The effects of wave induced pore pressure on slope stability of conventional and berm breakwaters considering wave height and water depth

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Alireza Shafieefar, Ali Fakher

Monday 29 june 2015

16:30 - 16:45h at Asia (level 0)

Themes: (T) Water engineering, (ST) River and coastal engineering

Parallel session: 3E. River engineering

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Wave action on rubble mound breakwaters causes an excess pore pressure due to some physical processes e.g. phreatic storage and dynamic impact. This excess pressure is attenuated by the porous flow inside the breakwater core. Slope stability of a rubble mound breakwater is usually measured by checking the safety factors in extreme tidal levels with constant water levels and pore-water pressures. A semi dynamic approach is used in this paper to analyze slope stability of conventional and berm breakwaters. The "pore water pressures at discrete points" ability of GEO-SLOPE/W is used for slope stability analysis. Wave induced pore pressures in the core are determined by the calculation method presented by Troch et al. in 2012. These pressures plus hydrostatic pore pressures for some selected points in the core are assigned in the model and the safety factor of the breakwater section against sliding is calculated. The obtained safety factors with and without considering excess pore pressures are compared in order to study their effects. In this paper the impact of breakwater type, wave height, and water depth are studied on the pore pressure effects. For this purpose, a number of breakwater sections were designed for wave heights ranging from 1 to 7 meters and water depths ranging from 5 to 30 meters. Both conventional and berm types of sections were designed for each environmental condition. The results show that considering the excess pore pressures reduces safety factors. While increasing wave heights leads to further reduce in the safety factor, the opposite happens to the water depth. The results also show that the pore pressure effects are more important in conventional breakwaters, but also indicate a difference between the stability behaviors of berm sections in different water levels i.e. after a certain depth, the berm sections act similar to conventional sections.