122 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



down on the ground ; their dimensions were marked, and they 

 were spaced so far from each other as to leave a distance of 15 

 inches between the adjacent sides of the curbs. Experiments 

 had shown that if in sinking a row of such foundation blocks 

 every alternate one was lowered, the condition of the intermediate 

 ground remained unaffected; the work was therefore carried 

 on in this manner until all the curbs were in place and spaced 

 at such intervals apart that there was a distance of 15,J 

 inches between them (Fig. 87). None of the curbs were filled 

 with concrete until the adjoining ones were in place, in order 

 to avoid any trouble that might arise from the displacement 

 of the sand beneath the foundations. When a series had been 

 completed and filled, the consecutive blocks were cemented 

 together. This was effected in the following manner. On the 

 front and back faces of the blocks iron plates (Fig. 87) were 

 sunk by means of a water jet to the bottom of the foundations 

 which thus enclosed the space between two consecutive blocks. 

 The sand was then removed by the sand pumps, and the space 

 filled in with hydraulic concrete. 



The larger blocks were sunk with as much accuracy as the 

 smaller ones, but some difficulty was experienced in connecting 

 them together on account of the sand forcing its way through 

 the joints between the plates and the faces of the blocks. 



The time occupied in sinking the smaller blocks to a mean 

 depth of 15 feet varied from 10 hours to 35 hours, or an 

 average of 22 hours for each foundation curb. The volume of 

 sand displaced per hour was 225 cubic feet. The larger blocks 

 occupied a longer time in sinking, the average being 44 hours 

 each, and the amount of sand displaced 380 cubic feet per hour. 

 The sinking of some still smaller blocks was carried on very 

 rapidly, about 440 cubic feet of sand being displaced per hour. 



The sections of the north-eastern and south-western quay 

 walls of the outer harbour are shown by Figs. 80, 81. The 

 superstructure is entirely of solid masonry set in cement 

 mortar. Near the base the face is vertical up to the lowest 

 sea level ; above this, the face has a batter of 1 in 10. 



The quay wall of the floating basin, east side (Fig. 82), 

 rests upon a foundation of concrete 20 feet 8 inches wide, 

 carried down to a sufficient depth into the sand to secure 

 absolute safety, and enclosed both front and back with closo 

 sheet-piling. The height of the coping above the concrete 



