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Deformation and time-dependent behavior of rocks are closely related to the stability and safety of underground structures and mines. In this paper, a numerical-analytical model is presented to investigate time-dependent damage and deformation of rocks under creep. The proposed model is obtained by combining the elastic-visco-plastic model based on the theory of over-stress and stress hardening law with the sub-critical crack growth model. The advantage of this model is that it is in incremental form and therefore can be implemented numerically. First, the governing equations of the model and its numerical computational algorithm are described. The proposed constitutive model is then implemented in the FLAC code using the FISH function. Determination of model parameters and calibration is done by various laboratory tests performed on a type of gypsum. The creep test was performed on gypsum under a stress of 13 MPa, which is equal to 70% of its compressive strength. After determining the parameters, by fitting the creep curve of the presented analyticalnumerical model, a good agreement is observed with the creep curve obtained from the laboratory data. It is also observed that during creep, the damage parameter and wing crack length increase. [ABSTRACT FROM AUTHOR]

Due to the widespread need for the urban transportation network, construction of underground railway lines by mechanised shield-tunnelling increases in metropolises. The case of the Shiraz (Iran) subway twin tunnel construction is an example of transport network extension. In the present paper, a three-dimensionalnumerical model was developed to investigate the tunnel's lining behaviour and the ground displacement surrounding the second line of the Shiraz subway tunnels. All the excavation phases of EPB-TBM (Earth pressure balance, Tunnel boring machine) were simulated using the finite difference method. In most numerical simulations, the segmental joints were assumed parallel to the tunnel axis, despite the fact that the longitudinal joints make an oblique angle with the tunnel. Three kinds of lining pattern were then considered: continuous, straight and oblique joints. The numerical results indicated the necessity of using segmental lining with oblique joints pattern to obtain an accurate evaluation of the structural forces applied in segmental lining. The excavation of a new tunnel near to an existing tunnel with high lagging distance between twin tunnels leads to increase in the normal and the longitudinal displacements, in the internal lining forces and to a decrease in the ground surface settlement above the tunnels. [ABSTRACT FROM AUTHOR]

Analysis of stresses and displacements around circular opening excavated in rock mass has been one of the significant issues in tunnelling. A plastic zone is formed around underground opening as a result of high induced stress magnitudes. The ground response curve is one of the best methods to investigate the tunnel stability that represent the relationship between the decreasing of inner pressure and the increasing of radial displacement of tunnel wall. In recent years, several methods have been suggested for analysis of ground response curve by many researchers, however, some of the analytical solutions that have been presented, are relevant to elastic-perfectly plastic or elastic-brittle-plastic behaviour of rock. But real behaviour of plastic zone is strain softening with variable dilatancy. In this study, it is attempted to take into account the post-peak rock mass behaviour (drop modulus and variable dilation angle) in the stress-based finite difference approximation numerical procedure, so an algorithm is suggested to analyse the tunnel stresses and convergences. In order to verify the proposed algorithm, the results were compared with FLAC numerical solution. For showing the applicability of the proposed algorithm, the Ghomroud tunnel convergence was calculated based on the proposed algorithm and compared with the monitored tunnel convergence. At the end, the effect of various parameters including dilation, critical softening parameter and rock mass quality (GSI) was studied on the tunnel convergence and plastic zone thickness. Based on the obtained results, the higher quality of the rock mass surrounding the tunnel has, the narrower plastic zone forms and the lower tunnel wall converges. Also, the rock mass with higher brittleness means more convergence and wider plastic zone. Furthermore, constant dilation in plastic zone overestimates the tunnel wall convergence. [ABSTRACT FROM AUTHOR]