Drainage behind retaining walls was reviewed as the first stage of a research project carried out at TRL. The review is based mainly on literature published since 1992 when the subject was last reviewed for the Department of Transport. The drainage of both granular filters and fill is considered, but that of geocomposite filters is only touched upon because these were reviewed in 1994. The drainage of highway retaining walls in the UK seems to be generally satisfactory. However, the research project has afforded an opportunity to evaluate the advantages and disadvantages of producing performance specifications for drainage. Among other detailed conclusions are that piezometric studies of the fill behind retaining walls would be worth making, that research into the cause of segregation in granular fill should be carried out with the aim of preventing it from occurring in practice, and that research into the problem of compacting fine sand fill may be needed. Attention is drawn to the susceptibility of certain fill materials to rain. (A)

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