动态柔性侧限约束下软黏土的变形时效机理及蠕变-固结耦合模型研究

Deformation of soft clay is closely related to time, which is influenced by the interaction between creep and consolidation as well as lateral deformation. In this research, short-term and long-term deformation mechanics of a typical soft clay in the Greater Bay Area would be studied, with considering the effects of lateral deformation and time-dependent characteristics using experimental tests, theoretical study and numerical analysis. The mechanics of creep effect and consolidation effect will be studied by self-designed experimental device. Based on this achievement, the quantitative relationship of creep deformation in the primary consolidation stage will be deduced and a non-linear elastic-viscoplastic constitutive model will be developed further. A consolidation test under flexible lateral constraint will be proposed, which gives the opportunity to obtain insights into the development law of confining pressure and the mechanism of the deformation characteristics of soft clay with lateral deformation, and further contribute to the establishment of nonlinear consolidation equation considering the dynamic change of lateral restraint. The creep-consolidation governing equation under flexible lateral constraint will be obtained by combining the above non-linear elastic-viscoplastic constitutive model and consolidation model, and the deformation as well as long-term deformation mechanism of soft clay will be revealed through experimental verification and finite element analysis. This study aims to further improve the research of deformation mechanism of soft soil foundation and help to improve the theoretical level of engineering design on deep soft foundation.

软黏土变形与时间密切相关，受蠕变效应和固结效应的共同作用，且侧向变形的发生也会对软土沉降产生不利影响。针对这一问题，本项目拟以“粤港澳大湾区”内典型的海相、海陆相沉积软黏土为研究对象，采用试验研究、理论分析与数值模拟相结合的方法，同时考虑时效特性和侧向约束条件对软黏土变形及长期变形特征的影响。基于自主设计的试验装置，阐明蠕变效应与固结效应的共同作用机制，探讨柔性侧限条件下围压的发展规律，揭示侧向变形对软黏土力学响应的影响机理。基于试验成果，提出考虑固结作用的蠕变变形定量关系式，建立非线性的弹黏塑性本构模型，结合侧向约束的动态变化，实现柔性侧限条件下的蠕变-固结耦合作用，给出模型参数的获取方法，通过试验验证及有限元模拟，明确软黏土变形及长期变形的机制。本研究成果可进一步完善软土地基变形的机理研究，有助于深厚软基上工程设计理论水平的提升。

软黏土广泛分布在“粤港澳大湾区”内，软土沉降问题是大湾区两类重大地质问题之一。软黏土具有高含水率、低渗透性、强黏滞性、高压缩性等不良特性，其变形过程与时间密切相关，固结效应与蠕变效应相互作用机理复杂，且由于泊松比较大，软黏土侧向变形对沉降的影响不容忽略，这都给深厚软基上的建设及后期维护带来了极大困难和挑战。本项目针对以上问题，利用加高环刀法和串联固结单元的方法，开展了不同排水距离的固结试验，并设计了柔性侧限固结试验，探讨了侧向变形对沉降的影响。试验结果表明：(1)随着排水距离的增加，主固结完成时的应变值增加，土体的E-O-P曲线越靠下，主固结阶段的变形是固结效应与蠕变效应相互作用的结果；(2)随着排水距离增加，变形~时间曲线最终趋于重合，次固结系数也几乎保持不变；(3)土体的渗透特性及次固结系数是决定主固结阶段蠕变变形的重要影响因素；(4)当排水条件不好的情况下，土体中的孔隙水压力可能会上升，这是土体蠕变的结果；(5)侧向变形的发生会增加土体的主固结变形量及次固结变形量，且侧向围压与竖向压力比值越小，影响就越大。利用固结单元，还开展了不同排水边界条件、不同固结度条件、不同加荷比条件下的固结试验，试验成果揭示：(a)随着排水条件逐渐变好，应变~时间曲线越靠下，土体固结速率越快；(b)土体的一维固结不只有完全透水和完全不透水这两种极端的边界条件，排水边界条件越差，主固结完成时的应变值越大，但排水边界对次固结系数影响不大；(c)加荷比的增大，不仅仅会提高孔压上升的程度，而且会降低到达孔压峰值所需的时间，这可能是因为较大的荷载更容易打破土颗粒之间的平衡状态，孔隙水在孔隙中更容易流动传递压力；(d)随着固结度的提高，在相同的荷载增量作用下，初始孔压的上升幅度是逐渐降低的。最后，在试验成果的基础上，建立了柔性侧限条件下的蠕变-固结耦合控制方程，并与太沙基理论进行了对比。本项目能为湾区开发建设项目提供一定理论依据和技术支撑。