Case studies for tunnel stability based on the critical strains in the ground

This paper discusses on the validity of a method to assess the stability of tunnels under construction. Key values of the assessment are critical strains that may be evaluated using the in-situ displacement measured at the construction fields. In this work, firstly the definition of the concept of critical strains is reviewed based on the previous research results and a theoretical study related to the critical strains is newly conducted from the viewpoint of tunnel engineering. Then a new assessment technique with the critical strains concept is proposed to assess the stability of a tunnel for the practical application to the filed. Lastly some case studies are performed - quantitative assessments using a method proposed in this study are conducted for actual tunneling fields. The results conclude that the proposed method can be applicable to assess the tunnel stability using the displacements measured at the sites.