Causes analysis and treatment of extra-long Yunzhongshan tunnel collapse

This paper introduces the whole process of arch top instability and collapse at left railway line LK43+642~LK43+660 of extra-long Yunzhongshan tunnel,the paper analyzes the collapse causes from three aspects of geological causes,leakages and erosion,and construction factors and inaccurate preliminary geology prediction and so on.Combining with specific engineering conditions,it puts forward safe and reliable collapse processing measures.In the process of treatment,it neither influences the security of existing railway line nor fail to complete the construction at collapse section.