Soil liquefaction caused by earthquakes is a devastating occurrence that can compromise the foundations of buildings and other structures, leading to considerable economic losses. Among the new remedies against liquefaction, Induced Partial Saturation (IPS) is regarded as one of the most promising technologies. In order to improve liquefaction resistance and the fluid phase's compressibility, gas or air bubbles are introduced into the pore water of sandy soils. This article deals with the general laboratory evaluation of a sand under partially saturated conditions and under cyclic loading to assess if this technology is applicable for a ground improvement of the examined soil. The use of the Axis Translation Technique for sample desaturation and diffusion-stable butyl membranes significantly influences the laboratory results. Additionally, it is found that the trapped air bubbles of the partially saturated samples act like a damping mechanism, which are reflected in the stress paths of the deviator stress q over the mean pressure p with an inclination of 1 : 3. Zum Verfl & uuml;ssigungsverhalten von teilges & auml;ttigtem SandDie durch Erdbeben verursachte Bodenverfl & uuml;ssigung ist ein verheerendes Ereignis, das die Fundamente von Geb & auml;uden und anderen Bauwerken gef & auml;hrden und zu erheblichen wirtschaftlichen Verlusten f & uuml;hren kann. Die induzierte partielle S & auml;ttigung (Induced Partial Saturation, IPS) gilt als eine der vielversprechendsten Technologien unter den neuartigen Baugrundverbesserungen gegen Verfl & uuml;ssigung. Um den Verfl & uuml;ssigungswiderstand und die Kompressibilit & auml;t der fl & uuml;ssigen Phase zu verbessern, werden dabei Gas- oder Luftblasen in das Porenwasser sandiger B & ouml;den eingebracht. Dieser Beitrag besch & auml;ftigt sich mit der generellen labortechnischen Evaluierung eines Sandes unter teilges & auml;ttigten Verh & auml;ltnissen und unter zyklischer Beanspruchung zur Beurteilung, inwiefern sich diese Baugrundverbesserung f & uuml;r den untersuchten Boden eignet. Die Verwendung der Axis Translation Technique zur Probenentw & auml;sserung und die Verwendung von diffusionsstabilen Butylmembranen haben einen erheblichen Einfluss auf die Laborergebnisse. Au ss erdem ist festzustellen, dass die eingeschlossenen Luftblasen der teilges & auml;ttigten Proben wie eine D & auml;mpfung wirken und sich in den Spannungspfaden der Deviatorspannung q & uuml;ber dem mittleren Druck p mit einer Neigung 1 : 3 widerspiegeln.

This paper addresses the cyclic behaviour and stiffness degradation of subgrade soils subjected to stress-controlled cyclic loading, with particular emphasis on soils that are prone to mud pumping or subgrade instability. With continuous passage of trains over weak, saturated, low-plastic subgrade foundations, the finer fraction of the soils tends to fluidise (i.e., behave like a fluid) and migrate upwards, thereby, fouling the ballast and hindering the long-term performance of the rail track infrastructure. This leads to significant costs associated with annual track maintenance. Through a series of undrained cyclic triaxial testing varying the cyclic stress ratio (CSR, representing the axle loads) and loading frequency (simulating train speeds), the authors noted a significant upward migration of finer fraction coupled with internal moisture redistribution within the failed specimens. Further analysis revealed the instability of specimens was caused by early softening behaviour, and it is accompanied by a sharp reduction in the specimen stiffness. To tackle this, the stiffness was evaluated in terms of axial dynamic modulus and strain energy per cycle was evaluated to better understand the fluidisation behaviour. A novel quasi-linear relationship between threshold residual strain and number of cycles is proposed to serve as a practical guide.

Accurate simulation of laboratory undrained and cyclic triaxial tests on granular materials using the Discrete Element Method (DEM) is a crucial concern. The evolution of shear bands and non-uniform stress distribution, affected by the membrane boundary condition, can significantly impact the mechanical behavior of samples. In this work, the flexible membrane is simulated by using the Finite Element Method coupled with DEM. In addition, we introduce a hydro-mechanical coupling scheme with a compressible fluid to reproduce the different undrained laboratory tests by using the membrane boundary. The evolution of pore pressure is computed incrementally based on the variation of volumetric strain inside the sample. The results of the membrane boundary condition are compared with more classical DEM simulations such as rigid wall and periodic boundaries. The comparison at different scales reveals many differences, such as the initial anisotropic value for a given preparation procedure, fabric evolution, volumetric strain and the formation of shear bands. Notably, the flexible boundary exhibits more benefits and better aligns with experimental data. As for the undrained condition, the results of the membrane condition are compared with experimental data of Toyoura sand and rigid wall boundary with constant volume. Finally, stress heterogeneity during undrained monotonic and cyclic conditions using the membrane boundary is highlighted.