عنوان مقاله [English]
Predicting the behavior of urban tunnels in weak rocks with a behavior similar to soils' or rocks' by swelling and squeezing ability is one of the important challenges in tunnel engineering and rock mechanics. In this research plane strain two-dimensional model of a real urban tunnel with horseshoe cross section is modeled through 2D finite element method. The aim of modeling is the investigation of the effects of considering or ignoring time factor in the constitutive model of materials on the interaction behavior of tunnel support system and also stress-strain and deflection behavior of surrounding rock masses.For numerical modeling of tunnel-support system interaction two constitutive models including Mohr-Coulomb model (time-independent model), MC, and soft soil creep model (time-dependent model), SSC, similar and constant rock mass properties were considered. The results of these two models in the framework of structural behavior of tunnel support system and also stress-strain and deflection behaviors of its circumference rock mass were compared. The results of study show that considering time effect on some cases caused an
approximately 63 percent difference between two models' results. For verification of research problem, a tunnel with similar conditions and jointed rock mass constitutive model in the frameworks of 2D and 3D finite-element analyses were used. The results of verification show good agreement between the obtained results by numerical models of the present paper and numerical models of the reference paper.Mohr-Coulomb constitutive model is a model independent of time, stress history conditions, consolidation state, creep, hardening and softening, in order that no change could occur in the results obtained with this model in plastic numerical analyses by changing time intervals of numerical computations. However, considering creep of materials and time factor will generally increase the values of structural interaction parameters (secondary parameters such as bending moments, shear forces and axial forces in shotcrete and rock bolts) and geotechnical interaction parameters (initial parameters suchas stress-strain relationships parameters, displacements and deflections of rock materials) of SSC model rather than MC model in the excavation of tunnel and installation of its support system. Impressibility of secondary parameters (i.e., structural parameters) in support system of tunnel compared to initial parameters (i.e. geotechnical parameters) is half by changing time intervals of implementation of creep plastic analyses. In other words, with respect to the obtained results bychanging real time in numerical analysis of geotechnical parameters (initial parameters) is approximately 2.30 times greater than structural parameters (secondary parameters), because the occurrence of geotechnical parameters will generate and mobilize secondary parameters (structural parameters) in the interaction of support system of tunnel-rock.