A New Calculation Approach To Design Flexible Facing System For Soil Nailing

According to the experience of several researchers, under certain conditions the soil nailing facing system can be developed with nails in cooperation with steel mesh (i.e. flexible structural facing). The goal of this system is to improve the slope face stability and allow the vegetation to grow. A simple design approach was introduced a few years ago that analysed the behaviour of the mesh by comparing the maximum volume of debris that can move among the nails to the maximum volume that can be held by the mesh. Even if it took into account the real interaction between mesh and soil, such procedure was quite rudimental by solving the non-linearity of the load-displacement problem. Recently, a new design approach using forces generated by the soil pushing on the mesh was proposed considering the most unfavourable case between the two wedge analysis and the single wedge, one for slope failure mode (according to the standard BS 1006 – 2010). Concerning the mesh resistance, the new approach overcomes the non-linearity of the problem and allows a more realistic calculation approach. This has been feasible thanks to the interpretation of the load-displacement curves generated in accordance to the UNI 11437 (2012) Standard as well as to the introduction of the “scale effect” that modifies the nail spacing and mesh behaviour accordingly.

For sure the methodology is not perfect, but at least it allows appreciating the Ultimate Limit State and the Serviceability Limit State with a simple calculation. This paper analyses the main calculation steps and concepts of this new approach implemented in the new Bios 2 software which is used by Maccaferri for the design of flexible facing of cut and natural slopes.