Profiling OCR in Stiff Clays by CPT and SPT

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Courtesy of ASTM International

Standard penetration tests (SPT) and cone penetration tests (CPT) have conventionally been used to index profiles of undrained shear strength su in clay deposits. Since su is related to stress history, an alternative use of penetration resistances is the profiling of in-situ overconsolidation ratio (OCR). An empirical methodology is developed based on compiled data bases from 50 sites investigated by SPTs and 40 sites tested by CPTs. The study indicates general trends occur between the in-situ OCR and penetration resistances normalized to effective overburden stress in clays. Site specific calibration with laboratory consolidation tests is required, however, for profiling. Electric CPTs are preferable over SPTs and mechanical CPTs for profiling stress history because they are more repeatable and less subject to operator influence.

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