Compaction And Compactability Assessment Of Difficult Soils – An Alternative Approach

Typical Australian industry processes for verifying compliance of earthworks compaction can result in production delays and cost impacts when difficult soils are encountered. Difficult soils can comprise high plasticity clays and halloysitic clays. Insufficient curing of high plasticity clay samples during rapid compaction testing can result in unrepresentative measurement of maximum dry density and optimum moisture content. This can cause apparent nonconformances, trigger the requirements for proof rolling and incur delays to construction. Verification of lot conformity is often delayed until the following working day due to the period of time required for measurement of moisture contents. Halloysitic clays present a problem because their structure irreversibly changes when they are oven dried. Oven dried soil tested in the laboratory does not represent field conditions because the soils are physically changed. This can cause apparent non-conformances, unnecessary rework and consequential delays. An alternative approach to Australian industry accepted compaction testing has been developed by the UK based Transport Research Laboratory (TRL). The Moisture Condition Value (MCV) test is used to assess whether a soil is suitable for use prior to compaction. End product verification is achieved through on-going calibration to standard Proctor density tests and field certification using the nuclear densometer. The MCV apparatus and theory are introduced and an example of how the process is implanted from site investigation to construction verification is presented.