Pipeline plough performance in sand waves. Part 1: model testing

Offshore pipelines are often buried in the seabed by ploughing a trench,
placing the pipe at the base, and then backfilling. The ploughing
operation is critical in terms of cost and project time, with increased
risk due to uncertain soil conditions or geohazards. One problem that
can be encountered is the presence of sand waves or megaripples on the
seabed surface. This may affect the progress of the plough, prevent the
plough from generating a level trench or modify the size of the spoil
heaps for backfilling. These aspects have been investigated by
conducting a series of small-scale model tests in the laboratory. These
have revealed information about the plough kinematics and the resulting
trench conditions when ploughing in sand waves with different
wavelengths and amplitudes. It is shown that it may be possible to
plough through regions of sand waves and estimate likely plough
performance by knowing the sand wavelength and amplitude relative to the
plough size.