Hydro-mechanical network modelling of porous geomaterials

Athanasiadis, Ignatios (2017) Hydro-mechanical network modelling of porous geomaterials. PhD thesis, University of Glasgow.

Due to Embargo and/or Third Party Copyright restrictions, this thesis is not available in this service.


The microstructure of porous geomaterials strongly influences macroscopic hydro-mechanical
properties, such as fluid retention, conductivity and stiffness. These properties are of importance
for predicting the performance of many engineering applications, such as waste
barriers and flood defence embankments. Predicting these properties with confidence requires
a thorough understanding of processes at the microscale and their effect on macroscopic
phenomenological properties. For unsaturated geomaterials, providing this understanding
requires still further research. In this study, network models representing processes in the
pore structure and solid skeleton were developed with the aim to improve the required understanding
to link processes at the micro-scale to macroscopic properties. The objectives
were to develop a new coupled hydro-mechanical network model, with main application the
improvement of understanding of the influence of microstructure on the retention behaviour
and conductivity of porous geomaterials, the mechanical response in the form of the elastic
stiffness, and their interaction. The model is valid for investigation of transport and mechanical
aspects geomaterials such as concrete, rocks, sand and clay soils with length scales of the
pore radii spanning from sub-μm to mm.

In the present network models, the microstructure of the material is idealised by means of
a network of voids for the transport response and a network of grains/particles representing
the solid skeleton response. For the transport network, the void structure is idealised by
spheres representing large voids and pipes for the interconnecting narrow throats. The
structural network of grains is modelled by rigid polyhedra connected by springs which
contain information related to the constitutive response of the skeleton. The geometry of the
networks is determined by dual irregular Delaunay and Voronoi tessellations based on random
sets of points. For the transport network, the spheres and pipes were placed on the Voronoi
polyhedral vertices and along the ridges, respectively. The mechanical elements were placed
on the edges of the Delaunay tetrahedra. In addition to the irregular arrangement of elements,
microstructural heterogeneity was introduced by assigning the radii of the spheres and pipes as
well as the polyhedra contact areas from probability distributions. New techniques to provide
Periodic Boundary Conditions for representative cells generated by the irregular networks
were developed. Another new feature of the model is a pore scaling technique which improves
the modelling of the retention behaviour.

For being able to perform simulations of representative cells of the coupled networks, the
model was implemented in a finite element framework. The correct development and implementation
of the network models was verified by comparison with a range of analytical
solutions. Furthermore, a sensitivity study was performed to investigate the qualitative
macroscopic response of the material in the form of retention behaviour, conductivity and
stiffness for important model parameters. For the influence of the cell size on the macroscopic
properties, it was found that for large cell sizes, the macroscopic response of the model is
independent of a change of the cell size. For all macroscopic properties investigated, the
mean converges to a representative value. Furthermore, the standard deviation approaches
zero for large cells for almost all cases. Only for a small range of very low conductivities for
highly unsaturated conditions, the standard deviation did not decrease with increasing cell
size, which was attributed to the occurrence of percolation. In addition to the verification part,
a calibration strategy was developed for the transport part of the model. Then, the model was
used to predict the relative conductivity of unsaturated geomaterials reported in the literature.
The agreement between the numerical prediction and the experimental results for degree
of saturation and relative permeability was found to be very good. The model presented
possibility to predict evolution of relative permeability when calibrated to match retention
experimental data.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Network model, periodic boundary conditions, hydro-mechanical, coupling, microstructure, conductivity, degree of saturation, calibration, verification, representative volume element.
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
Colleges/Schools: College of Science and Engineering > School of Engineering > Infrastructure and Environment
Funder's Name: Engineering and Physical Sciences Research Council (EPSRC)
Supervisor's Name: Grassl, Dr. Peter and Wheeler, Professor Simon
Date of Award: 2017
Embargo Date: 19 May 2019
Depositing User: Ignatios Athanasiadis
Unique ID: glathesis:2017-8204
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 26 May 2017 07:26
Last Modified: 14 Aug 2017 13:07
URI: http://theses.gla.ac.uk/id/eprint/8204

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