Arman Khoshghalb

Effect of Gradation and Particle Shape on Small-Strain Young’s Modulus and Poisson’s Ratio of Sands

AbstractThe influence of gradation and particle shape on the small-strain Young’s modulus of dry sands is investigated through a comprehensive set of resonant column tests in the flexural mode of vibration. Experiments are performed on an array of sands with different coefficients of uniformity and particle shapes. The effect of gradation is investigated using tests on sands with similar particle shapes. The effect of particle shape is then examined through the experimental results on sands with a range of particle shapes. A new model is developed to incorporate the effects of gradation and particle shape into the prediction of the small-strain Young’s modulus. The proposed model is verified and compared with the existing models in the literature using the state parameter in the critical state soil mechanics framework. It is shown that the proposed model outperforms the previous ones considering the significant effect of particle shape on the small-strain Young’s modulus. Using the theory of elasticity, a...

Pitfalls in Interpretation of Gravimetric Water Content–Based Soil-Water Characteristic Curve for Deformable Porous Media

AbstractPitfalls in the common approaches to obtaining material parameters from soil-water characteristic curves (SWCCs) are discussed, and the typical mistakes made in the literature are highlight...

Hysteretic Model for the Evolution of Water Retention Curve with Void Ratio

AbstractThis paper presents a model for the evaluation of the void ratio dependency of water retention curve (WRC) in deformable porous media. Models currently available in the literature for this ...

Comment on “Bridging Effective Stress and Soil Water Retention Equations in Deforming Unsaturated Porous Media: A Thermodynamic Approach”—J. M. Huyghe, E. Nikooee, S. M. Hassanizadeh; Published online: 4 March 2017—DOI 10.1007/s11242-017-0837-9

The authors present a semi-empirical relationship for the determination of the effective stress parameter for unsaturated soils based on thermodynamics considerations. The model proposed requires as input: suction value of interest, air entry value (AEV) of the soil, slope of the soil water retention curve (SWRC) in the log–log plane and a fitting parameter, ξ , obtained by matching model predictions to experimental effective stress parameters at a reference net stress. The predictive capacity of the relationship proposed, along with that of Khalili and Khabbaz (1998), is examined using three shear strength data from the literature. A critical step in such a comparison is the correct determination of the input data. Unfortunately, this vital step has not been treated with care in the contribution by Huyghe et al., leading to erroneous predictions and conclusions. Two shortcomings appear to underpin the incorrect extraction of the input data from the source data: (i) determination of the AEV and (ii) selection of the SWRC.

Meshfree Method Analysis of Biot's Consolidation Using Cell-Based Smoothed Point Interpolation Method

A set of cell-based smoothed point interpolation methods are proposed for the numerical analysis of Biot’s formulation. In the proposed methods, the problem domain is discretized using a triangular background mesh. Shape functions are constructed using either polynomial or radial point interpolation method (PIM), leading to the delta function property of shape functions and consequently, easy implementation of essential boundary conditions. The Biot’s equations are discretised in space and time. A variety of support domain selection schemes (T-schemes) are investigated. The accuracy and convergence rate of the proposed methods are examined by comparing the numerical results with the analytical solution for the benchmark problem of one dimensional consolidation.

A CELL-BASED SMOOTHED POINT INTERPOLATION METHOD FOR AXISYMMETRIC PROBLEMS

A cell-based smoothed point interpolation method (CSPIM) for the numerical modelling of saturated porous media in axisymmetric conditions is proposed. Spatial discretisation is performed using a simple triangulation. Both displacement and fluid pressure gradients are smoothed by incorporating the smoothing gradient operation technique. Thus, the integration over the supporting domains (i.e. elements) is transformed to that over the boundary of the elements. The field variables, the displacement and excess pore water pressure, are interpolated using point interpolation shape functions (polynomial and radial), which possess the Kronecker function property and facilitate imposing the essential boundary conditions. The global property matrices of the discretised system of equations are derived using the generalised smoothed Galerkin method and the three-point time discretisation scheme for discretisation of the governing equations in space and time, respectively. A novel approach is introduced for the computation of the property matrices, which avoids the singularity problem that will otherwise arise when cell-based smoothed interpolation method is used in axisymmetric conditions. The salient feature of the proposed method is that it incurs no additional computational costs, and it does not compromise on accuracy of the method. The validity of the proposed method is investigated by simulation of Cryer’s benchmark consolidation problem. The numerical results are in excellent agreement with the analytical solution.

On Creep Laboratory Tests in Soil Mechanics

Soil exhibits creep behaviour, which is the development of time-dependent shear and/or volumetric strains at a state of constant effective stress. Creep is controlled by the viscous like resistance of soil structure. Creep behaviour influences the long-term settlement of grounds and movement of slopes; therefore it is of significance in geotechnical engineering applications. Creep laboratory tests, mainly one-dimensional and triaxial creep tests, are used to investigate the creep characteristics of soils and to predict the creep behaviour of soil in the long term. Conventional creep tests involve loading a soil sample to a specific effective stress and then allowing the sample to creep under constant effective stress. However, in order to capture the long term creep behaviour of soil, long duration creep tests are required. Therefore, the creep tests are not only laborious and time-consuming which render them impractical in many applications, but also associated with some difficulties and inaccuracies that need to be dealt with. In this study, a review on the conventional laboratory creep tests, the main difficulties associated with them, and the solutions proposed to alleviate these difficulties (if there are any) are presented. The possible sources of inaccuracies in the test results are discussed and practical recommendations are proposed to minimise the inaccuracies in the results.

Coupled Flow Deformation Analysis Using Meshfree Method

A fully coupled meshfree algorithm is proposed for numerical analysis of Biot’s formulation. Spatial discretisation of the governing equations is accomplished using radial point interpolation method. Temporal discretization is achieved based on a novel three‐point approximation technique with variable time step, which has second order accuracy and avoids oscillatory response observed in the conventional methods of time discretization. Application of the model is demonstrated using two numerical examples with analytical solution. It is shown that the model proposed is efficient in simulating the coupled flow deformation behavior in fluid saturated porous media with good accuracy and stability irrespective of the magnitude of the time step adopted.