Electronic Thesis and Dissertation Repository

Degree

Doctor of Philosophy

Program

Civil and Environmental Engineering

Supervisor(s)

Dr. Timothy A. Newson

Abstract

Artificial cementation of soft clays has been used for several years for different ground improvement projects. Although considerable work has been done to develop advanced machinery and techniques for the implementation of artificial cementation, less knowledge is available on the mechanisms involving the formation of the artificial structure and the resulting mechanical behaviour. The primary objectives of the present work were to investigate the formation of microstructure in artificially cemented material with Portland cement, find the relationships between cementitious bonding and clay mineralogy, and create constitutive frameworks for predicting the mechanical behaviour of cement-treated clays.

Qualitative and quantitative microstructural characterisation of reconstituted and cemented material has been performed using scanning electron microscopy (SEM) and mercury intrusion porosimetry (MIP). The results confirmed the transformation of the void microstructure from a bimodal, dispersed material into a unimodal, flocculated material due to artificial cementation. The addition of cement was found to reduce the amount of macro-pores within the cemented material, resulting in a significant reduction in hydraulic conductivity.

A further parametric study was conducted on data obtained in the laboratory by the author combined with those found in the literature, to investigate the effect of clay mineralogy on artificial cementation. The results indicated the major influence of the activity of the clay, along with the cement and water content, on the results of the cement treatment. The observed variations in the mechanical behaviour with respect to mineralogy and the important effect of curing time have been explained in terms of the pozzolanic reactions, and the limitations of applying Abrams’ law to cement-admixed clays are discussed.

In addition, an experimental study has been conducted to investigate the yielding and stress-strain behaviour of artificially cemented Ottawa clay and to compare it with the behaviour of the same soil in its naturally structured state. The results indicate that although the natural clay exhibits a meta-stable structure, resulting in an abrupt post-yield loss of strength, the artificially cemented material undergoes a more gradual breakage of the cementitious bonds. This allows for the use of the critical state concept, along with a pseudo-normal compression line, to develop a constitutive model for the artificially cemented material.


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