A Treatise On The Principles And Practice Of Harbour Engineering

BREAKWATER CONSTRUCTION. 169 object of these was to prevent the sliding of the blocks transversely when struck broadside by a heavy sea. The system, however, did not prove a success, and is unlikely to be repeated. Both the foregoing arrangements are costly and view may be achieved to some extent by means of bed-plugs. These are projections of stone or iron standing up above the level of one course of blocks and fitting into apertures in the under- side of the next course. Metal crampe form an effective connection, pro- vided they are protected from the possibility of rusting and corrosion. This can only be satis- factorily realised by bedding them below the tedious. The object in Fig. 143.—Bed-plug. in Portland cement. surface of the stone and completely inclosing them Sloping Bond.—The term sloping bond has been applied to an arrange- ment of blocks whereby they lie tilted on end a little out of the vertical—the angle of inclination varying from 80 to 60 degrees, or rather less. By this system the blocks are fairly free to slide, in case of settlement, without disturbing the adjoining courses. When, however, as in many cases, dowelling introduced, this freedom of action exists only to a restricted extent, the frictional resistance to movement being considérable. The horizontal bonding of blocks — of dubious advantage, as it is in the upper part of a breakwater where the blocks can be accurately adjusted, and the bed-joints well flushed with cement—is a matter of almost positive harm in the courses which lie below water level, where, in most cases, blocks have to be laid without bedding, and where the joints are left open. It is manifest that, under such circumstances, the blocks are not bearing equally on their beds, and it is readily conceivable that a long block extending over three others in a lower course might only be and bed-plugs are also Fig. 144. — Sloping Bond of Break- supported at each end. The risk of fracture waters. See also fig. 129, p. 157. wQuld then be very great During the progress of the work, and especially at the commencement of a winter season, or other period when operations are intermittent or entirely suspended, care should be taken to see that the end blocks of the work actually executed are amply secured. Grouting 'under Water.—The joints of work under water may be filled, to a certain extent, by means of grouting from the surface. A pipe or tube is arranged so as to communicate with the part proposed to be dealt with, and through this tube, under a considerable head or under direct