Geotechnical profiling of the middle globigerina limestone at Mriehel on the basis of index tests

Abstract

Geotechnical investigations and classifications allow the essential physical properties of soils and rocks to be assessed and classified accordingly. In Malta, research on ground materials has been limited to geological rather than geotechnical considerations. The Globigerina limestone, as a distinct geological formation, has only been studied in terms of its stratigraphy, weathering properties and basic mechanical characteristics - and then only for the Lower member. Consequently, research into the geotechnical properties of Middle Globigerina Limestone is non-existent. This study provides a detailed geotechnical investigation of one such profile of the Middle Member at Mriehel. The charactersitics of the various layers in the profile are studied and classified to identify subtle changes in composition with depth, hinting at variations in their mechanical properties. Numerous samples of soils and rocks were collected from 16 different levels along the profile under study, and were subjected to five different types of index tests: moisture content; Atterberg limits; bulk density; carbonate content; particle size distribution; particle density; and activity. The observed strata were further described according to BS classification systems to obtain qualitative data. Experimental studies were performed on the quantitative results attained from the index tests, combined with the qualitative descriptions for more reliable analysis. The outcomes of this study confirm that the bulk density, dry density and carbonate content increase with depth, while the porosity, void ratio and degree of weathering decrease with depth. Variations in the Atterberg limits and moisture content suggest the presence of different types of minerals and changes in permeability within this Middle Member. Furthermore, the study confirms that an increase in carbonate content leads to a decrease in the plasticity index for Middle Globigerina Limestone.