Sands Of Different Grain Sizes Research Articles

The simultaneous passivation of arsenic and cadmium in contaminated soil through combined use of schwertmannite and calcium carbonate

Schwertmannite was proved to be an efficient material for the remediation of arsenic-contaminated soil. Given that arsenic (As) and cadmium (Cd) coexist in soils and have opposite chemical behaviors, stabilizing them simultaneously is challenging. Here, we reported a compound passivating agent (AMSC) which simultaneously passivated As and Cd in contaminated site soil containing 1659 mg/kg As and 32.26 mg/kg Cd. It consisted of alkali-modified schwertmannite (denoted as AMS) capable of preferentially adsorbing As and fine calcium carbonate (denoted as C) for mainly stabilizing Cd. It was found that the addition of AMSC into the contaminated soil at 5 % for 60 days could drastically reduce water-extractable As and TCLP-As concentrations by over 84 %, and water-extractable Cd and TCLP-Cd concentrations by over 94 %, respectively, due to the conversion of the labile fraction of As or Cd into more stable fractions. Additionally, pH in the AMSC-amended soil was increased to 6.74 from initial 4.50. As was mainly adsorbed into schwertmannite of AMSC by ligand exchange of SO42- with As, while Cd was jointly passivated mainly by calcium carbonate and fewly by schwertmannite. To identify the mineral phase changes of AMSC, quartz sands of different grain sizes were selected for Mössbauer analysis. The percentage of schwertmannite in the sediment amended with AMSC decreased slightly from 51.1 % to 48.9 % within 30 days, while Fe(III) oxyhydroxide (48.9 %) was converted to ferrihydrite (30.3 %) and lepidocrocite (20.8 %), respectively. Therefore, it was expected that AMSC could act as a high-performance and environmentally-friendly amendment to remediate As and Cd-contaminated soils.

Experiments reveal effects of particle and pore-scale heterogeneity on thermal dispersion during porous media heat transport

The growing applications of heat transport in engineering and hydrogeology, including ground source heat pump systems and the assessment of water flow and sediment thermal properties, necessitate precise thermal dispersion modeling. Despite various factors like particle size, shape, and distribution impacting dispersion in porous media, a lack of experimental data and analysis has limited our grasp of the relationship between flow velocity and thermal dispersion. To address this gap, we conducted solute and heat tracer experiments using sands of different grain sizes, employing analytical models based on a universal power law relationship for dispersion. Additionally, we systematically compiled dispersion data from the scientific literature to assist in interpreting of the effects of particle size, shape, and pore-scale heterogeneity on dispersion. Our findings reveal that solute and thermal longitudinal dispersion align for high flow velocities in the dispersion-dominated flow regime (Pe > 5), where the velocity-dispersion relationship is linear. However, in the transition regime (advection approx. equal to diffusion, 0.1–0.3 < Pe < 5), the observed deviation from linearity (R2<0.9) is linked to increased pore-scale heterogeneity, particularly in smaller particle sizes. This study underscores the pivotal role of thermal dispersion and underscores the need for caution when estimating thermal dispersion based on solute dispersion, given the intricate nature of real-world conditions and the potential influence of factors such as grain size distribution and pore-scale heterogeneity in natural porous materials.

Sand-geogrid interfacial shear response revisited through additive manufacturing

Though it is known that the geometric features of geogrids are crucial for deriving optimal interface shear strength, not much work is done to optimize the size and shape of the apertures relative to the particle size of the soils in contact. Most of the commercial geogrids have rectangular or square apertures, which are many times bigger than the soil particles. The present study explores the effects of aperture size and shape of geogrids relative to the size of the sand particles on their interface shear response through direct shear tests and digital image analysis. Geogrids of different aperture sizes and shapes were manufactured using a 3D printer. Shear tests were carried out on three sands of different grain sizes interfacing with geogrids of five different aperture sizes and three different aperture shapes. Through these tests, interface shear response with a wide range of aperture ratio and different shapes of geogrids is understood. Shear zone thickness of different sand-geogrid interfaces was computed through Particle image velocimetry (PIV). Based on the tests and analyses, triangular apertures are found to be more efficient compared to other apertures. The optimal range of aperture ratio is found to be 2–11.29.

Investigation of the effect of grain size on liquefaction potential of sands

Due to the permanent damage to structures during earthquakes, soil liquefaction is an important issue in geotechnical earthquake engineering that needs to be investigated. Typical examples of soil liquefaction have been observed in many earthquakes, particularly in Alaska, Niigata (1964), San Fernando (1971), Loma Prieta (1989), Kobe (1995) and Izmit (1999) earthquakes. In this study, liquefaction behavior of uniform sands of different grain sizes was investigated by using the energy-based method. For this purpose, a total of 36 deformation-controlled tests were conducted on water-saturated samples in undrained conditions by using the cyclic simple shear test method and considering the relative density, effective stress and mean grain size parameters that affect the cumulative liquefaction energy. The results showed that as the mean grain size decreases, the liquefaction potential of the sand increases. In addition, with increasing effective stress and relative density, the resistance of sand against liquefaction decreases. Multiple regression analysis was performed on the test results and separate correlations were proposed for the samples with mean grain size of 0.11-0.26 mm and for the ones with 0.45-0.85 mm. The recommended relationships were compared to the ones existing in the literature and compatible results were obtained.

Hydrostratigraphy and Its Relation to Ground-Water Potentiality of an Area of the Ganges River Delta in Bangladesh

To identify the potential groundwater bearing zones for future groundwater resources development of the study area, an investigation has been made using lithology, groundwater monitoring and elevation data. The stratigraphic cross-sections of the area reveal six distinct hydrostratigraphic features viz. clay-silt-sand, fine sand, fine to medium sand, medium sand, medium to coarse sand and coarse sand. On the basis of lithological information, the groundwater bearing zone of the area has been divided into two main hydrostratigraphic units viz. aquitard and aquifer, which consist of clay-silt-sand and sands of different grain sizes respectively. The aquifer zone is further divided into two categories: “small scale aquifer” made dominantly of fine and “main aquifer” comprising of fine-medium to coarse sand. The annual fluctuation of water table in the study area is observed from 4.9 m to 5.6 m. The area is demarcated as three different groundwater bearing zones based on Catastrophe theory using GIS.

Effects of grain size and gradation on the dynamic responses of quartz sands

The dynamic compression responses of quartz sands of different grain sizes and gradations are tested with a modified spilt Hopkinson pressure bar in which a single-pulse loading system is implemented. The yield stresses, the compressibility and the energy-absorption densities of the granular materials are calculated from the compression curves. The effects of the grain size and the gradation on those dynamic macro responses are investigated and presented. The grain size distributions of the samples after loading are obtained with a laser diffractometry instrument, and are analyzed quantitatively with the Hardin relative breakage index. The effects of the grain-scale properties on the dynamic macro responses of granular materials can be interpreted well with the particle breakage mechanism. The Theoretical analyses show that the energy-absorption density and the particle breakage extent are linearly related to the logarithm of axial stress respectively, and the slopes are both proportional to the compressibility. Moreover, a simple model for predicting the dynamic energy-breakage efficiency of the granular materials is derived. Based on the discrete element method (DEM), simulation of the granular material under one-dimensional dynamic compression is conducted to further interpret the experimental results. The size dependence of the coordination number of grains and its influence on particle breakage is discussed.

Effects of sand grain size and morphological traits on running speed of toad-headed lizard Phrynocephalus frontalis

We conducted a manipulative experiment to investigate the influential factors of locomotor ability in steppe toad-headed lizards. By using a video-base method, we measured running speed of the lizards when they run on sands of different grain sizes. We also considered body condition, tail length and sex as fixed factors to analyze their effects on running speed of the lizard. Results showed that running speed of the lizard significantly differed among different trials of sand grain size. Specifically, the peak and the nadir values of the running speed were found on sands of 0.5–1 mm and 0.075–0.25 mm grains, respectively. When lizards ran on sands of different grain size their running speed changed significantly. Body condition and tail length also had significant effects on running speed. The findings indicated that locomotor ability of lizards depended on both body condition and the external environment. We hypothesized that sand grain size is one of the factors that influence the habitat selection in steppe toad-headed lizards. Moreover, this lizard may be used as an indicator of the development of sand dunes.

Incorporation of Dynamic Capillary Pressure into the Green–Ampt Model for Infiltration

The Green–Ampt model describes infiltration of water into soil. A sharp front separates the saturated from the unsaturated zones, and capillary pressure is assumed to remain constant during infiltration. We generalized this model to account for a capillary pressure that depends on the flow velocity. Based on dimensional analysis and physical considerations, we posited a functional form for dynamic capillary pressure and assumed the nonequilibrium capillary pressure to depend on the capillary number in the form of a power law. Our model for dynamic capillary pressure describes measurements of capillary pressure versus Darcy velocity by D.A. Weitz et al. and S.L. Geiger and D.S. Durnford. Moreover, the dimensional analysis allows us to collapse three dynamic capillary pressure curves that Geiger and Durnford measured for sands of different grain size onto one curve. Furthermore our model describes capillary rise experiments performed by T. Tabuchi well. We also derived an implicit analytical solution for the front velocity.

Laboratory measurements of non-Darcy flow coefficients in natural and artificial unconsolidated porous media

The estimation of non-Darcy flow regime is often a critical issue in petroleum engineering, as it is a key parameter to estimate and predict the correct production performances and behavior of hydrocarbon reservoirs. Non-Darcy flow is typically observed in gas wells when the fluids converging to the wellbore attains the velocity peculiar of turbulent flow. As a consequence, pressure drop around the wellbore cannot be estimated from the classic Darcy's law, where the pressure gradient is a linear function of the flow velocity. In fact, the use of Darcy's law would lead to inaccurate production performances evaluation. The most commonly used tool to approximate the non-linear behavior of the flow velocity is the well-known Forchheimer equation, deploying the “inertial” coefficient β that can be estimated experimentally, by means of direct measurements on core samples. In gas wells the inertial coefficient β is usually estimated by means of indirect measurements, through the analysis of multi-rate pressure tests performed on site during the routine well testing programmed after well completion. Unfortunately, such data are not easily available in many cases, and new measurements are very expensive, since well testing is accomplished by gas production shutdown for several tens of hours or days. So, it is a common practice to use particular theoretical and empirical correlations that can be derived by exploiting experimental values of the inertial coefficient. This experimental study reports non-Darcy flow laboratory investigations performed on natural and artificial unconsolidated porous media (glass beads and loose natural sands of different grain size). The inertial coefficient β and permeability has been calculated for several samples (with both peaked and flat grain size distribution, obtained by sieving glass beads and sand); experimental data suggest that also β is to some extent affected by pore structure. Moreover, the Forchheimer number has been calculated and its non-linearity with respect to superficial velocity has been checked. In the light of the above, specific laboratory equipment has been devised in order to rely on a wide range of flow rates under appropriate pressure gradients.

Solute mixing during imbibition and drainage in a macroscopically heterogeneous medium

We studied the flow of water and the transport of solutes in a heterogeneously packed sand tank by performing transport experiments with a fluorescent tracer. The packing consisted of an inclined, layered sand bedding characterized by a large number of thin layers of three quartz sands of different grain sizes. The purpose was to evaluate to which extent the preceding wetting‐draining history affects the mixing of solutes in presence of textural heterogeneities. We irrigated the surface at stepwise increased flow rates (imbibition) and afterward at stepwise decreased flow rates (drainage). At each step the flow rate was kept constant to monitor the transport and spreading of several tracer plumes in the stationary flow field. The results show that during imbibition, mixing at the textural boundaries is hindered and the solutes are funneled through connected preferential flow paths. During drainage we observed enhanced mixing resulting in a definitely less heterogeneous transport regime. These results stress the role of the preceding wetting‐draining history for determining the characteristics of solute transport in heterogeneous media. We demonstrate this using the integral mixing characteristics “dilution index” and “reactor ratio,” which quantify the degree of preferentiality of flow and transport.

Transport and degradation of phytoplankton in permeable sediment

In flume and field experiments we demonstrate that interfacial water flows, generated when bottom currents interact with sea bed topography, provide a fast and efficient pathway for the transport of suspended phytoplankton into subsurface layers of permeable sandy sediments. The advective transport, associated with small mounds and ripples as commonly found on shelf sediments, increased penetration depth of unicellular algae (Dunaliella spec.) into sandy sediment (permeability k = 4 × 10−11 m2) up to a factor of 7 and flux up to a factor of 9 relative to a smooth control sediment. The pore water flow field produced a distinct distribution pattern of particulate organic matter in the sediment with subsurface concentration maxima and zones depleted of algae. Flux chamber simulations of advective transport of algae into sands of different grain sizes revealed increasing fluxes, algal penetration depths, and degradation rates with increasing permeability of the sediment. Two experiments conducted in intertidal sand flats confirmed the importance of the advective interfacial transport of phytoplankton for natural settings, showing permeability‐dependent penetration of planktonic algae into embedded sand cores of different grain sizes. The significance of our results is discussed with respect to particulate organic matter flux and mineralization in shelf sands, and we suggest the concept of a decomposition layer.

GPR modeling study in a contaminated area of Krzywa Air Base (Poland)

Krzywa Air Base is a former Soviet military base which is highly polluted because of soil contamination during the dismantling of fuel tanks after the 1990 political changes in the U.S.S.R. The contaminated sites are indicated as magazines 1 and 2 in Figure 1. The area is located within the pre‐Sudetic block, where Tertiary and Quaternary deposits lie on Mesozoic crystalline basement. The deposits consist of sands of different grain sizes, gravels, clays, and interbedded silts, with a total thickness ranging from 80 to 100 m. In the extreme cases, the pollution is so intense that the spilled fuel can be extracted in the system of drainage wells. In general, the contamination can be correlated with the geologic structure. As a prelude to acquisition of field data, we simulate and evaluate the expected ground‐penetrating radar (GPR) responses for uncontaminated and contaminated layers.

Fluid Flow Across Capillary Heterogeneities, Experiments and Simulations

A comparative study of numerical modelling and laboratory experiments of two-phase immiscible displacements in a 33 cm × 10 × 3 cm thick cross-bedded reservoir model is reported. Dynamic two-dimensional fluid saturation development was obtained from experiments by use of a nuclear tracer imaging technique and compared to numerical predictions using a full-field black oil simulator. The laboratory cross-bedded reservoir model was a sandpack consisting of two strongly waterwet sands of different grain sizes, packed in sequential layers. The inlet and outlet sand consisted of low permeable, high capillary, sand while the central crosslayer with a dip angle of 30° was a high permeable, low capillary, sand. Results on moderate contrasts in permeability and capillary heterogeneities in the cross-bedded reservoir model at different mobility ratios and capillary number floods temporarily showed a bypass of oil, resulting in a prolonged two-phase production. The final remaining oil saturations, however, were as for isolated samples. Hence, permanently trapped oil was not observed. Simulations of waterfloods, using a commercial software package, displayed correct water breakthrough at low flow rate and unity viscosity ratio, but failed in predicting local saturation development in detail, probably due to numerical diffusion. The simulator was used to test several cases of heterogeneity contrasts, and influence from different relative permeability curves. Further, by altering the capillary pressure at the outlet, the end effects were proven important.

APPARATUS AND PROCEDURE FOR THE DEMONSTRATION OF GROUNDWATER FLOW AND CONTAMINANT TRANSPORT PROCESSES TO CHILDREN

Environmental education is currently encouraged within our society. Understanding and appreciation of processes and principles of natural systems should begin with education programs for children and young people. With the objective of providing an awareness of groundwater flow and contamination processes a hands-on demonstration for school children was developed. Small groundwater models (easily carried by one person) were fabricated from acrylic and filled with sands of different grain sizes. A water well was installed at the end of each model. Water, highlighted with food dyes, flowed through the sand and was pumped from the model well.The demonstration was successfully used during a science and engineering summer camp (SCI-FI) with 400 children. SCI-FI is a summer program for school children (ages 9–14) developed and operated by undergraduate engineering students at the College of Engineering, University of Saskatchewan. The children were given the problem of selecting a site for a town garbage dump...

Experience in using sands of different grain size for concretes of the Sayano-Shushenskoe hydroelectric station

1. For preparing hydrotechnical concretes it is permissibleto use fine sands, provided the correct assignment of the content. Relatively low contents of fine sands require reliable operation of the proportioning devices and efficient control of the technology of preparing the concrete mix. 2. The relation between the content and size of sand in concrete is nonlinear, which must be taken into account when designing concrete mixes, especially with coarse and fine sand. 3. When using sands of a quarry having large variations of size and specific surface it is necessary at the stage of designing concrete mixes to experimentally determine the optimum contents of sand in the entire range of possible variations of size. The relations between the content of sand and its size established on the basis of this work permit prompt correction of production compositions when preparing the concrete mix. 4. Consideration of fraction 2.5–5 mm separately as a fine component of coarse aggregate permits a more accurate assignment of cement content in concrete.

Membrane Penetration in Triaxial Tests

Interpretation of data of the writers and other investigators relating to volume changes due to membrane penetration in sands of different grain sizes has led to the following conclusions: 1. Volume changes due to membrane penetration are influenced by the following primary factors: (a) Grain size; (b) effective confining pressure; (c) density index; and (d) geometry of sample. 2. These volume changes can be predicted with reasonable accuracy. 3. The effect of membrane penetration can be considerably minimized by adopting large diameter test samples, and with other parameters remaining constant. (Author)

Sterile Culture of Excised Tomato Roots in Sands of Different Grain Size

A simple technique to grow excised tomato roots in sand in sterile culture is described. The apparatus consists of a culture tube filled with sand linked to a small flask containing the nutrient solution. By raising the lower-placed flask the sand is flushed with solution, thereby replenishing nutrients at the root surface. Lowering the flask again allows air to enter the sand, thus effecting sufficient aeration. It is further demonstrated that growth of the roots is related to acration and not to mechanical impedance in sands of different grain size.