The Most Commonly Used TBM Types and Their Suitability for Hard and Soft Grounds

Tunnels are underground passages ensuring crucial functions as transportation, conveyance of materials and storage. Among the main advantages of these increasingly widespread structures minimizing traffic jams in overcrowded cities by implementing railway, highway and metro tunnels. Tunnel construction methods are subdivided into two major categories: the classical method and the mechanized method. The classical method consists of the conventional blasting (Drill and blast). In contrast, the mechanized method ensures the excavation of the tunnel by utilizing roadheaders, continuous miners, partial-face excavation machines, hydraulic hammers and TBMs. Today, the continuous evolution of tunneling machines enabled the mechanized method to be an efficient and economically profitable excavation method choice due to the safety, stability and low construction time it provides. In fact, among these tunneling machines, TBMs are widely recognized for their several benefits as ensuring continuous operations and causing less rock damage and less disturbance to the surface. This review paper analyses the conditions under which TBM tunneling is advantageous especially when compared to the classical tunneling method and presents commonly used TBM types and their technical features. This study also highlights the essential parameters to consider in the decision-making process of selecting the appropriate TBM type for a tunneling project and discusses the suitability of each TBM type for hard and soft grounds.