Content Of Fine Particles Research Articles

Permanent deformation prediction model for freeze–thaw coarse–fine mixture of geomaterials with varying fine content: Influence of loading frequency

The impact of cyclic loading frequency (fcyc) on the permanent deformation (εp) of freeze–thaw coarse–fine mixture of geomaterials (FTCF) has been extensively investigated. In this work, long-term cyclic triaxial tests were conducted on FTCF specimens with varying fcyc and deviatoric stress (qcyc) with different numbers of freeze–thaw cycles (NFT), in order to investigate εp under freeze–thaw cycling. This study systematically analysed and discussed the effects of fcyc and qcyc on εp of FTCF samples with different fine particle contents (FC). A rate-dependent multistage load-prediction model for εp was proposed and evaluated. The results showed that the freeze–thaw cyclic had a less significant impact on εp when compared to the dynamic triaxial loading. The speed and piston effects of the FTCF under dynamic loads were mutually restricting, with their combined impact closely related to the loading frequency. A higher deformation resistance for a coarse-grained skeleton is attained with the effective filling of fine particle clusters in the pores of skeleton. A function was proposed to describe the relationship between the hyperbolic model parameters and fcyc, qcyc, as well as FC. This function could be used to estimate the hyperbolic model parameters under different dynamic stresses and material states. An equivalent stress-state parameter was introduced to consider the effect of the loading frequency, enabling the exploration of dynamic loading's influence on the equivalent vibration number (Neq). A comparison between the predicted results and the test data showed that the proposed model could accurately reproduce the cumulative behaviour of the εp of FTCF under different fcyc and qcyc.

Experimental Research on the Physical and Mechanical Properties of Remolded Fine-Grained Debris-Flow Deposits

Abstract To make better use of debris-flow deposits, this paper adopts fine-grained debris-flow deposits (< 2 mm) sampled from Jiangjia Gully to constitute 17 gradation structures and determines the shear strength of the remolded structures at different moisture contents and vertical loads. Furthermore, the role and mechanism of each grain size interval in the remolded soils is discussed in depth. Grey correlation analysis is also introduced to evaluate the degree of influence of each factor on remolded structures. The results indicate that the difference in grain size distribution causes different physical and mechanical characteristics for remolded structures under different external conditions. The correlation degree of each influencing factor on the shear strength of remolded soil is ordered as follows: vertical load > moisture content > structural gradation. At different moisture contents, fine particles exert the greatest effect on the physical and mechanical characteristics of remolded soils, especially variation in the content of fine particles of less than 0.16 mm. At low moisture content, both fine particles and coarse particles facilitate the improvement of shear strength, and the increase in particle content in the range of 0.315–0.16 mm helps to enhance the mechanical properties of remolded structures. At high moisture content, the influence of the variation in intermediate particle content should be considered, especially the increase in particle content in the size range of 0.63–0.315 mm, which helps to improve the shear strength. The change in moisture content affects the cohesion of fine particles in the structures, and the change in vertical load shifts the contact form between particles in the structures, thereby affecting the internal frictional resistance and cohesion of remolded structures. The results obtained from this research are expected to provide a good basis for the reutilization of debris-flow deposits.

Effect of Crushing Method on the Properties of Produced Recycled Concrete Aggregates

Construction and Demolition Waste (C&DW) is generated around the world and its quantity will increase in the future. Recycling has become the favored method of dealing with concrete waste but, to avoid its downcycling, it is important to develop a recycling process which is able to produce high-grade recycled concrete aggregates (RCA). To that end, studying the influence of the production process on the properties of RCA can prove to be a crucial step toward a more circular construction industry. In this study, the influence of the crushing method is investigated. Samples of five laboratory-made concretes have been crushed using the most common mechanical crushing methods (impact crusher and jaw crusher), and the particle size distribution, morphology, hardened cement paste content and water absorption of the produced RCA have been measured and analyzed. The findings indicate that the use of impact crushers results in the production of RCA possessing more spherical geometric characteristics, albeit with a broader particle size distribution and a relatively higher content of fine particles as compared to those obtained from jaw crushers. Additionally, it is observed that the employed crushing technique seemingly exerts no discernible impact on the hardened cement paste content and the water absorption in the context of the studied concretes.

Effect of deformation parameters and Al2Cu evolution on dynamic recrystallization of 2219-O Al alloy during hot compression

The properties of Al alloy are significantly affected by the evolution of the microstructure during hot deformation. In this study, the 2219-O Al alloy was tested by hot compression at different temperatures, strain rates and compression ratios. Microstructures were analyzed at different parameters based on scanning electron microscopy and electron backscattered diffraction. With the temperature rising above 350 °C, more Al2Cu particles were dissolved. Instead, the increasing strain rate had a slightly positive effect on the precipitation of Al2Cu. The main dynamic recrystallization (DRX) mechanism in the 2219-O Al alloy was continuous dynamic recrystallization (CDRX) facilitated by fine Al2Cu particles. Particle stimulated nucleation (PSN) and discontinuous dynamic recrystallization (DDRX) were also observed. At 250–350 °C, the rising temperature gradually promoted the DRX with the stable content of fine Al2Cu particles. At 350–450 °C, the decrease of Al2Cu particles with rising temperature weakened the DRX. At 490 °C, all fine Al2Cu particles were dissolved, and the extremely high temperature significantly promoted the migration of grain boundaries, strengthening the DRX. The decreasing strain rate and increasing strain facilitated the DRX.

Effects of Soil Particle Structure on the Distribution and Transport of Soil Water and Salt

Unsaturated zones are critical for water and material exchange between groundwater and surface ecosystems. Understanding the migration patterns of soil water and salts in these zones can offer theoretical support for maintaining the equilibrium between groundwater and surface ecosystems in Northwestern China’s salinized regions. This study explores the correlation between soil particle composition and soil water and salt distribution at a test site in the lower reaches of the Shiyang River basin. It analyzes the way in which water and salt patterns vary with different soil structures over various timescales. The results indicate that lithological profiles with similar structures but varying fine particle contents exhibit distinct water–salt variation patterns. Higher fine particle content leads to increased water and total dissolved solid content, but a decreased infiltration rate. When the middle layer has the highest fine content, soil evaporation is partially inhibited. The more complex the lithologic structure, the less effective irrigation is in leaching salt. However, when the lithologic structure remains constant, fine particle content has minimal impact on salt leaching.

Effects of Drying and Wetting Process on the Tensile Strength of Granite Residual Soil

The tensile strength of granite residual soil has different changing laws during the wetting and drying process which often appears after rainfall. The microscopic relationship between tensile strength, bond force, and absorbed suction was studied using a self-developed soil tensile strength tester. The results show the following. (1) The change in tensile strength with saturation is a convex curve with a peak; according to the drying and wetting path, there are differences in peak value and amplitude of variation. (2) The sample with a higher fine particle content has a structure that is denser and has fewer pores, while an increase in gravel content will significantly reduce the tensile strength of the soil. (3) Absorbed suction and bond forces are important factors that control tensile strength in the drying process. The bond force contributes more than 70%, the tensile strength is in invariable constant saturation, and the wetting process is mainly controlled by absorbed suction.

Experimental Study on the Effect of Fines Content on the Frost Swelling Characteristics of Coarse-Grained Soil in Canal Base Under Open System

Abstract Engineering usually considers coarse-grained soils as non-frost swelling soils, but serious frost swelling still occurs in coarse-grained canal bases, which is directly related to the recharge conditions and the fine particle content in the soil. Little attention is currently paid to the effect of different fine particle contents on coarse-grained soil frost swelling, especially after the fine particle admixture content exceeds 16%. This paper considers the characteristics of coarse-grained soils in water conservancy projects with fines content between 0% and 50%. The coarse-grained soils with 5%, 15%, 25%, 35%, and 45% fines content were designed for freezing and swelling tests. The evolution of temperature and moisture fields and the amount of freezing and swelling of coarse-grained soils during the freezing process were studied by using servo-type freezing and swelling and thawing tester. The experimental results show that the cooling process of soil samples can be divided into a rapid cooling stage, a slow cooling stage, and a freezing stabilization stage. The cooling rate and the frost heave amount with increasing fines content showed a trend of first increasing and then decreasing.

Evaluation and comparison of various methods used for aggregates investigations

Natural aggregates from sedimentary rock, like limestone and dolomite, are of a great use in various practical applications. To evaluate their quality, among others, the test of methylene blue adsorption (MB value) using a filter paper is recommended. However, one can consider it as a rough test. In this paper we wished to evaluate its quality by comparison with a more precise spectrophotometric method, i.e., to perform adsorption isotherms of methylene blue from aqueous solutions, as well as determine other parameters characterizing the aggregates. For this purpose, methylene blue adsorption on samples of limestone and dolomite natural aggregates having various grain sizes were studied to assess quality (fine particles content) of the manufactured aggregates. To determine the amount of adsorbed dye two methods were used: the methylene blue stain test and the dye adsorption from its solutions at various concentrations under static conditions. From the linear form of Langmuir adsorption isotherms of methylene blue, the monolayer capacity was determined, and then the specific surface areas of all fractions of aggregates. The structural (N2 adsorption/desorption), textural (SEM/EDS) and crystallographic structure of the aggregates were studied. It was determined that the MB values for 0–2 and MBF for 0–0.125 mm aggregates fractions fulfill the criteria set out in the specifications required for pavement construction. A very good repeatability of the adsorbed amount of methylene blue on the dolomite and limestone aggregates were obtained by these two different methods. These results confirm the reliability of the method blue test used typically in industrial conditions. The measured specific surface areas of limestone and dolomite using N2 adsorption (SBET) are smaller than SMB determined by methylene blue adsorption from aqueous solutions. This is because in aggregates, apart from calcite and dolomite, there is a small admixture of quartz and clay minerals. During N2 adsorption in dry condition, the external surface of the grains is determined, while in the aqueous solution of methylene blue, both the external and inner surfaces of clay minerals are determined.

Research on micro-influence mechanism of fine particles on dynamic characteristics of graded macadam materials in heavy-haul railway subgrade beds

Fine particle content is an important physical state parameter of graded macadam materials used in heavy-haul railway subgrade beds. Understanding the micro-influence mechanism of the fine particle content on the filler’s dynamical characteristics is of great significance. In this study, the granular system generation logic in PFC3D software was modified to enhance efficiency and quality, and the three-dimensional discrete element numerical model of graded macadam materials dynamic triaxial specimen was established. The servo program was used to simulate the dynamic triaxial numerical test confining pressure and dynamic loading conditions. A series of laboratory tests were performed using a GCTS large-scale cyclic triaxial test system to calibrate and verify the numerical model. Finally, dynamic triaxial numerical tests were conducted for graded macadam materials with different fine particle contents. These tests had the aim of determining the variation law for the contact force chain distribution, mechanical coordination number, average rotational angular velocity, and energy dissipation of the specimens under cyclic loading with the increase of fine particles and then revealing the influence mechanism of fine particles on the dynamic characteristics of graded macadam materials used in heavy-haul railway subgrade beds from a microscopic perspective. The study’s findings serve as a framework for describing the mechanism of subgrade bed disease occurrence and proposing effective remediation measures.

Experimental investigation and prediction model of permeability in solidified coarse-grained soil under freeze-thaw cycles in water-rich environments

In freeze–thaw and water-rich environments, high-speed railway subgrade systems experience significant changes in their moisture field due to the combined effects of temperature and pore pressure gradients. This poses a serious challenge to the long-term safety of high-speed railways. To address this issue, the permeability of high-speed railway subgrade fill materials before and after modification was tested using a self-developed infiltration instrument. Modifications included increasing the fine particle content and adding self-developed solidifying additives. Based on experimental results and discussions on the solidification mechanism of the fill, a model for predicting the permeability coefficient of the fill was proposed and analyzed. Results show that the self-developed additive is an efficient material for reducing permeability, with effects reaching up to the order of 107. The additive also demonstrates excellent resistance to freeze–thaw environments. Mineral-based cementitious materials have a greater impact on permeability coefficient than cement-based materials. The permeability coefficient prediction model was validated, showing a 92.3% consistency level with laboratory test results. Parameter analysis revealed that the model's parameters effectively characterize the pore structure, fluid environmental temperature, pore pressure, and other characteristics of porous media. The findings have important implications for stable control and moisture field guarantee in high-speed railway subgrades under freeze–thaw and water-rich conditions.

Effect of Fines Content on Pore Distribution of Sand/Clay Composite Soil

Plant sand fixation is the most durable and environmentally friendly sand mitigation measure for windblown sand hazards. For aeolian–sand composite soil, the fines content is the main factor affecting the pore size distribution characteristics and determines the soil water retention characteristics. Sandy soil with uniform particle size was used as the material, low-plasticity clay as a fine particle, and composite soils with different fines content were prepared. The evolution of the pore size distribution of composite soils was quantitatively determined using low-field nuclear magnetic resonance technology, and the influence of the fines content on the pore size distribution was obtained. The results show that as the fines content increases, the pore size first increases and then decreases. The pore size distribution curve gradually changes from a single-peak structure to a double-peak structure and becomes a unimodal structure again. The corresponding dominant pore size of composite soils increases first and then decreases with the increase in the fines content. A critical fine particle content is identified to control the strong local honeycomb pore structure of composite soils, which provides a theoretical basis for the material selection and design of plant sand fixation measures.

Numerical investigation of variable-mass seepage mechanism of broken rock mass in faults

The continuous migration and loss of small particles in fractured rock mass with water flow is the main cause of water inrush in fault zones. In this study, a fluid–solid coupling model for fault zone was established to study the complex coupling between the groundwater seepage and migration of broken rock mass, and reveal the mechanism of erosion-induced water inrush. The rock skeleton and broken rock mass in the fault zone were modelled by large skeleton particles and small filling particles, respectively, in 3D particle flow software while the fluid flow through the fault was modelled by the built-in computational fluid dynamics module. The numerical results show that: (1) with the increase of water pressure, the loss of filling particles increases continuously, and the whole seepage process can be divided into three stages: slow seepage, abrupt seepage and steady seepage, (2) the mass loss, porosity and permeability first increase slowly, then increase rapidly, and finally tend to be stable, (3) higher fine particle content are more likely to cause structural instability due to mass loss, thus increases the risk of water inrush and mud outburst.

Damping Ratio of Sand Containing Fine Particles in Cyclic Triaxial Liquefaction Tests

Sand liquefaction triggered by earthquakes is a devastating geological disaster and has emerged as an engaging topic in earthquake engineering. With an enhanced understanding of pure sand liquefaction promoted by laboratory research, there is a growing concern, following filed investigations, over the influence of fine particles on the liquefaction potential of sand containing inclusions. Efforts have been devoted to clarifying the significance of certain physical indicators (e.g., plasticity index, particle shape and gradation characteristics), and fruitful conclusions can be found in the published literature. However, the relationship between the content of fine particles and the cyclic degradation in liquefaction process seems still unclear. To fill this knowledge gap, three sets of cyclic triaxial tests were performed on various sand–fines mixtures with the dry tamping method. The experimental results revealed that (i) fine particles provided a negative contribution to the global soil structure; (ii) however, the damping ratio measured from the obtained stress–strain loops manifested its independence from the fines content during cyclic degradation. In this paper, we propose a shearing mechanism on the microscopic scale to explain the above contrasting observations. For a given soil fabric, the fine particles around sand-to-sand contact points probably break strong force chains, intensifying the threat of liquefaction. By contrast, these fines play the same role in favouring relative sliding between sand grains during both the loading and unloading stages. As the maximum stored energy and the energy loss per cycle are amplified with the same scaling factor, the damping ratio, defined as the ratio between them, should display a macroscopic invariance in triaxial tests.

Technological solutions for rock jetting with controlled content of fine soil particles in pressure water of a hydraulic monitor

The Siberian Federal District of the Russian Federation has a significant number of placer gold deposits, composed of rocks with considerable clay content. The long time required for settling fine particle fraction of jet-broken mass leads to supplying pressure water with significant amounts of fine particles to the hydraulic monitor units. Based on the previous studies, the solutions are proposed that can be applied in developing deposits with rock jetting, water reuse from settling ponds, and significant amounts of fine particles in the developed soils. Based on these solutions, rock jetting can be conducted for both overburden and mining operations. For mining operations, it is recommended to limit the content of fine soil particles in pressure water to 60 g/l, and for overburden operations – to 100 g/l. A distinctive feature of these technological solutions is the process water supply to the hydraulic monitor with a controlled amount of fine soil particles in its composition. The accumulation of these particles in process water occurs naturally during the flushing season.

Study on shear characteristics of calcareous sand with different particle size distribution

For the island and reef project formed by filling calcareous sand, the problems of wide particle size distribution (PSD) and complex mechanical properties have to be faced. Therefore, in order to provide basic mechanical parameters for the construction of the island and reef project, triaxial shear tests were carried out on calcareous sands with five different typical PSDs. The results showed that as particle gradation became narrower, the axial strain corresponding to the strain-softening point all showed a decreasing trend and their differences gradually decreased; the confining pressure has a significant impact on the volumetric deformation modulus of calcareous sand with a wide PSD. The cohesion of calcareous sand showed a positive correlation with non-uniformity and curvature coefficients, while the variation of an internal friction angle showed a parabolic law; the internal friction angle also changes in the parabola with the change of fine particle contents. Furthermore, by establishing the PFC3D discrete element model, it was found that the numerical simulation results were in good agreement with the test results, which verifies the feasibility of the numerical simulation and the rationality of the mesoscopic parameter calibration. It was discovered that the wider the particle gradation range, the greater the axial strain corresponding to the critical coordination number; the sample with a narrow gradation interval was more likely to present a rotating displacement field to form a penetrating shear band. This study can provide design parameters for stability analysis of high and steep slopes in calcareous sand sites.

Influence of spatial distribution of fine sand layers on the mechanical behavior of coral reef sand

Fine coral sand commonly distributes in coral sand artificial foundation due to the effect of gravity sorting during hydraulic process and the particle breakage of coarse particle. Considering that the significant impact of the distribution form of fine sand on the strength and deformation properties of coral sand foundation, the effect of spatial distribution of fine sand layers on the mechanical behavior of coral sand was studied. The mechanical behavior of coral sand in the consolidated undrained (CU) shear tests were simulated by discrete element models (DEM) analysis method, and the impact mechanism of fine sand interlayers on mechanical strength was analyzed. The effect of thickness and number of fine sand interlayer on the mechanical behavior and shear deformation of coral sand specimens were analyzed based on the proposed uniformity degree, a parameter that quantify the spatial distribution of fine particle interlayers. The results show that the mechanical behavior of coral sand was simulated well by DEM based on particle scanning results. Under the condition of constant fine particle content, the average coordination number of particles increased and the minimum contact force between particles decreased when fine particles were distributed in the form of interlayer. It indicates that the fine particle interlayer has a diffusion effect on stress transfer, which revealed the mechanism of the macro increasing strength of 10%–20% under the same confining pressure. A linear relationship was found between the proposed parameter uniformity and the peak deviator stress of specimens, and the impact of uniformity on the strength was particularly significant under high confining pressures.

An improved model for predicting the thermal conductivity of sand based on a grain size distribution parameter

Soil thermal conductivity is a critical parameter in various fields related to soil heat transfer, mainly affected by porosity and saturation. In this research, the thermal conductivity of three types of sands with different properties was measured. Eight soil thermal conductivity models (including two semi-empirical models and six empirical models) were compared and evaluated. By analyzing the inadequacies of the existing models and microscopic mechanism of soil, a grain size distribution parameter was defined, and an improved model was proposed. The results showed that four empirical models from published literature provided relatively satisfactory performance but still required improvement. The improved model can accurately predict the thermal conductivity of different types of soils as the root mean square error for the three soils were 0.072, 0.073, and 0.056 W·m−1· k−1, respectively. Moreover, compared with the existing models, the improved model provided more scientific explanations for the limiting cases of porosity and saturation. In addition, this model revealed a close linear relationship between the thermal conductivity of soil and solid particles. The prominent nonlinear relationships between thermal conductivity and porosity or saturation were also depicted. Furthermore, the content of fine particles has a remarkable impact on the thermal conductivity of dry soil. It is suggested that the improved model can be used for predicting the complete thermal conductivity of soil in case there is no available field test data.

Study of decision tree algorithms: effects of air pollution on under five mortality in Ulaanbaatar

Objectives4.2 million people die every year from many diseases due to air pollution. The WHO confirms that 92% of the world’s population lives in areas where the air quality limit...

Experimental study of oil shale separation using binary medium by pulsed fluidized bed

ABSTRACT A large amount of the<6 mm fine particle oil shale created during mining and processing is frequently discarded, creating waste and an environmental hazard. A suitable fluidized dry separation technology would allow that fine particle to be de-ashed and improve the oil shale quality for effective utilization. This paper studies pulsed fluidized beds to determine the effectiveness of pulsation frequency, fines content and operating gas velocity on fluidization and separation of the fine oil shale. It was found that the introduction of fine particles could significantly improve the fluidization quality. When the content of fine particles is 5%, the average density of the bed is~2.3 g/cm3. The effective separation of the 6–3 mm oil shale was achieved using a mixed medium, with optimal separation conditions of 5% fine particle content, 4 Hz pulsation frequency, and 1.5U mf gas velocity. Finally, high efficiency dry beneficiation of 6-3 mm oil shale in pulsed fluidized bed was achieved, which is of great significance for future industrial applications.

An Experimental Study with Model Calibration for the Permanent Strain of Granite Residual Soil Subgrade under Drying-Wetting Cycles

The permanent strain is one of the most important dynamic properties of the granite residual soil. To systematically study the dynamic deformation characteristics of granite residual soil (GRS) under the drying-wetting (D-W) cycles, a series of dynamic triaxial tests is carried out to obtain the stress-strain relationship of GRS with various fine particle contents subjected to D-W cycles. The experimental results show that the growth of permanent strain consists of two stages, namely, compaction stage and compression stage. The main effect of D-W cycles is reflected in the compression stage. On the other hand, the influence of fine particle contents on the permanent strain occurs mainly at the compaction stage, which can be classified as the lubrication, densification, and asphyxiation, respectively. Subsequently, a new criterion to characterize the permanent strain of GRS is deduced from the experimental results, which accounts for both strains and rates of strains. This criterion illustrates that with the increase of D-W cycles number, the permanent strain evaluation pattern of GRS is gradually changing from plastic stabilization to plastic creep. Finally, a quadratic function model referring to the log-log scale is proposed to fit well the relationship between the permanent strain and loading cycle number of GRS under D-W cycles. It is found that the parameters of the proposed model can physically represent the strain rate, the compression strain, and the compaction strain.