This magnificent undertaking was, however, doomed to a second misfortune, of a more disastrous character, which took place in January 1828, and was attended with the lamentable loss of six lives. "The tide had just began to flow," says Mr Brunei, jun., "and finding the ground tolerably quiet, we proceeded by begin-ing at the top, and had worked about a foot downwards, when, on exposing the next six inches, the ground swelled suddenly, and a large quantity burst through the opening thus made. This was followed instantly by a large body of water. The rush was so violent as to force the man on the spot where the burst took place, out of the frame or cell, on to the timber stage behind the frames." A general retreat instantly took place; but the agitation of the air, by the rush of water, having extinguished all the lights, confusion ensued; the timber stage was thrown over by the torrent, knocking down under it several men, and the tunnel rapidly filled. Those who could get to the eastern arch effected their escape, while others were carried by the force of the current to the end of the shaft.
Of eighteen men, besides Mr. Brunei, jun., who were thus placed at the mercy of the torrent in utter darkness, six were drowned, and the remainder, more or less injured, were taken out of the water for the most part in a state of extreme exhaustion. The foregoing wood cut, which affords a correct representation of the lamentable occurrence, is inserted principally on account of its embracing an accurate longitudinal section of the tunnel, and of the mechanism of the movable shield on the left hand, through the upper part of which the water found entrance; the arched passages delineated in the hack-ground, represent three of the entrances into the eastern arch, which is a parallel tunnel; these arched passages are continued at uniform distances throughout the whole length of the work. One of the tunnels was intended for the traffic from the north to the south shore of the Thames, and the other for the traffic from the south to the north, to prevent interruptions; a flagged foot-path, as well as a paved carriage road, being made in both the east and west tunnels, as shown in the cross section of the work in the lower part of the preceding cut, which we shall presently explain.
Such was the deep interest taken by ingenious and scientific men for the prosecution of this tunnel, that soon after the first irruption, Mr. Brunei received, (according to report,) no less than 260 written plans, which, together with verbal communications, made altogether 400 proposed remedies for the disaster. Amongst these there were some which displayed considerable ingenuity; and the best, according to our information, was the following, which we insert, as the application of the principle of its construction may hereafter prove of eminent utility in tunnelling under a body of water. The inventor was a Mr. Garvey, a modeller, and an active member of the London Mechanics' Institution, and who, we regret to add, fell an early victim to the cholera in 1832. Mr. Garvey's plan, as stated by himself, "consists in placing at the bottom of the river, directly over the part undergoing excavation, a large platform or raft, with ledges proceeding downwards to fix into the soil, to prevent the water from entering the excavation."
The nature and operation of this will be understood by reference to the drawing on page 808, where S S represents a section of the tunnel; R the mud, gravel, etc, constituting the bed of the river; AS, the square platform, about twice the width of the tunnel, consisting of two layers of planks, crossing each other at right angles, and made water and air-tight by a stratum of artificial leather, tarpauling, or other elastic waterproof material, between the layers; G G, and H H, represent sections of the ledges or rims, which may be made of iron, or wood pointed with iron; the platform must be loaded sufficiently to sink in water. F is a pipe for the escape of the air while the platform is descending in the water and E is a pump to draw off the water from under it, when it reaches the bottom; v v are sliding valves, to be opened or shut at pleasure, by the cords passing over the pulleys m m and n n; the bent pipes i i are for the escape of the air or water, from the space between the ledges G and H. When the apparatus is put down to the bottom of the river, the water is to be removed from underneath by the pump E, which will produce a very great hydrostatic and pneumatic pressure on its surface, and cause the points of the ledges, G and H, to penetrate the bed of the river, and the whole to become firmly fixed in its place.
The cavity M, which extends of course all round the raft, is made conical, for the purpose of compressing the soil between the rims as they are forced down, and thus preventing the entrance of the water at the edges.
When the apparatus is to be moved forward to a new station, the pump E is to be converted into a condensing air-pump, by changing the valves; and air is to be forced under the raft till it is disengaged from the bottom, when it can with facility he moved forward in the water, and sunk as before.
When the bed of the river is very irregular and gravelly, it may be necessary to dredge it, and put down clay in some parts before the platform is brought to its place.
Having described that which is stated to have been the best of the rejected plans, (as acknowledged by Mr. Brunei to the inventor of it, the late Mr. Garvey,) we shall proceed to notice that which was unfortunately adopted in preference. The concavity in the bed of the river, and the hole through which the water rushed into the tunnel on the 18th of May, was first filled with clay, bags of clay and gravel; a large flat wooden raft, (without ledges,) was then sunk over the new-made ground, to prevent any sudden displacement of it, and by that means afford a full protection to the workmen, when they might recommence excavating underneath. The water, however, found its way under the raft, and the powerful engine and pumps were employed for a considerable period without lowering the level of it in the tunnel. The works were about half emptied of the water, when the force of the tide raised up one side of the raft, threw off the weights which had kept it down, and it floated up to the surface of the river. The ground in another part, contiguous to the former hole, now gave way, and the tunnel was again filled with water.