Abstract: This paper presents a case history of the treatment of roof collapse in an extra long highway tunnel excavation in Liuwei National Expressway, which connects the Duyun and Shangri-La in Guizhou Province between Liupanshui and Weining. The collapse occurred between Station TZK16+315 and TZK16+330 and a special outside tunnel treatment method was utilized. The collapse mitigation techniques included: 1) Backfill operation should be implemented immediately after the roof collapse and the second concrete lining reinforcement support should be applied in the collapse affected zone; 2) at least three meters thick C15 lean concrete should be backfilled at the collapsed area for the purpose of stabilizing the surrounding rock mass and minimizing the potential collapse. Drainage ditch should be installed around the collapsed area; 3) In the excavation of the collapsed area, the circular excavation around the backfilled lean concrete should be performed. The excavation is similar to S-Ta lining operation.

Key words: express highway, tunnel, roof collapse, treatment