Researches On The Breakwater-foundation Stability Under Wave Cyclic Loading

Strength softening may take place for the saturated soft clay under the action of wave cyclic loading. The strength of soft clay may further decrease and the modulus of deformation becomes smaller. As a result, the bear capability of the soft clay foundation will become significant lower and the stabilization of the structures will be worsened. Based on the analysis of the failure of the guide dikes for deepening of navigation channel along the Yangtze Estuary, it was proposed that the strength softening be considered when the harbor architectural or construct buildings such as guid dikes and breakwaters were buit on the soft soil foundations. The strength sofening property of the foundations soil on which the harbor buildings such as semi-circular caisson or suction caisson breakwaters were built was studied by means of performing indoor tests on the undisturbed samples taken from Tianjin harbor.1. Cyclic softening of the clay is related to the soil sensitivity. The sensitivity infulnece on clay is as important as that of the density on sand. The soil sensitivity were tested using indoor vane test device and the results revealed that the remodeled (fully disturbed) samples strength reduced to 22%～42% that of the undistrubed ones on anvarage, which can be used to determine the softening extent of the soil under fully disturbed condition.2. Depending on the research on the soft clay strength softening for the Yangtze Estuary guide dike foundations, more verification and comparison tests were performed. The tests gave similar results to those of the pervious research. The interior dynamic triaxial test method was introduced taking into account different load combinations and the actual loading path. The test results revealed obvious regularity when normalization was carried out on the dynamic and static triaxial test results. The relationship between discounting ratio and environmental and load conditions was established and then the strength discounting criterion of the soft clay could be determined which brought convinence to the engineering paractice.3. The shear strength of normal consolidated saturated clay will lowered after undrained cyclic shear which is similar with the metal fitague. The main reason is that cumulative pore pressure and unrecoverable structural failure has been caused in the clay. Based on the analysis of the accumulated pore pressure and accumulated deformation behaviour of the clay under cyclic loading, the strength discounting mechanics of the soft clay was also analyzed in the view of the energy transformation.4. According to wave loading distribution on the semi-circular breakewater and stress state of the foundation soil, the stability of the semi-circle breakwater foundation was analyzed before and after soil improvement combining the clay shear strength disconting ratio obtained from the test results with FE methods. The calculation results agree well with the observed data. The breakwater stability analysis method involving the soil softening effects was then put forward.5. By means of statistical regression analysis of the field vane test results of Tianjin Harbor soft clay, the thesis presented a method for how to determine the shear strength parameters of the clay using the in situ vane shear test results. The regression strength parameters can be used for slope stability analysis, earth pressure calculation and bearing capacity assessment. According to the correlated soil parameters, a simple analysis method for the suction caisson breakwaters was established also.