Combined effects of structure and partial saturation in natural soils

Abstract

The mechanical behaviour of natural clays is significantly affected by their in situ or initial structure in the form of cementation or interparticle bonding. This behaviour can differ substantially from the behaviour of reconstituted clays. Suction as well as plastic volumetric strains drive isotropic hardening/softening as this is a simple way to account for the phenomenon of volumetric collapse upon wetting and the stiffening effect that suction has on the soil skeletal response. A model that combines unsaturated and structured behavior is presented and then used to simulate stress strain behaviour observed for an unsaturated natural clay subjected to isotropic load paths. A parametric analysis is performed to observe the influence suction hardening has on mobilized strengths. It is also shown that the model can predict the maximum of collapse of unsaturated soils.

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

“…The model also suggests that, as the percentage of cement increases, the extra porosity sustained by capillarity tends to reduce compared to the extra porosity sustained by cementation. In other words, the contribution of capillarity to inter-granular bonding becomes less important as the degree of cementation increases, which is also consistent with previous studies [7]. As during calibration, experimental values of degree of saturation were used to calculate the mean cemented scaled stress in all simulations.…”

“…Many structured soil deposits are also found in the superficial ground layer and often exists in a partially saturated state. Partial saturation affects the mechanical behaviour of structured soils by causing irrecoverable degradation and softening of structured soils during loading [7]. The combined effects of partial saturation and cementation have been the object of increasing scientific interest thanks also to the development of advanced and accurate measurement techniques of suction and water content in unsaturated soils [8][9].…”

“…In contrast, other models predict the mechanical behaviour of unsaturated soils without accounting for the effect of cementation [21][22][23][24][25][26][27][28][29]. Only a handful of elastoplastic models account for the combined effects of both cementation and partial saturation on the mechanical behaviour of natural soils [5][6][7][30][31][32]. These models provide, however, a limited description of mechanical hysteresis and introduce unrealistic discontinuities at the transition point between elastic and plastic states.…”

A two-surface plasticity model for stiff clay

“…Lying within the framework of the bounding surface plasticity theory, the concept of sub-loading surface was proposed by Hashiguchi et al [13,14] and recently extended by Asaoka et al [1,2] based on Cam Clay model. Similar concepts were extended to account for unsaturated states by Pereira et al [25]. In these models, an additional evolution law is introduced to describe soil's structure degradation process from overconsolidated states to normally consolidated states.…”

A single-stress model for the prediction of yielding of unsaturated cemented soils under isotropic loads

“…Other authors have instead devised mechanical models that predict the unsaturated behaviour without accounting for the effect of cementation [12][13][14][15][16][17][18][19][20]. Only a handful of studies have proposed elastoplastic models that take into account the combined effect of cementation and partial saturation [21][22][23][24][25][26]. These models adopt distinct sets of equations to describe the soil behaviour in the elastic and elasto-plastic regimes by introducing yielding surfaces and hardening rules that govern the transition between the two regimes.…”