51.1 INTRODUCTION

Definition: A dredger is a piece of equipment that can excavate, transport and dispose of a certain amount of underwater-lying soil in a certain time.

The quantity of soil moved per unit of time is called Production. Dredgers can excavate hydraulically or mechanically. Hydraulic excavating uses the erosive working of a water flow. For instance, a water flow generated by a dredge pump is led via suction mouth over a sand bed. The flow will erode the sand bed and form a sand-water mixture before it enters the suction pipe. Hydraulic excavating is mostly done with special water jets in cohesionless soils such as silt, sand and gravel.

Mechanical excavating with knives, teeth or cutting edges of dredging equipment is applied to cohesive soils.

The dredged soil can be transported hydraulically or mechanically too, either continuously or discontinuously as shown in Table 51.I.

Deposition of soil can be accomplished in simple ways, for example, by opening the grab, turning the bucket of an excavator or opening the bottom doors in a ship. Hydraulic deposition happens when the mixture is flowing over the reclamation area or settles in the hopper of a Trailer Suction Hopper Dredger. The sand will settle while the water flows back to sea or river.

Dredging equipment can have these three functions integrated...