The Masada mountain is located on the western margins of the seismically active Dead Sea riit system. Therefore, dynamic key block stability is of primary concern in the densely fractured East and North rock slopes of the mountain. Recent seismogenic key block motions in the East face, detected by our in-situ monitoring system, are explained by the presently low factor of safety against sliding, and by a pronounced topographic site effect at Masada with peak spectral amplification of about 3.5. Two analysis methods are employed: l) Static and pseudo-static limit equilibrium analysis of removable key blocks in the East face where failure of large individual key blocks is of primary concern; 2) Static and true dynamic DDA modelling of a stochastically generated block mesh in the North face where the collapse of complete slope segments under dynamic loading is of concern. The deterministic analysis of removable key blocks in the East face reveals that when joint water pressures are considered application of a 2D solution proves unconservative. DDA modelling reveals the expected failure modes in the North face and the maximum depth of deformation as a result of dynamic loading.
Masada is the most important national monument in the state of Israel, as it draws over 800,000 domestic and international visitors a year. Mount Masada is situated in the Judean Desert on the western margins of the seismically active Dead Sea rift valley (Figure 1). The Roman King Herod the Great used the isolated mountain between 36 30 BC as an isolated resort and as a fortified shelter for times of political unrest. He has erected a magnificent palace on three natural terraces at the Northern face of the mountain and created a system of fortifications and civil structures, including storage facilities, watch towers, water cisterns, and even hot baths, across the mountaintop. The monument has attained its international fame however due to a later struggle which a small group of Jewish zealots conducted ?om its top against the Roman army, during a regional rebellion against Rome between 66 and 70 AD. When the Roman army finally broke into the mountaintop they discovered the bodies of 960 men, women and children who took their lives in their own hands. Thus Masada became a national symbol for the quest of?eedom and independence.
The elongated NNE striking mountain is in fact an uplifted, box shaped, horst, which is separated ?om the valley floor by steep slopes at least 250 meters high. The rock mass, which consists of bedded dolomites and limestones, is intensely ?actured by two closely spaced, orthogonal, sub-vertical, and very persistent joint sets striking roughly parallel and normal to the long axis of the mountain (Figure 2). The stability of two natural rock slopes, the East and North faces, is of concern and is discussed here. In the East face, a sub-vertical slope in which the cable car station is anchored, block theory is used in the analysis of large, marginally stable, key blocks which rest above the visitors path. In the North face a deterministic block theory approach can not be adopted because the face is comprised of closely spaced joints and bedding planes, the intersection of which forms a network of prismatic blocks having an average area (parallel to the face) of 3.22 m 2. In this slope two-dimensional DDA is employed for two extreme loading conditions: static, and true dynamic.
