Tuesday, 13 February 2018

4th Gotherington update


BRIDGE 34 – GOTHERINGTON – 4th  UPDATE REPORT ON REPAIRS   

MONDAY 12TH FEB









With a couple of dry days last week the contractors were able to blast clean the deck plates 
 










 and then prime them.
















On Thursday the waterproofing contractors came in and applied the waterproofing ...












... followed by the fitting of a double layer of quilting to prevent damage from the ballast.

The end is now definitely in sight and even bad weather will not affect progress significantly.

Most of the repaired timber ballast boards have now been put back, with just a few yet to go in.

With the deck waterproofing and quilt covering complete, (quilt yet to be laid on the upside) the next thing is to install the end of deck drains. The ones put in years ago were too shallow and were allowing water to come out on top of the padstones, corroding the steel bearings and also run down the face of the abutments wetting the abutment walls.
 
New ones, surrounded by pea gravels encased in a Geotextile quilt to stop silting up are being installed.

At the same time the new brick ballast walls are being given a concrete backing to protect them from any future mechanical tamping machinery.


New large (900mm diam) height warning signs are being fitted to replace the old very small triangular ones. We have also added wasp stripes to highlight the low bridge situation. Because the bridge is skewed at 60 degrees extra steelwork has had to be fitted to make the height warning sign square to the road.


 With all work beneath the bridge now completed the dismantling of the scaffolding started today.

This has already revealed the newly painted outer girders and the new sign and wasp stripes.



John Balderstone,
GWSR Structural Engineer,

Monday 12.2.2018

Tuesday, 6 February 2018

Steel repairs completed on bridge 34


BRIDGE 34 – GOTHERINGTON – SHORT 3RD UPDATE REPORT ON REPAIRS

With the benefit of a few days of dry weather progress has quickly accelerated.
 
Ballast walls being rebuilt, looking towards Gotherington station
 The welders finished mid-morning on Friday, one returning to Dundee, one to Cambridge and the Company owner to Walsall. The photograph shows finished ballast plates & ballast wall brickwork.

 
Cross beam connection


The bricklayers came along on Thursday to construct new ballast retaining walls at both ends of the bridge. There was a gang of 6 and when our engineer got to site at noon on Friday it was about 90% completed. The photographs show the view from the Gotherington end, and the last bit at the north end being finished.


 
View from Gotherington, looking north, down side


View from Gotherington, looking north, up side


 
North end ballast wall completed
When our engineer left they were starting to cover the finish painted steel so that they could blast clean and prime the deck over the weekend, as the deck water-proofers were due in.

The painters also finished on Friday. 
 
Finished painted steel

Brick layers working under the bridge


Apologies for the poor quality photograph here, but it's dark under the bridge.


The bridge repair contract is due to finish on Tuesday 27th February, and our P-way department then comes in on Wednesday 28th February to put the track back. What is left to do is not that much. The waterproofing only takes 1 day (Monday). The biggest job is to construct the end of deck drains. They have mostly been dug, but have to go a bit deeper and be backfilled with pea gravel. Then there is just the ballast to go back down. The biggest job of all is probably to remove the scaffolding and encapsulation, but that cannot be started until 15th as it is being used on Thursday & Friday to fit new low headroom signs and wasp stripes.
 
The first public trains run on Saturday 10th March, with the first race train running on Tuesday 13th March. It's a tight schedule.
  
 

John Balderstone,
Structures Engineer

Thursday, 1 February 2018

Update on bridge 34 at Gotherington



BRIDGE 34 –GOTHERINGTON - 2nd REPORT ON REPAIRS

Repair works on this bridge are progressing well, although the discovery of more rotten steelwork, combined with frequent prolonged rains alternating with low temperatures make the work very difficult. 


General view showing deck repair, drip strips and improved padstone support

The amount of welding work required has expanded from an original estimated 7 man days to a now most likely 40 man days!! Fortunately we now have 3 excellent men who are working in very difficult conditions and were there all of last weekend. 






 
Temporary covers are being used ....







Squeezing underneath




... but much of the work is below deck where access is very awkward.









As mentioned before a number of track bearer and cross beam ends have been eaten away and the scale and rust has first to be blasted away and then the rot left is cut away, back to good thick steel. Then new pieces of steel can be installed and welded into place. 

Corrosion identified

Track bearer repair and drip plate added.
Fortunately the 3 main girders have not suffered to the same extent, but some stiffeners have rotted and have now been replaced (see before and after photos below).

Corroded stiffener

Repaired stiffener



27 smallish pieces of plate have been welded to the deck to cover the many holed and thin areas. 

We had only estimated that about 6 would be required from what could be seen from below!






 
Drip plates fitted to the edges to stop the water running back underneath.
The rotting is caused by surface tension where the water running off them instead runs back underneath to the nearest cross member. We have now added a vertical drip plate along the edges.



We have seen how effective this is with all the rain that we have had. It also stiffens up the edge of the plates, reducing flexing under moving loads.

All work below the deck, the deck plate repairs and the drip strip are now completed.

 
Welding on vertical ballast plates





All that is now left is to complete the welding of the vertical ballast plates.







We expect that to be completed by Friday 2nd Feb. Then the deck can be lightly blast cleaned and the new waterproofing applied.


The work of grouting to fill the spaces beneath end bearing plates is in progress, but another setback arose with 4 of these where, many years ago (BR days), the original stone blocks had been cut back and new concrete padstones had been installed.







Unfortunately all of these had been made too small and some of the old stone left behind. This was breaking up, but worse, the steel hung over the ends (see photos) and was not fully supported.




The loose stone remnants have now been dug out and new thicker concrete padstone filling is being installed.






The final coats of paint are being applied to the steel the below deck and then bricklayers will be starting to rebuild the end ballast retaining walls on Thursday.

The painters are having a few issues with low temperatures and damp conditions, but are steadily progressing.


Report and pictures by:
John Balderstone,
GWSR Structures Engineer

Thursday, 25 January 2018

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 27th 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.