The motorway system in England and Wales is of sufficient age to allow a useful study of the condition of its earthwork side slopes. This Report describes the most extensive slope survey ever to be undertaken of this motorway system. The survey, covering a total length of 570 km, concentrated on selected lengths of motorway which included the principal geologies encountered on the motorway system, in particular, areas where over-consolidated clays predominate. It discusses the basic factors that have contributed to shallow failures on the side slopes of embankments and cuttings, and attempts to quantify any long-term problems. The results show a high incidence of failure associated with the major influences of geology, age of earthworks and geometry of slope. The slope angles recommended in this Report can be used in the design of new earthwork side slopes and to identify slopes at risk of failure in existing earthworks. An estimate has been made as to the extent of failures in the future which suggests that three times as many slopes are likely to fail than have failed so far. (A)

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