Engineering Design Consultants

Bringing 21st Centuary Design and Materials to Britain's Canals

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Twenty-first century materials and design techniques have been brought to bear by Bennett Associates on one of the UK’s most historic transportation networks and achieved a level of performance that would be the envy of even the most skilled craftsmen in their hey-day.

Over 40 years ago a length of canal connecting Speirs Wharf and Pinkston Basin on the Forth and Clyde Canal in north Glasgow was filled in, detaching the Port Dundas area from the canal network. The link is now being restored as part of a regeneration scheme for the area that will unlock unused land, improve the environment and provide opportunities for commercial developments.

One of the main elements of the project is the construction of two locks to provide access between Speirs Wharf and Pinkston Basin on the original canal and a new lake beside the M8 motorway. The water level of the lake is approximately 4.5 metres below that of the canal and has to be closely controlled because of its proximity to the motorway.

Bennett Associates were appointed by the main contractor for the project, C Spencer Ltd, to design the lock gates, safety booms, sluices and pumping systems for the locks and a pumping system to control the water level in the lake. Because of the difference in water levels, the gates at the lake end of each lock had to be unusually tall, measuring 7.2 metres high x 3.6 metres wide, while the upper gates are 2.5 metres high x 3.6 metres wide. The locks themselves measure 23 metres x six metres and are 5.2 metres deep.

Traditionally, lock gates were constructed from European green-heart oak or ekki, a West African hardwood. For the Port Dundas project both materials presented problems with regard to supply in the dimensions required, consistency of performance, installation time and other factors.

The gates are formed from mild steel horizontal beams faced with 8mm plate on one side, resulting in a structure that is 300mm thick. The sluice systems have been built within the lock structure itself, rather than the gates, avoiding the need to incorporate additional moving parts in the gates.

Bennetts decided that a completely new design using non-traditional materials would bring significant improvements in accuracy, speed of installation, durability, adjustability and ease of maintenance.

On traditional lock gates the heel and mitre posts perform three functions: they form part of the hinge mechanism, they have to withstand the weight of water upstream, and they have to prevent water from entering the lock. The triple function often particularly compromises sealing performance. Traditional gates also require specialist installation techniques, with limited fine-tuning on site possible, and they are difficult to adjust after installation if any movement or warping takes place.

Compromise concepts such as timber nosings and hybrid hinges were considered by Bennetts but abandoned in favour of a completely new design, including an all-steel structure, separate components for the load-bearing and sealing functions, polymer and rubber seals, adjustable hinges, stainless steel pins and Orkot bushes. Load bearing and sealing are performed by separate components.

Hinge supports consist of 200mm-diameter mild steel tube welded the full height of each gate, with stainless steel pins at the base and top. At the base the pins rotate on Orkot bearings within fixed galvanised steel blocks anchored with resin bolts to the lock floor, while the top hinges are held by fabrications with four threaded bolts that are cast into the lock wall and allow them to be adjusted. This design has resulted in a self-lubricating and wear-tolerant system.

The performance standards set by the British Waterways Board for the project required no more than 1 litre per metre of sealing face per minute to escape through the lock gates when they are closed. The use of different materials such as hard HDPE, P-seals, neoprene rubber and soft rubber to suit the conditions at different points of each structure has enabled an actual leakage rate that is 1.5 per cent of this figure to be achieved. The seals, which are positioned vertically on the heel and nose of each gate and across the base, will tolerate future deflection and can be replaced easily when necessary.

Each set of gates was installed in half a day -- far more quickly than traditional structures. After installation, steel plates were fixed to the lock floor and walls to provide a close seal with the base of the gates, which are opened and closed by hydraulic rams operated by an electrical control system. Boats are able to pass through each lock in about 15 minutes.

The whole project is being managed by British Waterways, which is also providing funding with support from Glasgow City Council, the European Regional Development Fund and the Garfield Weston Foundation.