Engineers Australia

A method for the prediction of soaked CBR of remoulded samples from standard classification tests

Peter G McGough

Abstract

Many authors in the past have investigated the ability of standard classification tests to provide an estimate of soaked CBR for remoulded samples across a wide range of materials with most classifications limited to fine grained soils with soaked CBR’s < 20. A method of estimating the soaked CBR of a remoulded soil from a PSD test and an Atterberg Limits test has been developed and tested against field data. It is valid for coarse grained or fine grained soils, or mixtures of both, and is not limited by the CBR value. The method also accounts for modified compaction of the material after soaking as the relative compaction prior to soaking did not influence the correlation. The method is based on more than 400 soaked CBR tests in a wide variety of soils from around Western Australia, South Australian and Northern Territory. The method has been compared against the results of soaked CBR test from several locations around the world and found to be comparable. The method is based on the Fine Material Factor (FMF) of the soil which is the product of the raw Plasticity Index and the proportion of the soil passing the 0.425 µm sieve. This method confirms the long held anecdotal evidence that materials with a FMF < 450 are typically suitable for sub-base use and in some cases suitable as base course. A series of correlations have been developed linking FMF and Soaked CBR for a range of MMDD Ratios.