Protecting Scotland’s rural landscape

AN initiative to remove electricity transmission lines currently impacting scenic landscapes across Scotland’s National Parks is underway, with Mabey Hire’s temporary bridging solutions playing their part in enabling the works.

In 2012, Ofgem announced plans for a £500 million fund to assist GB transmission owners in mitigating the visual impact of existing electricity infrastructure on nationally designated landscapes. Project VISTA (Visual Impact of Scottish Transmission Asset) is to play a key part in enhancing these landscapes within the north of Scotland transmission network.

As part of the project, principal contractor Morgan Sindall Infrastructure is engaged on a contract for SSEN Transmission to remove two overhead power lines from Killin to Inverarnan and St Fillans substations.

They will be replaced with new underground cables buried in uPVC ducting, installed by open cut trenching technique and by horizontal directional drilling (HDD) under the River Dochart.

Following energisation, 31 redundant steel towers will be dismantled and removed.

Given the rural nature of the project and site constraints, part of these works is being facilitated through the installation of a 45-metre-long temporary bridge designed, supplied and installed by Mabey Hire.

Constructed using the modular Mabey Universal bridging kit, Mabey explained that the bridge has been designed and built to divert heavy construction traffic away from the village of Killin in the Loch Lomond and The Trossachs National Park, avoiding a narrow historic bridge which attracts thousands of tourists to the area.

Mabey Hire was initially approached by Morgan Sindall Infrastructure Scotland and its consultant, Baker Hicks, two years ago at the early planning stages, when it was seeking competitive bids for the supply of a heavy duty access bridge to carry construction traffic up to a 55 tonne weight limit – including cable drum trailers and tractors – crossing the River Dochart.

With abutments already built by Morgan Sindall to the designs of Baker Hicks using a combination of reinforced concrete and Legato blocks, engineers took just three weeks to assemble the modular Mabey Universal Bridge sections and launch them using a 360 degree excavator. The completed 45-metre span bridge features an extra wide 4,500mm clear road width.

Alan Hendrie, the project manager for Morgan Sindall Infrastructure Scotland, said, “As a contractor covering a wide range of project types, Morgan Sindall Infrastructure has worked with Mabey Hire on many occasions in the past and so have a good understanding of the company. There are very few competitors who could have supplied the size of bridge required for the Killin VISTA project.

“The bridge was essential to minimise the amount of construction traffic travelling through the area, which would have caused disruption to Killin residents. We also had to consider the landmark Dochart Bridge, which is a single lane bridge measuring some 70 metres long. This bridge draws a lot of visitors and tourists, which would have made risk management more challenging.

“Mabey Hire shared its time lapse footage of past installations with the project team here during the tendering phase, which was very insightful, and the Mabey Universal bridge installed over the river has been specified to cope with heavy construction traffic, including low-loaders and the cable lorries. The work has gone well.”

The temporary bridge is expected to be in place for 62 weeks.

The current work in progress at Killin is the third phase of VISTA projects Morgan Sindall Infrastructure has undertaken, with 15km of transmission lines already moved underground in the Cairngorms and three 1,500m-long stretches addressed near Sloy