Abstract:

The function of the secondary lining is studied in terms of applicability, uncertain factors and mechanical performance of temporary support for bad surrounding rocks; and it is emphatically illustrated that the secondary lining is is key structure. The required planning service life of the secondary lining of every country is 100 years; the investigation results show that the service life of the secondary lining can reach 100 years under necessary maintenance. The degradation of the tunnel structure is mainly induced by degradation of the surrounding rocks, degradation of lining structure and construction quality. The durability of concrete is mainly decided by construction technology. The main problems of lining are as follows: 1) The lining concrete is not compact; 2) There are hollows behind the lining; 3) The thickness of lining is nonuniform, and the thickness of the crown is small; 4) There are potential crack in the lining concrete. The countermeasures for improving the durability of the secondary lining are summarized as follows: 1) Reinforced concrete lining should not be used as much as possible; 2) The thickness of the protection cover should not be less than 50 mm when reinforced concrete lining is used; 3) The protection cover of 50 mm thickness should be used when shotcrete technology is used; 4) The invert should be used; 5) The ring of invert and side wall should be closed; 6) The construction technology for concrete should be improved; 7) The initial structural disadvantage of concrete lining should be minimized. The author believes that countermeasures 6） and 7） are most important. The key lining construction technologies in Japan, grouting, tamping and steam curing, are introduced， so as to provide guidance for the lining construction in China.

Key words: tunnel, mining method, secondary lining, lining durability, surrounding rock durability, grouting, tamping, steam curing