40 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



In cases of scgmental dams of very sharp radius, a difficulty 

 may be experienced in obtaining suitable timber with which to 

 form solid walings. To meet this difficulty, laminated walings 

 have sometimes been adopted, by building up to the required 

 dimensions with planks, care being taken to effectually break 

 joint. 1 



To guard against the risk of floating, which is augmented by 

 any light movement induced by blows from heavy vessels, or by 

 excessively high water, it is a wise precaution to drive the gauge- 

 piles deeper into the ground than is absolutely necessary for the 

 general piling, in order to get a good hold on the bottom. 



With reference to the use of timber as compared with iron, 

 Mr. Abernethy has expressed an opinion that timber is to be 

 preferred, both on account of cost, and the more important 

 element of time. 2 



Dams constructed of a Single How of Timbers. A good 

 example 8 of a dam constructed of a single row of piles was that 

 designed by Mr. B. B. Stoney, for enclosing the foundation of 

 a large bridge over the Liffey. This dam consisted of a 

 single row of whole-timber piles, which were driven until they 

 reached the rock into which the points of the piles were 

 embedded, and were shored against the outside pressure in the 

 usual manner. The piles were sawn parallel on the meeting 

 sides, and driven in close contact, and the joints caulked. 

 Before driving, the piles were fastened together in sets of three, 

 by means of elm dowels sunk 3 inches into each pile at 

 intervals of about 8 feet, and with IJ-inch wr ought-iron dogs. 

 This left only every third joint to be caulked after the piles 

 were driven. The total depth of this dam was 25 feet below 

 high water, or 17 feet below low water, to the rock, which 

 was taken out to 20 feet below low water. This dam proved 

 thoroughly efficient in every way. 



A dam used in constructing a quay wall at Kio de Janeiro 4 

 is shown by Figs. 24, 25. This dam, which was constructed in a 

 depth of 25 feet at low water, and 30 feet at high water, 

 consisted, on three sides, of a single row of grooved and tongued 

 piles, 11. inches square, driven into the silty clay bottom to a 

 total depth of 42 feet 6 inches below high water, or 22 feet 

 6 inches into the ground. The tongues were made of flat bar- 



1 M.P.I.C.E., vol. li. p. 152. * Ibid., vol. liv. p. 27. 



* Ibid., vol. li. p. 155-160; vol. Ixii. p, GO. * Rid., vol. xxxi. p. 28. 



