Content Of Fine Particles Research Articles

Effect of coral sand powders and seawater salinity on the impact mechanical properties of cemented coral sand

Coral sand is one kind of the important building materials in coral reef engineering practice. The use of cement as a stabilizing agent can significantly improve the mechanical properties of coral sands and is widely applied in the subbase engineering construction in coral reef islands.Cement-stabilized coral sand structures may contain high contents of fine coral particles and salinity because of the high crushability of coral sands and the existence of seawater surrounding them. In this study, the effects of coral sand powders and seawater salinity on the dynamic mechanical properties of cemented coral sand (CCS) were investigated through the split Hopkinson pressure bar (SHPB) tests and Scanning Electron Microscope (SEM) analysis. It was found that the strength (i.e., the peak stress) of CCS specimens increased firstly and then decreased with the increase of powder content. The specimens reached the maximum peak stress when 3% powder content was included. The initial improvement of CCS strength was attributed to the pore-filling effect of coral powders, namely, the micro pores of the CCS specimens could be more effectively filled with higher percentages of coral powders being used in the experiments. However, excessive coral powders resulted in the reduction of specimen strength because these powders could easily be cemented into agglomerates by absorbing water from the specimens. These agglomerates could reduce the cementation strength between the coarse coral particles and the cement. Meanwhile, the peak stress of CCS specimens was found to be negatively correlated with the average strain rate and the ultimate strain. The degree of specimen fracture was found to be correlated with the amount of specific energy absorption during the tests. Furthermore, the “sulfate attack” caused by the inclusion of salinity of water had different influences on the CCS specimens with different coral powder contents. The ettringite and gypsum produced in “sulfate attack” could fill the pores and lead to cracking of the specimens, significantly affecting the specimen strength.

Fluid–solid coupled model for the internal erosion of gap‐graded soil–rock mixtures with different fines contents: Its verification and application

AbstractSoil–rock mixtures are widely encountered in geotechnical engineering projects. Gap‐graded soil–rock mixtures are prone to internal erosion because the fine particles are easily removed by seepage flow within the large pores between the coarse particles. Internal erosion has been the focus of geological disaster research. As concluded from different studies, the fines content (FC) of gap‐graded soils is a crucial factor in controlling soil stability. For this reason, a fluid–solid coupled model with the computational fluid dynamics—the discrete element method, with an indoor physical permeability test, was conducted to study the evolution characteristics of internal erosion of gap‐graded soil–rock mixtures of different FCs. After the erosion test, the vertical section of the sample was divided into three areas according to changes in fine particles: top, middle uniform, and bottom loss areas. The study showed that a large number of particles in the bottom loss areas are lost at first and the top loss area will enter the middle uniform loss areas. The fine particles in the middle are affected by the fine particle content, from accumulation to equilibrium to loss. Fine particle loss occurred at different sample heights. The top particle loss is the most serious, followed by the bottom and then the middle, and this is consistent with the changes, from a particle‐size perspective. An FC of 35% may be the critical value of the coarse‐fine particle skeleton structure in the preset working conditions of coarse and fine particle diameters. There are apparent ‘island’ effects in the sample where FC = 40%. This can be analysed through strong force chain analysis, from the particle‐size perspective that ‘island’ effects continue to disappear under the influence of internal erosion.

Effect of back pressure on the separation performance of a hydrocyclone

In industrial process applications, to shorten the process flow and use the residual energy of hydrocyclone overflow, the overflow outlet is often directly connected to the subsequent equipment, and the back pressure of the subsequent equipment inevitably affects the normal operation of the front-end hydrocyclone. Therefore, this paper uses numerical simulation to study the effect of overflow back pressure on the internal flow field and separation performance of hydrocyclones. The results show that increasing the overflow back pressure increases the total pressure drop of the hydrocyclone, has no significant effect on the internal radial pressure gradient, and only increases the energy consumption of the hydrocyclone. With the increase in the overflow back pressure, the solid phase yield of the underflow increases, the content of fine particles gradually increases, the content of coarse particles decreases, and the separation accuracy of the hydrocyclone decreases. • The effects of back pressure on the flow field were investigated. • The influences of back pressure on the separation performance were studied. • The particle size distribution of the products were analysed.

Influence of particle size distribution on fractal characteristics of waste rock backfill materials under compression

Broken waste rock as backfill materials is filled into the underground goaf and will encounter particle breakage under the overburden pressure. The damage degree of the crushed waste rock materials directly affects the compression properties of the backfill body and the control effect of strata movement and surface subsidence. Fractal theory can be used to quantify the breakage degree of waste rock particles. In this study, compression tests are carried out on the broken waste rock materials with different particle size distributions to investigate the influence of the particle size distribution on the fractal characteristics of waste rock backfill materials under compression. The results show that the waste rock specimens with discontinuous size grading and containing more coarse particles have higher stress when entering the stable deformation stage, larger strain if at the same stress level and larger breakage ratio after compression. The particle size distribution of the crushed waste rock specimens after compressive loading has superior fractal characteristics and the fractal dimension increases with the content of fine particles and decreases significantly under discontinuous size grading. The fractal dimension has significant negative exponential function regression relationship with the strain and the breakage ratio. The strain and the breakage ratio decline with the growing fractal dimension. If the waste rock specimens have continuous particle size gradation and higher content of fine particles, the fractal dimension, the strain and the breakage ratio of the waste rock backfill materials tend to be optimal and stable, proving a desirable initial particle size distribution of the waste rock backfill materials.

A Binary Medium Model for Frozen Silty Sand Simplified by Breakage Parameter

In order to investigate the strength-deformation characteristics of frozen silty sand, the triaxial compressive strength tests of saturated frozen silty sand under different fine particle contents were carried out, and the binary medium theory was introduced to interpret the stress-strain relationship. Due to the characteristics of the existing binary medium model with many parameters and complicated determination method, a simplified binary medium model based on breakage parameter is proposed. The derived model was verified by the triaxial tests of frozen silty sand. The results show that the stress-strain relationship can be divided into three stages with the increase of axial strain, namely, linear elastic deformation stage, plastic deformation stage, and strain softening stage. All three stages can be well explained by the transformation theory of bonded element and frictional element with the binary medium model. In the linear elastic deformation stage, the external stress is mainly borne by the bonded element. In the plastic deformation stage, the stress sharing ratio of the bonded element decreases and that of the frictional element increases. In the strain softening stage, the stress sharing ratio of the bonded element decreases rapidly, while that of the frictional element increases rapidly. Under the same confining pressure, both deviator stress and the maximum values of bulk expansion decrease, while the shear strength decreases linearly with the increase of fine particle content. By comparing the measured deviator stress in triaxial test with the calculated values of binary medium constitutive model simplified by breakage parameter, the proposed model can better simulate the stress-strain relationship of frozen silty sand. The results of the study can provide some theoretical reference for the constitutive model of seasonal frozen soil.

A Multidisciplinary Approach for A Better Knowledge of the Benthic Habitat and Community Distribution in the Central and Western English Channel

About 80% of the seabed of the English Channel (EC) is covered by coarse sediment, from coarse sand to pebbles. Quantitative data on the benthic macrofauna in these types of sediment remains are rare due to the difficulty of using grab corers in such hard substrates. The deepest central part of the EC (45–101 m depth) was prospected during two VIDEOCHARM surveys in June 2010 and June 2011 to increase knowledge of such sublittoral coarse sediment benthic habitats. Sampling focussed on a longitudinal transect in the deepest part of the EC (13 boxes), extending from the western approach to the Greenwich meridian. Both indirect (side scan sonar, Remote Operated Vehicule) and direct (grab sampling with benthos determination, and grain-size analyses) approaches were used and combined, permitting description of the benthic habitats and communities using seven methods. Five benthic EUNIS habitats (European Nature Information System) were reported: MC3215, MD3211, MC4, MC3212 and MC4215, of which two extended main habitats (MC3211 and M23212) corresponded to an eastern/western gradient from sandy gravel to sandy gravel and pebbles sediment. Three other spatially discrete habitats were associated with poor coarse sand and gravel habitats as well as sandy gravel and pebbles with the presence of the brittle star Ophiothrix fragilis. Taxonomic richness of both extended habitats was on the same order of magnitude as the coarse sand habitat reported elsewhere in the EC, whilst the abundances were among the lowest in deeper areas with low nutrient input and low primary production. The epifauna appeared relatively homogenous in this type of sediment at the scale of the sampling area and was not determined to assign a EUNIS habitat/class. ROV footage illustrated the presence of large epifauna and provided valuable information to ground truth in other sampling methods such as side scan sonar mosaic. Grab photos showing surface sediment was relevant to determine the sediment type, whilst granulometric analyses gave additional information on fine particles content (typically very low).

Mathematical modeling and distribution characteristics evaluation of fuel particles in iron ore sintering process

The distribution characteristics of fuel particles is a key factor affecting the thermal state of sintering. To find out the fuel distribution under different granulation conditions, a mathematical method based on the particle population balance and Lister’s model was established in this study. In combination with experiments including granulation and the fixed carbon and sulfur content of detection, the relative error of this model is within ±1.5. The proportion and particle size composition of fuel are selected to evaluate quantitatively the distribution characteristics. The result shows that the fuel distribution in granules mostly accumulates in the middle size granules. The increase of proportion and fine particles content of the fuel leads to the decline of the fuel content in +5 mm granules. With a higher ratio and higher content of fine particles in the fuel, the fuel distribution in the upper and middle of the sintering beds rises while that of the bottom layer is down, which is conducive to changing the nonuniform distribution of thermal. The fuel particle size composition has greater impact on fuel distribution than its proportion. To better investigation, further parameter simulation and optimization of granulation is necessary.

Experimental study on sand control gravel particle gradation optimization in mud hydrate reservoir

Sand production significantly influences the safety and stability of gas hydrate exploitation in reservoirs with high mud content. Gravel packing is an effective method for sand control. The median grain size ratio (D50/d50) values and fine particle content of gravel pack are important factors in sand control during natural gas hydrate exploitation. This paper focuses on the sand blocking effect and permeability characteristics of different grades of gravel. The sand retention test was carried out on four samples with different ratios. The optimal D50/d50 value and fine particle content for gas hydrate production were obtained. A laser particle size analyzer and geotechnical test found the reservoir and gravel layer pore structure change. The results show that the optimal GSR was 24.5, and the optimal fine particle content was about 38%. The permeability decline of the gravel layer occurs in the early stage of production, and the fine particles in the gravel will slow down the degree of seepage damage. For gravel with the same particle size range and different median particle sizes, it has little effect on sand control accuracy but mainly on permeability. The research in this paper can provide a reference for selecting sand control gravel for natural gas exploitation in marine areas.

Dynamic Characteristics of Reconstituted Silt Influenced by Axial Unloading Intensity and Fine Particle Content

The stress disturbance induced by adjacent construction has a significant impact on the dynamic characteristics of the soil, resulting in complex long-term tunnel settlement under train vibration load. Through a series of dynamic triaxial tests, the effects of different fine particle contents and axial unloading intensities on the permanent axial deformation and excess pore water pressure of reconstituted silt under long-term cyclic loading were investigated. The findings show that as fine particle content in the silt increases, the threshold dynamic stress and failure cycle number decrease at first, then increase, reaching a minimum value at 10% fine particle content. The dynamic characteristics of silt are significantly affected by axial unloading, and the dynamic stress threshold amplitude of a soil sample decreases as the unloading strength increases. The accumulation of silt deformation caused by long-term cyclic load can be effectively controlled by ensuring drainage conditions.

Impacts of moss-dominated biocrusts on rainwater infiltration, vertical water flow, and surface soil evaporation in drylands

Globally widespread biocrusts form a “living skin” on most dryland soils, helping govern fundamental ecosystem functions, particularly hydrological processes. However, the underlying mechanisms of biocrust effects on soil water infiltration and evaporation are still controversial. Biocrusts possibly regulate infiltration and evaporation due to their unique physicochemical properties and influence on surface soil moisture (θ), and these assumptions were verified in this study conducted on the Loess Plateau of China. The differences in vertical soil moisture distribution and flow patterns of infiltration water between moss-dominated biocrusts and bare soil were investigated through dye tracing experiments. The evaporation characteristics of biocrusts and bare soil were also obtained by weighing micro-lysimeters in both simulated and in-situ experiments. Results showed that biocrusts retarded deep soil water infiltration below ∼ 15 cm and significantly (F = 48.15, P < 0.001) decreased the stained area ratio (percentage of stained area to total area at the same soil depth) by 16% in contrast to bare soil. Because the infiltrated water was mostly retained in shallow soil (0–15 cm) in biocrust-covered soil, their ratios of low interaction flow (stained path width < 20 mm) and high interaction flow (20 mm < stained path width < 200 mm) were significantly higher (F ≥ 7.82, P ≤ 0.007) than those of bare soil. After the dye tracing experiments, the biocrusts modestly increased θ by 17% throughout the soil profile (0–50 cm), but they remarkably increased θ by 33%−78% in the top 20 cm of soil. Additionally, the biocrusts increased soil daily evaporation rate (E) by 27%−39% (with only the exception of the beginning) and the cumulative evaporation amount by 14% in contrast to bare soil over an 8-day field measurement. More importantly, the biocrust-affected soil properties, such as the contents of fine particles and organic matter, as well as saturated water content and field capacity, were closely correlated with E (|ρ| ≥ 0.52, P ≤ 0.08). Consequently, it was concluded that biocrusts restrict the depth of rainwater infiltration and increase surface θ, which may greatly enhance surface soil evaporation in the Chinese Loess Plateau.

Determination of criterion for selectivity of disintegration of technogenic raw materials for environmentally oriented processing

Production and consumption wastes reduce utilization efficiency of natural resources and negatively affect ecosystems. More than 500 thousand hectares of land are occupied for the storage of mining waste in Russia, and the negative impact of the waste extends to territories exceeding this area by 10-15 times. Content of ferrous and non-ferrous metals in wastes of metallurgical and mining industries is comparable to content of these components in ores of promising deposits. Involving these materials in processing is an urgent priority. The most important factors determining the efficiency of processing are the selectivity of penetrating a valuable component, determining the optimal grinding size and the content of fine particles. The structure, material composition and physical and mechanical characteristics of metallurgical slags differ significantly from natural ores, so the disintegration schemes of man-made raw materials must be chosen for each material depending on its individual characteristics. The paper defines significant criteria for assessing the characteristics of the composition and properties of man-made raw materials for choosing the rational method of slag destruction according to the selectivity and energy intensity using the case of metallurgical slag.

Influence of Fines Content on the Stability of Volcanic Embankments under Rainfall and Earthquake

This study aims to investigate the effects of fine content on the mechanical behavior of embankments constructed from volcanic soil subjected to rainfall and earthquake. To accomplish this purpose, a series of 1 g model experiments on slopes using Komaoka volcanic coarse-grained soils as materials was conducted with a spray nozzle and shaking table. In the experiments, shear strain, acceleration, pore water pressure, and saturation degree were monitored and measured to provide an understanding of the failure mechanism of the model embankment with different fine particle contents during post-rainfall earthquakes. The results show that the increase in the fines content of the volcanic soil reduces the permeability of the volcanic embankment but has no significant effect on rainfall-induced slope failure until the shear strain is less than 6%. Moreover, the seismic resistance of volcanic slopes subjected to previous rainfall increases when the fine particle content increases to a certain threshold of about 27%.

Comparison of Microstructure, Microhardness, Fracture Toughness, and Abrasive Wear of WC-17Co Coatings Formed in Various Spraying Ways

WC-Co cermet materials serving as protective coatings are widely used in many fields. Conventional WC-17Co coatings were formed in high-velocity oxygen-fuel (HVOF), warm spraying (WS), and cold spraying (CS), respectively. Deposition behavior of a single WC-17Co particle, as well as the microstructure, microhardness, fracture toughness, and abrasive wear of WC-17Co coatings formed in various spraying ways were investigated. The results show that the deposition behavior of a single WC-17Co particle was different after it was deposited onto a Q235 steel substrate in various spraying ways. The WC-17Co splat deposited by HVOF showed a center hump and some molten areas, as well as some radial splashes presented at the edge of the splat. The WC-17Co splat deposited by WS presented a flattened morphology with no molten areas. However, the WC-17Co splat deposited by CS remained nearly spherical in shape and embedded into the substrate to a certain depth. All the WC-17Co coatings had the same phase compositions with that of feedstock. The microstructure of all the WC-17Co coatings was dense with no cracks or abscission phenomena between the coatings and substrate. Moreover, fine WC particles were formed in the coatings due to the fracture of coarse WC particles, and the content of fine WC particles in the cold-sprayed coating was significantly more than the other coatings. A stripe structure was formed by the slippage of fine WC particles with a plastic flow of Co binder in the warm-sprayed and cold-sprayed coatings. More fine WC particles, as well as the stripe structure, in the coatings were conducive to improve the microhardness and fracture toughness of the coating. The microhardness and fracture toughness of the cold-sprayed WC-17Co coating were the highest among the coatings. The main wear mechanism of all coatings was the groove and some peel-offs. The cold-sprayed WC-17Co coating with the lowest wear loss presented the highest wear resistance among the coatings.

Effect of Particle Combination Ratio of Soil Rock Mixture on Shear Strength

With the increase of fine-grained soil content, the properties continue to transform to fine-grained soil, which will affect the permeability and strength of the soil. Even if the content of silt and clay in fine-grained soil is not high, it will significantly impact soil properties. When the content of coarse particles is low, the nature of soil depends on the fine particles in the soil. When the content of coarse particles gradually increases, and the coarse particles are overhead, the nature of soil only depends on the coarse-grained soil, and the influence of fine particles on the nature of soil gradually weakens. To reveal the interaction mechanism between coarse and fine particles in high moisture content clayey gravel, this project conducts a systematic experimental study on the high moisture content clayey gravel, takes 0.5mm as the particle size limit, takes the separation of coarse and fine particles in the soil sample as the control test, and systematically tests the shear strength of the separated fine particles; systematic shear strength tests were also carried out on the separated coarse particles. In addition, shear strength tests were carried out on soil samples with different fine particle content.

Investigation of optimal design and separation performance of the hydrocyclone with a vorticose involute-line diversion feeding body

As an important transport channel for multi-phase flow, the feeding body imposes significant effects on the formation of granularity layer and pre-separation of particles. In a conventional feeding body, particles are generally under a turbulent state and intensively collide with the wall surface, thereby leading to the decline in particle separation precision. In this study, a novel hydrocyclone with a vorticose involute-line diversion feeding body was designed, and meanwhile the feeding body was optimized in structure. By means of numerical analysis, the inner flow field and particle separation performance were examined. It was found that using the novel structure of the feeding body can effectively reduce the inner turbulence in the hydrocyclone, accompanied with the enhancement of flow field stability and particle separation precision. Compared with the conventional hydrocyclone, the content of fine particles in the overflow can be enhanced by 32.68% while that in the underflow can be reduced by 43.17% using the novel feeding body. To be specific, the quality efficiency and quantity efficiency of the novel hydrocyclone were 15.66% and 14.87% higher than that of the conventional hydrocyclone, respectively, exhibiting remarkable improvement. Finally, the effect of inlet flow rate on the separation performance of the novel hydrocyclone was investigated. Results show that fine particles moved gradually outwards with the increasing inlet flow rate, accompanied with gradually increasing content of fine particles in the underflow and the decline in the mass of coarse particles. The cutting capability can also be enhanced with the increase of the inlet flow rate. At an inlet flow rate of 4.1055 L/min, the separation precision reached a peak. The present conclusion can offer insightful guidance for the further development of novel hydrocyclones.

Discrete Element Modeling of Instability Mechanisms of Unbound Permeable Aggregate Base Materials in Triaxial Compression.

Unbound permeable aggregate base (UPAB) materials with strong load-transmitting skeleton yet adequate inter-connected pores are desired for use in the sponge-city initiative. However, the micro-scale fabric evolution and instability mechanism of macroscopic strength behavior of such UPAB materials still remain unclear. In this study, virtual monotonic triaxial compression tests were conducted by using the discrete element method (DEM) modeling approach on specimens with different gradations quantified by the parameter of gravel-to-sand ratio (G/S). The realistic aggregate particle shape and inter-particle contact behavior were properly considered in the DEM model. The micromechanical mechanisms of the shearing failure of such UPAB materials and their evolution characteristics with G/S values were disclosed from contact force chains, microstructures, and particle motion. It was found that the proportion of rotating particles in the specimens decreased and the proportion of relative sliding between particles increased as the content of fine particles decreased. The plastic yielding of the specimens originated from the failure of contact force chains and the occurrence of the relative motion between particles, while the final instability was manifested by the large-scale relative motion among particles along the failure plane (i.e., changes in the internal particle topology). By comparing the macroscopic strength, microstructure evolution, and particle motion characteristics of the specimens with different G/S values, it was found that the specimens with G/S value of 1.8 performed the best, and that the G/S value of 1.8 could be regarded as the threshold for separating floating dense and skeletal gap type packing structures. The variation of Euler angles of rotating particles was significantly reduced in the particle size range of 4.75 mm to 9.50 mm, indicating that this size range separates most of the particles from rolling and sliding. Since particle rolling and sliding behavior are directly related to shear strength, this validates the rationality of the parameter G/S for controlling and optimizing gradations from the perspective of particle movement. The findings could provide theoretical basis and technical guidance for the effective design and efficient utilization of UPAB materials.

Characterizing and Predicting the Resilient Modulus of Recycled Aggregates from Building Demolition Waste with Breakage-Induced Gradation Variation.

Building demolition waste (BDW) has been massively stockpiled due to increasingly rapid urbanization and modernization. The use of recycled BDW as unbound granular base/subbase materials is among the sustainable, cost-effective, and environmentally friendly pavement construction alternatives. The resilient modulus is an important mechanical property of BDW-derived aggregates and mechanistic design input of pavements incorporating BDW. This paper presents the results of a comprehensive laboratory study on the shear strength and resilient modulus characteristics of BDW-derived aggregate materials. A series of monotonic triaxial compression tests and repeated-load triaxial (RLT) tests were conducted with five different gradations representing particle breakage and different stress paths. The apparent cohesion and internal friction angle of recycled BDW aggregates under consolidated drained conditions ranged from 35.3 to 57.5 kPa and from 30.2° to 54.3°, respectively. The apparent cohesion and internal friction angle also increased and decreased non-linearly with the increasing relative content of fine particles, respectively. The resilient modulus of recycled BDW aggregates gradually decreased with increasing relative content of fine particles at the same stress level. Both the deviator stress and confining pressure exhibited significant influences on the resilient modulus, while the effect of confining pressure was more profound. Based on laboratory testing data, a mechanistic-empirical model was developed to predict the resilient modulus of recycled BDW aggregates from gradation and stress-state variables. The findings could be useful for extended engineering applications of BDW in unbound granular pavement base/subbase construction.

Study on the Desliming Performance of a Novel Hydrocyclone Sand Washer

A novel hydrocyclone sand washer featured by connecting a cylindrical hydrocyclone and a conical-cylindric hydrocyclone in series was developed to improve the poor grading performance in current machine-made sand processing technology. The former hydroycyclone with a flat bottom was designed to enhance the centrifugal intensity, thereby achieving the pre-grading of fine and coarse particles and ensuring the discharge of most fine mud particles from the overflow pipe. The latter hydrocyclone was designed to achieve the secondary fine separation and therefore reduce the content of fine particles in the underflow product. Firstly, the flow field inside the consecutive hydrocyclones was simulated using an RSM and VOF model. The DPM model was introduced to trace the particle motion trajectory and validate the feasibility of hydrocyclone separation. Then, the experimental study was performed using the control variable method, and the effects of the first-section overflow pipe diameter, the feeding rate, and the mud–sand mixing ratio on the desliming performance were examined. Results show that the content of particles with a diameter of below 75 μm in the second-section underflow drops significantly after the separation in the hydrocyclone sand washer. When the first-section overflow pipe diameter, the feeding rate, and the mud–sand mixing ratio are set to 34 mm, 60 kg/h and 1:1, respectively, the desliming rate of the novel hydrocyclone sand washer can reach 94.31% and the loss rate of quartz sand is only 1.28%.

Multiscale Study on Deterioration Characteristics of Soil-Rock Mixtures Under the Immersion-Air dry Circulation

Soil-rock mixtures (S-RMs) composed of rock slope colluvium and landslide deposits are common in superficial hazards of bank slopes. The physical and mechanical properties of S-RMs are closely related to environmental conditions, especially reservoir water level fluctuation. Therefore, immersion-air dry (I-AD) circulations tests were carried out to simulate the phenomenon in this study. The macroscopic, mesoscopic, and microcosmic studies of S-RMs are carried out after experiencing cycles (N) of 0, 1, 5, and 10, respectively. Conventional triaxial tests, particle analysis tests, and scanning electron microscopy were performed to study the physical and mechanical properties of S-RMs. According to test results, the maximum deviator stress of S-RMs samples with confining pressures of 100, 200, 300, and 400 kPa after ten cycles is reduced by 41.13, 37.11, 32.17, and 30.20%. With the increase in N there is a significant trend towards reducing the strength of S-RMs, and the strength deterioration after the first I-AD circulation reached 15.73%. After I-AD circulations, the content of fine particles in S-RMs decreases, the grain-size characteristic and non-uniformity coefficient increase significantly, and the gradation of S-RMs shows discontinuity. Moreover, the repeated changes of water pressure have an irreversible impact on the microstructure of S-RMs, which will cause an increase in pore size and a higher pore disorder. In addition, it is found from the established strength parameter evolution equation that when N approaches infinity, S-RMs decomposes the weathering into cohesionless silt with an angle of repose of 0.90322φ0. The study results in this paper clarify the deterioration characteristics of wading S-RMs, and might be used in the bank slopes stability analysis.

Experimental study of the dynamic characteristics of Songhua River silt with fine grains under freeze-thaw cycles using asymmetric hysteresis

The contact and bonding of soil particles are affected by the fine particle content of silty sand and the freeze-thaw cycle effects in the seasonal frozen zone, which are reflected as the dynamic characteristics of silty sand from the macroscopic point of view. The dynamic stress, dynamic shear modulus, dynamic shear modulus ratio, and damping ratio of Songhua River silt with different contents of fine soil particle (less than 0.075 mm) after repeated freeze-thaw cycles were studied respectively using a low-temperature dynamic triaxial test system and were compared with those of quartz sand. In order to approach the real test results, a piecewise equation was used to solve for the dynamic parameters. The results show that repeated freeze-thaw cycles have a great influence on reducing the dynamic stress, the dynamic shear modulus, and the dynamic shear modulus ratio, while they increase the damping ratio. For a given fine particle content and number of freeze-thaw cycles, the dynamic stress, dynamic shear modulus, and damping ratio of the Songhua River silt with fine particles are larger than those of quartz sand when the dynamic strain reaches 0.2%, and the difference gradually decreases as the number of freeze-thaw cycles increases. The dynamic shear modulus of the Songhua River silt with fine grains decreases more slowly with increasing dynamic strain than that of quartz sand. Therefore, a normalized empirical model was established to describe the relationship between the dynamic shear modulus ratio, the damping ratio, and the dynamic strain. This model is suitable for Songhua River silt with different fine particle contents and numbers of freeze-thaw cycles, and it provides good prediction results. Furthermore, the evolution of the model parameters with the experimental conditions was analyzed, and the limit value of the fine particle content was determined to be 10%. After repeated freezing and thawing, the influence of the fine particle content on parameters a and c weakened. The regression relationship between the model parameters and the test conditions can be described by a binary quadratic equation. It is suggested that the soil parameters should be used for the dynamic response analysis of Songhua River silt with fine grains after five freeze-thaw cycles.