Gilmerton Station Road, Edinburgh – Consolidation of Mine Workings

Project Outline

GBLE undertook bulk infill consolidation of shallow mine workings in the Edge Coals beneath a large (43 hectare) site on the outskirts of Edinburgh in order to provide surface stability for the construction of over 400 residential units. The works were carried out simultaneously under three separate contracts for three housebuilders, under the instruction of two specialist Engineers.

The sites were previously green field agricultural sites, albeit with a long history of coal mining attached to them. The Edge Coals are well known for being situated within sharply dipping rock strata, particularly so in this area where they vary from 50 to 75 degrees from the horizonal.  For this reason they are known to be challenging to consolidate due to the difficulty in pinpointing the multiple outcropping seams, and in retaining the injected grout in-situ at the shallow depths where it is required.

In addition to the old workings recorded on abandonment plans, archaeological surveys uncovered other possible mining features through the site, leading to additional mine entries requiring treatment. Our strategic approach was therefore continuously being updated and amended to achieve and maintain program.

Following commencement of the first package of works for Miller Homes at West Edge Farm, the sites for Barratt Homes and Persimmon Homes further north began and GBLE had 3 sites running side by side as separate contracts. To execute the contracts effectively, GBLE utilised a total of fifteen drilling rigs, three separate mixing compounds including Cement silos and electric mixers and a workforce of over fifty personnel.

Across the 3 sites, over 16,500 boreholes were drilled, 26 mine entries were investigated (17 of which were treated) and in excess of 20,000 tonnes of grout were injected. Pressure injection of 240 test holes upon completion confirmed the successful stabilisation of the workings and allowed the developments to proceed.