Page:The American Cyclopædia (1879) Volume VI.djvu/175

 DOCK 167 water in the dock below the upper platform at low tide. The entrance from the tidal basin into the dock is by means of a single pair of gates, similar to those of the lock, placed be- tween two dumb jetties or walls which sepa- rate the basin from the dock. (See fig. 1.) The basin and dock are 4,050 ft. in length and 1,050 ft. in width. There are six jetties the two just mentioned, which are each 485 ft. long, and four others extending from the north wall into the dock a distance of 581 ft., including the pointed terminations. These with the sides of the dock and basin afford nearly three miles of quay room. The four in- terior jetties are each 140 ft. wide for 497 ft., and the surface of the quay varies from 6 to 9 ft. above high-water mark. The side walls are vertical and constructed of cast-iron piles 7 ft. apart from centre to centre, filled in be- tween with brick set in Roman cement, the brickwork being arched toward the back to give strength. Behind the piles and brickwork there is a wall of concrete which was carried up from below the clay bottom, and behind this a filling of clay. The piles are T-shaped in section, and are 35 ft. long and 1 ft. wide on the face, averaging 1 m - in thickness, and weighing about If ton each. They are driven to a depth of 28 ft. below high-water mark, and therefore 4 ft. below the bottom of the dock. The brickwork commences one foot above the bottom, and rests upon concrete 3 ft. thick. The wall is covered with a cast- iron plate bolted to the heads of the piles, and upon these lies a timber sill. The piles in the op- posite jetty walls are connected by cross bars, 5 and 17 ft. below their heads. Upon each jetty there is a warehouse 500 ft. long and 80 wide, leaving wharf room 30 ft. wide ; and it is also supplied with nine hydraulic cranes, one FIG. 1. Plan of the Victoria Docks at London. of five tons power at the pointed end, and eight others of two tons power each along the sides. Connected with the north side is a basin which opens into eight graving or dry docks. (For a more detailed description of this work, and also of the docks upon the Tyne, see Spon's " Dictionary of Engineer- ing," London, 1871.) The West India "docks, constructed in 1802 in a gorge in the Isle of Dogs, comprise an import dock of 80 acres, an export dock of 25 acres, communicating with the Thames at Blackwall, and a bond- ed timber dock of 19 acres. The gates are 45 ft. wide, admitting vessels of 1,200 tons. The whole space occupied by docks and ware- houses is 295 acres. The East India docks, also at Blackwall, completed in 1806, belong to the same company as the former. They in- clude an import basin of 18, an export basin of 9, and an entrance basin of 2f acres. The gates are 48 ft. wide, and the depth of water 23 ft. The Commercial docks, situated on the opposite side of the river, existed in 1660 under the name of the Howland great wet dock, and subsequently of the Greenland docks, having been prepared for the accommodation of the Greenland whaling vessels. In 1807 they were greatly enlarged and received their present name, and are now used chiefly to receive ves- sels laden with corn, iron, lumber, guano, and other bulky articles. They cover an area of 120 acres, 70 of which are water. The gran- aries will contain 140,000 quarters of corn. The other principal docks here are the London and the St. Katherine docks, the latter situated between the former and the tower. The warehouses in the St. Katherine docks are built upon the water's edge, without a quay ; but this plan has since been disapproved on_ ac- count of interference with the ships' rigging. The docks at Liverpool were authorized by an act of parliament in 1708. There are numerous other mercantile wet docks in Great Britain, a list of which, including entrance basins pro--