Study On The Variation Laws Of Soil Indexes And Bearing Capacity Of The Soft Clay Foundation Under Load Action

Nowadays, with the rapid development of national waterway transportation industry, more and more port and coastal engineering projects have been constructed on the thick soft clay foundation under poor natural conditions. Thus accurate analysis of bearing capacity of foundation is especially important which will directly affect the safety and economy of projects. However, the variation tendency of shear strength and indexes of soil remains unclear when using drainage consolidation method for soft soil foundation reinforcement at present. At the other hand, along with gradual construction of the upper structures such as rubble bed, caisson, filling and breast wall etc, the effects of vertical load to the indexes and bearing capacity of foundation soil shouldn’t be ignored. These are all problems in practical engineering design which are further concerned and urgent to be solved.Aiming at these problems, combined with the construction project of Ministry of Communications, relying on the Phase II Breakwater Project of the west Yantai port area, in this paper a number of conventional physical properties tests, consolidatedundrained triaxial tests and finite element numerical simulation are carried out. Then the variation laws of shear strength and indexes as well as the bearing capacity of soft clay foundation under different consolidation pressures and different consolidation degrees will be obtained. The main research contents are as follows:First, the control methods of consolidation degree are divided into four types by summarizing various kinds of experimental studies involving consolidation degree at home and abroad, which are the methods of confining pressure ratio, loading time, pore water pressure and pore water output. Based on the method of pore water output, an improved triaxial tests study is developed which can take the two factors of anisotropic consolidation pressure and consolidation degree into consideration at the same time.Second, ABAQUS software is used to establish the two-dimensional elasticplastic finite element numerical model of vertical breakwater structure, analyzing the vertical displacement of foundation and the additional stress generated by the upper structure under design load action at various working conditions.Third, using SLB-1 type triaxial shear test instrument, consolidated-undrained triaxial tests are carried out on the undisturbed samples of mucky silty clay, then the variation laws of the soil shear strength and indexes accompanied with the increase of consolidation degree and axial deviatoric stress are obtained. According to the experimental data, the calculation formulas of soil indexes under load action are put forward which can be used in practical engineering design.Fourth, the verification triaxial tests are carried out on the undisturbed samples of silty clay, which prove the conclusive variation laws are universally applicable for soft clay. Then the recommended usage of calculation formula is given.Fifth, based on the established finite element model, calculate the bearing capacity of soft clay foundation separately using the original indexes and the changed indexes considering load action. Through comparative analysis, a conclusion could be drawn that the bearing capacity of soft clay foundation will increase about 11% when using stage construction method.