ENCLOSJN-G DAMS. 75 



tively at about 18 feet and 30 feet from the bottom of the basin ; 

 the intention of this bracing was to prevent the dam losing its 

 symmetrical form, all the parts being so attached as to resist 

 strains, whether of tension or compression. Beyond this there 

 was no shoring, for the only piles provided within the dam had 

 simply to support the bracing, though of course forming part of 

 the whole. 



The ends of all the shores or braces abutted against massive 

 oak seatings, so as not to admit of much compression in any part. 

 After the piling and other timber-work was so far completed, a 

 slight amount of dredging between the piles was done to remove 

 chips or similar rubbish. Stamshaw clay puddle was then filled 

 in to a height of about 2 feet above the lower waling, the inner 

 row of piles having been carefully caulked to about 1 foot below 

 that waling ; the clay being rather higher against the inner row, 

 the water from this level was resisted only by the inner row. 

 The outer row of piles had, however, been carried up so as to 

 come above the upper \valing with a view to protect the inner 

 piles from injuiy, and to make the dam more rigid against pos- 

 sible blows from vessels using the steam basin ; distance-pieces 

 were also inserted between the upper walings, with diagonals 

 again carefully fitted between them, the farther to carry out this 

 idea. Through the lower walings 2J-inch tic-bolts, spaced about 

 6 feet apart, passed, under the heads and nuts of which heavy 

 cast-iron plates, 16 inches long by 12 inches wide, were fixed. 

 These plates were webbed at the back to resist pressure, and 

 had the faces next the timber curved in their length, to avoid 

 their cutting the fibre of the timber when the pressure came 

 on ; 2-inch tie- bolts, with plates 9 inches by 13 inches under 

 the heads and nuts, were fixed at similar intervals through the 

 upper walings. The ordinary depth of water against this dam 

 was 29 feet, which was occasionally increased to 32 feet, in 

 order to meet the requirements of some of the heaviest ships in 

 the navy. 



Before the water was removed from inside the dam, and 

 consequently before any pressure came upon it, a straight line 

 was cut upon the timbers forming the upper tier of bracing, 

 and so tightly had everything been previously wedged up that 

 not more than about 4 inches deflection was shown when the 

 water was removed and the full pressure of 29-feet head had 

 come upon it. This was near the crown of the arch, and 



