204 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



was preceded by the sinking of a new well and the erection 

 of a new building to contain the pumps, engines, etc. 



The original building was founded partly upon piles and 

 partly by the aid of compressed air. In order to avoid the 

 inequalities in bearing this method of construction would have 

 engendered, a method was devised of founding the entire build- 

 ing on concrete by the aid of compressed air, and special arrange- 

 ments which enabled the work to be executed at a pace but 

 little above that for pile foundations. These foundations con- 

 sisted of four piers of the following dimensions, one 10 feet by 

 10 feet, one 19 feet 8 inches by 10 feet, and the remaining two 

 32 feet 5 inches by 10 feet. They were constructed of concrete, 

 upon a working chamber also constructed of the same material. 

 The side walls were surrounded by a plate-iron casing, and 

 armed on the lower edge with an iron shoe. 



The iron casing was secured to the concrete by bolts attached 

 to the plates, and embedded in the mass. The whole was further 

 strengthened by anchor-bolts, which tied the shoe to the block 

 forming the top of the working chamber. The object of these 

 bolts was to prevent the displacement of the shoe, should the 

 caisson or chamber encounter an obstruction. 



As regards air and water tightness, the concrete working 

 chamber gave the best results. The arrangement was also one 

 which admitted of a minimum quantity of iron being used and 

 left in the work. 



Sinking the New Pump-wells, and Connecting with the Dock. 

 This work was also carried out by the aid of compressed air, 

 and was executed before the extension of the dock was 

 commenced. 



The caisson was 42 feet 6 inches long by 31 feet wide. As 

 in the case of the large caisson, the ordinary iron roof was 

 replaced by a platform of brick arches upon iron girders. The 

 caisson was sunk at about 3 feet 3 inches from, the outer face 

 of the old work, with the view of clearing the massive founda- 

 tions of the dock, which extended 3 feet outside the back lines 

 of the wall. 



The sinkino- terminated at 44 feet 3 inches below datum. 



O 



It was then necessary to make a water-tight connection with 

 the old dock, at a depth of 26 feet 3 inches below water level. 

 This was effected in the following manner. On three sides oi 

 the well, the masonry was carried up within the casing, whilst 



