Tunnelling through Maltese rock : with particular reference to the lower coralline limestone formations

Abstract

This dissertation focuses on two techniques used to classify rock masses, better known as RMR and Q-index. These two methods are used as guidelines in the analysis of the rock mass in a sewage tunnel being built at Rinella in various layers of the Lower Coralline Limestone formation. From this analysis and from further research made, more light is shed on various methods of site investigation that may apply to the Maltese context and why traditional methods such as boreholes are of little relevance for the Maltese context. The limitations of the RMR and Q-index for local application where identified and suggestions for their modification was made to try and make them more relevant for local use. Finally a discussion on support decisions is made and through observations made the writer was able to pinpoint support criteria that are tailor-made for the site in consideration. A 50 metre length of tunnel was chosen and a scanline survey was made in this area. Various features were observed, with the three dominant features being, karstic action, discontinuities and their infill, and frequent change of material properties over a short span. From the observations made a correlation was made between these features and the topography above. This gave light on how site investigation could be used to try and identify various problems from an early stage through simple observation and knowledge on what to look for. Laboratory tests such as the point load test and water absorption test were performed as a check on the observations made and to give a more clear comparison between the rock compositional changes present in the 50 metre scanline considered.