ABSTRACT
This study uses numerical analysis to preliminarily model the anticipated ground deformation and surface settlement that could occur during tunnelling though weak deposits of phosphatic chalk using the finite element program RS2. This paper focuses on the factors that lead to increased and severe surface settlement and proposes mitigation measures. According to this analysis, the main factors contributing to extreme settlement increases are: high ground water levels, weak tunnel crown lithology, stress interaction between the twin tunnels and discontinuities within the rock mass. It is suggested that further detailed site investigation work is required to refine the understanding of the ground conditions be-fore excavation can commence. It should be noted and highlighted that the results of this study should not be used for any design purposes as it was a theoretical exercise to highlight the factors influencing ground movements induced by tunneling through the phosphatic chalk.
