Monday, 12 March 2018

Completion of bridge 34


This is the longest bridge on the railway and it had leaking deck plates, leading to corrosion of major steel structural beams. Deep ballast led to rotting of timber ballast boards and the vertical steel ballast retaining plates. End of deck brick ballast retaining walls had partly collapsed allowing ballast to slip onto the bearings and into the road. This problem and, as the  end of deck drains were too high, allowed water to get onto the padstones and exacerbate the corrosion of the steel and cause the padstone to wear quicker. Also some padstones were too short and the steel was overhanging them. This led to vertical movement of the track bearers when trains were passing. The main structural steelwork to the underside of the bridge had not been cleaned or painted for at least 37 years (more likely 50 years) allowing corrosion to proceed more quickly. The repair and construction works were completed in 7 weeks despite sub-zero temperature mixed with almost continuous rain during January.

The following photos illustrate samples of the problems and the work done to rectify them:-

1.    Removing old ballast & waterproofing (5.1.18).

 2.    Encapsulating the entire bridge ready for shot blasting and painting. (22.1.18)

3.    Cross beam connection showing corrosion (21.10.14).

4.    Cross beam connection after blasting and painting (2.2.18).

5.    Cross girder notched and overhanging padstone (29.1.18).

6.    Cross girder repaired (28.1.18).

7.    Track bearer corrosion and notching and overhanging padstone (17.1.18).

8.    Track bearer repair (28.1.18).

9.    Padstone built up and grouted (also bottom flange repair) (30.1.18).

10. Holes in deck plates (8.1.18).

11. Cutting plates for repairs (19.1.18).

12. Deck plate repairs completed (28.1.18).

13. End drip plates welded on (26.1.18).

14. Ballast board and vertical steel ballast plate corrosion and timber ballast board rot (10.1.18)

15. Down side showing replacement ballast plates (19.1.18).

16. Blast cleaning deck for waterproofing (7.2.18).

17. Deck after orange priming (8.2.18).

18. Up side deck after waterproofing (white) (9.2.18).

19. View of deck – down side quilted, up side waterproofed (9.2.18).

20. Up side showing ballast walls being built (2.2.18).

21. View showing end of deck drains (12.2.18).

22. Down side with sleeper laying just started (21.2.18).

23. Down side view with track re-laid (7.3.18).

24. View of cleared former sleeper storage yard at Gotherington (7.3.18).
25. View at road level towards Gotherington
26. View at Road level towards Gretton

John Balderstone, Bridge Engineer.

Tuesday, 13 February 2018

4th Gotherington update



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


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


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