Article - Issue 6, November 2000

Severn tunnel

Gerald David OBE FREng

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The estuary of the river Severn had always been an obstacle to trade between South Wales and the west of England which was overcome to some degree by shipping arrangements: a very good trade built up between Bristol, Gloucester and the South Wales ports, although it should be remembered that Cardiff was only a village in 1830 and Barry and Penarth were only hamlets. A very heavy trade existed, however, between Cardigan, Milford, Carmarthen, Burry-Port, Swansea, Briton Ferry and Bristol: the Severn Trows did a brisk trade up the Severn and Wye estuaries far above what is now considered as navigable water. A ferry service was installed by the Great Western Railway between New Passage on the Bristol side and Portskewett on the Chepstow side, where piers were built and railway access was provided. Passengers disembarked from the trains at the pier and took the paddle steamer across the estuary to a corresponding rail service on the other side.

With the rapid development of the railways and the discovery of extensive coal fields in South Wales between 1830 and 1850, the need for links between South Wales and England became an engineering pipedream for many of the shrewdest visionaries of the industrial revolution.

Brunel Brunel had been very active in getting the broad gauge into South Wales and his tubular bridge at Chepstow was evidently a practice run for his great Saltash bridge. But by the time the railway had reached Swansea in 1850, Brunel had already embarked on other major projects such as his ships: the Great Eastern was beginning to occupy his every waking moment.

The construction of the Saltash bridge in the early stages involved Brunel a great deal and it is noted in many of the biographical records of his life that large numbers of cigars and amounts of brandy added to the many arduous days of twelve hours in the saddle were material contributions to his failing health. There were many ideas he had envisaged and discussed with others which eventually were carried out by his friends and colleagues in the industry. A good example of one of these is the Severn Tunnel which is first noted in the records of the Great Western Railway as a bridge proposal got up by the Great Western Railway consulting engineer John Fowler. The plan was for a new railway entitled the Great Western Railway and South Wales Direct Railway which would be double track mixed gauge of forty miles in length from Wootton Bassett to Chepstow crossing the Severn estuary at Aldbury Sands via a bridge or viaduct not less than 2.5 miles long and 100 feet above high water.

The addition of standard gauge rails between Didcot and Wootton Bassett and between Chepstow and Cardiff was to be arranged with the Great Western Railway. This plan was called ‘Fowler’s Line’ and duly authorised by Parliament in 1865.

Charles Richardson

A separate project called the South Wales Junction Railway by a much less well-known engineer, Charles Richardson, was for a tunnel beneath the Severn between Pilning and Rogiet. However, the board of the Great Western Railway and its advisers did not favour Richardson’s plan and it was never put forward to be authorised by Parliament. The company was dissolved in 1870.

Charles Richardson, however, did not give up easily and deposited a Bill for the 1872 session of Parliament ‘To authorise the construction of the Severn Tunnel Railway and other purposes in connection therewith’.

Since Brunel was now dead it seemed strategically useful to Richardson to engage Brunel’s old critic, Sir John Hawkshaw, as consulting engineer. He was now successful in getting the Great Western directors to adopt the scheme and they reported to the shareholders in February 1872 ‘That the railway proposed be constructed and that the authority of this Bill extended from Pilning station on the Bristol and South West section to a point on the South Wales Railway near Portskewett. The length of the line is about eight miles and the estimated cost was £750,000.

’ The proprietors adopted the scheme as proposed and it was duly sanctioned by Parliament and work began at Sudbrook on the shaft in March 1873.

Owing to the funnel-like shape of the Severn estuary, the tides are the highest in Europe, spring tides rising at the mouth of the Wye to 50 feet above low water. At the site chosen by Richardson for the tunnel the estuary is 2.25 miles wide. Of this distance, the first mile and a half from the Gloucestershire side consists of a level of rough rocks, known as the English Stones, which are uncovered at half tide; then comes a deep channel about 400 yards wide and 80 feet deep, called the Shoots, through which the strong current of the river runs at low water; and next about half a mile of more half-tide exposed rocks, called the Lady Bench.

The railway was designed to pass under the Shoots at a level of 50 feet below the rock bottom and from this, its lowest point, to rise in each direction at a uniform gradient of 1 in 100. The total length of the tunnel was to be 7,942 yards or just over 4.5 miles, a little more than half under the river, about threequarters of the remainder being under the land on the Monmouthshire side, where the mouth is on the north side of the South Wales line.

March 1873 – August 1877

The first thing to be done was to explore the strata that would be met in the excavation of the tunnel and for this purpose it was decided to sink a shaft at Sudbrook as near as possible to the west bank and drive a heading from it under the river, the shaft to be 15 feet in diameter and about 200 feet deep and the heading to rise gradually from its bottom, so as eventually to drain the tunnel at is lowest point. A dozen cottages and an office having been erected near by and a temporary railway laid to Portskewett Station, work was started on 18 March 1873 by men employed by the Company under Richardson and his assistants.

With so small a provision progress was necessarily slow and in August 1877, after four and a half years’ work, all that had been done consisted of the sinking and lining of the shaft, afterwards known as the Old Shaft, and the driving of about 1,600 yards of a seven-feet square heading under the river. A second shaft had been commenced in which it was intended to fix the permanent pumps to drain the tunnel but this was only about half sunk and was unlined. Save for a short length of coal shale, the heading passed through hard Pennant sandstone, all of which had to be drilled and blasted.

At this date the Directors advertised for tenders for the whole work. Three were received and rejected. They then made two small contracts: one with Oliver Norris of New Passage, to sink a shaft on the Gloucestershire side, afterwards known as the Sea Wall Shaft and drive headings east and west from it; and another with Rowland Brotherhead to sink two shafts on the Monmouthshire side, some distance west of Sudbrook and drive headings each way from them. These were named Marsh Shaft and Hill Shaft respectively. Pumps were established in all these four shafts and also in the permanent shaft at Sudbrook, known from its lining as the Iron Shaft, as soon as it had been completed by the Company’s men. These pumps easily disposed of all the water met with in the workings, none of which came from the river.

The Great Spring halts work

The work went on steadily until the middle of October 1879, by which time the original heading from the Old Shaft had been driven nearly two miles under the river and was within 130 yards of Norris’s westward heading from the Sea Wall Shaft, while other headings had been made in each direction form the Marsh and Hill Shafts and also at a higher level than the original one, from the Old Shaft (see Figure 2). In this last heading men working westward some 300 yards away from the river on 16 October suddenly tapped a large spring of fresh water, which poured in in such volume that it utterly overpowered the pumps and within twenty-four hours all the workings connected with the Old Shaft were full up to the river level. Fortunately the men were able to escape by a cross-heading into the Iron Shaft, so no lives were lost.

By the irony of circumstances it happened that the Severn Bridge at Sharpness was opened next day and at the luncheon Sir Daniel Gooch, unaware of what had happened, invited the company present to visit the tunnel in about six weeks and walk through the heading under the river, which would then be completed, at the same time warning them that it might be rather wet!

T. A. Walker and Sir John Hawkshaw

Determined to proceed in spite of this melancholy discouragement after nearly seven years’ work, the Directors asked Sir John Hawkshaw to take charge of the works and carry them on as he thought best. Sir John agreed on condition they would engage a contractor for the whole in whom he had confidence and on their acceptance sent for T. A. Walker, one of the three who had made tenders in 1877, with whom Hawkshaw had been associated in the extension of the East London Railway under London Docks. Walker renewed his former offer with certain modifications; his figure of £948,959 was accepted and the works were handed over to him on 18 December 1879.

His description of the scene he found is as follows:

Nothing could be more desolate than the appearance of the works at this time. There were near the main shaft only six cottages and a small office, the necessary boiler-houses and engine-houses, a small carpenter’s shop, a fitter’s shop, a blacksmith’s shop and two low buildings or sheds, used as cottages also. The tramway which had been originally laid to Portskewett Station had been pulled up and in lieu of it another tramway had been laid following (on the surface of the ground) the centre line of the tunnel itself from the Old Shaft to the Marsh Pit and joining the Great Western Railway a mile west of Portskewett Station at Caldicot Pyll. The engines of the main shaft stood idle, the boilers were out of steam, most of the men who had been employed had left in search of other work and the water in the shaft was standing up to the level of high water in the Severn. The pumping engines at Sea Wall, Marsh and Hill Pits were still at work, as the working of those pits had been in the hands of Mr Norris and Mr Brotherhood; but no work was being done below, orders having been given to these gentlemen to suspend their operations.

The pumps were able to keep the Hill Pit dry, but were not sufficiently powerful to drain either of the dipping headings from the Marsh or Sea Wall Shafts, while the main shaft and heading were full of water.

Hawkshaw decided to lower the tunnel under the Shoots 15 feet, maintaining the gradient eastward at 1 in 100, 15 feet below the former level throughout and making the westward gradient 1 in 90 instead of 1 in 100, so as to run out into the old levels on the Monmouthshire side. This, of course, entailed deepening all the shafts and the construction of a new drain from the new bottom under the Shoots to the pumping shaft and made the work much more difficult for the contractor as it converted the bottom heading already driven into a top heading.

Some larger pumps and engines having been ordered, four new shafts were commenced, one at Sudbrook, one at Sea Wall and two at a point 26 chains west of the Sudbrook Shafts and beyond where the Great Spring had broken in, in the hope of pumping all the water from it there and so keeping the rest of the work dry.

Owing to the time taken in the delivery and fixing of the new pumps, the failure of the measures taken to shut off the Great Spring effectively and a chapter of accidents, the works were not clear of water till 7 December 1880.

Diver assists with the drainage work

In the course of the pumping operations a diver named Lambert performed a very brave act well worth recording. It being necessary to close a flood door in the long heading under the river, 340 yards from the shaft, Lambert went down to grope his way under water, in total darkness, over the debris in the heading, which he had never seen, past overturned skips, beams, tools and lumps of rock for the 340 yards. Though two other divers came down to pass his air-hose forward, it floated so hard against the rough roof that he was unable to drag it along farther than 270 yards and after some vain efforts had to return. The journey was still more perilous as the hose on which his life depended, curled up in kinks and coils about the timber and other obstacles and he had to find, gather up and carry all these coils, which were constantly slipping from his grasp.

About this time Walker had heard of a new apparatus for diving without an air-pipe by means of a knapsack of compressed air, which Fleuss, its inventor, was exhibiting at the Westminster Aquarium. He accordingly telegraphed to Fleuss to come and try if he could do the work. Fleuss arrived full of confidence and went down with Lambert to the mouth of the heading but when he found the sort of place he was expected to go into for nearly a quarter of a mile, his heart failed him and he came up, saying he would not go and close the door for £10,000. Lambert then borrowed the apparatus from him and after some practice with it under water, succeeded in reaching and closing the door.

As soon as he had mastered the water, Walker began work underground with great energy, his first step being to build a strong wall in the westward heading from the Old Shaft to imprison the Great Spring. This was accomplished early in January and the water from the spring entirely shut out from the works. He had already made considerable progress in providing dwellings for the men at Sudbrook and founding what soon became a small town, with its mission room, school, hospital and post office, besides a large brickyard and the engine houses and other buildings of the tunnel works.

At the Sea Wall Shaft on the other side of the river, the brick arch of the tunnel itself had been begun in December and the bricklayers were at work when, one day towards the end of April, water suddenly burst in from the roof, putting them to flight and soon flooding that bit of the tunnel. To Walker’s dismay it was found to be salt and therefore from the river. Above, at low water, was a pool near the shore called the Salmon Pool, only about 3 feet deep, so a number of men were sent to join hands and walk through the pool to find the hole. Soon one of them found it, suddenly disappeared, and was pulled up by his neighbours. The hole was then stopped with clay and loose sand in bags and later made secure with cement concrete. Fortunately the long heading under the river had not yet been completed or it would of course have been flooded throughout. The two headings were joined up on 26 September 1881, opening the way under the river between the Sea Wall and Sudbrook Shafts and enabling through ventilation to be established by means of a Guibal fan at Sudbrook, in place of compressed air.

The Great Spring halts work again

Steady progress was made with the tunnel and the long cuttings at either end until 10 October 1883 when the Great Spring again burst in in much greater volume than before, drowning the works at Sudbrook and under the river. Two days later the largest pump at the shafts 26 chains west of Sudbrook broke and in a few hours those detached works were also full of water. Then on the night of 17 October came a tidal wave, inundating the lowlands west of this and pouring into the low lying Marsh Shaft. At the bottom of this shaft about a quarter of a mile of tunnel had been completed and eighty-three men were at work in it. As the water rose they retreated up the gradient to the scaffolding at the west end. Above, help was got from Sudbrook, whence some men waded to the shaft and managed to form an emergency dam around it. In spite of all that could be done, the water rose in the tunnel to within eight feet of the crown of the arch. At last the men were rescued by means of a small boat lowered down the shaft. The tidal wave flooded the cutting at the west end of the tunnel, fortunately not yet connected with it and also the fields on the Gloucestershire side. So on the morning of 18 October 1883 the works were in a worse state than they had been since 1880.

Lambert was once more engaged to close a door shutting off the Great Spring which he succeeded in doing on 30 October and a few days later all the works were free of water.

By the end of the year 2.25 miles of full sized tunnel had been completed and rapid progress was being made with the remainder and also with the open cuttings at each end.

Early in 1884 it was decided to reduce the length of the tunnel from 7,942 yards to 7,666, the cutting at the west end being lengthened 276 yards to provide material for making sidings at the new station near Rogiet, afterwards named Severn Tunnel Junction.

The whole of the tunnel, except rather less than 300 yards where the Great Spring had been shut in by two head-walls and the cuttings were now fully at work. The largest possible number of men – at one time 3,628 – was employed and all the plant and machinery that could be used, including several more pumping engines, was on the ground.

The Great Spring is tamed

In order to deal with the Great Spring, Hawkshaw determined to drive a side heading parallel with the line of the tunnel from the Old Shaft at Sudbrook to intercept the spring. The water having been allowed to run into the old heading and so to the pumps, this side heading was pushed forward till it reached a large open fissure in the strata which had formed the channel for the underground stream. Then by diverting it into the side heading, the tunnel was left for the time almost perfectly dry. Finally in 1886 a new large shaft was sunk at the side of the tunnel and six big pumps fixed in it and so the Great Spring was permanently mastered. The last three Cornish beam engines remained at work until replaced by electrically worked pumps on 6 November 1961.

At the end of 1884 the whole of the tunnel was completed, except about 200 yards just west of Sudbrook, and 500 yards of invert under the Shoots, where connections remained to be made with the drains. On 18 April 1885 the last length of brickwork in the tunnel was finished. Altogether 76,400,000 bricks were used in the construction of the tunnel and bridges.

Much work still remained to be done in the long open cuttings, especially on the Gloucestershire side. These cuttings are protected from any such inundation by a tidal wave as occurred in October 1883 by high banks. The western one was finished first and the permanent way having been laid there and through the tunnel, a special train with Sir Daniel and Lady Gooch and a party of friends was able to make the first journey from Severn Tunnel Junction through the tunnel into the cutting on the Gloucestershire side and back on 5 September 1885.

On 9 January 1886 an experimental coal train ran from Aberdare to Southampton, through the tunnel, resulting, as the Directors proudly reported in February, ‘in coal which had been raised at the Colliery in the morning being delivered at the Port in the evening of the same day’.

The opening for traffic was delayed for the completion of the new pumping arrangements at Sudbrook already mentioned and the installation of a large Guibal fan, 40 feet in diameter and 12 feet wide to ventilate the tunnel. This fan was completed and set to work on 31 August and on 1 September 1886 the line was opened for goods traffic.

Colonel Rich having made his inspection on 17 November and reported favourably to the Board of Trade, passenger trains began to run between Bristol and Cardiff on 1 December 1886, whereupon the ferry service between New Passage and Portskewett Piers ceased and the railways to the Piers were closed.

The permanent way consisted of steel bridge rails, 68 lb to the yard on longitudinal timbers in the tunnel and elsewhere of 86 lb bullhead rails in 43 lb chairs on cross-sleepers.

The total cost of the new line was £1,806,248.

To provide for the heavy traffic expected on the opening of the new route to South Wales, the single line of the old Bristol and South Wales Union Railway, between the junction of the Avonmouth Branch at Narroways Hill near Stapleton Road Station and the new Severn Tunnel Railway at Pilning was doubled, a separate Up line being made between Pilning and Patchway with a uniform gradient of 1 in 100 and a tunnel exactly a mile long – Patchway – Narroways Hill opened 1 September 1886 and Pilning – Patchway 27 May 1887. The old line has 1.25 miles of 1 in 68 and tunnels of 1,246 and 62 yards.

At Bristol a short loop was constructed between Dr Day’s Bridge Junction (named after a local medical benefactor) and North Somerset (formerly Feeder Bridge) Junction to enable trains to run direct to and from the east, making the distance between Paddington and South Wales 15 miles less than by the old Gloucester route. A through train each way, by no means fast, was established in July 1887. At the eastern end of this loop a large yard of sorting and marshalling sidings on both sides of the main line (Bristol, East Depot) was laid out. The construction of shunting necks for those on the Up side involved the demolition of Brunel’s No. 1 Tunnel, 326 yards long and the widening of the resulting cutting. This was safely completed in March 1889 without interrupting the traffic and early in the following year the new yard was brought into use. Meanwhile it had already been found necessary to quadruple the South Wales line from the north end of the loop, through Lawrence Hill and Stapleton Road Stations, to the junction of the Avonmouth Branch at Narroways Hill and this was finished in November 1891.

Thus was completed the great link between the South Wales coal field and its markets to the east and it is worth noting that since the 19th century all the engineering proposals for crossing the Severn estuary have been by bridge rather than tunnel and when one looks at the history of the difficulties encountered by the builders of the Severn Tunnel it is not surprising that engineers have preferred to be above the waters of the Severn rather than beneath it.

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