Nonlinear Rheological Model Of Thin-layer Carbonaceous Phyllite And Its Application In Engineering

Construction of tunnels and other underground projects under complex geological conditions has gradually become an inevitable trend in recent years.Carbonaceous phyllite is a common soft rock in western China.Thin-layer carbonaceous phyllite is a special form of carbonaceous phyllite.Its thickness is thinner,the rock mass is more broken,and the mechanical properties are worse.Tunnels and other underground projects in this stratum are prone to large deformation.In order to avoid construction diseases such as large deformation,support failure and underground structure failure,the constitutive relationship of thin-layer carbon phyllite is explored to analyze the stability of surrounding rock in underground engineering.In this paper,starting from the engineering characteristics,microstructure and mechanical properties,the nonlinear rheological model of thin-layer carbonaceous phyllite and the constitutive equations under different conditions are established,and the calculation formula of surrounding rock displacement for analyzing the stability of surrounding rock is derived.The main contents are as follows:(1)The microstructure and composition of thin-layer carbonaceous phyllite were analyzed by SEM and XRD,and the differences in microstructure and mineral composition between thin-layer carbonaceous phyllite and carbonaceous phyllite were explored.Through observation and field test,the longitudinal wave velocity and engineering properties of thin carbonaceous phyllite are analyzed and summarized.Combined with the indoor mechanical test,the mechanical properties and deformation characteristics of thin carbonaceous phyllite were explored.(2)Combined with the wave velocity characteristics of surrounding rock and the deformation characteristics of thin-layer carbonaceous phyllite,the rheological model of thin-layer carbonaceous phyllite was established,and the constitutive equation and strain equation under different stress states were deduced,which can be used for stability analysis.The three-dimensional difference form of the model is used to establish a dynamic link library,which is imported into the built-in constitutive model library of flac3 D and can be used for numerical simulation analysis.(3)Combined with the softening characteristics of thin carbonaceous phyllite,the softening factor was established and introduced into the Drucker-Prager strength criterion for correction.Based on the wave velocity characteristics,the surrounding rock zoning of thin carbonaceous phyllite stratum was analyzed.Based on the new nonlinear rheological model of thin-layer carbonaceous phyllite,combined with the modified D-P strength criterion and surrounding rock zoning,the deformation equation of surrounding rock considering the whole process creep is deduced,and the calculation formula of surrounding rock displacement is established.(4)Aiming at the problem that it is difficult to obtain the surrounding rock parameters of thin-layer carbonaceous phyllite through experiments,a coupling algorithm is established,which can use the displacement data of surrounding rock to inverse the surrounding rock parameters.The inverted surrounding rock parameters are brought into the numerical simulation software and the calculation formula.By comparing with the actual displacement,it is found that the error of displacement calculation formula is small,and the displacement trend is basically the same as the actual situation.Numerical simulation results are slightly larger,the displacement tends to be stable for a longer time.