The stability of drystone retaining walls on highways

Surveys of the stock of masonry-faced earth-retaining walls in five local a uthorities showed that there was about 93 km of such walls on the 1475 km o r so of trunk roads within the boundaries of these authorities. Their repla cement cost was approximately pound 1.16 million per km of wall, while expe nditure on maintenance and replacement of the whole 93 km of walls was a li ttle over pound 800 000 annually. Extrapolation of the data is difficult, b ut 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 900 0 +/- 2000 km. The current stock of these walls on highways in Great Britai n 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 co des preclude the use of many of these optimistic, but nevertheless real, fa ctors. Improved methods of assessment should help ensure that the current s tock on our highways is kept in good order so that this part of our nationa l heritage is preserved for many generations to come.