Review of design methods for geosynthetic reinforced soil walls - an Australian perspective

The design of reinforced soil walls, in particularly segmental retaining walls have been documented comprehensively in Australia and around the world. International design standards have been developed, with segmental block manufacturers incorporating these different standards in their design software. In practice, most design methodologies are conservative and it has been documented through full-scale field studies that actual applied forces are lower than calculated theoretical forces in reinforced soil walls. Nevertheless, it is generally good practice to design conservatively, especially when soil parameters have not been tested and only based on soil descriptions and assumptions. Since different standards apply in different countries and for different government authorities within a country, inexperienced practicing engineers face a confusing task when designing reinforced soil walls for their clients. With increasing research and development occurring for designs of reinforced soil walls using geogrids, and better sharing of current knowledge and new design techniques on an international scale, it would be ideal to see design standards adopted around the world reflect the new developments, having a universal approach to designing reinforced soil walls using geogrids. But like other design codes such as those for steel and concrete structures, standards will vary from country to country, however, the basic design concept should be consistent no matter where you go around the world. The review of existing standards should also be carried out on a periodic basis to incorporate the latest proven theories and methodologies. The most important issue to engineers is safety or structural integrity, but designers also have a duty to provide their clients with the most cost-effective solution available on the market while meeting serviceability, architectural and construction requirements. Therefore, building a safe and economical structure should be the goal for every design engineer. This paper will review the current state of knowledge for designing segmental retaining walls using geogrids in Australia and detail how practitioners in Australia adopt a limit states or working stress approach to designing segmental retaining walls using geogrids. The focus will be on the reduction factors for geosynthetic geogrids and connection strength values for geogrids in segmental retaining walls using the Australian design standard for earth-retaining structures, AS4678-2002. Other international design standards will also be briefly investigated and compared on specific issues. A discussion on the direction of future design methodologies will be explored, with emphasis on the importance of geogrid connection strength values and the use of relevant partial or reduction factors for determining long-term connection strength capacities.