Foundations

Stone, piles, and iron cylinders are used for foundations of moderate depth. Open cai ons are used for depths of water le than 30 ft. Pneumatic piles and cai ons have a limit of ab. 100 ft. Deeper foundations are constructed by the crib method, the crib being forced down by the weight of the superstructure, while the mud and earth are removed by dredging through open pockets. The piers of the Hawkesbury Bridge. -Cai on No. 6 in proce of sinking; showing Excavators and Shore Chains for maintaining vertical position. Hawkesbury Bridge in Australia, the deepest foundations ever constructed, are 161 ft. below the water level. The Poughkeepsie Bridge over the Hudson R. has foundations 130 ft. deep. The largest pneumatic cai ons ever constructed were those of the East River Bridge between Brooklyn and New York 102 by 168 ft., one being sunk to a depth of 78 ft. The pre ure on the base of an important foundation should not exceed 150 lbs. per sq. inch, and it is usually considerably le ; in the Forth Bridge it is ab. 90 lbs. per sq. inch.