Analysis Of The Foundation Bearing Capacity Of Gravity Breakwaters Considering The Weakening Effect Of Soft Clay

In recent years, the domestic port construction has been a vigorous development with the characteristic of large scale and deepwater. Most of the superior coastal zone has been developed, the new breakwaters have always been constructed under more severe conditions, with abominable wave condition and foundation composed by soft clay. Therefore, the soft clay with weakening effect due to the action of wave cyclic loading, reduces the foundation bearing capacity, which is a urgent problem needed to be researched to ensure the safe use of the structures. In order to archive this research objective, this paper carry out a series of researches on the weakening state of the soft foundation under the action of wave cyclic loading, on the basis of the dynamic weakening law of Tianjin and Yantai soft clay strength. In addition, the feature of bearing capacity of soft foundation is also included. The main contents include the following several aspects :1.Together with the theory of quasi-over-consolidation, the pore pressure model and the reduction law of shear strength, a law of strength weakening which takes confining pressure, deviator stress, dynamic stress and cycle times into account was put forward for the soft clay. This law reflects the dynamic weakening procedure of the soft clay shear strength under wave cyclic loading.2.With a method of secondary development in ABAQUS, a user subroutine, USDFLD, to make material parameters change with user-defined field variable is programmed. The above dynamic variation is shown on two indicators of soft clay strength, internal friction angle ? and cohesion c, making the indicators vary with both deviator stress and dynamic stress level and decrease with cyclic times gradually in every time step, to establish the FE model considering the strength weakening of soft clay.3.A self-defined reduction coefficientK?, is used to represent the weakening level of foundation bearing capacity by soft clay cyclic weakening effect. The relationship between dynamic wave loading, static loading by structure and the width of foundation with the reduction coefficient K? is fitted with simlation results. Therefore, the safty factor N WK on foundation bearing capacity including weakening effect can be derived by the the safty factor WK on foundation bearing capacity without weakening effect and the reduction coefficientK?. Then, the foundation bearing capacity condition can be distinguished by the safty factor WK.4.On the purpose of studying the semi-circular breakwater, a FE model considering the strength weakening of soft clay is established on the basis of the dynamic law about strength weakening of Tianjin soft clay. The strength weakening state of the soft foundation of semi-circular breakwater under cyclic wave loading is studied. Besides the influence of the value of wave loading, sand filling quantity in the structure, the width of foundation, the thickness of clay replacement are also taken into consideration. Then the bearing capacity of the foundation under semi-circular breakwater is studied with the consideration of strength weakening of soft clay, and comparation between the one without weakening effect is also made. And the influence on foundation bearing capacity by weakening effect of soft clay is discovered to be significant.5.In order to study the caisson breakwater, a FE model considering the strength weakening of soft foundation is established on the basis of the dynamic law about strength weakening of Yantai soft clay. The strength weakening state of the soft foundation of caisson breakwater under cyclic wave loading is studied, with the influence of several aspects. Then the bearing capacity of the foundation under caisson breakwater is studied with the consideration of the weakening effect of soft foundation.