A micromechanical Sliding-Damage Model Under Dynamic Compressive Loading

For most rock materials, there exists a strong coupling between plastic flow caused by sliding along micro-crack faces and damage evolution due to nucleation and growth of wing-cracks. The aim of this article is to develop the self-consistent based micromechanical model by taking into account the coupling between frictional sliding and damage process under dynamic compressive loading. The developed model algorithm was programmed in the commercial finite difference software environment for numerical simulation of rock material to investigate the relationship between the mechanical behaviour and microstructure. Eventually while the stress intensity factor at flaw tips exceeds the material fracture toughness, the wing-cracks are sprouted and damage evolution occurs. For frictional closed cracks, an appropriate criterion for the onset of frictional sliding along micro-cracks was proposed in this paper. Also, plastic strain increments were determined by the flow rule, consistency condition and normality rule within the thermodynamic framework. The simulation results demonstrate that the developed micromechanical model can adequately reproduce many features of the rock behaviour such as hardening prior to the peak strength, softening in post-peak region, damage induced by wing-cracks and irreversible deformations caused by frictional sliding along micro-cracks. Furthermore, the softening behaviour of material in post-peak region is affected and the material undergoes higher values of strains and damage up to the residual strength. Therefore, the rock sample simulation with the coupled frictional sliding-damage model could increase plasticity and ductility of the rock in post-peak region because of regarding plastic strains caused by the frictional sliding along micro-cracks

Numerical Analysis of the Segmental Supporting System Under Earthquake Loading

Today, precast concrete lining (segmental) are used as system maintenance in the majority of tunnels excavated by TBM. On the other hand, the mechanism of the joint between two segments is not known under seismic loads. In this paper a numerical study about the effect of the earthquake on the segmental supporting system and the resultant vertical and shear forces on the contact surface between two segments is investigated. The Tehran -Karaj water conveyance tunnel (Amirkabir) was used as a case study. In this study, the UDEC software was used. At the first step, the segmental lining were simulated under no slip and full slip conditions and the normal and shear forces were studied. Finally, the effect of joint stiffness between two segments were investigated. Results showed that with increasing the interface properties, the normal and shear forces in the segmental joints increased. Also with increasing the joints stiffness, the normal and shear forces on the joints increased and the normal and shear displacement decreased. In other words, the rigidity increament of supporting system is associated with flexibility decrement of lining with respect to rock medium. So, the stresses increased and displacement decreased

A new constitutive model for the time-dependent behavior of rocks with consideration of damage parameter

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