To explore the influence of fly ash (FA) and silica fume (SF) on the mechanical properties of self-compacting concrete (SCC) under uniaxial and triaxial, the compressive strength test, splitting strength test, ultrasonic testing test, and triaxial test were performed in this paper. The results show that the 3 days compressive strength and splitting strength of SCC decreased with the increase of FA substitution rate. The 28 days, 56 days, and 91 days compressive strength and splitting strength of SCC increased first and then decreased with the increase of FA substitution rate. The peak stress and peak strain of SCC gradually increased with the increase of confining pressure. The peak stress and strain of SCC increased first and then decreased with the increase of FA substitution rate. Moreover, the relationship models between compressive strength and splitting strength, between compressive strength and amplitude, between peak stress, peak strain and confining pressure under different FA substitution rates were proposed. As a conclusion, the addition of SF can increase the strength of SCC obviously. Under uniaxial stress, SCC failure mode is splitting failure, under triaxial stress, SCC failure mode is shear failure. Based on the Mohr-Coulomb strength theory, the failure criterion of SCC with FA and SF was discussed. Self-compacting concrete (SCC), also known as self-leveling concrete, is a kind of concrete which can fill all parts of concrete formwork and steel bar gap compactly and uniformly without vibration or slightly vibration under the action of its own gravity . CompareAt present, the output of fly ash (FA) in China is about 550 million tons , and theThe good working performance of SCC is the basic premise to ensure the mechanical properties and durability of concrete, and the safe and reliable mechanical performance is an indispensable condition to ensure concrete. Therefore, under the premise of good working performance, reliable mechanical properties can ensure the high durability of concrete. Thus, it can be seen that the working performance is the premise, the durability is the result, and the mechanical properties are guaranteed to meet the durability requirements under the working performance. Therefore, mechanical properties have always been the focus of concrete research. At present, domestic and foreign scholars have conducted a large number of experimental studies on the mechanical properties of SCC. Mohammed et al.  studied This paper mainly discussed the effects of 4% SF and different substitution of FA on the mechanical properties of SCC under uniaxial stress and triaxial stress, which provided reference for the theoretical research and engineering application of SCC with FA and SF. The time-varying change law of mechanical properties of SCC under uniaxial stress was studied by compressive strength test and splitting strength test. The triaxial test was carried out to analyze the change law of mechanical properties of SCC under different confining pressure and to discuss the failure criterion of SCC strength. The relationship between amplitude and compressive strength was analyzed by ultrasonic test.3 and a fineness modulus of 2.63. The coarse aggregate used was continuously graded gravel in Yinchuan. UEA concrete expansion agent produced in Yantai, Shandong Province, China was adopted. Polycarboxylic acid superplasticizer was used with a water reducing rate of 30%. Tap water was used.In this study, cement used was Ningxia horse racing P·O 42.5R . The grade П FA was produced by Yinchuan Thermal Power Plant . The main performance indexes of cement and FA are shown in According to the provisions and requirements of SCC in The Technical Specification For Application of Self-compacting Concrete (JGJ/T283-2012) , and conSCC was prepared according to the test mix proportion, two types of test specimens with dimensions of 100 mm × 100 mm × 100 mm and Φ 50 mm × 100 mm were made after poured and formed. After the specimen was formed for 24 h, the mold was removed and put into the HBY-40B cement constant temperature and humidity standard curing box  .Compressive strength and splitting strength test. The compressive strength and splitting strength of SCC were tested according to The Standard for Test Methods for Mechanical Properties of Ordinary Concrete (GB/T50081-2002) . The tesUltrasonic testing test. Ultrasonic testing of specimens was determined by NM-4A non-metallic ultrasonic testing analyzer  producedσ1 = σ2 = σ3). After reached the predetermined design value, kept the lateral confining pressure constant. The axial load adopts the load control loading system, and loaded at the rate of 0.5 MPa/s until the specimen was damaged. Triaxial test. The test was carried out on the YY-RBSZ-1000 rock triaxial (creep) tester developed by Rugao City Yuanye Exploration machinery Co. Ltd, . As the basic index value of mechanical properties of SCC, compressive strength was also the basis for the study of other mechanical indexes. The results of SCC compressive strength test at different ages are shown in 2 and Al2O3 in FA reacted with Ca(OH)2 produced by cement hydration to form dense C-S-H and C-A-H gels [As shown in A-H gels , namely:2 increased correspondingly, while the decrease of the proportion of cement led to the decrease of the amount of Ca(OH)2 produced by hydration, which slowed down the overall rate of secondary hydration. As a result, the connection between C-S-H and C-A-H gels particles was not dense enough, which reduced the compressive strength of SCC.C-S-H and C-A-H gels tighten the relationship between FA particles and cement particles and improved the compactness of the internal structure of SCC. Meanwhile, FA particles and SF particles are smaller than cement particles and can be filled between cement particles to further improved the stability and compactness of SCC. Therefore, the compressive strength of SCC increased with the increase of FA substitution rate. With the further increase of FA substitution rate, the degree of secondary reaction of hydration increased and the consumption of Ca(OH)2 produced by cement hydration to form C-S-H gel. C-S-H gel can improve the pore structure and make the microstructure of SCC more compact [When the substitution rate of FA was the same, the compressive strength of SCC with FA and SF was higher than that of SCC with FA at the same age. On the one hand, because the particle size of SF was smaller than that of FA and cement particles, it can form a micro-filling effect between FA and cement particles and improve the compactness of SCC. On the other hand, because silica fume has strong pozzolanic activity, it can quickly react with Ca(OH) compact , thus imThe splitting strength test results of SCC at different ages are shown in According to the result, the effect of FA substitution rate on the splitting strength of SCC varies with ages. The 3 days splitting strength of SCC decreased with the increase of FA substitution rate, compared with control SCC of the same age, the strength decreased by 3.56–33.62%, the change law and the cause were the same as those of the compressive strength test.2 can react to consume Ca(OH)2 produced by hydration of cement to produce C-S-H gel material, and improved the splitting strength of SCC. The 56 days splitting strength of SFSCC20 reached the peak value of 7.25 MPa of this age, which was 9.02% higher than that of 28 days SFSCC20. The 91 days splitting strength of SFSCC20 reached the peak value of 7.97 MPa of this age, compared with the splitting strength of SFSCC20 at 28 days and 56 days, splitting strength increased by 18.07% and 9.93% respectively.The 7 days splitting strength of SCC with FA increased by 5.07–10.63% compared with 3 days, and that of SCC with FA and SF increased by 8.25–23.63% compared with 3 days. Thus, it can be seen that the addition of SF has a significant effect on the increase of early strength of SCC. This is because SF particles were very fine and had strong pozzolanic activity, which can control the reaction of alkali aggregate. Its main component SiO2 to excited FA in SCC, the increase of the amount of unreacted FA deteriorated the pore structure of SCC, thus reduced the splitting strength of SCC [The 28 days, 56 days and 91 days splitting strength of SCC increased first and then decreased with the increase of FA substitution rate. On the one hand, this trend was caused by the failure mode of splitting test specimen. The splitting failure extended from the microcracks in the aggregate transition zone to both sides, and deflected when it met the interface transition zone, resulted in the formation of a main crack and damaged. When FA substitution rate increased, the interface transition zone increased, and the continuous migration of microcracks consumed more fracture energy, thus improved the splitting strength of SCC. On the other hand, due to the increase of FA content, the filling effect of FA and the efficiency of secondary hydration reaction were improved, the compactness of SCC increased, and the splitting strength of SCC was improved. As FA substitution rate continues to increase, the proportion of cement clinker was correspondingly reduced, and there was not enough Ca(OH)h of SCC ,31.ft is the splitting strength of ordinary concrete, MPa; fcu is the compressive strength of ordinary concrete, MPa.Splitting strength as another important index value of mechanical properties of concrete, the relationship between it and compressive strength was also the focus of people’s research. The conversion relation between compressive strength and splitting strength of ordinary concrete commonly used in China  is shownfctm is the average splitting tensile strength of ordinary concrete, MPa; fc’ is the compressive strength of cylinder, MPa.The relationship between the average splitting tensile strength of ordinary concrete and the prescribed compressive strength of a cylinder given by ACI318-08  in the Ufc’ and the average cylinder compressive strength fcm’ according to Table 5.3.2.1 in ACI 318-08, and the cylinder compressive strength and cubic compressive strength are converted according to the European standard EN 1992-1. Approximately transformed into the power function relationship between the average splitting tensile strength and the cube compressive strength [fcum is the average compressive strength of cube, MPa.Convert the cylinder compressive strength strength  shown inAccording to the test results, the development characteristics of compressive strength of SCC and ordinary concrete were different. Therefore, the strength conversion formulas of ordinary concrete were no longer applicable to SCC. Through the analysis of the test results, the relationship between splitting strength and compressive strength of SCC was obtained as shown in ft is the splitting strength of ordinary concrete, MPa; fcu is the compressive strength of ordinary concrete, MPa.The fitted relations are as follows:Through the fitted results, it can be seen that the two relations were in good agreement with the experimental data. Equations (5) and (6) can accurately reflect the conversion relationship between SCC compressive strength and splitting strength. Based on the experience of used power function in ordinary concrete, it is suggested that Equations (5) and (6) be used to predict the splitting strength of SCC.After sampling, the measured sound wave was converted into frequency spectrum by FTT, and the peak value of spectrum amplitude was taken as the test value. The spectrum of SCC is shown in According to the test results, The relationship between amplitude and compressive strength of SCC with FA and SF was obtained as shown in The following calculation formula can be obtained by fitted:As can be seen from the fitting results, the fitting curve was in good agreement with the measured value. Then Equation (7) can be well used to reflect the relation between compressive strength and amplitude of SCC.The failure modes of SCC specimens under different confining pressures are shown in σ2 = σ3 = 0 MPa , the failure mode of the specimen was splitting failure, and the specimen after failure basically maintains its original integrity, and there was no obvious spalling of concrete fragments. In addition, there were many cracks on the failure surface of the specimen, and some cracks penetrate both ends of the specimen, which made the specimen lost the ability to continue to bear load, thus caused damage to the specimen. When the confining pressure value σ2 = σ3 = 5 MPa, the failure mode of specimen changed from splitting failure to shear failure, and the mortar and coarse aggregate on the failure surface were cut and accompanied by the spalling of concrete. There was a main crack on the failure surface of the specimen from top to bottom, and the crack direction was no longer parallel to the direction of the principal stress, but at an angle of about 5° to 10° with the direction of the principal stress. When the confining pressure value σ2 = σ3 = 10 MPa, the crack angle varied in the range of 20°–30°, and there was a main crack on the failure surface that ran through both ends of the specimen. Moreover, the concrete at the penetration has staggered with each other due to shear action, and there was a slight bulge in the middle of the specimen. When the confining pressure value σ2 = σ3 = 15 MPa, there was a main crack on the failure surface of the specimen, which was about 45° to the direction of the principal stress. The concrete on both sides of the main crack was sheared with each other, and there was crushed concrete powder on the failure surface.By observing the crack direction and shape of the specimen, it can be found that the failure mode of the specimen has little to do with the substitution rate of FA and SF, but was mainly affected by the confining pressure. When the confining pressure value σ-ε curve as shown in σ is the axial stress value of SCC under different confining pressure, MPa; P is the axial load, N; Aa is the cross sectional area of the specimen in the process of shearing, mm; ε is the axial strain; Δl is the axial compression deformation of specimen, mm; H is the height of specimen, mm; and A0 is the initial cross sectional area of specimen, mm2.The load-displacement data were collected by YY-RBSZ-1000 rock triaxial (creep) tester, and converted into stress and strain values by Equation (8), and drew the σ2 = σ3 = 0 MPa, the stress-strain curve of the specimen has obvious peak, the peak stress and the peak strain are smaller than those of the specimen with confining pressure, and the curve of the descending section was steeper, which indicated that the plastic deformation of the concrete was small. With the increase of confining pressure, the peak value of the curve increased gradually, while the peak became smooth, and the peak stress and peak strain increased gradually. When the confining pressure value σ2 = σ3 = 5 MPa, the peak of the curve can be seen clearly, but the slope of the curve in the descending section decreased gradually. When the confining pressure value σ2 = σ3 = 10 MPa, the peak of the curve was no longer obvious, and the curve became smoother after the peak, showing good ductility. which showed a good ductility characteristic. When the confining pressure value σ2 = σ3 = 15 MPa, the spike no longer existed, and there was basically no yield drop in the curve after the peak. This phenomenon can be seen well from the comparison of the stress-strain curve in As shown in According to the stress-strain curve of the specimen, the peak stress of SCC under different confining pressures can be obtained as shown in As can be seen from σ1 is the peak stress of SCC under different confining pressure, MPa; σ0 is the peak stress of SCC under uniaxial stress (σ2 = σ3 = 0 MPa), MPa; σ2 is the confining pressure, MPa; and A is the coefficient related to FA substitution rate γ.The following relation was obtained by fitting:γ. The fitting curve shown in According to the fitting results in Bring Equation (10) into Equation (9), the relation of peak stress and confining pressure of SCC shown in Equation (11) can be obtained.Peak strain was an important part in the study of mechanical properties of SCC under triaxial stress, which was of great significance for in-depth analysis of deformation and failure characteristics of specimens. The strain of SCC peak under different confining pressure is shown in ε is the peak strain of SCC under different confining pressures; ε0 is the peak strain of SCC under uniaxial stress (σ2 = σ3 = 0 MPa); and B is the coefficient related to FA substitution rate γ.As can be seen from The relationship between coefficient B and FA substitution rate γ is shown in According to the fitting results in Bring Equation (13) into Equation (12), the stress-strain and confining pressure relation shown in Equation (14) can be obtained.τ, but also by the normal stress σ on the shear plane [τ is the shear stress, MPa; c is the cohesion, MPa; σ is the normal stress, MPa; and the φ is internal friction angle, °.Many strength theories have been obtained in the study of mechanical properties of ordinary concrete, among which the strength theory proposed by Mohr-Coulomb was typical. Based on Mohr-Coulomb strength theory, this paper discussed the failure criterion of SCC with FA and SF. According to Mohr-Coulomb strength theory, the compressive failure state of the material was controlled not only by the shear stress ar plane . The relc and internal friction angle φ of 28 d SCC with FA and SF under triaxial stress were obtained  was tangent to the stress circle, while the corresponding plane was called shear failure plane. When the concrete failed to reach the stress limit state, intercross between envelope and stress circle. The Mohr-Coulomb strength theory was used to process the data of obtained . It can τ was obtained by fitting analysis:σ0 is the peak stress of SCC under uniaxial stress (σ2 = σ3 = 0 MPa), MPa; Coefficient D is the ratio of cohesion c to σ0; and E is the fitting coefficient.After dimensionless processing of test data, the dimensionless diagram shown in The E = 1.091 was obtained by the least square method, then the empirical relation of shear strength of SCC with FA-SF can be obtained as follows:γ and the coefficient D of the test data in Through the regression analysis of the FA substitution rate The following relationships can be obtained.Then the failure criterion relation of SCC with FA and SF is as follows:It can be seen from The 3 days compressive strength and splitting strength of SCC decreased with the increase of FA substitution rate. The 28 days, 56 days, and 91 days compressive strength and splitting strength of SCC increased first and then decreased with the increase of FA substitution rate. When the FA substitution rate is 20% and SF substitution rate is 4%, the strength of SCC reached the maximum.According to the test results, the relationship model between compressive strength and splitting strength was proposed, the relationship model between amplitude and compressive strength was proposed, and the relationship model of peak stress, peak strain and confining pressure value of SCC with FA and SF under different FA substitution rate was proposed.The failure modes of SCC were greatly affected by confining pressure. When confining pressure = 0 MP, the failure mode is splitting failure. When the confining pressure increased to 5–15 MPa, the failure mode changed to shear failure.Based on the Mohr-Coulomb strength theory, the failure criterion of SCC with FA and SF was discussed, the fitting results were well good agreement with the measured values.In this paper, the compressive strength test, splitting strength test, ultrasonic testing test and triaxial test of SCC were carried out, respectively. The following conclusions are drawn:


Landfill leachate is a source of environmental pollution and a major concern for human health because it contains high concentrations of organic and inorganic contaminants.3/h for 30 days using a bubble air diffuser in a relatively small volume of 1 m3. The principle of the technique is essentially based on acceleration of the degradation of the effluent as well as reduction of the organic and nitrogenous matter contents.The objective of the present study is to validate the efficiency of the forced aeration treatment technique, which consists of intensively injecting a continuous oxygen flow of 16.75 kg/m Forced aeration technology was used for the treatment of leachate from the Mohammedia-Benslimane landfill. The sample was treated by injecting a flow of oxygen to accelerate the biodegradability of the pollutants by the microorganisms.2/l), biological oxygen demand (BOD5) , and total Kjeldahl nitrogen (TKN) . The proposed treatment technique allowed relatively high purification yields to be achieved, with abatement rates for the major elements COD, BOD5 and TKN of 73%, 98%, and 85%, respectively.The physicochemical characterization of the raw leachate at the inlet of the aeration tank showed high values for chemical oxygen demand (COD) (38,600 mg OThe treatment of leachate by intensive aeration technology reduces considerably the pollutant load and achieves a high purification yield.The authors declare no competing financial interests. Improved living standards, continued growth in industrial production and trade, and increased consumption have led to an increase in the volume of municipal and industrial waste globally.2Morocco has not escaped this trend in the growth in the amount of waste produced, which has reached significant rates. By 2030, the total waste deposit estimated in 2015 at 26.8 million tons is projected to increase significantly to 39 million tons with an increase of 45%.4This increase has repercussions for the management and landfilling of waste, leading to a saturation of landfills that are designed for both storage and treatment of waste. A large part of the potential risks associated with the landfilling of waste results from leachate migration and the release of noxious gases. As a result, landfills become a source of pollution for soil, air and human health rather than a solution for waste disposal.5Leachate is the liquid waste produced by the percolation of meteoric precipitation water and runoff to which is added the water brought by the waste itself.7A number of measures have been taken by the Moroccan government to reduce the health and environmental impacts of waste, including implementation of a national strategy for the reduction and recovery of waste, establishment of a regulatory framework with the promulgation of Law 28-00 on waste management and disposal,There are various leachate treatment technologies, including coagulation-flocculation, adsorption by activated carbon, biological treatment and membrane separation processes, such as nanofiltration and reverse osmosis (RO).10A novel treatment process is “intensive aeration technology”. Aeration systems have two main objectives: to provide aerobic micro-organisms with the oxygen, generally borrowed from the air, which they need to degrade organic matter, and to induce homogenization and mixing sufficient to ensure close contact between the living environment, polluting elements and oxygenated water.The objective of the present study is to examine the efficiency and possibility of using intensive aeration technology for the treatment of leachate from the Mohammedia-Benslimane public landfill, Morocco by forced aeration at the national level, in order to assure a satisfactory pollutant load elimination rate and purification efficiency.. The aim of this work on the Mohammedia-Benslimane public landfill site was to continue studies and tests on the treatment of discharges from the prefectures served by the site using different techniques.The controlled landfill of Mohammedia-Benslimane is an interprovincial landfill intended to receive the waste of the prefecture of Mohammedia and the prefecture of Benslimane. It was created following the closure of the former Mesbahiat wild dump and occupies an area of 47 hectares AFNORAssociation Française de Normalisation (French Standardization Association)BOD5Biological oxygen demandCODChemical oxygen demandECElectrical conductivityThe Mohammedia-Benslimane landfill center is located about 8 km southeast of the center of Ben Yakhlef, 17 km east of the center of Mohammedia, 24 km southwest of the center of Benslimane, and 800 m from the provincial road RP 3313 precisely at Douar Beni M'ghit, on the edge of the left bank of Chaaba El Hamra, a tributary of the Oued Nfifikh.3/day recovered in storage tanks. The study concerns all the communes of the prefecture of Mohammedia, including Mohammadia, Ain Harrouda, Bni Yakhlef, Ech-Chellalte, Sidi Moussa Ben Ali, and Sidi Moussa Majdoub.The landfill is located on a site designed to accommodate five large traps (3 engineered and 2 projected with leachate and contaminated storm water drainage systems), five raw leachate ponds, one treated leachate pond, and one contaminated storm water pond. The site also contains a weighbridge to control waste intake and weighing and a bio gas drainage network for the closed bins is installed. There are also administrative offices, a weighing control office, room for a caretaker, and a maintenance workshop and repair. It receives an average waste flow of 564.78 tons/day and an average amount of leachate of 70 mThe quantities of waste produced are essentially based on the evolution of the population and the ratios of waste production per inhabitant. The values of the quantities of waste produced for each commune are represented in 3. A tank with a volume of 50 m3 is filled with raw leachate to supply the treatment station.The leachate is collected from the traps by a collection and drainage system located at the bottom of the traps, then transported by gravity through pipes connected to the main collector attached to a storage tank with a capacity of 30,000 mThe leachate is treated in the landfill by two methods: biological and physico-chemical. The physico-chemical treatment is characterized by addition of calcium oxide or lime to promote settling, addition of the coagulant ‘ferrous chloride' to settle the colloids, and addition of sulphuric acid and hydrogen peroxide to reduce their pollutant load. The biological treatment is based on filtration of the effluents by a sand filter planted with reeds in order to capture the residual pollutants in the leachate.In the study site, snapshot sampling was carried out weekly to monitor treatment progress over time. Samples were taken weekly for one day each week at a rate of 2 L/h for 8 hours. Leachate samples were collected in non-contaminating polyethylene vials, labeled with the date of collection and sample name, and transported to the laboratory at 4°C. The samples were collected from the leachate in a sealed, non-contaminating polyethylene vial.The first raw sample was taken from the leachate storage tank to identify its initial characteristics, with the first sample representing the study reference. Then, further samples were taken from the reactor during the treatment period.3 volume free surface polyethylene tank. The treatment of the discharge was carried out using an aeration technique ensuring the mechanical diffusion of air bubbles  which injected pressurized air at the bottom of the aeration basin with a flow rate of 18.6 L/min, corresponding to an oxygen quantity of 16.75 kg/m3/h, through a piston compressor with a maximum discharge capacity of 4.5 m3/h. The air insufflation system ensures a sufficient mixing of the mixture, homogeneous diffusion of air bubbles and the maintenance of a continuous agitation. The reactor operated at room temperature between 9°C and 12.7°C.The intensive aeration technology, shown in The duration of the aerobic treatment was 30 days, during which the purifying evolution was monitored by physico-chemical analyses. A weekly instantaneous sampling was carried out according to the French standard AFNOR,The main physico-chemical variables analyzed included electrical conductivity (EC), pH, chlorides (Cl-), chemical oxygen demand (COD), biological oxygen demand (BOD5), nitrates, ammonium, Kjeldhal nitrogen, suspended solids, phosphorus, and phenols.All samples were analyzed for physico-chemical variables according to the procedure established in the standard method of the French Standards Association (FSA), Association Française de Normalisation (AFNOR).11Chemical oxygen demand was determined using the open reflux method (5220-B) according to the AFNOR standard 1994.11The oxidation of the organic matter is carried out by sulphuric acid, silver sulphate and mercury sulphate acid. The sample was placed under reflux in a strongly acidic solution with a known excess of potassium dichromate. After 2 hours of digestion, the remaining potassium dichromate, which was not reduced, was titrated with ferrous ammonium sulfate. The Mohr salt determined the excess of potassium dichromate, according AFNOR standard 1994.11Biological oxygen demand was evaluated by the respirometric method known as manometric, which automatically monitors the evolution of the BOD5 during the oxidation of organic matter. The method consists of filling a sample in hermetically sealed bottles of an appropriate size and incubating them at a determined temperature (20°C) for 5 days, according to the AFNOR standard 1994.11The determination of suspended matter was carried out by the centrifugation method of the AFNOR standard 1994.11Phenolic compounds were determined by the colorimetric method using the Folin-Ciocalteu reagent. The determination of nitrate in the sample was carried out by the spectrometric method in the presence of sulfosalicylic acid according to AFNOR standard 1994.11The determination of total phosphorus was carried out by the spectrometric method according AFNOR standard 1994.11The determination of ammoniacal nitrogen was carried out by the spectrophotometric method using indophenol blue according to the AFNOR standard 1994.11Chlorides were measured by the Mohr method by titration of chloride ions. It consists of a silver determination of chloride ions by silver nitrate in the presence of sodium chromate. The latter is the colored indicator which reacts at the end of the dosage to form the silver chromate, appearing as a brick-red precipitate according to the AFNOR standard 1994.11 during the present study was 7.62, representing a neutral pH. A high level of electrical conductivity of the leachate was represented by 48.4 ms/cm.4+ concentrations of about 4,700 mg/l and NTK and NO3- concentrations of 5,932.45 mg/l and 33.14 mg/l, respectively. The concentration of chloride was 6204.27 mg/l and the phenolic compounds were measured at 0.11 mg/l.Chemical oxygen demand and BOD5 showed high concentrations of 38600 mg/L and 24,000mg/L, respectively, with a biodegradability ratio BOD5/COD of 0.62. The leachate from the Mohammedia-Benslimane dump is a young type, with high NH.The results of the monitoring of the purifying evolution of the treated leachate are shown in 2/L, and BOD5 concentrations increase from 24,000 to 400 mg O2/L .The results of the analyses performed showed that the COD and BOD5 values decreased over time. Chemical oxygen demand concentrations increased from 38,600 to 10,520 mg O.The nitrate content of the raw leachate was 33.14 mg/L. After biological treatment, this amount increased to 88.8 mg/L and then decreased to a concentration of 30.6 mg/L. Bacterial nitrification related to the mineralization of ammoniacal nitrogen to nitrate showed a decrease in ammoniacal nitrogen concentration from 4700 mg/L to 720 mg/L The removal of BOD5 had the highest percentage with a 98% allowance, as does the removal of COD with a 73% allowance. Ammonium ions and Kjeldhal nitrogen had similarly high removal rates of 85% and 79%, respectively. The purification yield for nitrates was low at 8%.et al. (2017) found the same pH value for leachates in India , and Mejraoua et al. (2017)found a basic pH value of about 8.99 for Meknes city landfill.21 This value falls within the defined range of old landfills, while Zalaghi et al. (2018) reported a pH value slightly lower than that of our previous case study for TAZA city landfill in Morocco .According to et al. (2018) found a chloride concentration of 4,289.51mg/l and an electrical conductivity of 33.26 mS/cm for OumAzza landfill of Rabat city .et al. (2018) of Cl- was 5731 mg/l for an EC of 35.63 mS/cm, and Naveen et al. (2017) reported a chloride ion concentration of 780 mg/l for an EC of the order of 3.87 mS/cm.18 It should be noted that the EC is proportional to the concentration of chloride ions . In contrast, in a landfill in Algeria, a chloride value of 6381 mg/l and an EC of 26.3 mS/cm were found, indicating that the leachates were not sufficiently loaded compared to the leachates in the present study .22Electrical conductivity is a variable that gives an overall assessment of the concentration of ions present in the leachates, essentially of mineral types,et al. (2017) reported higher leachate concentrations from an Indian landfill, with COD and BOD5 values of 57,300 mg/l and 39,500 mg/l, respectively, while Ogunlaja et al. (2018) presented low concentrations in terms of COD and BOD5 .20 The measurement of COD and BOD5 content is an indicator of the effluent loading by biodegradable and non-biodegradable organic matter.Chemical oxygen demand and BOD5 represent a high load of biodegradable organic matter. Leachate from a public landfill in Tunisia had a COD content higher than that of the present study with a value of 40,000 mg/l and a BOD5 content lower than that of the leachate in the present study with a value of about 10,900 mg/l, Arunbabu The BOD5/COD ratio is a good indicator of the biodegradability of the effluent. It has been shown that a BOD5/COD ratio value below 0.1 represents low biodegradability, while values above 0.5 represent very good biodegradability.Leachates are loaded with trace elements such as ammonium, nitrogen, and chlorides. These elements are the main pollutants in leachates given their persistence in the environment and stability in anaerobic conditions. The accumulation of ammonium ion and nitrogen concentrations varies according to different phenomena such as the decomposition of proteins, hydrolysis, and the biodegradation of organic compounds by microorganisms.4+ and nitrogen concentrations as high as 1,426 mg/L.4+, NTK, and NO3- concentrations characterize the “acetogenic” phase of the leachates where hydrolysis, transformation and fermentation of the organic matter is done by the presence of bacteria producing simple and soluble molecules .et al. (2018) reported concentrations of NH4+ and NO3-, respectively, of 2,825 mg/l and 137 mg/l, while El-Gohary and Kamel. (2016) found concentrations of NH4+ and NO3- of 5,208 mg/l and 0.05 mg/l, respectively .23 According to the results obtained in the present study and in the literature, it was observed that the concentrations of nitrates and ammonium opposed each other (phenomenon of nitrification/denitrification).Stabilized leachates generally have low biodegradability of organic content, with NH27 The composition of phenolic compounds in the leachate of the Mohammedia-Benslimane landfill greatly exceeded the acceptable concentration recommended by the World Health Organization (WHO) in drinking water of around 0.001 mg/l,10The chemical composition of the leachate is specific to each landfill. It has a composition rich in organic matter such as humic and fulvic substances, volatile fatty acids, phenolic compounds, ammoniacal nitrogen, chlorinated organic compounds and toxic metals. According to the United States Environmental Protection Agency (USEPA), phenol is one of the main pollutants with serious harmful effects in humans expressed by anorexia, nausea, headaches, swallowing problems and fainting.Characterization of the leachate from the Mohammedia-Benslimane landfill site showed the high biodegradability of the effluent which indicated the need for a biological treatment process as the bacteriological process is in an evolutionary phase. Biological treatment by intensive aeration is essentially based on the injection of a quantity of oxygen into raw leachate. To this end, the evolution of the chemical and biological processes is accelerated and consequently reduction of the pollutant load is promoted.28The decrease in conductivity is influenced, on the one hand, by the presence of microorganisms, which are naturally present in biomass leachates, indicating a strong correlation between electrical conductivity and biomass..4The BOD5/COD ratio indicates the biodegradability of the leachate and this ratio decreases rapidly with the age of the landfill.The observed reduction in pollution can also be explained by the activation of aerobic microorganisms consuming organic matter in the presence of sufficient oxygen, and the material present in the leachate is easily oxidizable and biodegradable. Biodegradability was also conditioned by the climate of the study site. It varied according to the seasons, as an increase in temperature favors the intensification of bacterial activity and therefore a more intensified degradation.4 and subsequent conversion of nitrite to nitrate , followed by anoxic denitrification denitrate/nitrite to nitrogen gas .304+ and NO3- concentrations highlights the nitrification/denitrification reactions. However, the treatment showed the nitrate removal cycle and a strong bacterial nitrification linked to the mineralization of ammoniacal nitrogen into nitrate which led to a decrease in the ammoniacal nitrogen concentration. Nag et al. (2019) reported the same concentrations of ammoniacal nitrogen.The variation in NHet al. (2014) found higher abatement rates than in the present case study with removal percentages of 99.3% for COD and 99.1% for BOD5.The removal of BOD5 and COD showed high abatement rates. Jirou et al. (2014) were higher than those found in the present case study due to the physico-chemical composition of the sample that was taken directly from the collection trucks (tipping trucks), with concentrations higher than those in the present study, indicating that it is fresh leachate, however the sample in the present study was taken from the leachate storage tank within the landfill.28The removal rates found by Jirou The energy consumption of treatment technologies is a limiting factor in their use despite their high profitability in terms of efficiency and pollution removal (purification efficiency). Estimating energy consumption and the cost of leachate treatment by intensive aeration will make it possible to prove the efficiency of this technology and encourage its use by companies concerned with the treatment of leachates rich in biodegradable organic matter.According to the present study, the leachate from the Mohammedia-Benslimane landfill showed a high load of biodegradable organic matter. Treatment by intensive aeration lasted 12 hours per day for 30 days. The electrical consumption of the pilot was as expressed in Calculation data: number of hours =12; number of days = 30; appliance power =250 watts.Using the calculation formula yields:Management of the public service of the production and transport of electric energy as well as the distribution of electric energy is ensured by the national office of electricity and water in Morocco.The electric energy is sold, tariffs vary according to the bands of consumption, and the price in KWh is 1.5958 Dihrams (Dhs) for private electrification.32The cost of consumption during the test period was calculated as 90 × 1.5958 = 143.9 Dhs.3 of leachate and during 12 hours of continuous treatment for 30 days. The estimated cost of energy consumption varied according to the operating conditions of the treatment, including the quantity of leachate to be treated, the power of the compressors, the rate of oxygenation, and the type of leachate . The cost of energy consumption is the major limitation for the use of this technique.The energy consumption costs of 90 KWh was 143.9 Dhs for the specific experimental conditions of a pilot of reduced size of 1 mThe results in the present study highlight the pollution generated by the Mohammedia-Benslimane landfill through production of leachates with a high pollution load. Characterization of the leachates identified their major characteristics, such as COD and BOD5, which showed high concentrations, and the BOD/COD ratio showed high biodegradability. Therefore, the discharge is of a young type and in a stage where biological activity is important.The choice of treatment was based essentially on the composition of the leachate, which represented a high degree of biodegradability. The forced aeration biological treatment technique is based on intensive air injection into the leachate. This treatment considerably reduced a large part of the pollutant load and made it possible to achieve very high purification yields.The estimate of the cost of electrical energy consumption for leachate treatment by forced aeration varied according to the specific operating conditions of each experiment, depending on the operational context chosen.


This article presents a methodology for designing belt grinding operations with grinding and lapping machines. It provides the results of a study on the machinability of various steels and alloys with belt grinding, which are then classified according to an indicator that we have developed. Namely, cast aluminum alloys, structural alloy steels, structural carbon steels, corrosion-resistant and heat-resistant stainless steels, and heat-resistant nickel alloys have been investigated. The machinability index is the ratio of the performance indicators of the grinding belt and the depth of cut to the indicators of grade 45 structural carbon steels (similar to steel AISI 1045) and similar steels and alloys. The performance indicators of the grinding belt are chosen from a set of calculated and estimated indicators. Experimentally determining the dependences of the performance indicators on the belt grinding modes and conditions, taking into account the established levels of machinability, allowed us to develop recommendations for designing belt grinding operations with grinding and lapping machines. The proposed methodology for designing belt grinding operations guarantees optimal performance and ensures that the necessary quality of the machinable surfaces is achieved. At the same time, it takes into account variable machining conditions, which change within specified limits. D3/mm·s) ,6. Durin0.02 µm) ,8 with a0.02 µm) ,10 and t0.02 mm) ,12,13,14Flexible-base abrasive tools can be used to machine round outer and inner surfaces, flat surfaces, and complex (including curved) surfaces of workpieces ,16,17, iDue to the tools’ features, grinding and polishing with flexible-base abrasive tools have become widespread processes that can compete with grinding with abrasive wheel disks ,24,25,26Studying the basic laws of these processes;Identifying the mechanism of interaction between the tool and the workpiece;Developing a methodology for choosing the main parameters of the processes.To expand the field of application for machining with flexible-base abrasive tools, the following steps are necessary for their optimization and in order to set the rational machining modes and scientifically grounded rate:These problems are solved by taking into account their complexity and diversity. These issues are at the junction of various fields of knowledge, including engineering techniques, material science, organic and inorganic chemistry, construction engineering, physics, and mathematics.Belt grinding occupies a special place in abrasive machining. In terms of kinematics, dynamics, and their accompanying physical phenomena, this type of machining occupies an intermediate position between grinding with “rough” wheels  and machining with loose abrasive grains ,31,32.There are three basic grinding patterns: rigidly-mounted grains on an abrasive wheel disk; grains fixed on a flexible base; loose grains ,34. Out It has been established that during grinding with an abrasive wheel disk, there is almost no elastic compression of grains in the process and the cutting depth is determined by the size of the free portion of the grain protruding from the adhesive. The grinding mechanism is different when using an abrasive belt because the belt becomes deformed ,14,37,38The nature of abrasive belt deformations during grinding ,37 indicIn addition, according to the works of Maslov , ReznikoOut of the whole variety of abrasive products, coated abrasives (CA) account for 39, and grinding operations based on their application are used in various industries at all stages of machining operations. Most coated abrasives (95%) are made of sandpaper, while the vast majority (63%) are products made of emery cloth ,55,56,57The market economy trend of improving the quality of products leads to a constant increase in the share of abrasive belt grinding operations out of the total volume of machining operations. Therefore, a relevant task needed to increase the productivity of operations with the use of abrasive belts is providing high requirements for the quality of the machinable workpiece surfaces. Analysis of the effectiveness of using grinding belts showed that the costs of machining parts frequently fluctuate due to irrational characteristics of cutting tools and modes in homogenous operations being set, with a tight annual production program.One of the most promising directions for improving the efficiency of abrasive belt grinding operations is developing technically sound recommendations for choosing the characteristics of cutting tools and modes. This can be achieved through thorough analysis and by determining the relationships between tool performance and the cutting conditions of steels and alloys with different levels of machinability. It is important to determine recommendations for cutting modes during abrasive belt grinding with grinding and lapping machines, and this paper deals with this topic.The objective of the work is to increase the performance rate of machining steels and alloys with abrasive cloth belts based on elaboration of the recommendations for the design of belt grinding operations.To determine the dependences of the performance indicators of the grinding belt on the type of material being machined;To develop an indicator for the machinability of materials with a grinding belt;To classify groups of materials machined by grinding belts based on quantitative assessment of their machinability;To develop recommendations for the use of tools for the belt grinding of materials with various levels of machinability with grinding and lapping machines.The main tasks are:The importance and relevance of the objective is determined by the significant volume of grinding belt usage, which accounts for about 77% of all manufactured coated abrasives, with a rather wide range of characteristics , as well as a variety of operations and uses in the most important industries ,55,56.The Department of Automated Mechanical Engineering of the South Ural State University studied the metal belt grinding operations. For deburring pads during flat grinding of 10KP carbon steel (similar to AISI 1010) in the production of metal fittings;For external circular grinding of cylinder rods made of 35KH carbon steel (similar to AISI 5132) in the automotive industry;For external circular grinding of bearings made of wear-resistant SHKH15 steel  in the bearing industry ,57.For example, sandpapers with the same characteristics ) are used to machine various materials and in different modes:The belt characteristics by type of operation , i.e., by the size of the stock allowance and the roughness requirements, are applied unsystematically. For example, the 14A16C belt is used during flat grinding of stainless steel with a stock removal allowance of 1.0 mm to achieve a roughness of 1.25 μm. When machining cutlery, a larger grain 14A25K abrasive belt is used to remove a stock allowance that is 2 times smaller (0.5 mm) and to achieve the same roughness. In other production, when machining similar products, a belt with 2–4-fold smaller grain sizes (14A4–8 SFG) is used to remove the stock allowance of 0.7 mm and to achieve the same surface roughness. As a result, during operation there is significant excess consumption of the tool and it is used with low efficiency.It has been determined that the difference in the performance of CA grinding of parts similar in size, accuracy, and surface quality, but made of steels and alloys of various grades and with all other things being equal, is preconditioned by differences in grinding machinability.To create a justified system of grinding belt settings when machining various steels and alloys and to develop appropriate recommendations, we need to grade materials by their belt grinding machinability. The dependences of the performance indicators of the grinding belt on the type of material being machined were determined by empirical calculation based on the theoretical principles of the grinding process ,59,60. TAccording to many researchers ap/=P,ε˙,T0)) ,63,64; KThe data on the stress intensity and the values of the coefficients a school ,65. TheyThus, we determined the values included in the formula for calculating the depth of cut:In Formula (2), the size of the grain blunting area grinding :(3)β=2·PP/ is the specific cutting force acting on one grain (see P [Using the designations of the parameters adopted in this work in Formula (3), the size of the blunting area VB=b·n volume :(5)FB=rBrain see , determin  and the geometric parameters of the relief (R) of the working tool surface, which depends on the properties of the bond :Analyzing the obtained expression for calculating The calculated conditional depth of cut with one grain (according to Formula (2)), taking into account the dependence of the blunting value The analytical model of the calculated depth of cut . Machinability has been considered by various researchers, including the machinability of aeroengine alloys , the macFor experimental studies, a test stand model “IS-78” was used ), which was created on the basis of a modernized cylindrical grinding machine model 3110M ). The contact length depends on the machinability group, type of processing , material, and type of contact roller . We used a sanding belt made of cloth abrasive paper on a cloth base made of normal grade 15A electrocorundum, with a grain size of 25, which complies with Federation of European Producers of Abrasives (FEPA) according to Russian standard (State standard) GOST R 52381 F60, on a synthetic bond according to Russian standard GOST 27181-86. The grinding modes used for experiments are given in For calculations and experimental analysis, materials from different groups were used, including cast aluminum alloys (AL4 and AK5M2/AL3V (similar to A319.0) according to Russian standard GOST 1583–93), structural alloy steels (30KHGSN2/30KHGSNA and 30KHGT according to Russian standard GOST 4543–71), structural carbon steels (08KP (similar to A619) and 45 (similar to AISI 1045) according to Russian standard GOST 1050-88), corrosion-resistant and heat-resistant stainless steels (12KHI3 (similar to AISI 410), 3KH19NMVBT and KH18N10T (similar to AISI 321) according to Russian standard GOST 5632–72), and heat-resistant nickel alloys (12KHI3 (similar to AISI 410), 3KH19NMVBT and KH18N10T (similar to AISI 321) according to Russian standard GOST 5632–72).The compositions and physical and mechanical properties of cast aluminum alloys, structural alloy steels, structural carbon steels, corrosion-resistant and heat-resistant stainless steels, and heat-resistant nickel alloys are listed in iσ). The data on the stress intensity (iσ) are taken from other publications [Studying the analytical model of the conditional depth of cut with one grain ications ,7,30,38 BV are conventionally taken as 0.01 and 0.05 mm for calculation. These values allow us to obtain comparable values of iq).Since the working layer of the belt has both very small and large areas of grains entering into operation, the grain flank wear rates yP per 1 mm2 of the contact was determined through experimentally obtained yP values acting on the entire contact area cF during grinding and the number of contacting grains acn located within the contact area.The radial force iσ) of various steels and alloys at yP = 0.15 N/mm2 ;Structural carbon steels and steels alloyed with chromium and nickel in combination with manganese, silicon, and molybdenum have better machinability;Aluminum casting (low silicon) and copper-doped (up to 6%) alloys have the best grinding machinability .When assessing the calculated values of the depth of cut yR. For steels of stainless and nickel alloys, with a change in yP, the depth of cut The radial force significantly influences the calculated change in metal removal, while the degree of this influence changes significantly with a change in the blunting area x) to the calculated depth of cut with one grain The calculated machinability index Steel 45  is a very common construction material in Russia. Many reference books take it as a reference . TherefoDiagrams 3–5 show the calculated machinability index cP is the force of clamping the tool to the workpiece; cυ is the cutting speed; τ is the tool operation time until the resistance criterion:n is the number of grinding sequences.The experimental machinability index Thus, five groups of materials machined by the grinding belt were identified depending on the quantitative assessment of their average machinability , abrasive grit, cloth backing , and type of bonding . Further, depending on the material group to be machined and the type of machining, we provided recommendations for setting the length of the contact between the tool and the workpiece, the speed of the tool and the workpiece, and the grinding pressure in order to achieve the recommended performance characteristics.The main reason for the low efficiency of belt grinding operations is the lack of technically sound recommendations for their design, and primarily the lack of recommendations for choosing tool characteristics and the estimated reasonable cutting modes for the relevant materials being machined. The development of recommendations for the design of belt grinding operations is constrained by the lack of a scientific and methodological approach to assessing the machinability of materials during belt grinding operations. This relevant task is solved by taking into account the machinability of steels and alloys when choosing the parameters of abrasive belts and setting effective grinding modes, taking into account the machinability indices for specific technological conditions.We developed an analytical model to determine the index of machinability with an abrasive tool (grinding belt). The machinability index is the ratio of the performance indicators of the grinding belt and the depth of cut to the indicators of structural carbon steels of grade 45 steel (and similar steels). In this case, the performance indicators of the grinding belt are chosen from a set of calculated and estimated indicators.We formed machinability groups for steels and alloys with a grinding belt based on the developed machinability index. The experimental studies determined the empirical dependences of belt grinding parameters for a number of steels and alloys.ρ = 0.87 ± 0.09).Our study allowed us to gather statistics on the performance indicators and machinability based on the cutting modes and characteristics of the grinding belt and assess them. Sufficient sensitivity and distinguishability were achieved for the estimates; the stability of the obtained results was at the required level and did not exceed 5–6%. We demonstrated the objectivity of the obtained results by comparing the laboratory and production estimates of the performances of grinding belts and their good correlation (correlation coefficient We recommend using our results in belt grinding operations on grinding and lapping machines. The use of the developed recommendations for choosing the performance characteristics of emery belts and grinding modes makes it possible to design belt grinding operations on a technically and scientifically reasonable basis. It also increases the durability of the grinding belts when machining structural carbon steels by up to 42%, reduces their consumption by 40%, and reduces the labor intensity of machined cast aluminum alloys by 4.5 times while ensuring operational requirements are met.This article has provided a scientifically determined means of choosing grinding belts for grinding operations based on the assessment of tool performance using the machinability index for steels and alloys.The proposed methodology for designing belt grinding operations for grinding and lapping machines, taking into account the developed classification of the machinability index for steels and alloys, will allow us to guarantee the optimal performance of grinding operations, while ensuring the specified quality of the machined surface manufactured under variable machining conditions changes within the specified limits.


Citrus clementina Hort ex Tan), and a dose of 240 mg Fe was applied by labeled fertilizer (92% atom 57Fe excess). Plants were uprooted at five different phenologic states: end of flowering (May 15), end of fruit setting and fruit drop (July 1), two fruit growing moments (August 1 and October 15), and at complete fruit maturity (December 10). The Fe accumulated in the root system exceeded 90% of the total Fe content in the plant. All organs progressively enriched with 57Fe . Reproductive ones reached the highest increase (111% between May and October). 57Fe enrichment from woody organs reflects an increasing gradient to sink organs. The root system accumulated 80% of the Fe absorbed from the fertilizer, but the young organs accumulated relatively more Fe uptake during flowering and fruit setting  than old organs (around 9.8%). Although iron derived from fertilizer (Fedff) preferably supplied young organs (16.7–31.0%) against old ones (2.5–14.9%), it only represented between 13.8% and 21.4% of its content. The use efficiency of the applied Fe (FeUE) barely exceeded 15%. The lowest FeUE were found in young and old organs of the aerial part . Since the pattern of the seasonal absorption of Fe is similar to the monthly distribution curve of the supplied Fe, it is recommended that the application of Fe chelates in calcareous soils should be performed in a similar way to that proposed in this curve.This work quantifies Fe uptake in young citrus trees, its partitioning among plant compartments, and the contribution of the Fe absorbed from fertilizer to the development of new tissues. A soil pot experiment was conducted using 4-year-old clementine trees ( Although most soils contain enough iron (Fe) to satisfy the needs of crops, in the presence of oxygen, an alkaline medium, and an excess of soil moisture, this ion precipitates as the insoluble hydroxide, which is a scarcely soluble Fe form that, therefore, causes serious problems of iron chlorosis for plants. Thus, in alkaline soils such as those in the Mediterranean basin, high levels of bicarbonate ions are the main cause of iron chlorosis in citrus plantations. The most effective way to combat this deficiency is by applying iron chelates. However, their use markedly increases operating costs, accounting for 14% of the total cost of fertilization [+, nitrate, oxygen, and sulfate [The importance of Fe in plants is well known, as it is involved in a series of metabolic processes that are fundamental to their development. This is the case of photosynthesis, since Fe participates in several of the steps of the chlorophyll biosynthetic pathway regulating the activity of the enzyme system for the formation of protochlorophyll and other pigments, besides being responsible for the morphology, structure, and maintenance of chloroplasts . So, the sulfate ,3. Final sulfate . Therefo sulfate .As a dicotyledonous plant, citrus develop a strategy I mechanism for mobilization and acquisition of Fe from the soil or soil solution ,7. RegarSeveral factors are involved in the absorption of Fe. In addition to those intrinsic to the plant (vigor of the variety and pattern and age), other examples include the culture medium , as well as irrigation management and fertilization practices. Despite the importance of this latter, few studies have focused on Fe dose, its time of application or seasonal distribution, and Fe fractionation (number of applications) in citrus.−1) could be considered the most convenient from a nutritional and economic point of view.The Fe dose depends on the characteristics of the plantation , as well as the nutritional status of the plant evaluated by leaf analysis. However, there are a few studies on the response of citrus fruits to differential doses of Fe. The application of two doses of Fe-EDDHA to adult mandarin trees increased the total leaf chlorophyll content and improved their yield, with an increase in the number of fruit sets . The lowThe time of application of nutrients is also important, as it is known that these are absorbed by citrus throughout the year but not steadily throughout the cycle. In general, the time of maximum absorption includes the end of spring, summer, and early fall, and the minimum during winter. The decrease in the absorption at very low temperatures seems to be due to a lower fluidity in the cytoplasmic membrane and, therefore, to a greater resistance to the passage of the ions. Moreover, the growth of the fibrous roots is also considerably reduced. Recent studies have established the distribution pattern of nitrogen fertilizer in citrus throughout the vegetative cycle of the plant , but sim57Fe not only determines the uptake of Fe by the crop [The interest of fractionation of the Fe dose lies in the fact that it fulfills the function of maintaining a level of this micronutrient available to the plant in a constant and prolonged manner, thereby improving the efficiency of its use and reducing the fertilization costs. However, a few results on this aspect can be found in the current literature, and, in general, the studies evaluate the relative distribution between the different organs of the total accumulated Fe in the plant up to the time of extraction, chlorophyll concentration, or increase in production ,11. Thusthe crop ,13, but the crop ,15.Finally, closely related to the dose of Fe applied is the Fe use efficiency (FeUE), which estimates the proportion of Fe absorbed by the plant in relation to the dose applied. Generally, FeUE decreases with the increase in fertilizer dose, so this parameter will be of agronomic interest as it influences the Fe consumption of the crop. A low efficiency is not always indicative of a low absorption capacity of the crop, but rather of an excessive dose. Therefore, better FeUE values will be obtained when the Fe dose is more matched to the needs of the plant, which will in turn reduce the fertilizer costs.57Fe allows them to be quantified exhaustively. In this way, this study will expand the knowledge of the Fe dynamics in plants, in order to establish the fertilizer criteria of this nutrient and to optimize its seasonal application, thus limiting the supply of excessive amounts of ferric fertilizers, which will result in a saving in production costs.Specifically, the objective of the present work is to quantify the effect of the seasonal distribution of a dose of Fe on the following aspects: (a) quantification of Fe absorption along the vegetative cycle and its use efficiency; (b) distribution of Fe absorbed among the different plant organs at different phenological moments; and (c) relative contribution of the Fe absorbed from the fertilizer to the fruit setting, as well as to the vegetative development of the different flushes. The use of a chelate enriched with Trees presented an average dry weight  of 746.0In the literature, the dry weight of the whole tree is closely related to the species, the age of the tree, cultivation practices, and the soil and climate conditions in the area. Our results are similar to the values found by other authors in young tress. Nules clementine trees harvested in December obtained a biomass at dormancy of 1.25 and 1.45 kg according to whether they received an organic fertilizer of plant or animal origin, respectively . Four-yeInterestingly, regardless of the increase in weight recorded, the relative biomass distribution (RBD) of the aerial part and the root system in relation to the total biomass of the plant b remaine−1 DW in the May sample) and the lowest in the leaves of the fall flushes, which are the youngest (27.1 ± 5.4 mg Fe 1000 g−1 DW in the October sample). In addition, both leaf types presented opposite patterns in the Fe concentration throughout the cycle. While the Fe concentration in the old leaves decreased irregularly over time, presenting an average concentration of 50.5 ± 5.2 mg Fe 1000 g−1 DW but without any significant differences between samples, it increased progressively in the young leaves of the different flushes  measured between their appearance  and the end of the cycle (December). Conversely, the concentration of Fe in the young reproductive organs (flowers and fruits) decreased very sharply  from May to December as a result of the dilution of this element associated with the increase in biomass in growing fruits. The old organs (branches and trunk) maintained fairly stable Fe values throughout the cycle with average values between 35.7 ± 1.2 and 40.0 ± 3.3 mg Fe 1000 g−1 DW, respectively. The coarse and fibrous roots showed average Fe concentrations of 188.2 ± 26.5 and 2428.7 ± 276.5 mg Fe 1000 g−1 DW, respectively, which were much higher than the aerial part, especially in the latter case, and displayed an increasing trend from flowering to the end of fruit set (July) and then decreased until the end of the cycle.The Fe concentration in the leaves is closely related to their age , and thuCitrus aurantium seedlings was of 77:1:11 between root system:stem:leaves, being the value in the root of 496 µg g−1 DW [−1 DW), and levels in the old leaves exceeded that in new leaves . In peaches, while the highest accumulation of Fe occurred again in the root system (1900 mg kg−1 DW), the fraction of the plant with the second highest concentration was the totally expanded upper leaves (220 mg kg−1 DW) and finally, the stem and basal leaves, which accumulated over 100 mg kg−1 DW [This pattern in the Fe concentration in the different organs of the plant has also been seen in citrus and other crops. The relationship in the Fe concentration in g g−1 DW , and it g g−1 DW , roots h kg−1 DW . Althoug kg−1 DW .The Fe content  increaseAerial part only accumulated 6–8% of the total Fe content , despite57Fe  achieved considerably greater enrichment than the old ones. The root system (coarse and fibrous roots) showed the least enrichment, again mainly due to the isotope dilution effect that reached the highest total Fe content . On the 57Fe in citrus and other crops [15N or 44Ca also in young citrus plants [44Ca quantified calcium partitioning even at cell level and resulted in significant enrichment in the cell wall of the pericarp through new cross-bridges of Ca-pectates, thereby enhancing fruit strength and delaying fruit degradation and bitter pit development [The differences in the enrichment of the various plant organs are consistent with the results obtained in other studies on er crops ,28,30,36s plants ,26,37,38s plants ,22,39,40elopment ,42.The Fe absorbed from the fertilizer  allows q57Fe concentration  to fruit growth (August), as a result of the Fe content  in a grentration  during t57Fe and biomass enrichment of the fibrous roots observed from May to December  compared to coarse roots .Around 80% of the absorbed Fe was accumulated (Fe uptake RD) in the root system and the remaining 20% in the aerial part in all the extractions . This is44Ca in the root system in beech (Fagus silvatica L.), associated to the low mobility of Ca and to physiological constraints in the phloem and the higher affinity of Ca for cation exchange sites, such as in the xylem cell wall [At this point, the mobility of the element seems to be decisive. Van der Heijden et al. (2013)  observedell wall .15N continuously from March to November, resulted on 75% and 61%, respectively, of the N absorbed from the fertilizer when sampling in December [Conversely, young orange trees of the Newhall and Valencia cultivars labeled with December ,48. ThesDecember . MoreoveDecember . Under cDecember , so a coFinally, Fe uptake RD among the organs of the aerial part varied according to the time of extraction. Thus, during flowering and fruit set, the young organs accumulated relatively more Fedff than the old ones, even though the FeRD was considerably lower in the young ones . Convers57Fe concentrations (57Fe of each organ or plant and the enrichment of the fertilizer applied (91.80% 57Fe). Throughout the successive extractions, the contribution of Fedff to the Fe content of the plant increased considerably as a result of the continuous seasonal input, from near to 2% during the flowering period to 8% in the ripening period.The tendency in the percentages of iron derived from fertilizer (Fedff)  is identtrations , since tIn all the extractions, the values of the Fedff in the young organs  were notably higher compared to the old organs although differences decreased as the cycle progressed , from mo57Fe for 28 days, and it was maintained even under stress conditions of low Fe levels in the medium [In kiwi, the age of the organ of the aerial part was negatively correlated with the percentage of Fedff when plants were labeled with This parameter is very useful since the use efficiency of a nutrient indicates the proportion in which the element applied as fertilizer is absorbed by the plant (this can only be quantified with the use of isotopes). However, it should be interpreted with caution because, as it is a relative value Equation (4)), a low efficiency is not always due to a low absorption capacity of the tree, but may be the result of the dose provided exceeding the needs of the crop.In our study, the young organs always reached higher FeUE than the old ones and the highest efficiencies were obtained in the root system . The FeU57Fe supplied, so plants absorb a higher proportion of the Fe available in the soil than that afforded by the chelate.Low efficiency may be due to two causes: (1) the dose of Fe applied far exceeds the needs for Fe of the plants, which does not seem evident since, according to Citrus clementina Hort ex Tan), grafted on Carrizo citrange (Citrus sinensis × Poncirus trifoliata) rootstock, were grown individually in containers of about 46 l  filled with 65 kg of loamy soil . The containers were placed outdoors and covered to protect them from the rain. The area was surrounded by a buffer row of identical trees to those used in the experiment. The trial was conducted in the IVIA experimental field station .Four-year-old Nules clementine trees  to discriminate Fe fertilizer from other sources of Fe . 3, Ca(NO3)2, H3PO4, MgSO4, Mn chelates, Zn chelates, and CuSO4, respectively, as proposed for citrus trees [Between March (spring growth resumption) and October (end of fruit development) of 2008, 20 trees were fertilized with 240 mg Fe plantut 60 cm ,54 . The amount of water applied to each tree was equivalent to the total seasonal crop evapotranspiration (ETc). The volume of water applied weekly was calculated using the expression: ETc = ETo × Kc, where ETo is the reference crop evapotranspiration under standard conditions, determined using the Penman-Monteith approach [The experiment, therefore, consisted of 20 trees arranged in a randomized block design with five harvests and four replicates of one tree each. The plants were watered using two drip emitters for each tree  as it was diluted with total Fe and we did not appreciate an increase in 57Fe in the soil at the end of the experiment (data not shown).The At five different plant phenological states, the end of flowering (15 May 2008), the end of fruit setting and fruit drop (1 July 2008), two fruit growing moments (1 August and 15 October 2008), and at complete fruit maturity (10 December 2008), a block of four labeled trees were destructively harvested to quantify total dry biomass.The aerial part was divided into young organs  and old organs . The root system was carefully removed from the soil to avoid tissue loss and divided into coarse and fibrous roots (less than 2 mm diameter). Fresh weights of tree organs were determined, and representative samples of each fraction were taken. All samples were washed in nonionic detergent solution followed by several rinses in deionized water, weighed, frozen in liquid nitrogen, freeze-dried , and powdered in a refrigerated ball mill  after dry-weight determination.57Fe concentrations.Prior to Fe content analysis, the plant material (0.5 g DW) was calcined in a muffle furnace for 12 h at 550 °C. Subsequently, Fe was extracted with 2% nitric acid  in an ultrasonic bath  for 30 min at 40 °C and diluted to 50 mL final volume. This extraction was divided into two subsamples to determine total Fe and 57Fe of each sample was determined using a multiple-collector inductively coupled to an isotope-ratio mass spectrometer  [Total Fe concentration was measured with the AAS analyzer . The abundance in All analyses were carried out with ultrapure water (Ultra Pure Water Systems Milli Q Plus). All determinations were performed in duplicate and a standard was run to ensure accuracy after each set of 10 samples.57Fe content in each plant compartment was calculated by Equation (1):57Fe excess was calculated by subtracting the natural abundance of 57Fe  from thThe content of Fe absorbed by the organ was calculated by Equation (2):Iron derived from fertilizer (Fedff) quantifies the contribution of Fe from fertilizer in relation to the total Fe in the organ (Equation (3)):57Fe fertilizer represents the proportion of applied 57Fe that is taken up by the tree and embodies its fertilizer Fe use efficiency ).57Fe taken upplant compartment (µg) = Ʃ57Fe (µg)organ.Total plant recovery of applied Data were subjected to ANOVA, and means were separated by the LSD test at the 5% level to determine the significance of differences among the Fe seasonal distribution within each harvest event, using SAS software .57Fe was mostly concentrated in the young organs of the aerial part, which acted as a sink for it. Despite this, between these organs and the old ones only about 20% of the total Fe was absorbed by the plant and the rest up to 100% was retained in the root set. (4) The highest rates of seasonal absorption of applied Fe were reached in the periods of fruit growth (beginning of July until the end of August), these being the times when the greatest contributions must be made. (5) The use efficiency of the applied Fe barely exceeded 15%, which reflects that despite the fact that it is a fairly calcareous soil, the supplied 57Fe was diluted with assimilable native Fe and the plants absorbed a greater proportion of the available Fe than that provided with the chelate. Finally, (6) as a basic conclusion, it is suggested that the monthly distribution and number of applications of Fe compounds to citrus should be performed following the pattern described in this study, since the seasonal absorption curve showed a very similar response to this one.From the results obtained in the study on the seasonal uptake of Fe in young citrus trees, we conclude that: (1) the biomass in the aerial part was almost twice the amount obtained in the root system. The highest Fe concentrations were achieved in the roots, with the absorbent or fibrous ones accumulating 13 times more Fe than the coarse ones. Therefore, the Fe content in both types of roots accounted for more than 90% of the total amount in the plant. (2) The contribution of applied Fe to the development of flowering and fruit set was only 17% and 27% of the total Fe content. This suggests that the Fe applied in the early stages contributed significantly less to the development of new tissues than that coming from the plant reserves and the soil. Hence, there is no need to bring forward fertilization or to apply excessive amounts of chelates in the abovementioned periods. (3) The applied


The purpose of this research was to investigate and improve the accuracy of the existing slab-track mat (STM) specifications in the evaluation of the vibration reduction effect. The static nonlinearity and dynamic mechanical characteristics of three types of STMs were tested, and then a modified fractional derivative Poynting–Thomson (FDPT) model was used to characterize the preload and frequency dependence. A modified vehicle–floating slab track (FST) coupled dynamic model was established to analyze the actual insertion loss. The insertion loss error evaluated by the frequency-dependent tangent stiffness increased with the increase in STM nonlinearity, and the error obtained by the third preload tangent stiffness was usually greater than that of the second preload. Compared with the secant stiffness, the second preload frequency-dependent tangent stiffness was more suitable for evaluating STMs with high-static–low-dynamics (HSLD) stiffness. In order to reflect the frequency dependence effect and facilitate engineering applications, it is recommended that second preload tangent stiffness corresponding to the natural frequency of the FST be used for evaluation. Furthermore, the insertion loss of the STMs with monotonically increased stiffness decreased as the axle load increased, and the opposite was true for the STMs with monotonically decreased stiffness. The vibration isolation efficiency of the STMs with HSLD stiffness was both stable and better than that of the STMs with monotonic stiffness. The convenience and energy-savings of urban rail transit (URT) have driven an increase in urban transportation-oriented development (TOD) construction. For instance, 46 cities in China have constructed 7142 km of URT lines, and the fastest operating speed has reached 160 km/h. However, the high density rail transit network and the fast operating speed inevitably cause more obvious environmental vibrations and noise problems , such asOptimizing the stiffness of the damping pad to reduce environmental vibration and structural noise has been extensively studied. Vogiatzis and Kouroussis ,12 estabSome theoretical models with a better performance have been widely used to accurately reflect the impact of the polymer’s mechanical properties on the track’s vibration characteristics. Wei et al. described the dynamic viscoelasticity and plasticity of a Vossloh 300 soft rail pad with a modified fractional derivative Zener (FDZ) model and a traditional Berg friction model, and analyzed the influence on the high-speed vehicle–slab-track coupled vibration . Zhu et In China, the provisional technical regulation TJ/GW 121-2014  indicateTo evaluate the VRE of the STMs conveniently and accurately, we improved the existing standard method by comparing the models that can reflect the actual dynamic characteristics. A modified FDPT model was proposed , which cTo describe pronounced nonlinear behavior depending on the preload and frequency, the modified KV  and PT  viscoelaP and the corresponding displacement is x. This model can be divided into two parts: the elastic spring part (K1) and the fractional derivative Maxwell (FDM) part consisting of the spring (K2) and Abel dashpot (K2γτ) in series. In this section, the classical FDPT model is first transformed into a temperature-dependent modified model, and then the preload-dependent nonlinear static stiffness and the frequency-dependent dynamic stiffness are respectively derived.The modified FDPT model is shown in τ is the relaxation time of the linear viscoelastic material and γ is the derivative order. It is worth mentioning that unlike the usual generalized fractional model, the spring stiffness in the FDPT model is considered separately. K1 and K2 reflect the static preload-dependent and dynamic frequency-dependent characteristics, respectively.The time-domain constitutive equation of the classic FDPT model and the complex stiffness obtained by Fourier transform (FT) are as follows:*K can be also written as the following equation. The specific calculation procedure can be found in [According to the time-temperature superposition (TTS)  of polymfound in .(3)K*, and the corresponding densities, respectively. α(T) is the conversion coefficient of the temperatures, in accordance with the following equation:In Equation (3), Tg) is regarded as the reference temperature, C1 and C2 are 17.44 and 51.6, respectively. If another temperature is selected as the reference temperature, C1′ and C2′ at the corresponding reference temperature can be calculated by using Equations (5)–(7).When the glass transformation temperature  measured by the harmonic excitation and the static nonlinear K1 obtained by fitting, the stiffness K2 associated with frequency dependence under different preload conditions can be shown by the following equations:rP and K2′ are a reference preload and the corresponding stiffness value, respectively. rβ is an exponential function related to the preload.After obtaining the complex stiffness (K′), loss stiffness (K″), and loss factor (tan δ) can be obtained as follows:The temperature-, frequency-, preload-dependent storage stiffness , three kinds of damping pads to be used by Guangzhou URT were adopted as the test objects—see The instrument is shown in During the test, the minimum load applied was the FST weight supported within the sample area, and the maximum load was the sum of the minimum load and axle load supported within the sample area when the vehicle ran above the track. It is worth noting that when the speed reaches 160 km/h, the axle load needs to consider a certain dynamic coefficient of 1.3. Three adjacent floating slabs were established by Ansys software , and the3, and the corresponding maximum load increases from 4.0 to 4.2 kN. To facilitate testing, the minimum load and maximum load were determined to be 0.8 and 4.1 kN, respectively.The maximum loads obtained by the different STMs’ stiffness were slightly different. The stiffness of the STMs increases from 0.01 to 0.03 N/mmA series of experiments were carried out to scientifically test and characterize the dynamic properties of the STMs see . Case 1 According to the test procedures, the static and dynamic characteristics of the test samples of the STMs were tested.Static loading with a nearly zero velocity was carried out on the STMs within the load range of 0 kN to 5 kN at an interval of 0.5 kN. The measured data and fitting results of the nonlinear force–displacement and stiffness–force curve are shown in a1, a2, a3, and a4 of STM-I, STM-II, and STM-III are shown in Although the force–displacement curve of STM-I in In order to avoid repetition, only part of the dynamic hysteresis loops within the service load range are shown, because its load and displacement are larger and the hysteresis loop area is more obvious see .It can be observed that the frequency-dependent stiffness and loss factor of STM-I and STM-II are basically the same, while STM-III not only has obvious frequency-dependent stiffness but also a higher loss factor . According to these measured hysteresis loops, the stiffness at different preloads and frequencies can be obtained. The test data and fitting results of secant stiffness and tangent stiffness of the STMs are shown in −5 and 6.83 × 10−5, respectively) are relatively small. The frequency-dependent effect of STM-III with strong nonlinearity in the service load range is obvious, and the stiffness growth rate is 1.25 × 10−4. For STM-III, which has a relatively small static stiffness in the load range of 2–3 kN, a moderately large frequency change effect can also effectively suppress the dynamic displacement of the floating slab. It is worth noting that the secant stiffness of STM-I and STM-II is between the preloaded tangent stiffness of 2 and 4 kN, while the secant stiffness of STM-III is greater than the preloaded tangent stiffness of 1 and 5 kN.Under different preloads, the stiffness of the STMs at a frequency approaching 0 is basically consistent with the static stiffness in K2′ and rP in the fitting. The fitting parameters K2′, r, τ, and γ are shown in The fitting process under a single preload can be directly calculated using Equation (2), and the stiffness and preload force values with a reference preload of 0.5 kN are selected as Using the modified FDPT model in In order to accurately evaluate the influence of the preload- and frequency-dependent characteristics of the STMs on the VRE of the rail transit system, a vertical vehicle–DPFST coupled dynamic model combined with the FDPT model for the STMs was used to investigate a URT under construction in Guangzhou see . In the The railway vehicle was generally simulated as a multi-rigid-body model with two suspensions. The degrees of freedom mainly included the up and down and nodding movement of a vehicle body, two bogies, and four wheel sets. The differential equations of the vehicle system can be found in . The parThe DPFST dynamic model consisted of a rail, fasteners, slabs, STMs, concrete bases, and subgrade. The floating slab was simulated as a free beam with discrete supports according to the sample sizes of the STMs. The concrete base was laid on the subgrade, which was simulated as a continuously supported free beam. The fasteners were simply modeled with the Kelvin model, and the STMs were modeled by the FDPT model proposed in this paper.mr, Er and Ir are the mass, modulus, and rotational inertia of the rail, respectively; Zr is the vertical displacement of the rail; xi and xwj are the positions of the i-th fastener and the j-th wheelset, respectively; Nf is the total number of fastenings; δ(x) is the Dirac delta function; Frsi is the vertical force applied to the rail by the i-th fastener, as shown in Equation (14); and pj is the vertical force applied to the rail by the j-th wheel.The vertical vibration equation for the rail can be written askq (t) is the kth generalized coordinate of the rail vertical deflection, lr is the simulation length of the rail, and kY(x) is the kth orthogonal function, defined as followsBy applying Ritz’s method and normalized shape functions of Euler beams, the partial derivative equation (Equation (14)) can be transformed into the time-dependent differential equations, as follows:Ms, Es, Ls and Is are the mass, modulus, length, and rotational inertia of the floating slab, respectively; Np and Ns are the total number of fasteners and STMs on each slab, respectively; and Fsg is the vertical supporting force applied to the floating slab by the gth STM, as shown in Equation (18). The detailed derivation process of the supporting force of the fractional-order model is detailed in Reference [sgN is the total number of the past integral steps , which makes the calculated support force take into account the loading history process. The fractional parameters G1–G3 are functions of K1(P) and K2(P), which makes the FDPT model not only reflect the frequency dependence of the STMs but also consider the influence of the imposed preload. Δt is the integral step and mA is the mth Grünwald–Letnikov coefficient, defined as follows:The differential equations of the floating slab supported by the STMs can be written as follows:eference .(18)FsgnT(t) is the nth generalized mode coordinate of the floating slab, and nX is the nth modal function, defined as follows:nC and nβ are constants of the free beam function.Similarly, the dynamic equation of the floating slab can be transformed into a second-order differential equationMc, Ec, Lc, and Ic are the mass, modulus, length, and rotational inertia of the concrete base, respectively.The differential equation of continuously supported concrete base is similar to Equation (21), and the second-order differential equation is directly givenFor investigation into the influence of the different evaluation methods on the train-induced vibrations and the VRE of the FST, some calculation cases were designed, as shown in Case 1 in La between the DPFST and the monolithic track in the 1/3 frequency band from 1 to 200 Hz, defined as follows:The VRE is usually evaluated by the insertion loss ΔVLq(i) and VLh(i) are the frequency division vibration level (dB) of the vertical vibration acceleration of the monolithic track and the DPFST at the ith center frequency in the 1/3 octave band. The frequency weightings in the 1/3 octaves refer to ISO 2361-1:1997 [1-1:1997 .To avoid repetition, the calculation results under the full load of the vehicle are illustrated. The vertical displacements of the rail and floating slab obtained by different evaluation methods in Cases 1–5 are shown in the 2, respectively. It can be found that the vibration acceleration of the slab without considering the frequency dependence of STM-I is the smallest among all the results, and the acceleration of the concrete base is the largest . The time-domain acceleration results obtained by considering the frequency dependence of STM-I in Cases 2–5 show only minor differences.The time-domain vertical acceleration and vibration acceleration levels (VALs) of the slab with STM-I and concrete base in Cases 1–5 are shown in It is evident from In Case 1, due to the fact that the frequency- and preload-dependent characteristics of STM-I are not considered, the natural frequency of the floating slab is relatively low, which is mainly reflected in the value of 20 Hz. Although Cases 3 and 4 consider the influence of frequency characteristics, the stiffness under different preloads also has a slight difference in the vibration in the range of 20–31.5 Hz at the 1/3 octave frequency. The greater the stiffness of the STMs, the greater the vibration energy of the higher frequency within the resonant frequency range of the system. Since the stiffness of STM-I increases monotonically, compared with the second preload parameter (Case 3), the VALs of the slab obtained by the third preload parameter are slightly higher at the 1/3 octave frequency of 31.5 Hz and slightly lower at the 1/3 octave frequency of 20 Hz. When the preload dependence is further considered in the Case 5, the lower stiffness nonlinear segment between the first preload and second preload of STM-I is introduced into the calculation. Therefore, the VAL of the slab decreases at the 1/3 octave frequency of 31.5 Hz and increases at the 1/3 octave frequency of 20 Hz compared with Cases 3 and 4. The above influence is also reflected in the VALs of the concrete base, which is also the reason for the difference in the insertion loss calculated by different stiffness evaluation methods. The insertion losses obtained by different evaluation methods for STM-I under the conditions of empty load and full load are shown in In contrast, the evaluation error in Case 4 is relatively large, regardless of whether the vehicle is empty or fully loaded, because the force that STM-I bears is less than, or has just reached, the third preload see . TherefoThe subsequent sections focus on the differences in the VRE of the STMs obtained by different evaluation methods; thus, the figures of the dynamic displacement that meet the requirements of safe operation are omitted. The maximum dynamic displacement of the slab in Cases 6–10 under the full load of vehicle was 2.7 mm. The time-domain vertical acceleration and vibration acceleration levels (VALs) of the slab and concrete base in Cases 6–10 are shown in 2, respectively. Similarly, when using STM-II, the impact of different evaluation methods on the DPFST is mainly reflected in the frequency band near the natural frequency, especially at the 1/3 octave frequency of 31.5 Hz. Since the stiffness of the third preload of STM-II is less than that of the second preload, the maximum frequency division vibration levels (VLmax) of Cases 8 and 9 are mainly concentrated at 31.5 and 20 Hz, respectively. Compared with Case 9, the nonlinear segment with higher stiffness before the third preload is considered in Case 10; thus, the VAL at 31.5 Hz is higher than Case 9 but lower than that in Case 8 when only considering high stiffness. The insertion losses obtained by the different evaluation methods are shown in The maximum vibration accelerations of the concrete base in Cases 6–10 are 3.69, 2.27, 2.53, 1.95, and 2.18 m/sThe effect of the frequency-dependent stiffness on the insertion loss is almost uniform for all of the STMs; thus, the insertion loss of Case 6 is the largest. The secant stiffness weakens the difference between different preloads of STM-II, meaning that the result of Case 7 is between that of Case 8 and Case 9. However, considering the nonlinear segment with the higher stiffness before the third preload, the actual VRE of Case 10 is less than that of Case 9. Moreover, unlike STM-I, the insertion loss of STM-II increases by 0.8 dB when the vehicle is fully loaded. This is because the increased load makes the lower stiffness segments of STM-II perform better. It can be concluded that the insertion loss error obtained by the third preload evaluation method is not negligible, but different from the evaluation for STM-I, and, thus, the VRE of STM-II will be overestimated.The maximum dynamic displacements of the rail and slab in Cases 11–15 under the full load of vehicle are 2.6 and 1.8 mm respectively, which is basically the same as the results of STM-I and STM-II. 2, respectively. Despite the fact that the frequency dependence is considered in Cases 12–15, the true strong nonlinearity of STM-III results in a significant difference between the maximum vibration acceleration in Case 15 and the results of other evaluation methods (Case 12–14). The VALs of the slab and concrete base in Cases 11–15 are shown in The maximum vibration accelerations of the concrete base in Cases 11–15 are 2.82, 3.52, 2.32, 3.12, and 2.45 m/sVLmax of Cases 12 and 14 are about 7 dB larger than Cases 13 and 15, which is very important for the insertion loss. As described in Compared with other STMs, the most significant difference between different evaluation methods for STM-III is that the frequency-dependent secant stiffness can no longer approximately reflect its true VRE. In addition, compared with STM-II, the third preloading did not overestimate its VRE of STM-III, but rather underestimated it. Another interesting finding is that the VRE of STM-III has little change in the no-load or full-load conditions, which is also what we hope to achieve under different axle loads. Compared with most STMs whose force–displacement curve is approximately linear , this type of STM with high-static–low-dynamic (HSLD) stiffness in the service load range is a good choice for improving the efficiency of vibration isolation.3, respectively. As the vibration level of an empty vehicle is low and the vehicle is almost always in a loaded state, we evaluated the VRE of the vehicle under full load according to the method proposed in this article. The vertical VALs of the concrete base and insertion loss calculated by the new method for the three types of STMs are shown in From the results of the above three STMs, it can be concluded that the insertion loss calculated by using the second preload frequency-dependent tangent stiffness is the closest to the real result. In order to facilitate its application, it is practical to adopt a single frequency parameter that can accurately reflect the vibration characteristics of the floating slab track and the VRE. Therefore, we proposed an improved calculation method for the second preload evaluation method, which uses the corresponding stiffness at the natural frequency to replace the frequency-dependent stiffness. It is worth mentioning that this natural frequency is not the tuning frequency under no load, but the natural frequency considering the P2 resonance during vehicle operation ,41. The VLmax that has a greater impact on the insertion loss).It is precisely because the parameters at the natural frequency can more accurately reflect the natural vibration characteristics of the DPFST that the VALs of the concrete base calculated by using the new method are relatively close to the actual results (especially the It is obvious that the maximum error between the result of the new method and the actual insertion loss calculated by considering the preload and frequency dependence is only 0.5 dB, which meets the error requirements of the engineering design. On the whole, this single parameter evaluation method at the natural frequency under the second preload is the most practical and accurate method at present.In specification TJ/GW 121-2014 , the metThe disadvantage of DIN 45673-7:2010  is that Among the above different evaluation methods, the evaluation method using the second preload frequency-dependent stiffness of the DIN 45673-7:2010  is the mIn terms of the VRE of the different STMs, the insertion loss of STM-I with a monotonically increased stiffness decreases slightly with the increase in axel load, while the insertion loss of STM-II with a monotonically decreased stiffness improves with the increase in axel load. The VRE of STM-III with HSLD stiffness characteristics is both better and stable. This advantage of STM-III comes from the lower stiffness under the second preload. In addition, this also coincides with the evaluation and design idea of using the second preload tangent stiffness to evaluate the VRE.A series of performance tests were conducted to study the preload dependence and frequency dependence of different STMs. The FDPT model was used instead of the KV model to accurately calculate the actual VRE obtained from the vehicle–DPFST coupled dynamic model. Next, the differences in the existing STM specifications in the evaluation of the VRE were analyzed. Finally, based on the above analysis, an accurate and practical single parameter evaluation method for guiding engineering design was proposed. The four main conclusions are as follows: