University of Manitoba

Dr. Pooneh Maghoul, P. Eng.

Assistant Professor - Department of Civil Engineering


Office: E1-432
Mail: Department of Civil Engineering
University of Manitoba
Room E1- 432 (EITC), 15 Gillson street
Winnipeg, Manitoba R3T 5V6
Phone: (204) 474-8475

THHM and HHM Models for Saturated and Unsaturated Soils under Thermal, Transient and Dynamic (Wave Propagation) Laodings

Thermo-hydro-mechanical (THHM) and hydro-mechanical (HHM) models are presented based on the experimental observations and with respect to the poromechanics theory within the framework of the suction-based mathematical model presented by Gatmiri (1997) and Gatmiri et al. (1998). In these models, the effect of deformations on the suction distribution as well as the temperature in the soil skeleton and the inverse effects are included in the formulation via a suction-temperature-dependent formulation of state surfaces of void ratio and degree of saturation. The linear constitutive law is assumed. The mechanical and hydraulic properties of porous media are assumed to be dependent on suction and temperature. In this formulation, the solid skeleton displacements ui, water pressure pw and air pressure pa are presumed to be independent variables.

Numerical Methods: FEM/BEM Coupling Method in Multiphase Porous Media

In order to model multiphase porous media behavior, first the governing partial differential equations should be derived and solved. Because of the complexity of the governing partial differential equations, with the exception of some simple cases, their closed-form solutions are not available. Therefore the numerical methods, such as the Finite Element Method (FEM) and the Boundary Element Method (BEM) , should be used for such partial differential equations. The FEM, the most popular method, regarding its vast ability in geomechanics as well as many other areas, has been used in many codes that have been developed for both saturated and unsaturated cases. The BEM, on the other hand, is a very effective numerical tool for dynamic analysis of linear elastic bounded and unbounded media. The method is very attractive for wave propagation problems, because the discretization is done only on the boundary, yielding smaller meshes and systems of equations. Another advantage is that this method represents efficiently the outgoing waves through infinite domains, which is very useful when dealing with waves scattered by topographical structures. When this method is applied to problems with semi-infinite domains, there is no need to model the far field. to take advantage of the benefits of the FEM and BEM, the combination of these techniques seems quintessential. This combination which results in a hybrid method, offer advantages not provided by a single method on its own.

During this project, the boundary element formulations (BEM) based on the convolution quadrature method (CQM) regarding the saturated and unsaturated porous media subjected to isothermal quasi-static and dynamic loadings are implemented via the computer code « HYBRID ». Having integrated the BEM formulations for the wave propagation, as well as the consolidation problems in the saturated and unsaturated porous media, it seems that now the first boundary element code is obtained that can model the various problems in dry, saturated and unsaturated soils.

The FEM/BEM coupling method used in « HYBRID » allows us to model the more complicated constitutive laws in the near field by using the FEM while large parts of the finite/infinite linear elastic domain in far field are treated using the BEM.

Closed-Form Solutions in Porous Media: Fundamental Solutions

In the BEM, during the formulation of boundary integral equations, the fundamental solutions for the governing partial differential equations should be derived first. Indeed, attempting to solve numerically the boundary value problems for unsaturated soils using BEM leads one to search for the associated fundamental solutions. In this project, for the first time, one establishes the boundary integral equations (BIE) and the associated fundamental solutions for the unsaturated porous media subjected to quasi-static loading for both isothermal (2D in the Laplace transform domain) and non-isothermal (2D and 3D in Laplace transform and time domains) cases. Also, the boundary integral equations as well as the fundamental solutions (2D and 3D in the Laplace transform domain) are obtained for the fully coupled dynamic model of unsaturated soils.

Seismic Site Effects

Once the computer code « HYBRID » is verified and validated, parametric studies on seismic site effects are carried out. The aim is to achieve a simple criterion directly usable by engineers, combining the topographical and geological characteristics of the soil, to predict the amplification of acceleration response spectra in fully-filled and semi-filled sedimentary as well as hollow valleys. The main results of this study are:

Foundation's Energy Efficiency in Cold Region

This project involved developing a numerical tool to model the coupled transfer of heat (conduction, convection, inter-particular radiation) and water in saturated and unsaturated soils by taking into account the effects of frost and snow cover through the global energy balance at the surface (radiation, convection, evaporation, etc.). This was performed by applying a mathematical and phenomenological model in which the soil freezing characteristic curve and therefore the ice content are obtained by combining a generalised form of the Clapeyron equation with the soil water retention curve (SWRC) and the thermodynamical equilibrium. The mass conservation was derived by considering the phase change and the water flux due to infiltration. Also, the heat conservation was derived considering phase change, conduction and convection of heat. This resulted in a system of coupled and highly non-linear differential equations. The numerical method used to solve the system of partial differential equations is based on a Galerkin Finite Element Method (FEM) with adaptive mesh refinement and dynamic time step control. The developed solution is validated by comparison with experimental data obtained from literature. Then, the impact of the insulator and the material used on the distributions of temperature and ice water content as well as the thermal performance of residential building foundations were studied.