Br. O8 – Stanton - RECENT WORKS and FUTURE PLANS

Interim work has just been completed on Bridge 8 at Stanton, taking the B4632 over the railway, to re-grade the verges and tarmaccing them. This is designed to stop, or greatly reduce the rainwater penetration of the verge areas, by tipping the water into the road. See before and after photos below:

North side - before.

North side - after adding the tarmac verge.

South side - before.

South side - after adding tarmac.

During the regular examinations done on this bridge, it was noticed that the deck and supporting steelwork below the actual road width was almost completely dry, whereas that below both verge areas was constantly dripping. The steelwork below the road was in much better condition and the paint applied in 2007 was generally in very good condition. We therefore deduced that the ¾” asphalt waterproofing, which was shown on the original drawings that we have, had probably been damaged by whoever carried out the installation of gas and water mains. These pipes have been changed, over the years, to put larger ones in place, which may have caused further damage. In addition, the entire road was modified (possibly in the 60’s) and it has been raised by app 300 mm and given a cross fall. The road modification work could also have added to the waterproofing damage. The effect of the thicker road construction is also to add app. 100T of extra weight for the bridge to carry!!

In addition, B.R. (or maybe earlier) carried out a repair to a down side cross girder, which can be seen by the bolts, in the splice plate just visible in the attached photo. 

 

2016 picture with splice plate

This may be due to steam loco emissions and a leaking deck.

Consequently, in October 2016 we started a contract to expose the deck and replace the waterproofing. We tackled the Low Mileage (LM) (Broadway end) verge first and quickly exposed a 150mm plastic water main and a 9”, probably steel gas main (see photo below), the latter sitting right on the deck. 

 

Gas and water mains exposed in an aborted repair in 2016.

We also discovered the original granite sett kerb, just below the water pipe (see close-up photo below). 

Water pipe laid on top of original setts.

To make the problem worse, the space between the granite kerb and the outer girder was entirely filled with concrete. We knew that the 200mm water main in the H.M. verge was concrete covered. (see photo of broken concrete below)

Water main and broken concrete in 2016.

To attempt to get underneath that could have caused the main to fracture. Consequently, the 2016 contract was abandoned, and the LM excavation backfilled with stone.

The steelwork to this bridge has suffered a lot of corrosion, over its app. 120 years life, and in 2007 we spent over £100,000 on major repairs. This was primarily to one short section of the downside end of the first short cross girder, which lies under the LM verge (see before and after photos) and one small section of another cross girder. 

 

A big hole in 2007

Welding repairs in 2007

14 years on, the current single lane restriction is now required because the thickness of the bottom flange plates of the two long cross girders (see 2007 photo below showing location), 

 

Cross girders, photographed in 2007.

 

has been substantially reduced by corrosion and delamination of the steel, which has considerably reduced its carrying capacity. The one advantage of a steel bridge is that poor parts can be removed, and new replacements can be installed. That is what we intend to do, this time.

To prepare the site to carry out the work, the track will have to be lifted and the ballast moved out, to create a flat level surface for heavy duty propping to be installed and make room for handling the steel that is to be removed and replaced. Then localised blast cleaning will have to be done to the existing steel to remove rust and scale before the steel repair work can be started.

Obviously, to allow the traffic to keep running, the rest of the bridge must be propped up so that we can do the repairs. Back in 2007, we had to prop 3 points and a 4-leg tower was used (see photo below). 

 

 

This time we will have to prop 20 points, so there will not be a lot of space down there for removing and replacing steel plates, app. 9M long and weighing about 1 ½ T.

The weakest part of the bridge is now the corroded bottom flange plates (up to 4 plates ½” thick, around the centre)

2007 repair to the outer girders, before extension track was laid.

 

which has reduced their thickness by a large amount. The repair proposed involves removing the corroded plates by drilling out app. 160 7/8” diameter rivets per girder, passing through steel plates between 1” and 2 ½” thick. The new plates will comprise two thicker plates, and these will be attached to the bottom flange connection angles with 22mm Torsion Control bolts. All the new plates will probably have to be drilled on site, as rivet spacing can be slightly variable.

In addition to this bottom flange plate replacement work, the vertical web part of the cross girders has also suffered considerable loss of thickness due to corrosion (see photos below)

 

 

Cross girder corrosion

Cross girder corrosion

and these web plates need thickening up by the welding in of additional plates. All welds will have to be tested, especially as early steel, made almost 120 years ago, is not as good as what we will now be putting back, and so welding will have to be very carefully done.

The other main work required is where the cross girders connect to the outer main girders (See photo)

2007 welding repair work

Detail of 2007 welding

 

The upper parts of the cross girders are enclosed in the Jack-arch brickwork, as can be seen in the photos, and so this will have to be cut away locally, to expose the steel angles which are rivetted to the vertical web of the cross girder. Again, drilling out of rivets is required, but this location only involves just 15 7/8” diameter rivets, but working in a very confined space.

Once the 2 new web connection angles are installed, the brickwork will have to be made good, possibly with concrete, as we did in 2007 (see photo below).

 

2007 repair in concrete

When all the steel repairs are completed, all new replacement steel, and probably some other, poor condition steel parts, will be cleaned and painted.

The one good thing about the work now required is that it is all below the deck and so will be sheltered from the weather, although cold temperatures, and short hours of daylight can restrict and delay certain works.

Depending on the costs, once we get tenders back, we hope to do the same repairs to the ends of the 2 short cross girders, which was not done in 2007. As before this will involve installing 6 props for each short cross girder.

There are other minor works to be done, including replacing missing, or damaged Jack-arch bricks, and possibly some small repairs to other steel looking in poor condition.

Finally, the ballast and track will have to be replaced and made safe to run trains again.

As mentioned in the recent V.A. the repair scheme for that work is in hand. This involves designing the changes to the steelwork, preparing detailed drawings and schedules of work so that we can go out for competitive tenders. We hope to be getting tenders returned sometime in September. This will then show us how much money will be needed, and how long the work will take.

The amount of work required to bring this bridge completely up to anything like the standard achieved on the Bridges to Broadway contract done in 2014, is likely to take far too long to be done in one shut-down period, and so it will almost certainly need to be split into 3 stages. Stage 1 will see the removal of the traffic lights, at last.

I hope that this is of interest, and understandable!

 

 

John Balderstone – Structures Engineer - 29.7.21

 

Stanway viaduct update

As everyone will be aware, our biggest structure is the Stanway viaduct. Standing app. 41’-0” (12.46M) above road level and with 15 arches, each spanning 41’-3” (12.573M) and large end abutments it has a parapet length of app. 633’ (192.9M). It is built entirely of Staffordshire Blue Engineering bricks and is a very robust structure.

However, at over 115 years of age, it is not immune from deterioration, and has to be examined as part of a 6-year rolling programme, to ensure that it is safe to carry trains. So, in October/November 2018 we had a further detailed examination carried out by specialist consultants. Due to its size it is not an easy one to examine, as you can imagine!! 

 

Stanway viaduct being inspected from ropes.

Inspection of an arch

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Rope anchors for the external examination

 

The Consultants' very detailed report, received on 12.2.2019, ran to 228 pages and listed a vast number of defects (fortunately mostly minor – much hairline cracking, mortar pointing needed, frost damaged and loose and missing bricks and also some “hollow” brickwork), There were also many damp penetration issues, which had exacerbated most of the defects listed.

At that time (Jan/Feb 2019), we had contractors on site constructing the king post ballast retention scheme. This was to stop the ballast migrating away from the trackbed and slipping down the embankments on the 4 corners. In the fourth picture you can see how much higher the trackbed is compared with the embankment below it, which is why there was a problem.

The picture below shows the situation prior to the start of work on the king posts:

This old arrangement eventually failed, leading to the requirement for a new construction with deeper posts:

 

On the LH photo, showing the steel columns, there is a steel bracket near the top. For the benefit of the curious, these were to attach tie rods, running beneath the track which tied the tops of pairs of columns together to stop them spreading under the lateral pressure.

On the RH picture is the job completed. You can see the steep fall of the embankment, and the high ballast bed of the trackbed above it.

Just 3 months later (13.5.2019) the owner of horse in the field below reported that some brickwork had fallen off one of the piers.

Fallen brickwork on Pier 8.

 

 

After assessing the report's findings, we tried to create a programme of repairs. You may have heard that the Severn Valley did a similar, but far more comprehensive scheme to include adding concrete to the arch slopes, and then waterproofing on top of that; to do that on their 7-arch viaduct cost over £1,000,000. To do the same on ours would have cost something like £2.5M!! There was no chance of coming up with that amount, and so we had to try to prioritise things, and concluded that the first thing to do was to improve the deck drainage. This was done by replacing the blocked and contaminated ballast and cleaning out the drainage pits to ensure that the water could escape through the outlet pipes. 

A contract was awarded, and the work was done in Jan/Feb 2020.

 

Waterproofing one of the brick arches, with a central inspection pit.

Back filling with clean ballast.

 

Then, with the Lockdown still in place, there was an opportunity to apply for money from the Government’s Culture Recovery Fund. This was done, and we were fortunate to be awarded just enough to do the repairs on one pier. The work had to be completed by 31^st March, to qualify for the grant. At quite short notice a quotation was obtained, and an order placed. Following an extremely wet few months, the site was a total swamp with millions of horse hoof prints each filled with 2” to 3” of water, but the contractor was prepared to go ahead and laid duckboards to create a path across the field for walking and as a barrow track for materials. From above the field looked like a WW1 battlefield, with all the mud and holes from the horses' hooves.

 

MEWP in use on a pockmarked field.

 

 

 

 

The contractors brought in a crawler mounted MEWP mobile platform, which could cross the land.

 

 

 

 

 

 

 

 

The first task was to cut out the defective brickwork, which was a long and tedious process. Work started on the missing corner (photo earlier) and a lot had to be cut out to get back to sound brickwork (cut-out completed photo below). To give added strength, 6mm diam helical bars were built into the joints, and wrapped around the corner, for added anchorage. The finished result proved to look as good as original.

A couple of awkward spots were on corners where chamfered bricks extended around corners. 

Chamfered corner, as original.

 

A curved, chamfered brick was needed, and these bricks are exceedingly rare. By extreme good fortune, we managed to find all of the bricks needed from our own recovered brick piles, at Winchcombe, including these “specials”. It's quite possible that some of these originated from the ruins of Broadway, gathered from the site in the early days.

Damaged plinth corner.

Corner rebuilt with specials from our stock of reserves.

 

A large part of the work was to replace about 30 loose or frost damaged bricks:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

In this picture you can see missing bricks and plant growth.

Pier 8, after corners were cut out

Pier 8, corner repair.

 

The largest part of the work was to cut out and re-new defective pointing. As the money available was limited, we had to restrict what was done, but we could easily have done at least as much again. The photos do not do justice to the amount of work involved. 

Pier 8, pointing and holes to be repaired.

 

Pier 07

 

Pier 8 was marginally the worst pier, but as can be seen on the photo of Pier 07, there is a similar problem to be dealt with. All piers have similar faults, but some are worse than others

 

Pier 03

 
The worst pier we have had to deal with, so far, is 03 (photo above). This was repaired in March 2014

 

                                                                                                                                          

John Balderstone – 6^th April 2021.

 

Bridge 8 in 2007

CIVIL ENGINEERING HISTORIC ACCOUNT OF STRENGTHENING WORK DONE on Br. 08 CARRYING THE B4632 ROAD over the RAILWAY at STANTON

 

When I started the “Bridge dept” in August 2005, the first job was to examine all 46 bridges and decide what work needed doing. There was a lot, especially on the bridges north of Toddington and a small team was created which went round cutting back vegetation around bridges, repairing or replacing fences, repairing, and pointing brickwork and deciding what repairs were required on the steel bridges. Work started at Broadway and slowly progressed southwards. Eventually it was mentioned that there was “a bit of a problem” with Bridge 08, so I went and had a closer look. 

Large hole in the web.

 

 

 

 

 

 

 

 

 

 

Tear in bottom flange plate.

 

 

 

 

 

 

 

 

 

 

 

Apart from looking like a paint sample test operation, there was a large hole in the bottom of the web (see photo, and another of a tear in the bottom flange plate) of the main girder supporting the whole bridge!!!! Clearly some repairs were essential.

A detailed examination of the bridge was needed, but it was so heavily rusted that a shot blasting operation was needed before this could be done. 

 

Shotblasting, with hole in the web visible.

 

Shotblasting the damage.

 

Blast cleaning and primer painting was done in late July 2006.

West section, showing jack arches.

North East corner.

and it then looked quite respectable!!

On 3.8.06, I met an Engineer from Atkins (acting for Gloucestershire County Council) who had looked at the bridge and was very concerned about its condition. It was agreed that we should introduce a 3T weight limit on the bridge, with traffic lights to keep traffic to the other side of the bridge, and that propping should be installed, and a repair scheme prepared.

Engineer John Sreeves (now a volunteer) of Halcrow of Swindon was contacted, and came and looked at the bridge, and they were instructed to design a suitable propping scheme. On 10.8.06, John returned and did a detailed examination, using a MEWP. (Mobile platform)

 

Propped section of B4632 bridge, in 2006.

 

 

 

 

A propping scheme provided by Mabey was approved and installation took place on 12.9.06. After a further inspection of the tower, traffic was then returned to normal.

 

 

 

 

 

 

 

A detailed repair scheme was then designed by Halcrow and, after tendering, a contractor was appointed and a pre-start meeting took place on 3.4.2007. By then it was discovered that each of the 20 alcoves on top of the abutments was filled with nesting birds, so the start date was put back! Eventually work began on 5.7.2007. Almost immediately it was discovered that there was extremely thick scale (up to 10mm) in places, which meant that the repair scheme had to be modified and a localised heavy duty blast cleaning operation was required. That started on 5.7.07, and the steelwork contractors were able to make a start on 6.7.07. 

 

E. end N. side of cross beam - shotblasting, water leakage.

Cross beam 2.2 shot blasted.

Cross beam 1 repair - south view.

Cross beam 1 - jack arch fill.

 

Cross beam cut out for new web plate.

N.W. view old repair to cross beam 1.

S.E. view of web repair cross beam 1

S.W. view of repair to cross beam 1.

Second cross beam repair. 

 

Water & Gas pipes from below_

West girder splice.

Web repair.

West girder web repair after painting.

The first item tackled was the hole in the web. Overplating was required, which entailed drilling holes to go over rivets. This was then extended to 3 panels as the steel was so thin. Work progressed for a couple of weeks and then on 20.7.06, there was torrential rain, and the cutting was flooded to a depth of 3Ft!! Amazingly the water had virtually all disappeared the next day – down the excellent track drains!!

More difficult were the problems with the cross girders where there were holes right through the web. Eventually sections of Jack arch brick had to be broken out. These areas were eventually repaired with concrete.

I attach a group of about 12 photos showing various shots of the steel repairs. These show much of the work that was done. In places old bolts can be seen, which formed part of strengthening work done by B.R.

Finally, the whole of the bridge was blast cleaned and given a 3-coat, resin-based paint treatment which was supposed to give about 25 years before touching up was needed. 

West Girder repaired and repainted

All work was completed, and the contractors left site on 13.9.2007. The bridge was re-opened to dual 40T vehicles.

Volunteers then spent a further 6 weeks doing brickwork repairs to the tops of abutments and wing walls, and installing netting across the alcoves to stop future nest building.

 

PWay extension train under bridge 8, with Hawksworth Mess Coach.

Track laying towards Laverton Loop had then reached the Bridge and on 17.11.07 the first train (P-way) was able to pass under the bridge.                                                                                                  

John Balderstone - Structures Engineer

 

Blogger's note:

This was all in 2006 / 2007, but was not blogged before, and we thought you might find it interesting.

What of bridge 8 today then, hasn't it got a speed restriction and a traffic light on it? Well, it does need further structural work after 14 years, that's the reason for the restrictions. A repair scheme is being designed, to return the bridge back to dual lane 40T capacity, but the start of works has been delayed by the pandemic, as you can imagine. 

 

Addendum

Four extra pictures from John which show the extent that Station Road bridge at Broadway was covered. The fourth picture is of Pry Lane, one of the few made of brick.

Ivy, and collision damage to the flange of the main girder at Broadway.

Wild tree growth at Broadway, adjacent to the station approach.

Pry Lane bridge, just short of Broadway.