There are two principal methods of tunnel construction: the single-shell known as the Norwegian Method of Tunneling (NMT) and the double-shell referred to as the New Austrian Tunneling Method (NATM). Staunch supporters of both the methods consider their method to be the perfect one. Actually, nothing is perfect in this World and each method has its own merits and demerits. So, I invite the relevant experts to share their knowledge on the comparison of NMT and NATM, please