Rheological Behavior Of Circular Tunnel Based On D-P Yield Criterion

The continuous deformation of the tunnel wall,the gradual increase of the lining stress and the long-term stability of the tunnel are key problems in the tunnel engineering.These problems all involve changes in the stress or strain of the material over time.The theory of elastoplastic mechanics cannot describe the time-varying properties of materials.Therefore,the tunnel should be studied from the perspective of rheological mechanics.It takes a certain amount of time to apply the supporting force after the tunnel is excavated.The simplification of the supporting force in the current theoretical research is quite different from the actual project.Rock and soil materials will change in volume under the action of shear stress.When analyzing the stress and deformation of rock and soil materials,the dilatancy of the materials cannot be ignored.This paper mainly discusses the supporting force and surrounding rock mechanics model through theoretical analysis,supplemented by numerical simulation.Based on the Drucker-Prager yield criterion and element constitutive model,the stress field and displacement field of the surrounding rock after tunnel excavation are analyzed.Consequently,some valuable results and conclusions can be attained:(1)The simplification of supporting force in most mechanical models is discussed.The mechanical model of surrounding rock considering delay support is established.The loading and unloading of plastic zone under the action of delay support is judged theoretically.The results show that the plastic zone of surrounding rock is unloading after the active supporting force is applied.The theoretical analysis is verified by numerical simulation.(2)The constitutive model of surrounding rocks is assumed as the Nishihara model and the Drucker-Prager yield criterion is selected which the dilatancy characteristics of plastic zone are taken into consideration;theoretical solutions of plastic zone radius,stress and displacement for surrounding rocks after the excavation of circular tunnel are derived.When the dilatancy angle is equal to zero,the solutions are return to the viscoelastic-viscoplastic solutions of Nishihara model based on Mohr-Coulomb criterion with the assumption of constant volume.The viscoelastic-viscoplastic displacement solution and viscoelastic-plastic displacement solution are compared and analyzed.Through a numerical example,the effect of dilatancy angle on radius of plastic zone,tunnel-wall displacement and stress field are analyzed.The results show that before the surrounding rock reaches the stable state,the effects of dilatancy angle on stress field and the radium of plastic zone stress are relatively smaller while the effects of dilatancy angle on tunnel-wall displacement is relatively larger.The stress field and the radium of plastic zone stress for stable surrounding rocks are irrelevant to the value of dilatancy angle,however the tunnel-wall displacement of stable wall rock increases obviously with the dilatancy angle.When the dilatancy angle is large,the displacement of stable wall rock will be underestimated if the viscosity of plastic zone is not considered.(3)The constitutive model of surrounding rocks is assumed as the Combined model of K-H model and plastic element,the Drucker-Prager yield criterion is selected,and the surrounding rock after excavation of the circular tunnel is deduced by considering the dilatancy of the plastic zone and the delay support.The influence of the timing of the supporting force on the wall displacement is analyzed.The results show that the delayed support can fully release the deformation energy of the surrounding rock,and the timely support can better control the displacement of the surrounding rock.