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Estimating undrained shear strength of clay from cone penetration tests Greig, James William


This paper discusses several proposed methods for estimating undrained shear strength from cone penetration tests. This correlation has been studied in the past, however, most have focussed only on the cone bearing. In addition to discussing these traditional methods, this paper evaluates recently proposed methods of estimating Su from CPT pore pressure data. The results of field vane and cone penetration tests from five lower mainland sites are presented in relation to the different proposed correlation techniques. The results show that there is no unique cone factor for estimating Su from CPT for all clays, however, a reasonable estimate of Su can be made by comparing the predictions from several of the proposed methods. With local correlations these techniques can be quite reliable. The results also show that the estimation of Su from CPT is influenced by various factors relating to: the choice of a reference Su, cone design, CPT test procedures and the soil characteristics. In particular, the estimation of Su from CPT is strongly influenced by such soil parameters as stress history, sensitivity and stiffness. Increases in OCR and sensitivity were reflected by increases in the traditional cone factors Nc and Nk. The use of pore pressure data appears to be a promising means of estimating. Su from CPT. Expressions have been developed that predict excess pore pressures based on cavity expansion theory and attempt to include the effects of sensitivity, stress history and stiffness. In addition, comparisons between friction sleeve measurements and Su and a method for estimating sensitivity from friction ratios are presented. Lastly, recommended procedures for estimating Su from CPT are given.

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