Hydraulic properties and microscopic mechanism of Marine silty soil improved by polymers

Marine silty soil exhibits strong rheological, dispersive, softening and deformable properties. The high organic matter content and salinity in the soil pose great challenges to engineering construction in coastal areas. In this paper, through disintegration tests, splitting tensile strength tests, scanning electron microscope tests (SEM), X-ray diffraction tests (XRD), nuclear magnetic resonance tests (NMR) and fractal theory, the hydraulic characteristics and microscopic mechanisms of marine silty soil improved by the organic polymer calcium lignosulfonate (CLS) and polyacrylamide (PAM) were systematically analyzed. The disintegration rate of the specimens doped with cement and CLS curing agents is positively correlated with the number of dry-wet cycles and negatively correlated with the doping amount. In contrast, the anti-disintegration property of the PAM-improved soil is particularly excellent. In addition, PAM can also significantly enhance the tensile strength of the silty soil, and this enhancement effect is particularly significant when the PAM doping amount is higher than 3%. Microscopic analysis further reveals that ion exchange reactions occur between PAM, CLS and the surfaces of silty soil particles, generating new minerals such as chlorite, albite, calcite, dolomite and potassium feldspar. These cements effectively fill the pores, thereby enhancing the cohesive force between the silty soil particles. This makes the soil less prone to volume expansion, structural softening and disintegration when encountering water. Finally, qualitative and quantitative analyses on the microscopic pore structures show that the fractal dimension of pores, the fractal dimension of porosity distribution and the area probability distribution index exhibit certain regularities, that is, remolded soil (0 cycles) < 5% CLS (0 cycles) < 3% PAM (6 cycles) < 5% PAM (6 cycles) < 7% PAM (6 cycles) < 5% PAM (0 cycles). The changing trends of the average shape coefficient and probability entropy are opposite to the above, which reveals the influence of the changes in the microscopic structure of the improved soil on the mechanical properties of the soil. As the number of dry-wet cycles increases, the double peaks in the pore distribution curve shift to the right, the overall pore size distribution tends to develop towards medium and large pore sizes, and the higher the PAM doping amount, the less significant the pore development. The research results are expected to provide certain technical references for the reinforcement of coastal silty subgrades and foundation pits.

滨海淤质土壤表现出显著的流变学、分散性、软化及变形特性。土壤中高含量的有机质与盐分对沿海地区的工程建设构成了重大挑战。本研究通过碎裂试验、抗拉强度试验、扫描电子显微镜测试（SEM）、X射线衍射测试（XRD）、核磁共振测试（NMR）及分形理论，对经有机聚合物木质磺酸钙（CLS）和聚丙烯酰胺（PAM）改良的滨海淤质土壤的力学特性和微观机理进行了系统分析。添加水泥和CLS固化剂的试样碎裂率与干湿循环次数呈正相关，与添加量呈负相关。相比之下，PAM改良土壤的抗碎裂性能尤为出色。此外，PAM还能够显著提高淤质土壤的抗拉强度，当PAM添加量超过3%时，这种增强效果尤为显著。微观分析进一步揭示，PAM、CLS与淤质土壤颗粒表面的离子交换反应发生，生成新的矿物如绿泥石、长石、方解石、白云石及钾长石。这些矿物有效填充孔隙，从而增强了淤质土壤颗粒之间的凝聚力。这使得土壤在水的作用下更不易发生体积膨胀、结构软化及碎裂。最终，对微观孔隙结构的定性和定量分析表明，孔隙的 fractal 维数、孔隙分布的 fractal 维数及面积概率分布指数呈现出一定的规律性，即重塑土壤（0次循环）< 5% CLS（0次循环）< 3% PAM（6次循环）< 5% PAM（6次循环）< 7% PAM（6次循环）< 5% PAM（0次循环）。平均形状系数和概率熵的变化趋势与上述规律相反，揭示了改良土壤微观结构变化对土壤力学性能的影响。随着干湿循环次数的增加，孔隙分布曲线的双峰向右移动，整体孔隙尺寸分布趋向于中等和大型孔隙，PAM添加量越高，孔隙发育程度越低。本研究结果预期将为滨海淤质路基和基坑的加固提供一定的技术参考。