Work on bridge 34 at Gotherington

As the works on bridge 1 at Broadway draw to a conclusion...

... extra maintenance work has started on bridge 34, the long skew bridge (near our former sleeper depot) over the main road at Gotherington. Here is our report on the work, currently still ongoing.

BRIDGE 34- REPAIR WORKS

During our regular Principal Inspection, some bad corrosion of the structural steelwork was revealed below the deck on this bridge. During the non-running season window, and with the aid of the PWay department, we have therefore lifted the track and removed the ballast and old waterproofing materials.

You can see that this is quite a sizeable bridge, double track, and that it crosses the road at an angle.

Removing the ballast has also revealed rot in the sloping timber ballast boards, and even worse rot in most of the vertical steel ballast retention plates. 

These are now being cut out and new ones welded in.

This is one of the replacement steel ballast retention plates. You can also see how the deck has been cleared of track and ballast.

More rot has been revealed in some deck plate edges (see photos), also allowing water through to the structural steel below.

The plates are many and variable in size and shape and are being cut on site (see photo). The second photo shows the cut plates lying roughly in position ready for welding.

This water penetration has caused rotting of parts of the bottom flanges of the steel beams, in localised areas, where the beam sit on the padstones on the abutment walls. Notches have formed up to 80mm wide x 300mm long where the steel has been completely eaten away. 

Further rot has been revealed in some of the track bearers and web stiffeners, all of these will need repairs. To stop the water getting onto the padstones supporting the steel, deeper end of deck drains are to be installed (see photo of trench).

Part of the problem is the partial collapse of the ballast retaining walls at the ends of the bridge. These walls stop the ballast falling down on the road, but had failed to do the job properly in recent times. The walls are being broken out, and will be replaced.

Linked to that, the end of deck drainage was too high allowing water to get onto the padstones adding to the corrosion of the steel bearings. (See the deeper drainage trench on the photo further up).

There is also a problem with wear of the padstones beneath where the end bearing plates sit. This is aggravated by the presence of water. (see photo below of the water filled space). 

This allows the ends of the beams to move up and down under train movements. The movements can cause tearing of the deck plates, so the track bearer ends will have to be packed and the gaps filled with grout. Once all of the steel repairs are completed the whole deck will be waterproofed again.

The largest job of all is to blast-clean and paint the entire soffit of the bridge. This has not been painted since we acquired the trackbed about 35 years ago, and probably not in the last years of B.R. ownership either!!! Blasting and painting requires the entire road space beneath the bridge to be filled with scaffolding to form a working platform. Being the largest and longest bridge on the railway the scaffolding is a major task and again a full road closure has been necessary; no doubt you can see why.

The scaffolding has taken over 10 days to complete.

As you can see we have provided a walkway through the works to allow pedestrians and cyclists to get through.

The scaffolding has now been fully sheeted to contain the emissions from the blasting and painting operations. Blasting started last week and is being done in phases with priming in between, to stop surface corrosion of the cleaned steel from starting. We have been told that they may have up to 8 painters on site to get the work done as quickly as possible. Although the work is mainly underneath the bridge, painting cannot be done if the temperature is below 5 degrees, so forecasting completion, at this time of year, is almost impossible. The paint is a 3-coat; twin pack resin based system and should give at least 20 years before needing any attention.

Whilst the blasting is in progress little other work can be done in case any of the blast particles find their way through the gaps between the main girders and the deck plates. Fortunately, as the bridge is so long that welding can be done at one end whilst paint spraying is done at the other. The blaster/painters are also planning to work on Saturdays, when no one else is on site, to minimise any risk of conflict.

The work on bridge 34 is progressing well, but being our largest one everything is taking longer. We have until 27^th February to complete this one, but we have found quite a lot of corroded steelwork which we did not include originally, but which we now feel is essential.