Deformation And Stress Analysis Of Phyllite Tunnel During Construction

With the continuous development of transportation infrastructure,it is inevitable to build tunnels under complex geological conditions.Among them,the engineering problems of tunnel construction in phyllite stratum are particularly prominent,and it is widely representative of broken and weak geology.Therefore,the deformation and stress analysis of phyllite tunnel in the construction process are studied to reveal the internal mechanism and law of large deformation and support structure damage of phyllite tunnel.It is of great significance to solve the engineering problems that restrict the tunnel construction in phyllite geological layer,improve the level of tunnel construction technology and theory in China,and promote the strategy of traffic power.Based on the long-term monitoring of phyllite tunnel construction process,this paper adopts the methods of experimental research,theoretical analysis,tunnel deformation monitoring,data analysis and back analysis calculation to study the physical and mechanical properties of phyllite and the deformation and stress analysis of phyllite tunnel construction process.The main research contents are as follows:(1)The physical and mechanical properties of phyllite are studied by means of test method and engineering geological report analysis.It is recognized that the moderately weathered and slightly weathered phyllite belongs to hard rock,while the highly weathered phyllite belongs to weak surrounding rock with extremely low strength,weak rock,smooth joints and easy to be broken.(2)According to the characteristics of softening,dilatancy and strong rheology of broken phyllite,the viscoelastic plastic mechanical model considering softening and dilatancy is used to analyze the surrounding rock of tunnel theoretically,and the theoretical analytical equations of stress,strain and displacement of viscoelastic,viscoelastic plastic and broken state are obtained.The results reveals the internal mechanism of large deformation with rheological characteristics caused by volume expansion during the construction of broken phyllite tunnel because the surrounding rock changes from viscoelastic state to viscoplastic state,and then to broken state.(3)The monitoring measurement and section scanning data in the process of tunnel construction are sorted out and analyzed to reveal the temporal and spatial law of deformation in the process of broken phyllite tunnel construction.Its deformation has the characteristics of convergence time,large amount of deformation,greatly affected by the excavation construction,showing the characteristics of stage growth.The spatial distribution is uneven,and the maximum deformation occurs at the joint of arch and truss.(4)The time series analysis method is used to analyze the deformation data,and the uncertain time series Holt two parameter model is established.The Holt model is used to predict the tunnel deformation.Combined with the requirements of tunnel construction deformation management,the scene of tunnel deformation control management is designed.(5)Based on the actual displacement data and particle swarm optimization,the optimal parameter solution of viscoelastic plastic model for softening and expanding of phyllite is obtained by back analysis.The results show that the displacement sequence and circle range calculated by back analysis are consistent with the actual monitoring displacement sequence and measured loose circle results,which verifies the rationality of back analysis mechanical model parameters and the accuracy of back analysis calculation.(6)Based on the analysis of the tunnel surrounding rock stress and the support resistance of the support structure,the results show that:in the broken area,the surrounding rock stress increases sharply with the increase of the radius;in the viscoplastic area,the surrounding rock stress decreases rapidly with the increase of the radius;in the viscoelastic area,the surrounding rock stress increases slowly with the increase of the radius,which is close to the original ground stress.To a certain extent,enough support force has a significant effect on the deformation control of surrounding rock.We should pay attention to the deformation control effect of grouting,advance support and other measures to improve the mechanical parameters of rock.