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A brief review of the standard dimensions, insertion procedures, and rates of rotation of the field vane is followed by consideration of those factors that influence the undrained shear strength measured by the field vane. These factors include the disturbance effects of vane insertion, the consequences of a “rest” period before shear, strain-rate effects, the rotation rate necessary to ensure undrained conditions during shear, and the method of calculation of cu. Following a discussion of the relative magnitude of cu, measured by the field vane, it is concluded that there is a consistent relationship with other measures of cu, depending on the plasticity index, provided the other strength measurements are made on specimens reconsolidated to the in-situ stresses. After consideration of a number of case records reported in the literature, it is suggested that for “standard” clays the approximate expression, cuσv = S1 (OCR)0.95, may be useful as a check on the measured field vane strength, or as an estimate of OCR. In this equation the strength ratio S1 = (cu/σv) is that given by Bjerrum for “Young” clays, for which OCR ≅ 1.0.
field vane shear tests, in-situ undrained shear strength, soil mechanics, state-of-the-art review, strain-rate effects, undrained strength relationships, plasticity index relationships
Reader in soil mechanics, Imperial College, London,