Page 351 - Pipelines and Risers

322 Chapter I7

The three main rockdumping techniques are:

- Side dumping;
- Fall dumping;
- Bottom dropping.

17.5.1 Side Dumping
General Principle
This method involves loading selected stone onto a flat decked ship, positioning the ship over
the required location to dump rock, and pushing rock over the side is by hydraulic rams which
clear the rock from the center line of the vessel and outboard.

Installation CapabilitieslConstraints
This method of rockdumping is very efficient at dumping large quantities of rock in short
lengths. This is suitable for protecting bases of jackets or subsea manifolds, but is wasteful of
rock for dumping of flowlines.

17.5.2 Fall Pipe
General Principle
The method is based on loading the selected stone onto the vessel, mobilizing offshore to the
selected location to rock dump, and dropping the rock down through a tube to the location. To
provide further accuracy the “fall pipe” has a remote operated vehicle at the end so the
location of the rock can be monitored and controlled.

Installation CapabiIitiedConstraints
This method of rockdumping was developed for dumping of rock on pipelines/flowlines. It
provides accurate dumping, which minimizes wastage and permits long stretches of rock to be
dumped during one trip.
17.5.3 Bottom Dropping
General Principle
There are two methods of bottom dropping. One method incorporates ports which open at the
bottom of the hold and the second is to apply a split barge which drops all the rock at once.

Installation CapabilitiedConstraints
Both methods are again suitable for dropping large quantities of rock, when great accuracy is
of less importance. This method is not suitable for rock dumping on flowlines.