Environmental and mechanical aspects of an anchored mesh for stabilisation of a cliff at La Alhambra

Abstract

The wire meshes described herein are anchored flexible steel nets used for slope stabilisation. They enable post-tensioned loads to be transmitted to the ground through anchors. The objective of this work is to consider the design of these systems and their environmental impact. Extensive laboratory tests on normalised meshes were conducted in order to assess their parameters in simulated field conditions. The simple theoretical equations employed by the specialised enterprises for design are presented. The design is applied to San Pedro Cliff, a unique geological transgression. It is a dihedral, 65.5 m (215 ft) high, which has progressed to place itself at a distance of 23.8 m (78 ft) from the Alhambra palace that is a World Heritage site. The western part of the cliff is a fault-line scarp, modified by river erosion and latterly by successive slab falls. Stability analyses suggest that the factor of safety of this slope under 1,000-year return period earthquake loading may drop below 1.0 and the critical slip surface could penetrate the Alhambra walls. To raise the safety factor up to 1.0 and to counteract extensional stress in the cliff, a solution with minimal visual impact is proposed, consisting of a high-yield-stress wire mesh, post-tensioned by anchors and coloured to blend with the cliff. Two-dimensional finite element analyses have allowed testing the design methods indicated above. It is shown that the simple methods used up to now have many shortcomings.