Constitutive modeling of time-dependent stress–strain behaviour of saturated soils exhibiting both creep and swelling

Abstract

In general, clayey soils exhibit more or less both creep and swelling. In this paper, “creep” means viscous compression under a constant load condition in an oedometer test, while “swelling” means viscous expansion under a constant load condition in an oedometer test and is a reverse behaviour to creep for all saturated soils. Clayey soils containing the clay mineral montmorillonite show strong creep and swelling characteristics. Both creep and swelling characteristics have a significant influence on the deformation and failure of geotechnical structures. This paper presents main data from tests on a mixture of bentonite–silica sand in one-dimensional (1D) straining. Tests include (i) multistaged loading tests with unloading–reloading and enough time for creep and swelling in 1D straining and (ii) step-changed constant rate of strain (CRSN) compression tests with unloading–reloading in 1D straining as well. From the test data, the creep, swelling, and strain rate effects are observed and discussed. Based on the test data and a 1D elastic viscoplastic (1D EVP) model developed by Yin and Graham (1989, 1994 ), the authors propose a new 1D elastic viscoplastic model considering both creep and swelling (called 1D EVPS). The data from the multistage oedometer tests are used to calibrate the new model. After this, the new model is used to simulate the step-changed CRSN compression tests and make a comparison. In this way, the new model is verified. The new 1D EVPS is then used to simulate CRSN tests with a single strain rate, relaxation in the creep or swelling region, and constant rate of stressing tests. It is found that the new model can simulate well the strain (or stress) rate effects, loops in unloading–reloading, and stress relaxation in the creep region or stress increase in the swelling region, which are all caused by both creep and swelling of the soil.