Bonnington Weir and Stonebyres Bridges

Project Description

The Project required the reconstruction of two multi span bridges over the Lanark Gorge within a site of special scientific interest. Tight physical constraints and the proximity of high voltage cables added to the complexity of the Project.

Project Details

Client Scottish Power
Date 2009-2010
Skills Project Management, Design (Permanent Works), Design (Temporary Works)
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Our Role in the Project

The Project brief required the replacement of a reinforced concrete deck which was calculated to have insufficient capacity for maintenance vehicles. Site constraints include overhead high voltage power cables, close proximity to hydroelectric inlet gates and limited freeboard to spillways under the bridge. Diversion of the high voltage cables would have cost several hundred thousand pounds, so temporary works were designed to enable the bridge to be constructed with no crainage other than a 1T manual hoist. A crash deck was installed under the bridge, fixed using macalloy bars installed by a roped access team. The bridge was demolished by hand and using mini diggers, before the deck was in-situ reinforced concrete deck constructed on permanent formwork. Torus Design Ltd undertook all temporary and permanent works design and site supervision.

On completion of Bonnington Weir Bridge, a second structure at Stonebyres was completed. In additional to the works noted above, a temporary pedestrian bridge was provided to maintain access to a public right of way.


The bridges were constructed to the satisfaction of the Client, and are currently being used for maintenance access for the weir gates, and for foot traffic.

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