Tuesday, 28 July 2015

All quiet on the Western front

The temporary ramps that have been in place at the centre of Hammersmith Flyover for over a year have finally been removed.

The tarmac ramps and hinged covers were put in place to allow work to be carried out at night on the replacement of the expansion joint - before being lowered again in the morning for the rush hour traffic to pass over.

The only problem with this system was the noise created by the cars, lorries and coaches as they clattered over the joint at often more than the regulation 30mph.  Residents in nearby flats overlooking the flyover have had to endure months of disturbance as the works have progressed.

Over the last few weekends, the new expansion joint has been installed - during a full closure of the flyover to allow the concrete to set without any undue vibrations.  Working throughout the 48 hour weekend closures, day and night teams worked continuously to ensure that the road was ready for Monday morning.

Installing the expansion joint - at night
First of all the Eastbound joint was installed and then the Westbound joint was set in place a week later.  At just under a ton each, each metre long segment of the joints had to be aligned and levelled to a high accuracy as cars would be speeding over the joint in all weathers and conditions.

Aligning and levelling the joint
Each steel joint must slope from the verge at the edge of the bridge towards the central reservation at the middle to follow the alignment of the road surface.  This is to allow any rainwater to be collected and removed along drainage channels in the kerb.  In addition, the joint also slopes from East to West to follow the natural "hump" of the brdige.

The specialist joints allow the bridge to expand and contract with changes in temperature and are made up of two interlocking "combs" that are expected to move by 100mm on each side of the bridge between a cold Winter and hot Summers' day.  Movements of 20mm are not uncommon during a single 24 hour period.  The teeth maintain a road surface whatever the gap in the concrete bridge underneath.

Interlocking teeth
Over the last weekend, the ramps and temporary covers were finally removed and a fresh layer of tarmac was laid flat at the same level as the rest of the bridge allowing vehicles to travel over the bridge without even realising that they were "jumping" across a gap between the two halves of the flyover.
The new joint in place
There is still work to be done installing the drainage channels and replacing the central crash barrier, but the local residents can sleep peacefully once again!

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