Discussion: Road subgrades

DR R.H. JONES, University of Nottingham The suction index approach provides a useful framework for discussing pavement design and has also been used as a basis for establishing criteria for muck suitability. Although my main interest is in the ancillary uses, I should like to discuss the method in the context of pavement design.

Figure 1 on page 38 of the paper by Black and Lister appears to be an extension of fig.9 presented by Black in reference 1, which was basically for saturated clays. In reference 1 a correction was proposed for unsaturated materials, i.e. those having a lower pd. This correction could lower the predicted CBR by 20% at va = 5%. To what degree of saturation does fig.l on page 38 apply? Are corrections envisaged for other values?