Sand Particle Size Research Articles

Study on the Compressive Properties and Factors of Recycled Mixture with High Content of Iron Tailings Sand

This paper focuses on the disposal of iron tailings sand (ITS) and recycled aggregate of inorganic (RAI) and proposed the “ITS plus RAI” solid waste treatment methods, which uses ITS and RAI as a new base course material to replace new aggregates by 100% to apply in the pavement renovation project of national and provincial roads in Linfen city, Shanxi Province. In this paper, the compressive strength characteristic of recycled mixture with different ratios is studied for the dual waste treatment methods, and the influence factors are analyzed by multiple regression analysis. Results show that the strength of the recycled mixture composed of a high content of ITS (the mass ratio to RAI exceeds 60 : 40) ups to 7 MPa, which can meet the pavement requirements of 7d unconfined compressive strength of inorganic stabilized base material under various traffic load conditions. The factors affecting the strength of recycled materials include the content of various components, while the particle size of iron tailings sand is the most significant influence factor. Therefore, the proportion of iron tailings sand in the recycled mixture can be further improved by screening coarse iron tailings sand so as to maximize the content of iron tailings sand, which will lead to an excellent engineering value.

Effects of particle size optimization of quartz sand on rheology and ductility of engineered cementitious composites

In this study, the effect of particle size of quartz sand on the fresh and hardened properties of engineered cementitious composites (ECC) was investigated. For this purpose, three ECC mixtures that are identical except for the gradation of quartz sands used in their composition were designed. One of the mixtures includes a combination of quartz sands with amounts determined by the Andreasen and Andersen particle size optimization model while the remaining two have a finer and a coarser gradation. In the fresh state, mini slump, mini V-funnel and bleeding tests were applied, and rheological parameters were determined according to Bingham and modified Bingham models by using a rotational viscometer. In the hardened state, flexural strengths, mid-span deflections and numbers of microcracks formed under flexural loading were determined at 7 and 28 days. It was observed that the particle size optimization of the quartz sand can provide a balance between flow and bleeding characteristics of ECC mixtures. Although a reduction in flexural strength occurred at both ages in the optimized ECC mixture, the deflection capacity and the crack formation capacity under loading were significantly increased, reaching a deflection value of over 10 mm with at least 11 cracks formed during the test. As a result, it was revealed that particle size optimization can yield a mixture with the highest ductility without compromising the workability of ECC.

青海湖裸鲤自然产卵场的生境特征及无人机遥测判别——以泉吉河为例

PDF HTML阅读 XML下载 导出引用 引用提醒 青海湖裸鲤自然产卵场的生境特征及无人机遥测判别——以泉吉河为例 DOI: 10.5846/stxb202107191949 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 青海省自然科学基金面上项目（2018-ZJ-908）；中央公益性基本科研业务费项目（2020TD08，2019HY-JC01） The spawning habitat characteristics of Gymnocypris przewalskii and its identification by the UAV in tributary of Qinghai Lake—taking Quanji River as an example Author: Affiliation: Fund Project: Natural Science Foundation of Qinghai Province, Central public welfare basic scientific research business expenses project 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:自然产卵场是维持物种延续最关键的栖息地，青海湖裸鲤（Gymnocypris przewalskii）的自然繁殖栖息地状况和生境特征尚缺乏详细的定量研究。以青海湖入湖河流泉吉河为例，在平水期采用现场调查和无人机遥测的方法对青海湖裸鲤的自然产卵场分布及生境状况进行调查，确定其产卵场生境特征参数，建立基于无人机遥测识别产卵场的方法并进行复核验证。结果表明：泉吉河河道形态可分为弯曲型、分汊型和顺直型等三种典型河型，青海湖裸鲤自然产卵场主要分布在弯曲型和分汊型河道中，分汊型河道几乎100%都有产卵场分布，弯曲型河道有70%为产卵场；产卵场河道平均长度（135.13±61.13） m，平均宽度（30.01±17.51） m，平均曲折度1.09±0.07；平均面积（4586.6±4201.61） m2；产卵场常位于缓水浅滩处，平均水深（0.19±0.10） m （范围：0.03-0.44m），平均流速（0.24±0.20） m/s （范围：0.01-0.81m/s），河床质为含有沙粒的卵石（粒径：163-256mm）底质。河道形态、沙洲分布、水深特征等特征参数可作为无人机遥测识别产卵场的判断条件，并实现验证成功。研究结果可为开展整个流域的青海湖裸鲤自然产卵场现状评估及保护对策制定提供技术支撑。 Abstract:The natural spawning grounds are the most critical habitat for maintaining the Gymnocypris przewalskii resources in the Qinghai Lake, while they were not well studied yet. This study aims at analyzing the habitat characteristics of the spawning grounds of G. przewalskii in one of the tributaries of the Qinghai Lake, Quanji River, via field survey and unmanned aerial vehicle (UAV) identification technique. The results showed that the morphology of Quanji River could be divided into three types:meandering, braided and straight river channels. The natural spawning grounds of G. przewalskii were mostly located in the braided river channel (100%), less in the meandering channel (70%), and rare in the straight channel. The average length, width, tortuosity and area of the spawning grounds in the Quanji River was (135.13±61.13)m, (30.01±17.51)m, (1.09±0.07)and the (4586.60±4201.61)m2, respectively. The spawning grounds often located in the river with riffles, the average water depth was (0.19±0.10)m(range 0.03-0.44m) and an average velocity was (0.24±0.20)m/s (range 0.01-0.81m/s), the substrate was pebble and sand (particle size 16-256mm). The riverbank morphology, the distribution of the island and the water depth could be used in UAV image for identifying the potential spawning grounds in the whole Quanji River, the result can be verified by the field data. The research is benefit for the assessment and protection of the natural spawning grounds for G. przewalskii and provides a case study for future spawning grounds investigation in some tough field survey areas. 参考文献 相似文献 引证文献

Estimation of interface friction and concrete boundary layer for 3D printable concrete pumping

3D concrete printing technology is a revolutionary method having multiple benefits over the conventional method of construction. Currently, the 3DCP process is in its initial stage hence required detailed investigation on many points. In the 3DCP process, pumping pressure plays the foremost role as the continuous, uniform and controlled flow of concrete is required to achieve desirable printability. To estimate the pumping pressure effectively, it is necessary to study the pumping parameters & interface friction. The interface friction at boundary layer is largely affected by the concrete composition. The estimation of pumping pressure for conventional concrete was found in past study in which the piston pump and metal pipe was used as a pumping assembly but no work has been found to estimate pumping pressure for 3D printable concrete using progressive cavity pump and high density polyethylene (HDPE) rubber hose pipe. In this study the interface friction between high density polyethylene (HDPE) rubber hose pipe and different 3D printable concrete mix was estimated by performing tribometer test. Effect of 3D printable concrete composition on thickness of boundary layer was also studied. From the experimental results, it was found that the interface friction is decreasing with the more workable concrete mix and the boundary layer (BL) was formed by the cement, water & smaller size of sand particles (<1.18 mm).

Influence of Sand Particle Size on the Erosive Wear of Compressor Blade in an Aero-turboshaft Engine

Influence of Sand Particle Size on the Erosive Wear of Compressor Blade in an Aero-turboshaft Engine

Steam migration and temperature distribution in aquifers during remediation using steam injection

Steam injection technology is commonly used to rapidly remove volatile and semi-volatile organic pollutants in aquifers, and its remediation effect is highly related to steam migration and temperature distribution. However, systematic studies on steam migration and temperature distribution across different types of aquifers are lacking. In this study, the steam migration and temperature distribution in an aquifer were investigated through a series of two-dimensional sandbox experiments with different groundwater velocities, steam injection flow rates, and stratigraphic structures. The experimental results indicated that the temperature distribution in the aquifer was related to the formation permeability and steam injection flow rate. When the hydraulic conductivity of the aquifer was lower than 10−3 cm·s−1, the heating zone in the aquifer had an H-shaped distribution, and when it was higher than 10−2 cm·s−1, the heating zone had a V-shaped distribution for a high steam injection flow rate (1 kgh−1), and an H-shaped distribution for a low injection flow rate (0.5 kgh−1). Under the same injection steam flow rate, the total area of the heating zone in the aquifers with different media was in the following order of sand particle size: coarse sand > fine sand > medium sand. Owing to the heat pipe and heat dispersion effects, the heating zone area in the fine sand aquifer was larger than that of the medium sand aquifer. Groundwater velocity did not affect the area of the heating zone. With the increase in groundwater velocity, the heating zone expanded downstream. In layered heterogeneous aquifers, the upper fine and lower coarse structures formed a steam-blocking interface, resulting in steam accumulation and temperature increase in the lower layer. These findings are significant for improving our understanding of steam migration and temperature distribution in aquifers, leading to an improved design and prediction of the steam remediation required for mitigating aquifer pollution.

Study on the Water Blocking Capacity and Influencing Factors of Hydrophobic Gravel Beds.

Excess water production is a common and extremely serious problem during the process of reservoir development, especially in the middle and later stages of unconsolidated sandstone reservoirs. High water content ratios will negatively affect the recovery efficiency and equipment safety of oil and gas wells. In this study, a hydrophobic quartz sand proppant was prepared with 1,1,1,3,3, 3-hexamethyldisilazane (HMDS) for gravel packing technology. The capillary resistance of hydrophobic quartz sand beds to water was used to achieve water inhibition and oil enhancement. Then, a theoretical capillary bundle model of a quartz sand bed was developed to predict the capillary resistance and water blocking capacity of the quartz sand bed. An evaluation of the experiment results shows that the activation index is up to 96% and the water contact angle is up to 151° after treatment by 0.6 wt % HMDS, which indicates that the quartz sand after modification has strong hydrophobicity. The calculation results demonstrate that the capillary resistance (CR) and the water blocking capacity (WBC) decrease with increasing quartz sand particle size and porosity of the quartz sand bed. As the water contact angle increases, the CR and WBC are also increased. In addition, to make the WBC of hydrophobic quartz sand bed δ > 20%, the parameters of the quartz sand bed must be satisfied: particle size dg < 50 μm, porosity ϕ < 30%, water contact angle θ > 150°, and production pressure difference Δp < 1 MPa. The results of this study could provide theoretical guidance for the construction parameters of hydrophobic gravel packing in high water-cut oil and gas fields.

Controls on the Spatial Distribution of Trace Metal Concentrations along the Bedrock-Dominated South Fork New River, North Carolina

In marked contrast to alluvial rivers, few studies have examined the physical and geochemical controls on the spatial distribution of toxic trace metals along bedrock channels. This study examined the factors controlling the geographical pattern of selected trace metal (Cu, Cr, and Zn) concentrations along the bedrock-dominated channel of the South Fork New River (SFNR). The SFNR is located in the Blue Ridge Physiographic Province of North Carolina, and is representative of many rivers in mountainous terrains that are often subjected to the influx of toxic trace metals from historic and contemporary mining operations. The topography of the SFNR’s channel bed is highly variable and can be subdivided into pool and shallow bedrock reaches. The latter contained localized cascades characterized by topographically higher bedrock ribs that are separated by topographic lows, both of which are oriented oblique to flow. Accumulations of bed sediments are predominantly associated with the traverse bedrock ribs that generate high hydraulic roughness. Except for a few localized zones of enrichment, sediment-associated trace metal concentrations tended to vary within a narrow range of background values over the 36 km study reach. Elevated trace metal concentrations were closely linked to zones of high Fe and Mn concentrations, and were associated with pools located within or immediately downstream of bedrock cascades. The elevated concentrations of the metals appear to be derived from the erosion of lithologic units within the cascades that contain sulfidic layers or zones of mafic mineral enrichment, and which are known to occur in the underlying bedrock. Once eroded, these minerals and/or rock fragments were deposited within low-velocity zones created by the transverse ribs or within downstream pools. The enrichment of trace metals downstream of the cascades may also be due to the formation of Fe and Mn oxyhydroxides as turbulent flows aerate river waters as they traverse the cascades. Chemically reactive fine-grained (&lt;63 µm) sediments had a relatively limited influence on the downstream variations in metal concentrations, presumably because the channel bed sediments are composed primarily of sand-sized and larger particles. Although a principal component analysis (PCA) suggested that reach-scale variations in channel and valley morphology may have partly influenced downstream variations in trace metal concentrations, the geographical patterns were primarily controlled by local geological and geomorphic factors associated with the bedrock cascades. The design of future sampling programs along such coarse-grained, bedrock rivers should consider the significance of these local controls on trace metal storage to effectively characterize and interpret downstream patterns in metal concentrations.

Characteristics of hydrate formation, decomposition, and phase equilibrium in the transition area formed by the high-pressure jet breaking and sand filling method

Marine hydrates mainly occur in clayey silt sediments, and their occurrence environment has the characteristics of a high clay content and low permeability, which seriously inhibit an increase in the gas production rate. This study presents a new method, the high-pressure jet breaking and sand filling method, to transform the natural gas hydrate (NGH) reservoir near the production well, whereby a water jet is used to form an area of sediment with large particle diameters and high permeability. Based on indoor experiments, we report the characteristics of hydrate formation, decomposition, and phase equilibrium in the transition area formed by this method under different sand particle sizes and mass fractions. The addition of sand at a high mass fraction with a large particle diameter significantly shortened the time required for rapid hydrate formation, prolonged slow hydrate formation, and reduced the increase in temperature. With an increase in the mass fraction of large-diameter sand, the free water content of pores increased, which made it easier to form hydrates with large particles, thus delaying the hydrate decomposition rate. The phase equilibrium curves of hydrates in clayey silt sediments with sand added at mass fractions of 30% and 50% were close to that of bulk hydrate in pure water at lower temperatures. As the temperature increased, the phase equilibrium curves gradually approached those of hydrates in clayey silt sediments.

Morphology observation on formation and dissociation cycles of methane hydrate in stacked quartz sandy sediments

In this paper, multi-formation and multi-dissociation experiments of methane hydrate in quartz sands (6.5–355 μm) were carried out in a high-pressure visible reactor. The results showed that the cumulative amount, saturation and initial formation rate of hydrate increased with the size of sand particles decreasing, and also increased with the cycles of hydrate formation under the equal experimental time. When the sand particles ranged from 6.5 to 48 μm, the hydrate saturation reached the maximum of 59.5%. Performing experiments with sands of 109–120 μm, the hydrate saturation at the three repetitive formations were 26.2%, 39.3% and 41.7%, respectively. Besides, the hydrate dissociation process was affected by the initial hydrate saturation and the way of its occurrence, which suggested that a higher hydrate saturation would lead to a longer dissociation. The morphology observations indicated that the hydrate formation in the quartz sand mainly existed in the form of pore-filling, and the formation process was actually a dynamic process accompanied with dissociation. Furthermore, in the experiment of layered accumulations, the hydrate firstly formed in the layer of large particle sand, and the forming process of fracture-type hydrate was observed in the layer of 6.5–48 μm particle sand. The results of this work may provide a new insight on the formation and dissociation laws of hydrate and some useful information for the natural hydrate exploration.

Experimental Study of the Water-Sediment Two-Phase Seepage Characteristics in Rock Fractures and the Influencing Factors

The water-sediment two-phase seepage in coarse fractures is one of the major factors to trigger mine water inrush disasters. Based on seepage mechanics theory, a mechanical model of the water-sediment two-phase seepage in coarse fractures was established. An experimental system was also developed to study the seepage characteristics under various conditions. The relationships between the absolute value of the pressure gradient and the seepage velocity were analyzed during the test process. The nonlinear characteristics of the seepage test were revealed. In addition, variation laws of the absolute value of the pressure gradient with the sand volume fraction and the sand particle size were illustrated, which were related to the loss of pressure during the particle movement. The impacts of the sand volume fraction and the sand particle size on the equivalent fluidity and β -factor of non-Darcy flow were discussed and analyzed. It was determined that the local turbulence was the main reason for the change of nonlinear variation characteristics of seepage parameters.

ECO-Friendly approach in strengthening the different grain size particles by utilizing Sporsarcina pausterii NIOT1

A distinct grain size of 600, 425 and 212 μm sand column was developed to test the efficiency of bacterial strain Sporsarcina pausterii NIOT-1. The bacterial strain was effectively able to precipitate calcite crystals between the soil particles through enzymatic hydrolysis of urea which increases ammonium concentration to the maximum of 371.43 mM, 314.54 mM, 302.49 mM, EC of 98.81 ms/cm, 101.84 ms/cm, 101.34 ms/cm and pH of 8.80, 8.90, 8.80 respectively. The synthesized biomaterials have the maximum UCS of 2400 Mpa with 212 μm grain size followed by 425 and 600 μm with 2200 and 2100 Mpa. Scanning Electron Microscopy and XRD results justify the precipitation of CaCO3 bridging the sand particle. In the study, the maximum UCS attained with fine sand particle size and reduced with the increasing grain size. The current study observed an inverse relationship between grain size and strength. The current green synthesis study also attempts for the feasibility approach to reduce coastal erosion.

The influence law of concrete aggregate particle size on acoustic emission wave attenuation

Elastic waves have different attenuation laws when propagating in various materials, which is one of the important challenges in the application of non-destructive testing methods, such as acoustic emission (AE) technology in geotechnical engineering. The study presented in this paper investigated the influence mechanism of concrete composition materials and parameters on the propagation law of elastic waves using concrete specimens produced in six different particle sizes of sand or gravel. The burst AE signal was generated through the lead-breaking experiment, and ceramic piezoelectric sensors were used to record the signal waveform at different propagation distances. Through parameter analysis, spectrum analysis, and pattern recognition techniques, the influence of the concrete aggregate particle size on AE wave propagation and attenuation was revealed. The results show that the attenuation of elastic wave amplitude, energy spectral density, and frequency all were positively correlated with the aggregate particle size, and the elastic wave spectrum center of gravity generally decreased with the propagation distance. The ring count gradually decreased with the propagation distance, and the specimens with a larger aggregate particle size underwent a relatively faster ring count attenuation rate. The rise time increased rapidly with the propagation of the elastic wave, and the specimens with a larger aggregate particle size experienced a relatively rapid increase in rise time. In addition, in the feature spaces of ring count-amplitude and rise time–amplitude, the size of aggregate has an obvious influence on the distribution of these feature vector.

Experimental and Computational Investigation of Flow Fields using Accelerated Erosion Test Ring (AETR)

The erosion of the blades of hydraulic pumps and turbines, caused due to the water that has enormous suspended particles and erosive agents, is a severe global challenge among scientists and engineers. In the present work, an attempt has been made to compute the extent of erosion caused by water when it passes through devices like hydraulic machines, centrifugal pumps and turbines. Experimental and computational techniques using pitched turbine blades with 45o with the horizontal plane under down pumping condition is employed for investigation of the suspension phenomena for calculating erosion wear by sand suspended in water in river, canal on turbine, pump blades. An experimental set up, named as Accelerated Erosion Test Rig (AETR), is developed through dimensional analysis. For experimental analysis, the sand particle size and propeller dimensions were varied while running the propeller at different speeds. Experimental results revealed that the propeller speed must be maintained at an optimum value, preferably lower speeds, to ensure maximum lifting of impurities and sand particles from the base of the cylinder.

The initial fabric of undisturbed and reconstituted fluvial sand

High-quality undisturbed samples of fluvial sand were obtained from the field using the ground freezing technique. In the laboratory, the in situ void ratio of these high-quality undisturbed frozen samples was replicated using four different reconstitution methods: dry deposition, moist tamping, water sedimentation (by spooning) and slurry deposition. The initial fabric of the specimens was evaluated using X-ray micro-computed tomography and advanced image analysis. Initial fabric features were assessed in terms of the particle orientation, anisotropy, void ratio distribution and particle sizes within the specimens. Fabric analysis results suggest that none of the laboratory reconstitution techniques used captures the true three-dimensional initial fabric of undisturbed fluvial sand. However, the slurry deposition method managed to reproduce the inherent particle orientation, anisotropy and the variations of void ratio and particle sizes of the undisturbed fluvial sand. This observation explains why previous rigorous studies on the macro-mechanical behaviour of sands deposited under water have systematically demonstrated that slurry deposition is the most suitable method to reconstitute in the laboratory natural sands deposited under water. This has major implications for geotechnical testing and analyses of liquefaction of sands deposited under water such as fluvial, offshore and tailings sands.

Investigation of the material mixtures and fiber addition for 3D concrete printing

The era of Construction 4.0 is characterized by technological advances used in the construction industry. One of the advancements is the use of 3D concrete printing in construction. However, until now, the development of 3D concrete printing in Indonesia is still minimal. The main challenge is to determine the composition of the material mixtures for making the mortar, having good extrudability but still has sufficient strength. The rapid initial setting time required was also different for the concrete for typical construction. Our previous mixture composition incorporating calcium oxide to accelerate the initial setting time was adequate. However, the extrusion process was still not satisfactory. In this study, the effect of cement to sand ratio, sand particle size, and the addition of synthetic micro-fiber was investigated on the main properties of 3D printing materials, i.e., initial setting time, flowability, extrudability, and compressive strength. It was found that using smaller maximum particle size sand increases the initial setting time. The addition of synthetic microfiber reduces the strength and the workability of the mortar. However, fiber inclusion has advantages as it reduces the possibility of cracking in the printed concrete. The extruded concrete specimens were shown to have significant strength reduction due to lack of compaction, and it was affected by the direction of printing showing orthotropic properties of the 3D printed concrete.

Jet fires involving releases of gas and solid particle

The high-pressure leakage of underground pipeline could entrain the nearby sands and soils, and thus cause the jet fire of gas-solid mixtures. In addition, the thermal runaway of Lithium ion batteries could also cause a typical gas-solid jet diffusion flame. In comparison with the gaseous jet diffusion flame and the gas-solid-air jet premixed flame, the gas-solid jet diffusion flame lacks of exploration. Thus, a new facility consisting of a jet fire apparatus and a sand feeder, was designed to explore the gas-solid jet fire. The test repeatability was justified for the proposed facility. The dynamical differences of gas-solid and gaseous jet fires are clarified. It is found that the gas-solid jet fire holds a larger lift-off height, a less visible flame height and a less radiative fraction than the purely gaseous jet fire. In particular, for gas-solid jet fires at high exit velocities, the lift-off height increases, but the visible flame height and radiative fraction seem to decrease, as the particle size of sand decreases to increase the jet height of sand. (1) Inside the flame volume, the sand plays a role of heat sink to decrease the flame temperature and thus the flame burning velocity. Moreover, in the lift-off region, the sand dilutes the gas fuel and isolates the surrounding oxygen to inhibit the combustion. Both effects of sand cause a large lift-off height, especially for the sand of little particle size. (2) A large lift-off height means the increase of the air mass entrained from flame base or the portion of the premixed flame to the whole flame. In addition, the sand particle-laden flow would significantly increase the ambient air entrainment rate of fire plume. Both effects result in a less visible flame height. (3) The portion of the premixed flame increases in the bottom, which reduces the total soot amount inside the whole flame volume. The decrease of the flame temperature and the total soot amount reduces the radiative fraction. (4) The sand significantly affects the flame geometry and radiative fraction, which alters the radiant heat flux distribution and challenges the development of thermal radiation model for gas-solid jet fires. The gas-solid jet fire holds a less peak radiant heat flux but a higher positon of peak radiant heat flux than the gaseous jet fire. In addition, the line source radiation model available in literature is revised to well predict the radiant heat flux distribution of the gas-solid jet fires.

Sand Particle Size and Phosphorus Amount Affect Rhizophagus irregularis Spore Production Using In Vitro Propagated Spore as a Starter Inoculum in Rhizosphere of Maize (Zea mays) Plantlets.

Microbial inoculants, particularly arbuscular mycorrhizal (AM) fungi, have great potential for sustainable crop management. In this study, monoxenic culture of indigenous R. irregularis was developed and used as a tool to determine the minimum phosphorus (P) level for maximum spore production under the in vitro conditions. This type of starter AM fungal inoculum was then applied to an in vivo substrate-based mass-cultivation system. Spore production, colonization rate, and plant growth were examined in maize (Zea mays L.) plant inoculated with the monoxenic culture of R. irregularis in sand graded by particle size with varying P levels in nutrient treatments. In the in vitro culture, the growth medium supplemented with 20 µM P generated the maximum number of spores (400 spores/mL media) of R. irregularis. In the in vivo system, the highest sporulation (≈500 spores g−1 sand) occurred when we added a half-strength Hoagland solution (20 µM P) in the sand with particle size between 500 µm and 710 µm and omitted P after seven weeks. However, the highest colonization occurred when we added a half-strength Hoagland solution in the sand with particle sizes between 710 µm and 1000 µm and omitted P after seven weeks. This study suggests that substrate particle size and P reduction and regulation might have a strong influence on the maximization of sporulation and colonization of R. irregularis in sand substrate-based culture.

Size effect on contact behavior in DEM simple shear tests

The 2–2.5 times the simulated sand diameter is widely accepted in giving reasonable DEM simulation results for geotechnical testing. However, it neglects the effect of a specimen height to maximum particle diameter ratio in a specific laboratory test, which may lead to a strong stress concentration and flawed simulations. This study compared laboratory simple shear tests with corresponding DEM simulations with different particle sizes. The DEM model used clump rings to simulate physical rings in the test, and decreased the additional stress applied by the widely used wall-type rings. Results showed that (1) DEM models with tested particle size and twofold sand particle size (1D and 2D tests) can better capture the tested stress–strain behavior, volumetric changes, and noncoaxiality, the 4D model has an asymmetrical distribution of contact force and contact number, indicating the specimen is inhomogeneous and has a strong stress concentration. (2) a specimen height to maximum particle diameter ratio smaller than 10 (it is greater than 10 in the ASTM D6528) could provide reasonable macro-meso mechanical behaviors. Similar studies should be carried out after trial tests on determining a reasonable specimen height to maximum particle diameter ratio under the guidance of ASTM D6528.

Correlation Analysis between Color and Grain Size of Sand Using a Colorimeter

Nam, J.; Hong, S.; Lee, Y., and Kim, I., 2021. Correlation analysis between color and grain size of sand using a colorimeter. In: Lee, J.L.; Suh, K.-S.; Lee, B.; Shin, S., and Lee, J. (eds.), Crisis and Integrated Management for Coastal and Marine Safety. Journal of Coastal Research, Special Issue No. 114, pp. 201–205. Coconut Creek (Florida), ISSN 0749-0208. To determine the cause of coastline changes, it is necessary to monitor various parameters such as wave data, changes in water depth, seabed topography and quality, as well as sea currents. This study aims to derive a correlation between grain size and color of sand on a coast undergoing erosion in Namae 3-ri∼Sodol beach. Therefore, for a period of six years (2013 to 2018), the depths of the foam zone, the breaking band, and other factors were divided for each cross-base line (DL(±) 0.00 m, DL(-) 3.00 m, DL(-) 6.00 m, and DL(-) 9.00 m). Seabed samples were collected from four vertices, and the median particle size and color characteristics of sand were recorded. Results showed that the average D50 particle sizes for DL(±) 0.00 m, DL(-) 3.00 m, DL(-) 6.00 m, and DL(-) 9.00 m were 0.615 mm, 0.432 mm, 0.416 mm, and 0.410 mm, respectively. In addition, the color of the sand that was passed through the colorimeter is represented by L* (white-black), a* (green-red), and b* (yellow-blue); these colors were expressed as a number to present a unique value. DL(±) 0.00 m = L* 61.12082, a* 5.757663, b* 17.93326; DL(-) 3.00 m = L* 61.81803, a* 5.03382, b* 16.79151; DL(-) 6.00 m = L* 61.74719, a* 4.886109, b* 16.54382; and DL(-) 9.00 m = L* 61.70353, a* 4.815222, and b* 16.42189. Furthermore, the sand color values a* and b* were coordinated, distributed on the beach, and then a color range converted to the value of the radius of the polar coordinate (r) was presented and compared with the particle size. To compare the a* and b* values with the sand particle size, r is expressed as a first-order function. The R-square of the first-order function was 0.9411, which was found to be highly reliable, and the exponential function was found to have a reliability of 0.5573. This result shows that the a* and b* values can be inferred according to the particle size of the sand.