Progress Report 2 – 26th April to 27th May 2016:
Welcome to the second instalment of our series of progress reports on the Civil Engineering works at Bridge Road, Exeter. As work has begun on a variety of structures, this latest update is divided into sections.
You can see the locations of the various bridges and structure by clicking “Plans” in the bar to the left.
Countess Wear Flood Relief Bridge
The majority of the work on this bridge in the past month has been hydro-demolition – if you’ve passed the site in this time you may have noticed a blue tanker and a green tent.
The operative working inside the green tent holds a high pressure water jetting gun; the water disintegrates the concrete but leaves behind the steel reinforcement.
By removing strips in a grid pattern the concrete was broken into chunks:
During night shifts an excavator was used to take the weight of a “chunk” of concrete, then the steel bars were cut and the chunks lifted onto a dumper to be taken away.
Hydro-demolition of the concrete will allow us to attach new reinforcement bars to the old ones, in addition to drilling in additional reinforcement bars in-between the existing bars using a resin anchoring system.
In locations near the supports where there will be higher stress, additional reinforcing steel will also be lapped in to the upper part of the existing bridge – in these locations patches of the existing steel were exposed to allow this:
Throughout this process, the concrete debris was caught by the temporary access platform seen in the previous report, the excess water was collected below and pumped to a “Siltbuster” unit which removes silt and restores it to neutral pH before discharging into the sewer.
The next step is to tidy up the area ready to start fixing new steel reinforcement next week.
Railway Bridge Approaches
In the early part of the month, following installation of a temporary steel crash barrier, the existing steel crash barriers were removed:
Work has then started on excavating the embankment to the South of the railway line:
This will be extended up to the railway line, but before this can happen we need to install a line of steel sheet piles to support the edge of the excavation as the slope steepens. Once completed the excavation will provide access for a piling rig which will install the bored piles supporting the South abutment of the new footbridge. This piling rig will then work backwards away from the railway, installing more piles for the retaining walls which will support the footpath approaching the bridge. A similar process will happen on the North side later on.
Kerbing and Services
Kerbing and services work has continued at the North end of the site, including the removal of the island at the junction with Glasshouse Lane.
You may have noticed the holes in the kerb – as mentioned in the previous report, these will allow rainwater to drain into the kerbs themselves – when not blocked by this mysterious woollen figure who appeared overnight!
My colleague Mike managed to get his camera inside the kerb drains, producing the most artistic site photo to date:
Telecommunications and water services have been diverted; blue is for water, green for Virgin Media:
These services were then encased in foamed concrete to protect them from future traffic loading:
Exe Channel Flood Relief Bridge
Work started this month on this bridge, which is located between the canal and the railway; although you would hardly notice it from the road – the photo below gives a view from the flood channel to the South.
You will notice the crash barrier and grassy verge. Following installation of a temporary crash barrier, the existing barrier was removed, and the road was dug down to the top of the existing concrete deck. We were pleased to find the existing deck waterproofing is in good condition.
By removing the verge, we can bring the kerbline nearer to the edge of the bridge deck, widening the road – but this requires a new reinforced concrete retaining wall to support traffic loads here. The next steps will be to drill and fix stainless steel dowel bars into the existing deck which will anchor the concrete retaining wall down to the bridge deck below. This wall will have a new crash barrier fixed to it; the dowel bars will provide a strong connection in the case of a crash.
Canal Swing Bridge
The eventual plan for this historic bridge is to rotate it by 4.2 degrees, which translates to around 1.6m at the “nose” end. This will allow a better alignment of the road as it passes over it, removing the “kink” on the South side and allowing two lanes of traffic to use this narrow bridge.
This rotation will require new foundations to support the bridge in its new position; this month we undertook some trial openings in order to gauge the space required for a mini piling rig to get in to drive new piles:
During the trial opening I had the opportunity to stand on the Swing bridge whilst it was rotated; allowing me to snap this photo whilst the road was pointing in the wrong direction:
We’ve also started some detailed survey work to allow the Contractor to set out locations for the new foundations; as this is a huge machine with a lot of moving parts, accuracy will be vital here. This video of the Canal bridges opening gives you an idea of the range of movement.
Before undertaking these surveys we had tried to discourage nesting on the South side of the Swing bridge by installing deterrents in likely nesting spots. To offer an alternative we are encouraging the Swallows to nest on the North side of the bridge (which will be further away from our working area) by attaching artificial swallow cups there:
Two of these cups have been taken up. However, swallows are very determined and have actually nested within the deterrent spikes, as shown in the photo below:
We have an Ecological Clerk of Works who is working with DCC and the Contractor to monitor the nest and ensure it is protected during construction works. The bridge will be kept in a partially open position across the canal during construction work on the new foundations, which will allow adult swallows to access the nest and feed their young.
Once all the survey work is completed the next step will be to install some sheet piles into the Canal itself , extending the concrete area at the “nose” bearing on the South side of the canal in order to begin bored piling there – see photo below:
That wraps up the main activities for this month; come back in a month’s time for another update.
Luke Walker CEng MICE
Senior Bridge Engineer, Devon County Council