| Soft rock with high geostress has the characteristics of high geostress,rock fragmentation and large convergence after excavation,which is particularly common in the western mountain tunnel,and brings great inconvenience to construction.However,the development of deep space is the inevitable trend of tunnel and underground engineering in the future.With the promulgation of relevant national policies and the active participation of scholars in various fields,many achievements have been made in recent years.This paper takes the Muzhailing Tunnel of Weiwu Expressway as the engineering background,theoretical analysis and numerical simulation are used to study the reasonable support parameters and the best time of the second lining support of the tunnel in high ground stress soft rock,and compared with the monitoring section data under the actual engineering background.The main research work and conclusions are as follows:(1)By summarizing the research status of the support parameters of soft rock large deformation tunnels at home and abroad,combined with the definition of soft surrounding rock,deformation characteristics and the initial support and secondary lining support ideas in the tunnel design,and according to the actual engineering background,it is proposed It is applicable to the supporting research ideas of this article.(2)Mainly introduces the engineering geological characteristics of Muzhailing Tunnel and According to the geological and hydrological characteristics of the tunnel and the design principles of the tunnel,the construction scheme suitable for the project is selected.The final selection is: two single line tunnels + three inclined shafts.(3)The theoretical analysis,calculation and prediction of the Muzhailing tunnel are carried out.According to the results of the theoretical calculation,the tunnels in the prediction section are all large deformation sections.In addition,the measured data of the monitoring section is compared with the theoretical calculation data.The comparison results show that the measured data of the three monitoring sections differs from the theoretical calculation value by only 0.9% and 6.2%,indicating that the theoretical calculation value has a certain effect on the actual project.Reference value.(4)This paper systematically expounds the importance of monitoring and measurement,and sums up the monitoring data of the two sections in the high ground stress section of the tunnel.Through the analysis of the cross-section monitoring data on the construction site,it can be seen that the deformation of the Muzhailing tunnel generally shows the characteristics of rapid initial deformation(deformation day 1 to day 10,reaching more than 70% of total deformation),large total deformation(the crown settlement reach up to 520 mm,and the arches waist convergence reach up to 1200mm),and long deformation stability time.(5)According to the actual project,the finite element software FLAC3 D is used to perform numerical simulation,and the parameters of the lock foot anchor pipe under different working conditions are optimized and analyzed,and the cloud arch settlement and the arch waist convergence cloud map under different lock foot anchor parameters and the steel arch are obtained.According to the comparison of the force diagram of the frame,the parameters of the lock foot anchor rod are preferably selected.The length is 6m,the downward slope angle is 22°,and the lock foot anchor pipe is 89 mm in diameter.(6)As an important part of the initial support,after determining the bolt application scheme,the displacement field and stress field of the tunnel under the action of different shotcrete thickness are compared and analyzed,and the most appropriate shotcrete thickness is selected from the perspective of economic,reasonable and safety.We should adopt a length of 5m-7m anchors(7)As an important part of the initial support,after determining the anchor application scheme,the tunnel displacement field and stress field under different thicknesses of shotcrete are compared and analyzed.From the perspective of economic rationality and safety,the most suitable shotcrete thickness is selected as 30 cm.(8)In the optimal analysis of the steel arch frame,by comparing different working conditions,the preferred parameter of the steel arch frame is finally determined to be the HW175 type steel arch frame with a spacing of 50 cm.(9)Based on the load-structure model,the three load cases with different load sharing ratios of the secondary lining were simulated and analyzed.It was concluded that the secondary lining structure of the Muzhailing tunnel bears the most reasonable load under 60% load. |
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