考虑颗粒径向移动影响的疏浚泥砂井大应变固结模型研究

Vacuum preloading in combination with vertical drains is a well established method in geotechnical engineering for ground improvement of naturally sedimentary soils. However, it has been well documented that unlike natural soft ground, in the engineering practice of reclaimed land of dredged clays with high initial water contents, particle radial movement generally occurs during the vacuum preloading. Hence, the treatment can not meet the requirements of design capacity. To solve the above problem in engineering practice, it is necessary to understand the change law in grain size distribution caused by particle radial movement during consolidation under vacuum negative pressure. In this study, a series of model tests as well as laboratory physical tests and mechanical tests will be performed to investigate the main factors affecting the behavior in particle radial movement. Based on the analyses of the test results, this study aims at proposing a method for predicting the change in fine grains due to particle radial movement, and discussing the law in change of well resistance and smear effect. Consequently, the mechanism of clogging inherent to vertical drains is investigated. On the other hand, a modified oedometer apparatus and a modified equipment of hydraulic conductivity tests are adopted for avoiding soil squeezing which occurs in conventional test apparatus. A series of oedometer tests and hydraulic conductivity tests will be conducted to investigate the effects of initial water content and liquid limit on the compression and hydraulic conductivity during consolidation for dredged clays with high initial water contents. Based on the comparisons of mechanical behavior between vacuum negative pressures and load pressures, the large-strain relationships of void ratio versus effective stress and void ratio versus hydraulic conductivity under vacuum negative pressures are discussed. Finally, a new large-strain constitutive relation will be established with considering the effects of particle radial movement for the reclaimed land of dredged clays with vertical drains under vacuum negative pressure. Compared with the traditional symmetric consolidation model with vertical drains, the assumptions of small strain consolidation and without particle radial movement are abandoned. It is expected that the results of this study can provide an effective way of solving the clogging problem in engineering practice, consequently improving the treatment efficiency of vacuum negative preloading in combination with vertical drains on reclaimed land of dredged clays with high initial water contents.

为了突破负压排水固结技术处理高含水率疏浚泥堆场经常遇到效果达不到设计要求的工程困境，需要揭示负压作用下疏浚泥颗粒径向移动规律。围绕着这一关键科学问题，本项目拟通过模型试验与理论分析，研究负压作用下发生颗粒径向移动的主要影响因素，建立负压作用下疏浚泥细颗粒含量的变化规律，探讨颗粒径向移动引起的井阻增大和涂抹区渗透系数降低的变化规律，揭示负压作用下高含水率疏浚泥发生阻塞的机理。同时，通过负压固结模型试验以及采用课题组研制的特殊设备进行一系列压缩和固结渗透试验与分析，建立负压作用下疏浚泥物理参数与大应变压缩性状和渗透性状的定量关系。在传统的砂井轴对称固结理论基础上，摒弃没有颗粒径向移动和小应变的假定，建立考虑颗粒径向移动影响的高含水率疏浚泥砂井大应变固结模型。研究成果为实际工程中确定负压作用下高含水率疏浚泥排水通道发生阻塞的原因提供有效的分析方法，从而为提出能够改善处理效果的施工工艺奠定基础。

负压排水固结技术处理高含水率疏浚泥堆场经常遇到效果达不到设计要求的工程困境，其关键科学问题是负压下排水淤堵机理，围绕着这一关键科学问题，本项目以高含水率疏浚泥为研究对象，采用试验、理论分析与数值模拟相结合的方法，进行了以下四个部分的研究。第一部分研究了负压下高含水率疏浚泥排水淤堵机理和高含水率疏浚泥沿着径向的物理性状变化规律，探讨细颗粒径向移动性状，分析负压下高含水率疏浚泥井阻效应和涂抹区物理性状。第二部分研究了负压下高含水率疏浚泥压缩-渗透-强度性状，探讨负压下高含水率疏浚泥排水淤堵的主要影响因素，分析细颗粒含量变化对高含水率疏浚泥渗透性状的影响规律，构建负压下高含水率疏浚泥大应变材料非线性变化规律。第三部分构建了负压下高含水率疏浚泥大应变固结模型。第四部分通过现场试验对高含水率疏浚泥大应变固结计算模型进行了验证。本研究获得的两个主要创新成果如下：（1）建立了能够考虑淤堵效应的高含水率疏浚泥砂井大应变固结模型，突破没有考虑淤堵影响的局限和摈弃小应变的假定，解决了传统砂井轴对称径向排水固结理论与高含水率疏浚泥实际工况不吻合的问题；（2）提出了负压下高含水率疏浚泥颗粒的径向移动规律和排水淤堵性状，揭示了真空负压作用下高含水率疏浚泥发生排水阻塞的机理，为解决负压排水固结技术处理高含水率疏浚泥堆场经常遇到效果达不到设计要求的技术难题提供了有效路径。