Abstract: By using triaxial apparatus, 36 consolidated drained tests were conducted on the unsaturated soil to determine the parameters and the model of the high-fill soil-rock mixture project. The effects of compaction degree, matric suction and mixing ratio on the strength and deformation characteristics of the unsaturated remoulded mixture were quantitatively examined by controlling net confining pressure. Modified expressions for shear strength, tangent deformation modulus and tangent volume modulus of unsaturated compacted soil were also developed. The experimental results showed that the failure stress and cohesion increased linearly with the increase of suction, whereas the changes of suction had little influence on the effective internal friction angle. It was found that failure stress and strength parameters increased with the increase of compaction coefficient. The failure stress and strength parameters of soil samples with the ratio of 4: 6 were slightly higher than those of soil samples with the ratio of 2: 8. Moreover, the effective cohesion increased with the increase of silty clay content. For the same mixing proportion and compacting coefficient of soil samples, the intensity of sample grew with the increase of net confining pressure and suction. Correspondingly, its volume gradually changed from shrinkage to dilatancy. For the same net confining pressure, the suction and the mixture ratio of soil samples, the strain curve progressively turned from the strain hardening type to the ideal elastoplastic type with the increase of compaction coefficient. However, partial soil samples tended to strain softening type under the low net confining pressure. It is verified that the revised incremental nonlinear constitutive relationship of unsaturated soil is consistent with the practical project of large area fill. Thus, this study can be used for calculating the deformation of high-fill foundation and analysing the stability of the high embankment slope.

Key words: soil- rock aggregate mixture, shear strength, nonlinear model parameters, compactness, matric suction