CONCRETE TUNNEL LINING

Press, Volume LXXIV, Issue 22388, 29 April 1938, Page 12

CONCRETE TUNNEL LINING

EXPERIMENTS IN LONDON

TUBE RAILWAY

EXTENSION THOUGHT LIKELY

Crjtgu OTTB OWB COBBBSPONSBHT.) v LONDON, April 2. A new principle ,in tunnel construction, at least for London, is being adopted in a two and a half mile extension of one of the tube lines. For 40 yeafs cast iron, in the forfn of segments placed in position and bolted together by band, has been used tt? line tube tunnels. The possibility of using reinforced concrete has been investigated for some time, and when, six months ago, serious difficulty was found in obtaining supplies of cast iron for new wor.ks, experiments were made with a concrete segment claimed to be as strong and as easily handled as metal. Many interesting tests were carried out. An experimental tunnel," Bft 6in in diameter,- was driven, half of it formed of cast iron ringi • and half of concrete rings. The top of the tunnel, was only 2ft 6in below the surface of the ground, so, to represent greater depth, a stack of iron weighing 175 tons was built immediately over the tunnel. Under this burden, the concrete proved to be as capable of carrying weight as the cast iron. The same result followed when 228 tons of iron were piled on top of a tunnel 12ft in diameter.

To prevent the : concrete, crumbling where the segments were bolted together, the holes were lined with steel ferrules. Double the customary number of steel rod reinforcements were used in the. concrete. The thickness of the. skin of the concrete segments was 2in. compared with Jin in the case of the cast iron’segments, but because the concrete was lighter than iron the total weight was not increased. In view of these satisfactory tests it was decided to use the new segments-on a wonting section of the tubes. If the trial section proves successful, the principle will probably be extended considerably.