i$6 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



length, and between them like distances were left, and were 

 filled in afterwards when the first sections had been raised to 

 a certain height ; in other words, the sections of wall up to a 

 height of 23 feet were divided from each other in the first 

 instance by sections of undisturbed material, by which means 

 the treacherous nature of the ground was more easily dealt 

 with. The wall was thus built in the dry, the water from 

 infiltration was pumped out by machinery conveniently placed 

 for the purpose. 



The foundation consisted of a mass of concrete 10 feet 

 thick, composed of 2 parts of Pozzuolana to 1 of lime and 3 

 of broken stone. The body of the wall was of rubble set in 

 Pozzuolana, and the facing of bricks and ashlar stone, the former 

 being more convenient to handle than ashlar in the close 

 timbered trenches. 



Since these works were completed, only a slight settlement 

 had been observed in a few places, but the walls had nowhere 

 been thrust out of the perpendicular. 



This result indicated that if careful precautions were taken in 

 the erection of dock walls on ground peculiarly liable to slip, as 

 at Spezzia, and a sufficient weight given to the wall to sustain 

 unusually great lateral pressure, an almost certain immunity 

 from failure may be secured without resorting to bearing- 

 piles. 



The Rhone. At the mouth of the Rhone, facing the river 

 entrance to the St. Louis Mari times Canal, 1 the quay walls are com- 

 posed of four concrete 

 blocks (Fig. 138), each 

 11 feet long, 8 feet 7 

 inches wide, and 4 feet 

 1 inch high, built up on 

 a base of pierres per- 

 dues, 26 feet wide and 

 G feet 6 inches high. 

 This concrete wall was 

 surmounted by a su- 

 perstructure of rubble 

 FIG. 138. faced w ith ashlar, 8 



feet 3 inches in height, and 9 feet 6 inches wide. The total 

 height from the coping to the bottom of the dredged trench was 

 1 M.r.LC.E., vol. lv. pp. 105, 106. 



