The influence of change in subgrade conditions on the performance of roads in Malta

Abstract

The purpose of structural design is to limit the stresses induced in the subgrade by traffic to a safe level at which subgrade deformation is insignificant, whilst at the same time ensuring that the road pavement layers themselves do not deteriorate to any serious extent within a specified period of time. By the nature of the materials used for construction, it is impossible to design a road pavement which does not deteriorate in some way with time and traffic, hence the aim of structural design is to limit the level of pavement distress, measured primarily in terms of riding quality, rut depth and cracking, to predetermined values. Generally these values are set so that a suitable remedial treatment at the end of the design period is a strengthening overlay of some kind, but this is not necessarily so and roads can, in principle, be designed to reach a terminal condition at which major rehabilitation or even complete reconstruction is necessary. However, assessing appropriate remedial treatments for roads which have deteriorated beyond a certain level is a difficult task. In most design methods it is assumed that adequate routine and periodic maintenance is carried out during the design period of the road and that at the end of the design period a relatively low level of deterioration has occurred.