Study On Measures For Preventing Or Reducing Sedimentation In Alongshore Pile Wharf

With the development of coastal and offshore engineering,the alongshore pile wharf has been widely used in recent years.The velocity of flow in engineering area will decrease with different degree,and the current will move to the non-pile cluster due to the flow resistance of piles,which makes the velocity of non-pile cluster increase.The change of the hydrodynamic conditions will inevitably lead to change in sedimentation,which may affect the normal working of the wharf.For ZhenHai Refining wharf,this paper studied the causes of the berth's deposition by means of current and sediment numerical simulation.Preventing or reducing sedimentation engineering measures were put forward,and the reducing sedimentation effect of the measures were calculated.Meanwhile,simulation of dragging silt with dredgers was done.The main contents and conclusions in this thesis are listed as follow.(1)The tidal current of JinTang channel is mainly reciprocating flow,and tide flow parallels to the bank.The sediment of JinTang channel is from the outer waters instead of the coast,and the main form of sediment transport is suspension.Sediment movement of flood tide is not different with the ebb tide's,and the sediment concentration of spring tide is greater than neap tide's.(2)From offshore to inshore,trend from erosion to siltation was presented.Waters 300 meters away from the wharf showed erosion,and the micro siltation occurred between 60 meters to 300 meters.Siltation gradually occurred within the 60 meters,and heavy silting zone was formed near NO.1 and NO.2 berth,and the max sediment strength monthly could reach 1.05 meters.(3)Causes of sediment deposition include geographic location and terrain,the arrangement and direction of berths,the mooring of ships,the discharge of a adjacent power plant,wharf's pile foundation and dredging and so on.Then analysized the influences of berth deposition on conditions that whether ships docked or not,the adjacent power plant discharged or not,wharf pile foundation existed or not and the water depth of adjacent power plant's water intake area.By the comparative analysis with current condition,short dike behind NO.1 berth and a modest increase of allowance for siltation were recommended.(4)For the NO.1 and NO.2 berth which were seriously deposited,a two-dimensional mathematical model was applied to study the dragging silt with dredgers.Study on the change of tidal level,tide movement,sediment movement and siltation with different sail speed and dredging capacity of dredgers was done.Dragging silt with dredgers could achieve certain dredging deepth and scope in a short period of time,and suspended sediment could be taken away from port field by current.So the suspended sediment that formed from dragging silt wiyh dredgers had little effect on the siltation of surrounding harbor.