Bridge update Nr. 5

There are several bridge related things going on at the moment, so here is an interim update of work concerning our many bridges.

BRIDGE 08 – B4632, STANTON & 

BRIDGE 07- STANTON FIELDS - PRINCIPAL INSPECTIONS

On Monday 8^th October a new contractor came along to carry out a principal (detailed) inspection of these two bridges. They brought with them two vehicles:

 In the picture you can see a MEWP and a van.

You're probably asking: what is a MEWP?

It's a Mobile Elevating Work Platform.

You may know it under its more common name of cherry picker.

In this picture it is parked underneath bridge 08. That's the main road (B4632) passing diagonally over the railway at Stanton.

They will be returning in November to do a Principal Inspection of bridge 11 – Stanway Viaduct. 

Most of this inspection will be done from a MEWP working from the field below, but at least 5 of the 15 arches will be done using aerial rope workers, which will be a new activity for us.

BRIDGE 09 – AQUEDUCT/ PEDESTRIAN FOOTBRIDGE

START OF REPLACEMENT NOW IMMINENT

For those who are not familiar with the Railway, this bridge is about 1¼ miles north of Toddington. 

It is a 3-span structure, comprising an open topped steel box channel approximately 34m overall length. The channel carries a small stream across the railway, which is dry for much of the year. The top flanges of the channel have timbers bolted to them, which carry further timber at right angles, forming a pedestrian walkway with steel handrails. 

Unfortunately the timbers have caused water to be trapped against the steel, which has caused unbelievably extensive corrosion of steel ½” thick (see picture) and odd bits have fallen off. In addition the sides of the channel have been reduced to about half their original thickness, and some holes have also appeared. The footpath has had to be closed for safety reasons.

Fortunately the two brick piers are sound and will be retained. The bank seat on the Malvern side was rebuilt in concrete in 2002, but no provision was made for expansion. In consequence the thermal expansion (up to 25 mm) all occurs at the Cotswold end, where the water enters, and consequently leaks occur at the joint between the stream and the steel box. It is in poor condition and will be re-built as a fixed end.

 

Manufacture of the new structure is being done by a contractor in North Wales, who has done several other bridge works for us. Two photographs showing the new closed channel showing progress of the fabrication, can be seen above.

BRIDGE 12 – STANWAY VIADUCT.

We have had an ongoing problem with the 4 end corners of this structure, where gradual erosion of the embankment against the end brick piers has been undermining the edges of the track bed, leading to slippage of the ballast.

A temporary retaining wall was created using concrete sleepers as can be seen in the adjoining pictures

 

but the continuing movement is now causing them to lean over, so a more permanent retaining scheme needs to be put in place. 

As the embankments are mostly made of clay fill a soil investigation has had to be carried out, so that a properly designed scheme can be prepared. A drilling rig went to the site for two days last week to do the bore holes and take soil samples. In the picture you can just make out the top of the viaduct on the left.

A Topographic survey will also have to be carried out to establish the ground contours, which has meant a huge job for Mike Peers and his team, so that the surveyors can see exactly what is there.

ONGOING ANNUAL VISUAL INSPECTIONS

All the time throughout the year, Alastair Watson soldiers on with doing the visual inspections of each of our 46 bridges and about 60 Culverts. A typical photo group for bridge 25 (Working Lane at Gretton) compiled by him is given below. A written report is also produced.

 

View on down side showing one large elderberry left after clearance in December 2017

Damaged fence on down/Cheltenham wing wall

Close up of pointing done in October 2016 showing cracking at low level

Up/Cheltenham wing wall showing growth and damaged fencing

Up side parapet showing fresh graffiti

 

Photos courtesy of John Balderstone, Jonathan Symonds, Alastair Watson & Brunswick Ironworks.

24.10.2018 - JOHN BALDERSTONE

Broadway - final installation

BRIDGE 1 – COLLISION PROTECTION BEAM – WEEKS 3 TO 5 OF INSTALLATION

Following the successful fixing of the support channel to the north abutment, the traffic management was switched to the other side of the road so that work could be done on the south abutment.

This is virtually identical to the north, so work started with lifting the channel into place onto the Mabey props. The photograph shows it in place at the end of day 2.

Then the drilling went ahead. 

Soon all the resin anchored bolts were inserted and the shuttering to the soffit was fitted ready for grouting between the brick face and the back of the channel.

Packings being removed on the second support channel

On Monday 1^st October the road was completely closed to accommodate the delivery lorry, a lorry with a crane attachment and two cherry pickers. 

Unloading the east beam.

The beams spanning the road are app. 10.5M long, are filled with concrete and each weighs about 5 tonnes. To facilitate the lifting, the “LOW BRIDGE” signs and the wasp stripe panels had to be removed and relocated later. The wasp stripe panels were fitted to the beams before lifting started. New height warning roundels were to be fitted so the old ones also had to be removed.

The east beam was lifted first.

 Then the two Lorries were moved over and the west beam was lifted

 

At the end of the first day the east side was virtually completed. The second day saw the completion of the west beam and both were then packed to the correct level.

Detail of one of the connections showing how the cross beam is bolted on to the channel.

The new CPB seen from underneath, showing its relationship to the bridge.

Here our bridge engineer is in discussion with our consultants Jacobs (formerly Halcrow). Both beams are in place now; the 40 bolts fixing the channels to the abutments can also be seen clearly. 

The low headroom roundels are electrically lit and their re-location meant that the electrics had to be modified. These are not warning signs (which would be triangular) but actual prohibition signs.

Finally, a view of the bridge with everything in place. As the CPBs sit immediately behind the wasp stripes, they are almost invisible.

3.10.2018 - JOHN BALDERSTONE

Photos by John Balderstone & John Fancote

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?