Engineering Feat

Manawatu Times, Volume 63, Issue 309, 30 December 1938, Page 10

Engineering Feat

UNDERGROUND RAILWAY ON STILTS A few weeks ago the newspapers in New Zealand published u cablegram telling of tho near completion of a remarkable engineering feat in the London underground railways. The detail s , of the work, Avliicli is now completed, are explained by C. A. Lyon in the following article which was published in tho Sunday Chronicle. A job that would have tested the wisdom of Solomon and tried the patience of Job is nearing completion in the East End of Loudon, he says. Tho scene is the London underground railway near Aldgato. The problem might be called: “Hoav to make a tunnel outside another tunnel in the bowels of the earth and then knock down the old tunnel and lay the vails in tho neAV and do it all Avithout stopping the trains.” In the Petticoat Lane area of I.ondon, just past the old eastern gates of the city, there is a little triangle of underground lines. Tho sides of this triangle aro so short that modern trains of eight cars stick out at the ends. The overlapping thus caused makes Aldgatc a bottleneck. It is, iu fact, the Aveak point on the whole London underground system. It causes dozens of other stations on mauy lines to have a worse service than they otherwise would. It stands in the Avay of progress. After much thought tho engineers decided that the only remedy Avas to lengthen two of the sides and move Aid gate East station further east along tho line. Like this:

To make the south side Avas a straightforward job of cutting a neAV 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 Avere great. The earth in which the neAV tunnel Avas to be built was a maze of cables and pipes serving half London. The new tunnel had to have its floor partly 7ft. below the floor of the old one to enable the new station booking halls 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 be 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 theso difficulties was triumphantly overcome. Work began two years ago. The Uuc runs along the line of Whitechapel High Street. They put a hoarding all down the middle of the street and confined the traffic to the southern half. They wnipped up the pavement and dug a trench 400 ft. long aud 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 ah interruption of the service. They moved the sewers and the water and the electri-

city. Thousands of now connections—all made without a hitch. Then all along the trench they built the north wall of tho tunnel in concrete 4ft. to 10ft. 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 ioundations 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 tho air supported on beams. And not a crack has appeared in a single walll Two walls up. Now the roof. In the short four hours of each night when the trains were not running a kind of false roof made of girders and corrugated iron was hoisted up on 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 line because of the false roof. During the night long trucks would be towed iuto the tunnel. Each truck boro a half-girder weigning up to 20 tons. The girder was delicately balanced on a turntable in the middle of the truck, and in this position it had been towed down from the makers in Monmouthshire. When the truck was exactly in position 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 oa the other set of rails, and the two halves were bolted together.

This had all been rehearsed in a dummy tunnel of Avood in Monmouthshire. Now there are two Avails up, tho neA\ 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 Avere 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 wooden trestles to support the rails. The tunnelling was repeated and repeated until all the line was on trestles. This is the position at this moment. The whole line has been transferred to a 1400 ft. timber viaduct. Not a train has been stopped. Nothing has e\’cr been done like it