File:The Americana - a universal reference library, comprising the arts and sciences, literature, history, biograhy, geography, commerce, etc., of the world (1903) (14587223767).jpg

Identifier: americanaunivers15beac (find matches)
Title: The Americana : a universal reference library, comprising the arts and sciences, literature, history, biograhy, geography, commerce, etc., of the world
Year: 1903 (1900s)
Authors: Beach, Frederick Converse, 1848-1918 Rines, George Edwin, 1860- Scientific American, inc
Subjects: Encyclopedias and dictionaries
Publisher: New York : Scientific American compiling dept.
Contributing Library: University of California Libraries
Digitizing Sponsor: Internet Archive

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t centre line for the purpose of attacking the excavation at as great a numberof points as possible. They enable the work to be extended both ways from the point where the shaft is sunk and also form points at which the excavated materials are raised from the tunnel; they also permit material for lining or other purposes to be lowered into the excavation and put in place. Central shafts are usually employed, although French engineers frequently adopt side shafts having their axes 30 to 40 feet on one side of the centre line of the tunnel. At the present timepower elevators are used in shafts for raising and lowering men and material. When the shafts are left open and lined where necessary, they become permanent features of the completed structures, affording ventilation.Where shafts are filled after the work is completed they are called temporary shafts, and they may be circular in section as is usuallythe case where they are lined, or they maybe rectangular, their sides being braced with TUNNELS.
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PENNSYLVANIA RAILROAD TUNNEL UNDERNEATH THE HUDSON RIVER. TUNNELS AND TUNNELING timber to prevent material falling in. Centralshaits are more convenient tlian side shafts,ll water flows into tlic tunnel excavation oris found in shaft sinking, it must usually be pumped to the surface. Tunnels are usually classified in relation to the material in which they are driven, such as tunnels in hard rock,in loose soil, in quicksand, cut and cover tunnels, sub-aqueous tunnels. On the whole,hard rock is probably the safest material in which to drive a tunnel and it gives the least difficulty. This is true chielly in view of the effective explosives and convenient power-drills and other machinery now available for the purposes of excavation. Rock tunnels may be driven by using either a heading ora drift, depending upon the local circumstances in choosing the method. Tunnels in soil may involve serious difficulties if the soil is saturated with water. The excavation maybe first made near the top, that is

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