VARIOUS TYPES OF BREAKWATERS. 



193 



spaces between the bags in bag-work, especially at their ends, 

 it is not desirable to expose a bag-work face to the stroke of 

 very heavy waves. This class of work is therefore best adapted 

 for sites of small or moderate exposure, or for foundations well 

 below the low- water level. 



If protected by a wave-breaker on the weather side, as shown 

 in Fig. 37, bag-work may, however, in some cases be brought 

 up to or above the level of low water with advantage ; but, 

 should it be intended to use the breakwater as a quay, the 

 projecting ends of the bags on the harbour side would be found 

 inconvenient. 



FIG. 37. Type section of breakwater with bag-work base, mass-work superstructure, 

 and pell-mell block wave-breaker. 



A monolithic pier has lately been constructed at Skinning- 

 grove, on the Yorkshire coast. In this pier the concrete forming 

 the base, instead of being confined within temporary frames, was 

 deposited in its loose state, and allowed to take its natural slope. 



The depth at low water springs was 6 feet, and the concrete 

 used was of the following proportions : 2 \ parts of broken slag 

 of varying size, J part of rough gravel, 1 part of sand, 1 part of 

 slag cement. 



It is stated that the loss of concrete due to rough weather 

 was very small. The slope on the harbour side was cut away 

 after the concrete had become hard, in order to enable vessels 

 to lie alongside of the pier. 1 



6. Breakwaters of Concrete Blocks, laid in Sloping Courses. 



Sloping-coursed work in which the blocks or stones are 

 set on edge, after the fashion of steeply inclined beds of stratified 

 rock is very suitable for breakwaters, either of the purely 

 vertical type or in combination with a rubble base. 



1 Engineering, vol. liv. p. 456. 



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