Gas Main Slope Stabilisation

Scope

Working alongside our geotechnical engineers, Coffey Geotechnics, Vertical Access was appointed to deliver a comprehensive stabilisation solution to the affected western embankment.

The works included soil nailing across the unstable slope, installation of erosion control measures and construction of a new drainage system to manage water across the embankment. The programme formed part of the wider remediation of the former industrial site and had to be completed without delaying ongoing works.

The Challenge

The movement of the embankment created difficult ground conditions across an already complex former industrial site. The affected slope comprised varying layers of soft overburden, mudstone and coal seams, requiring the stabilisation design to respond to changing conditions below the surface.

The works also needed to be delivered within a tight programme to prevent delays to the wider site remediation. Trial drilling and anchor testing were therefore required to establish accurate ground information and allow the final design to be developed efficiently.

The site's former industrial use presented an additional environmental consideration. With extensive remediation already underway, the stabilisation works had to be carefully managed to prevent further ground contamination while working across the affected embankment.

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Our Response

Vertical Access worked closely with Coffey Geotechnics, using information gathered through trial drilling and anchor testing to develop the final stabilisation design around the conditions encountered on site.

Our geotechnical team utilised 35-tonne long-reach excavators, operated by our own CPCS-qualified drivers and fitted with specialist TEI drill masts. This arrangement enabled a total of 587 soil nails, ranging from six to eleven metres in length, to be installed through the soft overburden and underlying mudstone and coal seams.

Remote-control drilling systems were used to allow operatives to remain separated from the drill rig during installation, while work restraint systems designed and installed by Vertical Access provided safe access for personnel working across the embankment.

Following the soil nailing works, MacMat R erosion control matting was installed across the slope using work restraint techniques to provide additional surface protection.

Managing water across the embankment formed another important part of the stabilisation strategy. New crest drains, approximately 450mm wide and reaching depths of up to 1.6 metres, were excavated using a six-tonne excavator operating along the crest. Geotextile, drainage pipe and stone were installed before the system was connected into precast concrete chambers and brick-built catch pits.

Given the site's history and ongoing remediation, defensive bunds were also installed around the working area to reduce the risk of further ground contamination during the works.

Close coordination between the site team, geotechnical engineers and VolkerStevin allowed the stabilisation programme to progress alongside the wider remediation works without impacting the main project programme.

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Outcome & Feedback

The embankment stabilisation and drainage works were successfully completed in accordance with the agreed programme, allowing the wider remediation of The Avenue to continue without delay.

A total of 587 soil nails were installed alongside the erosion control and drainage measures, providing a comprehensive stabilisation solution for the affected western embankment. The works were completed without safety issues while operating within the challenging conditions of a former industrial site.

Upon completion, a detailed As-Built Report was provided to the client in accordance with the contract, incorporating the final drawings, drill logs and records of the completed stabilisation and drainage works.

The wider project subsequently received an Outstanding Achievement Award under the Civil Engineering Environmental Quality Assessment and Award Scheme (CEEQUAL) in 2019.