Comparison of seismic stability for slopes with tensile strength cut-off and cracks

The strength of geomaterials is typically predicted by the Mohr-Coulomb yield criterion in slope stability analysis. The tensile strength of soils in this yield criterion, which is an extrapolation of the triaxial compression test results, is usually overestimated. Generally, the influences of tensile stresses in slopes are evaluated by two approaches: 1) introducing cracks to eliminate the tensile stresses in slopes, and 2) truncating the strength envelope to reduce the tensile strength of the soils. However, comparative analyses of the two approaches have not been fully implemented, especially under dynamic conditions. In this study, three slope failure mechanisms corresponding to the predictions of slope stability by the mentioned two approaches subjected to seismic loadings are systematically evaluated. The stability factor considering the pre-existing crack, crack formation, and tension cut-off are compared one another. The most unfavorable crack locations corresponding to the different mechanisms are evaluated. The influence of tensile strength on the factor of safety of slopes is estimated as well. Further, the critical acceleration and the permanent displacement of slopes with pre-existing crack, and tension cut-off are derived in the framework of the kinematic theorem of limit analysis. The vertical effects of seismic coefficient on critical acceleration and permanent displacement are discussed. Conclusions can be drawn that the consideration of tension zone effects can sharply reduce the stability factor of slopes, especially for steep slopes and large horizontal seismic loads; different from the static condition, the slope with pre-existing crack is not always the most vulnerable to collapse, the tension cut-off mechanism in steep slopes may predict the lowest stability factor. In addition, the calculation shows that an evidently increase in the slope displacement is induced by the increasing downward vertical loads, while a decrease occurs if the vertical loads are upward.