I got lucky and found the following:
It's on page 9 of:
http://www.ilo.org/public/english/employment/recon/eiip/asist/publ/techbrf/techbrf9.pdf
I reckon there might be things on earth shoulders as well, but I haven't read it thoroughly yet.
BigH
I think that the " plasticity modulus" might derive from Phil Paige-Green's (and especially Frank Netterberg and also Sampson) work on unsealed (unpaved or gravel) roads. The TRL people also picked up on it from joint research in Botswana. Performance-related specifications have now been...
These sorts of soils are common in South Africa. The South African design standard (TRH 14) provides subgrade to a maximum PI = 10, EXCEPT for materials with a large coarse fraction for which a higher PI of the soil fines may be acceptable.
As a guide, the acceptable PI can be calculated from...
