Abstract: Upon completing large-area layered filling, the foundation soil exhibits transverse isotropy and is predominantly unsaturated, making post-construction settlement prediction challenging. Additionally, the creep model considering transverse isotropy and unsaturated characteristics has not been proposed. Therefore, the true triaxial apparatus for unsaturated soil was enhanced, and transversely isotropic unsaturated loess samples were prepared. The relationship between matrix suction and moisture content at various depths in transversely isotropic unsaturated loess was determined using soil-water characteristic curve tests. The creep characteristics of loess fill under varying moisture content, degree of compaction, deviatoric stress, and net confining pressure were examined using a consolidation drainage test system. According to the creep curve, the expressions for six parameters in the modified Burgers element model were determined, establishing a post-construction settlement prediction method for transversely isotropic unsaturated loess fill foundations. The results show that the transversely isotropic unsaturated loess exhibits distinct creep characteristics, primarily nonlinear attenuation creep. The degree of compaction, moisture content, deviatoric stress and net confining pressure significantly affect its creep characteristics. Creep stability strain is linearly related to the degree of compaction. Enhancing soil compaction can effectively reduce post-construction settlement of the fill foundation. A prediction algorithm based on the modified Burgers model, which reflects the influence of degree of compaction, moisture content, and stress level, and accurately describes the post-construction settlement behavior of transversely isotropic unsaturated loess fill foundations, is established. Actual engineering monitoring results demonstrate that the proposed settlement prediction algorithm is simple, practical, and effective. The research results can enrich and advance the creep model of unsaturated soil, and provide a scientific basis for solving the problem of deformation calculation of high fill foundation.

Key words: transverse isotropy, unsaturated loess, fill ground, triaxial creep test, modified Burgers model, post construction settlement prediction