Julio R. Valdes

Particle Clogging in Radial Flow: Microscale Mechanisms

Summary Fluid-flow-driven particle migration through porous networks reflects the interplay between various particle-level forces, the relative size between migrating particles and pore constrictions, and the spatial variability of the velocity field. Experimental evidence shows that particle migration in radial fluid flow results in selfstabilizing annular clogging patterns when the particle size approaches the constriction size. Conversely, flow localization and flushing instability are observed when the particle size is significantly smaller than the pore-throat size.

Sand–rubber mixtures: Experiments and numerical simulations

This paper documents the results of laboratory experiments and numerical simulations conducted to examine the behavior of mixtures composed of rubber and sand particles of similar size. Emphasis was placed on assessing the role of loading type on the load-deformation behavior and selecting appropriate parameters for the discrete element modeling of sand–rubber, with relevance to the use of compressible particulate systems for filtration control. Experimental results show that sand–rubber exhibits load–unload hysteresis and residual strains post-unloading due to particle–particle and particle–wall locking effects that arise from sidewall friction. It is shown that the discrete element modeling of sand–rubber requires unconventional schemes because of the stiffness contrast between sand grains and rubber grains. The results have implications in the design of compressible particulate systems for seepage and filtration control and in the development of prediction tools for the field performance soil–rubber, w...

Clogging: bridge formation and vibration-based destabilization

The migration of mobile particles through porous networks is restricted when the size of the migrating particles approaches the size of pore throats. In this case, single particle retention or entrapment by bridge formation takes place. Experimental results show that bridge formation and stability are controlled by particle shape, relative throat-to-particle size, and skeletal forces. Forced-vibration studies provide additional insight into bridge stability and the potential for vibra- tion-based unclogging, and show that it is easier to prevent bridge formation than to destabilize already formed bridges. Results from these pore-scale studies are relevant to filter clogging and unclogging, water and oil extraction, sand produc- tion in oil wells, and in food grain, aggregate and powder handling operations.

A Numerical View into Direct Shear Specimen Size Effects

The ASTM D 3080-04 standard, Standard Test Method for Direct Shear Test of Soils under Consolidated Drained Conditions, indicates that the direct shear test specimen width L must be at least ten times larger than the largest particle in the specimen, L/d ≥ 10. The results documented in this note provide visual insight into specimen size and boundary effects through discrete element simulations conducted with numerical specimens ranging in size from L/d = 6.5 to L/d = 177. Particle translation data indicate that in the tested configuration, localized shear zones located far from the specimen boundaries develop only when the specimen size is L/d > 58. The results provide a description of the microstructure evolution during shearing and suggest that the ASTM specimen size criterion may be inappropriate when localized shear banding in uniform granular materials is sought.

Particle transport in a nonuniform flow field: Retardation and clogging

The authors examine the time delays experienced by migratory particles inside nonuniform flow fields using experimental and numerical methods. Particle trajectories are affected by the particle-fluid density ratio and the flow direction, such that particles may precede or trail the fluid. In flow toward an orifice, the time delay suffered by a single particle is a function of the Froude number Fr and the Archimedes number Ar. When multiple particles are transported radially through a porous medium, time delays manifest through localized annular clogging when 0.05 1. Applications include filtration and reservoir fluid extraction.

Monitoring the Oedometric Compression of Sands with Acoustic Emissions

The development and use of a noninvasive technique to monitor the acoustic emissions (AEs) generated during the oedometric compression of coarse-grained soil are documented. Technique implementation is described with the aid of experiments conducted on sands with contrasting grain features. Results indicate that the proposed technique is capable of capturing the onset of characteristic stress-strain behavior regimes exhibited by the soil during loading. The clarity of such capture is, however, dependent on the amplitude of the AE relative to that of the background noise and, as such, dependent on the soil type. The technique is anticipated to aid in enhancing the fundamental study of soil behavior at high stresses and may find potential use in the realm of penetrometer-based stratigraphy characterization.

Monitoring the Hydraulic Conductivity of Crushing Sands

Crushing occurs when particles are subjected to sufficiently high external stresses. The crushing process leads to the production of fragments and to ensuring changes in void ratio, pore sizes, specific surface, and hydraulic conductivity. This paper presents a study of the changes in hydraulic conductivity that take place during particle crushing in sand specimens. A new one-dimensional compression cell modified for double-ring permeametry was used to measure the hydraulic conductivity of various sands during crushing and is described in detail in this paper. The device, procedures, and data analyses incorporate arching and localized crushing effects, and are presented as a development towards a new testing standard for determining hydraulic conductivity degradation curves that result from crushing of sands subjected to large stresses. Results show that the hydraulic conductivity degradation curve is dependent on sand type, in particular the particle shapes and mineral composition. The role of arching on the compression behavior and the associated post-crushing grain size distribution curves is also addressed.

Plankton filtration with compressible crumb rubber packs

The experiments described provide insight into the feasibility of using compressible particulate packs to filter live plankton. The pore constriction sizes are controlled by subjecting the filter pack to isotropic confinement, thereby allowing for: (1) enhanced filtration upon confinement and (2) enhanced unclogging upon relaxation. Results show that filtration efficiency increases with increasing confinement; however, complete plankton retention is difficult to attain due to the planktons ability to pass through pore constrictions that are smaller than the plankton size. The results are anticipated to offer potential benefits to ballast treatment and aquatic filtration operations.

Slope Interrupter Best Management Practice Experiments on a Tilting Soil Bed with Simulated Rainfall

This paper documents an experimental study conducted to evaluate the performance of two commonly used sediment treatment control products, albeit with contrasting treatment technologies: a fiber roll or wattle (i.e., three-dimensional filter) and a perforated pipe wrapped by a pervious geosynthetic material (i.e., boundary filter). Emphasis was placed on (1) simulating field conditions and (2) describing performance via runoff, sediment yield, and particle-size measurements. Scaling problems typically associated with erosion experiments were minimized by using standard-size products (not scaled models) and a large-scale erosion bed with overhead rainfall simulators, with which dominant forms of soil erosion and sediment transport were attained. The results indicate that the experimental procedures and measurements utilized are appropriate for quantifying the erosion control performance of the products tested. In particular, the measurements revealed the important role of installation quality on BMP performance. Results also indicate that the magnitudes of peak discharge and total runoff from compacted, bare soils on steep slopes can approach values typical of highly impervious surfaces.

Characterizing Potential Water Quality Impacts from Soils Treated with Dust Suppressants

Two separate laboratory experiment series, surface runoff and steady-state seepage, were performed to determine if dust suppressant products can be applied to soils with an expected minimal to no negative impact on water quality. The experiments were designed to mimic arid field conditions and used two soils (clayey and sandy) and six different dust suppressants. The two experiments consisted of: (i) simulated rainfall (intensities of 18, 33, or 61 mm h(-1)) and associated runoff from soil trays at a surface slope of 33%; and (ii) steady-state, constant head seepage through soil columns. Both experiment series involved two product application scenarios and three application ages (i.e., to account for degradation effects) for a total of 126 surface runoff and 80 column experiments. One composite effluent sample was collected from each experiment and analyzed for pH, electrical conductivity, total suspended solids (TSS), total dissolved solids, dissolved oxygen, total organic carbon, nitrate, nitrite, and phosphate. Paired t tests at 1 and 5% levels of significance and project specific data quality objectives are used to compare water quality parameters from treated and untreated soils. Overall, the results from this laboratory scale study suggest that the studied dust suppressants have minimal potential for adverse impacts to selected water quality parameters. The primary impacts were increased TSS for two synthetic products from the surface runoff experiments on both soils. The increase in TSS was not expected based on previous studies and may be attributed to this studys focus on simulating real-world soil agitation/movement at an active construction site subjected to rough grading.