Abstract: Based on the analysis of the characteristics of strong continuous plastic flow failure and extreme difficult support of soft rock tunnel in complex environment, the stress transfer process and mechanism of deformation failure of soft rocks in complex environment were studied.In the practice of Guhanshan soft rock tunneling engineering, the strong tunnel deformation was controlled, and the tunnel was kept stable.Analysis and calculation was made for soft rocks in similar complex engineering environment, and the control target of soft rock tunnel support defined; the principles for controlling plastic zone development was proposed; and the mechanical properties of shallow wall rock of tunnel and the support method for residual strength were given.Successful experience is provided fro the tunnel control with similar engineering conditions.

Key words: Plastic zone, Crushing stress, Expanding stress, Residual strength, Confining pressure