冻融后的改性聚乙烯醇与石灰固化滨海盐渍土的微结构与强度研究

Saline soil solidified with modified polyvinyl formaldehyde and lime can be used as the fillers of roadbed, and the better solidified effect is verified by laboratory and in-situ tests. Phenomenon of freeze during winter and thaw during spring is the climatic characters in northern, China, it will cause some diseases like salt expansion, frost heave and collapsibility, and then that damage the soil structure and decrease the strength and anti-deformation. Main study contents include: (i) Optimized mix proportion is proposed on solidified soil after freeze-thaw cycling on the basis of unconfined compression test and triaxial shear test. (ii) Composition and patterns of cements, pore structure, micro fractures, change of ice location and area are analyzed with methods of XRD, FTIR, CT Scanning, SEM and Low Field Nuclear Magnetic Resonance. (iii) Image of microstructure and micro fractures are calculated by software of Leica QWin 5000. (iv) Effect of freeze-thaw cycles, salt content, solidified materials, admixture amount, alkalinity of soil solution, active ion, etc. on strength of solidified soil are discussed through multiple stepwise regression method to obtain the relationships between microstructure and strength of solidified soil. The results will enrich the strength theory of solidified soil and guide technical research to proportion design of solidified materials and road maintenance in saline soil area.

以改性的聚乙烯醇和石灰联合固化滨海盐渍土作路堤填料，其室内和现场测试结果均证实其固化效果良好。北方的冬季冻结和春季融化引起固化盐渍土的盐胀、冻胀、溶陷问题，使固化土的结构受到损伤破坏，引起固化土的强度和抗变形性能下降。开展冻融后固化土的抗压试验和三轴压缩试验，优化固化材料配合比；利用XRD、FTIR、CT扫描、SEM、低场核磁共振等手段，研究固化土多次冻融过程中的胶结物成分和胶结方式、土孔隙结构和微裂隙的变化、冰的位置和面积变化；借助Leica QWin 5000图像处理软件计算固化土的微结构指标和微裂隙尺寸；以多元逐步回归法对冻融固化土的强度影响因素，诸如冻融次数、含盐量、固化材料成分和掺入量、土溶液碱度、活性阳离子等进行分析，探寻冻融循环后改性聚乙烯醇和石灰固化盐渍土微结构和强度的变化规律。研究成果可丰富固化土的强度理论，为北方滨海盐渍土路堤填料的固化配比设计和道路维护提供技术支持。

经宏观(冻融后固化土的抗压试验和三轴压缩试验)和微观指标（SEM、低场核磁共振等）测定结果证实，采用石灰、粉煤灰和高分子材料SH固土剂固化滨海盐渍土可改善土的抗冻融稳定性。.研究工作为：（1）多次冻融条件下固化盐渍土的强度及变形特性；（2）抗冻融性与固化材料配合比之间的关系；（3）固化土抗冻融性的影响因素及敏感性。（4）单次和多次冻融对固化盐渍土微结构的影响；（5）单次及多次冻融过程中水-盐迁移及冰水界面的变化；（6）冻融后固化盐渍土的微结构指标与强度变化规律研究。.取得成果：（1）SH固土剂可包裹土颗粒，并在颗粒间和孔隙中形成了丝网状连接结构，石灰和粉煤灰碳化反应生成胶结物填充与土颗粒孔隙，两者作用相结合改善了土的强度；（2）冻融循环过程中结构形态未松散破坏，结构依然存在，石灰、粉煤灰及SH固土剂物理化学反应具有不可逆性和结构稳定，在一定程度上保证了固化土的抗冻融稳定性；（3）固化盐渍土的微结构参数与力学强度有一定的相关性；（4）冻融循环改变含水率和含盐量的纵横向迁移，初始含水率对水盐迁移影响显著，固化土水盐的重分布相似，盐分的迁移受受制于水分迁移。（5）冻融循环作用使固化土中产生了新的孔隙，但未出现孔隙明显变宽的现象，固化土内部未出现较为严重的冻融损伤。