Stiffness moduli in triaxial tests on a loess-sand mixture

Stiffness is one of the most important characteristics of geomaterials, and at the same time one of the most difficult to evaluate. It can be described by means of various stress-strain moduli, whose values strongly depend on the strain range and on the method of determination. The aim of the article is to evaluate and compare selected stiffness parameters (Young’s modulus E and shear modulus G ) of an anthropogenic soil on the basis of triaxial tests. The experiments were carried out on samples consisting of loess mixed with sand. Loess is a collapsible aeolian sediment with a high calcium carbonate content and so it is a very challenging material for geotechnical applications. The addition of sand improves its properties and increases its suitability for earthworks. The specimens were compacted with normal Proctor energy at the optimal water content, which ensured repeatability of the results. Standard triaxial tests (drained and undrained) were carried out at the effective confining stresses in the range of 50 – 350 kPa. The specimens’ deformation was measured by means of external and local displacement transducers. Additionally, bender elements were used to assess the initial soil stiffness. The applied research methods allowed determination of the deformation characteristics in the range from very small to large strains. The stiffness moduli were assessed using different definitions and methods. It was confirmed that the stiffness of loess is improved by its proper compaction and addition of sand, when compared to the results available in literature for natural loesses.