Research And Application Of Dynamic Displacement Back Analysis Based On Tunnel Monitoring Data

During the construction of the tunnel,the mechanical parameters of the tunnel surrounding rock will continue to deteriorate with time and the spatial change of the forward movement of the palm face.This degradation of the surrounding rock parameters has an important impact on the stability of the tunnel.This paper takes the Yunling tunnel in Yixing as the engineering background,and uses the dynamic displacement back analysis method to study the deterioration process of the surrounding rock parameters of the tunnel.According to the specific conditions of Yunling Tunnel in Yixing City and the standard requirements of tunnel monitoring and measurement,the field monitoring and measurement plan of Yunling Tunnel and the construction management benchmark of surrounding rock deformation were established,and the monitoring and measurement work was carried out according to the monitoring plan.In order to reduce the accidental error generated during the monitoring process,regression analysis was performed on the field monitoring data.Many previous research results have shown that the consideration of the existence of surrounding rock loose circles in displacement back analysis is of great significance to improve the accuracy of the calculation results.Therefore,the numerical model of this paper considers the existence of surrounding rock loose circles and uses geological radar instruments Detect the range of loose circles.On the basis of grasping the tunnel deformation data and the scope of the tunnel loosening circle,this paper carried out a dynamic displacement back analysis calculation study.The purpose of the calculation is to explore the specific process of the continuous deterioration of the elastic modulus of the tunnel surrounding rock as the tunnel is excavated Finally,the functional relationship between the parameters of the surrounding rock of a fixed section of the tunnel and the distance of the section from the palm face is obtained.Finally,this paper uses this functional relationship to study the stability of the surrounding rock of the tunnel under different supporting conditions and the optimal timing of the second lining.The main research conclusions and results achieved in this article are as follows:(1)For the tunnel wall rock vault settlement and horizontal convergence displacement data measured at the site of Yunling Tunnel,three function models are used to perform regression analysis on the measured data,and finally the best fitting result of the horizontal convergence deformation data is obtained The analytic formula of the function is,the analytic formula of the best fitting result of the settlement data of the vault is: Based on the above fitting results,the stability of the surrounding rock of the tunnel is analyzed,and the reasonable support time of the second liner under the deformation rate criterion and the deformation limit displacement criterion is 16 m away from the palm face.(2)In order to carry out back analysis and calculation of the displacement of the tunnel more accurately,the dynamic analysis and back analysis of the paper consider the existence of the surrounding rock loose circle.By comparing various detection methods of loose circles,considering the advantages of the geological radar method for detecting loose circles,the geological radar method is used for detection.In this paper,the surrounding rock loosening circle within 7m range near K1 + 880 of Yunling Tunnel is detected,and the range of surrounding rock loosening circle here is roughly 2m deep.In order to facilitate the later numerical calculation of inversion,the scope of the loosening ring was simplified to extend evenly 2m outward along the tunnel boundary,and a dual-medium numerical model was established.(3)In order to explore the specific process of the continuous deterioration of the elastic modulus of the surrounding rock within the tunnel loosening circle as the tunnel is excavated,this paper has carried out a dynamic displacement back analysis calculation study.In this paper,the dynamic back analysis calculation method is to first assume the deterioration function of the surrounding rock elastic modulus with tunnel excavation,and then verify the accuracy of this function.Assuming that the function selects two function forms: a linear function and a sine function,the calculation results show that the sine function has the best fitting effect.Finally,the expression of the sinusoidal function of the deterioration of the elastic modulus of the surrounding rock is taken as.(4)Using the above functional relationship between the elastic modulus of the surrounding rock and the distance n from the cross section to the palm face,the study of the influence of the tunnel's secondary lining on the stability of the surrounding rock at different times is carried out.Six working conditions with different distances from the face of the second lining were selected for numerical simulation.It was found that as the support time of the second lining was delayed,the settlement and horizontal convergence of the arch of the tunnel gradually increased.In order to explore the best application timing of the second liner,the internal force variation of the second liner under different support timings was further studied.By simulating the internal force of the second liner under different operating conditions,the The best time to apply the second liner under the minimum support resistance criterion is to apply the second liner at a distance of 20 m from the palm face.