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Influence of the stress state on the dynamic response of unsaturated sand with fines

Abstract

The behaviour of soils under dynamic loading, caused e.g. by earthquakes, vibration of machine foundations, or traffic, can be described by the dynamic soil properties, i.e. the maximum shear modulus at small strains and the decrease of the shear modulus and the increase of the damping ratio with increasing strain level. Above the groundwater table the soil is commonly in an unsaturated state, that means the pore space is only partly filled with water. Effects of capillarity then influence the dynamic soil properties. This influence of partial saturation has not been sufficiently investigated yet. Usually the dynamic soil properties for dry or water-saturated soils are used in the analyses. Therefore, the aim of this research project is a thorough experimental investigation of the influence of partial saturation on the dynamic properties of sand with fines. The experiments are performed in the resonant column (RC) device on mixtures composed of 70 % (by weight) Hostun-Sand and 30 % Kaolin. The samples are prepared outside the RC device by means of Proctor compaction at the optimum water content. Afterwards the samples are dried to different target water contents and corresponding suction values, either from the optimum water content or after a saturation to a degree of saturation of almost 100 %. Other samples are dried and afterwards re-wetted, in order to study the influence of a drying - re-wetting cycle. After the mounting of the samples in the RC device the target suction is applied by means of the Axis Translation Technique (ATT). Having reached an equilibrium state, shear modulus and damping are measured as functions of shear strain. Based on the results empirical equations for the dynamic soil properties will be extended by the influence of partial saturation. Finally, the influence of the unsaturated state on the ground response during a seismic event will be investigated in numerical analyses of a soil column.