疏浚泥负压传递衰减规律与径向固结机理研究

Vacuum preloading in combination with vertical drains is a well established method in geotechnical engineering for ground improvement of natural clays. In recent years, such a method has also been applied on reclaimed land of dredged clays with high initial water contents, but engineering practice often shows a poor effect. The differnece in treatment effect of vacuum preloading for natural clay ground and reclaimed land of dredged clays should be attributed to the difference in their soil behavior. The natural clays have a much higher undrained shear strength than the dredged clays due to the effect of the soil structure developed during the depositional and the post-depositional processes. The dredged clays are also in flow under self-weight. On the other hand, the state-of-the-art comparisons of performance in engineering practice with vacuum preloading for natural clay ground and reclaimed land of dredged clays illustrates that the damping with distance during the transmission of vacuum loadings is the essential factor responsible for poor effect of applying vacuum preloading on reclaimed land of dredged clays. Therefore, how to evaluate the effects of strength and flow value on loading damping of dredged clays with high initial water contents is an essential issue for applying vacuum preloading on dredged clays. Toward this end, a comprehensive study of model tests, macro-mechanical and micro-structure tests, theoretical analyses and in-situ large-scale model tests / field tests will be carried out. The following three issues will be focused on: (1) the relationships among deformation, undrained shear strength and hydraulic conductivity under vacuum loadings; (2) the large-strain non-linear relationships of void ratio versus effective stress and void ratio versus hydraulic conductivity under vacuum loadings; (3) the quantitative relationship between damping rate of vacuum loading transmission and the undrained shear strength behavior/flow value of dredged clays. Based on these results, the calculation model of large-strain radial consolidation will be established by taking into account of large-strain non-linear relationship under vacuum loadings and damping behavior of vacuum loading transmission. Then, the radial consolidation behavior under vacuum loadings will be analyzed for understanding the influencing mechanism of the undrained shear strength behavior/flow value on the redial deformation of dredged clays. It is expected that the results obtained in this study can provide an effective way of greatly improving the treating effect of vacuum preloading in combination with vertical drains on the reclaimed land of dredged clays with high initial water contents.

天然沉积土与高含水率疏浚泥的本质区别在于流动性与强度的差异大，正是这一差异经常导致真空排水固结技术处理天然沉积土地基与高含水率疏浚泥堆场的加固效果截然不同。本项目基于相关研究现状的总结，凝练出高含水率疏浚泥中的负压传递衰减是导致真空排水固结技术加固疏浚泥堆场经常失效的本质原因，进而提出高含水率疏浚泥流动性和强度对负压传递衰减影响规律这一关键科学问题。拟通过模型试验、室内宏观力学-微观试验、理论分析和数值模拟相结合的研究手段，揭示负压下高含水率疏浚泥变形-渗透-强度的内在联系，明确负压下高含水率疏浚泥大应变材料非线性的变化规律，建立高含水率疏浚泥流动性和强度与负压传递衰减率的定量关系，进而构建考虑负压传递衰减和大应变材料非线性的高含水率疏浚泥径向固结计算模型，分析高含水率疏浚泥流动性和强度对负压径向变形的影响机理。预期成果将为大幅度提高疏浚泥堆场处理效果的技术创新提供有效路径。

工程实践中经常采用真空预压法处理高含水量疏浚泥，实践中发现真空加固效果主要体现在排水通道附近土体，以排水通道为中心，沿着径向和深度方向疏浚泥的强度逐渐降低，距离排水板一定距离和一定深度之外的疏浚泥强度几乎没有提高，形成“土桩”现象，导致处理效果不佳，其本质原因在于真空负压传递衰减。本项目围绕着真空负压传递衰减机理与控制因素这一关键科学问题，以高含水量疏浚泥为研究对象，采用单元试验、模型试验、理论分析与数值建模相结合的方法，展开了系统研究，获得了以下主要创新成果：1）揭示了高含水量疏浚泥中真空负压传递衰减的机理在于土体大应变诱发的能量消耗阻碍了荷载有效传递，明确了真空负压传递衰减的控制因素为疏浚泥的液限孔隙比、初始孔隙比和施加的起始负压荷载值，构建了真空负压径向传递衰减模型，也建立了真空负压与固结时间关系的数学描述；2）发现了疏浚泥的渗透系数的控制因素为土体孔隙比和液限孔隙比，构建了疏浚泥渗透-压缩-强度性状的内在联系，突破了传统上单独分开探讨渗透、压缩和强度性状，从而不时导致矛盾的局限；3）基于Barron径向固结理论和Gibson大应变径向固结模型，导入真空负压沿PVD深度衰减系数和径向衰减系数以及荷载传递时间效应，建立了考虑真空负压传递衰减和时间效应的负压砂井大应变固结模型。本项目研究成果为改善真空预压法处理高含水量疏浚泥的加固效果，提供了有效的技术创新途径，能够增进疏浚泥资源化利用和服务于围垦土地资源开发利用。