Experimental investigations on the physico-mechanical and microstructural properties of loess reinforced with anionic polyacrylamide

The typical characteristics of loess, such as macropores, weak cementation, and strong collapsibility, can adversely affect the stability of building foundations, transportation infrastructure, and other geotechnical systems. To address this problem, a water-soluble anionic polyacrylamide (APAM) was used to improve the characteristics of loess. A series of multi-scale geotechnical engineering tests, such as sedimentation column, zeta potential, Atterberg limits, standard compaction, permeability, triaxial compression strength, scanning electron microscope (SEM), nuclear magnetic resonance (NMR), and X-ray diffraction (XRD) tests were conducted on the loess samples. The results showed that the APAM polymer could flocculate fine loess particles into stable agglomerates via a series of physical actions, including charge neutralization, adsorption and bridging, and hydrophobic interactions. The contact form among the loess particles changed from loose point contact to strong mosaic contact with the addition of the APAM polymer, the surface porosity, fractal dimension, and interplanar spacing of the treatment material decreased significantly. The considerable improvement of loess microstructure affected its macroscopic physical and mechanical properties. The optimum moisture content and permeability coefficient of the treated loess decreased with the increases of the APAM content, whereas the plasticity index and maximum dry density increased. Additionally, the failure strength of the loess samples first increased then decreased as the APAM content increased, which showed the maximum value at an addition amount of 0.30% content, beyond which its strength value decreased. The test results demonstrated that the APAM polymer treatment could provide significant improvement in the macroscopic physico-mechanical and microstructural properties of loess. This study will serve as a crucial resource for loess foundation stabilization using the environmentally friendly and cost-effective polymer.