. Handbook of construction plant, its cost and efficiency. e larger levees the use of thehydraulic suction dredge is entirely feasible in connection withthe use of other excavating machines. By the construction ofthe muck ditch a retaining bank will be built to as great heightas the earth can be made to stand. A similar retaining bank 222 HANDBOOK OF CONSTRUCTION PLANT will be constructed at the other toe of the levee by depositingearth excavated from the nearest margin of the ditch. Thespace between the two retaining walls can then be filled by ahydraulic suction dredge, the discharge pipe be
. Handbook of construction plant, its cost and efficiency. e larger levees the use of thehydraulic suction dredge is entirely feasible in connection withthe use of other excavating machines. By the construction ofthe muck ditch a retaining bank will be built to as great heightas the earth can be made to stand. A similar retaining bank 222 HANDBOOK OF CONSTRUCTION PLANT will be constructed at the other toe of the levee by depositingearth excavated from the nearest margin of the ditch. Thespace between the two retaining walls can then be filled by ahydraulic suction dredge, the discharge pipe being supportedby a cantilever. This machine (Fig. 82), in its present stateof development probably represents the most economical methodnow in use for excavating very large channels, unless the ladderdredge be excepted. The following table indicates the cost of operating a hydraulicsuction dredge on the New York Barge Canal in 1908. Thedredge in question is of modern construction, has a 20-inchdischarge pipe, and cost $115,000. A large part of the excava-. Fig. 82. Hydraulic Suction Dredge, Showing Discharge PipeSupported by Cantilever. tion was in stiff clay, though a part was in sand. The claywas of such firm texture that after remaining on the groundover winter the pieces had the same shape as when they weredischarged from the end of the pipe line, still showing themarks of the cutter. While removing the old rock wall of thecanal, the dredge was stopped sometimes twenty times a day,it is said, for removing boulders from the pump. Once duringthe season the dredge was sunk to the bottom of the the work was favorable, and the excavation madewas representative of the capacity of the machine in ordinaryclay soil. The charge against plant is intended to cover interestand depreciation at 15 per cent per annum. Under Materialare included coal waste, tug hire, and similar items. DREDGES 223 COST OP OPERATION OF HYDRAULIC SUCTION DREDGE ON THE NEW YORK BARGE CANAL FOR T
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