Research On Viscoelastic-plastic Constitutive Model Of Rock Based On Fractional Order Theory

With the development of economy and society,my country's public transportation and underground transportation networks have gradually improved and developed.At the same time,with the relaxation of my country's population policy,the number of people has increased year by year,and the existing urban clusters have been unable to meet the needs of the growing urban population.The expansion of the city is inevitable.However,in the actual development process,due to some reasons such as inadequate survey of hydrogeological conditions and rush to rush to the construction period,some engineering accidents that caused heavy economic losses and casualties occurred from time to time.Among them,the more prominent is the occurrence of rock masses during excavation.The creep phenomenon caused the gradual damage to the rock mass and eventually led to the instability of the project.Therefore,it is necessary to analyze the rationality of the whole process of rock creep and propose corresponding prediction models in order to have guiding significance for engineering practice.First,this article introduces some of the most widely used components in creep theory and some commonly used classical creep models formed by them in series and parallel,and analyzes the mechanical characteristics,scope of application and limitations of the classical models.Then according to the theory of viscoplasticity and damage,the classic Bingham model is improved.Because the traditional Bingham model can only reflect the constant-velocity creep stage of the rock but cannot describe the deceleration and acceleration creep stages,the three are connected in series by adding a nonlinear function that characterizes the deceleration stage and a damage equation that describes the acceleration stage.An improved Bingham model considering damage was obtained,and the Bingham model was fitted and verified by the actual creep data of green schist and red sandstone.It was found that the fitting result was basically consistent with the actual value and had a certain degree.applicability.Secondly,based on the fractional order theory,an R-L software component derived from the theory is introduced and its mechanical characteristics are analyzed.In order to completely describe the characteristics of elasticity,viscoelasticity and viscoplasticity presented in the process of rock creep,this soft component is connected in series with an elastic element Hooke body and an improved viscoplastic element to form a four-element rock creep based on the fractional theory.Viscoplastic model.According to the creep results of green schist and red sandstone,the fractional model is fitted to find the parameters,which shows that the fitting results are in good agreement with the actual creep results,which verifies the correctness and rationality of the fractional model.Finally,by selecting the Kouzidong Mine as an engineering example,selecting FLAC 3D numerical simulation software for engineering modeling based on the collection of relevant engineering backgrounds,and using C++ and Fish language to derive a three-dimensional difference form of a fractional four-element model.Afterwards,it was re-developed through the built-in interface of FLAC 3D.Through finite element analysis,it is found that the deformation value of the top and two sides of the actual roadway surrounding rock creep is more obvious and needs to be monitored.This is more consistent with the actual engineering and has certain guiding significance.