2 o6 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



When the ground had been excavated to a depth of 3 feet 



above low- water 1 < \ -1 . 

 water made its ap- 

 pearance, requiring 

 the constant use of a 

 12-inch centrifugal 

 pump to keep the ex- 

 cavations dry. Oper- 

 ations were continued 

 until a depth of 27 

 feet below coping was 

 reached, at which 

 level triune concrete 

 cylinders were sunk 

 to form the founda- 

 tion of the wing walls 

 and the apron of the 

 entrance (Figs. 192 to 

 194). These cylinders 

 were 9 feet in exter- 

 nal, and 5 feet 9 

 inches internal dia- 

 meter. They were 

 sunk 24 feet into the 

 ground, the tops being 

 3 feet below the sill 

 at the centre (Fig. 

 194). When down to 

 the required depth, the 

 interior was clcmvd 

 out, and filled up 

 with concrete. 



In order to deal 

 with the heavy leak- 

 age met with in the 

 gravel strata into 

 which the excava- 

 tions had to be car- 

 ried, the following 

 course was adopted. 

 One of the triune 



