Modular hydraulic props from Groundforce Shorco are providing support on the Teddington Launch Lock refurbishment project.

Teddington Lock is a complex of three locks and a weir constructed at the boundary between the 'retained' upstream river and the tidal downstream stretch.

Main contractor BAM UK & Ireland is currently carrying out civil engineering works for the Environment Agency (EA) to the lock gates in the Launch Lock – a conventional lock used for regular river traffic.

While work is underway on the Launch Lock, the adjacent Barge Lock remains operational to divert river traffic.

BAM has constructed temporary stop-log dams at either end of the 54m-long Launch Lock and emptied it with dewatering pumps to allow removal of the lock gates and access to the gate foundations and hydraulic opening mechanism.

Before dewatering commenced, Five Rivers Environmental Contracting used electro-fishing methods to rescue approximately 5,000 fish comprising 11 species from the lock, and relocate them away from the works area.

The Launch Lock is designed to drain and empty regularly but under normal operation it is refilled quickly after vessels have passed through.

However, BAM's contract requires the lock to be held in a de-watered state for an extended period of time – a condition the lock is not designed for.

This raised the possibility of unknown factors arising and the temporary works assessment adopted a 'belt-and-braces' approach, factoring-in the possibility of movement once all the foundations had dried out.

To ensure no structural movement occurs, Groundforce Shorco was engaged to design and install a temporary bracing system capable of restraining the walls and ensuring complete stability throughout the project.

The solution comprised nine of Groundforce Shorco's medium-duty MP50 props, each with a rated load capacity of 50 tonnes, installed as cross-struts over the 6m-wide lock.

The props were installed and pressurised to balance the earth pressure acting on the lock walls. A Mega Brace waling beam transfers the loads from the props to the concrete wall.

The Mega Brace system is most often used in conjunction with cross struts to support concrete or steel sheet-piled retaining walls in major excavations.

In these situations, the frame is usually sported by gallows brackets anchor fixed into the retaining walls.

At Teddington Lock, however, the temporary support structure could not be anchor-fixed to the permanent lock walls without damaging them.

Instead, Groundforce Shorco designed a system whereby seven suspension beams, each 10m long and assembled from Mega Brace components, are placed across the top of the lock and the support frame suspended below from heavy-duty chains.

Groundforce Shorco area manager Ken Sandell said:" BAM UK & Ireland provided timber pads for the 10m Mega Brace hanging beams to rest on.

"With the beams in place, the support frame was installed using the barge-mounted crane and supported in position using the chain hoists."

All the equipment was delivered to the site compound in Richmond, about 2km downstream of the job site, and then transferred upstream by barge.

Sandell added: "We have built up a good working relationship with BAM UK & Ireland over several previous projects and worked closely with their temporary works engineering team on this job to develop a robust solution."