Annual report of the Boston Transit Commission, for the year ending (1896) (14759490456)

Identifier: annualreportofbo21896bost (find matches)
Title: Annual report of the Boston Transit Commission, for the year ending ..
Year: 1895 (1890s)
Authors: Boston (Mass.). Transit Commission
Subjects: Boston (Mass.). Transit Commission Local transit
Publisher: Boston : Rockwell and Churchill
Contributing Library: Boston Public Library
Digitizing Sponsor: Boston Public Library



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e shield thus servesto hold up the earth for a few feet in advance of the perma-nent walls of the tunnel. The earth as excavated is carriedto the rear from the advance end of the shield through thebore of the shield itself and through the bore of the tunnel,and at some convenient place is hoisted by means of a shaftto the surface. One advantage of the use of this methodis that the surface of the ground is not disturbed at all underfavorable circumstances, except at the shafts where theshields and masonry material are put in and w^here the earthis taken out. The deep dry bed of clay underlying themetropolis of London is extremely favorable for this pro-cess. In soft, water-bearing material, however, where it isnecessary to use compressed air, considerable, and in somecases serious, disturbances of the surface have sometimesoccurred. In the portion excavated this summer of theprojected tunnel under the Spree, between Treptow andStralau, Berlin, considerable settlements took place on the
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Second Annual Report. 27 surface. A blow-out occurred last year from the 11-footcircular tunnel which was being driven under the YarraRiver, near Melbourne, Victoria, by which six men werekilled. Ninety-tive per cent, of all the tunnelling by this methodhas been for sizes much too small to admit of the passage ofa Boston street-railway car. The most famous use of itwas in the construction of the City & South London Railwaytunnels, which have internal diameters of 10 feet 3 inchesfor part of their length, and of 10 feet 6 inches for the remain-der. The tunnels for the Glasgow cable subway have inter-nal diameters of 11 feet; those for the Waterloo & CityRailway in London, now nearly completed, have for theirordinar) sections internal diameters of 12 feet 1; inches. Thetunnels for the Central London Railway from ShepherdsBush to Liverpool-street station, work on which has re-cently begun, will have internal diameters of 11 feet 8;inches. The projected Hammersmith & City Elec