COASTAL ENGINEERING - Introduction to Soft Soil Geotechnique: Content, Context and Application - page 289

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E p

E a

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E s

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Figure 16.21 Stability against squeezing

application 16.1
Two large breakwaters protect a new harbour extension, with at the leeside a
landfill (Fig 16.22a). At the connection between breakwater and fill, a drain (filter)
is placed to dispose overtopping water through the breakwater core, during storms.
It appeared that this drainage system did not work as expected, and the cause was
found to be internal set-up due to geometric nonlinear effects.

1 armour 25 ton concrete cube

2 filter a 1 - 3 ton rock

filter b 0.1 - 0.3 ton rock

3 filter seagravel wide grading

4 fill sand geo-textile face

Figure 16.22a Harbour breakwater, cross-section and leeside landfill

As to incorporate for the geometric non-linearity a sophisticated numerical
model was developed accounting for free wave action and the induced turbulent
groundwater flow, based on momentum, mass conservation and interface
continuity. Various waves and wind set-up scenarios were simulated.
A typical result shown in Fig 16.21b presents isochrones at each T /8 moments
during the once in 500 year significant wave H s = 6.5 m, for two cases; (1) for the
situation shown in Fig 16.21a and (2) with an open core (filter 2b replaced by
material 2a). The focus is at the leeside, on the set-up S and the local water table