Definition and experimental determination of a soil-water retention surface

This paper deals with the definition and determination methods of the soil-water retention surface (SWRS), which is the tool used to present the hydromechanical behaviour of soils to highlight both the effect of suction on the change in water and total volumes and the effect of deformation with respect to the water retention capability. An experimental method is introduced to determine the SWRS and applied to a clayey silty sand. The determination of this surface is based on the measurement of void ratio, suction, and water content along the main drying paths. These paths are established for five different initial states. The experimental results allow us to define the parametric equations of the main drying paths, expressing both water content and void ratio as functions of suction and initial void ratio. A model of the SWRS for clayey silty sand is established in the space (void ratio - suction - water content). This surface covers all possible states of the soil inside the investigated range for the three variables. Finally, the SWRS is used to study the relations between water content and suction at a constant void ratio and between void ratio and suction at a constant water content

Self-stresses and Crack Formation by Particle Swelling in Cohesive Granular Media

We present a molecular dynamics study of force patterns, tensile strength and crack formation in a cohesive granular model where the particles are subjected to swelling or shrinkage gradients. Non-uniform particle size change generates self-equilibrated forces that lead to crack initiation as soon as strongest tensile contacts begin to fail. We find that the coarse-grained stresses are correctly predicted by an elastic model that incorporates particle size change as metric evolution. The tensile strength is found to be well below the theoretical strength as a result of inhomogeneous force transmission in granular media. The cracks propagate either inward from the edge upon shrinkage and outward from the center upon swelling

Stress transmission in wet granular materials

We analyze stress transmission in wet granular media in the pendular state by means of three-dimensional molecular dynamics simulations. We show that the tensile action of capillary bonds induces a self-stressed particle network organized in two percolating "phases" of positive and negative particle pressures. Various statistical descriptors of the microstructure and bond force network are used to characterize this partition. Two basic properties emerge: 1) The highest particle pressure is located in the bulk of each phase; 2) The lowest pressure level occurs at the interface between the two phases, involving also the largest connectivity of the particles via tensile and compressive bonds. When a confining pressure is applied, the number of tensile bonds falls off and the negative phase breaks into aggregates and isolated sites

The VMC survey – XLI. Stellar proper motions within the Small Magellanic Cloud

We used data from the near-infrared Visible and Infrared Telescope for Astronomy (VISTA) survey of the Magellanic Cloud system (VMC) to measure proper motions (PMs) of stars within the Small Magellanic Cloud (SMC). The data analysed in this study comprise 26 VMC tiles, covering a total contiguous area on the sky of ∼40 deg2. Using multi-epoch observations in the Ks band over time baselines between 13 and 38 months, we calculated absolute PMs with respect to ∼130 000 background galaxies. We selected a sample of ∼2160 000 likely SMC member stars to model the centre-of-mass motion of the galaxy. The results found for three different choices of the SMC centre are in good agreement with recent space-based measurements. Using the systemic motion of the SMC, we constructed spatially resolved residual PM maps and analysed for the first time the internal kinematics of the intermediate-age/old and young stellar populations separately. We found outward motions that point either towards a stretching of the galaxy or stripping of its outer regions. Stellar motions towards the North might be related to the ‘Counter Bridge’ behind the SMC. The young populations show larger PMs in the region of the SMC Wing, towards the young Magellanic Bridge. In the older populations, we further detected a coordinated motion of stars away from the SMC in the direction of the Old Bridge as well as a stream towards the SMC

Stellar substructures in the periphery of the magellanic clouds with the VISTA hemisphere survey from the red clump and other tracers

We study the morphology of the stellar periphery of the Magellanic Clouds in search of substructure using near–infrared imaging data from the VISTA Hemisphere Survey (VHS). Based on the selection of different stellar populations using the (J − Ks, Ks) colour–magnitude diagram, we confirm the presence of substructures related to the interaction history of the Clouds and find new substructures on the eastern side of the LMC disc which may be owing to the influence of the Milky Way, and on the northern side of the SMC, which is probably associated to the ellipsoidal structure of the galaxy. We also study the luminosity function of red clump stars in the SMC and confirm the presence of a bi–modal distance distribution, in the form of a foreground population. We find that this bi–modality is still detectable in the eastern regions of the galaxy out to a 10○ distance from its centre. Additionally, a background structure is detected in the North between 7○ and 10○ from the centre which might belong to the Counter Bridge, and a foreground structure is detected in the South between 6○ and 8○ from the centre which might be linked to the Old Bridge

Effect of temperature on water retention phenomena in deformable soils: theoretical and experimental aspects

In this paper, a theoretical and experimental investigation of the effect of temperature on water retention phenomena in deformable soils is presented. A general law expressing the change in suction with water content, temperature and void ratio is proposed theoretically. This law accounts for the influence of density and temperature on water retention. It also provides a general framework which appears to be well-adapted to describe many particular cases. The effect of temperature is studied through a predictive relationship which is established in this framework. This relationship allows us to obtain the water retention curve at any temperature from that at a reference temperature, thus reducing strongly the number of tests required to characterize the thermo-hydraulic behaviour of a soil. The relevance of this relationship was experimentally verified from new tests as well as the results previously reported in the literature. The new tests were performed on two model media, namely, a terracotta ceramic and a clayey-silty sand. The tests taken from the literature concerned two different clays. Comparison between theoretical prediction and experimental data was particularly promising and shows the capability of the model to cover a wide range of soils