County Boundary Slip 2017

Page updated on: 22/11/17 at 21:22

Brent Cleeton's video 7.7.17 of soil nailing
Two drone videos from GIP added 16.10.17

November 22nd 2017

The contractors have now reached a stage of practical completion at County Boundary. The worksite area trackside has now been handed back to the SVR and all the contractor site cabins have been removed. The stoned haul road that was created to allow materials to be imported has been tidied up and left in place for the farmer to use as part of the licence agreement. It has also been agreed that the farmer will carry out the reinstatement of the SVR boundary fence next spring when the area of the riverside field that was used for contract operations has recovered sufficiently for stock grazing to resume. All in all, the job has proceeded very smoothly and the SVR is very grateful to the Peter & Michael Kirton who have put up with a tremendous amount of disruption to their farm in order to accommodate the works.

The only remaining work to be carried out during the shutdown, will be the removal of 4 panels of track and excavation of the around 600 tonnes of ash and ballast. This will be replaced by imported stone and reinforcing mesh topped off with re-laid track and fresh ballast (which you will notice is currently stored lineside at the location). These works recommended by the consulting engineer is the final part of the slip remedy and should ensure that there won’t be any post repair settlement problems. After completion of this, the area will be returned to line speed for the 2018 season.

A postscript to all this work, the SVR has taken advantage of the contractors presence to effect much needed repairs to the adjacent Bridge No.19. These have consisted of the removal of the wing wall coping stones for rebidding using lime mortar. Those stones deemed life expired are to be replaced with reconstituted stone versions in a matching colour and these will be put in place during the shutdown. The pictures shows the repaired west side of the bridge and the east wing walls awaiting their new coping stones. Some repoint has also taken place at the same time. As a result it will hopefully be very many years before any further work is required on this remotely site structure.

Chris Bond Infrastructure Manager

October 13th 2017

The works on the river side of the railway are almost complete with final landscaping and grading off finished. The drainage system is now taking water to the river and appears to be working very well. All that remains is to install new fencing along the original boundary line and recover the temporary fence. The bare areas of the embankment will be seeded with grass to bind the surface soil together.

The contractors will now be focussing on the remaining drainage works on the uphill side of the railway before they retreat from the site.

The ground investigation firm have taken some drone footage and stills which shows the extent of the work involved very well - three images added. 

Chris Bond Infrastructure Manager

October 1st 2017

An image from Paul Pearson added, from which the effect of the nearly-repaired slip can be seen. Embankment repairs will take place in October.

September 22nd 2017

Seven images added, with descriptions. 

B Cleeton

September 18th 2017

The remedial works at County Boundary are proceeding very well with the relatively dry summer weather helping to maintain stability in the area whilst the soil nailing was carried out. We are now at the stage of carrying out a very important part of the works, namely the installation of a network of “counterfort” drains below the sheet piling that Brent Cleeton has kindly uploaded pictures of. It is fairly certain that there exists a spring in the locality as the ground in some areas of the slip have remained boggy for the duration of the contract even during dry spells. The drainage network being installed will draw off the water in the embankment and discharge in the Severn. This combined with the other trackside drainage that has been put in, should improve matters greatly.

One sizeable job that remains involves some remedial works to the track bed itself. During two consecutive non-running weeks in October, four track panels will be lifted over the worst affected part of the slip. Around 800 tonnes of mostly ash will be removed and replaced with fresh imported stone infill reinforced with plastic “geomesh” grid. The track and fresh ballast will replaced for the intervening weekend to allow a service to be run.

The purpose of this exercise is to hand back the formation in the condition it was before the slip occurred and fit for line speed.

After this operation is complete, the contractors will withdraw from the site and reinstate the adjacent landowners ground as agreed.

As a footnote to this update, the opportunity to carry out some repairs to the nearby Bridge 19 has been taken. As the contractors are already on site at this remote location, it makes sense to use the site set up to carry out the works saving this cost in the future. The repairs will take the form of coping stone replacement where needed and repointing.

Chris Bond Infrastructure Manager

September 8th 2017

Eight images added, with descriptions. 

B Cleeton

August 25th 2017

Six images added by Brent Cleeton, with descriptions. Soil nailing has now finished, the long reach drilling rig excavator having moved off site.  The new drainage is already working, although it's not connected yet. Clamp beams have been dropped over the soil nails and bolted up to fit on the face of the sheet piles.

B Cleeton

August 15th 2017

Contractors are working with sheet piling at the foot of the slip. Two images added to the gallery.

S Duce

August 10th 2017

Contractors working with sheet piling at the foot of the slip

B Cleeton

August 9th 2017

The workers took the long section token Highley - Bridgnorth at 5 a.m. on August 9th to lay a new 225 mm. polypipe under the formation, and returned it at 9.08 a.m. for the daily service, with only minor sleeper packing to do between the trains.

A trench of two and a bit metres deep was dug, with shuttering planks to support the walls so the new pipe could be installed, and with the rail in situ but two concrete sleepers dropped out. The trench was then refilled with pea gravel before being levelled with little to show after the exertions.

Sheet piling is also on site awaiting for the drillers to finish netting the bank, before sheet piling can begin at the foot of the slip.

Images added to the gallery

B Cleeton

July 31st 2017

More updates on work at County Boundary. New catchpit going in on the river side of the line. And the view over the field now it's been reinstated and seeded over the new drainage pipe. Several images have been added to the gallery.

Brett Cleeton

July 27th 2017

July 26th 2017

Two images from Brent Cleeton added to the gallery from last week's works. Site conditions have nosedived after this week's rainfall, Brent comments.

 

July 21st 2017

Contractors are installing new drainage alongside the track, initial groundwork for the new culvert pipe and outfall and moving rock armour to the riverside, prior to laying in place. They continue to insert steel and concrete nails into the bank. A recent image from Stephen Duce is added to the gallery. More of Brent's excellent YouTube videos are available, if you click on the link there are several others too https://www.youtube.com/watch?v=opk9dnrfa48&feature=share

July 7th 2017

An image from Brent Cleeton shows modified drill tips. The adapter collar has been spiralling up the soil nails, leaving the drill bit disconnected. It is now welded!

Also added is one of Brent's excellent YouTube videos. If you click on the link there are several others too. 

June 30th 2017

Brent Cleeton has posted images of the first of 500 soil nails going in on June 23rd. For the technically minded the dimensions are 3m rod sections, 15m total drill depth, with 32mm diameter nails currently going into sandstone bedrock. These are hollow with as the grouting being pumped in as it's bored.

UPDATE - 

Since the last update much progress has been made on the site and it is to the relief of all concerned that the soil nailing has now started in earnest. The large long reach excavator that has previously graded the embankment, is being used as the platform for the drilling rig to work off. It is attached to the boom using a standard excavator “quick hitch” with the hydraulic power being derived from the machine. Also attached to the drilling rig is a line that contains liquid cement grout that is pumped into the end of the hollow nail sections as it is driven into the ground. This helps both lubricate the drill as it penetrates the ground and backfills the void. Once the grout sets, it helps to bind the nail to the surrounding ground. Thus far the bedrock that the nails are socketed in are between 8 – 11m below the surface and this will vary due to the uneven way the bedrock is laid down.

Elsewhere on the site, progress on the installation of the comprehensive drainage scheme has been taking place. The contractors are installing as much of the drainage infrastructure as they can now and will include the new drain and headwall that will discharge directly into the River Severn. The completion of the drainage will take place once the soil nailing is finished and the contractors gradually pull back off site.

The good news is that the ground movement has slowed down considerably and every soil nail installed added to the stabilising effect. Regular monitoring of the track using a specialised computerised recording trolley plus more traditional methods ensure that the PW gang can maintain the track to a safe standard whilst the works are taking place.

Chris Bond Infrastructure Manager

June 14th 2017

Three images of contractors at work added to the gallery, courtesy of Stephen Duce.

‘Look Out’ at County Boundary (paid position)

An opportunity has arisen for any volunteers who would like to undertake some paid work for the Railway as a ‘Look Out’ at County Boundary. See the Job Vacancies page.

Chris Bond Infrastructure Manager

June 9th 2017

Many of you will be aware that there have been problems with an embankment slippage around the Bridge 19 area also known as County Boundary. This NBI is to inform all staff of what the nature of the problem is and the work required to stabilise the area.

The railway at this point is built over ancient landslide deposits so can be prone to movement but the SVR has up until now, not experienced any great problems in the area of the County Boundary. This changed when a series of track “twist” faults started to be detected due to ground movement in 2016. After correcting these, further movements occurred so the consulting engineer was bought in to look at  the scale of the problem. His assessment was that there were signs of a more serious issue taking place and suggested a set of initial ground investigations. Once volunteers had cleared off the vegetation, large cracks in the embankment were to be seen. The digging of several test pits revealed two distinct slips at different depths taking place.

As a result of these initial investigations a comprehensive set of boreholes and test pits were sunk in order to build up a full picture of the underlying geology. This information would be required to design the remedial solution required to stabilise the area. This particular task has fallen to our consulting engineer Jonathan Symonds who having dealt not only with the 2007 flood damage, but the land slips on the Gloucs/Warks Railway, has all the experience needed to ensure a lasting solution is implemented.

As this year has progressed, movement of the embankment has continued with the PWay having to jack and pack the track regularly to compensate for the movement. A 10mph speed restriction has been placed over the site initially with a “stop and proceed” procedure in place. However, after review this was put back to a 10mph rolling limit to reduce the effects of hammer blow to a minimum on the area.

The design for the remedial work was eventually completed, and work has now started to prepare the site for the stabilisation scheme. The repairs will consist of the insertion into the bedrock of hundreds of soil nails using a special drilling rig. Once fully inserted, each nail has liquid grout pumped down the hollow centre to the tip where it flows out and backfills the voids around it. A set of sheet piles will be percussively driven into the foot of the embankment and a comprehensive drainage scheme installed to take water out of the embankment and into the river.

A licence has been agreed with the landowner for access through his fields and a stone haul road constructed. One difficulty on the site is the presence of an oil pipeline which runs under Bridge 19. This is subject to certain restrictions in regard to the movement of heavy plant over it and unfortunately we have not been able to reach an agreement with the operator to allow this to happen. This means that crossing the track is now the only method of accessing the river side of the railway so a wide crossing has been installed. During the hours that contractors are on site, trains will be flagged over the crossing to ensure no conflicting vehicle movements take place.

A large long reach excavator will soon be on site to grade off the embankment in preparation for the arrival of the soil nailing rig. This is coming hot foot from the Gloucs/Warks line having carried out a similar job at Broadway. The drilling is due to commence at the end of June and will last between 8-10 weeks with the whole contract due to finish at the end of October.

This is a large and geo-technically complex project which fortunately the SVR has insurance to cover. At time of writing, the slip is still active and the priority now is to start the soil nailing on time. There is a risk that until the stabilisation work is underway, the embankment could move sufficiently for the consulting engineer to advise the cessation of trains movements over the slip. An operations contingency plan is in place should this event occur, but until then it will be business as usual.

Chris Bond Infrastructure Manager 

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