The Severn Tunnel/Chapter 11

by Thomas Andrew Walker

CHAPTER XI.

SIDE-HEADING DRIVEN TO BIG SPRING—COMPLETION OF THE BRICKWORK—BIG SPRING SHUT OUT—WORKS PASSED BY BOARD OF TRADE.

Progress of the work—1884.The first nine months of the year 1884 were like those of 1883—uneventful months.

The whole of the tunnel, except rather less than 300 yards, where the Great Spring had been shut back by two head-walls, was fully at work. The largest possible number of men was employed upon the works, and all the plant and machinery that could be utilized was on the ground.

The carrying out of the works had originally been entrusted to two principal foremen—Mr. John Price taking the Gloucestershire side of the river, and Mr. Joseph Talbot the Monmouthshire side, which included the work under the ‘Shoots’ and the work at the three outlying shafts, 5 miles 4 chains, the Marsh, and the Hill, as well as the principal shaft at Sudbrook.

The greatest number of men employed in this year was 3,628; 1,641 being employed on the Progress of the work—1884. Gloucestershire side, and 1,987 on the Monmouthshire side.

The total length of tunnel executed on the Gloucestershire side of the river, under John Price, was 3,260 yards. In addition, he also executed about 100 yards of tunnel detached from the main tunnel, under the road known as Ableton Lane, The total length of tunnel executed under Joseph Talbot was 4,406 yards.

The length of the tunnel stated in the contract originally had been 7,942 yards; but this had been reduced in the beginning of the year 1884 to 7,666 yards; the cutting at the western end of the tunnel being lengthened to the extent of 276 yards, to provide the material required for making up the sidings at the station near Rogiet, afterwards known as Severn Tunnel Junction.

Every part of the works, except the 300 yards previously mentioned, was pushed on with rapidity, and only those ordinary accidents and delays which are inseparable from tunnel-work interfered with the progress.

Singularly enough, we generally found that when one accident occurred, others followed almost immediately. For instance, on February 15th the T-bobs of two of the pumps at 5 miles 4 chains broke down, and, in breaking, bent the crank-shaft of the engine. On the 17th the pump-rod of one of the pumps at the Marsh Pit broke; on the 18th a large pump at 5 miles 4 chains broke down; and on the 19th Progress of the work—1884. the rising-main of the 35-inch pump in the Iron Pit at Sudbrook split.

In order to relieve the water at 5 miles 4 chains, we had for some time kept the sluices in the big head-wall near Sudbrook partially opened; but when the 35-inch pump broke down it was necessary to shut these sluices, or the works under the river would have been drowned. Shutting the sluices increased the pressure to such an extent at 5 miles 4 chains and at the Marsh Pit that, in consequence of the breaking down of the pumps, these two pits were of a necessity partially filled with water, and the works stopped; and it was not till March 17th that the pumps were repaired and the work resumed in these two pits.

The whole of the tunnel on the Gloucestershire side, from the ‘Shoots’ to the open cuttings at the eastern end of the tunnel, was completed in August; and the whole of the tunnel from 5 miles 4 chains to the western end of the tunnel was completed in September.

Sir John Hawkshaw had determined to put down a new pumping-shaft just outside the western end of the tunnel, and to pump there, at a low lift, all the rainfall from the open cutting, which, with the sea-banks, contained an area of 14 acres. This shaft had been sunk, and a heading through the whole of the unfinished portion of the cutting completed, to bring the water to the pumps fixed there.

The water from the large cutting at the eastern Progress of the work—1884.

end of the tunnel was led into the tunnel itself, and pumped by the pumps fixed in the Sea-Wall pumping-shaft.

The two 70-inch engines and the two 60-inch engines were being erected in the houses provided for them, and the pumps were being fixed in the shafts.

In order to deal with the water from the Great Spring, Sir John Hawkshaw decided to drive a side-heading parallel to the centre-line of the tunnel, but about 40 feet to the north of it, from the Old Pit at Sudbrook to the point where it would intercept the spring itself.

The gradient of the tunnel rising 1 in 90, the heading was to be driven at a gradient of about 1 in 500; so that, when it reached the point where the Great Spring had broken in, it would be about 3 feet below the bottom of the invert of the tunnel.

The driving of this heading was commenced in July, both from the point at which it was to join the tunnel and at a point 50 yards to the west, by a cross-heading from the tunnel, in order to ensure the correctness of the lines. By the 20th September this side-heading had been driven about 18 yards past the point where the head-wall had been built across the tunnel.

Sir John Hawkshaw had further decided that, in order to reduce, if possible, the quantity of water to be dealt with—which, we knew, to a very considerable extent came from the loose bed of the little Progress of the work—1884. river Neddern—to construct a concrete invert in the bed of the brook for a length of nearly 4 miles.

This work was undertaken in August, and was completed by the 7th October; and three of the large engines and pumps being ready for work, on the 30th September it was determined at once to take in hand the work between Sudbrook and 5 miles 4 chains.

The sluices in the head-wall were gradually opened, and at the same time a hole was broken through the brickwork at the top of the head-wall.

In the first day’s work the head of water behind the head-wall was reduced 4 feet 6 inches, and after three days’ pumping all the water was out of the heading, and the foremen were able to go up and inspect the point where the spring had broken in. All the work was found in good condition, having been properly secured by timber just before the 10th October, 1883.

Another cross-heading was driven from the tunnel from behind the head-wall to connect with the side-heading; and the side-heading was pushed forward, and on the 19th December reached a large open joint in the strata, which had formed the channel for the subterranean water. A drawing is given showing a plan of this fissure, and the manner in which it was tapped by the side-heading.

By diverting the water of the spring into the side-heading the tunnel itself was left almost perfectly dry, except where, in taking out the invert, we Progress of the work—1884.

crossed other fissures in the rock in which the water stood a foot or two higher than in the one tapped by the side-heading.

As a precautionary measure, before starting the pumps at the end of September, we had built across the side-heading opposite the great head-wall in the tunnel a head-wall of brickwork in cement, with a door hung as in the previous head-walls. By the 6th October we had so completely mastered the water from the Great Spring that we found it possible to stop one of the largest of the pumps, and hold that in reserve. On the 17th October we effected a junction between the top heading from 5 miles 4 chains and the heading from Sudbrook, making a complete passage from end to end of the tunnel; and as it happened that, without warning, Sir Daniel Gooch, the Chairman of the Great Western Company, and the Earl of Bessborough, one of the directors, came upon the works the same day, we were able to pass them, at two o’clock on the 17th, through the last link of the works, for it was now possible to walk through from the open cutting on the Gloucestershire side to the open cutting on the Monmouthshire side. Though it was possible to pass through, it must not be supposed that the road was the very best or cleanest imaginable. The journey could be made by riding on trolleys from the eastern end of the tunnel to the shaft at Sudbrook; and could also be made from 5 miles 4 chains to the western end of the tunnel in the same way; Progress of the work—1884. but between Sudbrook and 5 miles 4 chains there was not only a quantity of water dripping from the roof, but there were ladders to climb, and, at any rate on the 17th October, a small and not very clean hole to crawl through, with a face of 4 feet or 5 feet between the two headings to be climbed up.

On the 9th August of this year the members of the Institution of Mechanical Engineers, who were holding their annual meeting at Cardiff, visited the Severn Tunnel Works, and were able to examine them all with the exception of the short length at the Great Spring. Arriving by train from Cardiff at the point since known as Severn Tunnel Junction, they were transferred from passenger carriages to trucks fitted up with seats, and drawn by one of the locomotives employed upon the works, in which they passed through the open cutting to the mouth of the tunnel. Descending from the trucks, some members of the Institution elected to walk over the top of the tunnel, but the greater number continued their examination, walking through the finished works underneath. Meeting with a rough road to travel and here and there some little water, other members chose to go up by the cages at the Hill Pit; others, again, dropped off when the Marsh Pit was reached; but a goodly number continued their walk through the tunnel to 5 miles 4 chains, and were then drawn to the surface, and found their train waiting for them. After examining the brick-making machinery they proceeded to Sudbrook,

progress of the work—1884.

made a thorough examination of all the pumping and ventilating machinery, descended the Sudbrook Shaft, and examined the tunnel under the river; and then returning to the surface, wound up with what Englishmen can never dispense with—a good lunch in the school-room, and on leaving the works, expressed themselves highly delighted with all that they had seen.

On the 15th September the members of the South Wales Institute of Engineers also visited the works, and made a thorough examination of them.

On the 22nd October the laying of the rails of the permanent road was commenced from the Gloucestershire side of the river; and on the 20th November the largest of all the pumps, the 37-inch plunger, was completed, and started to work in the Old Pit, thus giving us two pumps in reserve over and above what was necessary to deal with the Great Spring.

The bottom heading, between Sudbrook and 5 miles 4 chains, was completed on the 16th December, two days under five years from the date on which the contract had been signed.

The progress section, which is given on the other side, shows the work that was done in the year 1884; but shortly stated, the whole of the tunnel was completed, except about 200 yards between 5 miles 4 chains and Sudbrook, and 500 yards of invert under the ‘Shoots,’ where the connections were to be made with the 9-ft. barrel and the 5-ft. drain.

Progress of the work—1885. The work remaining to be done being now confined to a very short length, it was necessary to reduce largely the number of men employed, but as many were retained as could be kept at work, and in order to hasten completion, four break-ups were started in the short length near the Great Spring, at distances of only 44 yards apart. The running lengths were also commenced from both faces, and thus ten faces were kept at work through this short length of tunnel.

On opening out the full-sized tunnel, the fissure through which the Great Spring had passed was found to follow a most erratic course. In one place it passed directly across the tunnel from side to side, nearly at right angles to the centre line of the work. At another place it passed from side to side in an oblique direction, running for some small distance directly under one of the side walls. At another point where the tunnel had been perfectly dry, while the mining was done, the lifting of almost the last stone out of the invert set free an immense body of water which no pumps underground could cope with. At another point the water boiled up from a hole 18 feet in depth under the invert with such force that stones, the size of a man’s fist, dropped into the water would descend about 10 feet, and then begin to flutter like a leaf in the wind, and be thrown out again by the water. Into this hole a cast-iron pipe was lowered, attached to a bend at the top to lead the water into the side-heading. Progress of the work—1885. The cavity round the pipe was closed with concrete and brickwork in cement, and the place made perfectly sound and tight.

Where the fissure crossed the tunnel at right angles, two 15-inch cast-iron pipes were laid side by side under the invert, and were then covered with concrete and brickwork in cement, and an extra thickness of brickwork in cement was put into the tunnel invert.

The point where the water rose in the invert of the tunnel by the lifting of what I have called the last stone gave more serious trouble.

At last, at the suggestion of Sir John Hawkshaw, a wall was built round the hole, and inside it the water was allowed to rise. When it had risen about 4 feet, it remained stationary, as at that height the water escaped by other openings into the side-heading. When the water was stationary the whole of the cavity below the invert was filled up with Portland-cement concrete lowered down a wooden tube. After this had been allowed time to set, a hand-pump was set to work in the top of the hole, and it was found that the concrete had made a perfectly water-tight joint, and the hole was easily pumped dry. The concrete had been kept down to a level of 3 feet below the top of the invert, and on this the invert of the tunnel, 3 feet thick of brickwork in cement, was built, without any water to interfere with the work; and on April 18, 1885, at 8 a.m., the last length of the brickwork of the tunnel was keyed Progress of the work—1885. in, at a point nearly midway between Sudbrook and 5 miles 4 chains shaft.

The brickwork of the tunnel having been completed, the side-heading was arched over above the level of the water from the Great Spring, and over the arch filled up with rubble masonry from the point where the western end intersected the fissure. When the door was reached, one of the sluices was shut on July 13, and a 12-inch pipe being laid to carry the water from the other, the rest of the heading was filled up with rubble masonry, and the opening through the side-wall of the tunnel closed. The 12-inch cast-iron pipe was laid to bring water from the spring to the boilers, and a small shaft was sunk at the side of the tunnel, nearly over the end of the side-heading, and a pipe led down through the shaft to connect with the pipe in the heading.

In addition to the sluice at the head-wall, a sluice was fixed on this pipe at its eastern end. The sluice by the head-wall was opened before the heading was filled with masonry, and the sluice at the other end was kept at our command for supplying water as might be hereafter required. At the end of the cast-iron pipes a pressure-gauge was fixed to the pipes to indicate the pressure of the water, and so tell how much it had risen day by day. The following table shows the rate at which the water rose: Progress of the work—1885.

Table showing Rate at which Pressure Rose after Sluices were shut August 11, 1885.
Date		Pressure in lbs.	Date		Pressure in lbs.	Date		Pressure in lbs.	Date		Pressure in lbs.
Aug.	11	nil	Aug.	26	39¾	Sept.	14	47½	Oct.	27	54
„	12	9	„	28	40	„	15	47¾	„	31	54½
„	13	12	„	29	41½	„	17	48	Nov.	4	55
„	14	17	„	30	42½	„	18	48¼	„	7	55½
„	15	18¾	„	31	43	„	20	48¾	„	9	56
„	16	21	Sept.	1	43½	„	22	49	Dec.	3	57
„	17	22½	„	2	43¾	„	25	49¼	„	7	57¼
„	18	25	„	3	44½	Oct.	1	49½	„	20	57¼
„	19	27	„	4	45¼	„	4	49¾	„	21	30*
„	20	29¼	„	5	45½	„	7	50	„	22	25
„	21	32½	„	6	45¾	„	10	50¾	„	23	16
„	22	34¾	„	7	46¼	„	11	51	„	29	13
„	23	36½	„	8	46¾	„	15	52½	„	30	nil†
„	24	37½	„	9	47	„	17	53	* Valve opened 4″.
„	25	38½	„	13	47¼	„	24	53½	† Valve fully opened.
N.B.—Pressure is given in lbs. per square inch.

On 5th September Sir Daniel Gooch, accompanied by Lady Gooch and a party of friends, came with a Great Western engine and passenger train to inspect and pass over the works.

Arriving at Severn Tunnel Junction at 11 o’clock, the train passed through the open cutting and through the tunnel into the open cutting on the Gloucestershire side; returning again to the Monmouthshire open cutting, the train passed over the line laid to bring materials to the works to Sudbrook, where two or three hours were spent pleasantly Progress of the work—1885. in inspecting the engine-house, school-rooms, men’s houses, mission-hall, etc.

On the day the train passed through, the water had risen in the ground outside the tunnel to a height of about 105 feet, and the pressure shown upon the pressure-gauges was 45½ lbs. per square inch. At this pressure a small quantity of water found its way through the joints in the brickwork, and in some places made quite a respectable shower into the tunnel.

On the 7th September I left the works for South America. There had been a great strain upon me for many months, and I was glad to get on board the royal mail steamboat Neva, at Southampton, on the 9th, and to think that the tunnel was all right, and that I should be out of reach of all telegrams and letters for at least four weeks. We reached Buenos Ayres on the 6th October, and I purposed remaining there till the 17th November, to verify information which had been given to me, and to complete my estimates for the Madero Port at that place. On the 30th I received a telegram: ‘Sir John Hawkshaw says you must come home on the 1st.’ I replied that it was impossible. I finally left South America on the 18th November for Southampton.

Arriving at Southampton on the 14th December, I received the first intimation that there had been further troubles at the tunnel. After I had left on the 9th September, the water, continuing to rise

J. Clarke Hawkshaw

Engraved by W. H. Gibbs from a photograph by Witcomb

Progress of the work—1885.

in the ground where the Great Spring had been stopped back, had been of course producing a greater and greater pressure upon the brickwork, till the pressure had at last risen to 57¼ lbs. on the square inch. Under that pressure the bricks in the tunnel began to break, pieces flying off them with reports like pistol-shots, and the water shooting through the broken bricks quite across the tunnel.

Two of the largest of the pumps which had been fixed to deal with the Great Spring in the Old Shaft had been taken out before I left for South America, and only the 31-inch pump worked by a 60-inch beam-engine was left in that pit to deal with any extraordinary quantity of water which might find its way through the brickwork.

Mr. J. Clarke Hawkshaw had gone to South America with me, and had remained there when I returned. Sir John Hawkshaw was naturally extremely anxious about the state of the works, and when I had seen him, and heard what had occurred since I left. I visited the works and found them in a very serious, if not dangerous, condition, and I at once asked Sir John’s permission to take off the pressure. He was of opinion that our pumping-power was not sufficient, and that the water from the spring was coming in behind the work in greater volumes than we were able to pump.

Having, however, obtained his sanction to making the attempt, I broke out the pipe adjoining the sluice valve at the eastern end of the side-heading, Progress of the work—1885. and opened the sluice gradually as the pumps were able to take the water. The sluice was opened on 21st December, and the pressure was rapidly reduced from 57¼ lbs. on the square inch to 30 lbs.

Sir John Hawkshaw then determined that it was necessary to provide pumping-plant to pump the whole of the water from the spring, and not to subject the brickwork of the tunnel to the enormous pressure it would have to sustain to exclude this water.

Arrangements were made with me to sink a large shaft at the side of the tunnel, 29 feet in internal diameter. In this shaft were to be fixed six large pumps with six 70-inch Cornish beam-engines fixed in a house which entirely covered the shaft. It was also determined to fix two 65-inch engines with two new pumps in the pumping shaft at 5 miles 4 chains, and two 41-inch beam-engines with 29-inch pumps in the shaft at Sea- Wall.

A Guibal Fan, 40 feet in diameter and 12 feet wide, was ordered by the Company, and the designs made for the necessary buildings comprising fan-house, engine-house, and boiler-house. Two Lancashire boilers, each 26 feet in length by 7 feet in diameter, were provided for the fan, and a space provided for a third boiler, which was afterwards added. Twelve Lancashire boilers 28 feet in length, and 7 feet in diameter, were provided for the pumping engines at Sudbrook, and a new engine and boiler-house were built at 5 miles 4 chains, in which Progress of the work—1885. four Cornish boilers already there belonging to the Company were fixed with three new Lancashire boilers.

The 29-ft. shaft, which was 35 feet in external diameter outside the brickwork, the circular wall being 3 feet in thickness, was sunk in the manner described in the account of the sinking of the other shafts, and without any difficulty from water, as a bore-hole was dropped down into the side-heading below.

1886.The shaft was commenced the 8th February, 1886, and completed to the bottom on the 7th April. The brickwork lining of the shaft was completed on the 3rd June. The building of the engine-house at the top of the shaft was commenced on the 9th February, and completed on July 8th, 1886. The engines in this case were not only constructed but were erected by Messrs. Harvey and Co., of Hayle, the pumps being fixed by me; and the first engine and pump were ready to start and were started on the 1st July, 1886.

The length of the 12-inch cast-iron pipe laid in the side-heading was 515 feet; and when this pipe was running full bore, it still required a head of 70 feet to force the whole of the water through the length of pipe.

On the 1st July we had been able for some weeks to take the whole of the water this pipe would bring. The second of the large engines and pumps was ready to start on the 4th August. In the meantime, Progress of the work—1886. the rubble masonry with which the side-heading had been filled had all been removed, and the heading inside had been lined, as far as possible, with brickwork in cement. In order to complete the brickwork, a cross-heading from the tunnel was opened into the side-heading at a point west of the head-wall, the water being temporarily diverted through that cross-heading; the brickwork of the invert was completed, and the pipes broken off at the back of the sluice in the head-wall. The water was then allowed to flow down the brick-lined heading to the big pumps; and the length of 12-inch pipes being thus reduced to 12 feet, the sluice there was opened till the pressure was reduced to 12 lbs. on the square inch.

The second sluice (for there were two) through this head-wall was then opened, and all the water taken from the spring; and the pressure being entirely taken off the brickwork, all broken bricks were carefully cut out, and all damaged brickwork repaired.

On the 20th September the third of the large engines and pumps was started to work.

The fan was also completed on the 31st August, and the line was opened for goods traffic on the 1st September, 1886.

On the 17th November the tunnel-works were inspected by Colonel Rich, the Government Inspector, with a view to^ the opening for passenger traffic.

Progress of the work—1886. Colonel Rich, who is noted for the great attention he pays to all details, made a most exhaustive inspection of the tunnel itself and of all the machinery provided and fixed, and expressed himself perfectly satisfied with all that had been done: a copy of his report is appended below.

The work was finally opened for passenger traffic on the 1st December, 1886, nearly fourteen years from the time the Great Western Company had first commenced the works, and as nearly as possible seven years from the time they had let the contract to me.

[Colonel Rich’s Report.]

Railway Department,
Board of Trade,
22nd Nov., 1886.

Sir,

I have the honour to report, for the information of the Board of Trade, that, in compliance with the instructions contained in your minute of the 10th inst., I have inspected the Severn Tunnel Railway, which connects the Great Western South Wales Union Railway with the South Wales Railway.

The new line is 8 miles 26 chains long. The gauge is 4 feet 8½ inches.

The ruling gradient is 1  in 90, and the sharpest curve has a radius of 10 chains.

This curve is at the junction with the South Wales Railway, and is only about 1½ chains long.

The railway is double throughout, except about 37·54 chains at Pilning, which will be partly doubled before the line is opened, and the rest as soon as Progress of the work—1886. the alteration of the South Wales Union Railway is completed.

The permanent way consists for about 4 miles 29 chains in the tunnel of a longitudinal sleeper road, with a bridge-rail that weighs 68 lbs. per lineal yard; and the remainder of the Great Western standard pattern sleeper road, with an 86-lb. bull-headed rail and 43-lb. chair.

The rails are made of steel; the railway is well ballasted and well fenced.

The only stations are at Pilning and at Severn Tunnel Junction.

The works consist of three bridges under the railway, which have wrought-iron girders on brick abutments; three brick bridges and one wooden bridge over the railway; eight culverts; and the tunnel under the Severn, which is 7,664 yards long.

The tunnel is lined with vitrified brick in cement.

The sides, which rise about 7 feet above the rail-level, carry a semicircular arch of 26 feet diameter, which varies in thickness from 27 inches to 36 inches; and there is a brick invert, 18 inches to 3 feet thick, throughout the tunnel, which has a brick semicircular drain about 3 feet 6 inches wide over the centre, and a brick barrel-drain 5 feet in diameter under the invert. This latter carries the surface-water to a shaft at the north end of the tunnel, and drains the cuttings at both sides of the railway.

In addition to these there is an old heading 12 feet wide at the north end of the tunnel, which has been utilized for drainage purposes.

There are ventilating shafts at each side of the Progress of the work—1886. river. The one at the south side is 15 feet diameter; and the one at Sudbrook, which is at the north side, is 18 feet diameter.

The ventilating fan, which is at the north side of the river, is 40 feet diameter and 12 feet wide. It can be worked at a velocity of 60 revolutions per minute: less than half this speed is estimated to be sufficient to ventilate the tunnel.

I enclose herewith a statement of the several pumping shafts, and of the pumps that work through them to drain the tunnel, which, in addition to the water from the cutting at each side, and some very slight leaks through the brickwork of the tunnel, has intersected an underground stream of a considerable size. The water from this stream has to be pumped into the Severn from a shaft 29 feet diameter, which has been constructed to catch this water.

There are arrangements for shutting off and diverting the stream water by means of sluices from the 29-feet diameter shaft, and also for intercepting the drainage water from the cuttings and pumping it up from shafts at each side of the Severn.

In addition to the two ventilating shafts there are five pumping shafts with a power capable of pumping 38 million gallons of water per diem. The maximum amount of water to be pumped has been 30 million gallons, and the minimum has been 23 million gallons per diem up to the present time, so that there is an excess of pumping power of 8 million gallons per diem; but when the whole of the permanent pumping and engine power, which Progress of the work—1886. is now erecting, is completed, there will be a pumping power equal to 66 million gallons per diem, which will give 36 million gallons per diem in excess of the maximum quantity of water that has to be raised from the tunnel and discharged into the Severn.

The works appear to be very good and substantial, and to have been carried out with great care and judgment.

This work was commenced twelve years since, and the actual work of building the tunnel was commenced in 1881.

The difficulties of dealing with the large quantity of water, and particularly of dealing with the under-ground stream, which runs at a great velocity, have been considerable, but have now been successfully overcome, and the result is a tunnel of unusually large dimensions, which is particularly dry. The top of the tunnel is about 145 feet under the level of high-water spring tide, and about 50 feet under the bed of the river at its deepest point.

The means of ventilation are ample, but did not act well when I made my inspection.

This only requires a little attention and regulating. I was informed that no inconvenience has been felt from a want of ventilation during the running of the numerous goods and coal trains that have been sent through the tunnel for some time past.

I have, etc.,
(Signed)F. H. Rich,
Colonel, R.E.

The Secretary,
Railway Department,
Board of Trade.