Abstract: Due to the different degrees of weathering and the tectonic structures of the rock mass, the nonuniform strength in the rock mass is commonly encountered in the tunneling engineering. The variation of the rock mass strength might cause great difficulties for the tunnel construction. This paper presents a case study of mitigation of a large scale tunnel collapse in the Renge Highway Tunnel of ShuangYong Expressway in Longyan City, Fujian Province. The collapse occurred in August 2010 at the soft rock mass zone. The mitigation techniques involved using steel H beams placing at the arch of the tunnel and using small diameter casing in the aheadgrouting supporting.

Key words: Tunnel Construction, Soft and Hard Rock Masses, Factors Causing Collapse, Small Diameter AheadGrouting