A WONDERFUL ENGINEER ING FEAT

Dominion, Volume 32, Issue 66, 10 December 1938, Page 3 (Supplement)

A WONDERFUL ENGINEER ING FEA T

London Underground Railway On Stilts

A few the newspapers in New Zealand published a cablegram telling of the near completion of a remarkable engineering feat in the London underground railways. The detail? of the work, which is now completed, are explained by C. A. Lyon in the following article which was published in the "Sunday Chronicle.”

A job that would have tested the wisdom of Solomon and tried the patience of -lob is nearing completion in the East End of London, he says. The scene is tlie London underground railway, near Aidgate. The problem might be called :—“How to make a tunnel outside another tunnel in the bowels of the earth and then knock down the old tunnel and lay the rails in the new, mid do it all without stopping the trains.” In the Petticoat Lane area of London. just past the old eastern gates of the city, there is a little triangle of underground lines.

The sides of this triangle are so short that modern trains of eight cars stick out at the ends. The overlapping thus caused makes Aidgate a bottle-neck. It is. in fact, the weak point on the whole London underground system. It causes dozens of other stations on many lines to have a worse service than they otherwise would. It stands in the way of progress.

After much thought the engineers decided that the only remedy was to lengthen two of the sides and move Aidgate East station further east along the line. Like this:— To make the south side was a straightforward job of cutting a new tunnel. The north side meant enlarging the old tunnel to take four sets of rails instead of two and to make room for the new station. This was much more difficult.

The way it was done was to create a new tunnel in the earth right round the old one. The difficulties were great. The earth in which the new tunnel was to be built was a maze of cables and pipes serving half London. The new tunnel had to have its floor, partly seven feet below the floor of the old one to enable the new station booking hails to be underground instead of above ground. It seemed impossible to lower the rails without stopping the trains for days.

The new tunnel had to run right through the foundations and cellars of rickety old houses in Whitechapel High Street, and yet the houses must not fall down.

Every one of these difficulties was triumphantly overcome. Work began two years ago. The line runs along the line of Whitechapel High Street. Thev put a hoarding all down the middle of the street and confined the traffic to the southern half.

They whipped up the pavement and dug a trench 1400 feet long and 20ft. deep. They moved the gas pipes that supplied half North London —without the users realising it. They moved the telephone lines of perhaps a hundred thousand subscribers without an interruption of the service. They moved the sewers and the water and the electricity. Thousands of new connections—all made without a hitch.

Then all along the trench they built the north wall of the tunnel in concrete four to ten feet thick.

Then they put down the pavement again, changed the traffic over, and did the same on the other side. Thus was built the south wall.

These walls, particularly the south wall, ran through the cellars and foundations of houses.

Thirty-three houses had their foundations partly or wholly cut away from under them. New concrete support was substituted. The corner of a sevenstorey warehouse weighing a thousand tons now hangs in the air supported on beams.

And not a crack has appeared in a single wall! Two walls up. Now the roof. In the short four hours of each night when the trains were not running a

kind of false root made of girders ami corrugated iron was hoisted up oh pulleys under the roof of the old tunnel. During the day men would chip away a section of the old roof. Nothing would fall on the Hue be cause of The false roof.

During the night long trucks would be towed into the tunnel. Each truck bore a half girder weigh ing up to 20 tons. The girder was deli cutely balanced on a turntable in lb, middle of the truck, and in this posi tion it had been towed down from tlie makers in Monmouthshire. When the truck was exactly in posi tion the girder swung round on its turntable until it was at right angles to the rails and was hoisted into position.

A similar girder was being hoisted up from a truck on the other set of rails, and the two halves were boiled together. This had all been rehearsed in a dummy tunnel of wood in Monmouthshire.

Now there are two walls up, the new roof is on, and the old roof gone. Hoardings were put up and the side walls of the old tunnel were knocked down.

There remained the hardest part of all. The floor question. The rails were left isolated, standing on an embankment of earth. At intervals little tunnels seven feet wide and eight feet high were dug under the rails.

In each of these little tunnels three things were done. First the little section of concrete floor above the tunnellers' heads was torn away with pneumatic drills. Then a section of new concrete floor was made on the ground under their feet. Then the vacant space was filled out with heavy w-ooden trestles to support the rails.

The tunnelling was repeated and repeated until all the line was on trestles. That is the position at this moment. The whole line has been transferred to a 1400-foot timber viaduct. Not a train has been stopped. Nothing has ever been done like it in British railway history before.

The line is now, as it were, in midair.

To complete the job it had got to be lowered down seven feet to the new floor of the new and deeper tunnel. To do this all the gigantic structure of timber and beams which had taken months to put up and screw together, had somehow be whisked away in a few hours. How was it possible to do this? The way in which it was done occupied eighteen foolscap pages of detailed engineers’ instructions, so complicated is it. But I will try to explain it a little more simply. If you were in the tunnel and you looked up at the new concrete ceiling you would see rows of steel hooks embedded. From each of these on the Sunday that the final work was done, hung . a long steel hook. On the end of the hook was a steel chain and a hoisting block such as sailors use to hoist their sails.

The track of 1400 ft. wag divided up into five lengths. As it came to the turn of each of tbe five lengths each of the four rails —it is a double track, of course—was secured by the chains and scores of men hauled on the chains. Two lines of railway track complete with fish plates and sleepers went up in the air. They rose a foot and stayed there suspended for the moment. Then about 200 men rushed to take the viaduct to pieces beneath the hanging rails. Pneumatic spanners specially made for the job unscrewed the 10,000 bolts quicker than any human hands could do it.

As soon as the nuts were undone the beams were laid at the side of the track. The"rails were lowered on to the new track.

The floor of the booking hall was put in, as there was now head room for it. It was the end of a million pounds job.