Experimental and Constitutive Modeling of Relaxation Behaviors of Three Clayey Soils

The stress-strain behavior of clayey soil is time dependent. Laboratory study and constitutive modeling of the time-dependent stress-strain behavior are needed to understand the soil behavior and analyze displacements of reclamation works and foundations on clayey soils. The stress relaxation, as one of the significant time-dependent phenomena in clayey soils, has been observed and examined in excavations and constructions, such as the short-term change in lateral earth pressure after installation of a supporting system. In this study, Hong Kong marine deposits (HKMDs), which are clayey soils, and a sand-mixed bentonite (SMB) soil were investigated in relaxation tests. Relaxations were performed in both the loading stage and the unloading stage. This paper is focused on the testing study and modeling of the time-dependent relaxation behavior of clayey soils. Relaxation tests were carried out to measure the changes of the effective stress with time in one-dimensional (1D) straining condition. A new 1D elastic visco-plastic model considering swelling (1D EVPS) was used to simulate the relaxation tests. Analytical solutions from the 1D EVPS constitutive equations were obtained for relaxation tests. All parameters in this 1D EVPS model were obtained from a conventional oedometer test. The analytical solutions from the 1D EVPS model were used to simulate the relaxation behavior and compare with test data. Good agreement between the simulated curve and the measured data were found. (C) 2013 American Society of Civil Engineers.