Posted by: admin November 10, 2015


In November 2014, drilling of our southern coalfields vent shaft project reached its target depth of 516m. This is the deepest blind-bored shaft ever constructed by Abergeldie. It is a monumental achievement for the drilling team; even greater considering the shaft’s unusually broad 6.2m diameter and the challenges of very hard rock in the lower strata.

Fabrication of the 170 composite steel/concrete liner units was carried out in a temporary factory facility which Abergeldie set up on-site. Each segment is 3m deep, with a finished internal diameter of 5m. Once all the liners were installed, the annulus between the drilled shaft wall and the liners was filled with grout to give a smooth, hydrostatic finished surface.

Another of the team’s major challenges was working to the treat the drilling process water. The blind boring process uses up to 18 million litres of water, which carries away the drilled spoil as suspended solids. The concentration of suspended solids can be as high as 70%. The solids had to be removed so that the process water could be reused again and again as boring proceeded.

Despite some delays in drilling due to unusually difficult ground conditions, the project was successfully completed June 2015. Abergeldie is proud to deliver this significant project for a very valued client.

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Abergeldie was contracted by Centennial Coal’s Newstan Mine to sink and line a 180m deep, 6m finished diameter shaft. Liners were steel only rather than the traditional steel/concrete composite liners which have been previously used on other shafts.

Complex Challenges:

Due to clay bands in the strata Abergeldie used drill muds to prevent water absorption and maintain the integrity of the shaft walls. The unstable ground meant a large amount of soil needed to be excavated and benched to successfully install the pre-sink foundations. The sites footprint was very small and, as such this constraint has required the some creative thinking and ingenuity in installing the sedimentation ponds. Careful calculations and lateral thinking allowed the installation of 2 sufficient sedimentation ponds to allow for effective settling of the water which to be then used in the reverse circulation process of removing cuttings from within the shaft.

* Photos are courtesy of Centennial Coal