NUMERICAL ANALYSIS OF INTERACTION OF SUPPORT SYSTEM OF URBAN TUNNELS WITH ITS SURROUNDING ENVIRONMENT IN TIME-DEPENDENT AND TIME-INDEPENDENT STATES

Predicting the behavior of urban tunnels in weak rocks with a behavior similar to soil's or rock's 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 nite element method. The aim of modeling is the investigation of the eects 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 de ection behavior of surrounding rock masses.
For numerical modeling of tunnel-support system interaction two constitutive models including Mohr-Coulomb model(time-independentmodel),MC,andsoftsoilcreep 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 de ection behaviors of its circumference rock mass were compared. The results of study show that considering time eect on some cases caused an approximately 63 percent dierence between two model's results. For verication of research problem, a tunnel with similar conditions and jointed rock mass constitutive model in the frameworks of 2D and 3D nite-element analyses were used. The results of verication 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 such as stressstrain relationships parameters, displacements and de ections 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 implementationofcreepplasticanalyses. Inotherwords,with respect to the obtained results by changing 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.