循环荷载下天津软黏土不排水强度弱化模型研究及应用

Research on and Application of Undrained Strength Softening Model of Tianjin Soft Clay Under Cyclic Loading

波浪等循环荷载作用下,饱和软黏土产生超孔隙水压力,土体强度弱化,导致地基承载力和防波堤等近海结构稳定性降低.基于土体强度弱化的原理,建立一种表示土体不排水强度在不同动应力水平下随循环荷载作用次数变化的强度弱化模型.模型通过建立软黏土不排水强度与孔隙水压力增长规律的关系,表示出软黏土不排水强度弱化的具体过程.在有限元软件ABAQUS上进行二次开发,对天津港防波堤地基软黏土的动、静三轴试验进行数值模拟运算,并与试验数据对比.结果表明,文中建立的强度弱化模型简单准确,能够较好地表示土体不排水强度弱化过程.将模型应用到波浪荷载作用下部分回填换砂处理的软土地基上沉箱结构进行沉降变形分析,并与未考虑土体强度弱化的静力、拟静力有限元分析结果进行对比,研究了强度弱化对结构沉降变形的影响.

Strength softening happens to the saturated soft soil under wave cyclic loading such as wave loads for the excess pore pressure produced,resulting in the significant loss of bearing capacity of soil foundation and stability of breakwater and other offshore structures. Based on the mechanism of strength softening effects,a strength softening model which could express the change rules of soil strength with the changing cyclic number under different dynamic stress levels was established. The process of soil strength softening was represented by means of building relationships between undrained shear strength and the development of the pore water pressure. Secondary development of the model was conducted on finite element software ABAQUS and used to simulate dynamic and static triaxial tests.A comparison between numerical results and experimental data shows that the proposed model is simple and accurate, which can express the process of strength softening. The undrained strength softening model is applied to caisson structures lying on partly sand-backfilled soft foundations to analyze the settlement of the caisson. By comparison with static and pseudo-static models which ignore strength softening,the impact of strength softening of soft clay on struc-tural settlement is illustrated.