| The construction of tunnel in the country before the1980s mostly adopted mining method as the excavation technology, especially in low-grade roads. In that way,overbreak being a prevalent phenomenon during excavation, cross-section of different sizes, usually having no primary support and secondary lining, brought security risk to the normal operation. In order to ensure the safety of operations,various regions gradually undertook reinforcement of that type of tunnel in recent years. However,on account of that the original tunnel is generally unlined opening, partly stone-lined structure,and some lining had multiple fractures with some degree of seepage,there exist serious potential safety hazard. Therefore,it has important practical significance to construct reinforcement in the class of the existing tunnel and it will be a very important role of guidance and reference for the construction of similar projects in the future.This paper takes "Zhejiang Yongkang Wang Zhao lines, Yongxiang tunnel repair and reinforcement project"as studying background, fully absorbing the results of the research at home and abroad,using the methods of expanding excavation and reinforcement treatment to eliminate security risks.By this way,the operation capability can be improved and the safety of the tunnel is guaranteed. The research work and research include:(1) Targeted analysis of surrounding rock and structural stability in construction process is made according to the condition that the road tunnel section is small, and the majority of the original supporting structure has been damaged, cracking, water seepage;it calculates and analyzes the stabilities of different programs of expanding excavation and various support parameters,which lay the foundation for the support parameters design.(2) The primary support adopts basalt fiber composite shotcrete,which basic mechanical properties, toughness and flexural strength test have been done.Requirements of shotcrete for raw materials, a variety of fiber performance parameters,and toughness index of fiber shotcrete lining are proposed according to geological conditions of existing tunnels for the road.(3) Security of surrounding rock of primary support with composite fiber shotcrete and basalt fiber shotcrete has been analyzed by software Ansys and Flac3D. For the primary support with composite fiber shotcrete and basalt fiber shotcrete, security requirements of the surrounding rock structure can be met in condition that simply adjusting the thickness of the lining and cancelling steel mesh.(4) The tunnel are back analyzed by software GeoFBA based on the convergence data collected in the field around it. Elastic modulus E and lateral pressure coefficient λ,obtained by back analysis, are greater than parameters of simulation formation in other chapters.This explains that use composite fiber shotcrete and basalt fiber shotcrete as primary support can meet the security requirements of the surrounding rock structure.(5) In order to determine the optimum mixture ratio, combined with the engineering characteristics of the tunnel, usability experiments have been done,which include fiber shotcrete mixing, dispersion of fiber in the shotcrete, material flow, process parameters of productivity and condensation effect, process parameters of first shotcrete layer thickness and the spring rate of the side wall and arch. According to the specific circumstances of the on-site implementation, it summaries the difference of dosage and springback between fiber shotcrete and ordinary shotcrete,and analyses that advantage of basalt fiber and composite fiber shotcrete in economic and social benefits. |
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