Overconsolidation Ratio of Clays from Penetration Pore Pressures

Abstract

A method is proposed for evaluating the overconsolidation ratio in clays based on the distribution of dynamic pore pressure around a penetrating cone. For this purpose the pore-pressure measurements at or on the tip and at the base of the tip are normalized with respect to the hydrostatic pore pressure. The difference between the two normalized values is shown to correlate well with changes in the overconsolidation ratio. The conclusions are applicable to depths of about 30 m with water table near ground surface. Results obtained from various North and South American clays are evaluated resulting in a linear relationship between a defined pore pressure parameter and OCR. It would appear that this relationship can be applied to clays in general. However, the relationship may be dependent on the sensitivity of the soil. The proposed relationship can be considered appliable for overconsolidation ratios up to 10–15. At higher OCRs the effect of fissuring appears to modify the drainage conditions of the test, possibly producing a lower pore pressure parameter than expected, resulting in poor agreement with the proposed relationship.