The middle globigerina limestone at Mrieħel, Malta

Abstract

The geology of the Maltese Islands has been extensively studied over the last two centuries, but very little attention has been given to the geotechnical behaviour of the various layers. This thesis attempts to initiate detailed investigation and engineering analysis of the Maltese stratigraphy, presenting the possible methodologies and the theoretical background through which this can be done. This work is limited to the Middle member of the Globigerina Limestone formation. An attempt is made to present the diversity of facies and of engineering behaviour, beyond the typical ‘franka’ and ‘soll’ building stone layers, which have been the focus of considerable attention in the past years. The weaker facies are considered, not as building materials, but as ground sediments which invariably need to be excavated and built upon. The particular case of structural problems at Santa Marija Church, in Mrieħel, Birkirkara, is presented as an example of the implications of the engineering behaviour of these weaker materials. The microstructure of these sediments is explored through mineralogical studies, geotechnical index tests and the use of the scanning electron microscope, with the aim of understanding how these materials have been formed, what they are made of and what makes them different. Compressibility characteristics are studied by high-pressure oedometer tests with pore pressure measurement, and shear behaviour with the use of low-pressure and high-pressure triaxial tests. Classical soil mechanics and rock mechanics theory, combined with recent advances in understanding the geotechnical behaviour of hard soils and soft rocks, are shown to be valid approaches in understanding these materials. Structure, in the form of fabric and bonding, and particulate behaviour, as influenced by pure friction and dilatational characteristics between particles, are both explored, and their interplay is investigated as the source of strength and deformability characteristics of these materials.