滨海相软土场地水泥土长期劣化过程试验研究

The cement soil, in corrosive environment for a long time, would be deteriorated inevitably as the corrosive mediums. Aim at deterioration problem of cement about cement soil in site of marine soft soil, in this application, the prepared cement soil specimens will be put into the coastal environments (seawater, saturated soft soil and site environment) immediately. Then the forming process and deterioration process of cement soil in site of marine soft soil will be simulated and realized. Based on the heterogeneous characteristics of deterioration cement soil, the temporal and spatial distributions of the strength are revealed through the full-automatic micro penetration test, and the deterioration layer, translation layer and non-deterioration layer will be investigated and quantified reasonably, then the deterioration depth can be determined. The scanning electron microscopy test, X-ray diffraction test, chemical analysis and infrared spectroscopy test would be conducted to study the distribution of the cement strength, microstructure characteristics, mineral composition, chemical composition and organic in time and space as well as their inter-relationships. The deterioration mechanism and mode of the cement in marine soft soil will be revealed and clarified, and the long-term degradation depth prediction model will be established. The research results can provide theoretical basis for the design, construction and durability evaluation of the cement-soil composite foundation in coastal area.

长期处于腐蚀场地中的水泥土会在腐蚀介质作用下发生劣化。针对形成于滨海相软土场地中水泥土的劣化问题，本申请项目通过将制备的水泥土试样不经脱模，立即与滨海环境（海水环境、原土环境和现场环境）接触的方式，模拟滨海相软土场地中水泥土的形成和劣化过程。基于水泥土劣化后的非均质特征，利用全自动微型贯入试验分析水泥土强度的时空分布规律，量化水泥土的劣化层、过渡层和未劣化层，确定劣化深度；借助扫描电镜、X射线衍射、化学分析及红外光谱等多种试验手段，多角度地综合研究水泥土的强度、微细观结构特性、矿物成分、化学成分、有机质含量在时间和空间上的分布规律及内在联系，揭示滨海相软土场地水泥土的劣化机理与过程，明确滨海相软土场地中水泥土的劣化过程模式，建立长期劣化深度预测模型。研究成果可为滨海地区水泥土桩复合地基的设计、施工及耐久性评价提供理论依据。

水泥土加固体具有整体性强、设计灵活、施工方便、噪音小、造价低和引起附加沉降小等优点，被广泛应用于土木工程和水利工程。长期处于腐蚀场地中的水泥土加固体，会不可避免地发生强度降低、渗透性增大的劣化现象。针对滨海相软土场地形成的水泥土强度劣化问题，本项目通过将制备的水泥土试样立即与腐蚀环境接触的方式，模拟滨海场地水泥土的形成和劣化过程。主要创新工作及研究成果如下：. （1）通过微型贯入试验，研究了水泥土强度的时空分布规律，在此基础上，定义了水泥土的劣化层和未劣化层。研究表明，水泥土的劣化深度随着时间的增长不断增大，随着水泥掺入比的增大而减小，养护至360天，水泥掺入比为7~20%的水泥土在海水环境中的劣化深度为1.0~8.7mm，在原土环境中的劣化深度为4.0~11.9mm，水泥掺入比为15%的水泥土在现场环境中的劣化深度达到3.4mm。. （2）与未劣化层相比，劣化层的微观结构孔隙增多，水化产物减少。钙离子、碳酸根含量及pH值随着取样深度和水泥掺入比的增大而增大；随着养护时间的增长，劣化层的钙离子含量和pH值逐渐减小，镁离子、硫酸根、氯离子含量逐渐增大；原土环境和现场环境中水泥土的pH值比海水环境中水泥土的pH值小。原土养护环境下水泥土中官能团含量高于海水养护环境中水泥土的官能团含量。. （3）提出了滨海相软土场地形成的水泥土劣化过程模式。侵蚀性物质通过物理化学反应及在水泥土中的不断渗透和扩散，导致水泥土表层劣化，使劣化过渡层不断转化为完全劣化层，未劣化层不断转化为劣化过渡层，即水泥土的劣化过程是随时间由表及里不断深入的过程。. （4）建立了水泥土长期劣化深度的预测函数。结果表明，海水环境中水泥土的劣化深度与养护时间基本呈对数函数增长；原土环境和现场环境中水泥土的劣化深度与养护时间呈幂函数增长，360天时水泥土劣化深度仍然发展较快。