Abstract

To monitor deformation in a road tunnel in service, periodical inspections are performed and countermeasures are taken as needed. Cracking of the permanent lining and heaving of the road surface often occur. However, it is difficult to assess the development of such deformation features from data acquired during the construction and service stages. In this paper, the deformation mechanism and the effect of countermeasures are discussed based on the results of in-situ measurements over a six-year period and of numerical analysis. The relation between tunnel deformation and the occurrence of defects are examined using boring data. In addition, the mechanism of tunnel deformation when the characteristics of the ground indicates a swelling condition, and the relation between the load acting on tunnel lining and the behavior of countermeasure are also clarified.

Introduction

In Japan, temporary tunnel support of mountain tunnels is constructed in accordance with the ground grade, which is reevaluated on the basis of observations and measurements during the construction stage. The construction concept of permanent lining is described in the technical standard of the Japan Road Association (2003) after the displacement of section is judged to converge.

Road tunnels in Japan are periodically inspected every five years, referring to the technical regulation by MLIT (2014). After tunnels open for operation, the countermeasure, installing inverted arches with large cracks over lining and pavement and heaving of road surfaces have been reported (Okui et al. 2010). Such deformation develops very slowly and the kinds of mechanisms have been discussed (Shimamoto et al. 2009). It is difficult to evaluate deformation only from construction and periodical inspection data.

The authors have reported in situ measurements in a tunnel constructed in swelling rock condition and a quantitative health evaluation methodology (Isago et al. 2013). In this paper, the results of observation and measurement of an existing tunnel with large deformation are shown and the characteristics and mechanism of deformation are discussed. Next, the results of numerical analysis are compared to assess the tunnel deformation process and the effects of the use of inverted arch concrete as a countermeasure.

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