arXiv subjects

Jean Vaunat

Publications and source records attributed to Jean Vaunat.

3 recordsLinked to original sources

arXiv2026

A Non-Isothermal Viscoplastic Constitutive Model for Clay Slip Surfaces

Clayey slip surfaces control the reactivation and long-term deformation of slow-moving landslides and may experience thermal fluctuations from climate, seasonal ground-temperature changes, or subsurface heat sources. Experiments show that residual shear strength depends on temperature and shearing rate, yet most numerical approaches use temperature-independent strength parameters. We present a non-isothermal viscoplastic constitutive model for clayey slip surfaces implemented with zero-thickness interface elements. It includes temperature-dependent normal and tangential stiffness, progressive degradation of cohesion and friction angle, and rate-dependent viscoplastic slip governed by a non-associated flow rule. Coupling with hydraulic and thermal balance equations allows the interface response to evolve with stress state, temperature, aperture, and accumulated irreversible displacement. Validation against temperature-controlled drained ring-shear tests on bentonite and smectite-rich soils covers heating--cooling, cooling--heating, and combined thermal paths. The simulations reproduce thermal strengthening at slow shearing rates and thermal weakening or limited sensitivity at higher rates. Application to the Congress Street cut benchmark shows that zero-thickness elements improve the representation of strain localization and progressive failure. Increasing temperature progressively degrades interface strength, increases displacement, joint aperture, and shear strain, and accelerates sliding. Temperature-dependent interface degradation can therefore reduce the apparent stability margin of clayey slopes and should be included in slope-stability assessments involving thermal fluctuations.

physics.comp-ph↗

arXiv2010

Is the degree of saturation a good candidate for Bishop's X parameter?

In unsaturated soil mechanics, the quest for an effective stress playing the same role as Terzaghi's effective stress does for saturated soils has introduced a long standing debate, dating back to the 1960s. Several contributions have been proposed since the early work of Bishop. It is well recognized to date that a single constitutive stress is not sufficient by itself to catch the main features of the behaviour of unsaturated soils and it is often combined with matric suction. In this paper, focus is given to a largely used formulation for such a constitutive stress, based on the use of an averaged pore pressure. In particular, this paper discusses on thermodynamics bases the validity of the choice of the factor X weighting the fluid pressures contribution to the constitutive stress. This factor is usually assumed to be equal to the degree of saturation of water. In this work it is shown that the choice of this natural candidate implies restrictive assumptions on the plastic flow rule. As shown from experimental data obtained from a literature review, this choice may not be pertinent for certain classes of materials, particularly high plasticity clays.

physics.geo-ph↗

arXiv2010

Revisiting the thermodynamics of hardening plasticity for unsaturated soils

A thermodynamically consistent extension of the constitutive equations of saturated soils to unsaturated conditions is often worked out through the use a unique 'effective' interstitial pressure, accounting equivalently for the pressures of the saturating fluids acting separately on the internal solid walls of the pore network. The natural candidate for this effective interstitial pressure is the space averaged interstitial pressure. In contrast experimental observations have revealed that, at least, a pair of stress state variables was needed for a suitable framework to describe stress-strain-strength behaviour of unsaturated soils. The thermodynamics analysis presented here shows that the most general approach to the behaviour of unsaturated soils actually requires three stress state variables: the suction, which is required to describe the invasion of the soil by the liquid water phase through the retention curve; two effective stresses, which are required to describe the soil deformation at water saturation held constant. However a simple assumption related to the plastic flow rule leads to the final need of only a Bishop-like effective stress to formulate the stress-strain constitutive equation describing the soil deformation, while the retention properties still involve the suction and possibly the deformation. Commonly accepted models for unsaturated soils, that is the Barcelona Basic Model and any approach based on the use of an effective averaged interstitial pressure, appear as special extreme cases of the thermodynamic formulation proposed here.

physics.geo-ph↗