考虑径向变形的疏浚泥负压砂井大应变固结模型研究

Vacuum preloading in combination with vertical drains is a commonly used method to fast deal with large area dredged clays at high water content in sea land building and reclamation land project. How to accurately predict the large strain consolidation settlement of dredged clays at high water content under the negative pressure in combination with vertical drains is a difficult problem to be solved in the engineering. The key problems to solve the above puzzle is to understand the change law of compression considering radial strain and permeability properties under negative pressure. In this study, a series of laboratory tests, theoretical analysis and numerical simulations are performed. The behavior of large strain compression affected by radial deformation caused by the negative pressure is put forward. The relationship between permeability coefficient and physical index under negative pressure is cleared. Coupling Barron classic consolidation theory, Gibson large-strain consolidation system and variable vacuum negative pressure, abandoning the assumption of small strain and no radial deformation, introducing relationship between volume deformation and radial strain under negative pressure, the large strain consolidation model with vertical drains under negative pressure is established. Project examples that have been reported are predicted and simulated to verify the validity of the model. The existing material nonlinear properties of consolidation theory under negative pressure depend on positive pressure loading and extension of remoulded clays with low water content. Research results of this project can break the above limitations and overcome the bottleneck that most of consolidation with vertical drains can't consider the radial deformation. It is excepted that the results of this study can provide an effective way to predict the consolidation of super soft foundation at high water content.

围海造陆工程及吹填工程中经常用真空预压法大面积快速处理高含水率疏浚泥，如何准确预测高含水率疏浚泥在负压下的砂井大应变固结是工程中亟待解决的难题，掌握疏浚泥发生径向变形的大应变压缩性状和考虑负压水力梯度的渗透性状是解决这一难题的核心科学问题。本项目通过室内试验、理论分析和数值模拟，提出疏浚泥负压各向等压固结引起径向变形对大应变压缩性状的影响规律，明确负压下渗透系数与物理指标的关系，耦合Barron经典固结理论、Gibson大应变固结体系以及可变负压荷载，取消小应变和无径向变形假定，引入负压体积变形与径向应变相关关系，建立疏浚泥负压砂井大应变固结模型。针对已报道的工程实例和现场试验进行预测模拟，验证本模型的有效性。本项目研究成果可突破现有负压固结理论主要依赖于正压荷载和低含水率重塑土外延的材料非线性性状的局限，克服砂井固结中大多无法考虑径向变形的瓶颈，为高含水率超软地基固结提供有效的预测方法。

真空预压法处理高含水率疏浚泥在工程中得到广泛运用，但固结预测时误差较大，明确负压下高含水率土体的固结性状和建立考虑侧向变形的轴对称大应变固结模型是解决这一难题的核心科学问题。本课题围绕土体负压固结参数变化特征和固结模型的建立，通过室内试验、理论分析与数值模拟相结合的方法，进行了以下研究：（1）研制了能够考虑侧向变形，同时实现正、负压加载的固结试验装置，提出了降低汽化影响的不同真空梯度的负压固结试验方法，解决了传统固结仪不能用于高含水率土体负压固结的难题；（2）明确了负压下初始含水率、起始真空度、土性对压缩性状的影响，建立了基于重塑土屈服压力概念的高含水率土体有效应力与孔隙比的归一化关系式并进行了验证；（3）基于负压固结试验中土体实际固结度达90%对应的时间，建立了渗透系数与物理参数的定量关系式；（4）基于Barron经典理论和Gibson大应变理论，取消小应变和无侧向变形假定，引入等体积应变假定和泊松比参数，考虑了固结过程中材料和几何非线性、自重应力、涂抹、淤堵、真空度沿深度衰减等因素，建立了负压下高含水率疏浚泥考虑侧向变形的轴对称大应变固结模型，并通过CS2大应变固结模型、负压非达西定律径向固结模型、大尺度自重固结及排泥场真空预压现场工程验证了模型的适用性，明确了侧向应变和淤堵对固结度的影响规律。结果表明：固结速率随着泊松比的增大而增大，大应变固结理论下的等应变解答高估了地基的固结速率；不同泊松比下孔隙比和超静孔压沿竖向深度分布的差异随着固结时间的增加而逐渐显著；淤堵降低了土体的固结速率，且外部淤堵比内部淤堵对固结度的影响更大；考虑因淤堵导致土体的涂抹比以及非扰动区与涂抹区渗透系数的比值的变化，能更准确地预测实际工程中土体的固结过程。研究成果丰富了真空预压加固土体的固结理论，为吹填工程、围海造地工程、超软地基处理提供理论支持和工程设计参考。