Abstract: Compaction test, unconfined compression test and triaxial test were carried out to study the strength characteristics of expansive soil modified by fly ash and weathered sand composite material. Results demonstrated that when keeping fly ash dosage unchanged, increasing the content of weathered sand enhanced the maximum dry density at first but then weakened, while gradually lessened the optimum water content; when keeping the content of weathered sand unchanged, increasing the fly ash dosage deteriorated both the maximum dry density and the optimum water content. When the proportion of fly ash and weather sand together remains at 20%, with the climbing of weathered sand proportion, the unconfined compressive strength and triaxial shear strength of expansive soil augmented firstly and then declined. The strength of expansive soil reached the maximum when weathered sand proportion was 5% and fly ash proportion 20%. In addition, the influences of fly ash and weathered sand dosages on the internal friction angle and cohesion of expansive soil were also examined.Internal friction angle inceased but then reduced with the rising of fly ash and weathered sand content; when the sum of fly ash and weathered sand content reamained unchanged, cohesion developed in negative relation with fly ash content, and in positive relation with weathered sand content.

Key words: expansive soil, fly ash, weathered sand, unconfined compressive strength, triaxial compressive strength