Indexing the engineering properties of residual soil Available to Purchase

The geological study of the formation and structure of in situ residual soils is well advanced; the study of the engineering properties of these soils much less so. In particular, no methods exist whereby mechanical properties can be related to geological descriptions, or to simple index tests, as is done for sedimentary soils. The methods for sedimentary soils are inappropriate for residual soils, yet no alternatives have been developed.

Most residual soils are weakly bonded, and they may have widely varying void ratios. A laboratory study of how these two features influence engineering behaviour is being conducted, based mainly on the testing of an artificial material in which both can be varied under control. Initial results from this study show that engineering behaviour depends on the void ratio of the soil related to that which the soil can have in the un-bonded ‘de-structured’ state. This indicates that it is useful to index the in situ void ratio of residual soils in relation to void ratio in the de-structured state, in a manner similar to the indexing of sands by relative density or of sedimentary clays by liquidity index. Simple methods whereby this may be done are suggested and discussed.

• Abstract

• Introduction

• Characteristics of in situ residual soils arising from their genesis

• The models of conventional soil mechanics and their relevance to residual soil

• A framework describing the mechanical properties of residual soil

• Test results from artificial residual soil

• Application of the framework to natural residual soil

• A simple relationship between density and yield

• The use of conventional index tests

• Indexing using the oedometer test

• De-structuring of residual soil by remoulding

• Summary and conclusions

• References