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.

海相粉土具有显著的流变性、分散性、软化性与变形特性。土体中较高的有机质与含盐量，给沿海地区的工程建设带来了极大挑战。本文通过崩解试验、劈裂抗拉强度试验、扫描电子显微镜试验（Scanning Electron Microscope Tests，SEM）、X射线衍射试验（X-ray Diffraction Tests，XRD）、核磁共振试验（Nuclear Magnetic Resonance Tests，NMR）结合分形理论，系统分析了有机高分子材料木质素磺酸钙（calcium lignosulfonate，CLS）与聚丙烯酰胺（polyacrylamide，PAM）改良海相粉土的水力特性与微观机理。掺加水泥与CLS固化剂的试样，其崩解速率与干湿循环次数呈正相关，与掺量呈负相关。与之相比，PAM改良土的抗崩解性能尤为优异。此外，PAM还可显著提升粉土的抗拉强度，当PAM掺量高于3%时，该增强效果尤为显著。微观分析进一步揭示，PAM、CLS与粉土颗粒表面发生离子交换反应，生成绿泥石、钠长石、方解石、白云石与钾长石等新生矿物。这些胶结物质可有效填充孔隙，进而提升粉土颗粒间的黏聚力，使得土体在遇水时更不易发生体积膨胀、结构软化与崩解现象。最后，通过对微观孔隙结构的定性与定量分析可知，孔隙分形维数、孔隙分布分形维数与面积概率分布指标均呈现一定规律：重塑土（0次干湿循环）<5%CLS掺量试样（0次干湿循环）<3%PAM掺量试样（6次干湿循环）<5%PAM掺量试样（6次干湿循环）<7%PAM掺量试样（6次干湿循环）<5%PAM掺量试样（0次干湿循环）。平均形状系数与概率熵的变化趋势则与上述规律相反，这揭示了改良土微观结构变化对土体力学特性的影响机制。随着干湿循环次数增加，孔隙分布曲线的双峰向右偏移，整体孔径分布向中、大孔径方向发展；且PAM掺量越高，孔隙发育程度越弱。本研究成果可为沿海粉土路基与基坑加固工程提供一定的技术参考。