Study On Nishihara Rheology Model And Its Application Considering Damage

Rheological model of rock mass is the core component of rock rheological theory.With the development of China's economy,the scale of infrastructure construction in China is growing rapidly,and rock rheological problems in engineering are becoming more and more complex.The results show that the rock mass parameters will be attenuated as the damage changes with time.Therefore,only from the viewpoint and method of rock rheology and damage theory can we consider the rheological,mechanical and deformation characteristics of rock,so as to serve engineering practice more reasonably and effectively.Based on the Nishihara rheological model,which can reflect the elastic-viscoelastic-plastic rheological properties of rock and soil more comprehensively,and combined with the parameter attenuation caused by damage,a Nishihara rheological model considering damage is proposed in this paper,which is used for the secondary development of FLAC3 D custom constitutive model and engineering application.The main contents are as follows:(1)Based on Mohr-Coulomb yield criterion and damage theory,the Nishihara rheological model considering damage and the damage threshold determined by triaxial compression test are proposed,and the finite difference scheme of Nishihara rheological model considering damage,the stress renewal equation and the stress correction equation used in FLAC3 D are derived.(2)According to the difference format,the model is redeveloped by using the secondary development platform provided by FLAC3 D software,and the important methods,key variables and coding flow in the redevelopment are listed in detail.According to the comparison test of the degraded FLAC3 D built-in Burgers rheological model and the laboratory test in the literature,it is verified that the model in this paper has not entered the yield state and has entered the yield state.Correctness and applicability after status;(3)Based on the numerical experiments,the sensitivity analysis of the parameters in the proposed model is carried out with strain and displacement as indicators.The model is applied to simulate creep,relaxation and step-by-step cyclic loading and unloading tests,which proves that the model in this paper can simulate these tests well,especially for the simulation of accelerated creep stage.(4)Taking a red bed soft rock tunnel in Yunnan as an example,the damage threshold is 0.25%.based on triaxial compression.Combining with the relevant parameters in the literature,the calculation results of the model and the degenerated model(without considering the damage)and the field monitoring are compared and studied,which proves that the Nishihara model considering the damage in this paper is more practical.In addition,the tunnel excavation method is also studied based on the model in this paper.The simulation results show that the double-sided tunnel excavation method is safer than the two-step method and the single-sided tunnel excavation method.