The Life of George Stephenson and of his Son Robert Stephenson / Comprising Also a History of the Invention and Introduction of the Railway Locomotive

by Samuel Smiles

The Tunnels on the line are eight in number, their total length being 7336 yards. The first high ground encountered was Primrose Hill, where the stiff London clay was passed through for a distance of about 1164 yards. The clay was close, compact, and dry, more difficult to work than stone itself. It was entirely free from water; but the absorbing properties of the clay were such that when exposed to the air it swelled out rapidly. Hence an unusual thickness of brick lining was found necessary; and the engineer afterward informed the author that for some time he entertained an apprehension lest the pressure should force in the brick-work altogether, as afterward happened in the case of the short Preston Brook tunnel upon the Grand Junction Railway, constructed by his father. The pressure behind the brick-work was so great that it made the face of the bricks to fly off in minute chips, which covered his clothes while he was inspecting the work. The materials used in the building were, however, of excellent quality, and the work was happily brought to a completion without accident.

At Watford the chalk ridge was penetrated by a tunnel about 1800 yards long, and at Northchurch, Lindslade, and Stowe Hill there were other tunnels of minor extent. But the chief difficulty of the undertaking was the execution of that under the Kilsby ridge. Though not the largest, this is in many respects one of the most interesting works of the kind. It is about two thousand four hundred yards long, and runs at an average depth of about a hundred and sixty feet below the surface. The ridge under which it extends is of considerable extent, the famous battle of Naseby having been fought upon one of the spurs of the same high ground, about seven miles to the eastward.

LINE OF THE SHAFTS OVER KILSBY TUNNEL. [By Percival Skelton.]

Previous to the letting of the contract, the character of the underground soil was fairly tested by trial shafts, which indicated that it consisted of shale of the lower oolite, and the works were let accordingly. But they had scarcely been commenced when it was discovered that, at an interval between the two trial-shafts, which had been sunk about two hundred yards from the south end of the tunnel, there existed an extensive quicksand under a bed of clay forty feet thick, which the borings had escaped in the most singular manner. At the bottom of one of these shafts, the excavation and building of the tunnel were proceeding, when the roof at one part suddenly gave way, a deluge of water burst in, and the party of workmen with the utmost difficulty escaped with their lives. They were only saved by means of a raft, on which they were towed by one of the engineers swimming with the rope in his mouth to the lower end of the shaft, out of which they were safely lifted to the daylight.

The works were of course at that point immediately stopped. The contractor who had undertaken the construction of the tunnel was so overwhelmed by the calamity that, though he was relieved by the company from his engagement, he took to his bed and shortly after died. Pumping-engines were erected for the purpose of draining off the water, but for a long time it prevailed, and sometimes even rose in the shaft. The question arose whether, in the face of so formidable a difficulty, the works should be proceeded with or abandoned. Robert Stephenson sent over to Alton Grange for his father, and the two took serious counsel together. George was in favor of pumping out the water from the top by powerful engines erected over each shaft, until the water was fairly mastered. Robert concurred in that view, and, although other engineers who were consulted pronounced strongly against the practicability of the scheme and advised the abandonment of the enterprise, the directors authorized him to proceed, and powerful steam-engines were ordered to be constructed and delivered without loss of time.

In the mean time Robert suggested to his father the expediency of running a drift along the heading from the south end of the tunnel, with the view of draining off the water in that way. George said he thought it would scarcely answer, but that it was worth a trial, at all events until the pumping-engines were got ready. Robert accordingly gave orders for the drift to be proceeded with. The excavators were immediately set to work, and they had nearly reached the quicksand, when one day, while the engineer, his assistants, and the workmen were clustered about the open entrance of the drift-way, they heard a sudden roar as of distant thunder. It was hoped that the water had burst in—for all the workmen were out of the drift—and that the sand-bed would now drain itself off in a natural way. Instead of which, very little water made its appearance, and on examining the inner end of the drift, it was found that the loud noise had been caused by the sudden discharge into it of an immense mass of sand, which had completely choked up the passage, and thus prevented the water from draining off.

The engineer now found that nothing remained but to sink numerous additional shafts over the line of the tunnel at the points at which it crossed the quicksand, and endeavor to master the water by sheer force of engines and pumps. The engines, which were shortly erected, possessed an aggregate power of 160 horses; and they went on pumping for eight months, emptying out an almost incredible quantity of water. It was found that the water, with which the bed of sand extending over many miles was charged, was in a great degree held back by the particles of the sand itself, and that it could only percolate through at a certain average rate. It appeared in its flow to take a slanting direction to the suction of the pumps, the angle of inclination depending upon the coarseness or fineness of the sand, and regulating the time of the flow. Hence the distribution of the pumping power at short intervals along the line of the tunnel had a much greater effect than the concentration of that power at any one place. It soon appeared that the water had found its master. Protected by the pumps, which cleared a space for engineering operations—carried on, as it were, amid two almost perpendicular walls of water and sand on either side—the workmen proceeded with the building of the tunnel at numerous points. Every exertion was used to wall in the dangerous parts as quickly as possible, the excavators and bricklayers laboring night and day until the work was finished. Even while under the protection of the immense pumping power above described, it often happened that the bricks were scarcely covered with cement ready for the setting ere they were washed quite clean by the streams of water which poured from overhead. The men were accordingly under the necessity of holding over their work large whisks of straw and other appliances to protect the bricks and cement at the moment of setting.

The quantity of water pumped out of the sand-bed during eight months of this incessant pumping averaged two thousand gallons per minute, raised from an average depth of 120 feet. It is difficult to form an adequate idea of the bulk of water thus raised, but it may be stated that if allowed to flow for three hours only, it would fill a lake one acre square to the depth of one foot, and if allowed to flow for an entire day it would fill the lake to over eight feet in depth, or sufficient to float a vessel of a hundred tons' burden. The water pumped out of the tunnel while the work was in progress would be nearly equivalent to the contents of the Thames at high water between London and Woolwich. It is a curious circumstance, that notwithstanding the quantity of water thus removed, the level of the surface in the tunnel was only lowered about two and a half to three inches per week, showing the vast area of the quicksand, which probably extended along the entire ridge of land under which the railway passed.

The cost of the line was greatly increased by the difficulties thus encountered at Kilsby. The original estimate for the tunnel was only £99,000; but by the time it was finished it had cost about £100 per lineal yard forward, or a total of nearly £300,000. The expenditure on the other parts of the line also greatly exceeded the amount first set down by the engineer, and, before the railway was complete, it had been more than doubled. The land cost three times more than the estimate, and the claims for compensation were enormous. Although the contracts were let within the estimates, very few of the contractors were able to finish them without the assistance of the company, and many became bankrupt. Speaking of the difficulties encountered during the construction of the line, Robert Stephenson subsequently observed to us: "After the works were let, wages rose, the prices of materials of all kinds rose, and the contractors, many of whom were men of comparatively small capital, were thrown on their beam-ends. Their calculations as to expenses and profits were completely upset. Let me just go over the list. There was Jackson, who took the Primrose Hill contract—he failed. Then there was the next length—Nowells; then Copeland and Harding; north of them Townsend, who had the Tring cutting; next Norris, who had Stoke Hammond; then Soars; then Hughes: I think all of these broke down, or at least were helped through by the directors. Then there was that terrible contract of the Kilsby Tunnel, which broke the Nowells, and killed one of them. The contractors to the north of Kilsby were more fortunate, though some of them pulled through only with the greatest difficulty. Of the eighteen contracts in which the line was originally let, only seven were completed by the original contractors. Eleven firms were ruined by their contracts, which were relet to others at advanced prices, or were carried on and finished by the company. The principal cause of increase in the expense, however, was the enlargement of the stations. It appeared that we had greatly under-estimated the traffic, and it accordingly became necessary to spend more and more money for its accommodation, until I think I am within the mark when I say that the expenditure on this account alone exceeded by eight or ten fold the amount of the Parliamentary estimate."