Abstract: In response to the problem of the insufficient strength of the aeolian sand in engineering, an alkaline solution (NaOH) is used to treat the aeolian sand. To verify whether the strength of the aeolian sand has changed, a direct shear test is used to determine the appropriate alkali concentration. To study the micro mechanism of the alkali solution in strengthening the aeolian sand, the microstructure of the aeolian sand was observed by using the electron microscopy scanning. The micro images of the aeolian sand were processed by using the IPP (Image Pro Plus) image analysis software and the PCAS software to extract micro parameters. The results indicate that: (1) the addition of the alkaline solution can significantly improve the strength of the aeolian sand, but the additional addition of Ca2+ will not result in a more effective improvement in the soil strength; (2) An increase in the alkali concentration will enhance the shear strength of the soil, but there is an optimal content range. Excessive alkali concentration will not significantly improve the shear strength; (3) There is a certain relationship between the changes in the strength of the aeolian sand after the alkali solution reinforcement and the changes in the pore microstructure; (4) In terms of the microscopic mechanism, the NaOH interacts with the soil to produce the sheet-like polymers to fill soil pores and adhere to the surface of particles, enveloping soil particles, and improving the soil strength.

Key words: Aeolian Sand, NaOH, Direct Shear Test, Microstructure, SEM