7. Analysis and monitoring of the Miyana railway tunnel constructed using the New Austrian tunnelling method

This paper presents a case study of the New Austrian Tunnelling Model (NATM) for the construction of a double-track railway tunnel through semi-hard dolerite rocks. The Japanese National Railways have studied and employed the NATM for their various tunnel projects since around 1976, and this tunnel, the Miyana Tunnel, can be considered as a forerunner for the NATM application in Japan. The agreement or lack of agreement between the calculated and the measured values are compared for convergences, ground displacements, axial forces in rock bolts and stresses in shotcrete layers. Some characteristics of tunnelling in semi-hard rocks by the NATM are carefully studied, and the appropriate design systems are introduced for the establishment of safe and economical construction methods. The measured values are generally on the safe side when compared with the calculated values, and it is suggested that the preliminary design of a tunnel in semi-hard rock could be reasonably conceived and carried out by linear elastic numerical analysis using the finite element method.