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Shoreline protection works are necessary to control flooding and erosion caused by the sea waves and other natural coastal disasters. Concrete revetment is used as a protective cover layer because it is capable of withstanding the force of wave action. Normally the revetments are designed by limit equilibrium method. This method can be used for calculating thickness of concrete revetment required to withstand certain wave heights. However, this conventional method cannot predict the deformations subjected to repetitive dynamic wave loads for the cover layer. The present study focuses on the modeling of concrete revetment against the dynamic wave impact loads. The finite element software Plaxis 2D was used to do the analysis. Flexible construction of concrete mattress revetment ensures that it can be laid to cope with variations in the embankment profile and can ensure protection against wave forces.
A parametric study was conducted by a series of numerical analyses using Plaxis 2D software. Concentrated dynamic load with magnitude 10.1 kN has been applied at mid depth of slope with dynamic multipliers of 1 m, 2 m, 3 m, 4 m, 6 m, and 8 m wave heights of 0.1 Hz, 0.2 Hz, 0.3 Hz, 0.4 Hz and 0.5 Hz frequencies. 400 mm and 800 mm thick concrete mattress were considered for the study. The characteristics of displacements at impact of wave, toe of slope and top of slope was assessed by the dynamic wave impact force.
The maximum displacement was found to be 822 mm for 400 mm thick mattress whereas the displacement value was only 24.9 mm for 800 mm thick mattress for 8 m wave height with 0.5 Hz frequency. The maximum displacement increases at point of impact about 21% (822 mm to 998 mm) for 400 mm thick revetment and about 25% (24.9 mm to 31 mm) for 800 mm thick revetment after considering 7.5 m toe scour with sheet pile. The maximum displacement decreases about 6% and 5% for 400 mm and 800 mm thick mattress revetment for 8 m wave height with 0.5 Hz frequency respectively by considering geotextile sublayer below the cover layer. Factor of safety against slope failure before and after construction of revetment was 1.61 and 1.96 respectively. With a 7.5 m toe scour, the factor of safety reduced to 1.49. The effect of 3.5 m toe scouring without sheet pile was also analysed and the variation of displacement was found to be 4% (24.9 mm to 23.9 mm) for 800 mm revetment and about 14% (822 mm to 937 mm) for 400 mm thick revetment with 0.5 Hz frequency with comparing to revetment system without scour. |
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