Rao Martand Singh An experimental and numerical investigation of heat and mass movement in unsaturated clays

Thesis submitted in candidature for the degree of Doctor of Philosophy at Cardiff University, 2007. — 405p.Published by ProQuest LLC 2013.
Study of moisture transport in soils under thermal gradients has been a topic of great interest since the beginning of the 19th century. Initially water movement in subgrade material, which is a common cause o f the structural failure of pavement surfaces, attracted the attention of highway engineers and scientists who found the wetting was attributed to a ‘transpiration current’ or an upward movement of moist air through the soilfrom the water table caused by a temperature gradient in the soil (Maclean and Gwatkin, 1946). The other problems of interest, where thermally induced moisture movement in unsaturated soils is an important phenomenon, are diurnal moisture movement in the ground, buried services (e.g. high voltage electric cables and hot water pipes), high level radioactive waste disposal, landfill liner performance, optimisation of geothermal energy utilisation (Rees et al., 2000) and thermally enhanced clean-up of contaminated land (Lee et al., 1999).
The main objectives of the present research may be summarised as follows:
Provide a state-of-the-art review o f the development of theories and experimental work related to heat transfer and moisture movement in liquid and vapour phases in unsaturated soils from the beginning of 19th century to date.
Design and build new test apparatus to facilitate a large number of various combinations of thermal gradient and hydraulic gradient experiments. Create new laboratory facilities to provide operational support for the new cells. Conduct a preliminary experimental programme to demonstrate the working capacity and functionality of the new apparatus.
Establish a basic experimental methodology for sample preparation to obtain uniform homogenous samples and subsequent testing. Determine basic geotechnical properties that include physical and chemical properties and flow parameters i.e. hydraulic and thermal material parameters of testing clays.
Perform thermal gradient, thermo-hydraulic gradient and isothermo-hydraulic gradient tests to investigate the heat, liquid moisture and vapour moisture movement in clays with different initial degree of saturation but same dry density.
Develop an empirical method to calculate the vapour flux using the conservative ion (especially chloride ion) movement. Develop a new vapour flux model for swelling or non-swelling clays and integrate it within an existing transient finite element model. Verify and validate the new vapour flux model against the results obtained from the heat and mass experiments performed in this study.
Scope and limitations
This section discusses the scope and the limitations of the experimental and numerical work pursued in this research study.
One of the principal assumptions of this study is that the soil is homogeneous though some heterogeneity (especially non-uniform dry density and water content) is observed
during the experimental work.
The new test apparatus is designed for one dimensional thermo-hydraulic testing only.
The new test apparatus can work up to a maximum temperature of 100 °C and an applied hydraulic pressure of 1.5 MPa.
This study does not include the hysteresis effects that have been observed in the soil water characteristic curve (or water retention curve).
Approximate methods are employed for numerical analysis to solve the governing equations of heat and mass transfer.
The numerical modelling in this study does not include deformation behaviour and chemical species movement.