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.

Influence of strain-rate on hydromechanical behavior of highly compacted GMZ01 bentonite

“…5 indicates that, with changing of the strain rate applied, the compression curve jumps from the current CRS curve to another one correspondingly. This observation was consistent with the results reported by Leroueil et al (1985), Watabe et al (2012) and Yin & Tong (2011) for saturated soils.…”

“…Based on multistage oedometer tests and CRS tests, Yin and Tong (2011) found that the bentonite-sand mixtures exhibit distinct nonlinear creep of swelling behavior, which demonstrates that time-dependent property of buffer/backfill material cannot be neglected.…”

“…Step-wise CRS test or step-changed Constant Rate of StraiN (CRSN) test (Yin & Tong, 2011) is also referred as a special CRS test (Leroueil et al, 1985), which several constant strain rates will…”

“…In this regards, contributions have been devoted to theoretically calculate the virgin compression index λ from parameters C c . Yin & Tong (2011) once come up with the relationship of the parameter as follows,…”

“…In this regard, enormous contributions have been made to the investigation of the buffering behavior of highly compacted bentonite (Romero et al, 2005(Romero et al, , 2013Alonso, 2005;Tang et al, 2008;Ye et al, 2009Ye et al, , 2010Ye et al, , 2012Gens et al, 2011;Villar et al, 2012;Wang, 2012Wang, , 2013. Results indicate that, during the long-term (>10 5 years) operation of a repository, it is of great significance to consider the possibility of barrier creep in the repository performance assessments (Pusch & Adey, 1999;Yin & Tong, 2011), even though the main determinant of the creep rate and the resulting canister sinking could be the magnitude of the mobilized shear strength (shear stress divided by shear strength) (Dueck et al, 2010). Furthermore, the buffer clay will be in unsaturated state for a long period of time, because of the low permeability of the material and the heat effects induced by the decay of radioactive waste in the canister .…”