Page 100 - Numerical Analysis and Modelling in Geomechanics

WAVE-SEABED-STRUCTURE INTERACTION 81

Figure 3.11 Configuration of the cover layer for protection of a buried pipeline.

material used within the cover layer, the greater the stability will be. With higher
stability it is also hoped that there will also be a reduction in the internal stresses
within the pipeline. The common values used in this model are again given in
Table 3.1.
Before evaluating the effects of the geometry of the cover layer (including the
width and thickness), the influence of the material present in the cover layer will
be examined. It is envisaged that the coarser the material present within the
cover layer, the higher the resulting pore pressure will be in the vicinity of the
pipeline. The influence of placing coarse sand and gravel in the cover layer will
be examined.
Figure 3.12 demonstrates the influence on the pore pressure in the vicinity of a
buried pipeline by varying the material present in the cover layer. Initially, there
is no cover layer in place and the seabed consists solely of fine sand, as shown in
Figure 3.12(a). The distribution of pore pressure is quite large and quickly
diminishes with a successive increase in depth into the seabed. With a cover
layer of coarse sand, the pore pressure increases significantly, especially in the
region above the pipeline (Figure 3.12(b)). Furthermore, with a cover layer of