Abstract: To explore the improvement effect of adding silt on expansive soil, the swelling-shrinkage characteristics, road performance and microstructure of expansive soil with different proportions of silt were tested. The results show that the incorporation of silt changes the composition and structure of soil particles, and inhibits the expansion and contraction potential of expansive soil. With the increase of silt particles, the compactness and unconfined compressive strength of expansive soil increase first and then decrease. The maximum dry density reaches 1.889 g/cm³ when the proportion of silt is 40%, and the unconfined compressive strength reaches the maximum when the proportion of silt is 10%. The California bearing ratio (CBR) value continues to increase significantly, and the rebound modulus shows a downward trend. All of these indexes meet the requirements of the specification. The feasibility of using silt to improve expansive soil is verified, and the optimum dosing ratio of silt is determined to be 40%. In order to facilitate onsite construction and consider the uniformity of onsite mixing, 3% low-dosage lime is first added to causes the performance of expansive soil to tend towards those of sandy soil so as to reduce the viscosity of the expansive soil and break it. On this basis, the expansive soil is applied to highway embankment filling after improved with 40% silt content, and onsite compaction degree, CBR value, deflection and other tests are carried out. The field test results show that the overall compaction quality of the experimental section improved by silt and lime and the control section treated by the single lime are controlled well, but the compaction degree of the test section is reduced due to the influence of the uniformity of the silt. The CBR value and subgrade deflection of the test section are comparable to those of the control section, and the silt improvement effectively compensates for the strength provided by the 2% lime reduced relative to the control section.

Key words: expansive soil, silt, improvement, swelling-shrinkage characteristics, road performance