Civil Engineering Blog: February 2019

BRIDGE 12 - STANWAY VIADUCT – KING-POST GROUND STABILISATION PROJECT

As with a few of our bridges the viaduct has a problem with ground erosion where the brick wing walls end and the embankments start. This slowly causes the track bed to become undermined.

All 4 corners of the viaduct are affected to some extent, those at the north end being the worst.

Current ballast restraint, north end of Stanway viaduct.

Some years ago a retention scheme using redundant concrete sleepers was installed, but the ground movement has slowly continued, allowing the sleepers to start leaning.

At the north end on the upside the ground of the sloping embankment is now almost 1M below the track bed level.

Following a massive vegetation clearance by our clearance team, a detailed topographical survey was carried out by Surveyors, Horner’s from Evesham, to establish the existing ground profile.

Tripod drilling rig

Then, to identify what the soil was like, a ground investigation was carried out by G.I.P. of Wolverhampton using a tripod drilling rig, and soil tests were done on the samples taken.

With this information available, a scheme has been designed by consultant J. Symonds to provide a more permanent solution. The contractors - Walsh’s of Worcester - started work on Wed. 13^th Feb.

Trench

Drilling with auger.

The first task was to excavate a trench deep enough for the new “walls” and to make room for drilling holes for the king-posts to be installed. Next a 360 excavator with an augering tool attached drilled holes app 450mm diam. down app. 3M into the ground.

Channel section attached to brickwork.

Galvanised steel columns and brackets.

Then 152 x 152 steel column sections, with a galvanised finish, were lowered into each hole and were concreted into place.

Because the ground is clay dumped from the cutting excavations it is not very well consolidated and so the tops of the king-posts will be tied together with steel bars below the track bed, using the brackets which are just visible. Where the viaduct walls end a 150 x 90 R.S. channel section is bolted to the brickwork.

Lowering SH concrete sleepers into the sections

Once the concrete has hardened sufficiently concrete sleepers, which are no longer suitable for track laying, are lowered into the steel sections.

The next task will be to excavate a narrow trench beneath the track bed to take the 25mm diam tie bars.

Once the tie bars are in place the space between the new sleeper wall and the edge of the track bed will be filled with ballast to stabilise the edges, which were starting to be undermined.

BR’s 24 (GREET TUNNEL), 43 (A435 – EVESHAM ROAD BRIDGE) & BR. 44 (HUNTING BUTTS TUNNEL) – DETAILED EXAMINATIONS. Mon. 18^th to Thursday 21^st Feb. incl.

As part of our continuing bridge examination programme, these 3 structures were due for their Detailed Examination, which we aim to do at no more than 6 year intervals. This matches the time scale used by Network Rail. These are fitted around the Annual Visual Inspections currently being done by our engineer – Alastair Watson.

As with all our structures vegetation is a constant nuisance and a very large clearance job was organised by Mike Peers using two contractors. That work extended to the land at the south end of Hunting Butts tunnel and right down to Br. 45 (Swindon Lane), to enable a detailed examination of the south end of Hunting Butts tunnel & Br. 45 Swindon Lane to be done later in the year.

Br. 24 (Greet tunnel) – Due to the size of these structures (app 7.5M to the crown of the brick arches) it is necessary to use a MEWP (Mobile Elevating Working Platform – railway name & abbreviation for a cherry picker).

Road/Rail MEWP

Unfortunately there is no road access to the tunnel and so a much more expensive Road/Rail MEWP has to be used. This was transferred from road to rail in Winchcombe yard, where it travelled up to the Greet tunnel. The examination work took 2 days (more photos to follow).

Br. 43 (A435 Evesham Road Bridge) – This is a 3-arch brick structure carrying the busy A435 road to Evesham. We had a choice of a Road/Rail MEWP, or an underbridge unit. A Road/Rail MEWP has some restrictions in trying to get into the two side arches and so we decided to use an underbridge unit instead.

A435 half closed at Cheltenham Race Course.

CRC side arch inspection with underbridge unit.

This machine would be parked on top of the bridge and thread its arms wherever it could. The road had to have a half closure and we had to provide traffic management. Glos. C.C. restricted us to between 9.00 a.m. and 4.00 p.m. This took just one day and more photos will follow.

Br. 44 (Hunting Butts tunnel) – This tunnel has always been packed with wagons (mostly awaiting removal from the railway), since the tracks were first laid into it nearly 20 years ago.