The Laboratoire des Ponts et Chaussees (LCPC) is engaged on a national research project (CLOUTERRE) on the technique of soil nailing. As part of a programme of cooperation between the Ground Engineering Division of the Transport and Road Research Laboratory (TRRL) and the Soils Division of LCPC, TRRL is publishing edited translations of several papers on soil nailing. This report is an edited translation of the third of these papers (see IRRD 120103). It examines the assumptions made in four computer programs available in France for the design of soil nailing: CLOUAGE; TALREN; NIXESC; and PROSPER. These programs were tested for a hypothetical case of a fixed slope and three configurations of nailing. Some difficulty was found in the definition of factor of safety. If a limit analysis and a factor of safety for the soil only is used, results are very close for methods which only consider tension in the nails, and are fairly close for those which also consider bending. In the second part of the paper, a more extensive comparison is made between TALREN and PROSPER. These programs consider both tension and bending in the nails, and the latter program allows the relation between displacement and mobilisation of stresses to be examined. While similar results were obtained for ultimate failure, the PROSPER program demonstrated that factors of safety are very sensitive to the assumed relations for the mobilisation of stresses in different nails within the soil mass, the soil-nail interaction, and the different criteria for failure that can be assumed. It is suggested that there is a need for further calibration of design methods against observations on actual structures.

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