ABSTRACT
It is a common tunnelling practice in Korea to take strain measurements in the shotcrete. However, the interpretation of shotcrete lining instrumentation is very difficult due to stress independent strains such as shrinkage and temperature changes and time-dependent creep deformations. For a NATM tunnel, these problems are obvious because the shotcrete is loaded at an early age. During this period, the curing shotcrete exhibits a complex mechanical behaviour that changes with the age. Cording et al. (1975) described methods for estimating these strains, which are not related to ground loads. The variation of the modulus of elasticity of the shotcrete lining with age can be estimated by means of an extensive series of laboratory tests as Kuwajima (1991) did. However, the suggested method can be very inconvenient. Therefore, the strain measurement in the shotcrete is usually used only for the estimation of the relative amount of the displacement of the shotcrete lining to ensure the stability of the tunnel.
