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THE SEVERN TUNNEL PUMPING WORKS.

BY H. CECIL MOORE.

SUDBROOK, in the parish of Portskewett, is occupied by the Severn Tunnel Pumping-Works, the largest concentration of pumping works in the world, their pumping capacity being calculated to discharge 66 million gallons in 24 hours. The question naturally occurs-wherefore this enormous pumping-power? Although there did occur occasionally during the construction of the tunnel some inflow of Severn water, it is satisfactory to learn, on the authority of Mr. Chas. Richardson, the acting engineer, dated June, 1889; "there is now positively no leakage from the River Severn." During the first six years of tunnelling under the river, everything had been progressing very satisfactorily. The key to the whole undertaking appeared to have solved all doubt as to its practicability, from the fact of solid hard Pennant rock underlying the 300 yards of deep water at low tide in the "Shoots" channel on the Monmouthshire side, and extending far beyond the channel, than which a stronger material, or one through which it would be more safe to carry the tunnel could not have been desired. An unforeseen and most formidable difficulty was encountered on the land side at Sudbrook, at a distance of 400 yards from the margin of the river. On October 16th, 1879, a big fresh water spring, appropriately called a subterannean river, was tapped, which rushed in at the rate of 6000 gallons a minute, and flooded the whole works for fourteen months. This proved to be an immense body of water which has its gathering ground in adjacent high hills. Even after the completion of the tunnel in the end of the year 1885, such serious damage was done to the brickwork from the surrounding water-pressure, amounting to nearly 60 lbs. upon the square inch, that security could only be obtained by continuous employment of pumping power, in order to relieve the water pressure. Hence will be seen the necessity of this large concentration of pumping power, involving an expenditure of about 40 tons of coal daily, and a staff of about ninety men.

Mr. Richard Hosken, the superintendent of the works, met our party and conducted them to the office, upon the walls of which were displayed elaborate plans and sections of the tunnel. Outside the office door was a fine fossil Reed, or Calamite, 3 feet 3 inches high whose longest diameter at the base was 18 inches, and 10 inches at the summit. Close to it stood a Stigmaria, 10 inches high, 11 inches at the base, and 5 inches at the summit. Both these specimens had been met with in the Coal Measures of the excavations.

From the office Mr. Hosken conducted the party to the huge building called No. 1 House, which covers six powerful pumps and their machinery. Iron staircases conduct to a platform above, where are seen six gigantic engine beams, each 35 feet in length, with a parallel motion attached to each end, which parallelizes the path of the piston and pump rods. Of the six pumps three on one

side are plunger-type, and on the other side are three drawing lifts, or bucket pumps. These pumps, in conjunction with others at different situations, have sufficient capacity to pump out the whole of the water that ever could come into the tunnel during the wettest periods, and leave a large and ample margin for break-downs or any other contingency. Whilst some, perhaps at times only three, are in use, the remainder are kept in reserve for contingencies. The engines are similar and all their parts are duplicates, so that any one piston rod or valve will serve for either engine. When repairs are necessary, huge machinery can be transported to its place by a powerful traveller which traverses the engine house in its entire length. Only a few weeks ago one of the huge 35 feet beams was placed in its position without for one moment stopping the usual daily pumping operations of the contiguous engines.

Each of these six pumps is capable of raising five million gallons a day. The scrupulous cleanliness, the smoothness of working, and the small amount of vibration were specially remarkable.

The power, description, and situation of the whole sixteen pumps employed is given in detail in the following table kindly furnished by Mr. Hosken.

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As before stated the pumping capacity of the whole machinery is equal to 66 million gallons in the 24 hours; but the maximum amount hitherto pumped in one day has been 32 million gallons, or 145,000 tons.

For this enormous discharge there are three outlets. Mr. Hosken took us to view one connected with the fresh water discharge from the subterranean river, which, at that time, was calculated to be discharging not more than 14 million gallons in the 24 hours. It presented a fine rush of water over a waterfall eighteen feet in width. This outlet is the fresh water discharge, the "Big Spring" water: it has discharged as much as 20 million gallons in 24 hours. The 5 miles 4 chains pumping station has a separate discharge; this is the water from the open cutting, and the percolations through the brickwork up to this point. There is also a separate discharge for the water from the 5 feet barrel tunnel drainage, which is pumped from Nos. 2 and 3 houses. There are also two engines at Sea Wall on the Gloucestershire side with a separate discharge.

It must not be supposed that all the fresh water is allowed to run to waste in the River Severn. Neighbouring villages, for a distance of five miles, whose wells have been dried by this incessant pumping receive a supply from Sudbrook in iron pipes. We shall not be surprised to hear at any time of its use as energy for the creation and supply of electricity.

Mr. Hosken had kindly made arrangements for such visitors as were so disposed to descend the shaft in parties of five at a time. Accompanied by a guide, and protected with overcoats and sou'westers, several made the descent, saw the great underground river, and thence entered the tunnel, the whole process of descent, exploration, and ascent, occupying about twenty minutes. The boiler department was inspected. Here two main steam pipes connect the boilers with the engines. These pipes are arranged with sluice-valves so that the engines can be worked singly or altogether. Other machinery was also visited, including that connected with the working of the huge Guibal Fan, 40 feet in diameter and 12 feet wide, which successfully ventilates the tunnel.

Through the influence of Mr. Hosken we have obtained permission of the Great Western Railway authorities to re-produce the accompanying plan and section of the Severn Tunnel, an examination of which is recommended in order to fully understand the various geological strata met with in its construction.

An inspection of the plan shows that the width of the river is 2 miles. The section shows that at low water the river is entirely confined to the "Shoots" channel, on the Monmouthshire side, only a quarter of a mile at the top, and 300 yards at the bottom. The remaining two miles are occupied by the half-tide rocks, a mile and a half wide, on the Gloucestershire side, called the "English Stones," and by the "Lady Bench " rock on the Monmouthshire side, half-a-mile wide.

The important question requiring solution for the practicability of the whole scheme was the nature of the formation underlying the 300 yards of deep water in the "Shoots" channel. It was accordingly proposed to sink a shaft through the low water rocks of the Lady Bench, close to the edge of the "Shoots." This met with such strong opposition from the local navigation board that the shaft

was placed on shore at Sudbrook at the distance of half-a-mile further from the "Shoots." The sinking of this shaft was commenced in March, 1873.

The most important geological sections recorded below, are from a paper in the proceedings of the Geological Association, Vol. VII., by Mr. Evan D. Jones, sometime assistant engineer in the works, as quoted in Professor C. LloydMorgan's pamphlet, on the Severn Tunnel Sections.

SHAFT No. 4 OR THE SUDBROOK SHAFT.

[blocks in formation]

Bottom Heading:-driven horizontally from the above Shaft.

[blocks in formation]

TRIAS

All beyond the Fault to the mouth of the tunnel and cutting

on the Gloucestershire side.

It fortunately happened that the Pennant Rock rapidly thickened downwards, with the result that for a mile under the river, including the part under the "Shoots" channel, the tunnel was driven through this hard rock.

The conception of the tunnel scheme is due to Mr. Chas. Richardson, C.E.,* a pupil of the elder Brunel during the construction of the Thames Tunnel in 1848. Mr. Richardson, whilst engaged in the Portskewett Ferry connection between Bristol and the South Wales Union Line, had numerous opportunities of studying the swiftly rushing currents and other objections to a bridge over the estuary here. In 1871 his plans were deposited, not for the first time, in Parliament. In 1872 the Act passed the House of Lords, and in March, 1873,

*Mr. Charles Richardson died, aged 81, at Clifton, on 10th February, 1896.-ED.

the Great Western Railway commenced the work, as before stated, by sinking the shaft at Sudbrook.

Under the surface soil and some dirty gravel, was a 5 feet bed of fine sand, and beneath this a bed of Yellow Sandstone rock which forms the Sudbrook cliff, the upper part of which was found riddled with pot-holes, some of them being four or five feet deep and only six inches in diameter, all filled with fine sand.

When the shaft had reached far below the low water level of the Severn, some fresh water springs quite pleasant to the taste were intercepted. When collected in wells they were found to be influenced by the tides of the Severn, the rise and fall being nearly two hours after that of the river.

In December, 1874, the heading from the Sudbrook shaft towards the "Shoots was begun. The mixed bed of Coal and Shales was troublesome heavy ground, so that the heading here had to be double timbered and floored, which made it small and low. Some copious springs were afterwards found in the Pennant rock, so that, in order to prevent flooding of the pumps in the event of a breakdown, a strong flood door sufficiently large to admit the passage of the trolleys, with a 12-inch sluice-valve was built in it at a distance of 340 yards from the shaft.

After passing the "Shoots" the heading emerged into the upper Coal Shales, thence through two small beds of coal, until it came to a vertical Fault at a distance of 2180 yards from the shaft, then suddenly entered the New Red Sandstone, and finally the New Red Marl on the Gloucestershire side.

In August, 1877, about 1600 yards of 7 feet square heading had been driven under the river, and a second shaft, afterwards known as the "Iron Shaft," had been half sunk for permanent drainage pumps. About this period two other shafts, called the "Marsh Shaft" and the "Hill Shaft" (see Section) were commenced, all on the Monmouthshire side, and on the Gloucestershire side a shaft known as the "Sea-Wall" pumping station (see Section) was begun. From each respective shaft headings were driven in both directions, and one or more Plunger Pumps were fixed at each shaft.

In 1879 when the heading landwards from the west side of the Sudbrook shaft had attained a length of 355 yards from the shaft, i.e., 400 yards inland from the high water margin of the Severn, a big fresh water spring, since known as the subterranean river, was suddenly tapped on October 18th, the water rushing in at the rate of 6,000 gallons a minute, and flooding the whole of the workings in twenty-four hours. Fortunately the men were changing shifts at the time, and were all able to escape. They, however, neglected to shut the flood door after them. The water rose in the shaft until it attained the high water level of average tides in the Severn, at which height it remained rising and falling with the tides nearly two feet, but always one hour and a half later than the tides.

This was a heart-rending result after six years and a half of work. Sir John Hawkshaw, formerly consulting engineer, now undertook the responsibility of chief engineer. Mr. Chas. Richardson became joint engineer, and as such could advise, but Sir John Hawkshaw would decide. Mr. Thomas A. Walker took

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