Sand Particle Size Distribution Research Articles

Study on factors influencing sand migration in wellbores

Accurate sand control design requires that the sand particles that break through the sand control facilities and enter the wellbore can be completely transported to the wellhead to prevent wellbore sand settling and blocking. At present, there are few studies on the migration and deposition of formation sand with a certain particle size distribution (PSD) after entering the wellbore with formation fluid. Most studies do not consider the sand PSD and treat sand particles as pseudo fluid. Therefore, this paper uses CFD-DEM (computational fluid dynamics-discrete element method) coupling method to conduct numerical simulation of sand migration in the wellbore, and obtains the influence rule of fluid velocity, viscosity, well deviation angle, formation sand production concentration, and PSD on cross-section sand concentration (sand carrying capacity of the fluid) and axial pressure drop in the wellbore section. Based on the simulation results and dimensional analysis, a prediction model for the volume concentration of sand particles in the wellbore was established, which is convenient for engineering applications to quickly determine the flow state of the wellbore. An engineering method for determining the critical non-deposition velocity of sand particles in wellbore was proposed, and the critical non-deposition velocity of sand particles under three effective particle sizes, three sand production concentrations, and three fluid viscosities was obtained. The research results can provide a theoretical basis for sand carrying and the production systems coordinated optimization design in weakly consolidated sandstone reservoirs.

Shear Mechanism and Optimal Estimation of the Fractal Dimension of Glass Bead-Simulated Sand

Spherical glass beads weaken the influences of particle morphology, surface properties, and microscopic fabric on shear strength, which is significant for revealing the relationship between macroscopic particle friction mechanisms and the particle size distribution of sand. This paper explores the shear mechanical properties of glass beads with different particle size ratios under different confining pressures. It obtains the particle size ratio and fractal dimension D through an optimal mechanical response. Simultaneously, we explore the range of the fractal dimension D under well-graded conditions. The test results show that the strain-softening degree of Rs is more obvious under a highly effective confining pressure, and the strain-softening degree of Rs can reach 0.669 when the average particle size d¯ is 0.5 mm. The changes in the normalized modulus ratio Eu/Eu50 indicate that the particle ratio and arrangement are the fundamental reasons for the different macroscopic shear behaviors of particles. The range of the peak effective internal friction angle φ is 23 °~35 °, and it first increases and then decreases with the increase in the effective confining pressure. As the average particle size increases, the peak stress ratio MFL and the peak effective internal friction angle φ first increase and then decrease, and both can be expressed using the Gaussian function. The range of the fractal dimension D for well-graded particles is 1.873 to 2.612, and the corresponding average particle size d¯ ranges from 0.433 to 0.598. Under the optimal mechanical properties of glass beads, the particle size ratio of 0.25 mm to 0.75 mm is 23:27, and the fractal dimension D is 2.368. The study results provide a reference for exploring friction mechanics mechanisms and the optimal particle size distributions of isotropic sand.

A new evaluation method for sand control performance of slotted screen

Evaluation method of slotted screen performance is a critical concern for sand control. Despite its significance, comprehensive investigations into quantitative study of sand retaining during the complex flow process need further in-depth study, particularly in numerical simulation research model of the slotted screen. This paper adopts the two-way coupling calculation method of computational fluid dynamics (CFD) and discrete element method (DEM) for the particle movement and fluid flow at the slotted screen and establishes a numerical model of the sand particle migration process through the slotted screen. The sand particle deposition and plugging dynamics on the surface of the sand retaining medium and the micro sand plugging mechanism and blockage pattern are studied. The fractal dimension of formation sand is introduced to characterize different distribution of formation sand. The effects of fluid viscosity, width of the slotted screen, sand production concentration, fluid velocity and particle size distribution on sand production, sand passing rate and particle size distribution of formation sand passing through the slot and plugging behavior are studied. The sand plugging process of slotted screen can be divided into three stages: the beginning of blockage, the intensification of blockage, and the balance of blockage. Under simulated conditions, the initial sand plugging rate is 87%, and as the blockage intensifies, the sand plugging rate gradually increases to 96.5%. Based on the analysis of numerical simulation results, the index of total seepage resistance damage amplitude and velocity, general sand retention ratio and passed-sand size were defined to construct the integrated evaluation method of slotted screen media, which involves the performance of sand retention, anti-plugging and flow ability. A brand new set of ideas on quantifying the integrated evaluation method were introduced to calculate the individual and integrated performance indicators of the slotted screen based on simulated data. The quantitative evaluation of the sand control performance of the slotted screen provides guidance and reference for the parameter design of the slotted screen in the target oil region and the accuracy optimization of the sand control medium.

Evolution features and a prediction model of casing perforation erosion during multi-staged horizontal well fracturing

Large-displacement high-intensity sanding hydraulic fracturing operations often cause casing perforation erosion and thus temporary plugging failures, exacerbate the unevenness of fracture initiation and expansion, and induce casing damage. In order to clarify the dynamic evolution of perforation erosion and predict perforation diameter, the effects of different types of proppants, the viscosity of sand-carrying liquids, and large sand-passing quantities on perforation erosion rate were experimentally explored in the study. The evolution of perforation erosion and the particle size distribution of quartz sand and ceramsite were analyzed in the experiment and a prediction model for perforation erosion under various fracturing parameters was established. Compared to ceramsite, quartz sand had the more significant effect on perforation erosion and the more serious particle abrasion and fragmentation under the same sand-passing quantity. Increasing the viscosity of the sand-carrying liquid slowed down perforation erosion and made the edge of perforation entrance more uniform. As the sand-passing quantity through the perforation increased, perforation erosion in the initial stage was concentrated at the perforation edge. Then, the inner wall of the perforation was also eroded, but the average erosion rate was reduced. A prediction model of perforation erosion considering multiple fracturing parameters was established based on the principle of fluid similarity. The errors between predicted values and downhole eagle-eye observation values were less than 15 %. The model provides an important basis for the optimization of fracturing parameters and downhole casing strength design.

Wind Tunnel Test of Sand Particle Size Distribution along Height in Blown Sand

In aeolian sand movement, the vertical distribution of sand particle size is intricately linked to sand flux, wind–sand flow field and dune development. In the present study, the distribution characteristics of sand grains in four particle size ranges at nine heights were investigated through sand blowing tests at five different reference wind speeds. The correlation between sand particle size and wind speed indicates that when the particle size was ≥0.35 mm, there was a linear variation of mass percentage with wind speed. When the particle size was <0.35 mm, when Z ≤ 0.15 m, a linear variation of mass percentage with wind speed was found; when Z > 0.15 m, an exponential modification in mass percentage with wind velocity was observed for sand grains falling within this specific range of particle sizes. The correlation between sand particle size and height indicates that when the reference wind speed was ≥15 m/s, the mass percentage of sand particles varied linearly with height. When the reference wind speed was ≤13.5 m/s, the mass percentage of sand grains with particle size in the 0.25–0.35 mm range increases first and then decreases with increasing height. The present results can provide a reference for subsequent research on the aerodynamic characteristics of wind–sand flow fields and on the mechanism of dune formation.

Assessment of the physical and mechanical characteristics of sand for the production of foam concrete using the two-stage foam injection method

The article presents the results of experimental studies of the properties of quarry sand to assess their suitability for use in the production of foam concrete. The sites of quarry sand extraction in the territory of the Akmola region are analyzed and their physical and mechanical characteristics are characterized. Evaluation of the physical and mechanical characteristics of sand was made for four types of sand. The main evaluation parameters were: particle size distribution, homogeneity, shrinkage, density and moisture content of sands. The results of the study showed that the physical characteristics of sands vary depending on their type, which indicates the differences in the natural composition and properties of these materials. Evaluation of the homogeneity of the different types of sands confirms the significant differences between the types. The highest homogeneity (xmax=77.45; xmax-1=14.98; Cc=73.5%) was observed in type 1 sand, while type 4 sand shows the minimum degree of homogeneity (xmax=47.30; xmax-1=42.28; Cc=8.7%). According to the test results, the maximum values of both densities in type 2 are: ρd=1.519 g/cm2, ρw=1.951 g/cm2, and the minimum values of both densities in type 4 are: ρd=1.438 g/cm2, ρw=1.894 g/cm2. The maximum natural moisture content in Type 1 samples is vn=9.5%, while the minimum values are 7.6% and 7.2% (Type 2 and 4). The obtained private density values have a high degree of convergence because the coefficients of variation have very low values: for Type 1 sands are 0.1-0.3%; for Type 2 sands are 0.7-0.8%; for Type 3 sands are 0.5-0.7%; for Type 4 sands are 0.4-0.6% (variation of private density values of dry and wet sands, respectively). Analysis of the results of tests on the shrinkage of samples showed that the maximum shrinkage is observed for sands of type 1 equal to 15.63%, while the minimum shrinkage is characteristic of samples of type 3 and 4 (11.25% and 11.88%). Taking into account the suitability of sand for the production of foam concrete, the most preferable is Type 1 sand mined in the Eltok building sand deposit.

Development and application of novel microfine cement-based grout

A novel type of effective microfine cement-based grout (EMCG) is designed for the complicated water-rich sand stratum. Superplasticizer (SP), compound excitation modulator (CEM), enhanced stabilizer (ES) and active activator (AA) were selected as optimizers. Through laboratory tests, main properties of EMCG i.e. fluidity performance, viscosity, bleeding rate, setting time, strength and volume stability were studied. Based on XRD mineral and SEM microstructure tests, hydration mechanism and microstructure of EMCG were studied. The results showed that the optimal parameters were 40% microfine fly ash (MFA), 14–18% microfine steel slag (MSS), 20–25% microfine slag (MS), 2–2.5% naphthalene-based SP (N), and 1–1.5% AA, 0.4–2.0% CEM and 6% ES. The 28d compressive strength of EMCG can reach 12.9–32.8 MPa. The 7 d strength can exceed 70% of 28 d strength. Through grouting injectability and reinforcement simulation tests, injectability of EMCG was acquired under different main influence factors i.e. sand particle size distribution, sand compactness, grout type, water-solid ratio (W/S), grouting pressure, etc. Quantitative relationships among enhancement strength or permeability coefficient and main influence factors were established. The microscopic slurry-rock interface reinforcement mechanism was obtained. Finally, based on field tests, the sealing and reinforcement effects of EMCG on water-rich sand stratum were acquired and discussed. Due to high overall performance and excellent engineering applicability of EMCG, it is an efficient and excellent cementitious grout especially for seepage prevention and reinforcement of water-rich sand stratum in geotechnical and underground engineering.

Effect of gradation and relative density on shear strength of coral sand

ABSTRACT Due to the wide particle size distribution of coral sand, There are significant differences in mechanical behaviour of coral sand with different particle size distribution. It is of great significance to propose a quantitative analysis method for mechanical properties considering the effect of gradation. In this study, 27 groups of coral sand specimens with particle size ranging from 5 mm to 0.125 mm were prepared. The consolidated undrained (CU) triaxial shear tests were carried out and the influence of gradation and relative density on the shear characteristic were discussed. The grading and relative density of coral sand are controlled by the median particle size (d50) and relative density (Dr), The results show that the peak deviator stress decreased, and the effective internal friction angle first increased and then decreased with the increase of d 50. Both the peak deviator stress and effective internal friction angle of coral sand increase with the relative density. A parabolic relationship was founded between the effect internal friction and d 50 as D r was constant. The effective friction angle peaked when d 50 was 2 mm. Finally, a calculation method of shear strength parameter considering the gradation and relative density of coral sand was proposed.

The Impact of Mining Waste and Biogas Digestate Addition on the Durability of Soil Aggregates

Waste management is one of the greatest contemporary challenges as the world strives for sustainable development. We set out to investigate the impact of mining waste (carboniferous rock) and organic waste (biogas digestate) on the physical properties of soils. The wastes were applied to Podzol, soil characterised by low chemical and physical quality with the particle size distribution (PSD) of loamy sand. The paper sets out to answer the question of whether a one-time application of mine and/or biogas digestate onto soil positively affects the durability of the soil structure and if the changes were permanent. For this purpose, we analysed soil texture, total organic carbon (TOC), water-stable aggregates and the mean weight diameter of water-stable aggregates (MWD). The combined addition of biogas digestate and the two types of waste improved the soil structure. The content of soil water-stable aggregates with dimensions 5–10 mm (A5–10) and 1–5 mm (A1–5) increased the MWD and the content of aggregates of diameters <1 mm (A<1) decreased. The effects of the experiment were permanent, as differences resulting from the soil treatments were still visible four years after the application. This shows that wastes, especially biogas digestate, could be successfully used in agriculture.

Numerical Investigation on the Compressive Behavior of Desert Sand-Based Backfill Material: Parametric Study.

As a key node in the promotion of the "Western Development" strategy in Xinjiang, China, the large-scale mining of coal resources is bound to cause a series of ecological and environmental problems, such as surface subsidence. Desert areas are widely distributed in Xinjiang, and from the perspective of reserves and sustainable development, it is crucial to fully utilize desert sand to make filling materials and predict its mechanical strength. In order to promote the application of High Water Backfill Material (HWBM) in mining engineering, a modified HWBM doped with Xinjiang Kumutage desert sand was used to prepare a desert sand-based backfill material, and its mechanical properties were tested. The discrete element particle flow software PFC3D is used to construct a three-dimensional numerical model of desert sand-based backfill material. The parameters such as sample sand content, porosity, desert sand particle size distribution, and model size are changed to study their impact on the bearing performance and scale effect of desert sand-based backfill materials. The results indicate that a higher content of desert sand can effectively improve the mechanical properties of HWBM specimens. The stress-strain relationship inverted by the numerical model is highly consistent with the measured results of desert sand-based backfill materials. Improving the particle size distribution of desert sand and reducing the porosity of filling materials within a certain range can significantly improve the bearing capacity of desert sand-based backfill materials. The influence of changing the range of microscopic parameters on the compressive strength of desert sand-based backfill materials was analyzed. This study provides a desert sand-based backfill material that meets the requirements of mine filling, and predicts its strength through numerical simulation.

Optimizing concrete performance: An investigation into the impact of supplementary cementitious materials and sand particle sizes

The significance of employing suitable grades of aggregates and binders combined with waste materials in optimizing the performance of concrete cannot be overstated. It is evidenced from research that supplementary cementitious materials (SCM) sourced from construction waste can enhance the properties of cured concrete with less environmental impact and substantial economic savings. This study investigates the effect of SCM modified with customized sand particle sizes as fine aggregates on concrete’s compressive strength and durability properties. The SCMs comprised silica fume (SF), glass powder (GP), and marble dust (MD) in different percentages (0%, 15%, and 20%). The results indicated higher compressive strength at 28-d could be obtained by adding SCM and finer sand particle size distribution than natural sand grain sizes. The study suggests an effective approach for the recyclability of locally available industrial by-products as ingredient modifiers, which possess great potential for cement production for improved performance and to benefit localities with the predominance of finer sand and soil varieties for usage as a substitute to the traditional grain size of fine aggregates.

Extended wet sieving method for determination of complete particle size distribution of general soils

The traditional standard wet sieving method uses steel sieves with aperture ≥0.063 mm and can only determine the particle size distribution (PSD) of gravel and sand in general soil. This paper extends the traditional method and presents an extended wet sieving method. The extended method uses both the steel sieves and the nylon filter cloth sieves. The apertures of the cloth sieves are smaller than 0.063 mm and equal 0.048 mm, 0.038 mm, 0.014 mm, 0.012 mm, 0.0063 mm, 0.004 mm, 0.003 mm, 0.002 mm, and 0.001 mm, respectively. The extended method uses five steps to separate the general soil into many material sub-groups of gravel, sand, silt and clay with known particle size ranges. The complete PSD of the general soil is then calculated from the dry masses of the individual material sub-groups. The extended method is demonstrated with a general soil of completely decomposed granite (CDG) in Hong Kong, China. The silt and clay materials with different particle size ranges are further examined, checked and verified using stereomicroscopic observation, physical and chemical property tests. The results further confirm the correctness of the extended wet sieving method.

Effects of Particle Size Distribution of Standard Sands on the Physical-Mechanical Properties of Mortars.

Obtained natural sands can present different particle size distributions (PSD), although they have the same mineralogical origin. These differences directly influence the physical and mechanical behavior of mortars and, therefore, the performance of mortar and ceramic renderings. Standardizing the particle size of sands based on pre-established requirements in normative standards (NBR 7214 or ASTM C778) is one way to minimize these effects. However, these standards do not consider the optimization of the granular skeleton through the analysis of bulk density and PSD, which may be insufficient to obtain satisfactory results. Therefore, this paper analyzes the effects of using different particle size ranges on the physical and mechanical behavior of cement and hydrated lime mortars. The properties of consistency index, bulk density, air content, capillary water absorption, water absorption by immersion, flexural strength, compressive strength, and dynamic modulus of elasticity were evaluated. For this purpose, standardized sands of the same mineralogical origin were made with different particle size ranges, being: (i) standardized sand constituted by 25% of coarse and fine fractions (S25-control), (ii) standardized sand constituted by 30% of coarse fraction and 20% of fine fraction (S30-20), and (iii) standardized sand composed by 40% of coarse fraction, and 10% of fine fraction (S40-10), respectively. The results indicated that variations in the particle size composition of the standardized sands are necessary to obtain mixtures with higher compactness and, therefore, mortars with better physical and mechanical performance. Thus, the dosage of the particle size fractions of standardized sand should consider the optimization of the granular skeleton, being the unit mass and the granulometric composition as important parameters to meet this premise.

Structural, Chemical and Magnetic Characterization of Quartz Sand from Cluj Area, Romania for Future Beneficiation in the Glass Industry.

For use in crystal glass production, quartz sand must contain less than 0.09% iron. If the sand contains more than 0.09% Fe, the iron must be removed. In the present study, quartz sand from tailings ponds near the Cluj area of Romania is analyzed for potential use in the glass industry, after magnetic separation. The particle size distribution of raw sand was determined, and mineralogical analyses was realized. Using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDX), morphology and elemental distribution maps on the particle was performed. The evolution of the iron content versus the particle size was analyzed. Using X-ray diffraction, the phases occurring in the sand were investigated in relation to the particle size. Magnetic separation with two magnets, having different energy, was performed for identifying the phases attached to the magnetic particles. Magnetic hysteresis measurements evidenced complex and multiple iron phase behavior.

Experimental Study on the Mechanical Properties of Saturated Tailing Sand with Different Particle Sizes

The particle size distribution of tailing sand will affect its strength, deformation and mechanical properties, thus affecting the overall safety and stability of the tailing dam. The main purpose of this study is to obtain the gradation of sand samples with the best shear strength and seepage effect by studying the influence of particle size on the mechanical properties of saturated iron tailing sand. The tailings were sampled from Yangjiawan tailing reservoir of Chengchao Iron Mine, and the moisture content test, particle size distribution analysis and scanning electron microscope test (SEM) were carried out on the samples. It is measured that the average moisture content of the tailings is 12%, and the gradation is generally poor. SEM was used to observe the microstructure of the three kinds of particles, and it was found that these structures were more likely to be damaged under load, which was not conducive to the improvement of the strength of tailings. Through the consolidation undrained test of five particle size groups, it is concluded that the larger the particle size is, the greater the shear strength will be. The Cu indicates the width of the distribution range of the grading curve, the Cc indicates the distribution pattern of the grading curve, and they are both used to indicate the particle grading of sand. Then, by changing the sample gradation, the coefficient of uniformity (Cu) and the coefficient of curvature (Cc) of the gradation parameters are controlled to remain unchanged, respectively. By changing another parameter, it is found that there is a close relationship between the coefficient of uniformity and the coefficient of curvature and the shear strength through the triaxial shear action, three kinds of tailing sand gradation with better strengths are obtained. Based on the study of strength characteristics, the permeability coefficients of three kinds of tailing sands are calculated by using the seepage failure test. The test results show that when the coefficient of uniformity is 5.5 and the coefficient of curvature is 1, the permeability coefficient is 1.699 × 10−3 cm/s, and the shear strength and permeability of the sample are the best.

Coarse-grained CFD-DEM simulation of coal and biomass co-gasification process in a fluidized bed reactor: Effects of particle size distribution and operating pressure

The co-gasification of coal and biomass through fluidized bed gasifier is a promising technology for the improvement of the utilization efficiency of fossil fuels and the development of renewable energy. In this work, a coarse-grained computational fluid dynamics-discrete element method (CFD-DEM) simulation is performed to investigate the co-gasification process in a bubbling fluidized bed gasifier. The effects of particle size distribution and operating pressure on the hydrodynamics, heat transfer, and co-gasification performance are analyzed. The results show that the increase of sand particle size distribution (PSD) width slightly affects the particle concentration distribution, particle residence time distribution, and co-gasification performance. The heat transfer rate of convection is an order of magnitude higher than those of conduction and radiation. At higher PSD width, the formation of the vertical solid temperature gradient at the bed bottom is attributed to the deteriorated solid mixing. As the operating pressure increases, the bed temperature decreases apparently. In addition, the variation of the convective heat transfer rate dominates the heat transfer efficiency as the operating pressure changes. The application of elevated operating pressure benefits to the thermal-chemical conversion of blend fuel since the char conversion reaction is accelerated.

Numerical simulation method of a circulating fluidized bed reactor using a modified MP-PIC solver of OpenFOAM

There are some previous works for simulating a bubbling fluidized bed (BFB) reactor using OpenFOAM's MPPICFoam solver, but those for circulating fluidized bed (CFB) reactors are few. In this study, the MPPICFoam solver was verified with a BFB reactor by comparing the solver's simulation results with the experiment and simulation results from the literature. By introducing the inter-boundary particle circulation function and a new module for setting sand particle size distribution, simulations were performed for a 0.1 MW th pilot-scale CFB combustor under isothermal conditions. The modified solver for the CFB reactor gives similar results as the experiment and commercial computational fluid dynamics (CFD) tool, well-predicting the pressure distribution and solid volume fraction in the riser. • MPPICFoam solver reliability for lab-scale bubbling fluidized-bed reactor verified. • Accurate solver prediction of solid volume fraction (horizontal) distribution. • Model used for numerical simulation to study riser hydrodynamics of a CFB combustor. • Particle size distribution module and new circulating boundary conditions added. • Improved solver shows superior predicted experimental results in dense bed region.

PENGUKURAN GAYA REAKSI TANAH DENGAN SATU BUAH SIRIP RODA SANGKAR TRAKTOR TANGAN DI BAK PENGUJIAN TANAH

The ability of a cage wheel to climb slopes depends on the grip of the lug on the sloped soil. A lug wheel that sinks deeper will generate more force when climbing. This study aimed to measure the soil reaction force on a single flat lug wheel in the slope soil bin so that the optimal lug angle is obtained to enhance the ability of cage wheels to climb sloped soil. The experiment was carried out using a model of a single flat lug wheel (length of 10 cm, width of 3.5 cm, radius of 30.4 cm, and slope of 30o). Measurements of soil reaction forces on the lug were carried out on five lug angles (-15o, 0o, 15o, 30o, 45o) at three various sinkage depths (2.5 cm, 5 cm, 7.5 cm) at a rotational speed of 11 rpm. The moisture content, density, porosity used in this study were 45.61% (d.b.), 1.02 (g/cm), 44.02%. In addition, the particle size distribution of sand, clay, and silt are 8.038%, 13.396%, and 78.564%, respectively. The limits of soil consistency used in this study, including the plastic limit, water limit, and index limit, were 64.57%, 80.86%, and 16.29%, respectively. A set of measurement and data logger equipment is used to measure the reaction forces of the soil. The results showed that at the angles of -15 and 0 the lugs were able to penetrate the soil faster and deeper to produce a greater pulling force. This implies that a smaller angle of inclination will be more beneficial to the tractors wheel applied for climbing than a greater angle of inclination.

Effect of Particle Character and Calcite Dissolution on the Hydraulic Conductivity and Longevity of Biosand Filters Treating Winery and Other Acidic Effluents

Acidic effluent such as winery wastewater is challenging to remediate. Biological sand reactors can simultaneously remove organics and neutralize winery wastewater via biotic and abiotic mechanisms. The systems have been shown to be suitable for treating the intermittent flow of wastewater at small wineries. It has been shown that dissolution of calcite is the most important abiotic mechanism for increasing the pH of the influent. In this study, sand column experiments were used to determine the effects of (i) sand particle size distribution on calcite dissolution kinetics, and (ii) the effects of calcite particle dissolution on the hydraulic conductivity. The results were then used to calculate the theoretical temporal abiotic neutralization capacity of biological sand reactors with differently sized sand fractions, including unfractionated (raw) sand. The results were compared with those determined from a pilot system treating winery wastewater over a period of 3 years. Sand fractions with larger particles contained lower amounts of calcite (using Ca as a proxy), but exhibited higher hydraulic conductivities (3.0 ± 0.05 %Ca and 2.57 to 2.75 mm·s−1, respectively) than those containing smaller particles and/or raw sand (4.8 ± 0.04 to 6.8 ± 0.03 %Ca and 0.19 to 1.25 mm·s−1, respectively). The theoretical abiotic neutralization capacity of biological sand reactors was compared with a pilot system with the same flow rates, and a temporal abiotic neutralization capacity of 37 years was calculated for biological sand reactors, which compared favorably with the theoretical results obtained for wastewater with pH values between 2 (8.2 years) and 3 (82 years). It was concluded that biological sand filters with around 10% calcite will be able to abiotically neutralize winery wastewater and other wastewaters with similar acidities for the projected life span of the system. Future work should focus on determining the effect of sand grain size on the bioremediation capacity, as well as the use of biological sand reactors for treating other acidic organic wastewaters such as fruit processing, food production and distillery wastewater.

Influence of the Fractal Distribution of Particle Size on the Critical State Characteristics of Calcareous Sand

To study the influence of the fractal distribution of particle size on the critical state characteristics of calcareous sand, a type of calcareous sand from a certain reef of the South China Sea was used in this study. For comparison, standard quartz sand was also used. A series of drained shear tests on the two sands were then conducted to investigate their critical state characteristics. It was demonstrated that the fractal dimension is suitable for characterizing the particle size distribution (PSD) of calcareous sand with different fine sand content. The critical state equation of sand proposed by Li and Wang (1998) is suitable for fitting the critical state line of calcareous sand. In the plane of deviatoric stress versus the effective confining pressure (q–p′ plane) and the plane of void ratio versus (p′/pa)α, the critical state lines of calcareous sand are always above those of quartz sand. The critical state lines of calcareous sand with different fractal dimensions in the q–p′ plane are unique. However, in the e–(p′/pa)α plane, the critical state lines appear to rotate anticlockwise as the fractal dimension increases. In addition, there is an “intersection” in the e–(p′/pa)α plane. Considering the influence of the fractal distribution of particle size, an expression for the critical state line of calcareous sand in the e–(p′/pa)α plane was proposed. The related constitutive model was also revised, where a complete set of model parameters suitable for modeling calcareous sand was provided.