Jet′ty.
1. (Hydraulic Engineering.) a. A construction of wood, rubble-stone, or masonry projecting into the sea and serving as a wharf or pier for landing and shipping, or as a mole to protect a harbor. Although limited to no particular form, a very common construction of the jetty is a timber framing A, secured by piles or loaded with rubble. It is often built in the manner of a sea-wall; having a double row of sheeting piles, the interval filled in with rubble or beton. The latter is excellent. The term jetty is also applied to expensive and solid erections of masonry, and to hards or landing-places for boats. Teford's jetty B at the eastern arm [1213] of Kingstown Harbor, Ireland, is an example of a jetty made of rubble, with a track and parapet of coursed masonry. The foreshore, in most works of this kind, is faced with pitched stones, that is, an outer layer in which the undressed stones are not laid at random, but deposited end on, beginning at the lower edge, and so caused to bind and become mutually sustaining. Jetties of masonry (C) have usually ashlar facings and heartings of rubble or concrete. The walls filled in with beton will be nearly equal to a solid mass; in fact, beton itself makes a wall of such tenacity that its strength is equal to a homogeneous block. When the ashlar masonry is filled in with earth it requires a bond; when this is of masonry, the counterforts take the form of division-walls, which thus reduce the jetty to a series of compartments. The stones of these horizontal bonding courses should be cramped and joggled together, and the top carefully paved to prevent infiltration. The southern jetty (D) of the port of Havre is exposed to violent storms and a powerful littoral current. It exemplifies the ashlar facing, horizontal bonding-walls, rubble filling, paving, parapets, aprons of piles and pierre-perdue to protect the foundations from the repercussion of the waves, all executed in a style which has provoked the admiration of those who have understandingly examined it. In the course of the improvement of the months of the Rhine, the northern arm of the Maese is being widened, dredged, and extended into the sea by jetties of about 1,200 feet long and 1,000 yards apart. The mode of their construction is as follows: — Long fascines are formed of brushwood and placed upon the shore near the site of the works; they are laid in courses, each course being at right angles or oblique to the previous one, until a thickness of about three feet has been obtained; strong stakes are then driven through the mass at frequent intervals, which project about 18 inches at the bottom, and 12 inches at the top. The stakes are then tied together with a willow binding. The work is made in sections measuring about 40 yards by 20 yards. When completed, it is floated to the site of the jetty, and sunk into its place by being evenly loaded with basalt stone, which is brought down the Rhine from quarries near Andernach. Piece after piece of this sort of work is added, until it covers the whole breadth of the base of the jetty for a portion of its length, after which another layer is formed in the same manner, and so on until the requisite hight and breadth of the jetty have been obtained, when a fresh length in advance is commenced. The projecting stakes soon take firm bold of the layers above and below them, the sand silts into the interstices of the brushwood, and in a few years forms an almost impenetrable mass, which, when consolidated, is covered with a paving of large basalt stones. b. A structure round the piled foundation of a bridge pier. 2. The part of a building which jets or juts over beyond the ground plan.
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