Abstract:
The design of a rubble mound breakwater resting on a problematic seabed consisting of a soft clayey soil is quite challenging and expensive. In the present study, stage-wise construction of a typical section of the breakwater for a proposed port on the eastern coast of India is carried out. The breakwater consists of 4 main components viz, the floor protector, core, underlayer, and cover layer. The breakwater is 60 m wide at the base and 10.5 m high. The seabed in the region consists of a thin layer of medium dense sand followed by a thick soft clay and a medium stiff clayey soil stratum.
The major challenge envisaged in the design of breakwater is the subsoil strata which consists of soft clayey soil. As it is difficult to improve the soft clayey soil in the marine condition, construction stages are meticulously planned in such a way that consolidation takes place due to the preloading of breakwater, which in turn leads to the strength improvement without any special ground treatment. Thus, the breakwater is designed to be constructed in 7 stages. An initial geostatic analysis is carried out, followed by a plastic stress-strain analysis, consolidation analysis, and safety analysis.
The stress-strain and stability analysis of the break water was carried out using finite element code PLAXIS. In the FE analysis, the sand and the clayey soil in the seabed are modelled by the Mohr-Coulomb model and the Hardening soil model. The floor protector, core, and under layer, comprising of stones is modelled by the Mohr-Coulomb model; while the cover layer comprising concrete armours are modelled as a linear elastic medium. It is found from the FE analysis that due to the presence of the soft clayey soil, the critical slip circle was formed in the base. It was observed that the staged construction over a period of 2 years provides a sufficient increase in the factor of safety of above 1.5 at the various stages of construction. It was recommended to construct the break water with 7 stages over a period of 2 years.
Abstract: Theme 5