Sand Samples Research Articles

How Wetting and Drainage Cycles and Wetting Angle Affect Capillary Air Trapping and Hydraulic Conductivity: A Pore Network Modeling of Experiments on Sand

Entrapped air in porous media can significantly affect water flow but simulations of air entrapment are still challenging. We developed a pore-network model using quasi-static algorithms to simulate air entrapment during spontaneous wetting and subsequent drainage processes. The model, implemented in OpenPNM, was tailored to replicate an experiment conducted on a medium-sized unconsolidated sand sample. We started building the model with three types of relatively small networks formed by 54,000 pore bodies which we used to calibrate basic network topological parameters by fitting the model to the water retention curve and the saturated hydraulic conductivity of the sand sample. Using these parameters, along with X-ray image data (µCT), a larger network formed by over 250,000 pore bodies was introduced in the form of stacked sub-networks where topological parameters were scaled along the z-axis. We investigated the impact of two different contact angles on air entrapment. For a contact angle of 0, the model showed good agreement with the experimental data, accurately predicting the amount of entrapped air and the saturated hydraulic conductivity. On the contrary, for a contact angle of π/4, the model provided reasonable accuracy for saturated hydraulic conductivity but overestimated the amount of entrapped air. Overall, this approach demonstrated that a reasonable match between simulated and experimental data can be achieved with minimal computational costs.

Beach wrack as a potential microplastic hot spot in the South-Eastern Baltic Sea environment

Beach wrack is considered as a major source of nutrients to the sandy coast ecosystems in the South-East Baltic Sea, and it serves as the natural beach sediment storage and habitat formation material. However, it also could be a hot spot for microplastic and other types of marine litter accumulation. We carried out the recovery rate experiments to determine the most reliable method for a rapid and cost-effective application to extract microplastics from the beach wrack. The aeration of media in a saturated solution of sodium chloride revealed to be statistically significant and reliable, therefore was selected as a most suitable to extract the microplastics from the beach wrack. This study shows that the concentration of microplastics is significantly different between the four analyzed compartments in the coastal zone. The microplastic concentration in a beach wrack, with a mean value of 0.47 ± 0.17 items/cm3, contained 4.7 times more microplastics than observed in the surface sand samples. This study estimated that on average over 450 million microplastic items could be found during the castaway event in the South-East Baltic Sea coast.

Research on 4N8 High-Purity Quartz Purification Technology Prepared Using Vein Quartz from Pakistan

This study investigates the potential of two quartz vein ores from the Hunza District, Gilgit-Baltistan, Pakistan, as raw materials to obtain 4N8 high-purity quartz (HPQ) sand. Various quartz purification processes were examined, including ore calcination, water quenching, flotation, sand calcination, acid leaching, and chlorination roasting. Analytical techniques such as optical microscopy, Raman spectroscopy, and inductively coupled plasma spectroscopy were employed to analyze the microstructure, inclusion characteristics, and chemical composition of both the quartz raw ore and the processed quartz sand. Microscopic observation reveals that the PK-AML quartz raw ore has relatively high purity, the secondary fluid inclusions are arranged in a directional–linear manner or developed along crystal micro-cracks, and most intracrystalline regions exhibit low inclusion contents, while the PK-JTLT quartz raw ore contains a certain number of melt inclusions. The two processed quartz sand samples exhibit a smooth surface with extremely low fluid inclusion content. A comparative analysis of different purification processes shows that quartz sand calcination has a higher impurity removal rate than ore calcination. After crushing the raw ore into sand, the particles become finer with a larger specific surface area. Quartz sand calcination maximally exposes the inclusions and lattice impurity elements within the quartz, facilitating subsequent impurity removal through acid leaching. Following the processes of crushing, ultrasonic desliming, flotation, sand calcination, water quenching, acid leaching, and chlorination roasting, the SiO2 content of PK-AML processed quartz sand is 99.998 wt.%, with only a small amount of Ti and Li remaining, and a total impurity element content of 20.83 µg·g−1. This meets the standard requirements for crucible preparation in industrial applications, making this vein quartz suitable for producing high-end HPQ products. In contrast, the overall purity of PK-JTLT quartz is lower, and the high contents of impurity elements such as Li, Al, and Ti are difficult to remove via purification experiments. The SiO2 content of PK-JTLT processed quartz sand is 99.991 wt.%, which is applied to higher-quality glass products such as photovoltaic glass, electronic glass, and optical glass, thus presenting broad prospects for application.

Relationships between fecal indicator abundance in water and sand and the presence of pathogenic genes in sand of recreational beaches.

For decades, the risk of exposure to infectious diseases in recreational beaches has been evaluated through the quantification of fecal indicator bacteria in water samples using culture methods. The analyses of sand samples have recently been developed as a complement to the monitoring of recreational waters in beach quality assessments. The growing use of molecular techniques for environmental monitoring allows for the rapid detection of pathogenic genes, thus providing more accurate information regarding the health risk of exposure to contaminated sand. The aim of this work was to determine the relationship between the fecal indicators abundance in water and sand and the presence of Shiga toxin-producer Escherichia coli (STEC) in sand by analyzing samples from touristic beaches using culture-dependent (fecal coliforms assay) and culture-independent (real-time PCR of stx1, stx2, and eae genes) techniques. We found a high concentration of coliform bacteria in water and sand in several beaches in eastern Uruguay, with different levels of sanitation networks and levels of urbanization. The presence of STEC virulence genes (mainly stx1) was confirmed in 8 out of 20 sand samples. The recreational use of sandy beaches may imply a risk to the health of its users, especially near streams and creek outflows, thus highlighting the need of monitoring sand bacteriological quality and pathogens using molecular tools.

Parasitic contamination of environmental objects with nematode eggs of Trichuris genus in the city of Poltava

The spreading of dog digestive tract helminthoses, including trichurosis, still remains a topical problem, where one of the factors of significant infestations’ spreading is the contamination of the environment with parasites’ eggs, which can be preserved in the environment for a long time and cause infestation of susceptible animals. Therefore, one of the important factors in maintaining veterinary well-being in relation to dog trichurosis is establishing the contamination level of environmental objects by propagative stages of nematode development. The purpose of the research was to determine contamination indicators of sand and soil in the city of Poltava with nematode eggs of Trichuris genus. The studies were conducted on the basis of the laboratory of parasitology of Poltava State Agrarian University. Sand samples from sandboxes located on the territory of the city of Poltava, as well as soil from the territories adjacent to them were studied. The main contamination indicators were the extensive contamination index and intensive contamination index. It was revealed by the conducted research that 61 out of 90 sandboxes in the city of Poltava were contaminated with nematode eggs of Trichuris genus, where the extensive contamination index made 67.78 %, and the intensive contamination index made 195.79±18.41 eggs/kg. The territory of Kyiv district was the most contaminated with nematode eggs, where 25 out of 30 sandboxes were contaminated with propagative stages of trichurises development, and the level of parasites’ contamination was 83.33 % and 218.91±17.27 eggs/kg. It was found that the most infected sand was taken from the surface at the edges of the sandbox, near its walls, where the extensive and intensive contamination indices made 41.11 % and 320.27±35.43 eggs/kg, respectively. Also, high rates of parasitic infestation were found during studying the soil, taken from the surface at a distance of 1 m from the sandbox, where, on the average, the extensive contamination index was 46.67 %, and the intensive contamination index was 263.90±28.87 eggs/kg. With an increase in the sampling depth, the indicators of contamination with trichurises’ eggs decreased and amounted to: on the surface – 36.67–46.67 % and 120.37–320.7 eggs/kg, at a depth of 5 cm – 14.44–30.00 % and 80.77–274.07 eggs/kg, and at a depth of 10 cm – 8.89–20.00 % and 62.50–125.00 eggs/kg. The obtained results of parasitological studies prove that the territory of sandboxes is a real factor in the transmission of invasive agents, which must be taken into account in assessing the risks of infecting dogs with trichurosis causative agent.

Enhancing aeolian sand stability using microbially induced calcite precipitation technology

This study investigates the effectiveness of Microbially Induced Calcite Precipitation (MICP) technology in enhancing the stability of aeolian sand. Applying MICP to desert sand samples from Kashi, Xinjiang, the results demonstrated significant structural stability and erosion resistance in treated soils during wind erosion tests. Particularly after 14 days of treatment, the soil samples exhibited optimal wind erosion resistance and surface crust strength. Additionally, the formation of calcite significantly improved the soil’s penetration strength and wind erosion resistance, with SEM analysis confirming that calcite “bridges” between soil particles enhanced inter-particle bonding. Environmental impact assessments indicated that MICP technology is not only environmentally friendly but also effectively reduces the risk of soil environmental pollution. These findings validate the potential application of MICP technology in enhancing the stability and environmental adaptability of aeolian sand.

Large-Scale Triaxial Test on Mechanical Behavior of Coral Sand Gravel Layered Samples

Layered structures comprising coral sand and gravel have been observed in hydraulic filled foundations in the coral reefs in the South China Sea, leading to anisotropy in their physical and mechanical properties. However, the effect of a layered structure on the strength and deformation of the coral soil foundation remains unclear. In this study, a series of large-scale triaxial compression tests and step-loading tests were carried out on four types of samples, i.e., clean coral sand, clean coral gravel, sand-over-gravel layered sample, and gravel-over-sand layered sample, to investigate the impact of confining pressure and the layered structure on the strength and failure modes of these soils. The results indicate that the stress–strain relationships of all samples predominantly exhibit strain hardening under drained conditions. Under identical confining pressures, the peak strength of clean coral sand is the lowest, while that of coral gravel is the highest. The peak strengths of the two layered samples fall between these extremes, with the gravel-over-sand layered sample exhibiting higher strength. All four samples have similar peak friction angles, slightly exceeding 40°. The difference in peak strength among the four types of samples is attributed to the variations in cohesion, with the cohesion of clean coral gravel being up to four times that of clean sand, and the cohesion of layered samples falling between these two. Both clean sand and clean gravel samples exhibit a bulging phenomenon in the middle, while the layered samples primarily exhibit bulging near the coral gravel layer. In the step-loading tests, the bearing capacity of the layered samples falls between those of clean coral sand and coral gravel, with the gravel-over-sand layered samples demonstrating higher strength. Moreover, the p-s curve of the gravel-over-sand layered samples obtained from the large-scale triaxial apparatus under a confining pressure of 400 kPa resembles that from the plate load tests on the same samples.

Patterns distribution, concentrations and sources of radioactive elements from black sand in the Red Sea coast, Egypt

In Egypt, the distribution of black sand in various coastal regions has been readily apparent by thorough research. Unfortunately, these investigations did not measure radioactivity in black sand, particularly in the vicinity of the Red Sea. Gamma-ray spectroscopy was used to detect the naturally occurring radioactivity from 238U, 232Th, 40K, and 226Ra in black sand samples from eight locations along the Red Sea coast: Ras Elbehar, Gemsa, Hurghada Elahiaa, Hurghada Titanic, Safaga, Qusier Elsharm Alqbly, Gabal Alrosass, and Marsa Alam. The resultant data were interpolated to represent the spatial distribution. Additionally, the potential rocks sources of radionuclides were geologically mapped to elucidate the relationship between rock components and radioactivity. The results showed that 226Ra, 232Th and238U were higher at samples collected from Ras Elbehar, Hurghada Elahiaa and Hurghada Titanic compared to the other sites. On the other hand, 40K showed the lowest mean value (75.3 ± 3.8 Bq/kg) in Hurghada Titanic samples, while it peaked (563 ± 28 Bq/kg) in Qusier Elsharm Alqbly samples. The interpolated results show notable differences in radioactive amounts between the north and south, which are indicative of several environmental conditions and human activities. Alkaline syenite, syenogranite, older granites (tonalite and granodiorite), and minor acidic volcanic/metavolcanic rocks make up the upstream area of the basin area draining into, for example, the Ras Elbehar locality (highest activity concentrations for 238U (1596 ± 80 Bq/kg) and 226Ra (886 ± 44 Bq/kg)), while alkali-feldspar granite, schist, and shale rocks make up the mid-stream area. The findings provide a basis for scientific forecasting on the impact of synthetic or naturally occurring radioactive isotopes introduced into aquatic environments.

Influence of shear strength parameters on loose fine sand treated with coir fiber and microbially induced calcite precipitation

In recent years, there has been an increasing use of Microbially Induced Calcite Precipitation (MICP) technology in ground improvement. Adding fiber to bio-cemented sand leads to significant improvements in its properties. This paper examines how coir fiber and microbially induced calcite precipitation (MICP) might be used to improve the engineering qualities of fine sand. The sand was mixed with Coir fiber at varying Fiber Contents (FC) of 0.1%, 0.2%, 0.3%, 0.4%, and 0.5% by weight of sand. Additionally, varied Aspect Ratios (AR) of 45, 90, 136, 182, and 227 were considered. The mixture also included urease-producing bacteria (Sporosarcina Pasteurii), as well as solutions of urea and calcium chloride with 3M molarity. The untreated and treated sand samples were submitted to a Direct Shear Test (DST). The study found that the shear strength parameters, such as the angle of internal friction, increased by 1.1 times compared to standard fine sand. Additionally, the angle of internal friction (ϕ) of fiber-reinforced sand with MICP showed 1.4 times increase, while the cohesion values demonstrated a sixfold increase compared to MICP fine sand. It was determined that the optimal aspect ratio was 182, and the optimal fiber content was 0.3%. Moreover, the Scanning Electron Microscope (SEM) was utilized to examine the calcite formations present in the treated sand samples, and calcite precipitation was observed between the pores of the soils.

Microplastic Abundance, Characteristics, and Heavy Metal Contamination in Coastal Environments of Western Sri Lanka

This study was conducted to assess the abundance of microplastics and associated metal contamination from selected beaches in the Western Province of Sri Lanka. Beach sand samples were collected from four beaches: Modera, Negombo, Mount Lavinia, and Panadura. Microplastics were extracted from dried sand samples using a saturated NaCl solution and sieved. Particles were identified using Fourier Transform InfraRed spectrophotometer, and associated heavy metals; Cr, Pb, Cu, Zn, and Ni were subjected to acid digestion for 24 hours before analysis using Microwave Plasma Atomic Emission spectrometry. More than half of the extracted plastics (56.31%) were identified as microplastics. The average microplastic abundance in beach sand samples ranged from 42.0-91.3 items/kg. The lowest and highest abundances were reported from the sand collected at Mount Lavinia and Panadura beaches, respectively. Hydrodynamic factors like ocean currents, wave patterns, associated Southwest monsoon period, and human activities may have caused the variability in microplastic abundances and metal contamination. The majority of the microplastics (52.29%) were polyethylene, whereas the second most abundant microplastic type was polypropylene (35.18%), resembling the records of the most common plastic waste types in the country. The majority of microplastics were fragments (87.95%) while white was the prominent color (53.49%). The toxic trace element concentration ranged from 5.0×10-3 to 1.8×102 μg/g in beaches. Furthermore, this study establishes a baseline for the west coastline prior to the X-press Pearl Ship Disaster in 2021. Future studies are encouraged to assess the beach microplastic pollution across the entire Sri Lankan coastline.

Geochemical characterization and reserve estimation of the economic heavy minerals of Sonadia Island, Bangladesh

The goal of the current study is to understand the elemental concentration, reserve assessment, mineralogical composition, and distribution of heavy minerals in the dune sands, foreshore, and backshore of Sonadia Island, Southeast Bangladesh. The study area yielded a number of drill hole composite sand samples that were used for density and magnetic separation of heavy minerals. These samples were then subjected to petrographic characterization, grain counting, mineralogical analyses using scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM–EDX), x-ray diffraction (XRD), and bulk sand geochemistry using X-ray fluorescence (XRF). The results of heavy liquid separation show that the total heavy mineral (THM) enrichments in foreshore sand (about 4.86%), backshore sand (about 9.03%), and dune sand (about 22.28%) are significantly higher. After characterizing the sand samples from Sonadia Island based on the abundance of each mineral species, the average content values relative to total economic heavy minerals (TEHM) were determined to be 38.14% ilmenite, 5.74% magnetite, 51.52% garnet, 1.01% zircon, 3.57% rutile, and 0.01% monazite. An SEM–EDX examination reveals that the elemental concentration of ZrO2 in zircon is 66.60%, while the average TiO2 content in rutile is ~ 95%, whereas TiO2 is 45% and the total Fe2O3 is 45.70% in ilmenite. Major phases including amphibole (tremolite) 45.9%, muscovite 15.6%, quartz 12.6%, garnet (almandine) 10.9%, dolomite 7.9%, ilmenite 4.1%, and kaolinite 1.3% are also identified by the XRD pattern. There are an estimated 19,794 tons of garnet in the foreshore sand, 47,324 tons in the backshore sand, and 276,868 tons in the dune sand within the reserve, making it the most prevalent heavy mineral. Ilmenite is the second most common heavy mineral, with quantities detected in the foreshore (15,016 tons), backshore (30,487 tons), and dune sand (215,092 tons).

Analysis of Liquefaction in Tailings Deposits by Fem Modeling of Undrained Cyclic Triaxial

In this article, a numerical calibration procedure for undrained cyclic triaxial tests is presented to evaluate the liquefaction potential in sand and silt samples from mining tailings in northern Chile. The numerical modeling of an axisymmetric specimen involved two stages: isotropic consolidation using the Hardening Soil Small (HSS) model and a cycling phase employing the UBC3D-PLM model to simulate the onset of liquefaction using the criterion that the excess pore pressure ratio Ru should exceed 0.8. The results demonstrate that the UBC3D-PLM modeling calibrated with experimental data from cyclic triaxial tests effectively represents the excess pore pressure in both sandy and silty soils from mining tailings. The accuracy of the modeling decreases when a single set of parameters is applied to the same soil at different cyclic stress ratios (CSR), highlighting the need for specific calibrations for each loading.

On the Initial Fabric of Naturally Occurring and Reconstituted Weakly Cemented Geomaterials

The understanding of naturally occurring materials such as clay, sand, hard and soft rocks under a common theoretical framework has been a topic of persistent research interest. Over the past few decades, various sample reconstitution techniques have been developed in the literature to mimic in situ conditions, and to parse carefully the influence of various components in a cohesive-frictional geomaterial such that their behavior can be folded into the broad ambit of a continuum mechanics framework. The initial fabric of natural rock specimens is compared with reconstituted cemented sand samples using X-ray computed tomography (XRCT) scans. The efficacy of laboratory reconstitution techniques in replicating the initial microstructural features of natural rocks is evaluated here. Additionally, discrete element method (DEM) protocols which are often employed in generating cohesive granular ensembles are employed here and compared against the naturally occurring and artificially reconstituted fabric. A significant difference is observed in the grain boundaries of reconstituted and naturally occurring rocks. Additionally, the arrangement of particles, the orientation of grain contacts, and their coordination number are examined to assess the efficacy of laboratory-reconstituted specimens at micro-length scale.

INJECTION OF TWO-COMPONENT GEOPUR RESIN FOR STRENGTHENING SANDY SOILS

The article explores the use of GEOPUR, a two-component polyurethane resin, for strengthening sandy soils. It highlights the process of soil stabilization through high-pressure grouting, which improves water resistance, stabilizes soil structures, and enhances anchoring strength. The research investigates the application of this resin in consolidating weak, loose soils and its effect on their physical and mechanical properties. Laboratory experiments were conducted on sand samples to simulate real-world conditions, testing the resin's effectiveness in improving soil density, compressive strength, and overall stability. The study analyzes how the resin's expansion within the soil structure impacts soil behavior, concluding that the GEOPUR resin significantly enhances the soil's load-bearing capacity. Various parameters, such as the volume of injected resin, consolidation efficiency, and the strength-density relationship, are evaluated to provide practical recommendations for soil stabilization using this innovative material. The findings demonstrate the resin's potential in geotechnical applications, particularly in situations where traditional stabilization methods are not feasible or efficient. The article concludes with suggestions for optimizing the resin injection process to maximize its effectiveness in both laboratory and field conditions, making it a promising solution for future ground improvement projects.

Complete genome sequences of Chitinophaga sp. strain MM2321 and Microbacterium sp. strain MM2322, isolated from a sand sample in Harsewinkel, Germany.

We cultivated bacteria contained in a sandy soil sample, isolated DNA from a single bacterial colony, and assembled from genomic reads the full genome sequence of Chitinophaga and Microbacterium strains, termed MM2321 and MM2322. Besides the genome sequences, the phylogenetic classifications of both strains are reported.

The effect of relative density, granularity and size of geogrid apertures on the shear strength of the soil/geogrid interface

The increasing use of geogrid in various geotechnical projects has made the evaluation of the shear behavior of soil reinforced with geogrid become particularly important. In this article, a series of large-scale direct shear tests have been performed on sand and gravel samples reinforced with geogrid. The purpose of the experiments was to investigate the impact of the geogrid mesh size and the relative density of the samples on the shear strength coefficient of the interface between soil and geogrid. In this study, 5 geogrids with different mesh sizes and one type of geotextile were used. According to the results, the average shear strength coefficient of sand and gravel samples reinforced with geogrid for different normal stresses and different relative densities was obtained between 0.72 and 0.94. As the relative density increases, the interface shear strength coefficient decreases, this means that the denser the sand, the more the shear strength of the sand/geogrid interface decreases. Based on the results, it was found that the contribution of particle interlocking in the shear resistance of the sand/geogrid interface is particularly important, so that the shear resistance coefficient of the interface increases with the increase in the size of the geogrid mesh.

“Once upon a time… a beach sand grain”: a bed-time story and scientific outreach activity for young children to increase sediment literacy

Abstract Purpose Learning science in early years can cultivate children’s curiosity and enjoyment in exploring the world around them, laying the foundation for the progression of science learning and ultimately increasing science literacy. Here, we present an example of a tailored preschool scientific activity designed to enhance literacy about sediments and illustrate their importance to both humans and nature. Methods The activity centres around a captivating story detailing the journey of a sand grain from the mountains to the sea. This storytelling experience is enriched with hands-on observation of various sand grains, informative cards on key topics, and culminates in a creative colouring activity. Results To date, the activity has been repeated five times, engaging 110 children (from 2 to 10 years). It has yielded positive outcomes with both preschool and primary school students, as they were actively engaged in the story and delighted in handling and observing the magnified sand grains. Conclusions The activity was successfully implemented for preschool and primary school students, fostering engagement with the story and the sand samples. However, while the immediate engagement was evident, the impact on sediment literacy remains to be measured. Future structured evaluations are needed to assess the long-term effectiveness of such initiatives in enhancing sediment literacy among young learners.

Characterization of Adsorbed Hydrocarbons in Deposit Sands and Well Fracture in the Burgos Basin

Objective: The objective of this research is to determine the potential adsorption by the solids carried by the hydrocarbon production stream to the surface by characterization to identify its origin. Theoretical framework: In the natural gas producing wells of the Burgos Basin, there is the presence of solids in the production fluids, these can be from the reservoir or from fracture. The reservoir solids are created from the carbonates, sandstones and shales inside the well, the fracture solids are better known as props, they are mixed with the drilling fluid so that inside the well they act as packs in the fractures where the hydrocarbon can flow for extraction. In this Basin, horizontal hydraulic fracturing is used for the extraction of hydrocarbons, the solids present adsorb part of the hydrocarbons and are contaminated with them. Method: Sand samples from 4 wells were used, which were extracted with Soxhlet equipment to separate the organic content of the sand. Using ASTM (2003) and US EPA (1996) methods D5369-93 and 3540C-3541 as a reference. Subsequently, the hydrocarbon concentrate was fractionated using the method reported in the manual of soil analysis techniques of Fernández et al., (2006) who adapted the methods 3600C, 3610B and 3611B of the US EPA (1996). The analytical method consisted of reading the spectra of each fraction in a UV-Visible Shimadzu UV-1800 spectroscopy equipment and by FT-IR spectrophotometry, in a Nicolet iS10 equipment, with a DTGS KBr detector. The physical characterization of the sands was performed by recording the particle size using the API-RP56 standard. Finally, X-ray diffraction is used to determine the phases of the sands by the method 05LA-34080109-DRX-MP-01. Results and discussion: The amount of total hydrocarbon extracted from the sands was in a range of 2,975-0,060 gr. The identification of hydrocarbons extracted by Uv-Visible and FTIR showed functional groups of aliphatic, polycyclic and nitrogen compounds. The particle size of the sands was measured between 45-311 nm. And finally RX identified the type of sand to analyze, being well 1: reservoir sand, well2: fracture sand, well 3: fracture sand and well 4: reservoir sand. Implications of the research: This research presents a study on the classification of the type of sands that are being dragged to the surface with the hydrocarbon stream of well production. These are data that show a fact that occurs and gives the certainty of what happens at the bottom of the well. Originality/value: The analysis of the results allows decisions to be taken to prevent corrosion and plugging problems of surface equipment, which can cause explosions such as the one of September 19, 2012 in the PEMEX gas pipeline at the Km 19 Measuring Center in Reynosa, Tamps. Mexico.

Critical state uniqueness of dense granular materials using discrete element method in conjunction with flexible membrane boundary

An explanation of the meso-mechanism of sand granular materials for the uniqueness of critical state is presented by means of the discrete element method (DEM) under flexible boundary loading conditions. A series triaxial drainage shear test (DEM simulations), in conjunction with the flexible boundary technique, of were performed for sand samples subjected to various physical states and with different particle size distributions. After carefully investigating the critical status of the results of the numerical calculation, the macroscopic failure modes and shear band evolution of sand, as well as the velocity vector field due to different initial states, were explored and classified. Furthermore, the evaluation rules and discrepancies between overall void ratios of the specimen and local void ratios within the shear band under the critical state were recorded and analyzed. The results proved that a sample with a small void tends to form a shear band, and the rotation of the particles in the non-shear zone is negligible. Conversely, sandy soil with large initial void ratios exhibited limited development of significant shear bands, and the change in void ratios within the shear region and the non-shear area are not significant. Interestingly, the particle-size distribution exerts minimal influence on the evolution rule which the void ratio converges within the shear band and diverges outside the shear region for both multi-stage and single-stage specimens. The void ratio within the shear band and deviator stress ratio tend to exhibit consistently for the same specimen with different initial physical states, thereby distinguishing the critical state. There is a significantly higher change in void ratio within the shear band compared to outside of it, yet it remains stable within a relatively similar range. Additionally, the invariant of the fabric tensor used to describe the critical state characteristics also demonstrates a high degree of consistency within the shear band. These findings strongly indicate that the critical state exists within the shear failure surface and is highly likely to be unique.

Qualitative analysis of rivers sand sources (Silica sand, Ravi river sand, Indus river sand, and Jhelum river sand) for metal casting: a comparative study

Abstract Recent geological investigations revealed extensive use of Silica sand in Pakistan resulting in depletion of tectonic resources. Hence, it is important to explore cost-effective and alternative sources of sand for its applications. Also, Pakistan has a river network that provides river sand as a potential substitute for Silica sand. However, it is essential to systematically study and assess the potential applicability of river sand as an alternative to Silica sand. In this context, this study examined sand samples collected from various rivers in Pakistan to investigate their suitability for metal-casting molds. For that purpose, random samples were selected from major rivers in Pakistan for characterization by utilizing chemical composition analysis, microscopy, XRD, TGA-DSC (thermogravimetric analysis), clay content analysis, grain size distribution analysis, pH measurement, green and dry compression strength testing, shear strength testing, permeability analysis, shatter index analysis, compactibility testing, and Specific gravity measurement. The chemical composition analysis revealed that all types of sands contained over 90% SiO2 content. The mechanical tests demonstrated that river sand exhibited acceptable mechanical properties, with a moisture content ranging from 4.5-5%. The pH value of all the sands exceeded 7, making them suitable for casting purposes. These investigations suggest that river sand can be effectively utilized in casting applications by implementing pre-processing techniques and incorporating additives.