Explore the vast range of titles available.

Internal erosion, characterized by the migration of soil particles within hydraulic earth structures due to seepage, is a significant global concern for risk management and maintenance. Among various mechanisms contributing to internal erosion, suffusion emerges as a prominent process. It involves the simultaneous detachment, transport, and potential self-filtration of fine particles through the pore network, leading potentially to a change in permeability and shear strength. Thus, investigating the link between permeability and microstructure is a key to achieve a better understanding of suffusion and to predict its consequences on the soil’s permeability. The proposed methodology involves generating discrete element method-based samples, characterizing their constriction size distribution, and computing permeability using fast Fourier transform. While the Kozeny-Carman model was initially developed for stable microstructures, it may not apply to suffusion due to microstructural evolution. Thus, a modified approach is introduced, incorporating a characteristic constriction diameter computed from the constriction size distribution. This modified model is being compared against the original Kozeny-Carman one on fourteen gap-graded specimens. Encouraging results are herein being obtained so that the modified approach will be later used on flow modified specimens.

Intestinal organoids capture essential features of the intestinal epithelium such as crypt folding, cellular compartmentalization and collective movements. Each of these processes and their coordination require patterned forces that are at present unknown. Here we map three-dimensional cellular forces in mouse intestinal organoids grown on soft hydrogels. We show that these organoids exhibit a non-monotonic stress distribution that defines mechanical and functional compartments. The stem cell compartment pushes the extracellular matrix and folds through apical constriction, whereas the transit amplifying zone pulls the extracellular matrix and elongates through basal constriction. The size of the stem cell compartment depends on the extracellular-matrix stiffness and endogenous cellular forces. Computational modelling reveals that crypt shape and force distribution rely on cell surface tensions following cortical actomyosin density. Finally, cells are pulled out of the crypt along a gradient of increasing tension. Our study unveils how patterned forces enable compartmentalization, folding and collective migration in the intestinal epithelium. Pérez-González et al. explore the mechanical properties of intestinal organoids, and report the existence of distinct mechanical domains and that cells are pulled out of the central crypt along a gradient of increasing tension.

Pore geometrical models are widely used to study transport in porous media, permeability, internal stability, and filter compatibility. Transport of fine grains through the voids between the skeleton of the coarser fraction is mainly controlled by the pore throats or constriction sizes. This study compares various constriction size distribution criteria and capillary tube models, which elucidate the limitations of the Kovacs capillary tube model, and this model is explained and developed. The new proposed threshold boundaries ( d 0 = 2 . 3 d 85 f and d 0 = 2 . 8 d 85 f ) categorized soil samples as internally stable, transient zone, or unstable. The model also incorporates the precise shape coefficient of particles. This improved model was validated based on a database from the literature, as well as performing 10 new experimental tests on two ideal gradation curves that identified the threshold boundary of Kenney and Lau criteria. This proposed model, which is dependent on grading, porosity, and grain shape, provides accurate predictions using a precise shape factor. This finding may enhance our knowledge about transport in porous media and contribute toward internal stability assessing for practical applications.

Forcing dense suspensions of non-cohesive particles through constrictions might result in a continuous flow, an intermittent one, or indefinite interruption of flow, i.e. a clog. While one of the most important (and obvious) controlling parameters in such a system is the neck-to-particle size ratio, the role of the liquid driving method is not so straightforward. On the one hand, widespread volume-controlled systems such as syringe pumps result in pressure and local liquid velocity increases upon eventual clogs. On the other hand, pressure-controlled systems result in a decrease of the flow through the constriction when a clog is formed. The root of the question therefore lies in the role of interparticle liquid flow and hydrodynamic forces on both the formation and stability of an arch blocking the particle transport through a constriction. In this work, we study experimentally a suspension of non-cohesive particles flowing through a constricted channel (with neck-to-particle size ratio $3.03\\leq D/d\\leq 5.26$) in an intermittent fashion, in which they are most sensitive to parametric changes. Due to the stochastic nature of the intermittency, we make use of statistical distributions of arrest times and of discharged particles, and surprisingly, we find that the transport of non-cohesive suspensions through constrictions actually follows a ‘slower is faster’ principle under pressure-controlled driving: low imposed pressures yield intermittent non-persistent clogs, while high imposed pressures result in longer-lasting clogs, eventually becoming everlasting, and thus reducing the net particle transport rate.

Filters managed in zoned dams are designed according to criteria based on the grain size distribution of both filter and eroded soil. However, the constriction size distribution of the filter is the key parameter which governs the filter retention process of flowing eroded particles. To assess the filter efficiency regarding eroded particles, several filters and base soils are tested in a vertical cell with a configuration coupling erosion and filtration processes. For setting the boundary condition of eroded particles at the filter inlet, hole erosion test (HET) was performed on the base soil. The investigation of the evolution of filter behavior shows that the void ratio and the grain shape are of a great influence on filter efficiency. A new approach of filter clogging was proposed by evaluating a damage index which is affected by various parameters such as the ratio D15/d85 and the size of eroded particles. An approach linking the geometrical parameters (damage index) to the hydraulic conductivity leads to an estimation of the filter performance which provides a more quantifiable and realistic criterion. The results indicate that even existing criteria were not met; the tested filters remain efficient as regards to experimental data. An analytical approach based on constrictions size distribution was used and pore reduction was matched with experimental results.

Exhaust emissions from shipping are a major contributor to particle concentrations in coastal and marine areas. Previously, the marine fuel sulfur content (FSC) was restricted globally to 4.5 m/m%, but the limit was changed to 3.5 m/m% at the beginning of 2012 and further down to 0.5 m/m% in January 2020. In sulfur emission control areas (SECA), the limits are stricter: the FSC restriction was originally 1.50 m/m%, but it decreased to 1.00 m/m% in July 2010 and again to 0.10 m/m% in January 2015. In this work, the effects of the FSC restrictions on particle number concentrations (PNCs) and particle number size distributions (NSDs) are studied in the Baltic Sea SECA. Measurements were made on a small island (Utö, Finland; 59∘46′50 N, 21∘22′23 E) between 2007 and 2016. Ship plumes were extracted from the particle number size distribution data, and the effects of the FSC restrictions on the observed plumes as well as on the ambient concentrations were investigated. Altogether, 42 322 analyzable plumes were identified during the 10-year measurement period. The results showed that both changes in the FSC restrictions reduced the PNCs of the plumes. The latter restriction (to 0.10 m/m% in January 2015) also decreased the ambient particle number concentrations, as a significant portion of particles in the area originated from ship plumes that were diluted beyond the plume detection limits. The overall change in the PNCs of the plumes and ambient air was 27 and 32 %, respectively, for the total FSC change from 1.50 m/m% to 0.10 m/m%. The decrease in the plume particle number concentration was caused mostly by a decrease in the concentration of particle sizes of between approximately 33 and 144 nm. The latter restriction also reduced the geometric mean diameter of the particles, which was probably caused by the fuel type change from residual oil to distillates during the latter restriction. The PNC was larger for the plumes measured at daytime than for those measured at nighttime, likely because of the photochemical aging of particles due to UV light. The difference decreased with decreasing FSC, indicating that a lower FSC also has an impact on the atmospheric processing of ship plumes.

Internal instability establishes when fine particles of bimodal soil migrate with seepage flow into voids created by coarse fabric, altering the original gradation. The tendency for soils to undergo internal instability centres on their compaction level and particle size distribution. This study employs the discrete element method to evaluate the potential for internal instability at the particle scale. Numerical simulations enable a thorough analysis of particle contacts in soils, encompassing both internally unstable and stable conditions. The study examines particle connectivity at different relative densities and uses particle connectivity and stress reduction factor to draw clear distinctions between soils that are internally unstable and those that are stable. Grain-scale data allows for a precise measurement of the stress reduction within the finer portion of the materials. The stress distribution is observed to be influenced by the particle-size distribution, percentage of finer fraction, and relative density. The predictions of the current numerical model align with the constriction-based criterion, enhancing practitioners’ confidence in a timely preliminary evaluation of soil internal instability potential.

Filter design aims to trap finer particles within the pore space of coarser particles by meeting macro-scale geometric criteria (particle size distributions or constriction size). These criteria fail to account for the significant effect of filter particle positions on filter performance. The current contribution evaluates the variability in filter structure using pore networks generated from discrete element method filtration simulation data. The pore network edges are directed and weighted using the constriction gravity-bias pore area. A study of the network maximum-flow and minimum-cost asserted the ability of graph characteristics to identify the statistically different filter samples. This demonstrates the potential for graph characteristics to link particle-scale behaviour to macro-scale observations.

The ability of granular materials to retain fine particles transported within their void space by seepage flow depends strongly on the geometric characteristics of their pore network (pore sizes and constriction sizes). Hence, characterizing the pore network of a granular assembly obtained by means of a micro-tomography scanning or a numerical discrete simulation is of great importance in assessment of its filtration efficiency. Here, we determine characteristics of the pore network of virtual samples composed of spherical particles simulated by using the DEM. A new criterion is proposed to merge neighboring tetrahedra issued from the weighted Delaunay triangulation. To do so, we extend the concept of inscribed void sphere, initially defined for each tetrahedron, to each polyhedral sub-domain constituted of merged tetrahedra. This inscribed void sphere fits the best the void space within the sub-domain. Flat tetrahedra are first eliminated by a primary merging procedure taking into account two basic geometric conditions required for each pore. Adjacent sub-domains are then merged depending on the level of overlap between their inscribed void spheres. The pore size distributions and constriction size distributions (CSD) of granular samples with different grain size distributions obtained with the new merging criterion are compared to those given by two other criteria often used in the literature. The new criterion allows us to reduce greatly the inherent subjectivity in characterizing the granular pore network and to remediate the drawbacks of the two considered criteria in the literature. Moreover, CSDs given by these different criteria tend to converge for gap-graded and widely graded materials. The CSDs obtained with the new merging criterion are used to estimate the controlling constriction sizes Dc∗ of the considered samples, and the estimated values of Dc∗ are compared to Kenney and Lau’s empirical rule.

Granular and geotextile filters are commonly provided in several hydrological infrastructures to limit soil erosion and allow unimpeded water seepage. The success of a filter depends on forming a bridging structure, which is governed by the grain size distribution of soil and the constriction size distribution of filter. Currently, the retention requirement is satisfied considering representative grain and opening size, whereas the hydraulic conductivity requirement is satisfied considering empirical factors for avoiding excessive clogging. In this paper, the design criteria for granular and geotextile filters are reviewed, and improved design criteria are presented. A probabilistic retention criterion is developed, considering the grain size and constriction size as random variables. The influence of filter thickness is incorporated into the criterion by considering the number of constrictions in a filtration path. A hydraulic conductivity criterion is developed theoretically based on governing flow equations and the expected partial clogging of geotextiles. The limit states for the developed criteria are evaluated based on the wide range of experimental data. The developed design criteria are applicable to granular and nonwoven geotextiles, which offers an improvement in design compared to the existing criteria in practice.