Bridge 32 repair.

 

BRIDGE 32 – REPAIR CONTRACT – JAN 2023 – first 3 weeks to 20.01.23.

Back in June 22, preparation of a scheme to carry out repairs and painting of Bridges 28 & 32 was started using the data from our Detailed Examination reports to create a comprehensive schedule of works required. Both bridges had similar issues – mainly, leaking decks, collapsed end of deck ballast walls, minor steel repairs needed, and were geographically quite close, so it was decided to do both. Neither had been painted since the GWSR acquired them over 40 years ago, so blast cleaning and painting was also to be done.

Up side view of rusty parapet.

The work would require the road between Gretton and Gotherington to be completely closed and so an application (min 12 weeks’ notice required) was made to Glos. C.C. by our Traffic Management company. GCC granted it without any issues. Unfortunately, being a country area, only a relatively long diversion route was available. Liaison with the two local schools and businesses on the route was also established. It later came out that GCC were planning to arrange their own road closure to enable them to carry out a road improvement and lining operation during part of our closure, but we beat them to it!!. After some negotiations we have managed to agree plans that both contractors are happy with, which will save another closure, at a later date!!

Volunteer Bridge design Engineer, John Sreeves was busy preparing the Construction drawings, specification and tender documents. Tenders were sought on 3^rd September but the programmes that came back showed that it would be extremely tight to do both bridges between 3^rd Jan. and 28^th Feb. Consequently the tenders had to be revised to omit Bridge 28.

The GWR Trust then agreed to fund it (partly with money from the estate of former volunteer Civil Engineer – Peter Muir). Finally an order for Bridge 32 work was placed with contractors, Walsh’s, on 14^th November 22.

Work started site on Tuesday 3^rd of January 23, with the installation of the contractor's welfare unit in the road below.

Contractor's cabin in the road.

and the arrival of items of plant and machinery. 

Contractor's machinery.

On Wednesday 4^th Jan. GWSR P-way then lifted the track and sleepers.

Track being lifted by the PWay volunteers.

 

Track removed (3 panels).

 You can see some steel brackets sticking up from the deck plate. 

Deck plate with former brackets.

These were to fix large (approx. 19” x 6”) hardwood timber way-beams to the deck. These carried the rails, and there was no ballast or sleepers. In March 1928, the timbers were removed, and ballast and sleepers were added. This added about 35T of ballast (340mm thick below the sleepers) to this small bridge, which has caused spillage problems, ever since!!

A very important part of the work would be the removal and eventual replacement of 6 of the 14 large stone pads which carried the main bridge steelwork. Obviously, the steelwork needed propping,

Up side view showing props.

 and a scaffold deck was also needed for the works.

Up side view showing scaffolding and encapsulation.

The paint to be used is a high quality 3-coat resin-based product (used on oil rigs, etc) and this requires shot blasting to give the necessary surface preparation required. This should give a min. 25 years life before any maintenance is required. The blast cleaning operation requires the entire steelwork to be encapsulated to stop the spread of blast emissions. 

Encapsulation of the works area.

The steelwork sub-contractor started on Monday 16^th Jan. removing the brackets from the deck, and was arranging for a couple of small areas where there are holes through the ends of the deck, to have plates welding in.

 

Deck plate holes revealed.

 

Investigation into the state of the end of deck ballast walls (One had virtually collapsed and the other 3 were cracked) was in hand.. 

 

End of deck ballast walls. with angles.

Parts of these were also broken out to expose the ends of the steelwork where repairs were needed. In parallel, below the deck breaking out of the cracked and defective stone bearing blocks was taking place. 

Deck plate holes and bottom flange plate missing.

 

Props installed.

After two days of delay due to the very cold weather the shot blaster started work on Wednesday and had already blast cleaned and primed the main central girder, by yesterday. 

Centre girder blast cleaned and primed.

Meanwhile, on the upside, low mileage side, the drainage outlet pipe from the planned end of deck drains, has been installed, together with a set of steps to make track access safer in future.

Drain outlet and steps.

Finally work has started to rebuild the top section of the brick wall which retains the road on the Upside, low mileage side. 

Retaining wall and standing water.

 

Work is also planned to investigate why standing water in the ditch from Culvert 31 B, which passes around the abutment, cannot get away.  

 

 

This causes the ditch to silt up and, in turn the inside of the 3Ft. x 3 Ft. brick culvert.

Interior of culvert.

Detail of internal view of culvert.

Thanks to Ian Scholey and Jonathan Taylor (Lineside drainage) for the photographs.

Report by John Balderstone

Structures Engineer GWSR (20.01.2023)

Br. 12 – STANWAY VIADUCT REPAIRS

Blog covering the entire 10-week contract.

Unfortunately, this our largest structure, required a large quantity of rather uninteresting repair works and, naturally there is a vast amount of repetition involved!! Not too exciting!! 

Stanway viaduct, with scaffolding.

Despite that, the GWR Trust kindly agreed that they would fund these very important works on what is a really iconic structure.

There are 4 main types of work required. These are: -

1. Corner re-casing. The problem is that vertical cracks appear close to the corner on both faces of a pier, and as happened to pier 8 in April 2019 (LH photo), the entire corner about 3M high x app 250 to 350 mm along both faces fell off. 

 

 

 

This was repaired in March 2021. The work involves removing the cracked bricks and toothing out the brickwork to enable new bricks to be inserted (see RH photo). 

The corners are then strengthened by the building in of 5mm diam stainless steel twisted helical bars into the joints. These wrap around the corners and extend along both faces to tie the corner into the sound face brickwork alongside.

 

Special repair of bullnose feature, from above.

 

2. Replacement of cracked, frost damaged, or missing bricks. This is fairly obvious as to what is required. A frequent item is missing bricks from the holes where the temporary curved formwork was supported during the building of the arches. (photo below).

Missing bricks

 

3. Hollow brickwork. This is where the bonding between facing brickwork and the inner core brickwork has failed with linking bricks cracking right through. The solution is to drill at an angle into the brickwork, through to the inner sound brickwork and install stainless steel anchors which are grouted into place.

4. Pointing. This is a very common problem on older structures and the old crumbling mortar has to be cut out and new rammed in.

 

 Repointing work on various parts of the arches.

 

The work started in mid-September 2022, and, as the ground gets very boggy and soft, the first thing was to construct a main access route onto site was created using very thick heavy duty interlocking plastic mats (see photos below).

 

Interlocking mats.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Naturally, as the work extended to all faces of the piers, including the spandrels (the high-level side walls above the piers/arches) very extensive scaffolding was required. (Photos below).

Extensive scaffolding

 

Spandrel above pier 7.

 

The work started with pier 7 and then 6 and 5, with the spandrels above, following. Some work was also done to the lower parts of the arches, just above the piers.

Repointing work done.

 

The extent of the work was based on the 228-page report received from the very detailed examination done in October 2018. Most of this was done by men working from the parapet, suspended by ropes (photo below). 

Abseiling to examine the state of the structure.

 

With the continuing deterioration in the subsequent 4 years and with the somewhat limited accessibility issue, an additional 15% to 20% of additional items have been found and dealt with. Our Chartered Engineer volunteer Peter Lewis, who joined early last year, did a magnificent job of surveying and identifying the extent of the hew work, in conjunction with the contractors.

Because of the scaffolding and the localised nature of the work, taking useful photos has been difficult, but a small selection is included.

All work on site, including the removal of the scaffolding, was completed before Christmas. The temporary road mats will be removed in the first week of 2023.

We are grateful to the local tenant farmer, who kindly moved the grazing horses into an adjacent field for the duration of the works, and to Lord Wemyss for permission to work on his land.

Photos have been provided by me, John Fancote. Peter Lewis and the contractors site manager – Mark Williams.

 

Prepared by John Balderstone - Structures Engineer GWSR. 2^nd January 2023.