The excavation of tunnels in heterogeneous geological formations represents a complex engineering problem, especially when the ground is composed of block-in-matrix rocks (bimrocks). These materials consist of competent rock blocks embedded within a weaker and continuous matrix, creating strong mechanical heterogeneity and scale-dependent behaviour. Because the size and distribution of the blocks may be comparable to the dimensions of the excavation, traditional design approaches based on homogeneous assumptions often provide incomplete or misleading predictions. This thesis investigates how bimrock heterogeneity influences the mechanical response of a circular tunnel during excavation. A series of two-dimensional finite element analyses were carried out using RS2, explicitly modelling the interaction between blocks and matrix.