Particle Size Grading Research Articles

The role of pH in red-stratum mudstone disintegration in the Three Gorges reservoir area, China, and the associated micromechanisms

The well-known slide-prone red-stratum mudstones in the Three Gorges reservoir (TGR) area are currently undergoing sharp changes in (i) water level driven by the impounding/discharging operation of the Three Gorges dam and (ii) the rain/water H+ concentration driven by recent rapid industrial/agricultural development, and these changes are expected to impact geohazards. This potential impact emphasizes the importance of understanding the role of pH in the drying-wetting disintegration of red-stratum mudstones. Although many investigations have focused on the role of pH in mudstone disintegration, the red-stratum mudstones in the TGR area differ from mudstones elsewhere, and the role of pH has seldom been studied in these rocks. This work adds to the limited body of research by (1) experimentally investigating the possible role of pH in red-stratum mudstone drying-wetting disintegration and (2) revealing the micromechanisms responsible for this role. In the experiment, six disintegration performance indexes and two mechanical indexes, i.e. particle size gradation, slake durability index, decay constant, surface energy, box dimension, fractal dimension, cohesion and friction angle, were monitored throughout the disintegration process. A tri-piecewise linear fractal model is proposed to better describe the particle size distribution. This research shows that the acid enhancements stimulate the disintegration of red-stratum mudstones and significantly affect shear strength. In comparison, alkaline environments inhibit the mudstone fragmentation and slightly degrade the shear strength. Two possible micromechanisms and three potential effects of acid or alkaline agents are presented to account for the role of pH. The findings provide insights into the potential geohazard impacts of sharp changes in the exposure environment (i.e., water level and H+ concentration) of the red-stratum mudstones in the TGR area.

Numerical Study on Movement of Iron Concentrate in a Cargo Hold Based on Discrete Element Method

Taking the cargo hold from a 57000 DWT bulk carrier as an example, the movement of iron concentrate particles in the cargo hold was simulated by using the discrete element software EDEM. The effect of water content on the movement of the cargo is replaced by variation of the particle’s friction coefficient. Considering the friction coefficient, particle size grading, particle collision recovery coefficient, rolling amplitude of cargo hold and cargo loading depth, 11 working conditions were designed and simulated. Results show that the decrease of friction coefficient, the increase of rolling amplitude and the loading capacity would aggravate the overall shift of the center of gravity of the cargos. In the case of the same loading depth, the more particles, the stronger the particle collision. And the collision recovery coefficient has little effect on the movement of particles.

The Shear Strength of Granite Weathered Soil Under Different Hydraulic Paths

At present, there is no clear understanding of the influence of differences in soil mineral composition, particle size grading, and hydraulic paths on the shear strength of unsaturated soil, and the related strength models are not applicable. The shear strength characteristics of different saturation specimens under different hydraulic paths were studied on two granite weathered soils. The experimental results show that the shear strength index of the prepared specimen is “arched” with the increase of saturation, and the dehydration specimen decreases linearly with the saturation. As considering the cementation of free oxides in soils and the interaction among soil particles at different saturations, it is assumed that there are three different contact modes among soil particles: direct contact, meniscus contact, and cement contact. The difference in contact modes will reflect the different laws of shear strength. A shear strength model capable of distinguishing between the capillary effect and the adsorptive effect was established. The model predicted and verified the shear strength data of granite weathered soil under different hydraulic paths well, and then theoretically explained the evolution law of the shear strength of granite weathering soil under the change of saturation.

Proppant Transportation in Cross Fractures: Some Findings and Suggestions for Field Engineering

The proppant transportation is a typical two-phase flow process in a complex cross fracture network during hydraulic fracturing. In this paper, the proppant transportation in cross fractures is investigated by the computational fluid dynamics (CFD) method. The Euler–Euler two-phase flow model and the kinetic theory of granular flow (KTGF) are adopted. The dimensionless controlling parameters are derived by dimensional analysis. The equilibrium proppant height (EPH) and the ratio of the proppant mass (RPM) in the secondary fracture to that in the whole cross fracture network are used to describe the movement and settlement of proppants in the cross fractures. The main features of the proppant transportation in the cross fractures are given, and several relative suggestions are presented for engineering application in the field. The main controlling dimensionless parameters for relative EPH are the proppant Reynolds number and the inlet proppant volume fraction. The dominating dimensionless parameters for RPM are the relative width of the primary and the secondary fracture. Transportation of the proppants with a certain particle size grading into the cross fractures may be a good way for supporting the hydraulic fractures.

Quantitative NIR spectroscopy determination of coco-peat substrate moisture content: Effect of particle size and non-uniformity

The particle size and non-uniformity of solid particle samples directly affected the acquisition of samples spectral data. In this study, different particle size samples and mixed samples with two different particle size grade samples were applied to investigate the impact of particle size and non-uniformity on near-infrared (NIR) spectroscopy detection of moisture content in coco-peat substrate. Simultaneously, the pretreatment effect and capability of MSC and SNV on spectral scattering were studied. The results showed that the prediction accuracy of the spectral detection model for moisture content in coco-peat substrate was higher with smaller particle size or smaller non-uniformity; MSC and SNV had better effects on improving the accuracy of prediction models with small particle size samples or small non-uniformity samples; the optimal moisture content spectral prediction models for single particle size grade samples and mixed samples of two particle size grades could be respectively established when SNV was adopted to pretreat the samples spectral data of A and A-B. And the corresponding correlation coefficients of the two optimal models were 0.9964 and 0.9959 for calibration set, 0.9959 and 0.9957 for prediction set, respectively; the root mean square errors were 1.2299% and 1.0090% for calibration set, 1.2820% and 1.0723% for prediction set, respectively; the ratios of prediction to deviation were 10.83 and 10.51, respectively. The prediction model with the minimal spectral scattering influence could be built by combining physical pretreatment with spectral pretreatment. This study would provide a reference for reducing the scattering effect of solid particle sample spectral detection.

Characteristics of Direct Shear and Particle Breakage of Pebble Gravel Materials

Particle size is an important factor affecting the Thermal-Hydraulic-Mechanical (THM) coupling behavior of graveled rock mass, especially for the shear mechanical properties. In this study, three groups of the particle size range and nine particle grading samples are designed for a large-scale direct shear test. The relationships between shear stress and shear displacement, shear strength, stress ratio, shear strength parameters, and particle breakage of pebble gravel are analyzed. The influence of particle size range and grade on the strength and particle breakage of gravel material is discussed. Results show evident particle breakage in the process of direct shear, and the degree of fragmentation is controlled by the normal load and the particle size distribution of the sample. The shear strength of the sample is no longer applicable to Mohr-Coulomb strength theory because of particle breakage that is more in line with the power function relationship. Shear strength of pebble gravel material has scale effect, and a corresponding relationship model between friction coefficient f of material and characteristic particle size of the sample is proposed.

Effects and optimization of ratio of particle size grading on compaction density of calcined coke particles

The bulk density of the anodes affects the energy consumption and associated carbon emissions of the calcined anodes over the course of the Hall-Héroult process. The bulk density of the anode mainly depends on the compaction density of calcined coke particles. In this paper, the vibro-compacting process of calcined coke particles is simulated using discrete element method. The particle behavior during vibro-compacting process and the inter-particle contact information with different ratios of particle size grading are investigated. The effects of different ratios of particle size grading on the compaction density and microstructure are studied. The critical average diameter which can distinguish whether the compaction density meets standard requirement is first proposed and obtained. The triangular coordinate graphical is introduced to optimize the ratio of particle size grading which is different from conventional method. The results show that the larger the proportion of coarse particle and medium particle, the more large voids between particles, and the increase of fine particle can effectively fill the inter-particle gap. The critical average diameter of calcined coke particles is 2.26 mm, and average diameter less than 2.26 mm can meet the standard requirement. The optimal ratio of particle size grading is 46% for coarse particle, 12% for medium particle and 42% for fine particle.

Three–dimensional mathematical model of a convective cloud with detailed account for the thermodynamic, microphysical and electric processes

A three–dimensional numerical model of a convective cloud developed by the authors, taking into account thermodynamic, microphysical and electrical processes, is presented. The model is characterized by the use of detailed microphysics with a large number of particle size gradations. There are taken into account: the accumulation of charges in the cloud, the electric field, the electric coagulation of cloud particles. The technique of formation of three–dimensional initial data at initialization of model is developed. On the basis of the developed model with a detailed description of the processes for the first time is studied the formation of macro– and micro structural and electrical parameters. The dynamics of changes in the characteristics of thunderstorm clouds at the stage of growth and maximum development are determined. Electrical characteristics of thunderstorm clouds at different times and their relationship with micro structural parameters are investigated. The spatial structure of voluminous electric charges in a cloud, three–dimensional distribution of electric field intensity are determined. A quantitative assessment of the effect of electric coagulation on the rate of precipitation in powerful clouds is obtained.

Eco-efficient earth plasters: The effect of sand grading and additions on fresh and mechanical properties

Earth-based plasters can be very eco-efficient both in terms of embodied energy and technical efficiency, although they are vulnerable to water when unstabilized. An experimental campaign was developed to assess the workability and the mechanical properties of formulated earth-based plastering mortars with a 1:3 (illitic clayish earth:aggregate) volumetric ratio. The aggregate components include different proportions of coarse and fine siliceous sands and the partial replacement of fine sand by a phase change material (PCM) or the addition of a low content of oat fibers. A pre-mixed earth mortar produced with clayish earth picked from the same pit was assessed as control. Mortars were tested to evaluate workability and density in the fresh state, and results were compared to dry bulk density, dynamic modulus of elasticity, flexural, compressive and adhesive strengths and dry abrasion resistance. Results show that even 15% replacement of the fine sand by the PCM significantly changes the workability, apart from decreasing the shrinkage and dry bulk density and reducing the mechanical strength of the mortars. Therefore, the addition of this type of PCM, that most probably have advantages in terms of thermal behavior of the plasters, may have important drawbacks in the fresh and hardened state of earth plasters that should also be considered. The addition of oat fibers does not show any improvement on the workability and mechanical characteristics of the earth mortars. In these mixed sand mortars, higher coarse sand content promotes a decrease in mechanical performance, showing the advantage of using sand with a well graded particle size distribution.

The effect of al particle size on thermal decomposition, mechanical strength and sensitivity of Al/ZrH2/PTFE composite

To study the thermal decomposition of Al/ZrH2/PTFE with different Al particle size as well as mechanical strength and impact sensitivity under medium and low strain rates, molding-vacuum sintering was adopted to prepare four groups of power materials and cylindrical specimens with different Al particle size. The active decomposition temperature of ZrH2 was obtained by TG-DSC, and the quasi-static mechanics/reaction characteristics as well as the impact sensitivity of the specimen were studied respectively by quasi-static compression and drop-hammer test. The results show that the yield strength of the material decreased with the increase of the Al particle size, while the compressive strength, failure strain and toughness increased first and then decreased, which reached the maximum values of 116.61 MPa, 191%, and 119.9 MJ/m respectively when the Al particle size is 12–14 μm because of particle size grading. The specimens with the highest strength and toughness formed circumferential open cracks and reacted partly when pressed. Those with developmental cracks formed inside did not react. It is considered that fracture of specimens first triggered initial reaction between Al and PTFE to release an amount of heat. Then ZrH2 was activated and decomposed, and participated in subsequent reaction to generate ZrC. The impact sensitivity of the specimens decreased with the increase of Al particle size.

Improvement of Sub-Base of Roads by Chemical Admixtures and Organic Materials

One of the aspects of increase of earlier damage and failure of traffic load, especially in clayey regions, is the deficiency of pavement subgrade. To prevent such damage, strengthening of the pavement by improving the subgrade layer is essential. Many investigators have carried out research on the subgrade layer, especially when containing clay particles, using several types of additives (stabilizers). Soil Stabilization is a method of improving the engineering properties of soil and therefore making it more stable. Generally, stabilization includes pre-consolidation, compaction and numerous other similar methods. However, stabilization is usually related to the processes which modify the soil composition itself for enhancement of its properties. Soil stabilization of pavements is usually designed based on the assumption that specified levels of quality will be achieved for each soil layer in the pavement system. Each layer must resist shearing within the layer, avoid excessive elastic deformations that would result in fatigue cracking within the layer or in overlying layers, and prevent excessive permanent deformation through densification. Engineers are responsible for selecting or specifying the correct stabilizing method, technique, and quantity of material required. Usually, the technology provides an alternative provision structural solution to a practical problem. The simplest stabilization processes are compaction and drainage. The other process is by improving gradation of particle size and further improvement can be achieved by adding binders to the weak soils. This study showed that lime activated by sodium chloride in combination with sugar cane ash could be effectively used to improve soft clay with low soaked CBR value and high plasticity. Therefore, from the environmental point of view, it was recommended that sugar cane ash can partially replace lime in clay stabilization to form material with cementitous properties

Experimental Study on Model of Red Mud Duncan-Zhang Model of an Aluminum Company in Shanxi

This paper takes the red mud, an auxiliary product of aluminum smelting industry in an aluminum factory in Shanxi Jinzhong as the research object, and tests the basic physical and mechanical parameters and Duncan-Zhang model parameters of red mud. According to the geotechnical test procedure, the parameters such as particle size gradation and liquid plastic limit of red mud were obtained. The stress-strain relationship curve of the red mud material was obtained by the triaxial consolidation compression test. The Duncan-Zhang model parameters of the red mud material were obtained according to the experimental data, which provided a reference for the stability analysis and calculation of the red mud yard in the future.

Using grain size to predict engineering properties of natural sands in Pakistan

Laboratory determination of strength and deformation behavior of clean sands and gravels has always been challenging due to the difficulty in obtaining their undisturbed samples. An alternative solution to this problem is to develop correlations between mechanical properties of cohesionless soils and their gradation characteristics. This study presents database of 3 natural sands with 11 varying particle size gradation curves to allow investigating relationships between mean particle size, maximum and minimum void ratio, relative density and shear strength of the test soils. Direct shear tests were performed at relative densities of 50, 75 and 95% to explore the effects of gradation and density on the angle of internal friction of the modeled sand samples. It is found that the mean grain size D50 bears good correlations with void ratio range (emax - emin) and peak angle of internal friction Φ\'peak. The generated regression models are in good agreement with published literature and can be considered as reliable for natural sands in Pakistan. These empirical correlations can save considerable time and efforts involved in laboratory and field testing.

Design and test of automatic detection platform for soil fragmentation rate in rotary tillage

As an important index of soil crushing performance of rotary tiller, the soil fragmentation rate is still limited to manual measurement. In this study, an automatic detection platform for soil fragmentation rate was designed, which integrated soil intake, screening, weighing and calculation of soil fragmentation rate. This platform can solve the problem that the index of the soil fragmentation rate cannot be detected quickly and effectively after rotary tillage, which leads to difficulty in field quality evaluation. The platform was mainly composed of a shovel soil module, conveying module, screening module, weighing module and automatic control system, which could realize single-line and multi-point automatic soil fragmentation rate detection. Based on the homogeneous dry slope model, the tilting angles of soil intake and soil feeding after rotary tillage on the platform were determined to be 30.10° and 26.67°, respectively. According to the principle of flow conservation, a rotary circulation screening module was designed to obtain soil particle size grading. A method based on the principle of multi-line and multi-point measurement was developed to detect soil fragmentation rate. The influence of screening speed on screening effect was analyzed, and the reasonable value of screening speed was determined to be 0.5 m/s. A field performance test was carried out in October 2019 to verify the detection performance of the platform. The results showed that, compared with the manual test method, the maximum test error was no more than 11%, the minimum test error was less than 4%, the maximum single test time was no more than 2 min, and the total test time of each test area was no more than 30 min. The efficiency of single-point detection was significantly better than the manual detection, which indicated that the design in this study met the requirements of rapid detection of soil fragmentation rate, and provided a new idea for the automatic detection of quality of rotary tillage. Keywords: rotary tillage, soil fragmentation rate, automatic detection, design, test DOI: 10.25165/j.ijabe.20201305.5678 Citation: Du X W, Yang X L, Pang J, Ji J T. Design and test of automatic detection platform for soil fragmentation rate in rotary tillage. Int J Agric & Biol Eng, 2020; 13(5): 40–49.

Experimental study on secondary bearing mechanism of weakly cemented broken rock mass

In order to study the secondary bearing mechanism of weakly cemented broken surrounding rock, the surface of granite, limestone and mudstone broken rock samples were poured by cement slurry, and the weakly cemented rock mass was formed by static pressure infiltration method, and then an uniaxial loading test was carried out. The results show that the weakly cemented broken rock mass has a certain bearing capacity, but the bearing capacity is low, and the dispersion is high. The secondary bearing capacity of weakly cemented rock mass is affected by factors such as broken rock strength, rock particle size and rock gradation. The larger the rock particle size and strength are, the higher the secondary bearing capacity of the weakly cemented rock mass is. The average bearing capacity of the mudstone weak cementation specimen is 18.77 kN, and the residual bearing capacity is 1.46 kN, and a dispersion coefficient is 0.34. The average bearing capacity of granite is 343.65 kN, and the residual carrying capacity is 25.81 kN, and a dispersion coefficient is 0.11. The average bearing capacity of limestone is 367.22 kN, and the residual carrying capacity is 22.78 kN, and a dispersion coefficient is 0.3. After a certain grading, the average residual secondary bearing capacity of the weakly cemented rock mass is obviously improved, and the dispersion coefficient of peak bearing capacity is reduced. The grading scheme 1 has an average peak carrying capacity of 330.06 kN, a residual carrying capacity of 34.56 kN, and a dispersion coefficient is 0.07. The averaging scheme 2 has an average peak carrying capacity of 297.8 kN, a residual carrying capacity of 29.86 kN, and a dispersion coefficient is 0.14. The cementation regeneration mechanism of the broken rock mass mainly includes the cement-bonding effect of the cement slurry inside and on the broken rock mass. Under the loaded condition, the internal load-bearing network of the broken rock mass is the main mechanism for the secondary load of the broken rock mass, and the stability of the force-chain network is affected by the constraint. After the loss of the confinement, the force chain network fails, and the residual secondary bearing mechanism of the weakly cemented broken rock mass is transformed into the friction between the broken rock masses in the residual core rock pillar.

Improvement of loess characteristics using sodium alginate

Loess often has poor engineering properties due to its loose accumulation and strong collapsibility. Therefore, improvement of the soil is necessary to meet the needs of engineering. In the current work, the improvement effect of sodium alginate added in different proportions to loess was studied. Limited water content test and particle size grading test were conducted to study the effect of sodium alginate on the basic physical parameters of soil. In addition, unconfined compressive strength test (UCS) and consolidated undrained test (CU) were used to analyze the changes in the mechanical properties of the soil after improvement. Additionally, permeation and disintegration tests were used to study the change in the soil’s water stability. What’s more, the microscopic mechanism of sodium alginate improved loess was also proposed based on the results of scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that sodium alginate not only can change the liquid-plastic limit and particle size gradation of loess but also improve the strength, shear parameters, and water stability of loess. SEM and XRD studies revealed that sodium alginate changed the microstructure of the loess, formed a colloidal material to encapsulate the soil particles, filled the pores between soil particles, and caused aggregation of the clay material in the soil to form larger particle size via flocculation. These results show that sodium alginate can be used as a more environmental friendly and sustainable additive to replace the traditional soil stabilization additives, such as cement or lime to stabilize loess.

Effects of particle sizes on compressive deformation and particle breakage of gangue used for coal mine goaf backfill

Broken gangue from the collapsing roof of a longwall coal panel can be used as the backfilling material for goaf backfilling. The particle size gradation has important influence on the compressive deformation of the gangue backfilling material and particle breakage. The compressive deformation of the gangue backfilling materials at 4 different particle size grades is simulated by PFC3D in this paper. The law of the compressive deformation of the gangue backfilling material, the particle cluster distribution and the variation of the gangue block shape are analyzed. The microscopic mechanism of the compressive deformation of the gangue backfilling material is investigated based on the force-chain distribution. The results indicate that when the gangue backfilling material has a small particle size, the specimen has low porosity and a few amounts of the broken particles can fill the pores of the material. When the particles have relatively large sizes, the specimen has relatively high porosity and the broken particles are unable to completely fill the pores. The loading conditions of the particles can only be changed by the frame structure formed by the large particles. If the proportion of the particle size grade is reasonable, a frame structure forms due to the large particles and the small particles with various particle sizes can fill the pores of the backfilling material. This enhances the deformability of the gangue and decreases the compressive deformation of the backfilling material. After backfilled into the goaf, the backfilling material bears the overburden pressure, which means the process of roof convergence is the process of compressive deformation of the backfill body. That is to say, the stiffer the backfilling material, the better the control effect. The importance of the reasonable proportion of the particle size grade is explained from the aspect of microscopic breakage of the particles, which provides a scientific basis for backfill mining.

Using viscosity-modifying admixture to increase the cohesion of low-cement concrete mixture

Low-cement concrete (LCC) is made by considering the particle packing of the constituent material. The minimal content of cement paste is achieved by optimizing the coarse and fine aggregate particle size gradation to reduce the void volume (Vv) between the aggregate particles. Theoretically, the minimum cement paste can be calculated as the cementitious paste volume (Vp) filling the entire void volume (Vp/Vv = 100%). Practically, low fine or powder material content would reduce concrete mixture cohesion and cause bleeding and segregation. Viscosity-modifying admixture (VMA) can be added as an alternative to adding more cement powder or supplementary cementitious materials to improve the cohesion and stability of the LCC matrix. This study investigated the role of VMA addition in increasing stability in low water to cement ratio (w/c) mortar with an excessive dosage of superplasticizer and in high w/c mortar designed with low cement content. The results showed that adding VMA reduced bleeding and increased cohesion in the fresh mixture, and also increased the compressive strength of the hardened mortar. Although the addition of VMA cannot increase the workability of LCC, it had a beneficial effect when added to an LCC mixture as the 28-day compressive strength of the concrete with w/c of 0.5 was increased from 18.68 MPa to 22.93 MPa by adding 0.4% VMA by mass of cement.

Research on the Model Test of the Debris Landslide’s Evolution Process in Tailings Reservoir

Based on the actual tailings reservoir project, a model test study on the evolution pattern of dam-breaking debris landslide is carried out. According to the similarity criterion of water flow and mud-sand movement, coal dust satisfying the similar relationship is selected as model sand. By analyzing the dam-breaking debris landslide’s range, propulsion speed, submerged depth distribution and particle deposition characteristics, the movement pattern of the landslide is obtained. In the short time after the dam break, the submergence range and advancing speed of the debris landslide increase rapidly. During the propulsion process, due to the increase of the debris landslide in the downstream of the valley, the debris landslide is diffused and the energy consumption during the flow is made. The advancing speed decrease until the landslide stops; The final submerged depth distribution of the dam breach has obvious randomness and non-uniformity, which is mainly related to the downstream terrain; According to the particle size grading analysis of the soil sample at the characteristic location, the further away from the dam toe, the finer particle content in the debris landslide.

A Liquefaction Resistance of Sand-Fine Mixtures: Short Review with Current Research on Factors Influencing Liquefaction Resistance

Sand is well understood as susceptible material to liquefy under seismic condition. In many cases of liquefaction, the loss of property and damages occurred due to the earthquake phenomenon are caused by sandy soils. Thus, many laboratory experiments and field tests on soil liquefaction engineering have been mandatorily focusing on the liquefaction resistance of sand-fine mixtures. The interaction between sand and fines particles appears to be well studied subject. However, there are some contradictory findings on some factors influencing liquefaction resistance in sand-fine mixtures. Therefore, this paper aim to present results and current findings from previous researchers which focused on sand-fine mixtures using various type of sand to interpret liquefaction resistance and its behaviour. In addition, microstructure test needs to be conducted for verification and analysis of the results on grading and particle sizes characteristics. It has been identified that recent findings on the particle size distribution and grading characteristics of sand in sand-fine mixtures are still contradicting. It has also been found that there are no study using different types of sand to reconstitute tropical sand-fine mixtures; and limited study focused on the coefficient uniformity, CU and coefficient of curvature, CC on liquefaction resistance relationship.