CALAIS DOCKS. 



195 



stout sheet-piling; bearing-piles were also driven by the aid 

 of the water-jet system with a 50-feet head of water over the 

 whole area enclosed. Above the piles was laid a bed of con- 

 crete 4 feet 11 inches thick, on which the masonry, laid entirely 

 in Portland cement, was commenced. Whilst the bed of con- 

 crete was being deposited, the whole area was kept submerged 

 under 3 feet of water. 



Calais Graving Dock. 1 This dock (Figs. 178 to 181) was con- 

 structed from the design of Mr. Yetillart, the engineer to the 

 Port of Calais. The total length from the line of the entrance 

 piers to the coping at the head is 546 feet 10 inches. On the 



FIG. 179. 



FIG. 180. 



. 

 FIG. 181. 



floor, from the inner recess of the caisson to the base of the 

 rounded end, the length is 463 feet 3 inches ; the additional 

 length obtainable by putting the caisson in the outer stop is 

 44 feet 3 inches ; therefore the maximum length on the floor 

 at the invert level is 507 feet 6 inches. The width of the floor 

 between the bottom altars is 30 feet 6 inches, including the side 

 drainage channels 15| inches wide, which are carried round the 

 floor of the dock. The four first altars, starting from the bottom 

 of the dock, are 13J inches high, and their width 4 feet 3 inches. 

 The width of the dock at the level of the fourth altar is there- 

 fore 64 feet 7 inches. From the top of the fourth altar to the 



1 Engineering, vol. xlvii. 



