From saturated to unsaturated conditions and vice versa

Abstract

Representing transitions between saturated and unsaturated conditions, during drying, wetting and loading paths, is a necessary step for a consistent unification between saturated and unsaturated soil mechanics. Transitions from saturated to unsaturated conditions during drying will occur at a nonzero air-entry value of suction, whereas transitions from unsaturated to saturated conditions during wetting or loading will occur at a lower nonzero air-exclusion value of suction. Air-entry and airexclusion values of suction for a given soil will differ (representing hysteresis in the retention behaviour) and both are affected by changes in the dry density of the soil or by the occurrence of plastic volumetric strains. The paper demonstrates, through model simulations and comparison with experimental data from the literature (covering drying, wetting and loading tests), that the Glasgow Coupled Model (GCM), a coupled elasto-plastic constitutive model covering both mechanical and retention behaviour, represents transitions between unsaturated and saturated behaviour in a consistent fashion. Key aspects of the GCM are the use of Bishop's stress tensor for mechanical behaviour, the additional influence of degree of saturation on mechanical yielding, inclusion of hysteresis in the retention behaviour, and the role of plastic volumetric strains (and not total volumetric strains) in the description of the water retention response. The success of the GCM in representing consistently transitions between saturated and unsaturated conditions, together with subsequent mechanical and retention responses, demonstrates the potential of this coupled constitutive model for numerical modelling of boundary value problems involving saturated and unsaturated conditions.

A bounding surface mechanical model for unsaturated cemented soils under isotropic stresses

“…Fig. 9b also demonstrates the capability of the model to capture the transition from unsaturated to saturated states during loading [41][42].…”

Numerical Implementation of a Critical State Model for Soft Rocks

“…It is therefore important to test first its numerical performance for saturated conditions, in view of any future extension of the saturated model to include unsaturated stress states. In this context, it is also important to ensure at this stage, that the saturated framework adopted is also a suitable platform from where the representation of the transitions between saturated and unsaturated states can be modelled (Lloret-Cabot et al 2017a) and that such representation is done consistently with the elasto-plastic critical state theory typically adopted to model saturated conditions (Lloret-Cabot et al 2017b).…”

Evolution of the soil water retention curve based on plastic volumetric strain

“…The modified suction was introduced for consistency with the work equation for unsaturated soils proposed by Houlsby (1997). Subsequently, Lloret-Cabot et al [10], Lloret-Cabot et al [12] reinforced this concept by defining SWRC as the relationship between and with supporting experimental evidence. More recently, Kodikara et al [13] utilised the same approach in the MPK generalised model to capture the hydro-mechanical behaviour of unsaturated soils.…”

“…Various researchers have endeavoured to consider the dependency of soil deformation or soil state on SWRC by incorporating governing variables. For instance, the SWRC has been coupled to the void ratio or specific volume [4,5]; soil density [6], volumetric strain [7], mean net stress [8] and volumetric plastic strain [9,10]. Specifically, Gallipoli et al [4] extended the Van Genuchten [11]-based SWRC as a function of specific volume in a study of compacted kaolin.…”