66 NOTES ON DOCKS AND DOCK CONSTRUCTION. 



waling to the under side of the top waling on the second row 

 of piles. 



The space between the second and the third rows of piles 

 was filled in with well-rammed clay and stones, a bank of the 

 same material being also placed both inside and outside the dam 

 to increase the stability. 



At either end, where the dam rested upon the rock, 6-inch 

 sheeting-piles were used, secured at the foot to inner and outer 

 sills laid in trenches cut in the rock. 



For controlling the water during construction, and for 

 letting in the water on completion of the work, three trunks, 

 closed with screw sluices, were fixed through the dam with the 

 sills at low- water level. 



When the water was pumped out, the dam proved perfectly 

 tight in every respect, and did not show any straining when 

 the full head of water was brought against it. No pumping 

 was required during the time the dam was in use a period of 

 seven years beyond that which was due to percolation through 

 the strata or rainfall. 



On the completion of the works, preparations were made for 

 removing the dam by digging away the earth and bank from 

 the inside. This having proceeded for some time, water com- 

 menced to leak through the dam. 



The possibility of the dam giving way was at once realized, 

 and endeavours were made to avert the danger by opening the 

 sluices to admit the water; while, however, there was still a 

 head of 10 feet outside, the dam gave way suddenly, an opening 

 being made about 40 feet wide. 



Amsterdam Canal. 1 The circular coffer-dam within which 

 the Zuider Zee Locks of the Amsterdam Ship Canal were 

 constructed was 525 feet inside diameter, and consisted of two 

 consecutive rows of sheet-piles of Dantzig white pine, with a 

 clear space of 6 feet 6 inches between them. 



The outer row of piles was of whole timbers sawn to 12 

 inches wide on the surfaces of contact. For the inner row, the 

 piles were sawn to 8 inches wide on surfaces of contact, except 

 the gauge-piles, which were of whole timbers. 



The puddled clay between the piles was carried up to the level 

 of the ordinary high water, and a mound of sand was deposited 

 on the inside as a counterweight to the pressure of the water. 

 1 M.P.I.C.E., vol. Ixii. p. 11. 



