Abstract: The swelling index, a crucial parameter for soil deformation, holds significant importance in the critical state elasto-plastic constitutive model. Unlike the compressibility index, which has been extensively reported in literature, the variation of the swelling index with matric suction has often been overlooked in theoretical studies of unsaturated soil constitutive models. To address this gap, oedometer tests were conducted on remolded silt specimens sourced from Hangzhou, China. Under suction-controlled conditions, utilizing an oedometer equipped with a GDS direct shear chamber, the experimental program comprised three tests conducted at matric suction levels of 50, 100, and 200 kPa. The relationship between matric suction and the swelling index, denoted as κ(s), was established and fitted. Validation was performed by comparison with previous experimental studies. Furthermore, this κ(s) relationship was incorporated into an unsaturated soil-extended Cam-clay elasto-plastic model. An explicit integration with a substepping error control algorithm was implemented within the ABAQUS finite element method (FEM) UMAT subroutine. The numerical modeling results of the silt oedometer tests, coupled with the UMAT subroutine, exhibited high agreement with laboratory tests.

Key words: unsaturated soil, matric suction, swelling index, constitutive model, finite element method