Shear strength and yield surface of a partially saturated sandy silt under generalized stress states

This paper studies the hydromechanical behavior of a slightly compacted mixture of sand and clayey silt (30%/70%) under a generalized stress state. The experimental study focused on analyzing the yielding response and shear strength behavior at different stress states (characterized by the intermediate principal stress parameter b, or Lode angle) and at different initial total suctions (as-compacted state). For the investigation, a hollow cylinder apparatus was used. The shear strength results allowed defining the variation of the critical state line with the Lode angle and the suction. Different models were proposed for isotropic and anisotropic yield surfaces, and their shape and rotation were calibrated with experimental results. The modeled yield surfaces fitted reasonably well the experimental results, considering their inclination and dependence on the suction, mean and deviatoric stresses and Lode angle. In addition, some relationships between the stresses and the model parameters were proposed to normalize the yield surface equation.

The use of the hollow cylinder apparatus to study stress paths relevant to railway track foundations

This paper presents and discusses results from a series of hollow cylinder tests, carried out to investigate the effects of principal stress rotation on the resilient response of soils in stress paths relevant to railway track foundations. Four sand-clay mixes, typical of the gradation of an in situ railway track foundation, were investigated. The aim of the research was to investigate the magnitudes of shear stress cycles for which the associated cyclic rotations of the principal stress direction may have a significant effect on the long-term stability of a railway track foundations.

Testing of Undrained Shear Strength in a Hollow Cylinder Apparatus

The paper presents the results of tests performed in a Torsional Shear Hollow Cylinder Apparatus on undisturbed cohesive soils. The tests were performed on lightly overconsolidated clay (Cl) and sandy silty clay (sasiCl). The main objective of the tests was to determine the undrained shear strength at different angles of rotation of the principal stress directions. The results of laboratory tests allow assessing the influence of rotation of the principal stress directions on the value of undrained shear strength that should be used during designing structure foundations

Influence of the rotation of principal stress directions on undrained shear strength

Influence of the rotation of principal stress directions on undrained shear strength. The paper presents the results of research on natural cohesive soil carried out in the Hollow Cylinder Apparatus (HCA). The main goal of this study was to determine the values of undrained shear strength at different angle of the rotation of principal stress directions. The research were carried out with anisotropic consolidation and shearing in undrained conditions (CAU) on cohesive soil with overconsolidation ratio (OCR) equals 4 and plasticity index (Ip) about 77%. The results of laboratory tests allow to assess the influence of the rotation of principal stress directions on undrained shear strength

Experimental Research on Dynamic Poisson’s Ratio of Silty Clay

Cyclic triaxial and cyclic torsional shear tests were performed on undisturbed marine silty clay by the hollow cylinder apparatus, and the Young’s modulus and shear modulus were obtained respectively. Furthermore, the influence of effective confining pressure and stress ratio on dynamic Poisson’s ratio was investigated on this basis. It was found that the dynamic Poisson’s ratio increases with generalized shear strain, but decreases with increasing effective confining pressure and stress ratio. The effect of effective confining pressure and stress ratio on dynamic Poisson’s ratio was weakened as the generalized shear strain was increasing. The dynamic Poisson’s ratio was about 0.48 when the Poisson’s ratio was increased to 1.8E-2 or so, and the test was terminated. There was no shear dilatation during all tests because the Poisson’s ratios were smaller than 0.5. It indicates that the marine silty clay tested in this paper has a good stability under cyclic loads.