| Ever since the reform and opening-up,China's economy,stepping into the fast lane of development,has made remarkable achievements.Building roads is the first step to become rich and the total mileage of the expressway in our country is among the best in the world.Due to the fact that China is a country with a vast territory and diversified topographic and geomorphic conditions and that there are many mountains in central and western regions with changeable geological conditions,it is inevitable to encounter situations where the net distance between the left and right line of tunnels does not meet the standard requirements in the construction of highway tunnel.Because of the limitations of route design and mountain conditions,sometimes the traditional double-track tunnel cannot fulfill the needs of engineering construction,and thus the small spacing tunnel emerges.CoMpared with the double-arch tunnel,the small spacing tunnel enjoys flexible layout,strong adaptability to geography,simple construction technology as well as low construction costs.Consequently,the small spacing tunnel is being used more and more widely for the construction of highway tunnel.The small spacing tunnel also has its own limitations.There are still many technical issues to be solved and the design criteria and failure criteria need to be improved.Especially there are certain iMpacts of the explosion excavation of following hole on the primary support in the existing hole.If the explosion is not appropriately controlled,the surrounding rock fissures will be rapidly developed and the stability of the surrounding rock will be greatly affected,thus courting a series of issues such as the cracks in the completed lining.By studying the tunnel rock blasting theory,collecting and organizing the monitoring database of tunnel explosion vibration and adopting the numerical simulation method,this paper,based on the case study of Xiangshan tunnel of the highway from Macheng to Zhuxi,analyzes the influences of the explosion excavation of following hole on the existing hole in small spacing tunnel with different lengths of top stages.The main ideas and relevant results of this paper are listed as follows:(1).The detailed engineering data of Xiangshan tunnel is obtained by referring to its geological data and the construction design drawing as well as the field research at the construction site.(2).By briefly illustrating key features of the geotechnical blasting and analyzing the rock crushing mechanism,this paper takes the stance that there will be fragment area,cracked area as well as vibration area after blasting.Meanwhile,this paper explains main factors of influencing geotechnical blasting and elaborates on common tunneling blasting schemes,including the full face excavation method,the bench cut method and CD method etc..What's more,this paper examines the formation and coverage of seismic wave of geotechnical blasting.(3).By employing finite element analysis software of MIDAS/GTS to perform numerical simulations together with the practical geotechnical parameters,this paper analyzes the iMpacts of the explosion excavation of following hole on the primary support in the existing hole with different lengths of top stages.(4).In the excavation process of tunnel construction,when take different methods of excavation,this paper research the influence of the first tunnel support stress and settlement of that first cavern excavation.andprovide some reference for the first excavation of the tunnel support parameters. |
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