18. A Numerical Study on Hydrodynamic and Liquefaction Analysis of Coastline Protected with Geotubes

Protection of shorelines from dynamic wave attacks is a significant problem in Coastal Engineering. Under the action of wave loading, a change in pore water pressure would be generated along the shoreline which is the major factor for the seabed liquefaction and shear failure. Geotubes are the new systems that have been widely utilized as breakwaters to reduce wave impacts and to promote sediment nourishment by reducing sea erosion at the sheltered area. The major failures of the geotubes are due to the instability of the ocean floor and the sliding of geotubes because of high wave attacks. Simulation of these failures and finding the factors responsible for the failure is difficult through field observations and general laboratory tests. Hence, a study was undertaken on these aspects on a coastline named Mandaikadu which is located in Kanyakumari District, Tamil Nadu. This coastline is generally habituated with fisherman settlements, the fishing harbour, tourism, and beach sand mining. Sea erosion is a significant problem in such areas of coastline. In this study, numerical models were constructed and examined for the stability of Mandaikadu’s coastline under dynamic conditions using PLAXIS 3D software. Two basic cases were considered for the analysis, i.e., coastline without geotubes and the one protected with geotubes of varying diameters and studied for wave-induced liquefaction by varying the depth of groundwater level. From the analysis, instability of the geotubes and the ocean floor was observed due to change in parameters such as void ratio, effective stress, and soil displacements with respect to the depth. The results of the analysis indicate that the stability of geotubes decreases with increase in the diameter of geotubes. The bottom edge geotubes on each side of the geotube embankment are the most critical geotubes which shows the maximum displacement. By lowering the groundwater level, there is an increase in global safety factor, and hence, the stability of both geotubes and ocean floor can be increased.