Coarse Sand Particles Research Articles

砂土粒间胶结性对砂土力学性质影响的三轴实验研究

本文采用对砂土进行胶结的混合法，在砂土中掺入硅酸盐水泥制成不同水泥含量的人工胶结砂土试样，通过对试样进行三轴固结排水剪切试验，研究砂土颗粒间的胶结对砂土强度特性，应力-应变特性及体积变形特性的影响。研究表明，同一围压下试样水泥含量越高粗砂粒间的胶结越强，试样的峰值强度越大；但同一围压下不同水泥含量试样的残余强度接近相等。同一围压下，试样水泥含量越高砂粒间的胶结越强，试样的初始压缩模量越大，应变软化越明显。试样水泥含量越高粗砂粒间的胶结越强，在低围压下排水剪切时越容易发生剪切膨胀，低围压下排水剪切时的体应变也越大。 In this paper, the mixing method is adopted to cement sand, and artificial cement sand samples of different cement content are made by mixing Portland cement with sandy soil. Triaxial consolidation drained shear tests on these sand samples are carried out to study effects of the cementation between sand particles on strength characteristics, stress-strain characteristics and the volume change characteristics. Studies show that under the same confining pressure, the higher the cement content and the stronger the bonding between the coarse sand particles, the bigger the peak shear strength of the artificial cement sand samples, but the residual shear strength of samples of different cement content is approximately equal. The higher the cement content and the stronger the bonding between the coarse sand particles, the bigger the initial compression modulus and the more obvious strain softening of the samples of different cement content under the same confining pressure. The higher the cement content and the stronger the bonding between the coarse sand particles, the more easily the artificial cement sand samples to dilate and the bigger the volumetric strain of these samples.

Depositional evidence of palaeofloods during 4.0–3.6 ka BP at the Jinsha site, Chengdu Plain, China

At the Jinsha site it has been discovered, through field surveys and observations of the geomorphology and sedimentology, that the direction of flow of ancient rivers, obtained through debris fabric measurement, was consistent with the direction in which buried palaeotrees had been broken, indicating that the Jinsha site possibly suffered palaeofloods. By sampling the suspected palaeoflood sediments at the Jinsha site and analysing their grain size distribution and Zr/Rb and Ba/Nb ratios, the paper discovered that the sediments tend to be composed of coarse particles, with a relatively high percentage of traction load components and saltation load components. Various samples had relatively great differences in particle size distribution; the change in the percentage content of coarse sand particles being very obvious, and the sedimentary particles exhibiting upward coarsening within the same layer. The Zr/Rb ratios and Ba/Nb ratios of the sediments reflect the changes in hydrodynamic forces within the sedimentary environment. When the hydrodynamic force was relatively weak, the Zr/Rb ratios are relatively low and the Ba/Nb ratios relatively high; whereas when the hydrodynamic force was strengthened, the Zr/Rb ratios increase and the Ba/Nb ratios decrease. On account of these sedimentological and geochemical characteristics, these sediments are judged to be palaeoflood sediments. The AMS 14C dating results of the palaeoflood sediments shows that the period when sudden flooding occurred frequently in the Chengdu Plain was 4.0–3.6 ka BP, contemporaneous with an ancient global flooding event. This palaeoflood event probably brought about the extinction of the Baodun Culture.

A study on the wind erosion potential of agricultural lands after crop harvesting (Case study: Damghan Region)

Aeolian process and subsequently soil erosion are key factors in dryland environments. Such phenomena are related not only to geoecological factors (lithology, topography, and climatology) but also to land-use and plant cover changes. Formation of new sand dunes in Damghan explains the development of human activities over the past. The aim of this study is to explain the land use changes and their contributions and impacts on Aeolian sediments in Damghan Region. The study was carried out using topographic and geologic maps, satellite imagery, aerial photographs, meteorological data, field observation and samplings. According to meteorological data, period of strong winds (May to Jun) were identified. This period is wind activity period. So, based on this period, unprotected soil surface by crop residues with the interpretation of satellite images was determined. The field samples were carried out from May to June 2008 when the wind was active. The study methods include sieving soil granulometry, and analyzing the particle size. Granulometric analyses were performed using conventional dry sieve method. The results of statistical analysis of grain size distribution showed that the mean and median of particle size were composed of coarse and very coarse sand particles. The study indicated that 90% of the agricultural lands contained more than 23% soil aggregates, where in areas with sensitive particles to erosion the Figure was 35%. It can be argued that agricultural land in study area are resistant to wind erosion.

Durability to Chemical Attack by Acids of Epoxy Microconcretes by Comparison to Cementitious Ones

This research deals with the durability of micropolymer concrete (MPC) obtained by mixing an epoxy resin with fine and coarse sand particles. In particular the resistance of the micropolymer concrete to chemical solutions (citric acid C6H8O7, sulfuric acid H2SO4, and hydrochloric acid HCl) is investigated and compared to this of Portland cement microconcrete. Two MPC are tested. The first is formulated with 9% mass fraction of epoxy polymer whereas calcareous fillers have been incorporated in the second formulation in order to reduce the percentage of the epoxy binder. It is shown that a microconcrete designed with 7% of epoxy, 10% of fillers, and 83% of aggregates is characterized by higher physical and mechanical properties than those of the MPC formulated with 9% of epoxy binder. The mechanical properties of the resulting materials after their exposure to the three selected acid solutions at different durations were studied through compressive, three points bending and ultrasonic wave propagation tests. The obtained results are compared to those of microcement concretes (MCC) tested under the same conditions as MPC. The results show that both microepoxy polymer concretes exhibit better mechanical properties and highest resistance to chemical attack than the microcement concrete.

Experimental evidence of statistical ensemble behavior in bed load sediment transport

AbstractA high‐resolution data set obtained from high‐speed imaging of coarse sand particles transported as bed load allows us to confidently describe the forms and qualities of the ensemble distributions of particle velocities, accelerations, hop distances, and traveltimes. Autocorrelation functions of frame‐averaged values (and the decay of these functions) support the idea that the forms of these distributions become time invariant within the 5 s imaging interval. Distributions of streamwise and cross‐stream particle velocities are exponential, consistent with previous experiments and theory. Importantly, streamwise particle velocities possess a “light” tail, where the largest velocities are limited by near‐bed fluid velocities. Distributions of streamwise and cross‐stream particle accelerations are Laplace in form and are centered on zero, consistent with equilibrium transport conditions. The majority of particle hops, measured start to stop, involve short displacements, and streamwise hop distances possess a Weibull distribution. In contrast to previous work, the distribution of traveltimes is exponential, consistent with a fixed temporal disentrainment rate. The Weibull distribution of hop distances is consistent with a decreasing spatial disentrainment rate and is related to the exponential distribution of traveltimes. By taking into account the effects of experimental censorship associated with a finite sampling window, the relationship between streamwise hop distances and traveltimes, , likely involves an exponent of α ∼ 2. These experimental results—an exponential distribution of traveltimes Tp and a Weibull distribution of hop distances Lx with shape parameter k < 1—are consistent with a nonlinear relationship between these quantities with α > 1.

SEDIMENTOLOGICAL ANALYSES OF EGGSHELL TRANSPORT AND DEPOSITION: IMPLICATION AND APPLICATION TO EGGSHELL TAPHONOMY

The interpretation of fossil eggshells can be problematic because eggshells may be transported by hydraulic flow in floodplains, making it difficult to interpret the reproductive behavior and ecology of parent animals. A series of flume studies was conducted to establish analytical techniques for assessing eggshell hydraulic transport in the fossil record. We investigated preferred eggshell orientation after transport, the relationship of flow competence with eggshell height and volume, and the size of clastic sediment expected to be associated with transported eggshells. Goose, emu, and ostrich eggshell fragments were released in a flume with decelerating flow. The transport of each eggshell was observed five times on each of four substrates (coarse sand, sparse gravel, dense gravel, and polyvinyl chloride). At eggshell deposition, eggshell orientation and flow depths were recorded. Critical bed shear stress for eggshell deposition was estimated based on the flow depth at the point of eggshell deposition, tested relative to eggshell height and volume, and used to estimate the size of hydraulically equivalent particles. The probability of concave-down orientation after transport was > 85% regardless of eggshell type or substrate. The bed shear stress at eggshell deposition reflected the eggshell height and volume. The estimated size of hydraulically equivalent particles was coarse sand or larger. A high proportion of concave-down eggshells in a fossil assemblage may indicate transport. In addition, eggshells may be sorted according to their height and volume. Coarse sand or larger particles observed in a matrix of fossil eggshells may suggest eggshell transport.

The influence of grain size, grain color, and suspended-sediment concentration on light attenuation: Why fine-grained terrestrial sediment is bad for coral reef ecosystems

Sediment has been shown to be a major stressor to coral reefs globally. Although many researchers have tested the impact of sedimentation on coral reef ecosystems in both the laboratory and the field and some have measured the impact of suspended sediment on the photosynthetic response of corals, there has yet to be a detailed investigation on how properties of the sediment itself can affect light availability for photosynthesis. We show that finer-grained and darker-colored sediment at higher suspended-sediment concentrations attenuates photosynthetically active radiation (PAR) significantly more than coarser, lighter-colored sediment at lower concentrations and provide PAR attenuation coefficients for various grain sizes, colors, and suspended-sediment concentrations that are needed for biophysical modeling. Because finer-grained sediment particles settle more slowly and are more susceptible to resuspension, they remain in the water column longer, thus causing greater net impact by reducing light essential for photosynthesis over a greater duration. This indicates that coral reef monitoring studies investigating sediment impacts should concentrate on measuring fine-grained lateritic and volcanic soils, as opposed to coarser-grained siliceous and carbonate sediment. Similarly, coastal restoration efforts and engineering solutions addressing long-term coral reef ecosystem health should focus on preferentially retaining those fine-grained soils rather than coarse silt and sand particles.

Interaction studies between high-density oil and sand particles in oil flotation technology

Abstract In the event of a sand contamination, the first course of action would be to ensure that a successful flotation is through the detachment of oil from sand for the ease of flotation. It is widely recognized that the initial oil–sand contact is crucial for oil removal and recovery. Due to its high viscosity and adhesive nature, high density bunker oil could pick up any silica particles (sand) of any size at a short contact time as low as several milliseconds. Nevertheless, the resulting detachment of sand particles from oil would vary under different conditions. Therefore, this study aims at investigating the interactions between oil and sand to further understand the detachment process between oil and sand in a flotation process under various conditions including pH, temperature, sand particle size and wettability. An increase in the water content in the sand sample from 0 wt% to 12 wt% aids the liberation of oil from contaminated sand from 0.7% to 65%, due to the presence of thin film of water which weakens the attachment forces between the oil and sand particles. On the other hand, the coarse sand particles of 1.0 mm easily detach themselves from the oil layer compared to finer sand particles of 0.125 mm which implicate that the attachment forces between oil and sand particles increase with the decrease in sand particle size. An increase in the solution pH from pH 6 to pH 14 and temperature from 20 °C to 60 °C also showed an increase in the sand detachment efficiencies from 25.1% to 60.9%, and from 15.2% to 85.1% respectively for 1 mm sand particle size. Further verification experiments including the differential zeta potential results and the DLVO theory supported the results of these former detachment studies, whereby differential zeta potential results showed that increase in pH increased the repulsive forces between particles, while the increase in temperature did not significantly affect the interparticle forces. Hence, the enhanced detachment efficiency due to increase in temperature is mainly attributed to the decrease in oil viscosity which reduces the adhesiveness of bunker oil which also facilitates oil liberation. Finally, the results are in good agreement with the oil flotation efficiencies.

Investigation of flame propagation over an inclined fuel wetted porous bed

This experimental study was conducted to investigate the rate of flame spread over an inclined porous solid (sand) wetted with finite quantities of fuel (iso-propanol). The study comprised experiments that were conducted over 15° and 30° inclined beds with depths ranging from 13.3mm to 39.9mm and consisting of average sand particle diameters ranging from 0.5mm to 5mm under quiescent, assisted and opposed airflow conditions.Analysis of the resulting data indicate that the rate of flame spread is significantly decreased by increasing the bed inclination angle or the airflow velocity and is applicable for both assisted and opposed directions. Furthermore, the rate of flame spread is decreased to the minimum value and actually ceased halfway along the bed with a 30° inclination angle. This behaviour was observed mainly for beds containing coarse sand particles. The rate of flame spread was higher for thinner beds rather coarse beds under any given airflow conditions. Finally, the rate of flame spread in upward direction was relatively quicker in comparison with downward direction counterpart.

Sands at Gusev Crater, Mars

Processes, environments, and the energy associated with the transport and deposition of sand at Gusev Crater are characterized at the microscopic scale through the comparison of statistical moments for particle size and shape distributions. Bivariate and factor analyses define distinct textural groups at 51 sites along the traverse completed by the Spirit rover as it crossed the plains and went into the Columbia Hills. Fine-to-medium sand is ubiquitous in ripples and wind drifts. Most distributions show excess fine material, consistent with a predominance of wind erosion over the last 3.8 billion years. Negative skewness at West Valley is explained by the removal of fine sand during active erosion, or alternatively, by excess accumulation of coarse sand from a local source. The coarse to very coarse sand particles of ripple armors in the basaltic plains have a unique combination of size and shape. Their distribution display significant changes in their statistical moments within the ~400 m that separate the Columbia Memorial Station from Bonneville Crater. Results are consistent with aeolian and/or impact deposition, while the elongated and rounded shape of the grains forming the ripples, as well as their direction of origin, could point to Ma'adim Vallis as a possible source. For smaller particles on the traverse, our findings confirm that aeolian processes have dominated over impact and other processes to produce sands with the observed size and shape patterns across a spectrum of geologic (e.g., ripples and plains soils) and aerographic settings (e.g., wind shadows).

Force measurement and calculation of the large immersed particle in dense gas–solid fluidized bed

Abstract The force characteristic of the large immersed particle in the dense gas–solid fluidized bed is the significant foundation to study the kinetic behavior of the large particle. We designed three steel balls with the density of 7500 kg/m 3 and the mean diameters of 8 mm, 10 mm, and 12 mm as the basic investigated objects. The coarse-sand particles and fine-glass powders were employed as different types of fluidized mediums. We used the self-designed measurement system to measure the force values of different steel balls with variable gas velocities, and the fluctuation characteristic of the forces was obtained finally. The experimental measurement results indicate that the force fluctuation of the large immersed particle with different diameters basically keeps stable after achieving the complete fluidization of the gas–solid fluidized bed. Meanwhile, the results show that the force fluctuation of the same large immersed particle is more stable when the coarse-sand particles are selected as the fluidized medium. The approach of theoretical calculation and numerical simulation has been combined to validate the reliability of measurement results. The comparison conclusions indicate that the measurement results agree well with the calculation and simulation results.

A probabilistic description of the bed load sediment flux: 2. Particle activity and motions

High‐speed imaging of coarse sand particles transported as bed load over a planar bed reveals that the particle activity, the solid volume of particles in motion per unit streambed area, fluctuates as particles respond to near‐bed fluid turbulence while simultaneously interacting with the bed. The relative magnitude of these fluctuations systematically varies with the size of the sampling area. The particle activity within a specified sampling area is distributed in a manner that is consistent with the existence of an ensemble of configurations of particle positions wherein certain configurations are preferentially selected or excluded by the turbulence structure, manifest as patchiness of active particles. The particle activity increases with increasing bed stress far faster than does the average particle velocity, so changes in the transport rate with changing stress are dominated by changes in the activity, not velocity. The probability density functions of the streamwise and cross‐stream particle velocities are exponential‐like and lack heavy tails. Plots of the mean squared particle displacement versus time may ostensibly indicate non‐Fickian diffusive behavior while actually reflecting effects of correlated random walks associated with intrinsic periodicities in particle motions, not anomalous diffusion. The probability density functions of the particle hop distance (start‐to‐stop) and the associated travel time are gamma‐like, which provides the empirical basis for showing that particle disentrainment rates vary with hop distance and travel time.

A probabilistic description of the bed load sediment flux: 4. Fickian diffusion at low transport rates

High‐speed imaging of coarse sand particles transported as bed load reveals how particle motions possess intrinsic periodicities associated with their start‐and‐stop behavior. The dominant harmonics in these motions have a primary influence on the rate at which the mean squared particle displacementR(τ) — a measure conventionally used to assess the possibility of anomalous diffusion — increases with the time interval τ. Over a timescale corresponding to the typical travel time of particles, calculations of R(τ) may ostensibly indicate non‐Fickian behavior while actually reflecting the effects of periodicities in particle motions, not anomalous diffusion. We provide the theoretical basis for this observed behavior, and we illustrate how the effective (Fickian) particle diffusivity obtains from G. I. Taylor's classic definition involving the particle velocity autocovariance, including its relation to the ensemble‐averaged particle velocity as articulated by O. M. Phillips. Cross‐stream diffusivities are an order of magnitude smaller than streamwise diffusivities.

Pipe-Wall Friction in Vertical Sand-Slurry Flows

This article describes the results of extensive laboratory tests of vertical flows of three sand fractions (0.12, 0.37, and 1.84 mm sands) in a 150 mm pipe. The tests revealed an interesting phenomenon of a surprisingly low contribution of the medium sand to the total friction of the mixture flow in the vertical pipe. The frictional pressure drop in highly concentrated flows at high velocities was lower for slurries of the medium sand than for slurries of both the fine sand and the coarse sand. The solids friction at the pipe wall is analyzed taking into account effects of particle-particle interactions and particle-liquid interactions in the boundary layer of a vertical flow of settling slurry. The analysis suggests that the observed phenomenon is associated with the hydrodynamic liquid lift force acting on solid particles traveling near a pipe wall. This off-wall force seems to be more effective for the medium sand particles than for the fine sand particles and coarse sand particles interacting with liquid in the boundary layer of the mixture flow. The excessive frictional pressure drop due to the presence of solids in vertical flows seems to be primarily produced by the combined effect of the Bagnold collisional force (the force that colliding particles exert against the pipe wall) and the liquid lift force acting on solid particles in the near-wall zone of the slurry flow.

Experimental research on removal of iron and ammonium ions from groundwater by natural silica sand

An experimental study of the removal of iron and ammonium ions from groundwater by natural silica sand was carried out. Coarse sand particles were used (0.7–2.0 mm): the silica sand filter medium being 750 mm heigh. Silica sand material was washed and dried at 105 °C in an oven before using it in the filter bed; 500 l of groundwater artificially polluted with iron sulphate and ammonium chloride solutions passed through the filter charged with silica sand. The best removal of iron compounds from the water solution was obtained by using a filter medium 1 m high with the finest silica sand. Iron removal efficiency was 95% using coarse silica sand. The highest ammonium removal efficiency (94%) was achieved using 0.7–2.0 mm silica sand.

Laboratory study of high frequency scattering from water-saturated sandy sediments

Backscattering from a water-saturated well-sorted fine sand and from this sand with various inclusions was studied in a laboratory tank at frequencies from 200 kHz to 3 MHz and grazing angles from 20 to 90 degrees. Acoustic and granulometric properties of the sand are presented and discussed in a companion paper. First, the measurements of the frequency-angular dependencies of the backscattering strength were made for a thick sediment layer with a smoothed surface and without any inclusions in the volume. Then glass beads and coarse sand particles were used as additional scatterers or inclusions placed on the sediment surface or covered by sediment layers of various thickness. The data were compared with a previously reported model of scattering from discrete inclusions in the sediment [A. N. Ivakin, J. Acoust. Soc. Am. 116, 2575 (2004)]. The model inputs are material parameters of the sediment and inclusions and the size-depth distribution of inclusions. The results of model/data comparison are discussed and possibilities for inversion of various sediment parameters from backscattering data are shown.

Initial particle velocity spatial distribution from 2-D erupting bubbles in fluidized beds

Some results on particle image velocimetry (PIV) in 2-D freely bubbling fluidized beds are presented. The PIV applications were used in order to determine the initial particle velocity of bubble eruptions. A two-dimensional non-reacting fluidized bed was constructed to measure the origin of the ejected particles and the initial particle velocity distribution, using coarse sand particles. The bubble ejection mechanism was observed taking into account the origin of particles ejected, the initial particle velocity distributions as well as the effect of other neighbor exploding bubbles. Our results show that the assumption of linear dependence of initial velocity with the angle predicts the velocity faithfully only for purely vertical-ascent bubbles. Measurements of ejection velocities show that initial velocities in the combined layer are higher than those of the particles in the nose of the leading bubble. Avoiding coalescence of bubbles at the bed surface can lead to less particle entrainment out of the bed and consequently to shorter fluidized beds.

Local solids concentration measurement in a slurry mixing tank

The local solids concentration in a mixing tank was measured using both sample withdrawal and a new conductivity probe. The conductivity probe was used to assess the errors associated with various sample withdrawa! techniques and to measure solids concentration profiles in the mixing tank. The effects of sampling tube design (tip shape, face angle and inside diameter), sampling position, bulk solids concentration and particle size on the sampling errors were examined in detail. Solids concentration profiles were also measured as a function of particle size, bulk solids concentration and mixer rotational speed. The experimental results indicated that on the impeller plane, the sample withdrawal techniques (tapered sample tube) gave a lower solids concentration than that in the tank at a sampling velocity ratio of unity. These results suggest that the flow at the impeller plane was three-dimensional. The errors associated with sampling techniques depended on the sample tube shape and location in tank, and were significant for the coarse sand particles of 1000 μm. When sampling at right angle to the flow, sampling errors increased with particle size, especially when a small diameter sample tube was used. The data provided in the present study can be employed to correct for the errors associated with the sampling withdrawal techniques over a wide range of parameters. Solids concentration profiles in the mixing tank were found to be a function of the particle size, bulk solids concentration and mixer rotational speed. Solids concentration varied with the radial position, except when fine sand particles of 82 μm were used. A strong variation in solids concentration with the axial position was observed at the impeller plane for the sand particles examined in the present study. This variation increased with the particle mean size and the mixer rotational speed.

Microhabitat of Anthopotamus verticis (Ephemeroptera: Potamanthidae)

A field and laboratory study was designed to elucidate the microhabitat of the North American riverine mayfly Anthopotamus verticis (Say). Previous reports have suggested that these mayflies are surface sprawlers or clingers; but despite a flattened body shape that is often associated with sprawling or clinging benthos, our investigation showed that larvae of A. verticis burrow and inhabit the hyporheic biotope. Substrate particle size was found to be a primary limiting factor in the microdistribution of the larvae. When homogeneous substrates (either fine, medium, or coarse gravel, or small or large pebbles) were provided, small, mid-sized, and large larvae significantly preferred coarse gravel or small pebbles. Small larvae were better represented in coarse gravel, and large larvae were better represented in small pebbles. Vertical distribution was deeper in coarse gravel than in medium gravel, and smaller larvae were generally found deeper than large larvae. In the field, larvae occur in gravel or pebbles (excluding coarse sand or smaller particles) or mixed substrates, often at the interface of large rocks and finer substrates. Videomacroscopic examination also indicated larvae to be interstitial dwellers. Although relatively crude burrowers, larvae do use their tusks to excavate substrate, and their gills to generate interstitial current. We distinguish the fossorial behavior of Anthopotamus from most other ephemeroid mayflies because tube burrows are not formed. Minimum-sized interstices may be required for filter feeding and/or adequate ventilation, and may explain a deeper penetration of smaller larvae in finer substrates.

Microscope visualization of solid particles in circulating fluidized beds

A particle image scope consisting of an image fiber and a video system was developed to perform microscope observations of solid particles in circulating fluidized beds (diameters of risers: 60 mm and 100 mm; height: 4500 mm and 5500 mm, respectively). The behavior was examined using coarse sand particles ( d p=0.30 mm, U mf=0.10 m s −1) and fine sand particles ( d p=0.057 mm, U mf=0.002 m s −1). The images obtained clearly showed the shape and the number of the solid particles. The particle velocity was also determined by adjusting the exposure time of the 35 mm camera or video camera. Therefore, the variation of the solid holdup as a function of time, or the particle velocity, was easily obtained. The results show that the particle image scope developed here is quite effective in the microscope observation of gas—solid flow.