A Treatise On The Principles And Practice Of Harbour Engineering

1/2 HARBOUR ENGINEERING. position they were only secured by being packed underneath with smaller stones and by leaning against one another. The stones were not further fixed, therefore, and although they were as closely packed on the surface as was possible, the remaining gaps, especially between the lower portions of the stones, afforded the waves sufficient front for attack. It was for this reason that the joints of the stones were at a later period closed with concrète, when a quiet sea and low water permitted such operations. These measures diminished the destruction, but did not by any means prevent it ; for the chief trouble arose from the insufficient loading of the stones, which could not be altered, and the part of the structure which was most exposed, i.e., the toe on the sea side, could not be strengthened and properly secured. The toe of the slope on the harbour side could be strengthened by forcing in several layers of balks behind the pile walls, and it was against these balks that the cubical stones of the slope were resting. Nothing of the kind, however, was possible on the open water side. Rubble mounds were useless ; for the stones were driven inland or raised up the flat slopes of the moles into the harbour. There was nothing left, therefore, but to place further fascines in front of the slope to fill up the hollows formed alongside the mole, and to restrict further injury to the pavement.”1 Another simple method of breakwater formation is to drive a double row of piles and fill the intermediate space with rubble, the piles being retained in position by longitudinal walings and transverse ties. The piles may be either of whole timber or of iron. In one case, at Touapsé on the Black Sea, railway metals were used for the purpose. On account of the disruptive tendency of the hearting, it is necessary to have good stout piling with strong transverse pieces capable of oftering ample resistance to the lateral pressure imposed upon them. The piles are sometimes driveu in an inclined direction, pointing inwards from the bottom towards the top so as to increase their stability. Examples of Breakwater Construction. North Pier at Tynemouth.2—“ The new length of pier (1500 feet long) is being made of Portland cement concrete blocks bonded from side to side of the pier, no mass work being used except above high water level. The heaviest blocks weigh (in air) from 30 to 40 tons, and those exposed to the sea are faced with Aberdeen granite. The blocks below low water are built without mortar joints, but they are interlocked by round joggles and other means to such an extent as to render relative movement among them impossible. Above low water the blocks are built with mortar beds, the joints being also grouted up. The material overlying the new foundations is excavated by means of grabs, and as soon as the grab has worked down to the shale, a diving-bell is used to level the bed for the blocks. 1 Anderson on Breakwaters, Proc. Int. Nav. Cong. Milan, 1905. 2 Barling on Tyne North Pier Reconstruction. Min. Proc. Inst. Mech. E Newcastle Meeting, July 1902.