Construction Crucial Technique Of The Long-span Tunnel Portals In Unfavorable Geological Condition

While road tunnel construction is developing quickly, there are also many severe tests, in which construction of tunnel portals is always an emphasis and difficult point. Portal section has its own characteristics compared with other sections: surrounding rocks are generally seriously weathered; there are many joints,faults,fractured zone here and the phenomenon of the eccentric compression is very common and severe. With the number of the large cross-section tunnel increasingly pronounced, the problem of the construction of tunnel portals has increasingly been prominent. So the construction crucial technique of the portal section needs further studying urgently.Based on the problems in the construction of tunnel portals, this paper puts forward the viewpoint that making entering portal safely by controlling for stability of face-upward slope and choosing reasonable construction methods and auxiliary processes is the key of the tunnel portal construction which is proposed by summarizing the present situations of portal construction and theory at home and abroad.This paper summarizes tunnel portal slope collapse modes in different kinds of construction. Therefore, the major factors impact tunnel slopes are produced. Combined with the engineering example of Fu-xi double unite arch tunnel in Tong-Huang high way, two-dimensional numerical simulation is made for the slope, which analysis the excavating effects on the slope in the different wall conditions,different gradient of the slopes and different tunnel buried depths; making three-dimensional numerical simulation for the section of tunnel portal in the real formation and surrounding rocks conditions in order to analyze the law of surrounding rock and mid-partition's deformation and stress changes; the reasonable construction scheme comparison and selection is made; different excavation orders of double unite arch tunnel are made to guide construction; Through the pile element numerical simulation, researching the advance strengthening of pipe shed and analyzing its mechanism in the construction of portal section.On the basis of the in situ monitoring data in Fu-xi double unite arch tunnel, analysis the problem in the construction of the tunnel and give the reasonable explanations, which can provide referential experience for related project.