JPE - Sept09 - cover2-4.pmd - Pipes & Pipelines International ...

192
The Journal of Pipeline Engineering
Fig.1. The CEL FE ice-gouge model. Fig.2. Simplified CEL FE ice-gouge model.
Fig.3. CEL FE model vs centrifuge data.
validation, sensitivity and hypothetical design studies that
have demonstrated the reliability and applicability of the
tool.
Ice-gouge model validation
Modelling of the ice-gouge phenomenon has been
approached through small- and medium-scale experimental
testing, analytical and empirical formulations, simplified
structural analyses, and advanced numerical techniques.
However, uncertainty remains on the magnitude and extent
of subgouge soil deformations, giving rise to uncertainty in
pipeline burial depth requirements.
The results obtained using the model were compared with
existing experimental centrifuge data. In order to match
the centrifuge testing conditions, the trench geometry,
trench backfill material, and the pipeline were removed
from the model, as shown in Fig.2.
Sample issue
The centreline horizontal subgouge displacement profile
resulting from a simulation with clay soil compared to
centrifuge data is shown in Fig.3. The gouge depth and
width were 1.2m and 10m, respectively. The accuracy at
one gouge depth is approximately 85% with good correlation
extending downward.
Ice-gouge model application
Using the developed model, a hypothetical study was
carried out assuming a 305-mm (12-in) diameter pipeline
with varying wall thicknesses. The pipe was placed in a 3.61m
deep trench, 1m wide at the bottom and with side slopes
2V:3H. The burial depth was 3m measured from the top of
the pipe. The trench soil was modelled using a softer
material relative to the surrounding native seabed. The
model was run a number of times for a range of D/t values
and depths.