Computer vision-aided DEM study on the compaction characteristics of graded subgrade filler considering realistic coarse particle shapes

The compaction quality of subgrade filler strongly affects subgrade settlement.The main objective of this research is to analyze the macro-and micro-mechanical compaction characteristics of subgrade filler based on the real shape of coarse particles.First,an improved Viola-Jones algorithm is employed to establish a digitalized 2D particle database for coarse particle shape evaluation and discrete modeling purposes of subgrade filler.Shape indexes of 2D subgrade filler are then computed and statistically analyzed.Finally,numerical simulations are performed to quantitatively investigate the effects of the aspect ratio(AR)and interparticle friction coefficient(μ)on the macro-and micro-mechanical compaction characteristics of subgrade filler based on the discrete element method(DEM).The results show that with the increasing AR,the coarse particles are narrower,leading to the increasing movement of fine particles during compaction,which indicates that it is difficult for slender coarse particles to inhibit the migration of fine particles.Moreover,the average displacement of particles is strongly influenced by the AR,indicating that their occlusion under power relies on particle shapes.The dis-placement and velocity of fine particles are much greater than those of the coarse particles,which shows that compaction is primarily a migration of fine particles.Under the cyclic load,the interparticle friction coefficientμhas little effect on the internal structure of the sample;under the quasi-static loads,however,the increase inμwill lead to a significant increase in the porosity of the sample.This study could not only provide a novel approach to investigate the compaction mechanism but also establish a new theoretical basis for the evaluation of intelligent subgrade compaction.

Gravel hardness effect on compaction characteristics of gravelly soil

The compaction characteristics of gravelly soil are affected by gravel hardness.To investigate the evolution and influencing mechanism of different gravel hardness on the compaction characteristics of gravelly soil,heavy compaction tests and crushing tests were conducted on gravelly soils with gravels originated from hard,soft and extremely soft rocks.According to orthogonal experiments and variance analysis,it was found that hardness has a significant impact on the maximum dry density of gravelly soil,followed by gravel content,and lastly,moisture content.For gravel compositions with an average saturated uniaxial compressive strength less than 60 MPa,the order of compacted maximum dry density is soft gravels>hard gravels>extremely soft gravels.Each type of gravelly soil has a threshold for gravel content,with 60%for hard and soft gravels and 50%for extremely soft gravels.Beyond these thresholds,the compacted dry density decreases significantly.There is a certain interaction between hardness,gravel content,and moisture content.Higher hardness increases the influence of gravel content,whereas lower hardness increases the influence of moisture content.Gravelly soils with the coarse aggregate(CA)between 0.7 and 0.8 typically achieve higher dry densities after compaction.In addition,the prediction equations for the particle breakage rate and CA ratio in the Bailey method were proposed to estimate the compaction performance of gravelly soil preliminarily.The results further revealed the compaction mechanism of different gravelly soils and can provide reference for subgrade filling construction.

Clogging caused by coupled grain migration and compaction effect during groundwater recharge for unconsolidated sandstone reservoir in groundwater-source heat pump

In unconsolidated sandstone reservoirs,presence of numerous movable grains and a complex grain size composition necessitates a clear understanding of the physical clogging process for effective groundwater recharge in groundwater-source heat pump systems.To investigate this,a series of seepage experiments was conducted under in situ stress conditions using unconsolidated sandstone samples with varying grain compositions.The clogging phenomenon arises from the combined effects of grain migration and compaction,wherein the migration of both original and secondary crushed fine-grain particles blocks the seepage channels.Notably,grain composition influences the migration and transport properties of the grains.For samples composed of smaller grains,the apparent permeability demonstrates a transition from stability to decrease.In contrast,samples with larger grains experience a skip at the stability stage and directly enter the decrease stage,with a minor exception of a slight increase observed.Furthermore,a unique failure mode characterized by diameter shrinkage in the upper part of the sample is observed due to the combined effects of grain migration and in situ stress-induced compaction.These testing results contribute to a better understanding of the clogging mechanism caused by the coupled effects of grain migration and compaction during groundwater recharge in unconsolidated sandstone reservoirs used in groundwater-source heat pump systems.

Micro-destructive assessment of subgrade compaction quality using ultrasonic pulse velocity

The ultrasonic pulse velocity(UPV)correlates significantly with the density and pore size of subgrade filling materials.This research conducts numerous Proctor and UPV tests to examine how moisture and rock content affect compaction quality.The study measures the changes in UPV across dry density and compaction characteristics.The compacted specimens exhibit distinct microstructures and mechanical properties along the dry and wet sides of the compaction curve,primarily influenced by internal water molecules.The maximum dry density exhibits a positive correlation with the rock content,while the optimal moisture content demonstrates an inverse relationship.As the rock content increases,the relative error of UPV measurement rises.The UPV follows a hump-shaped pattern with the initial moisture content.Three intelligent models are established to forecast dry density.The measure of UPV and PSO-BP-NN model quickly assesses compaction quality.

Overview on Soil Compaction and Sugar Beet Growth

With the advancement of agricultural mechanization,soil compaction has become a serious environmental problem.Soil compaction can increase soil bulk density and firmness,reduce porosity and permeability,and deteriorate soil structure,ultimately inhibit sugar beet growth and reduce both root yield and sugar content.However,few farmers recognize the link between soil compaction and these adverse effects.Soil compaction has a cumulative effect,with significant differences observed in the vertical range of compaction accumulation.The most significant soil compaction occurs in the topsoil of 0-10 cm,and the influence depth can reach 70 cm,but it is small in deep soil,and the inflection point is at a soil depth of 10 cm.The degree of soil compaction is related to soil type,water content,tractor shaft load,tyre type,tyre pressure and operation speed,etc.Therefore,in the production process of sugar beet,it is advisable to avoid high-humidity operations,use low pressure tyres,reduce the number of tractor-units passes over the farmland,and implement agricultural and agronomic measures to minimize soil compaction.These practices will help protect the soil environment and ensure sustainable production of sugar beets.

Urban Soil Compaction Remediation by Shallow Tillage and Compost in Hydroseeded Lawn

Construction activities often involve removal of topsoil and compaction of the exposed soil by heavy equipments. Such compacted soils with low organic matter can lead to low infiltration and poor vegetation establishment. The objective of this study was to investigate the efficacy of tillage (shallow till) and compost on soil physical and biological properties in a hydroseeded lawn as a post-construction best management practice for soil compaction remediation. The experimental site received a total of four land treatments in five replicated trials and it was hydroseeded with common Bermuda grass: 1) No Tillage + Compost (NT-C), 2) No Tillage + No Compost (NT-NC;control), 3) Tillage + Compost (T-C), and 4) Tillage + No Compost (T-NC). Bulk density (BD), infiltration rate (IR), and wet aggregate stability (WAS) in each plot were measured to assess soil physical properties while soil organic matter (SOM) and enzyme activity (β-glucosidase, acid-phosphatase, and alkaline-phosphatase) were measured for soil biological properties. Over a 15-months of monitoring period, the shallow tillage loosened the soil initially, but its effect on BD without compost was diminished to control plot level (NT-NC) within 4 months after hydroseeding. Both tillage and compost led to an increase in IR, and it remained higher than control by 2 - 3 times throughout the observation period. The WAS and β-glucosidase activity decreased in tilled plot unless there was compost application. Turfgrass showed greener leaves and aggregated roots in the compost-amended plots (NT-C and T-C). Our results suggest that compost application plays a key role in improving soil physical and biological properties in hydroseeded lawns from construction sites.

Influence of particle size on property of Ti-6Al-4V alloy prepared by high-velocity compaction

Three Ti-6Al-4V alloy powders with median diameters of 103, 66 and 44 pm, respectively, were pressed by high-velocity compaction （HVC） technology and then sintered in vacuum. The effects of particle sizes on forming as well as properties of sintered samples were investigated. The results show that fine powders are more difficult to press than coarse powders and its compact density is lower too. But the sintered density of fine powders is obviously higher than that of coarse powders. Compared with the powders with 103 and 66 ~un in diameter, the green density with 44 ~rn diameter powders is lower, which is 85.1% of theoretical density （TD） at an impact energy of 913 J. After sintering at 1300 ~C for 2,5 h, the sintered density of the compacts with 44 pm diameter powders is the highest, and reaches 98.2% of TD. Moreover, the sintered sample with 44 pan in diameter has the highest hardness and compressive strength, which are HV 354 and 1265 MPa, respectively.

Summary and Improvement Measures for Soil Compaction Caused by Machinery

As agricultural mechanization is becoming more and more popular, soil compaction, on basis of agricultural machinery, has become a serious problem that can not be ignored. Soil compaction, which is caused by frequent til age and large load in the field, may have different effects on various properties of soil. Soil com-paction may result in different conditions, such as increased soil density and the mechanical resistance, and decreased soil ventilation and the capacity of water holding and storage, but uptaking capacity of chemical elements is restricted. There-fore, soil compaction has some negative impacts on soil properties, physical y, chemical y, or biological y, as wel as plant growth. This research analyzed the cause and the harm of soil compaction in recent years, and some effective mea-sures were proposed to improve soil compaction, in order to reduce the extent of soil compaction caused by agricultural machinery.

Test and analysis of dynamic compaction vibration based on piezoelectric sensor

The paper takes a new campus project site of Shanxi university town for example, tests the influence of dynamic com- paction vibration and vibration isolation effect of isolation trench on this ground, and compares the influences of the dynamic compaction vibration on surrounding buildings with isolation trench and without it. Furthermore, the attenuation law of dy- namic compaction vibration in fill foundation of the loess area under different tamping energy and how to determine safe distance of dynamic compaction construction are studied. And then the quantitative relationship between acceleration and vibration source in new campus project site is presented. We derive the evaluation method that dynamic compaction construction affects adjacent buildings by contrasting with the existing standards and norms. The monitoring results show that isolation trench makes the amplitude attenuation of the horizontal velocity of dynamic compaction vibration reach above 75%, and the safe dis- tance be 30 m under the tamping energy of 6 000 kN · m. Therefore, isolation trench is better for vibration reduction under dynamic compaction construction.

Discrete element modeling of migration and evolution rules of coarse aggregates in the static compaction process

To investigate migration and evolution rules of coarse aggregates in the static compaction process, an algorithm of generating digital coarse aggregates that can reflect real morphology（ such as shape, size and fracture surface） of aggregate particles, is represented by polyhedral particles based on the discrete element method（ DEM）. A digital specimen comprised of aggregates and air voids is developed. In addition,a static compaction model consisting of a digital specimen and three plates is constructed and a series of evaluation indices such as mean contact force σMCF, wall stress in direction of zcoordinate σWSZZ, porosity and coordination numbers are presented to investigate the motion rules of coarse aggregates at different compaction displacements of 7. 5, 15 and 30 mm. The three-dimensional static compaction model is also verified with laboratory measurements. The results indicate that the compaction displacements are positively related to σMCF and σWSZZ, which increase gradually with the increase in iterative steps. When the compaction proceeds, the digital specimen porosity decreases, but the coordination number increases. The variation ranges of these four indices are different at different compaction displacements. This study provides a method to analyze the compaction mechanism of particle materials such as asphalt mixture and graded broken stone.

VITEK■ 2 Compact全自动微生物鉴定药敏分析仪虚拟仿真教学软件的开发与应用

文章主要介绍了VITEK■2 Compact全自动微生物鉴定药敏分析仪虚拟仿真教学软件的设计与开发,以及虚拟仿真融合线上线下混合教学模式在医学微生物检验实验教学中的应用。结果表明,该仿真教学软件的实际应用既有利于培养学生的实践操作能力及思维方式,又能弥补学校实训环境与临床实际不符的缺陷,为微生物检验实验教学质量的提升开辟新的思路。

The stress-strain-permeability behaviour of clay rock during damage and recompaction

Characterisation and understanding of the stressestrainepermeability behaviour of a clay host rock during damage and recompaction are essential for prediction of excavation damaged zone and for assessment of its impact on the repository safety. This important issue has been experimentally studied in triaxial compression tests on the Callovo-Oxfordian clay rock in this study. The samples were sequentially loaded by(1) hydrostatic precompaction to close up sampling-induced microcracks,(2)applying deviatoric stresses to determine damage and permeability changes, and(3) recompression along different loading paths to examine reversibility of the damage. The critical stress conditions at the onset of dilatancy, permeability percolation, failure strength, and residual strength are determined. An empirical model is established for fracturing-induced permeability by considering the effects of connectivity and conductivity of microcracks. The cubic law is validated for the variation of permeability of connected fractures with closure. The experiments and results are also presented and discussed.

Effect of Die Wall Lubrication on Warm Compaction Powder Metallurgy

Die wall lubrication was applied on warm compaction powder metallurgy in hope to reduce the concentration level of the admixed lubricant since lubricant is harmful to the mechanical property of the sintered materials. Iron-based samples were prepared by die wall lubricated warm compaction at 135 ℃ and 175 ℃, using polytetrafluoroethylene (PTFE) emulsion as die wall lubricant. A compacting pressure of 700 MPa and 550 MPa were used. The admixed lubricant concentration ranging from 0 to 0.6 wt.% was used in this study. Compared with non-die wall lubricated samples, the die wall lubricated samples have higher green densities. Results show that in addition to the decrease in ejection forces, green density of the compacts increased linearly with the decrease in admixed lubricant content. Mechanical property of the sintered compacts increase sharply when the admixed lubricant concentration reduced to 0.125 wt.% or less. Ejection force data indicated that samples with die wall lubrication show lower ejection forces when compared with samples without die wall lubrication. No scoring was observed in all experiments even for samples contain no admixed lubricant. Our results indicated that under experimental condition used in this study, no matter at which compaction pressure, compaction temperature, graphite and lubricant contents in the powder the die wall lubricated warm compaction would give the highest green density and lowest ejection force. It can be concluded that combination of die wall lubrication and warm compaction can provide P/M products with higher density and better quality. It is a feasible way to produce high performance P/M parts if suitable die wall lubrication system was applied.

Mechanical analysis of roof stability under nonlinear compaction of solid backfill body

Based on the compaction characteristic test and the nonlinear compaction deformation characteristics of backfill material, this paper applies the theory of nonlinear elastic foundation of thin plate to establish a mechanical model of backfill body and roof in solid dense backfill coal mining. This study critically analyses the deflection equation of the roof by the energy method, derives the conditions of roof breakage and combined with concrete engineering practice analyses, determines roof movement regularity and stability in solid dense backfill mining. Analysis of the engineering practice of the 13,120 backfill panel of Pingmei 12# mine shows the theoretical maximum of roof convergence in backfill mining to be415 mm which is in significant agreement with the measured value. During the advancing process of solid backfill mining at the panel, the maximum tensile stress on the roof is less than its tensile strength which does not satisfy the conditions for roof breakage. Drilling results on the roof and ground pressure monitoring show that the integrity of roof is strong, which is consistent with the theoretical calculations described in this study. The results presented in the study provide a basis for further investigation into strata movement theory in solid dense backfill mining.

Densification Mechanism of Warm Compaction and Powder Mixture Designing Rules

By phenomenological analysis of warm compaction, it is found that, compared with the contribution of particle plastical deformation to densification of powder compact,the particle rearrangement is a dominant densification mechanism for powder warm compaction, and the plastical deformation of particles plays an important role in offering accommodating deformation for particle rearrangement and densifying powder compact at the final stage of pressing.In order to attain density gain as high as possible during warm compaction, six rules for designing warm compacting powder mixtures were proposed in detail.

Mechanical and microstructural characterization of Al7075/SiC nanocomposites fabricated by dynamic compaction

This paper describes the synthesis of Al7075 metal matrix composites reinforced with SiC, and the characterization of their microstructure and mechanical behavior. The mechanically milled Al7075 micron-sized powder and SiC nanoparticles are dynamically compacted using a drop hammer device. This compaction is performed at different temperatures and for various volume fractions of SiC nanoparticles. The relative density is directly related to the compaction temperature rise and indirectly related to the content of SiC nanoparticle reinforcement, respectively. Furthermore, increasing the amount of SiC nanoparticles improves the strength, stiffness, and hardness of the compacted specimens. The increase in hardness and strength may be attributed to the inherent hardness of the nanoparticles, and other phenomena such as thermal mismatch and crack shielding. Nevertheless, clustering of the nanoparticles at aluminum particle boundaries make these regions become a source of concentrated stress, which reduces the load carrying capacity of the compacted nanocomposite.

Compaction Rate of an Early Permian Volcanic Tuff from Wuda Coalfield, Inner Mongolia

Compaction rates of sediments or volcaniclastic material are needed to reconstruct original thickness of a bed, which in turn is required to reconstruct subsidence rates, sea-level rise, or in the case of volcanielastic, the location or direction of the eruption site. The knowledge of compaction rates can also aid in the reconstruction of deformed fossils. The known shape of deformed fossils can allow the determination of the compaction they experienced. Here we report the compaction rate in an early Permian volcanic tuff from Wuda, Inner Mongolia, determined from the deformation of standing tree fern stems of known anatomy. The compaction rate has been found to be 0.56 in this case, indicating that 44% of original thickness remains.

DYNAMIC COMPACTION OF PURE COPPER POWDER USING PULSED MAGNETIC FORCE

The compaction of pure Cu powder was carried out through a series of experiments using dynamic magnetic pulse compaction, and the effects of process parameters, such as discharge energy and compacting direction, on the homogeneity and the compaction density of compacted specimens were presented and discussed. The results indicated that the compaction density of specimens increased with the augment of discharge voltage and time. During unidirectional compaction, there was a density gradient along the loading direction in the compacted specimen, and the minimum compaction density was localized to the center of the bottom of the specimen. The larger the aspect ratio of a powder body, the higher the compaction density of the compacted specimen. And high conductivity drivers were beneficial to the increase of the compaction density. The iterative and the double direction compaction were efficient means to manufacture the homogeneous and high-density powder parts.

Effects of temperature on the mechanical properties of Ti6Al4V powder compacts prepared by magnetic pulse compaction

The effects of temperature （0-500°C） on the compressive strength,hardness,average relative density,and microstructure of Ti6Al4V powder green compacts prepared by magnetic pulse compaction were investigated.The results show that with increasing heating temperature,the compressive strength first increases and then decreases with the maximum value of 976.74 MPa at 400°C.The average relative density and hardness constantly increase,and their values reach 96.11% and HRA 69.8 at 500°C,respectively.The increase of partial welding is found among the junctions of particles inside the compacts; there is no obvious grain growth inside the compacts within the temperature range.

RESEARCH AND SIMULATION OF THE INFLUENCE OF THREE-AXIAL COMPACTION ON POWDER METALLURGIC PRODUCT PROPERTIES

The warm powder compaction process is simulated by the finite element analysis software, MSCJMARC. The thermal mechanically coupled analysis method is applied on the basis of the updated Lagrangian Method, to simulate the warm powder compaction process. The warm powder compaction process is simulated, and the influence of friction condition and pressing styles are researched on the density of powder green and the mechanics behavior at certain temperature. The results indicate that for cylindrical compacts, with the improvement of the friction condition, the uniformity of distribution of green relative density is largely improved, the pressing force and stress decrease, and the nonconforming pressing processes influence the distribution of green density to some degree. The status of stress distribution of the process that punches firstly press and die finally press is different from the other three processes, and presents the figure of ＇flume ＇.