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A Second Bridge Is needed

The Severn Bridge became a victim of its own success ….

The original Severn Bridge was built as a key part of the M4 linking South Wales to London and the southern counties of England. Following its opening in 1966, it became increasingly popular. By the early 1980s, traffic was severely congested in the summer and at peak times. It was anticipated that traffic would continue to grow significantly, which it did at a rate of up to 8% per year. High winds meant restrictions and the occasional closure of the bridge, with a long diversion via Gloucester.

Delays cost time and money and hinder development. Enhancing the link to South Wales was seen as both a physical and psychological requirement, to ensure that confidence in development would be sustained. In February 1984, the Secretary of State for Transport announced “a study into how a second crossing of the Severn Estuary might be provided in the general corridor of the existing bridge.” The completion of this study would avoid unnecessary delay in providing a second crossing as soon as it was needed.

The Study was completed in 1986 and, in 1987, the consultants were reappointed to develop the scheme. Project management was transferred to the Department of Transport’s South West office at Bristol, to be taken forward in consultation with The Welsh Office under the direction of a joint Steering Group. The original programme, set out in 1987/88, was to start works in 1992 with completion in 1996. The new crossing was completed to programme and to budget.

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Building the Second Bridge

The challenge of nature… again!

The building of the Second Crossing faced the same challenges as the original Severn Bridge: the same 14 metre tidal range, eight knot tidal flows, and exposure to 100 mph winds. However, this was a much longer crossing, giving greater concerns for the environment and the aggressive site conditions.

Preparations for Construction

To meet these challenges, it would be necessary to minimise the impact of the tides, winds and weather during the four years of construction. This would be achieved by building as much as possible in large units, on land, before transporting the pieces out on to the estuary for assembly. This would require causeways, jack-up platforms, and large powered barges controlled by GPS (Global Positioning Systems).

Aerial view of the construction yard adjacent to the Second Bridge

Large construction yards were required on each bank of the estuary and there was a great deal of detailed planning, bringing together onshore construction expertise and knowledge gained from the offshore oil and gas industry.

There was a worldwide hunt for marine and other equipment that would be needed. At the same time, a start was made on the design and manufacture of items such as precast moulds, barges and gantries that were specific to this particular project. The length of time available to work on the English Stones between tides would be limited, as would the time to float large units out to the bridge at high tides. These restrictions had to be factored in. Above all, strong teamwork would be required from the men and women involved to develop innovative solutions and then to turn them into reality.

Building the Viaducts

Foundations and Piers

All the foundations were built using pre-cast concrete caissons, which are very large boxes without tops or bottoms. Most caissons were seated directly on the rock of the English Stones but some were on piled foundations.

To avoid any additional loading on the Severn Railway Tunnel, the lengths of all viaduct spans were adjusted to ensure that a longer standard length of span would be available at the point where the viaduct would cross over the railway tunnel. Also bored piles were used to support the caissons on either side of the tunnel because no change in the loading condition on the tunnel could be tolerated. Monitoring devices were fitted to the tunnel lining to check for any movement in the structure of the tunnel. Where movement did occur, it was found to be related to the very different loads imposed by high and low tide, rather than by the new crossing.

The Pier units were pre-cast. They were then transported from the yard and assembled on top of the caissons, ready to support the viaduct. These units were 3.5 metres long and weighed up to 200 tonnes. Approximately 2400 units were required.

For more on building the second crossing viaduct piers, Click Here

Caisson loaded on traction unit in construction yard

Caisson on tractor about to move down on to waiting barge

Caisson onboard barge

 

 

 

 

 

 

 

 

Preparing to lift caisson off barge

Caisson being lowered onto prepared bedrock under floodlights

The concrete batching plant for the Caissons, etc was kept close to the action

Viaduct Deck

The precast concrete deck units were “match cast” in the yards. Each unit was cast against its neighbour to ensure that it would fit correctly when it was assembled in the estuary.

Adjustments were made to the mould so that the correct curve of the viaduct could be created. This achieved a combination of factory production with repeated modular construction.

The viaducts were built progressively from each shore using a purpose built launching gantry that was supported on units already placed. Units were delivered along the completed part of the viaduct and picked up from there by the gantry.

Another view of the yard, with the mobile launching gantry at the eastern end of the viaduct, having already placed viaduct units either side of the first pier.

A view into the deepest viaduct unit that sits directly over the pier

The gantry is bringing the next viaduct unit to its intended location, adjacent to the unit against which it had been match-cast in the construction yard

The gantry has been moved forward to start building the viaduct out in both directions from the new pier, keeping the new section in balance over the pier

 

 

 

 

 

 

 

 

 

 

Building started by placing a deck unit on the first pier and holding it in place with temporary steel ties. Successive units were then added, one at a time, first to one side, then the other, to keep the two sides in balance. These additional units are held in place by steel strands positioned within the units that are tensioned horizontally. This provided a “balanced cantilever” form of construction.

Units were added until they reached half way to the next pier. The gantry was then moved forward over the completed work, so that it could be supported by the next pier. This sequence was repeated and the gaps behind were closed. Further longitudinal pre-stressing was then incorporated into the units to create a continuous structure.

For more on Building the Second Crossing Viaduct Deck, Click Here

The Shoots Bridge

The Pylons

The foundations for the two large pylons of the cable stayed bridge were built by using caissons in exactly the same way as for the viaduct. These two caissons were both in excess of 2000 tons and were among the first to be placed, in the Spring of 1993.

The pylons were the most significant parts of the crossing for which the general policy of precasting on land, proved unfavourable. They were therefore constructed of reinforced concrete, in situ. The reinforcement cages were prefabricated on land, transported out to the pylon locations, and lifted into place. The concrete was made in a batching plant located on the caisson. It was placed using one of two cranes and then, when the concrete was strong enough, an ingenious “self climbing” formwork moved up the pylon. Precast cross beams were lifted into place as the pylons were being built.

The upper cross beam of the pylon is being lifted into place

A pylon is under construction, with the lower cross beam already in place

The pylons are approximately 150 metres high, which is equivalent to a 50 storey block of flats. They have warning lights for aircraft at the top and they are hollow and have lifts, inside, to provide access for maintenance.

For more on Building the Shoots Bridge Pylons, Click Here

The first section of bridge deck is being lifted into place, on top of the lower cross beam

A side view of the top of a pylon. A pair of cables, one from each pylon, will support the most distant end of an individual deck unit

The Bridge Deck

The long span of the main bridge required lighter deck units, which were made of steel lattice girders. A concrete slab on top carries both the traffic loads and the large compression force introduced by the cable stays.

The steelwork for the units was fabricated off-site, brought to the site and assembled in the construction yards, complete with the concrete deck. The units were 7 metres long and full deck width. Unlike the viaduct units, which were progressively taken out to the launching gantry along the viaduct itself, the main bridge units were taken out to the site by barge.

Like the viaduct, the deck construction started directly over the pier and units were placed alternately on each side. The units were lifted off the barge by cranes located at the ends of the deck and were tied back to the pylon with inclined steel support cables to take the load. This required simultaneous work both at deck level and high up on the pylons.

Construction started at the eastern pylon and, once the eastern part of the deck was complete, construction of the western deck followed. A critical stage was when the eastern part of the deck was complete but was free to sway in the wind until the western side came to meet it, as if holding hands. The final deck unit, that closes the gap between the bridge deck and the approach viaduct, is seen being lifted from the barge into its final resting place.

The final deck unit, that will close the gap between the bridge deck and the viaduct, is being lifted from the barge into its final resting place

A close-up of the final deck section approaching the readied gap

A long view of the bridge deck approaching the end of the waiting viaduct

The style of support gives the cable-stayed form of construction its name. It is a key difference from suspension bridge construction, seen upstream on the Severn Bridge, where the deck is hung from the main suspension cables.

The overall sequence for placing the deck units took from September 1994 until 12th of November 1995 when the middle section was lifted into place, with 6 mm to spare on each side.

For more on Erection of the Shoots Bridge deck, using cable stays, Click Here

Watch the 12 Minute Video of the Construction Process

 

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Design and Contract Preparations

Initial Design. 1987 to 1990

Design work on the new crossing included further detailed studies, a hydraulic model to test pier positions, mathematical modelling, a bathymetric survey, and geotechnical and topographical surveys for the route corridors. Extensive research was carried out into wind shielding and also into climate change issues, which indicated a potential rise in sea levels. The viability of engineering concepts and innovations were confirmed, together with the buildability and quality of the scheme.

Extensive consultations were undertaken with all those affected to ensure that concerns were fully understood and positively addressed in the development of the scheme. Wide ranging studies were carried out into the existing environment, potential impacts were identified and removed where feasible, and proposals were developed for reducing remaining adverse impacts. The consultations also included navigation interests, industry, landscape advice, and the Royal Fine Arts Commission regarding the main bridge and other structures.

A series of public exhibitions was held in England and Wales in areas affected by the proposals, initially showing the results of the study and then the changes adopted as the design was developed to take account of local concerns and the results of surveys

Contract Arrangements

In April 1989, tenders were invited for the main crossing and toll Plaza. The tender details included highly detailed technical requirements, contractual/financial issues, constructional aspects, and environmental monitoring.

Separate bids were sought for two possible scenarios:
(a) to design, construct and finance the crossing, and to assume responsibility for operating and maintaining both it and the existing Severn Bridge during a concession period, in return for the toll revenue from both bridges during that period, and
(b) to design and construct the new crossing in return for staged payments from the government.

In 1990, following a rigorous assessment of the tenders, the Government accepted, in principle, the proposal of Severn River Crossing Plc to design, construct, finance and operate the second crossing. Severn River Crossing Plc was a consortium set up specially to bid for the project. It included major investment banks, a British contractor, John Laing Plc, and a French contractor, GTM Entrepose.

Obtaining Parliamentary Approval 1990 to 1992

Authority to build the scheme was obtained through Parliament. A hybrid Bill was used to seek the powers required to construct the estuary crossing and the approach roads, to compulsorily purchase the land, and to charge tolls.

The Severn Bridges Bill was lodged in November 1990 and, after thorough examination of the scheme by Parliamentary Committees, Royal Assent was granted in early 1992. The immense value of the extensive and detailed consultations, with over 40 affected parties, was shown by the small number of formal objections that were presented against the Bill.

A Concession Agreement, between the Government and Severn River Crossing Plc, was signed and construction was started in Spring 1992.

For more on concession and concessionaires strategy, Click Here

Final Design for the Second Crossing. 1992 to 1993

The Second Crossing is comprised of a cable stayed bridge spanning the main navigation channel, with a two kilometre length of approach viaduct on either side. At 5 kilometres, it is the longest river crossing of this type in the country.

The Viaducts.

There are 20 spans of approach viaduct on either side of the main bridge and each span is made up of 27 separate units of hollow concrete box girder, tensioned together using high tensile steel strands.

For more on Design of the Second Crossing Viaduct Piers, Click Here

For more on Design of the Second Crossing Viaduct Deck, Click Here

The Shoots Bridge.

The centre-piece of this crossing of the Estuary is the cable stayed bridge over the main navigation channel, known as the Shoots. The main channel resembles a steep sided trench at this location and, although it is only about 300m wide at the base, the pylon legs had to be set back, well away from the top edge of the trench, to ensure stability. After careful consideration, a main span of 456m was agreed upon. At the time of its design, there were no cable stayed bridges operating anywhere in the world with a longer span, although the Pont de Normandie in France was well under construction with a span of 856m.

For more on the Design of the Shoots Bridge Pylons, Click Here

For more on the Design of the Shoots Bridge Deck and supporting Cables, Click Here

Other Works

In parallel with these activities, the detailed design of the motorway approach roads was undertaken and tender documents were prepared. This work included the resolution of many issues affecting areas local to the roads, dealing with environmental, landscaping and community issues, and incorporating a wide range of mitigation measures.

Tenders for the approach roads were invited in October 1992 and contracts were awarded in time for construction to start in Spring 1993. The challenge was to construct the second crossing and the approach roads in time for an opening in 1996.

Outline of the Second Severn Crossing

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Surveys, Studies and Consultations

What to do?  How to do it?  1984 to 1986

In 1984 the government commissioned a detailed feasibility study into a second crossing. The challenge was to investigate the need for a new crossing and to identify the best type of crossing and its location.

The study area extended 8 km up and downstream of the Severn Bridge. Different types of bridge and tunnel were examined. Road connections to the existing motorway network were a vital part of the study.

The study considered all key issues, from the traffic demands to the environmental impacts and from engineering feasibility to economic viability and planning issues. Both local and wider regional effects were considered on both sides of the Severn estuary.

To find the right solution, the study needed to balance the expectations of society at that time for new infrastructure against costs and economic analysis and against the impacts upon both people and the natural environment. It needed to weigh benefits against disbenefits whilst reducing disbenefits where practical.

Plan showing the options considered for an additional crossing of the estuary

The study was completed in 1986. It recommended a bridge at the English Stones, with viaduct approaches 5 km in length, together with 20 km of approach roads linking to the M4 and M5. This was the scheme that promised best value for money. The Government accepted this recommendation and so the concept of a crossing at the English Stones, first actively considered in 1935, would now be brought to fruition.

 

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Postscript

A false start

On its completion in 1886, the Severn Tunnel was seen as a successful and lasting solution to the problem of crossing the estuary.  However, within a short period the first motor-cars began to appear on the roads of this country and, within a handful of decades, their numbers had increased to the point at which they were causing problems.

Before leaving the historic background to the motorway bridges, it would be fitting  to mention a harbinger of the great feats of engineering that would be brought to fruition on the sites of Old and New Passages in the second half of the twentieth century.  in 1934consultants, Mott, Hay and Anderson, acting on behalf of Gloucestershire County Council, sought powers from Parliament to build a bridge across the estuary.  It happened at a time when the country was recovering from the impact of the Great Depression, with pressure mounting on highway authorities from groups seeking action to deal with the ever-increasing numbers of vehicles on the nation’s roads. The situation was particularly acute for long distance journeys and the County Councils, who at that time were the highway authorities responsible for major roads, were right in the firing line.

Gloucestershire’s consultants had initially favoured provision of a high level suspension bridge on the Aust-Beachley line, with a 3,000 feet (950 m) span and a conventional truss deck (essentially the same as the initial proposals for the Severn Bridge that were brought forward again in the 1950s).  Monmouth County Council had by then joined with Gloucestershire Council and, together, they decided to promote a scheme, three miles downstream from the consultants’ first suggestion. This scheme, across the English Stones, would have been virtually identical to the Second Severn Crossing, except that it had a suspension bridge with a 900 foot (275 m) span, as its centrepiece across the Shoots channel, rather than the modern cable stayed bridge with a span of 456 m (1,395 ft).  Also, the spans of the viaduct sections on either side of the central bridge would have been shorter than those on the later Second Crossing.

Sketch of 1935 design for a Bridge and Viaduct at the New Passage

The two councils launched a Parliamentary Bill to obtain the necessary powers to build this second scheme, assuming that they would be able to persuade the Ministry of Transport to meet 75% of the costs. However, the Great Western Railway opposed the scheme in Parliament, ostensibly on the grounds of potential damage to the Severn Tunnel and, in 1936 a Select Committee of the House of Commons rejected the bill. By that time, the national debate about the management of the major road system was coming to a head and the two County Councils decided to take no further action on a lower estuary crossing until those issues were resolved.

The government was under pressure to change the existing system, with strong evidence from other countries, of the benefits to be gained from the construction of high speed inter-regional roads under central direction.  Recognising that the County Councils could not be expected to bear the burden of financing a new national highway system,  the Ministry of Transport concluded that a Trunk Road Network should be created and that it should be administered, financed and maintained by Central Government. This change was enacted through the passage on to the Statute Book of the Trunk Roads Act, 1936. The defined network included a Severn Crossing and an improved A48 road along the South Wales coast. However before any significant progress could be made, the Second World War intervened.

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The Severn Railway Tunnel

Preparatory work

It was while working on the ferry piers for the Bristol and South Wales Union Railway in 1862–63 that Charles Richardson first began to pursue the idea of replacing the ferry with a railway tunnel beneath the estuary.  However, it took him three attempts, over a period of ten years, to get the plan accepted.  His first approach, in 1865, was rejected because the GWR were in the process of seeking an Act of Parliament for a project, proposed by John Fowler, for a new double track, mixed-gauge railway, 41 miles (70 km) long, from Wootton Bassett to Chepstow, crossing the Severn at Oldbury Sands.  And by 1869, Richardson’s scheme also had competition from two other tunnel proposals.

Richardson’s estimate for his tunnel, and for the short lengths of railway at either end, was £730,000.  The tunnel’s chances of success improved dramatically when, in 1870, the newly elected chairman of GWR, Daniel, later Sir Daniel, Gooch, denounced the Fowler project (see previous paragraph) as an extravagance.  Apparently he had come to realise that the director who had been pressing the case for this project at Board meetings, had been doing so to further his own interests.  After further lobbying, Richardson’s scheme was adopted by the GWR Company in 1871 and, the following year, the Severn Tunnel Bill was approved by parliament.  Construction began in 1873, with Richardson as Chief Engineer and with John (later Sir John) Hawkshaw as Consulting Engineer.

Plan showing the Severn Railway Tunnel

The construction of what would become the longest railway tunnel under water in the world at that time, turned out to be a classic example of an engineer’s extreme fight against adversity.  It is surely the leviathan of all Victorian railway tunnels and one of the nation’s finest engineering achievements.  An excellent and detailed account of the works is contained in the book written by Thomas Walker, the contractor who assumed responsibility for their completion, after progress under Charles Richardson stalled, in 1877. The description of events, given below, is based on information obtained from that book.

The bold attempt fails

The original intention had been to put the work into the hands of an experienced contractor but Richardson was not satisfied with any of the bids he had received from contractors.  He was convinced that, by using the GWR Company’s own direct labour force, he could complete the job for 25% less than would be the case if he accepted any one of the bids he had received from contractors, and so he decided to go ahead on that basis.   However, four and a half years later, all he had achieved was one winding shaft and 1,600 ft (490 m) of 7 ft by 7 ft (2.1 m x 2.1 m) heading under the river.  In August 1877, the Directors of GWR intervened and instructed that tenders should be invited for the remaining works.

Appointment of the contractor
Sir John Hawkshaw, 1877

Sir John Hawkshaw, 1877

Only three tenders were received in response to the new invitation and Hawkshaw, acting as consultant, recommended acceptance of the tender from Thomas Walker, an experienced contractor in whom he had full confidence.  However, the Directors took the view that Walker was asking too much for contingencies.  In order to minimise their exposure, should a disaster occur, they decided not to enter into a contract with him until the ground had been proved by the completion of the 7 ft x 7 ft heading right through the length of tunnel under the river.  In the meantime, the heading was to go ahead using direct labour.  Certain other relatively small items of work were also allowed to proceed, some by using smaller contractors, others by direct labour.

The first major incident

The pace of the work picked up significantly but, on 18 October 1879 when the headings, that were approaching each other from either side of the river, were only 138 yards (125 m) apart at the east end, a great inrush of water occurred at the west end.  Within 24 hours, water had filled the works on the west side, up to the level of the tide.  Fortunately, the safety measures that had been put in place, enabled all the men working in the tunnel to escape with their lives.

There is little doubt that all the men who ran for their lives on that day were convinced that the river had broken into the tunnel.  However, when the initial shock had subsided and it became possible to rationalise events, it became clear that the point at which the water had broken in was not under the estuary itself but a short distance from the west bank.  We now know that the influx of water came from the “Great Spring”, a major aquifer that carries extremely pure water down from the Brecon Beacons and directly into the Estuary below low tide.  To day, over 130 years later, 20 million gallons (90 million litres)of valuable spring water are still being pumped out, each day, from the point at which the tunnel had had been cut into this aquifer. At the time, this flow represented the daily intake of either Liverpool or Manchester – or about one sixth of the consumption of London.

Thomas Walker

The aftermath

The ingress of the Great Spring, no doubt, caused GWR Directors to ponder their previous statements about the amount requested by their chosen contractor for contingencies.  Their reaction, to what had happened up to that point, was to invite Hawkshaw to take full charge of the works, as Chief Engineer, with authority to act as he thought fit.  Hawkshaw intimated that he was prepared to accept, but on condition that he be allowed to let the works to Thomas Walker.  The Directors concurred but still wanted the length of 7 ft by 7 ft heading to be completed under the deep channel known as “The Shoots” before any major works were undertaken elsewhere.  They asked Hawkshaw to seek a price for this element, alone.

Walker responded, suggesting that his 1877 tender should still stand, though modified to allow for the lapse of time and the amount of work still to be done.  He was prepared to concentrate on completing the heading under the river, as soon as he had dealt with the influx of water and pumped the workings dry.  This suggestion was agreed by all parties and the works were handed over to Walker on 18 December 1879.

Richardson’s Departure.

The events described above inevitably led to the departure of Charles Richardson from the project.  Great credit is due to him for the conception of the scheme and for its safe passage through the unpredictable Parliamentary procedures.  He also developed a system for successfully aligning the two headings with unprecedented accuracy.  However, while his administrative and conceptual expertise remained untarnished, his ability to drive a difficult project through to fruition, had been called into question.  The extent to which his difficulties stemmed from a lack of expertise or commitment on the part of the GWR direct labour force, is difficult for us to judge in the 21st century.  But before Richardson leaves the stage, it is worth mentioning that generations of boys, both young and old, should be grateful to him for conceiving the idea of inserting three layers of rubber into the cane handle of a cricket bat, a device that soon became adopted universally and is still employed, worldwide.  It is on record that several of his professional colleagues, including Brunel, often complained about the amount of time that he spent playing cricket!

Longitudinal Section of the Railway Tunnel

Dealing with the Flood Water

In January 1880, while Walker was setting up and organising pumping operations, Hawkshaw decided to lower the position of the tunnel under the Shoots Channel by 15 ft (4.6 m), preserving the previous gradient of 1 in 100, eastwards towards Bristol, but increasing the gradient westward to 1 in 90. It was possible to make this change without incurring large additional costs because the almost completed heading would still be wholly within the template of the amended tunnel. The greater security that this represented, against the threat of the river inundating the works, allowed him to authorise Walker to commence work at other points. Walker was then able to put in hand arrangements for recruiting and housing a very large work force (the maximum number employed, at any one time, eventually reached more than 3,900).

The immediate task was to seal off the heading into which the spring water had entered. Although the heading itself was quite short and wholly under dry land, it interconnected with the main heading in the Sudbrook pumping shaft. This meant that a shield had to be positioned in the shaft to seal off the problematic heading on both sides of the shaft.  Like so many other operations involved in the construction of the tunnel, the task was bedevilled by practical problems and pump breakdowns.  Divers were called upon to perform superhuman feats at what were extreme depths for the best survival equipment available at that time.

Sudbrook Pumping Station

A good example of this came about when Walker realised that, in order to clear all the water from the Great Spring out of the tunnel, it would be necessary to close an iron door in a headwall that had been left open, inadvertently, when the men evacuated tunnel on the day the inundation occurred. The job was given to his most experienced diver, who had to negotiate all kinds of obstacles in walking for 1,000 ft (310 m) though the flooded heading, all in darkness. The diver’s air pipe was connected to a static pump at the start point which meant that a very long length of pipe had to be dragged out behind him.  And because the water in the heading was under considerable pressure, the air pipe pressed hard against the top of the heading, producing a great deal of friction.  Even with several assistants to help convey the air pipe forward, the diver was unable to complete the assignment. The problem was only overcome when the engineers discovered that a Wiltshire man, named Henry Fleuss, had just developed a new type of diving helmet that connected directly to a cylinder of compressed oxygen strapped to the diver’s back – a very fortuitous piece of timing.

The Great Spring was eventually contained behind a long ‘cement’ headwall, 8 ft (2.5 m) thick, into which a door had been inserted. At a later stage, pumps were installed to take the water away to prevent it causing further damage – and to take advantage of the commercial potential thus available.

Other unexpected difficulties

At the end of April 1881, when the process of ‘breaking up from the initial 7 ft by 7 ft  (2.1 m x 2.1 m) heading to the required dimensions of the tunnel was underway on the Gloucestershire side, water suddenly burst in from the roof of the tunnel near the Sea Wall shaft. This time it was sea water; the river had broken in!  Fortunately the hole, which was close to the bank on a stretch of water known as the Salmon Pool, was not very large. The shape of the surrounding rocks was such that the Pool retained a minimum of 3 ft (1 m) of water even at low tide, making it impossible to locate the hole by sight. A number of men were called upon to walk slowly across the area, holding hands as they went, until one fell into the hole and had to be pulled out by his colleagues. The water was allowed to rise in the tunnel to the same level as the river itself and then, at high tide, a schooner was loaded with puddle clay and moved into position so that the hole could be plugged, using alternate layers of bagged and loose clay.

In December 1882, a major incident occurred, causing more than three hundred men to abandon their possessions and stampede out of the tunnel, shouting “The River is in”.  When the initial panic subsided and it it became possible to carry out a preliminary assessment, it became clear that the situation was not as bad as feared. In fact, the expected flooding of the tunnel did not occur. After a thorough investigation, it became clear that the panic was caused by a sudden surge in water from the Great Spring which had been damned behind a berm in an upper heading.  The level of this water had risen steadily and, after over-topping, it had washed it away the berm and surged into the lower heading. The men’s reaction was hardly surprising, given the conditions under which they were working. They naturally assumed that their worst nightmares were about to be played out.

On the 9th of February 1883, a terrible accident occurred as men on the night shift gathered round the bottom of a lift shaft, waiting to be brought up for supper.  Four or five men had just entered the cage at the bottom, when an iron skip at the top of the shaft was inadvertently allowed to move over the lip and fall 140 ft (c 45 m) on to the cage below, killing three men before bouncing into another group, standing by, where another man was killed and two seriously injured.

There was another emergency on 10 October 1883, when a great surge of water entered the works from the Great Spring, very much exceeding the capacity of available pumps. It swept the men and their iron skips, like so many chips, through the door leading out of the heading and into the finished tunnel, where the men were able to recover. None of the men were seriously injured but three colts were drowned. Headwalls were rapidly built to contain the flood, as water rose up against the pumps to a height of 52 ft (16 m). At first, it seemed that the works might have to be abandoned as all the available pumps, working to capacity, failed to make any headway against the floodwaters for several days. But eventually, the pumps slowly but perceptibly started to gain the upper hand, much to the relief of everyone involved. It seems that water from a nearby subterranean reservoir had suddenly been released but fortunately proved to be more manageable than seemed likely. It has been calculated that the maximum flow during this incident must have been about 27,000 gallons (c 125,000 litres) a minute, 16,000 gallons (c 70,000 litres) more than the available pumping power could lift.  Never the less, the Great Spring had been safely imprisoned again by the 3rd November.

Then, on the night of the 17th of October 1883, only a week after the Great Spring had renewed its assault, a tidal wave flooded the low lying area on the Sudbrook side. On a night when one of the highest tides of the year was expected and, during an exceptional storm, a tidal wave described as a solid wall of water, 5 or 6 ft high, swept in and entered the living accommodation provided for the workforce. About 90 men had just descended the Marsh shaft to continue opening up the heading into a full tunnel, near the western portal, when flood water over-topped the mouth of the shaft and fell into the workings. Three men attempted to climb a ladder out of the shaft in order to escape from the flooded works beneath; two emerged unscathed but the third was thrown off the ladder by the weight of falling water and killed. The water rapidly flooded the area at the base of the shaft, driving the men up the completed tunnel which rose at a gradient of 1 in 90. In the meantime, a workforce was rapidly gathered on the surface to build a make-shift wall around the top of the shaft in order to prevent additional water entering the works. Then a small boat was lowered down the shaft, to ferry men back to the base of the shaft where the water had by then risen to within 8 ft of the crown of the tunnel. Some had to wait hours for their turn in the boat but, by the morning of the 18th, the last remaining survivors emerged.

Completion

The incidents described above, and many other unexpected difficulties that bedevilled the operations, are all vividly described in Walker’s book, each one requiring men to work at the limit of human endurance and ability, while using the most advanced technology available at that time.  On several occasions, it seemed that the task would prove to be beyond the capability of the men responsible but, with outstanding skill and perseverance, they managed to overcome the obstacles and complete the task.

The first train journey through the tunnel took place on 5 September 1885.  A special coal train ran through from Aberdare to Southampton on 9 January 1886, but it was not until the end of 1886 that the tunnel was opened to regular traffic.  The construction of the 4 mile 628 yd long tunnel took almost fourteen years to complete.  The final cost was £1,806,248, two and a half times Richardson’s original estimate and nearly double Walker’s 1877 contract price.

The opening of the tunnel for regular passenger services on 1 December 1886 marked the end of Brunel’s unique steam ferry railway, the last crossing by the steam packet taking place the previous evening.  Over thirty years later, a ferry was re-introduced at New Passage, this time in order to transport cars and other road vehicles across the Estuary.  And later, with the inexorable growth in the car use after the Second World War, British Rail introduced an occasional piggy-back car-carrying service, through the tunnel.  Both these services ceased when the Severn Bridge opened on 8 September 1966.

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The Bristol and South Wales Union Railway

An improved ferry service – after a long gestation

In 1844, Brunel started to consider the possibility of reviving the direct route across the Severn, via the New Passage, by bringing together the convenience of a railway and the flexibility of a steam ferry.  The idea had much to commend it but, for various reasons, it did not get underway for another 14 years.   Brunel himself was involved from time to time, although he was also working on many other projects during this period.

The first positive proposal along these lines, known as the Bristol and South Wales Junction Railway, was approved by Parliament in 1846.  It comprised a branch line from Bristol to the pier at New Passage, a further short length of track  on the opposite side of the Estuary to connect from the ferry pier at Portskewett to the SWR, and a ferryboat to run between two piers.  The timber piers, designed by Brunel, were to be approximately 500 ft (155 m) long to accommodate the full length of the train and to reach out into the deeper water.  Financial problems led to the abandonment of the scheme in 1853.

Another project based on a similar principle and entitled the Bristol, Wales and Southampton Railway was brought forward in 1854.  It proposed to use a “steam bridge” across the river at the same point – with the railway carriages being hauled onto the ferry boat, thus allowing people to stay in their seats.  This project also failed from a lack of investment.

Finally, a scheme was brought forward by the new Bristol & South Wales Union Railway Company (B & S W U R), this time with strong Welsh backing and with the chairman of the SWR on board.  A public enquiry was ordered by the Admiralty and it opened in the New Passage Hotel on 25 March 1857.  Opposition was raised by the City of Gloucester and the Gloucester & Berkeley Canal Company, as well as owners of small craft and the steam packet Wye, that ran between Chepstow and Bristol.  Those who opposed the scheme had the mistaken impression that a chain ferry would be used.  Brunel, who had become engineer for the project in 1855, explained that this was not the intention; the project would be based on a train ferry and confined to passenger and light goods only.

An Act of Parliament for the B & S W U R was obtained in July 1857.

A Digression

Three years earlier, in 1854, when construction of the bridge over the River Tamar at Saltash was well underway, the new Duke of Beaufort had consulted Brunel about the possibility of bridging the Severn Estuary at Old Passage.  On 30 May 1854, Brunel replied through the Duke’s agent, in the following terms;

“I should be very glad, if the Duke thinks seriously that it would benefit his interests, to look seriously into the question and give the best advice I can.  And if I should be able to suggest a feasible plan and there should be friendly people ready to make it, I shall have the satisfaction of bridging the Severn, as well as the Tamar.”

Brunel’s sketch for a bridge across the Severn Estuary

Isambard Kingdom Brunel

Brunel is on record as saying that he believed there would be a bridge or a tunnel across the estuary within fifty years.  Although the Duke did not take the matter further, Brunel obviously kept the exchange in mind because, in April 1857, probably while attending the public inquiry into the B & S W U R, he made a sketch of a design with obvious similarities to that of the Tamar Bridge.  Under the drawing, Brunel had written ” Severn Bridge.  Q: is 1,100 ft practical”.

Construction of the B & S W U R

In September 1858, a contract for the 11½ miles (18 km) long single line railway from Bristol to the estuary was awarded to Rowland Brotherhood, with Charles Richardson as resident engineer, working under Brunel.  From the junction with the existing railway, ½ mile (1 km) east of Temple Meads Station, the line would include five local stations.  The piers leading into the river were the most innovative items, incorporating floating pontoons at the ends of the timber piers on to which the trains would run, with stairs and lifts down to the pontoons.  The piers extended far enough out to provide sufficient water for the steam ferry boat to come alongside at any state of the tide.  The pontoons floated with the tide and were therefore at the same level as the boat when it came alongside.  Sadly, Brunel died in 1859.

Charles Richardson

The full system from Bristol to New Passage, across the ferry, then on to the link to the SWR, for Cardiff, was achieved by November 1863, with the formal opening taking place in January 1864.  Initially, there were five trains a day, each way, and a single ferry, called “Relief”.  The route became so popular that other vessels were used from time to time to provide additional capacity.  Eventually, a second ferry was ordered from the Glasgow shipyard and named “Christopher Thomas” after the chairman of the company.

Old photograph of New Passage Hotel

Present day photograph of what was the New Passage Hotel, from the foreshore

Sketch of the Ferry Pier at Portskewett

Remains of the Portskewett Pier, with the Second Severn Crossing in the background

New Passage Hotel and Ferry Pier, on the opening of the Bristol and South Wales Union Railway in 1864

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The Coming of The Railways

Early proposals

The coming of railways encouraged engineers to explore other ways of crossing the estuary, especially for journeys between Bristol and the important and growing industrial areas of South Wales.  The coastal section of the South Wales Railway (SWR) had been completed as far west as Haverfordwest by 1854 and it soon began to displace shipping as the chosen method of transporting goods and people from one South Wales coastal town to another.  But the problem of negotiating the ferry at Old Passage remained.  Despite the improvements brought about by Telford, the ferry crossing was still treacherous in bad weather.  On a good day, the time taken to travel between Bristol and Cardiff, by coach and ferry, would be about seven hours.

The Post Office had considered installing a chain ferry during 1836.  James Meadows Rendel surveyed both the Old and New Passages but reported that tidal currents were too strong for his system which employed a steam engine on the ferryboat to pull, or warp, itself along a submerged chain.

By 1852, the SWR was connected by Brunel’s Chepstow railway, up the western side of the estuary to Gloucester.  This facility, together with the line between Gloucester and Bristol, provided a more attractive journey between South Wales and Bristol than was available using a coach and ferry, via the Old Passage route.  Accordingly, patronage of the Old Passage ferry declined rapidly and, by 1855, the use of steamboats could no longer be justified.  Attempts were made to keep the ferry open, using sailing boats, but eventually the passage closed.

Not enamoured with the circuitous route through Gloucester, the railway companies started to look into the possibility of crossing the Severn somewhere between Gloucester and Bristol.  This would provide a shorter route between South Wales and Bristol and it would please the colliery proprietors in the Forest of Dean who were seeking a less costly route for transporting their coal to English markets.  Also, the Great Western Railway Company (GWR) had concerns about the steep gradients in the Stroud Valley, between Gloucester and Swindon.

Proposed Rail Crossings of the Lower Estuary

Sketch of railway viaduct with 20 arches, proposed by Charles Vignoles in 1834

Early proposals for bridges in the vicinity of the ancient ferries included an ambitious 20-arch railway viaduct by Charles Blacker Vignoles in 1834.  He, like Brunel, had also considered the possibility of tunnelling under the Severn.

Thomas Fulljames, Chief Engineer to the Bristol and Liverpool Junction Railway Company, proposed a more practical scheme, published in 1845. He suggested two possible designs for what he described as the Aust Bridge, in the vicinity of the Old Passage, just a few hundred yards below the line of the present crossing. It took advantage of several rocky outcrops that were exposed at most low tides

Two designs for a bridge at Old Passage by Thomas Fulljames

James Walker FRS was commissioned by the Admiralty to report on the proposals.  Fulljames argued that his first design “could be achieved with perfect safety to navigation”. Walker disagreed, saying it would be objectionable on account of a pier, which “would be directly in the middle of the navigable channel”. Navigation was a most important consideration in 1845 and shipping trade through the line of the Old Passage exceeded 600,000 tons per year with the largest ships drawing 19 feet (6 m) of water. Mr Walker found no fault with the second design, but, in the event, the Aust Bridge was never built. James Williams, first class pilot for 13 years seems to have had the last words – “it will not do at all”

In 1845, S B Rogers of Monmouthshire proposed a toll-free road crossing at the English Stones. It consisting of 21 arches of 350 ft (about 100 m) span and which would be at least 120 ft (about 40 m) above high water mark. It was to have “shops, bazaars and a lighthouse”. However this scheme was not well received by entrepreneurs or navigation interests.

Other early proposals for a railway crossing on the lower Estuary were concentrated on the short stretch between Sharpness and the Horseshoe Bend at Arlingham. The very first was in 1810 when the Bullo Pill Railway Co. started to tunnel under the Severn, south of Newnham, primarily for its own benefit. The company had acquired the rights of the Newham Ferry and began to construct a road tunnel that would have enabled adapted tramroad wagons to gain access to the eastern side. However, a major influx of the river brought work to a halt and it was never resumed.

On behalf of the SWR, Brunel brought forward a proposal for a timber viaduct that would cross the river from Hock Crib to Framilode on the Arlingham Bend, about 5 miles (8 km) above Sharpness. In his report, James Walker described the proposal as being “at about the very worst place on the river for navigation” and the scheme was rejected by Parliament in June 1845.

Later, in 1865, a scheme by Sir John Fowler was rejected as an ‘impediment to navigation’. Like several other rejected proposals in this area, it would have been located above the entrance to the Sharpness to Gloucester Canal. There is, however, an interesting footnote to this tale. Sir John continued to develop designs for a Severn Crossing, with spans of up to 1,000 ft (310 m) and based on the use of steel, until, in 1872, the GWR obtained parliamentary powers authorising construction of a tunnel under the estuary.  At that point, Sir John took his plans up to Scotland where, assisted by Sir Benjamin Baker, he developed them further until the design emerged for what was to become the world famous cantilever bridge that now spans the estuary of the Forth.

The ill-fated Severn Railway Bridge

Eventually, in 1871, engineers George William Keeling and George Wells Owen, on behalf of the SWR, put forward a scheme for a railway bridge, to be located just above Sharpness. Parliament gave approval to the scheme in 1872. The design, for what became known as the Severn Railway Bridge, was for a conventional single line viaduct 4162 ft. long, comprising twenty-one spans supported on huge cast iron cylinders. The bridge was to be situated half a mile above the entrance to Sharpness docks and the canal to Gloucester.

It is rather surprising that investors were prepared to support this project at the time. Work did not begin until 1875 and, by that time, construction of the railway tunnel under the Estuary, on the direct route between South Wales and Bristol, had already been underway for two years. However, part of the motivation behind this investment was undoubtedly to support mining interests in the Forest of Dean and many of the investors were sceptical about the tunnel ever being completed.

Severn Railway Bridge, as built

The fate of the many earlier attempts to obtain authority to construct a rail link across the lower Severn Estuary indicated a general reluctance on the part of Government to approve a scheme if it were deemed to be a hazard to navigation. All the previous attempts, mentioned above, were abandoned, at least in part, because they failed to surmount that hurdle. It is therefore surprising and – with hindsight – rather disturbing, that construction of the Severn Railway Bridge should have been allowed to proceed.

Disaster struck on the night of 15 October 1960, when two self-propelled fuel barges missed the entrance of the Gloucester to Sharpness Canal. In the dense fog, both skippers attempted to get back to the canal entrance but the two vessels collided and became locked together. Minutes later, with a combined weight of 858 tons, they struck one of the piers of the railway bridge. The debris from the cast-iron pier of the bridge and the two adjacent spans crashed down onto the barges, igniting the fuel.  Five of the eight crewmen on board the barges lost their lives. The bridge was not replaced. Apparently, it had been hit many times previously but the cost of substantial protection around the bridge piers had always been considered prohibitive.

Severn Railway Bridge after collision

 

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History of Estuary Crossings

The River Severn

Throughout recorded history, until well into the Industrial Revolution, the most efficient method of transporting heavy goods was by river and coastal water. It is, therefore, not surprising that the majority of large urban settlements in all parts of the world are located in close proximity to an effective waterway.

The River Severn is the longest river in Britain. It played a crucial role in the economic development of the post-medieval nation. Prior to the development of canals, it carried a greater volume of traffic than any other waterway in Europe. Rising on the slopes of Plynlimon Fawr, it meanders through central Wales as far as Shrewsbury and then turns south, passing under the famous Iron Bridge at Coalbrookdale and several bridges designed by Thomas Telford. His bridge at Over, just downstream of Gloucester, was opened in 1830 and remained the lowest road crossing of the estuary until the M4 motorway was opened in 1966.

The golden age of water-borne transport came immediately before the coming of the railways, when all possible use was made of this mode. By 1800, small river craft were able to navigate up the river as far as Shrewsbury; while Bewdley was considered to be the upper reach for larger vessels. With the construction of new waterways such as the Staffordshire and Worcestershire Canal which gave access to the Black Country, the Severn played an even more important role in the economy of the region. Access up as far as Gloucester, was improved by the opening of the Gloucester to Sharpness Canal in 1827, after a tortuous gestation.

During the late 18th century, most roads in this country were in such a poor state that manufacturers often had to go to very great lengths to transport their goods. An example of this was the route chosen, in 1775, by a company from Wellington in Shropshire to deliver a consignment of pig iron to Chester, 60 miles (97 km) further north as the crow flies. The journey began with the iron being transported by cart to the Severn, to be loaded on to Bristol-bound riverboats. On arrival in Bristol, the material was transhipped to sea-going vessels and then taken right around the coast of Wales, into the mouth of the Dee, and so to Chester. This example, involving a journey of over 400 miles (644 km) by water with two trans-shipments, speaks eloquently about the state of the roads at that time.

Ancient crossings of the lower Severn estuary.

Crossing the river has always been hampered by the high tides and fast currents, causing a real problem for all the peoples who have inhabited its boundaries. An ancient crossing route has been identified from the end of an ancient ridge-way over the Cotswolds to Shepperdine on the English side and onto the Beachley peninsula on the Welsh side. After the retreat of the ice, this route would have been used by the first settlers, their primitive rafts taking advantage of the tidal flows to go E-W on the ebb and W-E on the flow. This crossing probably survived through the Roman period and into mediaeval times, as indicated by the location of the southern end of Offa’s Dyke, part way down the Beachley Peninsula.

No record survives of the efforts made in early times to provide a regular ferry service but there is archaeological evidence indicating shipping trade across the Estuary. The first record of a regular ferry is from AD 1131. It was used by monks at Tintern Abbey, under a grant from Winebold de Balon who owned the land. The ferry plied across at the narrow point between Aust to Beachley. This ferry route was maintained down the following centuries and is known as the Old Passage.

Plan showing the ancient ferries

The alternative ferry route, across the English Stones, might, in fact, be the older of the two. However, it was closed by Cromwell, following the drowning of Parliamentary troops marooned on the English Stones in 1645. After it reopened in 1718, it became known as the “New Passage”.

The early ferries were not for the faint hearted. Daniel Defoe described the Old Passage crossing from Aust to Beachley as an “ugly, dangerous and very inconvenient ferry over the Severn”. Travelling to Wales in 1725, he decided that the alternative route via Gloucester was the safest and surest way, taking account of the weather and seeing the sorry state of the ferry boats at Aust;

The sea was so broad, the fame of the Bore of the tide so formidable, the wind also made the water so rough, and which was worse, the boats to carry over both man and horse appeared so very mean, that, in short, none of us cared to venture. So we came back, and resolved to keep on the road to Gloucester”.

The Contribution of Thomas Telford

The route from the west bank of the Severn, opposite Bristol, through South Wales was in a poor state of repair throughout the eighteenth century and frequent calls were made for its improvement. Reductions in journey times became of pressing importance in the 18th century, as markets increased in scale and reach with the establishment of Empire and the impact of the Industrial Revolution. By the early 1800s steam pickets were plying between West Wales and Southern Ireland. In 1823, the Post Master General sought to improve the Mail Coach route between London and Milford Haven and he called upon Thomas Telford to advise on what should be done.

The advantage of replacing the long diversion around Gloucester whenever the ferry services were interrupted was evident to Telford and he believed that the value of the reduced journey times would justify the building of a permanent crossing. In modern times, major estuarial crossings have far outstripped other public works in economic gain, providing returns in the region of 200% in the first year alone.

Telford’s opinion of the New Passage crossing near the English Stones was unequivocal;

One of the most forbidding places at which an important ferry was ever established, a succession of violent cataracts formed in a rocky channel exposed to the rapid rush of a tide which has scarcely an equal on any other coast“.

Telford’s first proposal was a crossing from Uphill Bay in Somerset to Sully Island on the west side of Cardiff (this is similar to the line of the proposed Severn Barrage). It is possible to imagine Telford staring across the swirling waters in awe and excitement at the prospect of engineering such a structure and the wealth it would generate for the area. However, the proposal was rejected.

Telford then considered the Old Passage which crossed at the narrowest point on the estuary. At that time, his two suspension bridges were in the course of construction in North Wales, so it came as no surprise when, in 1824, he suggested a similar solution for the Severn at the Old Passage. However, his suggestion was not taken forward because, at that time, the route to Dublin via Holyhead carried more political clout than the South Wales route to southern Ireland. Nevertheless, on 26 November 1825, plans were announced for improvements to the Old Passage, including a new ferry and improved landing facilities on both sides of the estuary.

A short diversion — The Old Wye Bridge at Chepstow

Before moving on, the reader might be interested to learn about the existence of an old and historically-important road bridge situated less than 3 miles (5 km) from the western end of the Severn Bridge.

To the historically minded, the name of Chepstow conjures up visions of the medieval castle and Brunel’s magnificent Railway Bridge.  However, just upstream from the new Wye Crossing at Chepstow, there is a very interesting Grade One listed, five span, cast iron bridge which passed its 200th Anniversary in 2016.  Carrying the main road from Gloucester to South Wales, it was built to replace an older, wood and stone, bridge that had been struggling to cope with the prevailing conditions on the River Wye.

The tidal range at the Chepstow Bridge is only marginally less than that at the nearby Severn Bridge which, at 40 ft (14 m), is the second highest in the world.  This means that, for long periods every day, the view of the bridge on the water is constantly changing as water rushes up and down.  The bridge has five spans so there are four piers in the river that navigators need to avoid.

In 1811, in response to a request for bids to replace the old bridge, Watkin George of Cyfarthfa, Merthyr Tydfil, and John Rennie had each prepared designs for new cast iron spans on the existing piers and Rennie also prepared a design for a 250 foot (76.2m) span cast iron arch flanked with 72 foot (22m) span masonry arches.  These bids were all rejected, mainly on grounds of cost.

In 1812, a collision occurred between a vessel and one of the piers, causing 6 deaths and significant damage to the bridge.  This proved to be the catalyst for action.  The foundation stone for a new bridge, at the same location, was laid in 1813.  The following year, a contract to design and construct the new bridge was let to John Urpeth Rastick, Robert Hazledine, Thomas Davies and Alexander Brodie of Bridgenorth Ironworks.  Rastick was responsible for the design of the bridge and he supervised its construction.  Some of the ironwork was cast at Calcutts Ironworks in Shropshire, which was owned at the time by Brodie, and later by Hazledine.

The central span of the bridge is 112 ft (37 m) long and it is flanked by two 70 ft (21.6 m ) spans and then two end spans of 34 feet (10.5 m).  The overall length is about 487 ft (149.4 m) and it is 20 feet (6.1 m) wide. The piers and the abutments from the previous bridge were reused after being strengthened by a surrounding cover of large rectangular stone blocks (ashlar).  The deck for each of the graduated spans is supported by five, shallow lattice, cast iron arches (three of the outer lattice arches are visible on the photograph, below) and these elements, together with the vertically curved road profile and the decorative lamp standards, all contribute to the bridge’s attractive appearance.

The Chepstow Museum holds various prints of older bridges that had spanned the river at this point.

The bridge was opened on 24th July 1816.  The original contract price was £17,150, and the total scheme cost, including fees, was £22,116.  This was less than half of Rennie’s earlier bid.  The centre span was strengthened by the addition of steel ribs in 1889 and further extensive repairs and reinforcement were carried out in 1979-80.

When built, the new structure became the third largest cast iron bridge in the world.  It is now the largest surviving bridge of its type and era. The bridge carried the only trunk road into South Wales until 1988, when the Chepstow Inner bypass was opened.  It continues to carry local traffic across the river.

The design is generally considered to having been inspired by the work of Thomas Telford who built several cast iron arch bridges that can still be seen in Mid and North WalesIt therefore provides an opportunity for visitors to the area to see what Thomas Telford would probably have provided, had he been called upon to do so.

Rastick [1780-1856] is better known as a railway engineer and locomotive builder. He helped Richard Trevithick develop his ideas for steam engines and built a locomotive for him in 1808.  In 1829 he built the first steam locomotive to run in the USA.  In 1829, he chaired the judging panel at the Rainhill Trials for the Liverpool and Manchester Railway which led to the approval of Stephenson’s “Rocket” and he built many railways in Britain, including the London & Brighton Railway.