Page 91 - Numerical Analysis and Modelling in Geomechanics

72 D.S.JENG

Table 3.1 Input data for case study of wave-seabed-pipe interaction

anisotropic and isotropic soil behaviour in fine sand, which strongly highlights
the difference between the two cases.
To investigate further the influences of anisotropic soil behaviour on the pore
pressure distribution along the pipeline surface, a parametric study has been
performed. The preliminary results indicate that two anisotropic constants (n and
m) have more significant influence on the wave-induced pore pressure than other
anisotropic soil parameters in the wave-seabed-pipe interaction. Thus, we only
discuss the influence of n and m on the wave-induced pore pressure in this
section.
The anisotropic constant n establishes the relationship between µ and µ , as
xz
zx
well as E x and E . The elastic constant n can be increased when either the
z
Young’s modulus in the horizontal direction (E ) is increased or the Young’s
x
modulus in the vertical direction (E ) is decreased. As a result of E increasing,
x
z
the soil will be able to retain its structure better in the horizontal direction. For
isotropic soils, n equals one, n varies between 0.2 and 1.0 for most anisotropic soils.
Figure 3.6 shows the effect of changing the cross-anisotropic constant (n) in both
coarse and fine sand. With an increase in n, there is an increase in the pore
pressure, p/p , producing greater rigidity in the vertical direction. As a result, it is
o
easier for the water to penetrate the seabed in the horizontal direction, which