Abstract: Design methods for reinforced soil retaining walls consist of three main elements: method of calculation, material parameters and safety factors. Each of these is considered in turn to examine where conservatism may exist, so that there is scope for reducing the cost of a structure. The method of calculation, especially for internal stability, may result in considerable conservatism if many assumptions are required to carry out the calculation. This can be minimised by using more realistic methods of calculation, which make optimum use of the reinforcement, but at the same time identify the effects of any weak points (for example low connection strength between reinforcement and facing). Material properties are required for the fill soils, the reinforcement and the interaction between the two. Soil tests are required to define the fill shear strength and unit weight. The drained soil shear strength is required, therefore it is most important that the correct soil test procedures are used, especially for finer soils (quick undrained tests are not suitable). The reinforcement strength must be determined as suitable for the full design life of the structure, taking into account that degradation continues throughout its service life, but this must be assessed using accelerated test methods. Any idea of switching to a definition of reinforcement strength based on short term strength would be most unwise, resulting in a structure of unknown long term performance and inadequate serviceability. As regards the factors used, these are defined partly to take into account uncertainties, partly to ensure a safe structure and partly to ensure adequate serviceability during the life of the structure. With regards to reducing conservatism in reinforced soil design methods, the main elements to be considered are the method of calculation, and ensuring that appropriate and adequate shear strength testing is carried out on the fill material. There is also scope for choosing suitable factors. If design methods are developed to achieve less conservatism compared to current methods, then it is important that serviceability checks are included to ensure that post-construction strain in the reinforcement is not excessive.

Key words: reinforced soil, calculation method, material properties, factor, conservatism