. The Encyclopaedia Britannica; ... A dictionary of arts, sciences and general literature . l teeth, and driven by compressed air; the usual rate otprogress was 16 lineal yards per day. A partially constructed subaqueous tunnel now lies urownea underthe Hudson river at New York. An attempt was made to drivea double tunnel through the mud and silt forming the river 1880, when about a hundred yards had been completed, thewater burst in, and twenty men were drowned. Work was sub-sequently resumed on the following plan (see fig. 2). A pilot tunnel,consisting of an iron tube of 6 feet 6 incl
. The Encyclopaedia Britannica; ... A dictionary of arts, sciences and general literature . l teeth, and driven by compressed air; the usual rate otprogress was 16 lineal yards per day. A partially constructed subaqueous tunnel now lies urownea underthe Hudson river at New York. An attempt was made to drivea double tunnel through the mud and silt forming the river 1880, when about a hundred yards had been completed, thewater burst in, and twenty men were drowned. Work was sub-sequently resumed on the following plan (see fig. 2). A pilot tunnel,consisting of an iron tube of 6 feet 6 inclies in diameter, wasadvanced from 30 to 40 feet ahead of the main tunnel, to form a firmsupport for the iron plates of the latter by means of radial air, pumped into the tunnel at a pressure of about 20lb per square inch, prevented the weight of silt and water fromcrushing the plating and flowing into the tunnel. The excavated 624 TUNNELLING silt waa mixed with water and ejected by compressed air. Betweenthe shafts the length of the proposed tunnel is 1 mile, and about. jnc-cighth of the distance had been accomplished when the workswere stopped for financial reasons. Small Bubaqneous tunnels have been driven through clay withoutdifScalty under Lakes Michigan and Erie, and elsewhere in England a heading was driven nearly across the Thames in 1S07,and eighty years later two 10 feet 6 inch iron-lined tunnels wereconstructed under the river close to the foundation of LondonBridge by Mr Greathcad, with the aid of a simple annular shieldadvanced by six bydraidio presses. ^Vhere open gravel or waterhas to be tunnelled through a diaphragm must be fitted to theshield. Mallet proposed in 1S58 to carry in this way a tubulartunnel across the English Channel Various plans have beensuggested for the remuval of the soil in advance of the shield. MrGrea-head would effect it by the circulation of a closed current ofwater, carrying the stuff through the shield from fr
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