Index properties of sediments from the Maltese stratigraphy, containing clay minerals

Abstract

The purpose of this dissertation was to be another building block in obtaining an understanding of the engineering behaviour of sediments from the Maltese Stratigraphy. In an attempt to identify the nature and engineering behaviour of fine-grained ground materials, simple index tests have been made, with the aim of investigating the influence the clay fraction and carbonate content has on geotechnical properties. The results were then assessed for the general trend, noting the differences found in facies from the same stratum. Classification was done on the basis of the A-Line Plasticity Chart, the Activity Chart and the Swelling Potential Chart. Eventually, the properties were correlated to each other such that existing relationships could be investigated. From an engineering point of view, it was concluded that the materials making up the fine grained sediments of the Maltese Stratigraphy contain many similarities. The differences in index properties between the strata appeared to be related to the level of cohesion and cementation brought about by the clay fraction and carbonate content respectively. In fact, results from strata close to a weakly cemented clay indicated a gradual transition. The linear plot running on top and parallel to the A-Line, classified the materials as clays, which can also be termed as marls since most samples are rich in lime. The downward sequence is currently known by the names of Blue Clay and Upper, Middle and Lower Globigerina Limestone, on the basis of their geological and palaeontological classification. This dissertation however suggests that the nomenclature used to describe these ground materials may sometimes be misleading to a civil engineer, as it is not always suggestive of the type of behaviour that one would expect, from a geotechnical point of view. The gradual transition between the different strata imply intermediate modes of behaviour that could be better studied if soil mechanics principles are applied instead of (or together with) rock mechanics principles.