ABSTRACT
San Pedro cliff is a natural slope that cuts the Al-Sabika hill where the medieval fortress of the Alhambra in Granada (Spain) stands. This unique geological phenomenon forms an inherent part of the classic postcard of this important World Heritage Site, it has a height of 65.5 m and has progressed in its deterioration to stand today about 23 m from the walls of the Alhambra. The formation of the San Pedro cliff has been a consequence of the floods of the Darro River and, perhaps, of the seepage and runoff from the Alhambra, as well as of erosion and tectonics. In this work, a stability study of the slope in 3D in its current state is carried out, at three different scales: i) Al-Sabika hill scale, in order to locate the most unstable slope in the study area, ii) San Pedro cliff scale, in order to determine the global stability conditions of the slope as well as the possible effect on the walls of the monument and iii) detailed scale of the surface of the cliff, in order to locate possible areas of detachment and quantify erosion phenomena. The 3D stability analyses are carried out using the Finite Element method and the Shear Strength Reduction technique implemented in the GeHoMadrid code. The strength parameters of the material involved, the Alhambra conglomerate, are determined from already published data and new laboratory tests. For the 3 scales, the 3D finite element meshes are defined from digital terrain models obtained with LIDAR flight, detailed topographic map and laser scanner respectively.
