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Laboratory test programs on gravel are rare due to the maximum grain size of the material. In this paper an experimental program with triaxial tests under cyclic loading and oedometric tests on highly compacted gravel specimens, representative for bridge backfills materials, is summarized. It is used to calibrate a hypoplastic constitutive model, which includes an extension for intergranular strain to account for the cyclic loading behaviour. So far calibrated parameter sets of this soil model are scarce in literature, especially for coarse grained materials. The calibrated parameter set can be used in numerical studies, e. g. on the cyclic soil structure interaction of integral railway bridges.

The present study is devoted to the investigation of the dilatancy behaviour of a fine sand based on hollow cylinder tests. Medium and dense samples were tested at a constant average γ = 1, 2, 3 and 4%. Dilatancy curves along with shear wave velocity measurements to investigate the influence of the shear strain amplitude γampl in the shear modulus degradation curve are presented and discussed. The measured stress and strain paths were used to compare the performance of four advanced constitutive models especially in describing the dilatancy behaviour of sand. From the perspective of their constitutive equations, the differences between the simulations with various material models are examined. It may be concluded that all four models allow a proper prediction of torsional shear tests as long as a proper calibration of the material parameters is secured.

Translation abstract Investigations on the liquefaction resistance of an open‐cast lignite mine soil under loading by earthquake‐typical signalsFor the embankments of the planned opencast mining lakes in the Rhenish mining area, the proof of the stability under earthquake action must be provided. According to the guideline for the investigation of the stability of slopes in lignite opencast mines (RfS – Richtlinie für Standsicherheitsuntersuchungen [1]), the permanent slopes must be designed and constructed in such a way that a soil liquefaction is not to be expected. For the proof, in which actions and soil resistances are locally compared with each other, the irregular earthquake signal is converted into a regular signal with an equivalent number of cycles and constant amplitude. In this paper, this conversion is investigated for a typical earthquake signal of the Rhenish area, which was obtained from a dynamic finite element calculation. Triaxial tests with vertical cyclic loading and hollow cylinder triaxial tests with cyclic torsional loading are performed to investigate the liquefaction behaviour of an opencast mine soil under the influence of this earthquake signal. The results of these tests are compared with data from further tests with constant amplitude. It can be shown that the factor β for converting irregular to regular signals depends on the type of loading and the magnitude of the static shear or deviatoric stress. On the basis of the experiments, recommendations for the choice of β for the Rhenish mining area are given. [ABSTRACT FROM AUTHOR]

Compression behavior of sand‐silt mixtures The choice of an appropriate material model for mixed‐grained soils is crucial for the design of a challenging geotechnical structe. For the development of an accurate material model, the experimental investigation of the soil is indispensable. Hereby, the compression behavior of sand‐clay mixtures is investigated on the basis of oedometer tests of mixtures with different fines contents. It can be observed that with increasing fines content, the compressibility of the material increases significantly. Nevertheless, an exponential relationship between equivalent void ratio e* and vertical strain has been established independently of the fines content. On this course, the deformation model of Ohde (1939) was generalized to mixtures by considering e*. The simulations with hypoplasticity for granular soils and with the AVISA‐model for fine‐grained soils show a need for the coupling of the preconsolidation pressure as well as the normal consolidation line at a 1:1 ratio of sand to silt depending on the fines content. [ABSTRACT FROM AUTHOR]