This paper describes a method to evaluate the conditions of tunnel face stability in sand strata that contain a clay layers by model tests and numerical analyses. Experimental results show that soft clay strata make the collapse range wider and the position of soft clay stratum determines the range and magnitude of ground damage. These phenomena can satisfactorily be simulated by the two-dimensional rigid plastic finite element method. Parametric studies prove that the internal pressure required to stablize the tunnel face depends on the strength, position and thickness of the clay stratum. The method is proved to be equivalent to that with ground improvement by using the Mohr-Coulomb failure hypothesis. Then, the conditions of face stability can be obtained by the cohesion c, angle of internal friction φ for sand strata and cohesion c for clay strata.