Numerical Simulation Study On The Performance Of Pipes For Reinforcing Tunnel Roof In Loose Strata

Road tunnels, railway tunnels and subway tunnels and other works often encounteredloose strata. In order to prevent tunnel excavation affect the surface of buildings or cause largedeformation of stratum, we should use pipe roof reinforcement measures to reinforce thesurrounding in the front side of tunnel, it is an effective method in common use. Therefore,research on this technology is necessary.Pipe roof reinforcement technology in common loose strata tunnel is researchedspecifically in this paper, and numerical simulation analysis is combined with projects to findreasonable and efficient pipe roof reinforcement method. The main contents and conclusionsare as follows:(1) The concept of loose strata, surrounding rock failure mechanism and mechanicalproperties of the surrounding, deformation characteristics of surrounding, reinforcementmethods are analysed and discoursed. Pipe reinforcement can effectively control theexcavation of the front side loose broken strata, it can improve the strength and stability oftunnel surrounding rock, it is an effective reinforcement method.(2) Researched on the construction methods,classification, and application of the piperoof, and the characteristics of the pipe roof support in loose formation is analysed in thispaper. The mechanism of action of the pipe roof based on a detailed analysis, and put forwardrelevant parameter design method. Studies have shown that pipe roof reinforcement plays amultiple role in the loose stratum tunnel, factors of pipe roof reinforcement parameters is thetunnel geological conditions, depth, the sectional size, the layout of the pipe roof and theconstruction conditions.(3)The finite element simulation method is often used in underground engineerings. The numerical simulation method is analysed in this paper. Studies have shown that not only toconsider the role of the grouting of the pipe roof, but also to highlight its beam effect in thesimulation, and the method are analyzed.(4) Without reinforcement, only a small catheter grouting,only pipe roof forepolling piperoof and small pipe grouting four conditions studied by numerical simulation methods. Studieshave shown that it is unsafe without reinforcement under the conditions of loose strata, theeffect is finite with only a small catheter grouting, the rock self-stabilization ability is fullyreflected with pipe roof and small pipe grouting, it also reduces the internal forces on thesupporting structure, and it proves the supporting effect of pipe roof, regression analysis of theon-site monitoring data also shows that this support method is reasonable and effective.(5) It is reasonable using the spacing of pipe about0.40~0.50m under the condition ofthe pipe roof combined with small catheter grouting, it is not only can ensure that the effect ofthe support, but also can take into account the construction and cost. The diameter and lengthof the pipe roof influence each other, when the length of the pipe roof is small, pipe diameterchanges lead to the effect of pipe roof reinforcement change; when the length of the pipe roofis long, pipe diameter changes lead to a lesser effect on the supporting effect, when thediameter is more than300mm, pipe diameter changes in the supporting effect isincrease. Excavation step has a great influence on the deformation of the excavation near thesurface of the surrounding, but it has finite impact of disturbance range on the surrounding. Ithas obvious reinforcement effect before the excavation face0~0.5D, and it has lower effectbefore the excavation face0.5~1.5D.