Welcome to the first of a series of reports on the civil engineering works ongoing at Bridge Road, Exeter. Each report will briefly explain the work that’s occurred since the previous report, and will include areas not visible from the road.
Progress Report 1 – Start of works to 25th April 2016:
Early work involved setting up the Traffic Management (which commuters will be familiar with), and the site compound area – these porta-cabins will be our home for the next year:
The bridge over the river Exe is called Countess Wear Bridge, and houses a healthy population of Soprano Pipistrelle and Daubenton’s bats. The bridge is an ideal habitat for them as in the evenings they can swoop down from their roosts to pluck midge larvae from the surface of the river. As part of the scheme we have provided enhancement in the form of artificial bat roosts. Because this is a historic structure these have been camouflaged carefully to match the stonework of the bridge.
Following this work, the footpath on the Topsham side of Countess Wear Bridge has been removed in preparation for the new kerb line. To enable the widening of the road, the kerb line is being moved further to the East, nearer to the bridge parapets. Much of the work to date has been on diverting and re-laying the services on this side of the road; this is currenyly ongoing. We have a water main, telephone and fibre optic cables, electricity supply for the street lighting, and further telecommunications ducts to fit in a reduced space. The picture below gives an idea of the complexity:
At the North end of Countess Wear Bridge work has started on laying kerbs; however this has necessitated the removal of some buried concrete steps which date from the 1930s. At this time the bridge was significantly widened and the road level raised; these concrete steps stabilise the masonry parapet wall; but unfortunately occupy the space where our new kerb line should be. Therefore the upper part of the concrete steps has been broken out; this won’t affect the parapet wall as the kerbing will be supported by fresh concrete. This has enabled the start of the kerbing work.
You will note the holes in the kerbs; when completed, these will enable surface water to drain from the road into a channel inside the kerbs. Work has also started in laying drainage pipes down from the road and out to the East, where shallow swales will be constructed later.
The next bridge to the south of Countess Wear Bridge is the “Countess Wear Flood Relief Bridge”, a reinforced concrete structure which allows for floodwater to pass under Bridge Road when needed. To allow work to go on underneath this structure, an access track was made, and the soft muddy ground was improved with geotextile and stone.
As mentioned above, when the scheme is complete the kerb line will be much nearer the bridge parapet on the east side, with the result that vehicles will be driving on the area previously occupied by a footpath. This area of the concrete deck projects out from the support piers below; this is known as a “cantilever”; see photograph below:
The existing concrete cantilever here is not strong enough to regularly carry the weight of heavy good vehicles, and so the cantilever will be demolished and rebuilt with more reinforcing steel inside. To enable this work, a temporary platform has been constructed below the bridge, using a modular system of steel parts, similar to a large scale “Meccano” kit.
The three pictures below show the progress on building this platform:
Work is underway to divert the services from the Countess Wear Flood Relief Bridge, to allow demolition of the cantilever to begin later in the week. Part of this demolition will involve “hydro-demolition”, whereby high pressure water jets are used to cut away the concrete but leave the reinforcing steel intact. This technique will then allow the new concrete to be cast around the existing reinforcement (alongside newly drilled dowel bars), which will give a strong joint.
That’s it for now; stay tuned for another update in around a month’s time.
Luke Walker CEng MICE
Senior Bridge Engineer, Devon County Council