City Research Online

Abstract

The investigators interested in electrical dispersion of heterogeneous mixtures form two groups. The first group, which started in the last few decades of 19th century, resorted to microscopic models to depict the behaviour of mainly dilute suspensions of colloidal matter. Building on the results of these works, a second group of investigators started more recently using macroscopic models applied to rather concentrated systems such as consolidated soils.

A review of the literature on soil micro-structure and its characterization by the electrical dispersion method suggests the need for a reinterpretation of the associated electrical response data in order to account for some important aspects such as the very appreciable role of adsorbed water on clay. This requires the adoption of a more comprehensive macroscopic model, the elements of which reflect the properties of the microscopic components of the soil-water system.

While the researchers who used the electrical dispersion technique for soil investigation have attributed the main cause of electrical dispersion to one type or another of the relaxation mechanisms, the author believes in the possibility of various types of polarization and relaxation mechanisms taking place simultaneously within the soil-water system. Consequently, a broad spectrum of relaxation times should be expected.

Analysis of the available data suggests that at least one component of the soil-water system exhibits a frequency-dependant relaxation. This indicated that the adsorbed water phase could very well be the component responsible for such a phenomenon.

The experimental programme was designed to measure the dielectric constant and conductivity dispersion of saturated fine grained soils in the radio frequency range (10-110 MHz). Most of the compositional and micro-structural parameters of the soil-water-electrolyte system were deliberately and systematically changed to study their effects on the electrical responses of the system, and thus establishing the correlation between the electrical response and the soil microstructure.

The electrical dispersion curves produced experimentally were analysed and compared with theoretical curves computed for the model. In most cases agreement was found to be more than satisfactory.

The present thesis is thus devoted to the development of an elaborate electrical model depicting the macroscopic and microscopic structures of the soil-water-electrolyte system, accounting for the critical role of adsorbed water, recognizing the possibility of simultaneous polarization contributions of various mechanisms, allowing for a frequency-dependent component, and capable of predicting the experimental observations. It is shown that the model is an efficient means of investigating the engineering behaviour and microstructure of soil. This was achieved by deriving an expression relating the experimentally measurable characteristic time of the soil system to different micro-structural and compositional parameters of soil through a coefficient which the author calls "Micro-structure Electrical Modulus, M.E.M.". It is found that this modulus may describe the soil micro-structure in different directions in a numerical manner which permits a quantitative investigation of soil micro-structure. It may also be useful as a means of investigating the soil properties associated with hydraulic flow and wave propagation in different directions.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TA Engineering (General). Civil engineering (General) T Technology > TK Electrical engineering. Electronics Nuclear engineering
Departments:	School of Science & Technology > Department of Engineering Doctoral Theses

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