Undrained Cyclic Loading Response of Subgrade Soil Subjected to Varying Moisture Content and Stress Level

Abstract

Subgrades that are constructed from fine-grained cohesive soils undergo large settlements; therefore, the study of their deformation behavior is important to avoid early deterioration in the traffic infrastructure. In this study, the deformation behavior of two different types of cohesive subgrade soils at different compaction states has been addressed that considered the effect of influencing factors, such as water content, deviatoric stress, and confining pressure (σ3). The results from the unconsolidated undrained cyclic triaxial tests show that the deformation behavior of soil is highly influenced by the level of applied deviatoric stresses and moisture content on the wet side of optimum (WS) and is slightly affected by σ3 and moisture content on the dry side of optimum (DS). The elastic strain (ɛe) component showed a decreasing trend with an increase in the number of load cycles (N) and then attained a steady value toward a higher N; however, the plastic strain (ɛp) component continuously increased for a given magnitude of applied cyclic deviatoric stresses (σd,c). From the test results, logarithmic strain models were proposed to predict the long-term total (ɛt) strain and ɛp that developed in cohesive subgrade soils, which were subjected to various combinations of variations in moisture content and stresses. The proposed model has been compared with the existing model and shows better prediction ability with a coefficient of correlation (R2) of >95% in most cases.