Failure Mechanism of Support and Construction Force Analysis of New Support System in Loess Tunnel
The traditional supporting structure is widely used in tunnel excavation,but it shows local joint broken,out-of-plane instability,arch-shotcrete interface slipping under complex geological conditions,which can greatly weaken the overall strength of the supporting structure and lead to severe engineering disasters.Based on this,a plane strain model is established by finite element software ANSYS to reveal the failure mechanism of traditional support structure,and a new type of composite structure support that comprises of π-type steel frame is proposed.A three-dimensional numerical model is established to explore the influence of component parameters on the section details of the new steel frame.The stress of secondary lining under different support systems is compared and analyzed,and the structural safety is evaluated.The results show that under complex stress environment,the stability of surrounding rock and tunnel structure is difficult to be guaranteed due to the stiffness difference between in-plane and out of plane.The wall thickness and the release rate of surrounding rock have significant impact on the non-uniformity of the stress on the details of the arch section.Compared with the traditional support system,the axial force and bending moment of the secondary lining under the new support system have been significantly improved,and the safety of the structure has been improved by 56％.This study can further provide reference for the design of relevant supporting structures.
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