Abstract: The aim of this research is to investigate the impact of particle size and dosage of waste tire rubber on the mechanical properties of expansive soil. Following compaction tests, expansive soil was mixed with rubber particles of four different size groups, with dosages of 0%, 5%, 10%, 15%, and 20%, for expansion rate test, unconfined compressive strength test, and direct shear test. Test results indicate that the maximum dry density and optimum water content of the improved expansive soil decrease with increasing rubber particle size, despite the same rubber dosage. Rubber particles, regardless of its size, exhibit inhibitory effect on the expansion potential of the expansive soil, with this effect becoming more pronounced as particle size and dosage increase. The internal friction angle and cohesion of expansive soil mixed with rubber particles of small (<0.25 mm) and large (>2 mm) particle sizes fluctuate significantly with varying mixing amounts. The particle size range of 1-2 mm and dosage range of 10%-15% prove most effective in improving the shear strength of expansive soil. The unconfined compressive strength of expansive soil dosed with rubber particles with the same size initially increases and then decreases with increasing dosage. Similarly, the unconfined compressive strength of expansive soil mixed with rubber particles of the same dosage increases with increasing particle size. A particle size of 2-5 mm and a dosage of 15% are determined as the optimal mixing ratio for compression.

Key words: expansive soil, rubber particle size, expansion rate, strength characteristics, optimum mixing ratio