the grass."

He added: "They use machinery that weighs a couple of tonnes, and if they had gone over one of the holes, someone could have been seriously injured or killed".

The Solution

Due to the health & safety dangers and concerns relating to Council workers and the Children that play there, an urgent survey was required to understand and record where the voids may be located and to enable the Council to make the right areas of the amenity area safe.

Shrigley is located within a mile of Geotec Survey's Northern Ireland office, based in Killyleagh, County Down and as such Geotec Surveys were able to carry out a survey of the area almost immediately.

In order to achieve our objectives, Geotec utilised a trolley-mounted Ground Penetrating Radar System (GPR), designed to search for buried features and anomalies to a maximum depth of 2 metres from the ground surface.

This equipment was pushed across the site on an orthogonal grid, from which a series of parallel scans were made.

This physical detection method is also coupled with any available historical records which were given to Geotec Surveys, by the council, prior to starting on site.

Geotec Surveys also carried out a basic topographical survey of the area, so that we had sufficient information for the production of an AutoCAD base drawing, onto which the results from our underground mapping survey were overlaid, and presented in 2D plan view.

The survey identified that remedial works were required in the first instance and the results have enabled the Council to identify where these are required, allowing us to go out to tender to appoint a suitable contractor to carry out the appropriate work

Down CC

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Methods & Techniques

  • Radio Frequency
  • GPR
  • Resistivity / Imaging
  • Electro Magnetics
  • Micro-Gravity

The Result

Our on-site survey team identified areas of significant sub-surface disturbance, synonymous with land that has been subject to poorly compacted in-filling, highlighted in purple on the accompanying drawing, which could lead to the appearance of voiding in some areas.

The team also discovered areas of a hard, shallow, sub-surface which may indicate the position of a buried road, with depths indicated on the drawing.

The Council have since gone out to tender to appoint a suitable contractor to strip off the top soil, install hard-standing, compact this with a roller and then reinstate the ground so that it can be used as a safe play area for children, once again.

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