Engineering Wonders of the World
Volume I

THEIR DESIGN AND CONSTRUCTION. BY HARLEY H. DALRYMPLE HAY, M.Inst.C.E. PART I. The Deep-level Railway System of London is so unique that the following account, from the pen of an Engineer who has been associated with the construction of several of the “Tubes,” cannot fail to be of general interest. THE terrible congestion of traffic in the streets of the world’s greatest city, and the need for more rapid transit than could be afforded by road vehicles, led to the construction of the Metropolitan Rail- ways of London. These were laid out at a Need for Relieving the Congestion of London Traffic. shallow depth, and were formed either in open cutting between retaining walls or by the pro- cess of cut-and-covcr under roads. Existing buildings had to be underpinned or otherwise strengthened at many points ; of doing this, added to that of and the cost buying property and way-leaves, granting compensation, and prosecuting the actual engineering work under great difficulties, dis- couraged the immediate extension of under- ground traffic facilities. The present system of deep-level “ tube ” railways, with iron-lined tunnels, has, at least indirectly, its origin in the need for improving communication between the two banks of the Thames. In 1823, Marc Isambard Brunel commenced the Old Thames Tunnel, which, after enormous difficulties had been overcome, was completed in 1840. Brunel was the first engineer to use a movable shield to protect the working face during excavation and while the tunnel lining was being put in behind it. In the year 1862, while constructing the piers of Lambeth Bridge by means of cast-iron cylinders sunk vertically into the London clay, Mr. P. W. Barlow, F.R.S., per- ceived that by using a shield Barlow’s of improved design—so that it Omnibus should advance as a whole unnels. instead of by parts, as did Brunel’s—in conjunction with a cast-iron lining, tunnels might be driven through the London clay as easily as cylinders could be sunk. He therefore proposed a system of “ omnibus ” subways, the first instalment of which was realized in the small tunnel, named