The effect of topsoil on pavement performance

Abstract

A laboratory study was undertaken and a field test section was constructed to study the rate of pavement deterioration which results when topsoil is used in construction of a subgrade. An extensive laboratory testing program showed that the Proctor density of topsoil was less than for parent material and results indicated that this difference may be approximated by a change in plastic limit. A resilience test was developed to compare the elastic properties of top­soil and parent material. A theoretical relationship between elastic properties and depth of cover over topsoil and thickness of the topsoil layer was developed and various combinations were calculated on a computer. The results were plotted on graphs which may be used in subgrade design. A topsoil test section was constructed to check the accuracy of the theoretical deflection increase. It was found that the predicted deflection increase compared closely to the actual measured deflection increase. The deflection increased as the depth of cover decreased and the thickness of the topsoil layer increased. The accuracy of the predicted deflection increase and the loss in riding qualities resulting from topsoil in the subgrade should be studied further in future test sections.