Keyblock Stability in Seismically Active Rock Slopes—Snake Path Cliff, Masada

Abstract

Keyblock stability in the “Snake Path” cliff of the Masada monument, situated on the western margin of the seismically active Dead Sea transform, is studied using field mapping, mechanical analysis, and monitoring of displacement, pressure, temperature, and relative humidity, over a period of 11 months. A linear nonreversible displacement trend is interpreted as the block response to regional microseismicity. A more pronounced cyclic displacement trend however is shown to be a response to climatic changes on the cliff face. This finding introduces a new, time-dependent, failure process in jointed rock slopes—the degradation of shear and/or cohesive strength of joints due climatic effects. Using two-dimensional (2-D) and three-dimensional (3-D) limit equilibrium analyses it is demonstrated that the 2-D solution overestimates the factor of safety against sliding by as much as 15% if water pressures in the boundary joints are considered. Application of a 2-D solution for a truly 3-D case where prismatic blocks are considered proves therefore to not be conservative.