Page 106 - Numerical Analysis and Modelling in Geomechanics

WAVE-SEABED-STRUCTURE INTERACTION 87
approximation only considered the isotropic soil behaviour and a homogeneous
seabed. Recently, the general finite element model proposed by Jeng et al.
(1998) was extended to the wave-seabed-caisson interaction problem by
including the cross-anisotropic soil behaviour, and demonstrates the significant
effects of cross-anisotropic soil behaviour on the wave-induced pore pressure
(Cha, 2000).

Application of GFEM-WSSI
In this section, we will demonstrate the application of the proposed general finite
element model on the wave-seabed-caisson interaction problem. The
configuration of the problem is depicted in Figure 3.15. The boundary condition
at the seabed surface, rubble mound foundation and caisson can be written as

(3.23)

and

(3.24)

for the part subjected to wave motion, and p=0 for the part subjected to no wave
action. It is noted that only dynamic wave pressure is considered in the study.
The static wave pressure is not included here, since it remains a constant in the
whole computing domain.
To give a basic understanding of the mechanism of the wave-seabed
interaction around a caisson, we examine several characteristics in this section.
In the following examples, we consider the rubble mound as gravel, and the
seabed to be coarse and fine sand. The wave crests are assumed to arrive fronting
the caisson. The detail of soil properties, wave conditions, caisson and rubble
mound are given in Table 3.2.
An example of a finite element mesh for the wave-seabed-caisson interaction
is given in Figure 3.16. As shown in the figure, a finer mesh is used near the
rubble mound and caisson to enhance the accuracy near the interface of different
materials.

Contours of pore pressure distribution
Figure 3.17 illustrates the contour of the wave-induced pore pressure in the
vicinity of a caisson. In the figure, the result of the wave-induced pore pressure
in both isotropic seabed (dashed line) and cross-anisotropic seabed (solid line)
are included.