More on the north abutment support beam

BRIDGE 1 – COLLISION PROTECTION BEAM – WEEK 2 OF INSTALLATION

Last week almost all of the bolt holes had been drilled into the abutment brickwork to a depth of approximately 400mm.  These have now been extended to the required 650 mm depth. Those behind the Mabey supports will be done later.

 The next operation was to pump the resin into the holes (see above)...

 ...and then the first 6 bolts were installed at each end. 

Once the resin had hardened the steel channel was packed vertically, leaving a tapering gap behind it due to the leaning brickwork.

The Mabey props were then all removed, and the last 8 holes drilled. Then the resin and bolts were all installed in the remaining 28 holes and once hardened all bolts were fully tightened.

The gap between the back of the channel and the leaning brickwork was found to be between 12mm at the top and app. 40 at the bottom. This gap is to be filled by a rapid hardening liquid cement grout poured in from the top. 

 Temporary timber shuttering was attached to the bottom of the steel channel to prevent the liquid cement grout from running out...

 ...as grout was poured in at the top. 

 The top of the grout was then trowelled off, 

leaving the work complete.

Once the grout has hardened the shuttering will be stripped off and the entire north abutment support beam installation will be completed.

Next Monday, once the shuttering has been removed, the road closure and all fencing and equipment will be transferred to the south abutment and the whole process repeated for the other beam.

 8.9.2018 - JOHN BALDERSTONE 

Blogger's note: A holiday for Mrs. Blogger is now urgently due (he is joining her....) so there will be a two week break in the bridges blog. 

Excitement builds - how far will the team get?

Update on Broadway

BRIDGE 1 – COLLISION PROTECTION BEAM – WEEK 1 OF INSTALLATION

As mentioned last week, work on site on the north abutment started on Monday 3^rd Sept. In the last blog we reported that the two half length steel channel beams had arrived and 4 No. Mabey temporary support columns had been erected and bolted to the walls.

 

By Wednesday each half beam has been raised and manoeuvred into position and roughly to the correct level, using chain blocks attached to the bridge beams. 

Lifting the two half beams.

 

 

Extension pieces of Mabey columns were then bolted to the outer faces, at the tops of the main columns, to prevent the channel beams toppling over as the huge end brackets make them top heavy and unstable. 

Then the whole channel was raised to the correct level and packed there.

 

The joint between the two half beams

These two halves were then bolted together at the centre.

To make room for the new CPB’s the wasp stripe panels have been temporarily removed and will be attached to the new CPB beams spanning the road later. In addition the electric cables and conduits providing power to light the headroom warning signs have also had to be relocated temporarily.

 

Drilling holes into the abutment.

With the abutment channel beam now in place, drilling the 40 No. 35mm diam holes, extending 650mm into the abutment brickwork, was started. These will eventually take the 30mm diam resin anchor bolts. By Friday afternoon, all 40 holes had been drilled to a depth of app. 400mm.

 

General view of site, with drilling in progress.

As is the case with many of our bridges both abutment walls lean towards each other. At Broadway the lean is app 200mm in the 4.4M height. We believe that the reason for this is that the construction of the embankments was started before the brickwork had hardened sufficiently and so the brickwork (between 900mm thick at the top and about 2.2M at the bottom!!) was slowly pushed over as the embankment level rose. This line was built in a rush (some viaduct arches also fell down!!!), and we think that this was the result. When we did the major repairs and renovations in 2014 we discovered that the steel beams overhung the padstones at both ends – we imagine that the steel fabricator (Edward Finch of Chepstow) was somewhat baffled when they came to install them!!

As a result of this lean and some unevenness in the brickwork generally, the channels will have to be set vertically and packed in place. Then cement grout will be fed into the gap behind to fill the gap, which will be app 12mm wide at the top and 35 to 40mm at the bottom.

Once the CPB work is done on this side, the contractors have to do a small amount of minor repairs (scratched paint and wasp stripe panel replacement) to damage done on 1^st May 2018, for which insurers AXA will be paying.

Then the road closure arrangements will be switched over to the south half of the road and the similar work repeated on that abutment.

 8.9.2018 - John Balderstone and John Fancote

Work starts at Broadway

As usual bridge activities since 1^st January 2018 have been mainly about doing visual inspections of all of our structures, and planning projects for later in the year. Alastair Watson has done these visual inspections and produced reports with photographs for over 3 years since the restricted mobility of our structures engineer made it very difficult for him to continue with them.

During January 18, we carried out strike damage repairs to Bridge 1 at Broadway, which were entirely paid for by insurers Aviva. Damage caused to some of the steel on the Up side (above the eastbound lane) had required us to impose a 12T weight limit on that half of the bridge, just when we were trying to lay track into Broadway station! More details of the repairs were included in Blogs earlier this year.

At the same time as these repairs, we fitted “LOW BRIDGE” signs on both sides of the bridge as can be seen here.

Despite these signs, which have large letters 600mm high, the bridge has since suffered another 5 known very minor strikes, the last being on 1^st May 18. These strikes have only caused minor paint damage and buckled the wasp stripe on the west side, north section. The lorry owner’s insurers (AXA) have just agreed to pay for the repairs. These will be done in conjunction with the Collision Protection Beam works (see below).

Another “last minute” project, which was done in July, is at Bridge 38 near Bishops Cleeve, which has a Public footpath passing beneath it. This area has, for years, been a “den” for youths drinking, and causing damage to fencing, bridge brickwork, and also spraying many lots of graffiti all over the bridge brickwork. 

It was subjected to a very severe graffiti vandalism attack earlier this year. We believe that these youths had also set fire to our Greenmech vegetation clearing machine a couple of years ago where it was parked under the next bridge north. It was a total loss.

 

New anti vandal walkway under bridge 38

Stones were also recently thrown at our Drainage gang here, and broken bottles of alcohol were found up on the trackbed. Consequently we have decided to install palisade fencing, to prevent unauthorised track access, to reduce the area where the youths gathered and to stop them being able to reach the walls to do any more “artwork”!! Hopefully without a nice sheltered place in which to congregate they will stop causing us any more trouble. 

The fencing work was done by Gloucester firm Greenfields and was completed in about a week.

The work programme for the rest of the year is just starting, basic details being as follows:-

1.      BRIDGE 1 - INSTALLATION OF A COLLISION PROTECTION BEAM SYSTEM

The design was completed by Engineers Halcrow (now part of Jacobs) early this year and tenders were obtained. Then an order was placed on 25^th May with Nu-weld Engineering Services of Halesowen. Fabrication has been in progress ever since, followed by hot dip galvanising and then painting to match the bridge steelwork. 

Channel section during manufacture

Here is one of the substantial channel sections, seen during manufacture at Halesowen

Anchor bolts

A completed channel section

 The system comprises two heavily welded steel channel section beams which bolt to the upper part of the abutment brickwork. The beams are in two halves to simplify erection and fixing. Each beam is fixed to the brickwork with 40 No. 30mm diam resin anchor bolts, set 650mm into the brickwork. 

The actual Collision Protection Beams are made from 400mm square hollow box sections which are filled with concrete before installation. These will weigh app. 5.5T each when full of concrete and are designed to take an impact from a lorry travelling at 45 MPH. They are positioned app 200mm in front of the bridge steelwork and should deflect no more than 150mm if such an incident happened. These box beams span the road and sit on the upstanding brackets you can see on the ends of the abutment beams. 

This picture shows the upstanding brackets on the end of the abutment beams. The holes are for the resin anchor bolts which fix them to the abutment behind.

 

Delivery and installation started on Monday 3^rd September 2018. Each abutment beam will take about two weeks to install, and a half-road, traffic light controlled closure will be in place for this work.

The installation of the two cross beams will take place when the abutment beams are completed and grouting against the uneven brickwork behind is completed. Yesterday the two half-beams for the north abutment were unloaded, and temporary Mabey support columns to take the weight whilst the wall is being drilled were installed. 

Here is the north side abutment beam unloaded and ready for installation, to be temporarily held in place by the Mabey support columns.

The completed installation will look fairly similar to the system installed under the NR main line in Hyde Lane, Cheltenham: 

This bridge has a clearance of 3.9m, less than our bridge at Broadway. As can be seen it has already had plenty of use.

2.     

 BRIDGE 12 – STANWAY VIADUCT – DETAILED INSPECTION OF THE ENTIRE STRUCTURE

BRIDGE 8 – B4632 SKEW BRIDGE, STANTON

BRIDGE 7 – STANTON FIELDS PRIVATE ROAD

As part of the requirement to carry out a Principal Inspection (i.e. a detailed, close up inspection), of all of our Bridges on a 6-year rolling cycle basis, the time has come for Stanway viaduct to be done. The work will be carried out by a team from Bridgeway Consulting Ltd., who are bridge inspection specialists. The structure has 15 arches, each spanning approximately 12.6m, and rises to approximately 13m high to track level above the fields below.

The two arches at each end have sloping embankments under them and one span is over a small stream. Consequently only 10 arches can be done using a traditional Cherry picker and the remaining 5 will have to be done using aerial rope workers. Inspection of the 10 arches will start later this month, as it will not interfere with train operations. It should take less than a week. However the rope work requires the main support cables to be attached to the track and so this work will have to be done in November when no trains are running. Again about a week’s work will be involved. 

It is hoped that Bridges 7 & 8 can also be done in September, so that the same cherry picker can be used. These two can be done in a day and we do have an odd train-free day in September to slot it in.

There are also problems with ground slippage at each of the 4 end corners of the viaduct. 

A corner of Stanway viaduct after lineside clearance, and with earlier gabion repair

Failure of temporary wall

 A temporary solution using redundant concrete sleepers was installed a few years ago, but as can be seen, these are now leaning over and need to be replaced with a more substantial long term solution.

Concrete sleeper repair

A similar king – post scheme will be designed soon but requires some soil sampling to be done first. Our Lineside clearance team have been doing a great job of clearing vegetation all around this structure to make the viaduct inspection simpler, and the king-post design and ground investigation work much clearer.

3.     BRIDGE 9 – STANTON AQUEDUCT AND PUBLIC FOOTPATH

This is a 3-span structure formed from a steel box shaped channel, supported on two trackside brick piers and two brick or concrete abutments. A public footpath runs along the top of the channel.

General view of the aqueduct from below

The box leaks and is badly corroded with the steel thickness reduced to approximately half of its original thickness.

The leaking water here is softening the foundations of the abutment.












This view from above shows the Cotswolds entrance to the channel, and the footpath.

Level view of the aqueduct. It was constructed by E. Finch of Chepstow in 1904.

Bits of scale have been falling off and the wooden walkway is very unstable, and so it has had to be closed. The entry structure on the Cotswold side leaks and water is softening the ground beneath the supporting brick abutment. We have appointed contractor Stepnell and work will start on 1^st November and will take about 6 weeks.

The photographs in the Halesowen factory were taken by John Fancote, a welcome new volunteer recruit for the bridges team. John has spent 41 years working indirectly for Network Rail, mainly as an examining engineer for Amey.

Other photographs and the blog report itself are by John Balderstone, GWSR Structures Engineer.