Home Blog Page 190

Heritage signalling aspirations

It is always surprising to see the level of ingenuity that exists on heritage railways to overcome constraints in both operating and engineering practice. These railways do not have big budgets and solutions to problems have to be realistic on cost and cover any safety implications. The Keighley and Worth Valley line is no exception to this situation and a recent visit by the IRSE Minor Railways Section revealed some interesting aspects as to how the railway is signalled.

The line has been in the ‘preservation’ business for many years. Built by local mill owners but operated, and later taken over, by the Midland Railway to connect the main line through the West Yorkshire town of Keighley with the mills and associated communities up the Worth Valley, it was closed by British Rail (BR) in 1962 (pre Beeching). Most famous of these communities is Haworth, the home of the Bronte family where the famous sisters wrote their powerful novels in the Victorian era.

The terminus is at Oxenhope, some five miles from the starting point, so it is not a long line in terms of heritage operations. BR management was blinkered to the tourist prospects of the area but local interest was not so short sighted and a preservation society was duly formed.

It took until 1968 for the railway to re-open in a very basic form. Over time, a locomotive workshop and shed has been provided at Haworth, a carriage depot and exhibition shed at Oxenhope and a rail museum at Ingrow. The railway became famous when the ‘The Railway Children’ film was first shot on the line in 1970, using Oakworth station and tunnel as the centrepiece, traffic booming as a result. This created many capacity problems and new facilities including signalling became a necessity. In 2018, the railway will celebrate 50 years in preservation.

Operating the line

Before the BR closure, the whole line had been worked as one single line section and this was how the preservation days started. A BR signalbox existed at Keighley and controlled the connection to the main Leeds – Settle – Carlisle line but, at all locations on the branch, ground frames were used for level crossing protection, for access to sidings and for the run round loops at Keighley and Oxenhope. The single line One Train Working Staff incorporated an Annett’s Key to release the ground frame control levers.

With passenger levels rising following the Railway Children film, single section working could not cope with the crowds on busy days and thus, in 1971, an intermediate passing loop was provided at Damems, roughly half way along the line, to allow two train operation. This was a virgin site and had no electricity or running water when built.

Initially, the two ends of the loop were controlled by ground frames to enable early implementation. A signal box was subsequently provided, coming from Frizinghall on the Shipley to Bradford Forster Square line. With no electric power or mains water, the facilities here were at first very basic and signalling power came from dry cells. Subsequently, both utilities have been installed, making it more comfortable for the signalman.

One Train Working continues to be used for operation of a single train over the whole line, but when the signalbox is opened the OTW Staff is locked in the frame and Electric Token Block Working using Tyer’s Key Token instruments is enabled on the two sections thus created.

The signalled level crossing at Damems station (in truth a one coach halt) was originally ground- frame operated but, again, crossing keeper comfort needed attention and a small gate box was recovered from Earby on the now closed Colne to Skipton line. The gates still have to be manually opened and closed. Treadle-operated annunciators alert the crossing keeper to an approaching train.

At Keighley, the railway controls two platforms (numbers 3 and 4) but, on most operating days, only Platform 4 is used for passenger trains. The connections to Platform 3 at each end, needed for locomotive run round purposes, are operated by two ground frames, North and West. These are operated by the train crew using the Annett’s Key on the end of the One Train Working Staff or the Keighley section token. When Platform 3 is also to be used for passenger trains, Station Yard Working is introduced, as described later.

Sidings exist at Ingrow, Haworth (which also has a loop to facilitate entrance and exit to the locomotive shed from either direction, as well as local running round) and Oxenhope (for the carriage sidings and exhibition shed), all of which are ground frame controlled by Annett’s Key.

Signalling technology

As with most heritage lines, much of the signalling has been acquired after modernisation and closures on the main line network made equipment redundant. The railway has perpetuated some Midland Railway practice. The catch handle frame at Damems Junction passing loop box is of the Midland tumbler type, a locking technology requiring particular knowledge to modify and to record on drawings. The frame at Damems Crossing is a Midland tappet type. Home signals are a mixture of Midland lower quadrant (a type no longer seen on the main line) and LMS or BR(ER) upper quadrant semaphores with fixed distant signals.

With Damems Station and Junction being very close to each other, there was considered to be a risk of trains going towards Keighley ‘reading through’ the loop outlet signal at danger if the level crossing protection signal was off. To prevent this, the level crossing signal is ‘slotted’ from Damems Junction. In technical terms, this means having two return weights, requiring a lever in both boxes to be pulled off before the signal arm clears to proceed; an example of past technology that is rarely seen nowadays.

Another curiosity can be found at Oxenhope. The points leading to the carriage sheds and the run round loop at the North end have an ‘economical’ type of facing point lock mechanism developed by the Midland Railway to achieve movement and locking with only one lever.

The point stretcher bar has a vertical roller that engages with a slot cut into a movable plate. When the lever is pulled, the plate moves parallel to the track, with the roller being moved sideways by the main diagonal portion of the slot to move the switch rails. At each end of the slot there is a short portion parallel to the track that imparts no further movement to the switches. The plate incorporates a pair of lock hooks, one of which locates behind part of the stretcher during the final stage of the plate’s movement in each direction. Thus the plate performs both a moving and locking action.

This arrangement was always tricky to adjust and the points were often ‘heavy’ to pull. All other facing points on the railway have the more usual two-lever arrangement with the facing point lock activated separately.

The simple working method at Keighley is satisfactory for normal two-train operation but the use of both platforms for passenger movements enables more operational flexibility for special workings such as galas, including the running of Ingrow shuttle services. On such occasions, ‘Station Yard Working’ is introduced under the control of a Keighley signalman. An Outer Home signal (normally off) on the approach to Keighley is placed to Danger from an adjacent ground frame known as Globe GF after the adjacent public house. This releases a key for the signalman to release the two ground frames at Keighley station yard.

Shunt signals in the Keighley station yard area, which are normally physically covered, have their covers removed and are also worked from the ground frames. The Station Yard Working key enables the signalman to operate the ground frames and control the run round and other movements within the station yard with a train in section, the yard being protected by the Outer Home signal at Danger.

To allow a train to approach the yard from the section, the signalman clears a subsidiary signal beneath the Outer Home but controlled from Keighley West ground frame. The driver is thereby informed that Station Yard Working is in operation at Keighley, to approach cautiously, obey ground signals and deliver the Staff or Token to the Signalman on arrival.

The signalman has to walk to and fro between each end of the station for run round moves, which is a bit time consuming. The intention is therefore to have the station fully signalled from a conventional signalbox, already erected and having previously been at Shipley Bingley Junction. Additional levers have been added to the original frame making 32 in all.

The tappet locking has yet to be fitted and there is very much more work to be done in the box as well as outside, where ducted cable routes have been installed as a first step. The plan is to have mechanical signalling at the West end and power signalling at the North end with track circuits throughout. Signals have been recovered from various locations and a simple gantry is to be built. It is likely to be a five-year project at best.

There is a main line connection at Keighley, used for stock movements and the occasional incoming excursion train. This is protected by a mechanically-operated derailer and requires mutual operation of the release by both K&WVR staff and the signaller in York IECC.

Telecommunications

No railway can operate without communications and, unlike the signalling, the telecom systems and equipment are surprisingly modern. Unusually, the line plant still uses an overhead pole route, with 0.5mm drop wire twins rather than open copper wire. Two electronic exchanges exist (at Haworth and Ingrow) of the ISDX type interconnected by digital trunks. These provide a data capability as well as connectivity to the BT network.

To represent heritage practice, the exchanges still accept loop disconnect dialling and many old fashioned telephones exist to create the right ambience.

2.3Mbit data lines are provided to all stations, allowing a virtual network for credit card sales, and this will shortly be extended to gather data from EPOS terminals. Wi-Fi internet access is widely available to staff. An omnibus telephone line calling at all places is kept in place just in case all else fails!

The railway does not have a dedicated radio network other than back-to-back portables of a modern design that can range up to two miles. Other radio communication relies on the public cellular networks. CCTV with digital recording exists at the main places where passengers congregate and some vulnerable sites.

Main stations have PA systems and there is a remote link to Ingrow for when that station is unstaffed. Traditional master clocks drive slaves at some stations and one also sounds a time signal on the omnibus circuit twice daily to provide a common time reference.

Providing EPOS terminals on the trains is a planned next step using public Wi-Fi to link to the railway’s accounting system.

All in all, the K&WVR is a fascinating heritage line that has adapted well to the local area and modern tourist requirements. It has a delightful mixture of old and new technology, with the former comprising equipment no longer seen on the main line. Due recognition is taken of occasional anti-social behaviour in the locality and valuable assets are protected appropriately for when the line is closed. The future sees some signalling challenges at Keighley and we will all watch with interest how this progresses.

Written by Clive Kessell

Thanks to Bruce MacDougall, David Harrison and staff from the railway’s S&T department for their patient explanations.

In case you missed it – The reversible substation

Actively looking for new ways to improve its environmental footprint, Transport for London has recently performed a successful trial of Alstom’s reversible substation solution, also known as Hesop.

This new converter system can supply the train, providing voltage stability and regenerating the energy produced by braking trains and sending it back to the TFL electrical network to be used by other consumers or, potentially, sold back to the energy distributors. The results of this trial have highlighted the benefits of this new technology.

A challenging commitment

Public transport operators are expected to tackle, simultaneously, a number of challenges: improve energy savings, limit capital expenses, reduce life cycle cost, reduce carbon footprint, reduce heat emissions and improve the passenger experience.

While the Tube provides energy-efficient form of transport, London Underground’s electricity consumption is not negligible. The ‘LU Carbon Footprint Report’, published in 2008, states that London Underground’s electricity consumption represents 2.8 per cent of London’s total usage, making LU the largest consumer of electricity in the capital with an annual energy spend of over £100 million. So it is critical to increase efficiency, both from an environmental and a financial point of view.

Several applications have been developed to avoid energy losses and to reduce overall energy consumption. As a result, these systems can strongly impact operational costs linked to energy prices and substantially reduce emissions of CO2 and other harmful pollutants resulting from the generation of electricity in power plants. But finding the best-adapted technology and opting for the right implementation is not straightforward. It requires an analytical approach that takes many parameters into consideration.

For instance, on-board energy storage solutions, such as super capacitors or batteries, are great to store the excess energy temporarily and release it when needed. But, on the other hand, they are expensive to purchase and maintain, and they also make trains heavier, which increases the energy needed to move them and therefore the heat generated under braking.

So here’s the million pound question: how can an operator provide an environmentally friendly service without increasing costs?

Harnessing braking energy

The best solution is actually quite simple: use the energy elsewhere. This is currently made possible thanks to regenerative braking equipment on trains which allows the traction motor to work as a generator when the train is braking. The kinetic energy of the train can therefore be converted back into electricity.

A small portion of this energy can be reused to power the vehicle’s auxiliary systems (heating, cooling and lighting), while the remaining energy is returned to the network via the fourth rail system, (or via the overhead catenary or the third rail where applicable on other rail networks), to be used by other trains nearby that have a need for energy at the same time. Most modern rolling stock is now equipped with regenerative braking.

 

But, if there aren’t any other trains in the vicinity, this excess energy is generally wasted and has to be ‘disposed of’ in the braking resistors where it is simply dissipated as heat, thereby contributing to heating the Tube. And that’s the issue. There is not always a train nearby that needs energy (by accelerating) when the first train is giving-up energy (by braking).

Several further solutions have been developed to solve this problem, which can be classified in two families. On the one hand are the energy storage solutions. These can be either located on- board the train, where the energy can be used to power the vehicle and its auxiliaries, or they can be trackside, recovering the energy from any braking vehicle and powering any accelerating vehicle within the area of influence of the system.

On the other hand there are the reversible substation solutions, or ‘back to the grid’ solutions. The main difference with the previous applications is that ‘back to the grid’ applications do not store the recovered energy. Instead, they make it available to be used immediately by other consumers or potentially sold back to the energy distributors.

This is exactly what Hesop does. While most conventional substations only allow for unidirectional energy flow, Alstom’s reversible substation solution uses a purpose-designed converter, allowing the energy to flow in both directions.

The Hesop converter is a fixed piece of equipment that is installed within the power substation and allows for excess braking energy to flow back from the line to the distribution network. There, it can be used elsewhere in the substation, or in nearby stations for a variety of other purposes, such as lighting, cooling, lifts and escalators.

The benefits of Hesop

The Hesop product is the fruit of 10 years of development by a team drawn from various disciplines, from power electronics to traction components. It was developed jointly between two of Alstom’s Centres of Excellence, one in Paris, France, which covers railway infrastructure and turnkey engineering and the second one in Charleroi, Belgium, specialising, amongst other things, in traction and converter technology.

So what can this new technology help operators achieve? The simple answer is – energy savings. Hesop is able to recover 99 per cent of the available regenerated energy. The system senses the traction voltage and current to identify a braking profile and only then operates the inverter, prioritising the most efficient use of the regenerated energy.

To put a figure on the amount of energy that can be regenerated during a braking event, it generally represents around 40 per cent of the energy consumed by a train. Considering that, on average, 25 per cent of this energy can be used by other nearby trains (depending on parameters such as traffic density, distances between stations and slopes), this leaves us with an additional 15 per cent of energy that needs to be redistributed.

The more energy recovered, the less needs to be dissipated in the braking resistors, helping to reduce heat production and improve the passenger experience. Taken to its extreme, if the entire line is equipped with Hesop, the feedback control system effectiveness is such that the brake resistors could be entirely removed from the trains meaning zero heat emissions.

Saving energy in this way also means a net reduction in overall CO2 emissions.

The good news is that it saves energy with limited capital expense and reduced lifecycle costs. The regenerated energy is used elsewhere on the system, meaning that less energy is consumed overall, resulting in substantial reduction in operating expense (OPEX) and maintenance costs.

In the other hand, Hesop provides energy to the train with a constant voltage and therefore fewer power substations are required to run the system, resulting in substantial reduction in capital expense (CAPEX) costs.

Successful trial

The London Underground trial was a successful collaboration between three major UK-based organisations: London Underground, UK Power Network Services, and the Alstom Engineering team which is based in Victoria, London. Each organisation brought its own field of expertise and was fully committed to the trial’s success.

However, as can be expected for a research and development trial such as this one, extensive testing was required to ensure compatibility with the London Underground system.

Following initial factory testing and commissioning of the installation, it was gradually connected to the network in stages until it could finally be trialled using test trains during night shifts, to avoid disrupting the passenger service. The aim was to prove that the Hesop unit would have no effect on any of the existing subsystems, such as rolling stock or signalling.

The trial itself lasted five weeks and collected a large quantity of data on the resulting energy savings. Each braking event, on its own, is rather modest but, added up over a day, they represent an average of approximately 800kWh, enough to power 60 UK households or equivalent to the fuel needed for two round trips from London to Paris. And this was with a single unit.

London Underground confirmed that the energy saved over a week could power Holborn station for more than two days and save five per cent of its energy bill. This was without taking into account potential savings on capital investment (cooling system, braking resistors, and life cycle costs).

The results of this trial are a clear demonstration of the savings which the Hesop product and technology can deliver. Alstom’s Hesop solution has won awards for London Underground at the Railway Industry Association and London Transport Awards. Infrastructure owners in Milan, Sydney, Riyadh, and Panama City have all chosen Hesop for their latest urban transit infrastructure projects.

Written by Stewart Marshall, electrical design leader, and Xavier Billiard, electrification project manager at Alstom Transport

This article was first published in June 2016

In case you missed it – Successfully raising the formation! The Hinksey Flood Alleviation scheme

Rail travellers will be aware that flooding in the Hinksey area, on the route between Didcot and Oxford, has been a long-standing problem that has had a severe impact on the local community which relies on the railway. In the last 15 years, the route has had to be closed more than 11 times, causing extensive disruption to passengers and businesses through the cancellation and diversion of passenger and freight services.

The flooding of the railway is part of a much bigger flood problem that is being addressed by the Environment Agency as part of the Oxford Flood Alleviation Scheme. The area around the railway at Hinksey has been often described as a “bathtub”, with floodwater accumulating around and over the railway formation as it tries to find an easy path to the river Thames. The railway formation is acting as a barrier and generations of gravel extraction, followed by major land fill developments in the 1970s, has helped to create a pinch point for flood water at Hinksey.

Raising the railway

To address this problem, Network Rail developed its own Hinksey Flood Alleviation scheme. Joanna Grew, the Network Rail commercial scheme sponsor and Edward John, who is Network Rail’s scheme project manager, explained the work being undertaken.

“During the past two years, as part of our Railway Upgrade Plan to deliver a better railway for passengers, we have worked with the Environment Agency to find a long-term solution to the problem,” Joanne Grew stated. “This has involved carrying out detailed flood modelling and an in-depth environmental study to establish the cause of the flooding and the options available to reduce the chances of it happening again.”

The £21 million scheme involved raising the railway by approximately 650mm over a length of about 400 metres. This will bring the track above the maximum recorded flood levels along this section of railway. That doesn’t sound too challenging, but when it includes an overbridge and a series of underbridges, as well as four tracks – two of them 90 mph main lines – plus nine S&C units and the installation of a twin-box culvert 80 metres long, it gets a bit more interesting. Then, of course, there are the stray wallabies to contend with, but more about that later.

To enable this work to be completed before the winter sets in, a blockade was organised for 16 days, starting on 30 July lasting until Monday 15 August.

One of the consequences of raising the track levels, one that was identified at an early stage, was that the railway formation would, when raised, act as a dam across the floodplain. This means that there would be a potential increase in flooding to the west of Hinksey, an area which includes important link roads as well as residential properties.

Removing the dam effect

To address this potential problem, Network Rail procured the services of design consultant AECOM to develop an Environmental Statement for the Hinksey Flood Alleviation scheme. Detail flood modelling of the area concluded that the optimum solution was to install a culvert under the railway formation, removing the dam effect and ensuring that the scheme did not have a detrimental effect on the surrounding area.

Preparatory work started way back in 2012, when Network Rail replaced the overbridge at Abingdon Road, which crosses the railway right in the middle of the proposed track lift. At the time, when this work was planned, the main reason for the reconstruction was to improve gauge clearances for freight traffic and to prepare for electrification. Incorporating the need to accommodate the proposed 650mm track lift did not require major changes to the original scheme.

Further work started in February this year to prepare the area for the additional infrastructure improvements that included the repair and reconstruction of Stroud’s underbridges and the construction of the new culvert as well as the track lift itself. The work also included preparing the track and replacing signals, as well as setting up a site compound with welfare facilities at the Redbridge Park and Ride. This work was planned every Sunday right through to 17 July, in preparation for the main engineering work that was carried out during the 16 day blockade mentioned earlier.

Carillion was the principal contractor for the refurbishment of the civils work – the Stroud bridges and culvert installation – while, as part of its S&C Alliance with Network Rail, Colas Rail was the principal contractor for the track lift. Two laydown areas were created closer to the site on the east side of the railway line, and dewatering pumping systems in conjunction with a silt removal process set-up to allow the installation of the culverts to be undertaken. This work took place in preparation for the 16-day closure of the line between Didcot and Oxford stations, which started on 30 July.

The first five days were focussed on removing the old track and S&C, then carrying out repairs and replacement of parts of Stroud’s underbridge, which is located 100 metres to the south of the Abingdon Road overbridge previously referred to, and the construction of the new culvert which is located to the north of the overbridge.

Bridge jacking

The proposals prepared by AECOM included the replacement of parts of the four separate bridge decks that together form Stroud’s underbridge. This work included the retention of the two main line steel decks, jacking them up to accommodate the track lift, installing 220mm deep concrete bearing beams, and repairing and refurbishing the eight bearing pedestals. As the freight line deck was life expired, it was replaced by a Z-type steel deck structure. The fourth deck, which was in fact redundant, was replaced with a steel footbridge designed to carry signalling, telecommunication and power cables for the route.

Whilst this work was in progress, the new culvert was being installed across the railway formation. A total of 64 reinforced-concrete box units, each 2.5 metres long, 2.4 metres high, 4.2 metres wide and weighing 25 tonnes, had been delivered to site from Ireland, manufactured by Banagher Concrete.

The plan, which was successfully carried out, was to install 44 of the units during the possession, knowing that the rest could be installed with the route open. Using a 300 tonne crawler crane, operating from two crane pads, a consolidated base was prepared. Then the pre-cast units were positioned to form two box culverts side by side, approximately 80 metres in length.

Early handback

Following the success of the first five days of the blockade, Carillion handed over the mantle of principal contractor to Colas twelve hours early.

Using a Kirow 1200 crane, working south to north, Colas removed the remaining track, scarified the existing ballast and prepared the new formation, which included a geotextile blanket.

Once a waterproofing system had been installed on the Stroud bridge structures, 1,200 metres of plain line track was constructed along with nine new S&C units including one set of traps. Because of the hot weather, stressing and welding had to take place at night. The blockade was handed back three hours early, after completing all the stressing plus 200 welds, with a temporary speed restriction of 50mph.

Edward John was keen to point out that an integral part of the success of this work was the very effective way that the two principal contractors had worked together throughout the blockade. They carried out regular interface meetings which were “incredibly effective” in ensuring that the essential work during the blockade was completed.

Wallabies!

There were some sensitive environmental matters that had to be handled throughout the work. The works were carried-out under Section 61 consents and, with a campsite right next door, noise mitigation was paramount. All works within the local watercourses required Environmental Agency Consent.

Grass snakes, being excellent swimmers, appeared everywhere so they had to be relocated. A crow’s nest required a significant rethink to recapture the significant delays it created, and the problem of a nesting moorhen was resolved by Mother Nature in the form of a hungry stoat. Oh! And one must not forget the wallabies that apparently exist in abundance in Oxfordshire and, on occasion, enjoy a bit of train spotting!

There is still a fair amount of work to do – raising S&T location boxes throughout the area, constructing the culvert wing/head walls and installing gabions to help support the raised embankment. The channels and ditches need to be cleared of vegetation to improve water flows and scour protection is required locally at the culvert headwalls, requiring complete damming of the watercourse.

In addition, throughout the work, consideration has had to be given to the depth of digs and disturbance because the area is a site of medieval archaeological interest.

The culverts are designed to carry a water flow that forms part of the completed Oxford Flood Alleviation Scheme. However, at present, the Oxford scheme is not yet developed enough to cater for the anticipated increase in water flow. So, at the outlet side of the culverts, Network Rail is having to install ‘orifice plates’ which are designed to restrict the outflow until the Oxford scheme is able to cater for the increased flow of water.

Intriguing isn’t it?

Written by Collin Carr

This article was first published in October 2016.

In case you missed it – Broken bridge at Barrow

Barrow-upon-Soar railway station, nine miles north of Leicester on the Midland main line, was opened by the Midland Counties Railway in 1840. Thereafter, it changed its name a couple of times, from Barrow (1840) to Barrow-upon-Soar (1871) and then Barrow-upon-Soar and Quorn (1899). The station closed in 1968 and, despite the fact that much of its original Midland Counties architecture was still intact, it was completely demolished.

A new station, a simple couple of platforms, opened in 1994. It was a few hundred metres from the original location and accessed down steps from the bridge approach at Grove Lane. This bridge consists of two arch spans over four tracks, one arch for the two Fast lines and the other over the two Slows.

So it was a major problem in many respects when, on 1 August 2016, the southern parapet wall and spandrel of the Down Fast line arch of the bridge collapsed, together with the adjacent wing wall. (right) A significant quantity of debris fell onto the adjacent embankment and Fast Lines below, but fortunately rail traffic was stopped in time to prevent a train running into this.

Swift action

A short while earlier, a depression had appeared in the footway of the road above the Fast line arch. This had been seen and reported, with the result that investigatory works were under way on site at the time of the collapse. Nobody was hurt and the prompt actions of those on site enabled rail and road traffic to be protected.

The south footway was lost with the collapse of the structure, along with some of the fill beneath, and a water main and other utilities were left without adequate support.

Steps were taken by Network Rail and its contractors to make matters safe by closing the road to vehicular and foot traffic, and arranging for the affected utilities to be shut off. AMCO’s Asset Management Minor Works team came in at once to assist with this and to begin to clear up the debris. AMCO brought in the Derby office of consultant engineers Donaldson Associates to assist them at this stage. At the same time, Amey undertook checks on the bridge to ensure that the remaining structure was safe and not liable to further collapse.

As a result of these rapid actions, it was possible to reopen the Slow lines on the following day, with the Fasts being reopened 24 hours later. Some 200 tonnes of debris had to be collected and removed to permit this. The road over the structure remained shut to vehicles and pedestrians at this stage, however, and the utilities could not be reinstated either.

Permanent repairs

The next stage in the repair process involved the development and implementation of a suitable permanent scheme. The first priority had to be the reopening of the bridge to foot traffic and the restoration of the water and gas mains and the other utilities. Consultant HPBW was engaged by AMCO to design the permanent works to achieve these ends.

The work began with the stabilisation of the remaining structure of the Fast line span and of the fill above it. The fill that had not fallen had been left unsupported by the disappearance of the brick walls that had collapsed. It was at a fairly steep angle of repose and liable to possible further movement if, for example, there had been heavy rainfall.

To eliminate this risk, two measures were taken. Firstly, tie bars were installed by drilling right through the structure from the north spandrel parallel to the railway, to emerge at the failure surface on the south side.

Secondly, (right) sprayed concrete was applied to the exposed fill, to strengthen it and protect it from rainfall. The tie bars were secured using sprayed concrete, but in the final works they will be extended by the addition of further lengths of bar to bring them out through the rebuilt spandrel wall. Pattress plates have been fitted to the tie bars on the north spandrel face, and will be fitted similarly to the bars’ southern ends when the new spandrel is complete. In all some 20 tie bars have been installed in this way.

The drilling for the tie bars was demanding work since the holes had to pass through mudstone between the south and north sides of the bridge as well as through the remaining brickwork.

These works were completed, allowing pedestrian traffic across the bridge to resume three weeks after the original incident.

At the time that AMCO’s project manager Shaun Trickett and Network Rail’s scheme project manager Gary Matenga spoke to Rail Engineer, it was thought that the final structure was likely to be built in reinforced concrete and faced with bricks to match the existing work. Reconstruction entirely in brick would be feasible, but would take longer to reach a point where the restoration of utilities and vehicular traffic would be safely allowed. Given the priority attached to these restorations, the reinforced concrete with brick facing option is expected to be adopted.

Network Rail and AMCO have been at some pains to avoid unnecessary inconvenience and disruption to neighbours in Barrow. They held a public meeting in the village early on to explain what was happening and to consult with local people. They obtained the use of the local Scout hut for this meeting, and intend to thank the Scouts by carrying out some works for them in return.

Plans are afoot to avoid further works on Grove Lane bridge for the Midland main line electrification in the immediate future by doing these concurrently with the present repairs.

In particular, the parapets of the bridge need to be raised and modified to comply with electrification requirements. If this work is carried out now it will avoid the need for further noise, dust and road closures, minimising future inconvenience to local people.

Written by Chris Parker

This article was first published in November 2016.

In case you missed it – Tamping essential for good track alignment

Track tamping machines play a vital role in the maintenance of track. They are complex and expensive railway maintenance machines and can be found all across the world’s railways. Yet often little is known about them. For instance, what is their purpose and how do they work?

Firstly the reason tampers exist – railway track settles with the passage of traffic. This would not be a problem except that track doesn’t settle evenly, for many and various reasons, resulting in an uneven track formation. Trains require good alignment of the top of the rails. If not maintained correctly, rough riding and even derailments will occur. The faster the train travels along the track, the more important it is to maintain that good alignment.

The development of tamping

Years ago, alignment of track was manually maintained and required whole teams of men using sighting board levels and small tin cans full of 1⁄2” stone. They would manually align track with bars to improve lateral position using skill, string lines and sighting boards.

Track top alignment was achieved either by using levelling boards or by measuring dips to be corrected. Men would open out affected beds, jack the track (often in between trains) and add quantities of 1⁄2” stone skilfully placed from shovels. The amount of stone required was measured out from small tin cans at the rate of one can = 1/8” of lift.

Over the years, the then British Railways progressively phased out manpower, replacing it with tamping machines. We are now at the point today where tamping machines are used almost exclusively to achieve good top and line of the track. They work extremely well and are efficient and accurate.

The tamper adopts a different technique – it consolidates ballast beneath each sleeper creating pyramids of consolidated stone.

To do this, tamping tools are driven into the ballast, drawn together whilst vibrating at an appropriate frequency to fluidise the ballast. During the period the tines are driven into the ground, hydraulic jacks lift and align the rails.

Early tamping machines would simply pack the track but, as technology evolved, so did the tampers. There are several different types of tamper machines; plain line track tamping machines and points and crossing tamping machines, some with 12 tools for use on tracks with conductor rails, others with 16 tools where there is no conductor rail. Then there are also 32 tools to tamp two sleepers at a time and 48 tools to tamp three sleepers at a time. All are diesel powered and can travel across the country at speeds of up to 60mph (100km/h) – this same engine is used to power the track tamping equipment.

Balfour Beatty has a seven-year contract to supply the Network Rail National Supply Chain (NSC) with on-track machines including tampers, and has been providing track alignment services in the South East, Anglia and Wessex routes for over 25 years. This section of the railway is the most densely used by the travelling public, with people travelling or commuting in and out of London. Consequently, ensuring the track is perfectly aligned comes with great challenges and responsibility. Managing risk and safety is pivotal in all operational activity and, to assist with this, Balfour Beatty utilises a 24-hour control centre service which logs real-time data from live sites and provides activity reports on request to Network Rail and key stakeholders.

Why tamp?

Tampers fix track problems caused by the passage of traffic. The greater the tonnage often means the larger the movement of the track and the more tamping intervention is required. During a typical maintenance shift, a tamping machine may maintain around a mile of track. These days, to maximise the benefit of the tamping machine intervention, work can be focused into very short lengths of track to correct specific issues.

Network Rail operates various systems to understand the condition of its track assets; most obvious is the high-speed track recording train. This travels the entire national network recording track quality as it goes. The output is fed down to the local track managers who monitor trends in track degradation and, from that trend analysis, develop their maintenance plan, which also includes tamping.

Balfour Beatty’s Engineering and Technology Solutions business, in fact, supports Network Rail with collecting this data through innovative track measurement equipment that is deployed across the country and feeds into the National Gauging Database. The maintenance and tamping plan results in a tamping machine arriving at the worksite to correct the recorded track errors.

Tamping explained

All modern high-performance tamping machines have a measurement system to enable them to understand where faults exist on the track. This measurement system requires three trolleys – one at the front of the machine, one in the centre (known as the measuring trolley) and one to the rear. A straight line is created between these three trolleys in the form of a beam of light or a tension wire. At the measuring trolley, any misalignment – horizontal or vertical – is recorded as an electrical signal. These signals are fed into the tamper’s control system that directs the working units to adjust the track.

There are a number of ways in which a tamper works. Simple smoothing is where the tamper surveys and adjusts the track using errors measured only between the front and rear trolleys. The tamping machine can only see the errors between those two trolleys, therefore the machine can only improve track over that short distance. This can leave long-wavelength faults and is generally not used in the UK anymore.

The second method is more commonly used, and involves the tamper measuring the entire track length between ‘Point A’ and ‘Point B’, a distance which may be up to a mile in length. The machine’s guidance computer notes all the track errors and subsequently computes a track design using an algorithm to provide the best possible horizontal and vertical alignment through the points.

If, during the measurement process, there is a requirement not to move the track, for instance where a point passes close through a bridge, tunnel or station platform, the operator puts fixed points into the programme and that tells the computer to hold the track position at those points.

Once the computer has developed its programme the operator and inspector check it and, once satisfied, commit the program to the system, position the machine correctly and commence tamping. The benefit of this method of working is it has the effect of extending the length of the tamping machines guidance system to the full length of the site, ensuring there are no long-wavelength track faults.

The third method of working is usually known as the geometry method. This is most often used in track renewal on the West Coast main line, where the as-built design is available, especially around areas of switches and crossings. A design for the track to be tamped is developed off-site by technical staff, and is input to the tamper’s computer to allow it to understand what the finished track should look like. The machine makes a measurement run of the site and the output is the difference between the design and the track as it is before correction. A correction file is generated which informs the machine where and how much track to deploy.

New software has been developed that allows the tamping machine to repair discreet errors on a single rail. As described earlier, tamping machines use measuring trollies to understand where the track is and what errors may be in that track. The new piece of software allows the machine to correct discreet errors on single rails without the need to maintain hundreds of metres of track. This is particularly useful on high-speed railways, in particular High Speed 1. Using this innovation, tamping machines can rectify 20-30 metre faults without disturbing the other rail.

Youthful and versatile

Within its fleet, Balfour Beatty owns 17 tampers, which include eight Compact Plasser and Theurer machines, six Matisa Tampers and two Plasser Unimats. Of these tampers, 16 are under contract to Network Rail. The newest machines, the Matisas, were built in 2010 with an investment of approximately £20 million
for the six machines. The asset life of a tamper machine is 15-20 years and. with the exception of the Network Rail High Output fleet, Balfour Beatty has the most modern fleet of tampers in the UK.

All machines are fitted with the necessary equipment to work on the main line, just like the locomotives and multiple units that run on Network Rail tracks. To that end, they are fitted with Automatic Warning System (AWS), GSM-R, a Train Protection Warning System (TPWS) and On-Train Monitoring Recorders (OTMR). The whole fleet is also fitted with Track Circuit Actuators (TCA), to enable detection on track circuits when travelling on the network.

Balfour Beatty owns the only two Matisa B66UCs in the UK. These are continuous-action universal tamping machines, which can tamp plain line as well as switches and crossings. When in plain-line mode, these machines can operate cyclically or continuously.

Tampers have traditionally operated cyclically, that is why they stop over the sleeper/s to be tamped, complete the process and move onto the next sleeper. This requires the machine to stop and accelerate at every sleeper (or pair or three sleepers depending upon the type of tamper). When in continuous action mode, the body of the machine moves ahead continuously but the working units stop start and accelerate forward, saving fuel and improving the operator experience.

Tamping through switches and crossings is a slow process as the track geometry is constantly changing as the machine moves through the switch. Typically, it takes around 40 minutes to complete a single switch (lead), depending upon the cabling and condition.

Balfour Beatty has a significant footprint in the South, with depots at Woking, Colchester and Hither Green and further access to depots in Ashford, Romford, Eastleigh, Three Bridges and a Midlands depot in Sandiacre, Derbyshire. All of the fleet has been adapted to work within third rail environments, so Balfour Beatty machines can be easily deployed to operate across the network.

Track renewal and maintenance play a vital role in ensuring that the rail network operates safely and reliably. The function of tampers in maintaining track alignment is equally as important. Balfour Beatty has deep route knowledge, expertise and capability in maintaining the nation’s railways and is investing in research and development to further improve the infrastructure and help reduce the cost of track maintenance.

Written by Geoff Brown, engineering development manager, Balfour Beatty.

First published in August 2016

From TESCO to SNC-Lavalin

Between 1994 and 1997, British Rail was split up into almost a hundred separate companies. Amongst these, TOCs, FOCs and ROSCOs are well known within the industry. Not so well known are the TESCOs (Train Engineering Service Companies), the sale of which raised £2.5 million in 1996. Of these, there were two management buy-outs, Engineering Link (later bought by AEA Technology whose rail division was sold to become DeltaRail) and Interfleet, whilst Network Train Engineering Services was sold to WS Atkins.

Interfleet was formerly the fleet engineering division of British Rail’s InterCity sector. When sold, it employed 99 staff, had a turnover of £5 million and an office in Derby. On celebrating its fifteenth birthday in March 2011, it employed 600 staff in 22 worldwide offices and had a turnover of £50 million. Six months later, Interfleet was acquired by the Montreal-based SNC-Lavalin Group, which delivers projects in the infrastructure, mining & metallurgy, oil & gas and power sectors. This includes rail projects such as the design and build of a new automated metro to Vancouver airport.

Until 2016, Interfleet continued to trade under its own brand with Richard George as its managing director. However, in January 2016, it became SNC-Lavalin Rail & Transit, part of the group’s infrastructure sector with Richard as its group managing director. This enabled the group to serve its global rail clients better by uniting its rail expertise.

Although the company is well known for its technical rolling stock engineering expertise, it also provides associated business services, safety and assurance services and manages rolling stock projects. Rail Engineer was glad to accept an invitation from SNC-Lavalin to find out more about the work carried out at its Derby offices.

Long term planning

Rolling stock director Jason Groombridge is clearly proud of his team which, he notes, has a combined 4,000 years of rolling stock expertise. He considers the maintenance and development of this expertise to be a long-term investment that is vital to the success of the business.

An essential aspect of this is the recruitment of eight to twelve graduates each year. Part of the company’s graduate scheme is their participation in the IMechE’s Railway Challenge. Entering first as Interfleet, and in 2016 as SNC- Lavalin, the company is the only organisation to have entered the challenge each year since it started in 2012. It won the first competition and repeated that feat this year, winning by a comfortable margin.

Andy McDonald, director of system consulting and assurance, offers another example of a long-term strategy. He explains how SNC-Lavalin is evaluating Britain’s rolling stock requirements in accordance with the franchise bid timetable and Department for Transport franchise requirements, which now include quality criteria. In this way, for each forthcoming franchise, cost models are produced for new and refurbished fleets. This enables the company to develop an optimum rolling stock strategy in support of prospective franchise bidders.

SNC-Lavalin, supported by Arup, is the rolling stock and depots technical advisor to HS2. As such, it is providing technical, business case and commercial advice on the specification and procurement of high-speed trains. This includes the development of a rolling stock and depot strategy, a performance-based technical specification for both classic- compatible and captive high-speed trains, and determination of the optimum mix of this rolling stock.

South Africa and Hong Kong

Another rolling stock project is the replacement of South Africa’s electric commuter trains. In 2011, the Passenger Rail Agency of South Africa (PRASA) engaged SNC-Lavalin to undertake a feasibility study to assess the replacement of its ageing EMU fleet. Later that year, the company was appointed to lead the procurement of a new fleet of 3,600 vehicles and, in 2013, to undertake a design review of the new fleet.

The resultant £3 billion contract for 600 trainsets, to be delivered between 2016 and 2027, was let to an Alstom Gibela joint venture in October 2013. This included a requirement that 69 per cent of the train’s value would be sourced locally by year two as well as the  provision of technical support and spares over an 18-year period.

Kevin Crofts leads the specialist rolling stock engineering team. As an example of this work, he described how SNC-Lavalin supported the Changchun Railway Vehicle Company (CRC) in its contract to supply 148 new metro cars, and to life-extend a further 348 cars, for Hong Kong MTR’s East-West Corridor.

This commission required SNC-Lavalin to support CRC in developing the design of the vehicles’ car bodies and bogies to meet MTR’s specification, which is based on British Standards, and could therefore potentially help CRC to enter the British rail market. The requirements included confirmation of a 40- year bogie fatigue life, refining the lightweight five-door-a-side vehicle body shell and the development of innovative repairs for vehicle life extension.

Product acceptance

SNC-Lavalin’s novel approach to gauging was explained by Stephen Pell, who joined the company graduate scheme in 2009 and now leads the dynamics and testing team. He described how the GAUGYX system was being developed. This uses a multi-body simulator to predict vehicle movement for more accurate dynamic gauging and quantifies the risk of a vehicle infringement. Stephen expects that this system would help manage potentially bigger vehicles or reduce the cost of infrastructure works.

In recent years, much has changed in the world of assurance. The European common safety method on risk evaluation and assessment (CSM-REA), along with Technical Specifications for Interoperability (TSIs), have replaced Railway Group Standards.

An example of this approach was provided by John Ovenden, section head for on-track machines, who described the challenges of assurance for Plasser and Theurer’s fifth High Output Ballast Cleaning System (HOBCS5) which involved the delivery of 53 individual vehicles of ten designs. These include the RM900 ballast cleaning machine, 09-2X/

CM tamping and consolidating machine and material, conveyor and hopper (MFS) wagons. The system also has transport systems and wagons for spoil and new ballast.

John describes how this is split into two work streams. The first, safety assessment, covers CSM-REA risk assessment, infrastructure compatibility and Network Rail product acceptance, while the second, conformity assessment, involves compliance TSIs and other standards.

With each different machine having hazards that are both distinct and similar to other machines, the assessment was packaged as appropriate. For example, the safety assessment was split into material conveyor and hopper wagons, self-propelled machines and other dead-hauled machines (the core system).

Plush train interiors

In contrast to utilitarian yellow plant, plush train interiors are conceived by SNC-Lavalin’s industrial design section. Its head, James Alton, makes the point that the company not only designs trains that look good, but has the expertise to ensure these interiors can be built and maintained in a cost-effective manner. An example of this is the way his team worked with Saudi Railway Company (SAR) and Spanish rolling stock supplier CAF on trains for the new 1,320km Saudi North- South Railway.

These are 200km/h trainsets with diesel- electric power cars at each end. The trains include executive, business and economy class accommodation as well as restaurant and sleeping cars. They have to cope with sandstorms and desert temperatures up to 55°C and will be first used when passenger services are launched between Riyadh and Qassim at the end of the year. James explains how his team worked with CAF and SAR to develop high-end designs that had to satisfy complex cultural issues, customer aspirations, operational requirements and extreme environmental conditions.

James’s team also supported the 20-month £16 million programme to refurbish 14 Heathrow Express Class 332 units, which was completed in 2013 on the fifteenth anniversary of the launch of the Heathrow Express service. The refurbishment included new vehicle interiors, including 1+1 first class seating, and an upgrade of the passenger information system. SNC-Lavalin undertook the required vehicle acceptance and developed the specification for the refurbishment work, which was undertaken at Railcare’s Wolverton works (now Knorr-Bremse).

Electrification and plant

A presentation from Ganesh Ayyanan, section head of electrification and plant, showed that SNC-Lavalin’s Derby offices are not only concerned with rolling stock. Ganesh explained that, to deliver electrification projects, the company has a 48-strong team (E&P – 18, building & structures – 15, track and survey – 15). Many of these are graduates and technicians who have been trained in-house.

As part of the National Electrification Programme (NEP), Ganesh’s team has been engaged on three distinct packages of work for Network Rail and its contractors.

Between 2012 and 2014, as part of the forthcoming electrification from London to Sheffield, the team undertook a feasibility exercise to analyse upgrade and replacement options for the overhead line equipment (OLE) between London and Bedford, which was originally installed in the early 1980s.

This was followed by work on two sections of the West Coast power supply upgrade, which required both outline and detailed design of OLE and structure modifications for the autotransformer upgrade following a laser survey of the route.

SNC-Lavalin is also currently working for the lead design organisation on four of the Great Western electrification’s ten route sections.

Software solutions

An increasingly important aspect of the business is the software provided by Rail & Transit’s business services for asset management and service delivery. This is being led by head of software solutions Adam Collins, who considers that the success of these applications is due to SNC-Lavalin having the software and rail expertise to understand both what is required and how best to provide the required solution.

The suite of software consists of around 30 applications to support design, maintenance, management, control and train running. SNC- Lavalin also runs clyx.net, a web-based solution for managing data to support this software. Applications include Diagnostyx, for remote condition monitoring, as well as SSiFT (Signal Sighting Information Form Tool) and NIR online which were developed in conjunction with RSSB to manage the industry process for signal sighting audits and reporting high risk defects.

These applications have won a number of awards. Energyx won the ‘Environmental & Sustainability’ category at the 2015 UK Rail Industry Awards. It uses data from electric trains with energy meters and has enabled train operators such as London Midland to save energy by influencing driving styles and reducing consumption at depots.

Also shortlisted at these awards was Rail Companion, which uses a tablet to give different types of rail staff easy access to all the information they need. It also provides an overview to show how users have accessed this information.

Winner of the technical development category of the 2014 Rail Freight Group awards ceremony was the Timetable Advisory System (TAS) which had also won a Railway Industry Association innovation award the previous year. TAS operates on a tablet to advise the driver how the train is progressing relative to timetable. Adam advised that running a train just to timetable can provide energy savings of between two and eight per cent.

Derby’s pride

Derby’s locomotive works once employed 8,000 and had 20 acres of covered workshop on its 80- acre site. It built its first locomotive for the Midland Railway in 1851 and its last one in 1966. This was the last of over a thousand Derby-built diesel locomotives for British Railways.

The works was also a pioneer of rail research. Its laboratories were part of the LMS scientific research laboratory, which opened in 1933, and later became part of the British Rail Research Division.

After the works closed in the early 1990s, its buildings were demolished except for the manager’s office and the Roundhouse, which now forms part of the city’s college. The rest of the site has been redeveloped into Pride Park, where SNC-Lavalin has its offices on the site of the former wheel and traction motor shops. The work done in these offices continues Derby’s rail engineering tradition and, as shown above, makes a valuable contribution to the rail industry, both in the UK and overseas.

Written by David Shirres

This article was first published in November 2016.

In case you missed it – Planning makes perfect

DCIM100MEDIADJI_0038.JPG

As Network Rail strives to achieve a 24/7 railway, the process necessarily places both restrictions and obligations on its suppliers. Work has to be meticulously planned so that it takes place as efficiently as possible, achieving the maximum result in a short space of time. At the same time, record keeping has to be equally precise, so that the next contractor or maintainer to work on the same stretch of railway knows exactly what was done.

To find out what contractors are doing to meet these requirements, Rail Engineer met with Costain’s Peter Roberts, professional head of track, to hear about the company’s special approach.

“We have an ever-increasing need to work smarter,” he commented. “Costain’s aim is to understand the challenges and needs of its clients and, in particular, those of the actual user.”

Structured approach

‘Users’ is a broad term. It includes all stakeholders, passenger and freight train operators as well as the rest of the railway industry and the public-at-large.

The approach taken includes many well- known acronyms – a whole systems engineering ‘end-to-end’ (E2E) approach that has Safe by Design embedded as well as process assurance that includes Common Safety Method (CSM), Construction Design and Management (CDM) regulations, Technical Specifications for Interoperability (TSIs) and Asset Management Plans (AMPs).

For example, it is essential that contractors deliver assurance that the finished works meet the standards of quality specified, together with ‘as-built’ and other deliverables information that confirms what has been delivered to the client. They must do so in a format that complies with the client’s specification, standards for asset data/information and operability and sustainability. It must integrate with the client’s AMPs, including smarter maintenance systems, technology and digital information while including future systems where possible.

Costain sets out to give progressive assurance, including intelligent maintenance, to clients and end users without creating and handing-on masses of unnecessary and unhelpful data. It is understood that data, per se, is not valuable until it is turned into information.

What good looks like

How is this done? It is essential to engage the ‘hearts and minds’ of all personnel, from project directors to front line supervisors and operatives. Design plays a major part, and early engagement and a ‘safe by design’ ethos can improve the whole system, including maintenance regimes and the end state. Project outputs include the physical works, naturally, but there needs to be much more. Contractors have to constantly ask themselves, can we do it safer? better? smarter? leaner? When to use technology, and what form should that take?

All team members – clients, contractors and sub-contractors – need to know what good looks like from a quality perspective (at their level of responsibility). They must understand the value they can add to the team and the consequences of non-conformances on safety, performance and cost.

If successfully implemented, this will drive a ‘one team’ ethic and approach to quality. The natural results are better safety and improved health and environmental factors – a natural progression of this one-team approach as, individually, all will have differing issues and varying levels of risk and impact.

When Costain carries out a survey, it intends to do so once and to do it right. The initial survey forms the foundation of an E2E assurance process that is taken right through to the finished product. Verification and validation (V&V) is key, and must take place before a survey is used for design and implementation.

Sometimes, V&V is under-used or its importance is overlooked. Costain finds it best to engage early in the Network Rail GRIP process, say from GRIP 2/3 to 8, rather than from GRIP 5 to 8 ‘Design & Build’ that it is currently the norm. This early involvement ensures that greater ownership and understanding are embedded throughout, including risk.

Keeping technology in check

“I cannot emphasise enough the importance of ‘Right for the Job’, be it people, kit or plant,” Peter explained. “Experience, competence and understanding play a major part of the process. It is equally important to V&V that the right people, equipment and plant are going to be available with the right software to interpret and apply correctly the survey and design information for the job.

“This is particularly important for tamping and for dozing operations.”

He went on to explain further how important ‘getting it right’ was to those processes. Files pertaining to 3D dozing require V&V prior to the works to ensure the correct models (spacial, levels etc.) have been created and that they communicate correctly with the machine. Tamper files should go through a checking process to ensure they have been created correctly. Deficiencies with these can slow site processes and even lead to non-conformances and re-work. That can prove costly, particularly with the access and possessions implications.

Peter stressed that the selection of appropriate technologies is vital, but it isn’t good to get too bound-up in technology for the sake of it. Of course, it has its place, but LiDAR and point clouds are not always necessary – sometimes simpler things will suffice. “Even a tape measure can be appropriate if it is adequate and the results are verifiable and auditable,” he commented. “That is why we need to understand the end goals and what good looks like for the end user and all stakeholders.

“The objectives have to be to aid ‘entry into service’ and to ensure that clients are supplied with comprehensive data or, more importantly, information for the finished works in a format that is acceptable to them for simple entry to their asset management system. Take-off certification and health and safety files have to be provided at the right time, in the right format to the right recipients in a way that makes their lives easy. Data is fine but this has to be translated into user-friendly and intelligent information.”

Successful implementation

New developments by Costain include automated systems for monitoring track adjacent to civils works. These are designed to minimise the need for personnel to be on or near the line and to generate automatic alerts appropriately when a problem arises. Additionally, new survey managers have recently been appointed to the company to provide additional skilled resource.

The aim is to simplify wherever possible – to make it easy. To fill in forms using Electronic Data Management Systems (EDMS) and electronic signatures, aiding and supporting end product and particular users. To look outside of the box, not just stick to the normal “because that is what we have always done…”

A good example of this approach was the recent collapse of the Dover-Folkestone ‘sea wall’ and its subsequent reconstruction. Costain installed a concrete slab and flood defence prior to reinstatement of the track structure.

The Costain project team challenged the construction and design programme dates, and the actual logic in certain areas of the programme, improving timescales for delivery and reducing cost and risk. Bottom ballast was installed using 3D-controlled dozing, with the key being V&V prior to the works. Track installation was very closely monitored, in particular ‘bottom ballast’ levels, stiffness and uniformity using a lightweight deflectometer for added compliance and future quality and smoothness that would aid track ‘shelf life’.

Track alignment and geometry were controlled using the new Amberg IMS 3000 ‘one trolley’ system. This outputs geometry and alignments (including ‘as-builts’ and RED line drawings) directly into the tamper. The information also formed part of the H&S files and handover data, including data for the National Gauging Database (NGD), which were verified and ‘backed up’ using traditional techniques to ensure quality installation.

The track was pre-built and prepared in 108-metre long panels to aid installation speed and efficiency and also to support follow-on stressing and welding. The panels were installed using a Geismar PEM/LEM system, which was judged to be “right for this job”.

All deliverables, from an ‘Entry into Service’ and health and safety file perspective, were completed, automated, and delivered to the client as soon as reasonably practicable, closing out the AMPs and allowing the site to be taken into maintenance responsibility quickly.

As a result if these initiatives, Costain delivered the sea wall works three months ahead of schedule, giving Network Rail, train operators and the travelling public a railway line in which they can take pride.

Written by Chris Parker

This article was first published in November 2016.

Sighting or siting

Well, in the context of the subject, both could be true, but it is signal sighting that is the basis of this article. Positioning and aligning signals so that train drivers can read and interpret them has been an important activity ever since signalling was invented in the early days of railways. To the uninitiated, this might seem a rather trivial task, but it is not a straightforward process and there are many factors, both physical and human, that have to be considered and agreed to achieve a good result that is acceptable to everyone.

Within the UK, RSSB (formerly the Rail Safety and Standards Board) has been working for some time on a new rail industry standard (RIS) to achieve both nationwide consistency and a better understanding of signal sighting for the main line railway.

Before 1999, regional practices, developed over many years, were still being used for signal sighting and subsequent positioning of signals. A Group Standard did exist, but it primarily set out the basic requirements without any of the detail on why they were needed or how they could be met.

On 5 October 1999, two trains collided head on at Ladbroke Grove, on the approaches to Paddington, causing the death of 31 people and injuring more than 500. In the ensuing enquiry, one factor that emerged was the adverse effect of gantry-mounted signals and possible driver confusion for trains leaving the terminus. It became clear that better documentation and instruction was needed and a revised Group Standard (GK RT8037 Signal Positioning and Visibility) was published in 2001. This stabilised the situation and gave the necessary direction to the people carrying out signal sighting assessments.

Since then, the UK has implemented the Railway (Safety) Directive, Common Safety Method Regulations. These changes to legislation, together with ongoing changes to the structure of the UK rail industry, have highlighted the need to review and update signal sighting assessment requirements to take account of a further 15 years’ experience and understanding of the issues involved. The update will include an explanation of the need and rationale of each requirement along with guidance on how to meet these in terms of technical details, what needs to be assessed and who is responsible for the assessment.

Back to basics

So what is needed in the process of sighting (and indeed the siting of) signals? In simple terms, the goal is to confirm that drivers can reliably read and correctly interpret the displayed signal aspects and indications taking account of the train service being operated.

This might seem easy, but a number of people and organisations need to agree the suitability of each and every signal, indicator and sign. These include the signal engineer who provides and maintains the trackside equipment, the railway operators who plan the train services and the train companies who provide the drivers and operate the trains. These three are the nucleus of a Signal Sighting Committee (SSC), which brings together the necessary competence and experience to make the assessment. Cost, safety and engineering practicalities all have to be taken into account as well as future-proofing for the planning of new services and introduction of new rolling stock.

Key to reaching a good result is a good assessment plan that everyone agrees with and can support with the necessary resources.

In order to set down the requirements for signal sighting, it is necessary to understand the needs of the ‘end user’. This is the driver who has to, in sequence, read the signal aspect and indications, interpret their applicability, decide if they apply to the train being driven, interpret their meaning, decide the action to be taken and then do it.

Studies indicate that, on average, the time to assimilate all this for a simple signal is around seven seconds, taking into account conditions such as weather and day/night, although experienced drivers can do this more quickly. The actual time needed is assessed for each signal as the operational context is different for each location. From this a Required Readable Distance (RRD) is derived.

In many cases, the signal sighting is relatively easy to agree but there are instances where the RRD is difficult to achieve for a variety of reasons and this makes the signal sighting decision more difficult. So how does it all work in practice?

Positioning of new signals

When a resignalling scheme takes place, or when new signals have to be provided, the schematic plans show the signal layout that is needed for the train service to be operated, influenced by line speed, types of traffic, gradients, rolling stock characteristics and braking profiles, and other elements. The signal sighting assessment confirms that the proposed positions of signals and structures are compatible with the train service.

Factors that can influence signal sighting are:

  • Post or gantry position, left hand side, right hand side;
  • Existence of other infrastructure such as electrification stanchions, bridges, level crossings and stations;
  • Day and night conditions;
  • Impact of weather conditions, for instance direct sunlight;
  • Drivers’ cabs and viewing angles;
  • Risk of over reading (seeing the next signal beyond the intended one);
  • Intrusive local conditions including streetlights and traffic lights;
  • Multiple signals in a driver’s field of vision,such as on a gantry;
  • Type of signal: colour light (bulb or LED),semaphore, ground/shunt signal, banner repeater, route/stencil indicator, call on indication, trackside sign;
  • Curvature of track;
  • Tunnel signals and light/dark contrasts.

The SSC takes all of these into account during the assessment and reaches a decision on the optimum sighting arrangement that can reasonably be achieved. This might be a recommendation that a signal is positioned in a different location to that originally envisaged.

Ideally, the signal aspect should be positioned and aligned so that it appears close to the centre of the driver’s normal line of vision and the most prominent display should be the most restrictive (usually the red stop aspect).

Impact of change to existing signals

More difficult to assess is what happens when unplanned changes, both within the rail infrastructure and adjacent to the railway, take place. These can ‘creep’ in without any real recognition of the effect on signal sighting.

This was very much the case at Ladbroke Grove, where the signals had originally been sighted (and sited) to suit an all-diesel railway. The provision of electrification for the Heathrow Express service significantly altered the signal sight lines and worsened the readability of multiple signals on a gantry just outside Paddington.

Other things that can adversely affect signal sighting include:

  • Changes to the environment such as new buildings, roads, street lighting;
  • Growth of vegetation;
  • Changes to track geometry/position;
  • Changes to track layouts – provision of double track, bi-directional working;
  • Introduction of new trains with different driving positions or braking curves;
  • Revised line speeds;
  • New stations or revised station layouts;
  • Changes to level crossing type or operation.

There will be others, and most will hopefully be captured in the change process whereby signal sighting can be re-assessed. There is always the risk, however, that a change will occur gradually, so it is important that people remain vigilant and report emerging problems before anything untoward happens.

Means of sighting

So how is signal sighting actually achieved? In former times, it meant the SSC going out to site with a mock-up of the signal and holding it in the position intended so that all could make a judgement. As indicated previously, most positions were obvious but the difficult ones could cause a lot of options to be tested with, invariably, a compromise being reached.

Nowadays, with video wizardry, a more sophisticated method is available. Where a new signal is to be positioned on an existing and unchanged piece of track, signal positions can be superimposed upon a video showing the view from the cab. If, however, it is a new piece of railway or a substantially changed layout, then a simulated picture of the route is produced upon which the signals are placed. The level of certainty will depend on the sophistication of the video and the accuracy of the images shown.

Where there is doubt, site visits once the infrastructure is in place might be necessary. It is for the SSC to decide what is needed to support a good assessment decision. At the end of the day, the drivers will experience the results of signal sighting ‘in the flesh’.

A complementary article describing one innovation in the technology of signal sighting appears in this edition of Rail Engineer.

Mitigation, safeguards and risk assessments

As hinted, the positioning of some signals can never be ideal and a compromise has to be reached. If the sighting of a signal is known to be poor, then a banner repeater indicator is sometimes provided on the approach to the signal. This enables the driver to know whether the as yet ‘unseen’ signal is showing a ‘proceed’ or ‘stop’ aspect and therefore whether or not to continue braking.

Originally, banner indicators (effectively a black arm on a white background that moves through 45° when the main signal aspect is proceed – rather akin to a semaphore arm) only showed ON or OFF indications, but recently ‘green’ banner indicators have been implemented on some routes that offer a three-state indication, thus giving the driver better information on the actual aspect being displayed on the main signal.

Like all other lineside signals and indications, banner repeater indicators are also subject to signal sighting assessment.

Signal sighting is one of many assessments that may be necessary before a change to the railway is commissioned. Others include the risk of signal overrun, permissive working and signal layout driveability.

Drivers failing to obey signals or misreading them has been a problem for many years, with the term SPAD (Signal Passed at Danger) becoming a familiar word in the English language. Automatic Train Protection (ATP) systems exist to mitigate the impact of a SPAD and range from the least sophisticated like AWS, through to TPWS with a degree of speed measurement and control, and up to ETCS with constant train supervision. Where a signal sighting assessment identifies that a signal has poor readability but it is not practical to improve it, other risk mitigations are available.

Signalling policy in the UK is always to build in an overlap for main line running signals that provides a safeguard in case the driver fails to stop in time, whatever the reason. Poor adhesion conditions in the leaf fall season can be a real risk, as can adverse weather such as dense fog. However, despite the additional protection that an overlap provides, it should not be used as a means of easing the sighting requirements.

Into the future

As ETCS is gradually introduced with in-cab movement authorities replacing lineside signals, it could be presumed that signal sighting will become a thing of the past. This is not entirely true as even ETCS requires marker boards to define the places where trains may be required to stop, and these will need sighting criteria to apply as before. Ground and shunt signals are likely to remain in station areas and depots where sighting will continue to be important – many minor train collisions occur in these places.

Hence the need for improved documentation. Following a period of consultation, and with participation from a cross industry team involving Network Rail, RDG and the ORR, Rail Industry Standard RIS-0737-CCS was published by RSSB in June. It is very comprehensive and gives both detail and guidance on the multitude of situations that are likely to arise.

RSSB members are developing their own briefing materials to support introduction of this standard into their organisations. The RIS is more a reference guide rather than something that should be read cover to cover, allowing a reader to pick out an area of interest and learn how it should be done.

Thanks to Richard Barrow, lead CCS Engineer at RSSB, for both initiating and facilitating the article.

Written by Clive Kessell

This article was first published in September 2016.

In case you missed it – East Coast gears up for ERTMS

Training drivers on route knowledge and cab controls using simulators has been a useful tool for many years. First developed for the aviation industry, simulators for rail were first deployed in the mid-1960s when the initial electrification from London to Manchester was nearing completion. In those days, real film was taken of the cab view ahead with signals and other trackside elements being superimposed and capable of being programmed to mimic typical operating circumstances.

The simulator technology of today bears little resemblance to those early days. The cab view is now a digitally created image that can be modified when changes to the rail infrastructure occur. Different weather conditions can be simulated showing the impact of fog, snow, torrential rain and even fallen trees, all displayed with 3D graphics and accompanying sound. The view may not be quite the same as real film footage, but it is much more adaptable for training purposes as it can demonstrate a multitude of operational scenarios.

Many TOCs now possess simulators and they have been used on the East Coast franchise for almost ten years. With the franchise now with Virgin Trains, and with ERTMS (European Rail Traffic Management System, a combination of ETCS European Train Control System and GSM-R radio) pending, a complete update of the simulator equipment has been undertaken, ready for driver training when the new signalling system becomes a reality.

As well as having ETCS capability, more powerful graphics and computer hardware have been implemented, along with improved instructor and control interfaces. The simulator provider is CORYS, a French company and a global player in simulator technology for the rail and power industries. In early October, Rail Engineer was invited by Virgin Trains to the King’s Cross simulator suite to see what has been achieved so far.

Designing the requirements

Part of the Virgin franchise requirement was to review all existing simulators and prepare them for upgrade or renewal. Working with CORYS, the starting point was to decide which sections of the East Coast route would be initially modelled, what types of trains needed to be included and the list of operational conditions that would need to be simulated.

For the present, only the Class 91 electric locomotive desk and HST diesel cabs from the original simulator are in place but it is recognised that, in due course, the HSTs will be phased out and replaced by the new Class 800/801 Intercity Express ‘Azuma’ fleet, meaning that a new cab model for the Virgin Azuma is currently being constructed.

Paul Boyle, the Virgin Trains ERTMS implementation project manager, explained that a training base needed to be achieved throughout the length of the East Coast main line (ECML). Thus simulators are provided at King’s Cross, Leeds, Newcastle and Edinburgh. The sections of line modelled to date are Kings Cross to Peterborough, Newcastle to Alnmouth and Craigentinny Depot.

Whilst the precise form that ETCS will take on the East Coast route is not yet set in stone, the intention is that this will be ETCS Level 2 to Baseline 3 specification with no traditional lineside signals. The line-ahead graphics have been produced on this assumption, with ETCS marker boards and balises shown in the anticipated positions. These can be easily modified as necessary to reflect precisely the eventual signalling plan once this is finalised. One feature on the simulator is the use of kilometres and not miles in ETCS mode, since the system is a European standard and Virgin Trains want to understand the implications during the period of debate on changing from miles to kilometres for the UK railway.

As well as normal running conditions, the simulator must model out-of-course conditions. These will include temporary speed restrictions, single line working and permissive working, as well as many different equipment failure modes, plus the more usual but unexpected transition from fast to slow (and vice versa) and junction diversions.

The simulator in action

The room at King’s Cross has been purposely adapted to have a darkened ambience and houses two locomotive control desks (Class 91 and HST), each with a display screen showing the route ahead. For those readers who are familiar with ERTMS/ ETCS operation, the display follows a normal pattern: the permitted speed within the Movement Authority (MA) is shown as a grey circular band on the outside of the speedometer dial, the driver being required to keep the train speed within this limit.

Should this limit be exceeded, an orange warning will flash up as an overspeed tolerance of 3-4kph is allowed without the system taking intrusive action. If the speed should go beyond this tolerance, the orange warning changes to red and braking action will occur until the speed has dropped to below that permitted.

As a train approaches a speed restriction of any kind, so the permitted speed band reduces around the dial and the driver must apply the brakes so as to keep within the new limit. If the MA is such that the train has to be brought to a stand, then the speed band will gradually reduce to zero.

In circumstances where the stopping point must be precise, when the speed is reduced below a predefined value (which varies according to train type and the distance to conflict points), the ETCS system relaxes supervision to allow the driver to stop the train close to the ETCS block marker or buffer stop.

This is known as the release speed and acknowledges that ETCS must allow for a certain level of error within the system’s train position reporting. Without a release speed, the train may be forced to a stand before reaching its intended stopping point, for example before all of the train is alongside a platform. However, the system will never allow a train to reach a conflict point.

A separate indication (planning area) gives a scrolling linear read out on the distance ahead that the MA permits, changes in permitted speed and electric traction features, i.e. neutral sections and pantograph raising/ lowering zones. This display can be zoomed out to 32km so in theory the MA could be seen to extend to this distance, or beyond. This situation will only be present when traffic is light on very long stretches of line without level crossings (such as between York and Darlington).

The planning area constantly shows the 500-metre point ahead, halfway down the linear scale, regardless of the zoom value. This is so that the scrolling objects (such as End of Authority and target speed) appear at a consistent rate within this distance so helping the driver not to misjudge the approach. If a linear scale were used for the entire display, at low speed with a 32km zoom setting, objects would appear almost stationary.

Within the simulator, the train performance characteristics (acceleration, braking, coasting) can be changed. Characteristics representative of a freight train can be modelled by altering acceleration and braking performance. Furthermore, the ETCS braking curves (the data that determines at what point braking must begin and the amount of braking effort that must be used) can be manipulated. For example, a passenger train will be programmed with steeper curves than a freight train because of the better braking performance and hence, shorter stopping distance.

As these curves can be adjusted in the simulator, it is therefore possible to apply the braking curves of a freight train to the Class 91 or HST, thus creating the ETCS conditions which would be applicable to freight trains. It follows that, by altering the performance characteristics and braking curves within the simulator, it can be used to represent any type of train that is likely to use the route.

Next year, the simulator will be upgraded with the recently standardised ETCS baseline 3 release 2. Within this specification is the option to display the new Time to Indication (TTI) alert which appears 14 seconds before the orange band appears on the speedometer. This feature was proposed by the UK to give a conspicuous indication (audible as well as visual) of the impending need to begin braking. This is especially useful when low rail adhesion conditions exist when it is necessary to begin braking earlier than usual.

The current ETCS specification has an optional ‘slippery rail’ function which can be selected by the driver or triggered on the train automatically, for example if the signaller becomes aware of such conditions. Once triggered, this function ‘flattens’ the brake curves to command the driver to brake earlier and lighter.

However, the fixed value of these curves will, in many circumstances, be insufficient or will be overly restrictive due to the variable nature of low adhesion conditions (severity, locations or weather). The TTI option will provide drivers with an alert so that they can react according to the individual circumstances at the time. When upgraded, the simulator will be able to test the effectiveness of this function.

The stopping pattern of a passenger train is not built into the simulation, and thus drivers will continue to need detailed route knowledge and will be responsible for stopping the train at the timetabled calling points.

Level crossings

The ECML still has numerous level crossings along its route and the operation of these will need to be built into the ETCS design. Because of the high line speed, crossing barriers are currently controlled manually by CCTV monitoring to prove that the barriers are down thus allowing the route to be set by the signalling interlocking. A similar arrangement is needed once ETCS is introduced and thus an MA cannot be given until a level crossing ahead is proved closed to road traffic.

The simulator can reflect typical level crossing behaviour in that the MA will not be given until the train is in relatively close proximity. This will maintain road vehicle passage for as long as possible, but still be within time to avoid the need for the train to slow. It is to be hoped that, in time, many of these crossings will be eliminated or controlled differently.

This could mean the crossing being triggered by an individual train’s actual or potential speed, taking into account its maximum available acceleration. This will not happen until after ETCS has been introduced on the ECML.

Training logistics

The timetable for provision of the East Coast ERTMS project has still to be confirmed, but it will be 2020 before the first stage is implemented. This may be in ‘overlay’ mode, with lineside signals retained, and the simulator has to be capable of modelling all eventualities.

Around 350 drivers and management staff will need to be trained, so it will be a lengthy process and no timetable has yet been set for this to commence. In addition to the actual simulator location, an adjacent room has been equipped with screens and monitoring controls to display what is taking place whilst a driver is undergoing training. Thus, any mistakes or suboptimal practices can be observed by others, which will be part of the learning process. It is anticipated that eight trainees will take part at any one time, together with the instructor, at any of the four sites.

The simulator training can never be regarded as a one-off exercise and ongoing familiarity with the system will be needed. To support this, a replica of the simulator will be available for loading on to iPads or tablets such that ETCS driving conditions can be replicated away from the work place. This method will also be used in the classroom environment so that all trainees can operate a simulated train rather than one driving and the others observing.

The Virgin staff are mindful that the East Coast project is not the first in the UK – the Cambrian Line having been converted in 2010 – and also that many ETCS projects are in operation in other countries. Visits have been made to some of these to see what the real operation looks like and to learn from the training methods deployed.

The future of signalling is beckoning and Virgin Trains is well prepared for it.

Written by Clive Kessell

Thanks to Paul Boyle, Paul Lartey, Vicki Havron, Richard Stanton and Neal Smith for facilitating this fascinating visit.

Increasing clearances at Hanneys Bridge

The Great Western main line (GWML) is one of the oldest and busiest in the country, linking London with the Midlands, the South West and West and most of South Wales. Engineered by Isambard Kingdom Brunel, it was originally founded in 1833 and ran its first trains in 1838.

Now, with freight and passenger traffic continuing to grow rapidly, the line is undergoing a £2.8 billion process of upgrade and electrification to allow the introduction of faster cleaner and greener rolling stock which will provide a 20% increase in passenger capacity.

However, none of this expansion and improvement seems to come without its share of challenges to overcome. Not least of which is the re-engineering of many of the original overbridges, some dating back more than 150 years.

One such challenge is at Hanneys Bridge near Grove, Oxfordshire. Here, BAM Nuttall was faced with the challenge of raising the vertical clearance of a single span overbridge to accommodate overhead line equipment (OLE) as part of the electrification of the Wootton Bassett to Reading section.

Geotechnical solution

Hanneys Bridge carries an unsealed public byway across the line, providing north-south access to a sewerage works from the village of Grove, immediately south of the line. Built in the 1870s, the bridge required partial demolition and reconstruction to create sufficient OLE clearance.

BAM Nuttall site engineer Cathal Nee described the works: “The increase in elevation of the bridge deck, from four metres to 5.25 metres from the top of the rail head to the soffit, meant that the approach ramps at each side of the structure also had to be raised to meet the new bridge deck level. To achieve Eurocode compliant design criteria and accommodate the required 40 tonne vehicular loadings, the old ramps had to be cut down and completely replaced with new structures.”

Ground surveys identified predominantly soft surrounding soils, highlighting the need for major reconstruction. In light of these findings, and because of close previous working relationships and extensive experience in such conditions, BAM brought in geotechnical specialists Maccaferri to propose a value engineered solution based on the construction of new reinforced soil approach ramps.

On the plus side, the surveys revealed that the original Victorian brick abutments to the bridge were still in excellent condition and would only require stabilisation and relatively minor reinforcement to increase their height and bearing width to accommodate the new raised deck.

As the line had to remain operational throughout the reconstruction, the original bridge deck was removed and replaced over the Christmas period 2015. Two new cill beams were installed on the raised and deepened abutments and the new deck was craned into position.

Engineering a better solution

The solution proposed by Tony Gee and Partners, with detailed design work undertaken by Maccaferri, required the complete removal of the original ramps and the construction of a pair of replacement ramp structures. As there was no land-take, the design was to be undertaken within the footprint of the existing embankments. A number of options were considered but a reinforced soil solution was adopted, using the Maccaferri Green Terramesh system over a geogrid-reinforced load transfer platform.

Maccaferri engineer Nico Brusa takes up the story: “The stability of an embankment constructed on soft soil such as at Hanneys Bridge is governed mostly by the shear resistance of the foundation and is an issue of bearing capacity.”

According to BS8006:2010, reinforcement may be placed at foundation level to prevent shear failure both in the embankment fill and in the foundation soil. BAM excavated the subgrade beneath the exiting ramps to a depth of up to 400mm and Paralink, a high strength and stiff reinforcement layer, was then introduced to improve embankment stability. This reinforcement provided the additional strength needed to achieve the equilibrium state, increasing the safety factor against catastrophic failure.

Nico continued: “With the stiff geosynthetics reinforcement at the base of the embankment, the resulting stress condition will be ‘vertical and inward’ rather than ‘vertical and outward’, as would be the case for an unreinforced embankment.”

Stability analysis carried out using Mac.St.A.R.S 4.0 (Maccaferri Stability Analysis of Reinforced Soil and walls) and MacBars (Maccaferri software for Basal Reinforcement) indicated that the use of bonded geogrids made of straps comprising a core of high tenacity polyester tendons encased in a durable sheath of low- density polyethylene (LDPE) would provide sufficient support for the embankment to ensure that stability is enhanced to an acceptable factor of safety.

The material used, Paralink, is manufactured by Linear Composites, a Yorkshire-based Maccaferri subsidiary, and is used worldwide for the construction of embankments over soft soils, over piles and for those constructed over areas where voids are present.

According to Maccaferri, they are amongst the most tried and tested geogrids in the world offering 120- year design life and high performance.

Factory-made system

The new reinforced soil approach ramps were constructed using the Green Terramesh system and installed by BAM Nuttall under the guidance of Maccaferri. Green Terramesh is a modular formwork system designed to produce a steeply sloping vegetated face which will quickly blend in with the surrounding rural landscape. It is specifically designed for use in reinforced soil construction, supporting steep sloping embankments in road, rail, housing and commercial developments.

This system is a one-piece, factory-made unit, which includes an erosion control mat and factory-fitted brackets to create a steep slope face. The system is ready to install on site without any additional accessories.

After the foundation has been prepared, the system is placed in position empty, and securely fastened to adjacent units using C-rings along all edges, to form a continuously connected, monolithic structural unit. The erosion mat, pre-installed immediately behind the sloping faces of the unit controls erosion and promotes rapid vegetation establishment. A wedge of topsoil is placed behind and in contact with the blanket to provide a moisture and nutrient reservoir, essential for successful vegetation.

No external support, shuttering or accessories are required when installing Green Terramesh, which considerably increases the speed of the installation.

Courses of Green Terramesh units were placed back-to- back, between 10 and 14 metres apart at the base of the structure, to form the opposing faces of the 60 metre long approach ramps, with a maximum height of six metres. As installation progressed, Maccaferri Paragrid, biaxial-array geosynthetic straps, were introduced within the reinforced embankment to provide stability to the structure.

The backfill used to construct the ramps was a well- graded granular material in compliance with specification for highway works. The material, however, exhibited a sulphate content five times higher than normally allowed for 6I/6J material.

Kesternich testing to ISO 6998, undertaken on the durability of the polymeric-coated woven wire mesh on the Green Terramesh units, adequately demonstrated the high level of resistance to sulphate attack of the products. Also, the Paralink and Paragrid will remain stable in high pH environments, as declared on the BBA Certification, with a durability up to 120 years.

Adapted design

The geometry at the interface with the bridge abutments and the new ramp structure was highly complex, requiring significant use of 3D CAD modelling to determine the configuration of the various reinforced soil elements used. This geometrical complexity arose from the re-use of the existing abutments and installation of a narrower bridge deck.

Sam Doe, design engineer for Tony Gee and Partners, explained: “To overcome this complex interface geometry, the Green Terramesh system was adapted so it could be used to form an 85 degree slope rather than the more usual 70 degree. To allow for this, and to avoid compaction works taking place over the railway, the Green Terramesh units at the interface were backfilled with lean-mix concrete. This allowed for the tops of the abutments, which were exposed due to the installation of a narrower bridge deck, to be utilised in the design and allowed for an aesthetically pleasing brickwork cladding to be specified.”

With an increase in elevation of road level at the bridge of some two metres, it was necessary to similarly increase the level of the approach embankments while maintaining an adequate factor of safety of the abutments. This issue was addressed by constructing reinforced soil walls of Maccaferri Terrawall immediately behind the abutments, so that the forces exerted by the new structure onto the abutments were sufficiently low.

With consideration of long-term strain development within the geogrids, a detailed construction methodology was developed to minimise post-construction strains in the reinforced soil structures and minimise stresses transferred to the abutments.

Commenting on the successful implementation of the reconstruction work, Sam Doe said: “By combining reinforced soil walls, slopes and basal reinforcement, a highly adaptable and elegant design solution can be developed. The reinforced soil elements can be combined seamlessly to overcome the many challenges faced on a project such as Hanneys Crossing.”

Reconstruction of the Hanneys Bridge approach ramps began in late March 2016 and was due for completion during mid-May. Throughout the works, the GWML remained open to traffic, testament to the close working relationship between the design, supply and construction partners.

1...189190191...291Page 190 of 291