HYDROMECHANICAL BEHAVIOUR OF TWO UNSATURATED SILTS: LABORATORY DATA AND MODEL PREDICTIONS

This paper presents the results from a campaign of unsaturated and saturated isotropic tests performed on two compacted silts of different coarseness, namely a clayey silt and a sandy silt, inside triaxial cells. Some tests involved an increase/decrease of mean net stress at constant suction or an increase/decrease of suction at constant mean net stress. Other tests involved an increase of mean net stress at constant water content with measurement of suction. During all tests, the void ratio and degree of saturation were measured to investigate the mechanical and retention behaviour of the soil. The experimental results were then simulated by the bounding surface hydromechanical model of Bruno and Gallipoli (2019), which was originally formulated to describe the behaviour of clays and clayey silts. Model parameters were calibrated against unsaturated tests including isotropic loading stages at constant water content with measurement of varying suction. Loading at constant water content is relatively fast and allows the simultaneous exploration of large ranges of mean net stress and suction, thus reducing the need of multiple experiments at distinct suction levels. Predicted data match well the observed behaviour of both soils, including the occurrence of progressive yielding and hysteresis, which extends the validation of this hydromechanical model to coarser soils. Specific features of the unsaturated soil behaviour, such as wetting-induced collapse, are also well reproduced.

MHD Flow of Micropolar Fluid via Porous Medium Within the Rotating Frame of Reference

The present study reveals the heat and mass transfer on the MHD flow of micropolar fluid in a porous medium within a rotating frame. In order to facilitate osillatory plate velocity with constant suction and first order chemical reaction has been considered. Using small perturbation approximation, the governing non-dimensional equations are solved. The influence of pertinent physical quantities on the flow phenomena have been presented graphically. The skin friction coefficient, wall couple stress, Nusselt and Sherwood number have also computed for different flow parameters and have presented in table. In the study, the applied magnetic field sets in to produce the resistive force i.e. the Lorentz force that resists the fluid motion throughout the domain. Attenuation in the Prandtl number is because of the slower thermal diffusivity resulted in a sharp reduction in the thermal boundary layer thickness. The retardation in the polar fluid concentration is greater in amount for the influence of heavier species.

A constitutive model for hydromechanically coupled behavior of unsaturated soils with hydraulic hysteresis

There are several constitutive models developed for understanding coupled hydromechanical behavior of three phase medium of unsaturated soils as well as models for explaining hydraulic hysteresis in water retention. However, very few attempts that merge the two aspects of behavior are available. This study develops a one-way coupled model for understanding the hydromechanical behavior of unsaturated soils. In addition to the hysteresis between main drying and wetting retention curves, the model considers non-uniqueness of retention behavior resulting from void ratio changes due to compression under the stress application. As for the elastoplastic stress strain relationship of soil skeleton, the model is based on the formulation of classical plasticity relying on the critical state concept. Consequently, volumetric deformation due to wetting-drying cycles and its effect on elastoplastic behavior through simultaneously changing matric suction is modeled. Model results are calibrated with the results of isotropic compression stages of triaxial tests at both constant suction and constant water content conditions.

Two-Dimensional Flow Through the Uniformly Porous Horizontal Pipe with Thermal Radiation and Cross-Diffusion Effects

This paper is dedicated to the mathematical analysis of an axisymmetric, steady Newtonian fluid flow through a horizontal pipe within the occurrence of radiation, Dufour, and Soret effects. The flow is exposed to associate outwardly functional constant suction above the pipe along Z-direction. The homotopy analysis methodology (HAM) is utilized to get semi-analytical solutions for the coupled differential equations. The results of diverse rising constraints on velocities, thermal and solutal are discussed and pictured. The flow is studied through streamlines, isotherms and pressure contours area unit likewise shown as pictured. It is identified that the temperature can increase with an increase in Dufour parameter but decelerates with an improvement in the radiation parameter. For the given increase within the Soret number, the concentration decelerates.

Calibration of a generalized plasticity model for compacted silty sand under constant-suction shearing tests

The stress-strain response of compacted silty sand with over-consolidated stress history often exhibit distinct peak stress before reaching the critical stress type of response when subjected to suction-controlled triaxial shearing. Such heavily consolidated soil also tends to simultaneously manifest initial compression which transitions into dilational type volumetric response. Modelling such strain-softening type response, especially emulating the smooth transition from peak to critical state is a challenge. In this paper a previously developed generalized plasticity constitutive model, called MPZ (Modified Pastor-Zienkiewicz) is fine-tuned and calibrated using a set of suction-controlled consolidated drained triaxial tests conducted on compacted silty sand specimens. Firstly, the saturated and unsaturated silty sand characteristics and the experimental test program are briefly introduced. Secondly, the calibration of each component of the constitutive model, namely critical state, dilatancy, peak state, loading direction, water retention curve and bounding function are briefly explained. Furthermore, the material parameters are estimated, model performance is displayed, and finally discussed. Preliminary simulations show that the MPZ model is able to mimic overall suction controlled triaxial test response of compacted silty sand decently well by taking into account the changes in density, pressure and suction. However, the peak states are not accurately modelled for low-high suction levels which needs further modifications in proposed model.

Mechanical behavior of an unsaturated clayey silt: an experimental and constitutive modelling study

This paper reports an experimental study and subsequent constitutive modelling focused on the stress-strain and volumetric responses during deviatoric stress application of a partially saturated clayey silt. The material was statically and isotropically compacted at constant water content towards a pre-defined pre-consolidation stress. A series of strain-controlled triaxial compression tests on a state of the art device and isotropic experiments are presented and discussed. The triaxial tests started at the same stress state (i.e., identical matric suction and mean net stress) and were conducted at the same constant suction. Several stress paths under isotropic conditions (i.e., drying–wetting, loading–unloading, and wetting–drying) were followed to induce different overconsolidated states before shearing the specimens. The test results are initially interpreted using the elastoplastic Barcelona Basic Model (BBM). Independent tests were selected to determine the model parameters associated with the volumetric behavior of the soil. The BBM was not able to capture the dilatant behavior observed during shearing. An enhancement of the BBM is proposed in this work, which includes both, a more general hardening law and sub-loading concepts. The main capabilities and limitations of the original BBM and the enhanced model are discussed and compared. The modified BBM was able to handle the dilatancy observed in the experiments and provided a more realistic description of the experimental stress-strain response.