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