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When tunneling in a hard and brittle rock mass within a tectonic stress zone, dynamic failure of rock mass-rockburst may occur. Considering the occurrence of rockburst is generally induced by a sudden release of storage elastic energy, a numerical analysis based on the geotechnical conditions of the headrace tunnels of the Neelum–Jhelum hydroelectric project was carried out to investigate the variations of the storage elastic energy of surrounding rock mass during excavation in the tectonic stress zone. As expected, the numerical results show that the storage elastic energy concentration zones is elliptical around the tunnel due to the influence of the tectonic stress field and that the long axis of the ellipse is perpendicular to the orientation of the maximum principal stress of the tectonic stress. Furthermore, the calculated storage energy concentration zone is consistent with the locations of blasting overbreak in the tunnel. Rockburst predictions were carried out using the strength-stress ratio and energy criteria to identify the applicability of the criteria in a tectonic stress zone. The comparisons between the predictions and the field observations show that the strength-stress ratio criteria based on the uniaxial tests do not consider the influence of the tectonic stress on the strength of the rock. These criteria overpredict the extent of the blasting pits in the tectonic stress zone. However, the energy criteria based on the energy conversion of unloading confining pressure tests are able to reflect the influence of the tectonic stress, and the prediction results are more close to the field observations.

Boom clay can be considered as a transversely isotropic geomaterial. However, due to lack of experimental evidence and data base, it is still difficult to describe the transversely isotropic plastic behavior of this argillaceous rock. In this paper, we present first, by means of an experimental approach, the main features of the mechanical properties of Boom clay. Then, combining the transversely isotropic elastic model and the modified MohrCoulomb criterion, a suitable constitutive model is introduced so as to fully describe the mechanical behavior of the studied material, in which, an elastic damage law which takes into consideration, the transversely isotropic effect, a plastic hardening law and a plastic damage law were introduced to describe the nonlinear elastic, hardening and softening behavior of Boom clay. As a preliminary step, the evolution law of both elastic moduli and Poisson's ratio during the elastic stage was obtained by direct analysis of the test data. The synchronism of the elastic damage in both transversal and axial directions was proved by this method. Some of the parameters of the model in the elastic stage were also determined by direct analysis method and further verified by back analysis. Other unknown parameters in the model were determined by back analysis.

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Understanding the time-dependent behaviour of soft rock under high in situ stress is essential to the evaluation of the long-term stability of the deep-buried tunnels in expressways or coal mines. This paper presents an experimental and numerical study of the time-dependent behaviour of argillaceous red sandstone under high in situ stress. First, several triaxial creep tests for strongly and moderately weathered specimens under the confining pressure of 20-40 MPa were conducted, and the variation of time-dependent damage with time was obtained by investigating the evolution of volumetric strain during the creep process. The test results verify that creep damage has a similar effect on both axial strain and lateral strain of argillaceous red sandstone. Second, a creep damage model that is able to describe nonlinear variation in creep strain and volume expansion for sandstone under high in situ stress was established. Last, the parameters of the proposed model were determined by a back analysis method. The results of back analysis show that the model is able to describe the nonlinear variation in creep strain and volume expansion during the creep process very well.

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