Identification of Scales of Fluctuation in the Condition of Rotated Anisotropy of the Soil Based on Limited CPTU Soundings

In the reliability analysis of geotechnical structures, stationary anisotropic random fields are increasingly used to describe soil parameters. It is usually assumed that the principal anisotropy directions in such fields are vertical and horizontal. While rotated anisotropy is also possible ), existing methods rarely focus on determining the rotation angle of the principal anisotropy directions. This paper proposes a method for identifying that angle, which is an extension of the method proposed for identifying the horizontal scale of fluctuation. It enables the simultaneous identification of the rotation angle of the anisotropy and the principal values of the fluctuation scale of the stationary random field, based on the results of a limited number of CPTu soundings. As shown, the proposed method is particularly effective and precise in identifying the value of the rotation angle; this value is very accurately identified for both artificial (generated) and real (measured) CPTu values. For the artificial CPTu where the exact values used for generation are known the difference between the original and recognized value was not larger than 0.2°.For real data the correctness of results is confirmed by good convergence and significant improvement in convergence of scales of fluctuation. The rotation angle value is important since in many cases, it can significantly influence the probabilistic analysis results for the given problem. Moreover, the assumption of wrongrotation angle can lead to identifying wrong values of fluctuation scales. In this view, the common assumption of the principal directions being vertical and horizontal can lead to an incorrect assessment of the failure probability.

Keywords: Rotated anisotropy, Random field identification, Bayesian method.