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  Assessment of deterioration in underground structures using field inspection

  As soon as the infrastructure has been built, the deterioration started. The previous paper is focused on the influence of carbonation for the durability (Choo et al, 2014). This paper is the second part of the deterioration assessment related with the state of filed inspection: crack, leakage, effloresce, exfoliation, spalling, and so on. Based on the design approach of Duracrete, the corrosion is affected by carbonation and chloride penetration. The symptom of this deterioration is initially inspected with hair crack, and then the width of crack is mainly escalating to spalling when it reaches to 1mm wide. Soga et al (2005) explained that the whole aging process can be accelerated by defects of load bearing structures, which are stated for reinforced concrete. To evaluate the current state and predict when the best time to carry out repair works is, the ageing process of underground structure has been monitoring with fibre optical strain sensor, wireless system, and real time camera (M. Vanicek et al, 2007). Among the underground structures, the deterioration has been widely studied on the pipe line (FCM and NRC, 2003) and power cable (Thomas, 2009) than large size of tunnel or subway. The degradation of concrete lining is caused by carbonation, chloride ingress, sulphate attack, AAR (Alkali Aggregate Reaction) and deterioration related to seawater (Romer, 2013). Sandrone (2011) classified the lining degradation into three processes: ageing, weathering and others actions shown in Table 1. Sandrone and Labiouse (2010) described time effects on the rock mass with the ground characteristic curve which can be one of main influence factor of tunnel deterioration. Typical defects of lining in filed inspection are crack, leakage, efflorescence, exfoliation/ scaling, spalling, and exposure of reinforcement. Among them, the crack is the main influence factor in tunnel deterioration

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