A secured drapery system, consisting of rockfall netting and a systematic nailing scheme, is designed to stabilize surficial material on an exposed rock face. The design procedure can be very complicated because the geomechanical models are very complex or unrealistic, and obtaining accurate input data is rather problematic. This paper presents a simple design approach for secured a drapery system, which combines the field experience of geologists and engineers on one hand, and the results of full scale drapery field tests on the other. The proposed calculations assume that the rock face exists in a limit equilibrium condition. With this approach, knowledge of parameters like cohesive strength and friction angle that are difficult to obtain is not required. The necessary input data are geometric measurement of the rock face and the main performance features of the anchors and mesh. The safety factors proposed in the calculations are based on considerations concerning the slope morphology, the weathering of the rock mass, and the presence of additional loads such as snow or ice. In this way the designer can easily input data and deal with uncertainties related to the real slope situation. The calculation procedure allows for determining both the ultimate limit state (verification of breaking loads of the system components), and serviceability limit state (maximum permissible deformation of the facing). The design analysis has been implemented in the MacRo 1 software package from Officine Maccaferri. Nevertheless, even if the software allows a quick and simple calculation approach, onsite observations are always recommended to achieve a good design, with the ultimate goal of protecting property and the public.
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