Aqueduct update

BRIDGE 09 – AQUEDUCT/ PEDESTRIAN FOOTBRIDGE – UPDATE TO 20.11.18

With the aqueduct/bridge gone, the poor condition east end bank seat was carefully demolished.

and the old foundation widened with extra concrete to the front and both sides. 

Next the main bearing block was concreted; the enlargement of the base, underneath, can just be seen. 

Then the two side blocks were concreted.

The stream coming in from the field on the Cotswold side, into a concrete filled brick sided channel has always been a mess. The old concrete had a substantial dip at the centre causing the water to lie there. 

So that was all cleared away and a new one built with a pipe into the ditch in the field. 

The photograph shows it almost finished.

BRIDGE 12 – VIADUCT – PRINCIPAL INSPECTION (continued)

With 7 of the arches having been inspected with a MEWP a couple of weeks ago, the next task was to inspect the parapet walls and the spandrel brickwork. This was to be done by rope abseiling men. 

The ropes were anchored to the track, 

 

and then the men hung from the top of the parapet doing the inspections. 

The remaining arches were also to be done by aerial rope workers.

In this case a main cable was laid right around and through the viaduct arch, and was then pulled tight below the crown, being anchored to the track from both sides. Then the men attached themselves to this main cable and pulled themselves along.

 



Photos courtesy of John Balderstone and John Fancote.

20.11.2018 - JOHN BALDERSTONE

Royal Oak Landslip Repairs

Royal Oak Landslip Repairs - Official Report

History

Just south of Greet Tunnel on the Cotswold side of the track, the line is in a cutting and the side has been subject to slipping for many years. There is evidence of remedial works being done in BR days but with limited effect. There was a manhole at the top of the cutting to collect the water from the fields but by 2011 it looked like this:

By 2015, it had deteriorated to this:

By September 2017, sufficient funds were available to make a partial repair to the damage. This involved constructing a new manhole at the top of the slope connected to the drains from the fields together with a new outlet pipe taking the water down to the track drains. In this picture, the new manhole can be seen above the excavator arm with the new outlet pipe being laid under the arm:

This shows how close the slip was to the railway boundary together with the new manhole and drains indicated by the stone: 

Because of the limited funds, a proper reconstruction of the slope was not possible so the existing soil was reformed to provide a smooth slope:

Unfortunately the winter of 2017/2018 provided unusually wet especially over the Christmas period and the reformed slope was undermined by water flow causing a new slip. As the ground slipped down, it took the outlet pipe with it so that the water from the manhole was now flowing on to the slope making things worse. The ground was so soft and precarious, it would not have been safe to attempt an emergency fix at this time:

Conditions worsened until the new manhole was completely exposed:

It took the months of dry weather to dry out the ground and by this time, further funds were available. A consultant, David Symonds Associates, was engaged to prepare a design and drawings and then three firms were invited to tender to complete the repair works. After evaluating the tenders, Walsh Construction was awarded the contract. As a bonus for the railway, they had just had a project delayed so were able to start on site just a week later on 17^th September 2018 to take advantage of the continuing dry weather. The railway had already negotiated access across the fields with the neighbouring land owners and Walsh starting constructing an access road immediately:

In order to protect the site in case of further rain, the first task was to install new drainage in one of the fields so that any water was collected and sent to the manhole before it could soak the slipped area. A series of pipes surrounded in stone and membrane were laid in a herring bone pattern and then the topsoil was replaced:

Whilst the small excavator carried out this work, its larger companion finished off the access road and then started excavating the soil from the slipping area and putting it into a stockpile. After discussions with our consultant, this material was declared unsuitable for reuse and was removed from site:

The soil at the toe of the embankment was excavated down until hard clay was encountered below the slipped material. During this work, a clear slip zone could be seen in the face of the excavation between the lower hard clay and the softer upper clay sloping back up the embankment.  Water was percolating along this zone lubricating the surfaces and therefore aiding gravity to move the upper material down. This zone was in a bowl or valley shape and the excavation was taken beyond this on each side to ensure that it was removed. The excavation was brought up in a series of benches with the excavated material being passed from one excavator to the other and thence to the stockpile:

The shape of the slip zone determined the size of each bench and once most of the failed material was removed, work started on rebuilding the slope. A geotextile membrane was spread over the hard clay to keep the new fill separate and the stone was placed on top in layers and compacted with either a roller or a large ‘Wacker’ plate:

Initially only a thin layer of stone was placed to hold the membrane in place and protect the exposed good clay in case of rain whilst excavation continued at higher levels:

Then more stone was placed and graded to the required slope:

As the level of the stone fill rose, the new pipe to connect the top manhole down to the track drains was installed:

As the benches rose, the working area got smaller and a Wacker plate was used instead of a roller:

At this stage, the topsoil that had been saved was spread over the surface of the stone:

In order to hold the topsoil in place, a membrane was laid on top and pegged down:

As the stone got close to the final level, the drain along the crest of the embankment was reinstated surrounded in free draining stone and a membrane:

Here the stone fill is being placed before excavating for the crest drain visible in the background:

After the drainage was completed, the slope was topsoiled and the protective membrane laid before the entire area was hydro seeded:

New fencing was then erected, the temporary access road removed and the field reinstated:

A view of the completed works:

As a bonus, the material used in the temporary access road was taken around to Working Lane to improve our access up towards the tunnel:

Report and photographs by Alastair Watson.

Aqueduct removal

A new title for this blog, but just as much news. Actually, maybe even more, as it will now also feature other news from our civil engineering activities.

We carry on with:

BRIDGE 09 – AQUEDUCT/ PEDESTRIAN FOOTBRIDGE – FIRST WEEK'S ACTIVITIES

The contractors came to site on Monday 28^th October to set up their welfare and stores and other H & S requirements.  A line possession was put in place starting on Thursday 1^st November and work done at track level commenced. The first job was to remove the timbers forming the pedestrian walkway. This exposed the horizontal leg of the steel angle to which the timbers were attached. 

 




As you can see (photos) this ½” thick steel has been dramatically eaten away all along. 








 






Tremendous quantities of scale were also exposed, both on the top of the angle and also within the channel as well.










In places between 1.5 & 2m long sections of the top angle had completely gone. Just what supported the timber over those areas is a mystery. It’s a good job we closed it to pedestrians several months ago!!!

The next job was to provide support to the inner ends of the two outer spans to enable them to be cut away from the centre span, which was supported on the two brick piers. The support to the outer spans was provided by scaffolding which had jacks at the top to support the steel channel. 

The scaffolding was also there to provide stability to the slender brick piers during the dismantling work, and to provide access to cut the steel channel.

Next the ends of the steel channel had to be freed from the concrete encasement at each end.

 














The channel could then be cut through to leave it in 3 separated sections, weighing between 3 and 4 tonnes each. 

 














Then a mat of stone had to be prepared for the crane to sit on so that the outriggers would clear the rails. 

 

Last Thursday the 60t capacity crane came to site and its first job was to lay down timber pads for the outriggers to sit on. 

The tubular hand rails had been left until the last minute, to provide stability to the structure and were only cut through when the section was being supported by the crane.

With all outriggers deployed lifting was started, taking the Malvern side span out first. 














Then the centre span...

....and finally the Cotswolds side span.

The 3 sections (11 to 12m long) were laid down alongside the track and will be cut up and put in a skip, to go off site.

Work then commenced on the Cotswold side bank seat. First the stream (bone dry at the time!!) was blocked off and diverted down the embankment to our trackside drains. 

Photo in which the stream blocking bags and black plastic diversion pipe can also be seen

Next the brickwork was carefully dismantled as it was cracked, and the foundations were exposed. Investigations will now be done to see how deep the concrete is before any re-building is started.

Photos courtesy of John Balderstone, John Fancote & Richard Griffiths (Stepnell)

10.11.2018 - JOHN BALDERSTONE 




Additional photographs from another angle:

All three sections of the aqueduct removed

 Detail of corrosion:

Directly through the side of the channel

 Top flange and handrail bracket eaten away.













Cross section through the channel,showing varying thicknesses. The principal corrosion is in the lower half, where the water ran.









Section of channel showing corrosion of the flanges that supported the wooden walkway

 Maker's plate:

 E. Finch & Co Ltd. 

Engineers

1904

Iron Founders

Chepstow

Note the date is 1904, a year after the 1903 date on the canopy at Broadway, terminus of the first section of the Honeybourne line to open.

Cotswolds side pad on which the channel rested, temporary dam and pipe channeling the stream to the trackside drain. It was dry at the time of the photograph.
There was a significant leak here, as the stream took a shortcut down to the bottom right.

View of the pillars looking west

View of the pillars looking east, and Malvern side pad.

Malvern side pad and underground channel leading away. This pad was rebuilt by the railway in 2002.

The aqueduct works are due to be completed by the end of the month, in time for the DMU Santa shuttle to pass underneath on its way to Broadway.