Deep geological disposal is regarded as one of the most practical ways for the stratum disposition of the high-level radioactive waste (HLW). Moreover, it is known that soft rock is one of the most suitable host rocks for geological disposal because of its low water permeability and little cracks. However, there is lack of understanding of the influence of temperature on soft rock which is generated by HLW for long-term. Therefore, it is in demand to establish the way to evaluate the soft rock behavior under thermal loading. Even though previous studies have been revealed the mechanical behavior of soft rock subjected to high temperature and developed constitutive models to describe its behavior, long-term stability of tunnel, especially tunnel creep behavior, under high temperat...[ Read more ]

Deep geological disposal is regarded as one of the most practical ways for the stratum disposition of the high-level radioactive waste (HLW). Moreover, it is known that soft rock is one of the most suitable host rocks for geological disposal because of its low water permeability and little cracks. However, there is lack of understanding of the influence of temperature on soft rock which is generated by HLW for long-term. Therefore, it is in demand to establish the way to evaluate the soft rock behavior under thermal loading. Even though previous studies have been revealed the mechanical behavior of soft rock subjected to high temperature and developed constitutive models to describe its behavior, long-term stability of tunnel, especially tunnel creep behavior, under high temperature is not well investigated. The main objective of this research is to gain a better understanding of soft rock tunnel long-term behavior under thermal environment. Furthermore, this study aims to validate a newly proposed thermo-elastoplastic constitutive model by conducting the class C-predictions.

Triaxial compression tests and triaxial creep tests with artificial soft rock were carried out to investigate the mechanical behavior of itself and gain parameters for class C-predictions. A total of four tunnel modelling experiments at 20 and 60°C which consist of loading failure test and creep failure test were also conducted using artificial soft rock. Tunnel deformation, deviatoric strain on tunnel model surface and temperature history were measured during the test. Moreover, experiment data which is gained through this research is simulated with the proposed constitutive model.

The element test results reveal that the artificial soft rock used in this research can simulate the fundamental mechanical behavior of sediment soft rock and contributed to gain parameters for class C-predictions. It is also shown that increase of temperature weaken tunnel stability and shorten the tunnel failure time in tunnel modelling experiment. Temperature seems to have larger influence on creep failure time than loading failure time. Furthermore, tunnel model experiment results imply that the different loading method between tunnel failure test and tunnel creep test results in different destruction modes.

Even though class C-predictions results show that the constitutive model can capture the features of mechanical behavior of soft rock at element level, it is found that expanding it to FEM has some problems. In this study, computed result is presented mainly in order to interpret the gained experimental data.