Dzi

Tendency of overconsolidated clays towards critical state

The question must now be asked: Do undrained and drained stress paths for heavily overconsolidated clays reach the critical state line as do normally consolidated and lightly overconsolidated clays?

In an ideal situation the stress paths of heavily overconsolidated clays will reach the Hvorslev surface and then will continue to move up this surface to the critical state line. But ideal situations rarely occur and a more realistic picture is as follows.

Undrained stress paths

In undrained shear there is no change in specific volume and the stress paths of heavily overconsolidated clays after reaching the Hvorslev surface will continue upwards to the critical state line where failure will occur. Failure can always occur before the critical line has been reached if the irregularities in the soil are of significance.

Drained stress paths

With drained shear the stress paths of heavily overconsolidated clays reach the Hvorslev surface on the dry side of critical. At this stage the soil fails, i.e. it has achieved its maximum value of q. However if the test is allowed to continue the stress path will move up towards the critical state line. The specific volume will increase but, because of this, the value of will decrease as q also decreases so that the ratio of q/pg can increase to allow the stress path to reach the critical state line. That this situation will happen in an actual soil test is speculative but there is sufficient experimental evidence now available to say that there is a tendency for these stress paths to move towards the critical state line after failure.

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