Viscous Behavior and Constitutive Modeling of Peaty Soil in Kunming, China

Abstract

The Kunming peaty soil exhibits distinct physical and mechanical properties from the inorganic clay due to the special soil-forming process and material composition. To better understand the viscous behavior of peaty soil, a series of laboratory tests, including four types of oedometer tests (one- and multistage loading creep tests, constant rate of strain tests, and constant rate of stress) and constant rate of strain undrained triaxial compression tests, are conducted on the Kunming peaty soil. The experimental results demonstrate that the Kunming peaty soil shows significant secondary compression during oedometer creep tests. Meanwhile, the variations of the measured preconsolidation pressure and undrained shear strength with the strain rate are essentially linear in log-log plot for the examined range of strain rate. Based on the generalized power law overstress viscoplastic theory, it is confirmed that the rate-sensitivity and time-dependency of the Kunming peaty soil can be uniformly described using the sensitivity parameter involved in the theory, regardless of the applied loading conditions. The average value of 0.06 for the sensitivity parameter is generally greater than those for inorganic clay, indicating that the Kunming peaty soil exhibits more significant viscous behavior. Finally, by using the yield surface of the modified Cam–clay model, an overstress elastic-viscoplastic model is established and numerically implemented. The numerical model with a unique sensitivity parameter can well predict the rate-sensitive and time-dependent response of Kunming peaty soil under different loading conditions.