Taylor's slope stability chart for combined effects of horizontal and vertical seismic coefficients

Design standards and codes of practice on earth slope stability often recommend the pseudo-static method of analysis for determining the factor of safety of a slope subjected to seismic forces. In most pseudo-static methods of analysis, the horizontal seismic force is considered without due weightage to vertical seismic force. In the past, Taylor's stability chart for a homogeneous cohesive-frictional soil slope has been extended to consider the effect of horizontal seismic force only. In this paper, an attempt is made to develop an analytical formulation considering both horizontal and vertical seismic forces in order to estimate the factor of safety of the homogeneous, cohesive-frictional soil slopes with simple profiles using Taylor's stability chart. The analytical formulation is based on the friction circle method, which is one of the methods of static slope stability analysis. Several field cases have been analysed considering slope geometry, soil properties and seismic loading conditions so that Taylor's stability chart can be routinely used by practising engineers considering the effects of both horizontal and vertical seismic forces. An illustrative example is included in order to explain how practising engineers can use the graphical presentations developed in this paper as the design charts for stability analysis. This illustrative example has also been solved using Plaxis 2D, a commercially available finite-element software, as a comparison.