The Severn Railway Tunnel.
Chapter 3 - The Great Spring.
By the 16th of October 1879, the length of the heading under the river had progressed so well that just 500 feet intervened between the headings from the Old Shaft on the Monmouthshire side of the river and the Sea Wall Shaft on the Gloucestershire side. In addition, the workings from the new Hill and Marsh Shafts had reached an advanced stage. None of these headings up to this time had given any large amounts of water, but
as Oliver Norris's men toiled westwards along the top heading from the Old Shaft, disaster struck. A huge body of water was tapped and although efforts were made to dam it out by timber placed across the heading, the water poured in at such a rate that within twenty-four hours the tunnel was flooded to the level of the river. Fortunately no lives were lost as the men in the long heading were changing shifts, although their only means of escape was through the Iron Shaft. There were three pumps on the Monmouthshire side of the tunnel, but they were completely overwhelmed by this Great Spring flooding into the works at a rate of 360,000 gallons per hour.
Ironically, the following day, the last bolt of the Severn Bridge was tightened. Attending the ceremony was the chairman of the Great Western, Sir Daniel Gooch, and unaware of the disaster at the tunnel, invited the gathering to walk through the completed heading but warned them that it may be a little wet !
The Great Western directors decided to appoint Sir John Hawkshaw as Chief Engineer and to take full charge of the works, however, this he only agreed to if Thomas Walker was the contractor on the tunnel. Richardson would now only advise but Hawkshaw would decide.
The scene of desolation that greeted Walker when he arrived at Portskewett in December 1879 was
unimaginable. The pumps at both the Iron and Old Shafts were not in operation as most of the men had left in search of other work. The pumps at Marsh and Hill Shafts, however, were still in use but orders had been given to Oliver Norris and Roland Brotherhood to suspend all operations underground.
Prior to Walker's appointment, the Great Western had ordered two massive pumps and together with the existing pumps in the main workings could remove 460,000 gallons per hour. Walker's first task therefore was to build the two engine houses which would serve these two pumps; one house would contain six boilers, the other seven. This work would take about six months to complete without any possibility of work continuing underground until this time.
These two engines were of massive proportions. Built by Harvey & Company of Hayle in Cornwall, the larger of the two engines utilised a steam cylinder of 75 inches in diameter topped by a 30 feet beam weighing 23 tons. Supported in the centre by the end wall of the engine house, the beam was fixed at one end to the engine piston while the other end was connected to a series of operating rods down to the pumps underground. Working at eight strokes per minute, this pump alone raised 3,000 gallons every minute.
Walker investigated the work which had been carried out by Richardson and
devised an ambitious plan for temporarily stopping the Great Spring from flowing into the workings. Two heavy oak shields, shaped to cover over the two entrances to the top headings, would be lowered down the Old Shaft and wedged tightly into position by oak beams. Sealing the face of the shield was achieved by a soft material covered in tar. Walker's problem though was that the top headings were under 140 feet of water. A team of divers was employed, but to reduce the pressure on them, especially as these wore the heavy diving suits with large helmets, Walker started the pumps in the Old Shaft on the 6th of January 1880.
Four days later one of the pumps broke down when a valve would not seat properly then, on the 14th of January, this pump began working again after the valve had located into its seat by itself, but without warning, another pump which had been giving satisfactory service broke down completely. It was impossible to repair this pump underwater, a situation not helped by poor brickwork at the bottom of the Iron Shaft which leaked water at the same rate as the water being pumped out.
On the 24th of January, the shields were fixed into position but almost at once the shield on the Western heading began leaking. The divers passed bags of Portland cement through a small access door built into the shield, attempting to seal the shield with a good quantity of cement built up behind the shield. The pumps were then stopped so the cement would be able to set properly until the 5th of February when pumping was resumed. More pump failures then followed and together with the dangerous working conditions for the divers - in one instance, the leader of the divers, Alexander Lambert, was sucked against the inlet of one of the working pumps - meant that pumping operations were abandoned until the new larger pumps were in operation.
Sir John Hawkshaw meanwhile, had decided to lower the height of the headings by 15 feet which meant that the thickness of the rock between the Shoots and the new headings would increase from 29 feet to 44 feet. Due to this change, the gradient of the tunnel on the Monmouthshire side of the Severn was increased to 1 in 90, but the gradient under Gloucestershire would remain as 1 in 100. This of course meant the shafts would have to be made deeper; by 27 feet for the Sea Wall Shaft, 12 feet 7 inches for the Old Shaft at Sudbrook, 7 feet 9 inches at the Marsh Shaft and 4 feet 9 inches at the Hill Shaft. In addition, a further shaft was to be sunk adjacent to the Old and Iron Shafts at Sudbrook and two shafts were to be sunk west of the Great Spring at a point called 5 miles 4 chains.
During the sinking of the shafts, the engine houses for the Cornish beam engines at Sudbrook
were approaching completion and because of the increased workforce here,
additional cottages were built for the men. Walker had been experimenting with
the various clays and marls being dug out of the works for the possible
manufacture of bricks. These experiments proved so successful, that a brickworks
was erected close to the 5 miles 4 chains shafts. When these shafts were sunk, Walker noticed a strong resemblance to the material used by the Cattybrook Brickworks for making vitrified bricks. Vitrified bricks were to be used as the lining in the tunnel as they could resist enormous pressure underground.
In July 1880, pumping out the water in the Iron Shaft became the first priority as it was found that there were obstructions preventing the correct fitment of the 38 inch pump attached to one of the beam engines. In eight and a half hours, the pumps managed to reduce the water to a few feet off the bottom when, without any warning, the 38 inch pump burst apart. A piece of casing 18 inches long narrowly missed one of the divers, but as the pump-rods lost all resistance, the engine beam weighing 23 tons, crashed into the safety stop. Before the engine could be halted, the beam struck the stop again with another thunderous blow. As this left just one small pump in operation, it was stopped and in a few hours the workings were again full of water to the level of the tide.
Although it took two weeks to remove the broken pump, it took another four months to manufacture a replacement. In addition, spares were made for the existing pumps on the site so that on the morning on the 14th of October, pumping operations began again. After a few more problems with the pumps, the water was 160 feet below the surface by the 2nd of November, but it was noticed that a fair quantity of fresh water was entering the workings from the heading under the river. It was then realised that in the panic to get out of the workings, the men had not closed the iron door in the headwall that Richardson had built 340 yards from the Old Shaft. If this door could be closed, then Walker could concentrate his efforts on the Great Spring.
Three divers were called for and the leading diver, Alexander Lambert, would walk 1000 feet from the Iron Shaft to the headwall, shut an 18 inch flap-valve, pull up the two rails used by the skips, close the iron door and finally close a 12 inch sluice valve - all in complete darkness and dragging his air hose behind him. The other divers would guide the air hose - one from the bottom of the shaft and the other half-way up the heading. Armed with only a short iron bar, Lambert made his way up the heading, stumbling over debris, tools and skips which had been left in the panic. The air hose that Lambert used was floating hard against the roof of the heading, until 100 feet from the headwall and with the resistance of the hose, Lambert conceded defeat. But his return back through the heading was even more hazardous as the air hose would wind itself around the supporting timbers of the heading in addition to Lambert's meeting of the same debris that he had found walking towards the headwall.
A few years earlier, Henry Fleuss, a merchant marine from Wiltshire, began experimenting with a self-contained underwater breathing apparatus. It consisted of a flexible bag worn on the diver's back that contained a copper tank filled with compressed oxygen and a material that absorbed carbon-dioxide so that the same oxygen could be breathed repeatedly for up to three hours. Attached to the bag were two tubes connecting to a helmet similar to the diver's normal helmet. Walker had heard of Fleuss' invention and invited him to Sudbrook to see if he could close the door in the headwall, however, the deepest dive that Fleuss had attained with the
apparatus was in 18 feet of water off the coast of the Isle of Wight while tethered to a rowing boat. Although Lambert, dressed in his normal diving equipment accompanied Fleuss up the heading, Fleuss was obviously not an experienced diver and after three attempts, they returned to the surface.
Walker then asked Lambert to try Fleuss' invention for himself, and so after a little practice, Lambert plunged once again into the tunnel. Walker had warned him to take extra care in the headings as his life depended on one small bag that could easily be damaged by the timbers in the heading or from a fall over the upturned skips. Finally after an hour and a half, Lambert returned; he had reached the headwall, closed the flap-valve and pulled up one of the two rails, but the second had defeated him. To show the bravery of Lambert though, he was willing to go back as soon as he could, but Fleuss had to return to London to collect more oxygen and carbon-dioxide absorbent.
On Fleuss' return, Lambert again started down the heading. This time he managed to remove the second rail, close the door and screw the sluice valve the required number of turns to close it. After the pumps were brought to full power, all eyes were on the floats indicating the level of water within the shafts, but the water was only falling at a rate of 3 inches per hour and at high tide, the pumps could only manage to maintain a stable water level. For the next four weeks, between the 10th of November to the 7th of December, the pumps worked hard at removing all the water from the works, although the many pump breakdowns during this time slowed the task a little. Finally the Iron Shaft was empty and there was just two feet of water within the headings. It was now possible for James Richards, foreman of the pumps, to walk up the heading to the iron door that Lambert had shut and discover the cause of all their frustration. Water was pouring out of the 12 inch sluice valve. This valve must have been closed when Lambert reached it and although he had turned the valve the correct number of turns in a clockwise direction, it was then realised that the valve had a left-hand thread and in effect Lambert had fully opened the valve. Richards closed the valve and the effect of this was so immediate that the pumps could be slowed down.
It was now possible to examine the top heading leading to the Great Spring. On the 13th of December, Joseph Talbot, foreman of the miners, opened the door in the shield and explored the heading to see if it was safe for the engineers to walk through, and so Walker and J. Clarke Hawkshaw, son of Sir John, followed Talbot into the top heading the following day. Dressed in divers suits but wearing sou'westers instead of helmets, the party waded through water 3½ feet deep, 600 feet up the heading. A quantity of debris and smashed timbers greeted their arrival at the point where the Great Spring broke in. Retracing their steps, an area of sound rock was selected about 460 feet from the Old Shaft. Here a brick headwall of 8 feet in thickness with a heavy oak door was to be built across the heading, and so stopping the Great Spring while other work in the construction of the tunnels could be carried out. After allowing time for the brickwork to set, the door of the headwall was closed on the 4th of January 1881, and the Great Spring was
Copyright © by John Daniel 2013