负压条件下土体渗流固结特性研究

Vacuum preloading method is widely used in transportation and port engineering for soft soil treatment. However, limited studies on the seepage consolidation characteristics of soil were conducted under negative pressure conditions. Especially, great disagreements exist in the measurement and analysis on the underground water level. Based on soft foundation reinforcement on the road of Youth Olympic Games Engineering in Hexi New City in Nanjing, the seepage and consolidation properties of soft soil under negative pressure condition are studied by field testing combined with theoretical analysis and numerical calculation. Meanwhile, a new underground water level test technology under negative pressure condition is developed and used for filed test to reveal the formation mechanism of seepage filed and the characteristic of soil consolidation. Based on the testing data, considering the negative pressure and its attenuation law and well resistance effect, the free strain model of during seepage and consolidation process is established and its analytical solution is given, which can reflect the relationships among the drainage body features, excess pore water pressure and consolidation time. In addition, the new established model will be secondary-developed based on the software ABAQUS. According to the simulation of typical project case, the finite element calculation method of negative pressure seepage consolidation characteristics and "zero" pressure surface location are established by model verification and correction. The results will enrich and innovate seepage consolidation theory in vacuum preloading reinforcement engineering, and provide the design reference for the soft foundation treatment engineering such as transportation and port wharf.

真空预压法处理软土地基目前在交通及港口工程中广为应用，但对负压条件下土体渗流固结特性研究较少，尤其对负压条件下地下水位的测量与分析存在较大的分歧。本项目拟依托南京河西青奥新城道路软基加固工程，采用现场试验、理论分析和数值计算相结合的方法开展负压条件下软基渗流固结特性现场试验，研发一套负压加固地下水位测试技术并开展现场测试分析，揭示负压渗流场形成机理和土体固结特性。根据实测数据，考虑负压及其沿排水体衰减规律和井阻作用，建立排水体特性、超孔隙水压力和固结时间三者关系的渗流固结自由应变计算模型，得到加固范围内土体渗流固结解析解。将建立的负压渗流固结计算模型开发到岩土工程专业程序ABAQUS中，根据典型工程实例的模拟，对模型进行验证和修正，建立计算负压渗流固结特性和“0”压面位置的有限元计算方法。研究成果将丰富并创新真空预压负压加固土体渗流固结理论，为道路交通、港口码头等软基处理工程设计提供依据。

真空预压作为一种经济、高效的软基处理方法，在我国滨海及内陆河湖软土地区得到了广泛应用，但是其渗流固结特性的机理研究却远远落后于工程实践。本课题依托某海滨新城软基加固工程，开展了真空负压条件下土体渗流固结特性的现场试验研究，并通过理论分析和数值模拟相结合，对真空负压下地下水位的真实位置、“0”压面的概念、渗流场模型、土体径向固结理论及其影响因素等进行了探讨。主要完成的工作及所得结论有：（1）重新讨论了真空负压下地下水位的概念，并研发了一套新型的地下水位测试技术，采用内窥镜摄像头内置于水位管中，通过外置的传像设备在密封负压条件下实时观测地下水位的变化；（2）结合新型地下水位测量方法及现场试验得出的数据，揭示了真空负压软基加固中地下水位的真实变化规律和渗流场形成机理；（3）引入渗透系数呈双线性变化的渗流模式，同时考虑真空负压下的荷载情况，基于存在起始水力梯度的非达西渗流模型推导了土体渗流固结特性的径向解析理论；（4）建立了真空负压下渗流固结的三维数值模型，探讨了土体固结的影响因素，给出了真空预压地基处理工程应用的优化参数。研究成果将丰富并创新真空预压负压加固土体渗流固结理论，为道路交通、港口码头等软基处理工程设计提供参考。