盐水漏失后联络通道冻结壁多元变形机理研究

Brine leakage is one of frequently encountered construction safety problem in artificial freezing engineering. To reveal the strength and deformation characteristics of frozen wall in connecting aisle in the case of brine leakage, this program takes the soft clay in the yangtze river delta as the study object, and the specimens are produced by mixing Calcium chloride solution at various concentrations. Firstly, three temperature control paths are used in testing including freezing, thawing as well as cyclic freeze and thaw, to investigate the correlation between coupling migration of water and salinity and meso-level structure of soils at various temperature gradients, facilitated by CT and TDR. Then the shear tests and creep tests at triaxial conditions are carried out and the mechanism of how salinity affects the strength and creep was studied by CT. A constitutive model based on the hypoplastic model with four parameters is proposed by considering both freeze-thaw cycling and creep, and the tensors representing the cohesive forces and viscous strain rate are included. The hydraulic, thermal and mechanical interactions in soils after brine intrusion are analyzed and the modules are compiled for each source of deformation in COMSOL platform, forming a new computational method for estimating the multi-source deformation of frozen wall. Finally, the specific engineering conditions are modeled and the results will help improve the proposed numerical method. The research will give more targeted theoretical supports for emergency plan establishment when brine leakage occurred during artificial freezing construction, and also, benefit the scientific design of frozen wall in constructing connecting aisle in soft clay layers.

盐水漏失是冻结法施工中的常见施工安全问题。为揭示盐水漏失后地铁联络通道冻结壁的强度和变形特性，本项目拟以我国长三角地区常见的软黏土为研究对象，通过掺入不同浓度的氯化钙溶液制备试样，首先开展冻结、融化和多次冻融三种控温路径试验，利用CT和TDR研究冻融过程中温度梯度对水盐迁移的影响及其与细观结构演变之间的关联；开展多次冻融后含盐软黏土三轴应力下的剪切和蠕变测试，利用CT研究盐分对强度和蠕变特性影响的细观机理。基于四参数亚塑性模型，通过引入表征粘聚力的张量和黏性应变率张量，建立一种同时考虑冻融和蠕变的亚塑性本构模型；基于盐分介入后水热力相互作用，以COMSOL软件为工具，将各个变形元编译为可供调用的计算模块，建立冻结壁多元变形分析方法。结合冻结法施工联络通道的具体工程进行模拟与分析。研究成果将为软黏土地层中地铁联络通道冻结法施工的应急预案编制及冻结壁的科学设计提供更具针对性的理论支持。

针对人工冻结工程中盐水漏失带来的施工安全问题，本项目以苏州吴江区软黏土为研究对象，主要开展了三个方面的工作。首先，测试了软黏土的水热盐迁移特征参数、融化固结、强度和蠕变特性。其次，在经典Harlan水热分析模型基础上引入一个随水盐含量和冻融次数动态变化的冻结温度判断函数，采用Darcy定律和Fick定律描述土壤溶质的对流和扩散，并采用修正的von Wolffersdorff模型描述了软黏土的应力应变行为，建立了一种较为完善的水热盐力耦合理论模型。第三，采用PDE形式将上述理论模型数值化于COMSOL多物理场分析平台，模拟了软黏土地层实施单圈管冻结施工过程中的水分场、温度场、盐分场和地层变形。针对冻结管断裂工况下的冻结壁缺陷，提出了基于软黏土冻结温度动态变化的冻结壁位置和冻结壁厚度的动态判断方法。根据冻结壁厚度不均匀发展的特点，定义了基于目标冻结壁厚度和各位置冻结壁实际厚度为基础的量化指标——完整比，可实现对施工过程中冻结壁增厚和交圈过程的定量化评价。建议在实际施工过程中加强水热盐监测，采用上述方法实时判断冻结壁完整比，为实时调整冻结方案提供关键理论依据。总体来看，研究成果以解决人工冻结工程中盐水漏失带来的施工安全隐患为主要目标，积累了软黏土物理力学特征参数等重要数据，进一步夯实了人工冻结法的理论基础，可为盐水漏失等地层冻结施工的风险控制提供理论支持。