Jetties and breakwater.pptx

jetties and breakwater

1. CONSTRUCTIONS OF JETTIES AND BREAKWATER STRUCTURES BY : DEV NAIK G023

2. JETTIES A structure of wood or stone extended into the sea to influence the current or tide, or to protect a harbor or beach.

3. Purpose of a jetty In rivers , the jetties divert the current away from the river bank and thus, scouring action is prevented. As the current is diverted into deep waters navigation is also controlled In the sea, jetties are provided at places where harbour entrance is affected by littoral drift or the sea is shallow for a long distance. Thus they extend from shore to the deep sea to receive the ships.

4. TYPES OF JETTIES Type of a jetty depends upon: Physical characteristics of site. Exposure to wind, waves, current, tides. Possibility of ice damage. Meteorological conditions and their effects on water bodies. Types: Random stone Stone and concrete Caisson type Crib Asphaltic material

5. 1. Random stone jetty A rubble-mound structure 1s in fact a long mound of random stone. The larger pieces are placed on the outer face to afford protection from destructive waves, and the smaller sized stones are placed in the interior of the structure. This type is adaptable to any depth, may be placed on any kind of bottom, and absorbs the wave energy with little reflected wave action. This type requires relatively large amounts of material. If not carried high enough, storm waves may sweep entirely over the Jetty and cause a secondary wave action in the protected area, and if the voids between the stone are too large a considerable portion of the wave energy may pass through the structure.

6. 2.Stone and concrete Is a combination of rubblestone and concrete. This type ranges from a rubble-mound structure, in which the voids in the upper portion of the rubble are filled with concrete, to massive concrete superstructure on rubble-mound substructure. The mound is used either as a foundation for a high concrete superstructure or as the main structure surmounted by a concrete cap with vertical, stepped, or inclined face. This type requires less material, and 1sused where the foundation is soft or subject to scour. The superstructure may be undermined by wave recoil down the face; rubble foundations require time to become permanently stable and should be placed year before the superstructure. This type of Jetty, when properly designed and constructed, gives very satisfactory service. Cross-sections of stone and concrete jetties are shown in Figs.

7. 3. Caisson type jetty The first caissons were built of iron but today they are built of reinforced concrete, floated into position. settled upon a prepared foundation, filled with stone to give stability, then capped with cap stones or concrete slab, and, occasionally, parapet walls are added. Some caissons have a reinforced concrete bottom which is an integral part of the caisson, while others, such as the ones used in constructing the Welland Ship Canal, are bottomless and are closed with a temporary wooden bottom which is removed after the caisson is placed on the foundation. Caissons are suitable for depths up to 35 ft. Foundations are either rubblestone alone or piling and rubllestone. Riprap of heavy stone is used along-side to prevent scour, to provide resistance against sliding, and to prevent weaving under wave action. On sand bottom, considerable riprap is required

8. Contd.. The top of the foundation rubble is dressed with crushed stone and leveled by a diver before the caisson is placed. Periods of calm water are necessary to float the caisson into position and sink on the foundation. caissons are satisfactory. If properly designed and placed, Cross-sections of concrete caisson structures are shown in Fig.

9. 4. Crib They are built of timber, and some of the compartments are floored. The cribs are floated into position, settled upon a prepared foundation by loading the floored compartments, after which all compartments are filled with stone. The structure 1s then capped with a timber superstructure which is usually replaced by concrete when the timber decays. Stone-filled cribs can withstand considerable settlement and racking without rupture. Such structures are suitable for depths up to 50 ft. or more. Foundations are the same as for caissons but do not require such careful dressing. Timber structures are not suitable for saltwater where marine borers may occur. In Fresh water, timber-crib structures give long and satisfactory service.

10. 5. Asphalt jetty Asphaltic materials have been used to fill the voids of rubblestone structures above the low-water line.

11. breakwater • Breakwaters are structures constructed on coasts as part of coastal defense or to protect an anchorage from the effects of both weather and long shore drift. • A structure protecting a shore area, harbor, anchorage or basin from wave disturbance. • A barrier that breaks the force of waves, as before a harbor. • Breakwater are the structures constructed to enclose the harbours to protect them from the effect of wind generated waves by reflecting and dissipating their force or energy. Such a construction makes it possible to use the area thus enclosed as a safe anchorage for ships and to facilitate loading and unloading of water by means of wave breakers.

12. Types of Breakwater -Detached breakwate r -Head land breakwater -Nearshore breakwater -Attached breakwater -Emerged breakwater -Submerged breakwater -Floating breakwater

13. Detached Breakwater B reakwater without any constructed connection to the shore. This type of system detached breakwaters are constructed away from the shoreline, usually a slight distance offshore .they are designed to promote beach deposition. A ppropriate in areas of large sediment transport

14. Head land breakwater A series of breakwaters constructed in an “Attached” fashion to the shoreline & angled in the direction of predominant waves - the shoreline behind the structures evolves into a natural “crenulate” or log spiral embayment.

15. Nearshore breakwater • Nearshore breakwaters are detached, generally shore-paralle l • structures that reduce the amount of wave energy reaching a protected area. They are similar to natural bars,reefs or nearshore islands that dissipate wave energy. The reduction in wave energy slows the littoral drift, produces sediment deposition and a shoreline bulge or salient feature in the sheltered area behind the breakwater. Some longshore sediment transport may continue along the coast behind the nearshore breakwater

16. Rubble mound breakwater • Rubble mounds are frequently used structures. • Rubble mound breakwater consists of armour layer, a filter layer &core. • It is a structure, built up of core of quarry run rock overlain by one or two layers of large rocks. Armour stone or precast elements are used for outer armour layer to protect the structure against wave attack. Crown wall is constructed on top of mound to prevent or to reduce wave • A breakwater constructed by a heterogeneous assemblage of natural rubble or undressed stone.• When water depths are large RBW may be uneconomical in view of huge volume of rocks required. • Built upto water depth of 50m.• Not suitable when space is a problem. If the harbor side may have to be used for berthing of ships, the RBW with its sloping faces is no suitable for berthing. • These type of breakwaters dissipate the incident wave energy by forcing them to break on a slope and thus do not produce appreciable reflection.

17. Vertical breakwater • A breakwater formed by the construction in a regular and systematic manner of a vertical wall of masonry concrete blocks or mass concrete, with vertical and seaward face. • Reflect the incident waves without dissipating much wave energy .• Wave protection in port/channel • Protection from siltation, currents • Tsunami protection • Berthing facilities • Access/transport facility • Normally it is constructed in locations where the depth of the sea is greater than twice the design wave height.

18. Contd …

19. Case study for construction of Break water