Model uncertainty of cylindrical shear method for calculating the uplift capacity of helical anchors in clay

• The cylindrical shear method is improved using a regression equation calibrated from finite element limit analysis.
• The model factor for modified cylindrical shear method is modelled as a lognormal variable of mean = 0.92 and cov = 0.16.
• The proposed regression equation is verified with results from large-deformation finite element analysis.

In this paper, the uplift behavior of helical anchors in clay is investigated using the finite element limit analysis. According to the observations on the failure mechanism, the factors that influence the model uncertainty of the cylindrical shear method are examined. The finite element limit analysis is used to remove the correlation between the model factor M for the cylindrical shear method, which is defined as a ratio between the measured capacities Qu,m and the capacities Qu,c calculated from the cylindrical shear method, with the input parameters. A regression equation f is then proposed. Using the load tests database including 78 laboratory model-scale tests and 25 field full-scale tests, the model factor M’ = Qu,m/[fQu,c] is represented as a lognormal random variable with mean = 0.92 and coefficient of variation (cov) = 0.16. Finally, the accuracy of the modified cylindrical shear method (i.e., fQu,c) is examined using 19 large-deformation analyses.