The tunnel squeezing phenomenonwas first described byTerzaghi (1946)who associated squeezing mainly with clay-rich rocks. Consistent with Terzaghi’s original description, the focus of this paper is on tunnels in clays and clay-rich rocks such as clayshales. The paper develops a simple procedure to predict tunnel squeezing potential using normalized undrained shear strength, unconfined compressive strength and P-wave velocity. A collection of a large amount of undrained triaxial test data is used to show that the undrained shear strength of clay shales can be normalized with respect to the effective vertical stress. The normalized undrained shear strength can then be used to predict the squeezing potential since it can be directly related to Peck’s (1969) stability factor N. Values of N provide estimates of the degree of squeezing potential, with values of N >1 indicating potential for squeezing.