The Hydraulic and Geo-Environmental Behavior of the Sub-Pavement Environment

The paper considers the environmental properties and possible impacts of a wide range of candidate non-geologic, i.e. “alternative”, materials for pavement construction. Previous studies had shown that, depending on the material, they were likely to perform adequately from a mechanical point-of-view when used as-is, lightly stabilized and selfcemented. Thus the materials were subjected, in these conditions, to leaching testing (using two laboratory-based methods) and to outdoor lysimeter tests over a 1 year period at a test site. Outline results of observed performance are reported and the results compared and interpreted. The data was then used in a geo-environmental groundwater flow study, together with information on pavement run-off and percolation, in order to predict the mobility of both the run-off and the leached species in the sub-pavement environment. For the studies made, it is shown: that concerns about large scale pollution from leachate are unfounded; that, where there is excessive leaching from a contaminated base or sub-base layer ‘source’, the immediate pavement environment rapidly attenuates contaminant levels to acceptable values, and that, for most species, run-off should be of much greater concern than leaching from the pavement construction materials.