DETERMINATION OF OCR IN CLAYS BY PIEZOCONE TESTS USING CAVITY EXPANSI0N AND CRITICAL STATE C0NCEPTS

For piezocone penetration in clays, cavity expansion theory describes both the point resistance and induced excess pore water pressure in terms of the undrained shear strength (Cu) and rigidity index (Ir=G/Cu). Modified Cam Clay provides a simple effective stress representation of undrained behavior in terms of stress history. Therefore, the two theories may be combined to provide an approximate determination of the in-situ overconsolidation ratio (OCR = σp'/συo') in terms of the effective stress friction angle (φ') and normalized piezocone parameter (qT - um)/συo', in which qT=corrected cone resistance and um=measured pore water pressure. The approach distinguishes between piezocones which measure pore water pressures on the cone tip/face (ut) and those which measure just behind the tip (ubt). Specific examples are presented to show the general applicability of this simple effective stress model for estimating the in-situ stress history of clay deposits with 1<0CRs<60 and 20°

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