Reasonable Construction Method for Grade Ⅳ Surrounding Rock in Single-Hole Four-Lane Super-Span Highway Tunnel
In order to study the reasonable construction method of super-span highway tunnels,the Xinghuacun No.1 tunnel included in the reconstruction and expansion project of the Xiaocaohu-Urumqi section of the Lianyungang-Khorgos Expressway in Xinjiang was studied.The numerical simulation method was used to analyze the deformation and stress of the supporting structure of the Grade tisurrounding rock in the super-span highway tunnel constructed by the center diaphragm(CD)method,the upper-bench CD method,and the three-bench and seven-step excavation method.Under the premise that the deformation and the stress of the supporting structure met the design requirements,the advantages and disadvantages of each construction method were considered,and the most reasonable construction method was determined.The field test was implemented to analyze the feasibility of the construction method.The results show that:① The tunnel deformation calculated by the CD method,the upper-bench CD method,and the three-bench and seven-step excavation method are all less than 21 mm,and the safety factors of the supporting structure at the initial stage are 2.48,2.41,and 2.28,respectively,which are greater than the minimum safety factor required by the tunnel design rules.The deformation and the stress of the supporting structure all meet the design requirements;② the advantages and disadvantages of the three construction methods are compared,and the optimal construction method for the grade Ⅳ surrounding rock in the Xinghuacun No.1 tunnel is determined as the upper-bench CD method after considering tunnel geological conditions and other factors;③ according to the field test results,the grade Ⅳ surrounding rock is constructed by the upper-bench CD method.The maximum arch subsidence is 14.6 mm,and the maximum peripheral displacement is 15.0 mm,indicating a good tunnel deformation control effect.The minimum safety factor of the supporting structure at the initial stage is 6.94,which meets the design requirements.
tunnel engineeringsuper-span highway tunnelreasonable construction methodCD methodupper-bench CD method
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