SETTLEMENT AND BOND. 283 



Thus a settlement, even to the extent of 3 feet, occurring at 

 any point, and gradually dying away on either side of it in a 

 distance of, say, 200 feet, would be met by the opening of each 

 joint, assuming there to be 100 of them, to the extent of less than 

 yJ-0 of an inch, or little more than what is termed a " hair-crack." 



A good bond for sloping block-work is that which was 

 adopted for the Colombo breakwater (Fig. 38, p. 195). 



In that work, the blocks forming each tier, or tilted course, 

 " broke bond " to the extent of about 5 feet, and the tiers were 

 further bonded together by means of vertical grooves 18 inches 

 wide, which, coming opposite to each other, formed continuous 

 holes from the top to the bottom of the work. These were filled 

 with strong soft concrete in bags, well rammed in, which, when 

 hard, performed the part of dowels or joggles. There were five 

 such continuous dowels in each tier of blocks, and they were 

 placed about 6 feet 6 inches apart. 



In order to prevent blocks sliding upon each other in 

 horizontally coursed work, horizontal dowels may be introduced, 

 or short pieces of bar steel or iron," 1 may be placed vertically 

 half in each course, and grouted either through a hole provided 

 for the purpose, or through the lewis-holes in the blocks, as may 

 be most convenient. 



Instead of introducing pieces of rail, recesses may be formed 

 in the blocks immediately underneath the lewis-holes, which, 

 when grouted, will form cement dowels. The introduction of 

 short pieces of rail or iron dowels, however, adds greatly to the 

 strength of any such arrangement. 



In the Tyne breakwaters, Mr. P. J. Messent, M. Inst. C.E., 

 with the object of preventing the sliding of one course upon 

 another when struck by a 



, . J Vertical section. 



heavy sea, introduced what 

 he .called " piano blocks." 

 This system of bond is illus- 

 trated in Fig. 96, the " piano 



blocks" being indicated by FIG. 96. Sketch showing bond of blocks in Tyne 

 Shading. breakwaters. 



In addition to the several kinds of bond already described, 

 iron cramps and bolts are frequently used for tying work 

 together. 



1 Old permauent-way rails do very well. 



