THE STABILITY OF DRYSTONE RETAINING WALLS ON HIGHWAYS.

Surveys of the stock of masonry-faced earth-retaining walls in five local authorities showed that there was about 93 km of such walls on the 1475 km or so of trunk roads within the boundaries of these authorities. Their replacement cost was approximately £1.16 million per km of wall, while expenditure on maintenance and replacement of the whole 93 km of walls was a little over £800000 annually. Extrapolation of the data is difficult, but it would not seem unreasonable to suggest that there is a total of some 120-140 km of such walls on the trunk roads in England and Wales, and also that the total for all roads in Great Britain lies within the limits of 9000 ± 2000 km. The current stock of these walls on highways in Great Britain is therefore, by and large, performing satisfactorily and seems likely to do so for many more years. The explanation for the stability of such walls is complicated and a number of factors are involved. But current design codes preclude the use of many of these optimistic, but nevertheless real, factors. Improved methods of assessment should help ensure that the current stock on our highways is kept in good order so that this part of our national heritage is preserved for many generations to come.