A Treatise On The Principles And Practice Of Harbour Engineering

184 HARBOUR ENGINEERING. 5 to 4 on both sides, had to be reduced 011 the sea face to 5 to 2, and a further modification of the original design was the extension of the riprap 011 the port side so as to afford an additional 16 feet of base. The original and modified outlines are shown in the section. The work was completed in 1903. Un- fortunately, the subséquent history of the breakwater has not been free from disappointing incidents M. de Joly reports as follows : — “ In spite of their great size the artificial blocks are not absolutely stable. A north-westerly storm which occurred in February 1904, destroyed the regularity and symmetry of the breakwater in a few hours : not only did the blocks settle unevenly and cant slightly towards the interior, but some of them becaine wedged in after pivotting about their western ends. The displacement of the eastern ends amounted to as much as 6 inches, giving an angular slew of ^j^. “ An attempt was made to avoid any return by coucreting up the vertical Fig. 157.—Section of Bizerta Breakwater. joints, which occur every 100 feet or so; simultaneously the interior slope was strengthened as previously described. “The filling of the joints was just about finished when, at the end of November 1904, a storm arose from the east and occasioned further important dislocations. All the joints were split and some of the blocks seriously damaged. Fears are entertained that any subsequent storm will so increase these injuries as to completely fracture the joints and split the blocks vertically. “ It seems evident from the November experience, which is different from that of the February one, that the width of 26 feet 3 inches is somewhat insufficient for a 5000-ton block under existing circumstances, and that undoubtedly it would have been preferable to increase the width to say 33 feet, leaving the vertical joints between the blocks open so as to allow of settlement freely without tension or shear. Also, it may be questioned whether it would not have been a better plan to make the topmost layers of