海相沉积软土在沉积后阶段发生盐分溶脱，引起土体力学性状劣化，在车辆等荷载作用下易发生失稳、沉降过大等灾变，引发严重的工程问题，是沿海地区岩土工程长期安全运营需考虑的关键因素。本项目针对盐分溶脱导致的海相沉积软土动力特性劣化问题，拟采用宏观力学试验、微观测试、化学测试和理论分析相结合的研究方法，探讨海相沉积软土的动力特性与物理-化学性质随盐分溶脱发展的变化规律。分析不同盐分溶脱程度下土体微观孔隙结构、形态及分布的异同，以及土体物理-化学性质的变化，揭示盐分溶脱引起土体动力特性劣化的机理。明确盐分溶脱过程土体物理性质变化与动力特性劣化间的关系，建立可考虑盐分溶脱影响的海相沉积软土累积塑性应变及累积孔压的预测模型。耦合有效应力原理，提出可考虑盐分溶脱影响的海相沉积软土地基累积沉降计算方法。研究成果预期可为沿海地区长期循环动载下海相沉积软土地基的全寿命周期设计优化，及其服役性能的提升奠定理论基础。

It has been well known that natural marine soft clay usually suffer salt leaching in the post-depositional process, leading to degradation in the mechanical behavior. Then the structures of these soils become unstable and are easily destroyed under external loads. Many serious engineering problems induced by salt leaching, like excessive settlement, landslides and so on, have been reported for engineering practices in the coastal regions. This has become the key difficulty need to be resolved for the long-term service performance of important high-speed traffic engineering. In this study, the degradation and accumulative settlement of marine soft clay subgrade due to salt leaching, are investigated, using macro-mechanical test, microscopic test, chemical test and theoretical analysis. Firstly, the evolution of physico-chemical and mechanical properties of marine soft clay under salt leaching, is studied; Then, by comparing the microstructure of marine soft clay with and without salt leaching, and coupling with changes in physico-chemical properties, the micro-mechanism responsible for the degradation in mechanical properties is revealed; Finally, the influences of changes in the physical property caused by salt leaching on the cumulative plastic strain and cyclic pore pressure are discussed. Empirical models for predicting the cumulative plastic strain and cumulative pore pressure are established, considering the influence of salt leaching. Based on 'the theory of effective stress', a method is recommended for predicting the accumulative settlement of marine soft clay subgrade under traffic load. It is expected that the research in this study will provide a theoretical basis for the safety design in life cycle and development of effective catastrophe control technology of the important high-speed traffic engineering in coastal areas.