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International audience; This paper presents a two-surface plasticity model for describing some important features of saturated clay under cyclic loading conditions, such as closed hysteresis loops, cyclic shakedown and degradation, and different stress–strain relations for two-way loading. The model, namely ACC-2-C, is based on the elastoplastic model ACC-2 (an adapted Modified Cam Clay model with two yield surfaces) developed by Hong et al. (Acta Geotech 11(4):871–885, 2015). The small-strain nonlinearity concept is adopted to achieve the nonlinear characteristics of clay during unloading–loading stage. The new hardening law related to accumulated deviatoric plastic strain is proposed for the inner surface to describe the cyclic shakedown and degradation. Following the advantages of the ACC-2 model, the constitutive equations are simply formulated based on the consistency condition for the inner yield surface. The model is conveniently implemented in a finite element code using a stress integration scheme similar to the Modified Cam Clay model. The simulation results are highly consistent with experimental data from drained and undrained isotropic cyclic triaxial tests in normally consolidated saturated clay under both one-way and two-way loadings.

This paper presents an advanced thermomechanical model – TEAM in the framework of two-surface plasticity for saturated clays, with emphasis put on some important thermomechanical features of natural clays evidenced experimentally such as the limited thermomechanical elastic zone, the smooth transition from elastic to plastic behavior. Two plastic mechanisms are introduced in the model: one is to reproduce the ther-moplasticity involving thermal expansion and contraction observed at high over-consolidation ratios and the second one describes the temperature effect on the yield behavior. The model adopts additional yield surfaces , namely inner yield surfaces that are associated with the two proposed plastic mechanisms to account for the plastic behavior inside the existing conventional thermomechanical yield surface namely yield surfaces. The general expressions of the yield surfaces and plastic potentials in p′–q–T space are introduced. A progressive plastic hardening mechanism associated with the inner yield surface is defined, enabling the plastic modulus to vary smoothly during thermomechanical loadings inside the yield surfaces. Several tests on natural Boom clay along different thermomechanical loading paths have been simulated by TEAM, and results show its relevance in describing the thermomechanical behavior of saturated clays.

International audience; Moisture migration and distribution in the substructure are found to be the important reasons for water-related problems in high-speed railways. In this study, a numerical model of a double-line ballastless track-bed consisting of a substructure (subgrade surface layer, subgrade bottom layer and subsoil) and a superstructure (including two concrete bases right above the substructure) was established. The superstructure was considered as an impermeable boundary in this model, while two fissures were set at the joint edges of the left-line concrete base and the surface layer, simulating the infiltration area of rainwater. The effects of degree of compaction and fines content of the bottom layer due to moisture migration in the high-speed railway substructure were investigated on this model by applying and analyzing the 2013 rainfall data of Hangzhou, China, for a three-year period. The results show that the saturation zones develop in the subgrade, after a three-year period, with the size increasing with the increase in the degree of compaction or fines content due to higher water retention capacity and lower permeability of the soil. Furthermore, the variations of volumetric water content at different depths of the left-fissure profile indicate that as the degree of compaction or fines content increases, the arriving time of the wetting front increases, but the fluctuation amplitude of the volumetric water content after the arrival of the wetting front decreases on the whole. The degree of compaction appears to present a more significant impact on these two parameters. In particular, a threshold value of the degree of compaction between 0.90 and 0.93 is observed, prolonging the arriving time of the wetting front remarkably at a certain elevation. Besides, it takes a longer time for the wetting front to pass through the interface between the surface layer and the bottom layer for each case. From a practical point of view, it will be beneficial to employ drainage methods to drain out the water before it reaches the bottom layer.