Page 136 - Numerical Analysis and Modelling in Geomechanics

STABILITY OF UNSATURATED SOIL SLOPES 117

Figure 4.5 Pore water pressure distributions at initial steady state.
By considering equation (4.8), it can be deduced that for an isotropic and
homogeneous soil, the rise of the main water table is not only governed by the
ratio k/S , but it is controlled also by the ratio Q/k, even for a given set of slope
s
geometry and boundary conditions. At Section B-B, the initial main groundwater
table rises from 41.3 mPD (4.7 m below the ground surface) to 41.6 mPD. The
amount that the water table rises is found to be approximately proportional to the
rainfall intensity. This is consistent with the study reported by Pradal and Raad [
13]. The magnitude of negative pore water pressure at the ground surface
reduces to about half the initial value. However, the amount of reduction seems
to be relatively unaffected by the intensity of rainfall (compare Figures 4.6a and
4.6b).
Due to the proximity of the main water table to the ground surface at Section
A-A, as expected, rainfall of various intensities not only causes a rise of the main
water table but it also results in a reduction in the magnitude of negative of pore
water pressure at the ground surface. The rise of the main water table is greater
at this section than other sections (B-B and C-C). This is because of the