World-First ‘Mermaid’ Provides Innovative Solution in Scour Protection Project

Osborne and sheet piling sub contractor Suttle Projects recently collaborated to provide a world-first scour protection solution. 

The river bed needed to be dug out and replaced at the River Colne, near Staines in Surrey and due to deep, fast flowing water and low headroom of the bridge, traditional sheet piling techniques were not viable.  Therefore Osborne worked in partnership with Suttle Projects to overcome the problem by using its bespoke underwater remote control excavator nicknamed ‘The Mermaid’ for the first time commercially, believed to be the only one of its type to exist globally.

Working underwater brings a number of hazards and challenges, but Osborne worked with Suttle Projects to develop their own innovative solution. The mermaid was deployed, a remote-controlled fully-submersible digger, that scooped out the existing river bed.  Divers then set out grout bags – which had to be hand-placed underwater and layered to the right levels.  Finally silt could be laid over the top of the hardened grout bags. 

In the case of the Staines bridge, the headroom was far too low for a standard mini excavator to be used on a pontoon with an operative sitting in the cabin to work it.  In addition, the water was too deep to over pump the channel or divert flow to create a temporary dry work environment.  Therefore, the mermaid was deployed, situated on a floating pontoon to carry out the scour protection work.  Its lower height of 0.8 metres tall versus the standard height of around 2.7 metres meant it was able to work effectively under the bridge, and was safely activated a few metres away by an operative managing the remote control unit. 

The mermaid took 18 months to build in-house by converting a conventional mini excavator, with the project costing £65,000 overall.  This was done by removing the cabin and engine and adding remote controls.  The remote control unit was connected via hydraulic umbilical leads, supplying the machine with hydraulic power.  It works on a hydraulic pressure of around 150 bar, with a flow rate of 25-50 litres per minute, weighing 4 tonnes.  The mermaid is currently set up to work underwater up to 25m deep, but can easily be set up for deeper water conditions if required.

Paul Fagan, Osborne Site Manager, said:  “The use of this self-developed technology simplified a complex operation, significantly reducing the time divers had to spend in the water.  We are delighted with the outcome of this project and always look to new technology and better ways to deliver results.”

Director of Suttle Projects, Joe Paine, added ‘On a previous scour protection project with extremely heavy rainfall and a very low railway bridge, we used divers to place concrete, and also had to excavate with a type of venturi water suction pipe, suspended from our pontoon.  Although this did provide a solution, it was time consuming and costly.  We soon realised that a conventional small excavator that was able to work freely under water would provide the ideal, innovative solution.  We could find nothing of this type on the market globally, so with support from Ross Welsh at Pirtek Poole, who specialise in fluid transfer solutions, we decided to build our own machine, the mermaid, which we can also hire out to other companies, too.  By collaborating with Osborne to use this equipment in the project, we were able to provide an efficient and cost-effective solution for what was historically a complicated and expensive task.’