FO UNDA TIONS. 269 



above the water-level. The pipes should be carried well up, in 

 order that the " head " so obtained may force the grout amongst 

 the stones and out to the margin. By this means, if due care be 

 taken, a secure foundation may be formed; but it is evident 

 that, in the event of the broken stone not being satisfactorily 

 grouted, the very existence of the breakwater would depend 

 upon the marginal bags remaining undisturbed. 



In theory the system has the appearance of being a good 

 one ; but in practice it is found that, if the ground should be at 

 all uneven, it is exceedingly difficult for divers to place the bags 

 sufficiently level and regular to ensure the superposed blocks 

 compressing them all equally. It is, further, not possible to 

 provide against the concrete in the bags, after having been 

 squeezed even assuming that none of the bags have been burst 

 in the process falling away from the blocks to a small extent. 

 The blocks cannot follow such shrinkage, on account of their 

 being hard bedded on the broken stone ; so, when once the bags 

 have become slack \ inch settlement would suffice to free them 

 they are liable to be withdrawn by the sea, in which case 

 the broken stone would soon follow, thus causing voids, and 

 endangering the stability of the work. 



The foundation of the landward portion of the Hermitage 

 breakwater at St. Heliers, Jersey, was formed in this manner, 

 and it did not prove satisfactory. In reporting upon it, 

 Mr. Kinipple stated 



" From the foundation area, many of the smaller hags, the whole 

 of the broken stone, and some of the rubble and concrete filling 

 between, had been washed out by the action of the sea, leaving 

 cavities, in some cases, large enough to admit of a diver getting 

 underneath the foundation course of blocks " (Engineering, vcl. liii 

 p. 647). 



When the bed of broken stone can be placed at a sufficient 

 depth below low water, and secured by means of an efficient 

 apron, it forms a useful and ready means of preparing the bed 

 for the foundation course, and it is much used in founding block- 

 work upon rubble mounds ; but under other conditions it cannot 

 be considered a safe mode of construction, unless the broken 

 stone be effectually grouted, as just described. 1 



1 The system of passing cement grout through water for such purposes as the 

 stoppage of leaks in lock sills, etc., has been known and practised for a number of 



