A General Method for Quantifying the Shear Strength Anisotropy of Soil

Abstract

Although extensive investigations have been performed on soil anisotropy, little information is available regarding its quantification. The quantification of anisotropy reflects the extent to which the inherent anisotropy of soil controls its mechanical behavior and so it is crucial for connecting comprehensive experimental research with soil constitutive models and engineering practices. The present study evaluates the level of shear strength anisotropy in various types of soil. A database is compiled of the variations of shear strength with the direction of major principal stress (α) as established via hollow-cylinder torsional shear tests, covering more than 20 types of soil. This study reviews critically the existing methods for strength anisotropy, finding none of them quantifies anisotropy satisfactorily. The present study proposes using the bracketed area by the S(α)/S(0)–α curve and the line S(α)/S(0) = 1 to measure the level of strength anisotropy, where S(α) is the soil strength as a function of α. The proposed method in this study can measure the strength anisotropy levels of sands, silts, clays, residual soil, calcareous sand, mudstone, and glacial till, among others. Additionally, the anisotropy degree measured using the proposed method appears to be consistent with the results of microstructural anisotropy evaluations. This study enhances the understanding of soil anisotropy by providing a comprehensive database of soil strength anisotropy and proposing a general method for its quantification.