250
R.H. Charlier and Chr. P. De Meyer
3.1. 7.1.3 Stationary suction dredger
The stationary suction dredger, an older type of dredger, mostly used to mine
sand and gravel deposits, can be very useful for beach nourishment in specific
circumstances (Fig. 30c).
The deposit is dislodged and transported by a current of water agitated by the
dredging pump or sandpump. The suction tube's upper end is connected to the
hull by equipment allowing the necessary freedom of movement of the bottom
end or suction head, which is suspended by a wire rope, worked by the drum of
the suction tube winch.
If the quantity of sediment sucked up is too small, dredging is uneconomical ; if
too large, the sand pump may stall when the tube or the pipeline gets clogged.
Suction dredgers which raise sediment from the bottom steam ahead, or warp
forward and upstream by means of their fore cables and anchors. They aim at
making grooves in the bottom as straight as possible. The cutter suction dredger,
however, moves in a different way.
The stationary suction dredger with a suction tube hanging in a well, dredges at
anchor and discharges sideways into barges alongside moored barges, or in a
floating and shore pipeline.
These dredgers are usually equipped with high pressure water jets at the entrance
of the suction pipe to desegregate the dense to very dense sand.
Some trailing suction hopper dredgers can be converted to stationary suction
dredgers by replacing the trailing suction tube by a suction tube pointing ahead.
Stationary suction dredgers need a sandlayer minimum height of approximately
6 m (20 fi) to work economically.
3.1.Z1.4 Backhoe dredger
The backhoe dredger is basically an excavating machine mounted on a pontoon.
The backhoe digging bucket is operated in such way that the digging action is
performed towards the machine. Thus, when working a face, the bucket is made
to penetrate the soil from the top of the face, or, if the machine sits above the
face, digging is performed from the bottom of the face upwards. Backhoes are
powered by direct hydraulic linkage. The outer rim of the bucket is used as the
cutting edge and teeth are fitted to increase the point pressure on the material to
be dug. Pontoon and backhoe are often integrated (fig. 29d).
R.H. Charlier and Chr. P. De Meyer
3.1. 7.1.3 Stationary suction dredger
The stationary suction dredger, an older type of dredger, mostly used to mine
sand and gravel deposits, can be very useful for beach nourishment in specific
circumstances (Fig. 30c).
The deposit is dislodged and transported by a current of water agitated by the
dredging pump or sandpump. The suction tube's upper end is connected to the
hull by equipment allowing the necessary freedom of movement of the bottom
end or suction head, which is suspended by a wire rope, worked by the drum of
the suction tube winch.
If the quantity of sediment sucked up is too small, dredging is uneconomical ; if
too large, the sand pump may stall when the tube or the pipeline gets clogged.
Suction dredgers which raise sediment from the bottom steam ahead, or warp
forward and upstream by means of their fore cables and anchors. They aim at
making grooves in the bottom as straight as possible. The cutter suction dredger,
however, moves in a different way.
The stationary suction dredger with a suction tube hanging in a well, dredges at
anchor and discharges sideways into barges alongside moored barges, or in a
floating and shore pipeline.
These dredgers are usually equipped with high pressure water jets at the entrance
of the suction pipe to desegregate the dense to very dense sand.
Some trailing suction hopper dredgers can be converted to stationary suction
dredgers by replacing the trailing suction tube by a suction tube pointing ahead.
Stationary suction dredgers need a sandlayer minimum height of approximately
6 m (20 fi) to work economically.
3.1.Z1.4 Backhoe dredger
The backhoe dredger is basically an excavating machine mounted on a pontoon.
The backhoe digging bucket is operated in such way that the digging action is
performed towards the machine. Thus, when working a face, the bucket is made
to penetrate the soil from the top of the face, or, if the machine sits above the
face, digging is performed from the bottom of the face upwards. Backhoes are
powered by direct hydraulic linkage. The outer rim of the bucket is used as the
cutting edge and teeth are fitted to increase the point pressure on the material to
be dug. Pontoon and backhoe are often integrated (fig. 29d).