Bridge work overview

With the 5 bridges to Broadway now spick and span, attention has focused on the other end of the line, where other bridges of similar construction are also getting much needed attention.

Here is a tour of inspection and update of several of them, being bridges 28, 32, 34, 37, 38, and 45. The first 4 are in the Gotherington area, the last on the southernmost tip of the railway.

ACCOMMODATION BRIDGE 37

Work on this bridge was described in an earlier post, and is now complete, with the embankment back filled and re-graded. The two pictures below show you the vast improvement made to this bridge's brickwork:

 

Before work started, a collapsed wing wall on the up side....

 

 ... and a fully repaired wing wall on the down side, a few weeks later.

Here we can see both repaired wing walls on the up side, now in excellent condition. This arched bridge type is less common on the railway; most of our bridges having a metal deck.

There is still a lot of pointing work remaining to be done, but our budget this year does not extend to do all that was needed, so just the cracks and localised areas were done.

 

ACCOMMODATION BRIDGE 38

Apart from a final coat of paint on the handrails this bridge is also completed. The work here was tidying up the pilasters, where vandals had removed some bricks. In addition the parapet wall on the downside had to be raised as the ballast was too high and was spilling over onto the public footpath below. Due to the height of the ballast, the handrail was too low for safety reasons and so the pilasters were extended upwards and an extra rail inserted. Some fence repairs were needed, and Andy Prothero and gang did a brilliant vegetation clearance job, as shown on his last blog.

 

Pilaster tops missing, ballast spilling over under the rail.

The same view from underneath, with ballast sitting on the girder

Repair work completed: Extra rows of bricks, higher pilasters with caps, and an extra guard rail.

BRIDGES 28 (STANLEY PONTLARGE, 32 (PRESCOTT ROAD), & 34 (GOTHERINGTON SKEW BRIDGE)

These all had the same problems:-

 

1.      Rotting or missing ballast retaining boards

These are found on all steel decked bridges and are installed to stop any pieces of ballast displaced during ballast tamping, or from rail traffic vibration, from spilling down the sides of the steelwork and falling down onto passing vehicles, or pedestrians. From the sketch detail attached (see below) you can see that the bulk of the ballast containment is done by 300 mm high vertical steel plates attached to the deck. Then to close off the gap back to the web plates of the main bridge girders, sloping heavy wooden boards (38 mm thick) are fitted. Unfortunately many of our bridges only have thin (12mm) narrow boards battened together and these also tend to warp.With the height of the ballast being greater than it should be, the bottom edges lie in the ballast where they rot away allowing gaps to form, and, in the worst cases, allowing the boards themselves to slip down into the gaps!

 

 





Here is an example of a missing ballast board, replaced by a plank of wood, but still leaving a large hole.

 

A worse example is this one on bridge 28, where a piece of ballast board has slipped and is in danger of falling into the road.

 

Repairs at last! New bigger and thicker ballast boards are being cut to size here, with old examples in the background, and replacements newly fitted in the front.

Here is the drawing of the ballast boards referred to in the first paragraph.

2.      End gaps adjacent to the pilasters.

This is an extension of the ballast board problem, and occurs at the end of the deck, where there is a gap (varying in width), which again allows ballast to slip down onto the padstones under the steel girders, and eventually into the road again. The simple solution was to build a small brick pier against the pilaster brickwork, to close these gaps.

 

3.      Failure of mortar grout under the padstones (mainly of those beams carrying the track)

 

The problem with these is that the mortar breaks down beneath the plates which supports the ends of the beams that sit on the abutments. The resulting gap allows the steel beams to move up and down under moving wheel loads. Without the mortar support the beam ends are then only supported by the deck plates, and, as we found on the B2B contract, this leads to plates tearing followed by waterproofing breakdown allowing water in and causing the steel to corrode. The problem is not an easy one to solve, as it involves jacking the beam ends and inserting new grout. A temporary scheme of inserting temporary steel packs has been carried out, until we have funds to do a better job. Unfortunately there are no photographs of this work.

 

One final shot is of an inspection done on Bridge 45 (Swindon Lane), earlier this year. Quite a tricky one to get a machine to, but we managed it, thanks to a helpful farmer. The machine is standing on the disused trackbed, in GWSR ownership, south of Cheltenham Race Course station, between Hunting Butts tunnel and Pittville, where our trackbed ownership actually ends.

That is about all of the bridge work that can currently be done with the budget available. Hopefully there will be a fresh allocation next year.

New B & S blog

Just a quickie to advise you of Building & Services dept.'s new blog, launched today.

This is the link to it:

http://gwsrbuildingservices.blogspot.co.uk/

B & S build all sorts of interesting stuff around the railway, but have kept a low profile so far. Now they want to change that, so give them a visit, see what you think. Winchcombe platform 1 extension is their latest project.

Bridge 37 makes progress. Here are some more recent pictures of repairs to the 4 wing walls that were damaged.

This is the down side wing wall at the Cheltenham end,before work started.

And after work pointing and re-seating and at the ends, replacing the coping stones was completed.

Looks like new! Good for many more years now.

These are pictures of the down side opposite.

Again, a case of re-siting the copers and making good loose brickwork.

Despite several spells of bad weather the brick wing wall repairs & pointing works continue pretty well. As readers may know laying dense “Blue” engineering bricks cannot be rushed, especially when the weather is damp and there is no sun to help dry the bricks or the mortar. Having to lay them at a slope of 1 in 6 to the vertical is also a tricky job and slows the rate of progress.

 

This pictures shows the slope in question quite well. Yopu can see how the wall leans back into the infill.

This is the up side, at the Cheltenham end.

A little while later and we can see more wall rebuilt, and drainage pipes inserted to relieve the pressure from behind.

 

This one shows the same up side, but on the opposite wing wall, at the Broadway end.

A few days later, and the Broadway up side wing wall is almost finished. Replacement copers are being mortared on here. Note the hollow underneath, to help hold them on the mortar.

Still to go on is the large block on the end. It weighs 70 Kg, so the builders want to let the mortar in the brickwork underneath go off a bit more, before heaving that on.

Maintenance update

Following a year of fairly hectic bridge repairing activities last year, largely dominated by the BRIDGES TO BROADWAY contract, this year has mostly been about getting our bridge inspection programme up to date.

The GWSR has a programme of annual visual inspections carried out by our own volunteer members, with the aim of inspecting and producing reports for all 46 Bridges that we own. In addition, we inspect as many as possible of the 60 culverts or so that pass under the railway. However, every 6 years we undertake a principal inspection, which involves employing a professional chartered engineer with wide bridge experience. The use of a cherry picker is usually essential, since most of the problems occur on top of the abutments, and are completely invisible from ground level. This also means the full or partial closure of the road, as can be seen below. This too costs money, as well as causing some inconvenience to road users. 

Over the last 12 months we have carried out 30 of these inspections, catching up on a large backlog.

Bridge 15 - Didbrook 1, down side

Bridge 34 - Gotherington Skew - down side

Bridge 37 - farm accommodation bridge, Bishops Cleeve

Having got the inspection programme completed, we now have a little of the budget left to do some actual repair and construction work. The top priority, within the budget money left available, was to deal with some collapsed wing walls on Bridge 37 above. This is a farm accommodation bridge on the outskirts of Bishops Cleeve, with no direct road access.

In the picture you can see that a large chunk of wing wall on the up side, Cheltenham end, has fallen over.  What isn’t visible is that a second section, nearer the camera has also fallen flat on its face and is buried under vegetation. The danger is that the embankment could slide towards the camera, risking the start of another embankment slip.

Broadway end wall, bridge 37

The upside, Broadway end wall is going the same way but the damage is much less severe, as seen in the picture above.

The first thing to be done was to remove the damaged wall sections and their foundations, and this has already been done as can be seen in the photo above, taken by Andy Prothero.The view is from track level and shows the excavation for the new wall foundation on the up side, Cheltenham end.

24 hours later it looks like the photograph on the left. The concrete foundation was cast yesterday morning, to avoid the risk of the heavy rain forecast for the weekend filling the clay based hole and softening the bearing material. Note the clever use of the machine bucket to assist with levelling the concrete.

Here we can see the foundations in place for the up side Broadway end wing wall, ready for brick laying to commence.

Scaffolding, bricks, sand & cement and a water bowser are all arranged to arrive on site early next week. We then have a lot of loose brickwork to take down on all 4 wing walls, and need to prepare the old brickwork so that it is ready to be renovated. Construction of the new wall will get under way by about mid week. We will be hosting a couple of apprentice brickies, who will be on site to experience first hand the problems of building with hard, blue engineering bricks, which in our case need to be laid at a 1 in 6 lean back from the vertical! Rest assured, they will have top class people leading them. It's quite a challenge.

 

It is also a very remote site mid way between Bishops Cleeve and Manor Lane, Gotherington, so material movements are not straightforward.