Abstract: Aiming at the engineering disease problems caused by expansion and contraction of expansive soil and the pollution problems caused by lime improved expansive soil, this paper taked the expansive soil in Nanyang area of Henan province as the object of study, and prepared the specimens of vegetal expansive soil and improved soil with different dosages of lime and zeolite powder. The unconfined compressive test, free expansion rate test, triaxial test, X-ray diffraction (XRD) analysis and scanning electron microscope (SEM) test were carried out to study the strength characteristics and microscopic reinforcement mechanism of the lime-zeolite powder composite improved expansive soil. The results indicate that lime improvement and lime-zeolite powder composite improvement can effectively improve the strength of soil and reduce the free expansion rate, and the composite improvement effect is better. The optimum content of lime and zeolite powder is 6% (mass fraction) and 12% (mass fraction), respectively. The stress-strain curves of lime improved soil and composite improved soil are transformed into the strain-softening type. The addition of lime significantly improves the cohesion of the expansive soil. With the increase of zeolite powder content, the triaxial shear strength of composite improved soil increases continuously, and the internal friction angle increases first and then decreases. Zeolite powder reacts with lime to form a large amount of cementitious material, which fills the pores with soil and makes the microstructure more dense, increases the frictional resistance between soil particles, and increases the strength of the soil at the macro-level.

Key words: expansive soil, zeolite powder, lime, strength characteristic, unconfined compressive test, triaxial test, microscopic mechanism