Civil Engineering Blog: October 2018

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.