Subgrade engineering is a fundamental aspect of infrastructure construction in China.As the primary structural element responsible for bearing and distributing traffic loads,the subgrade must not only withstand the su...Subgrade engineering is a fundamental aspect of infrastructure construction in China.As the primary structural element responsible for bearing and distributing traffic loads,the subgrade must not only withstand the substantial pressures exerted by vehicles,trains,and other forms of transportation,but also efficiently transfer these loads to the underlying foundation,ensuring the stability and longevity of the roadway.In recent years,advancements in subgrade engineering technology have propelled the industry towards smarter,greener,and more sustainable practices,particularly in the areas of intelligent monitoring,disaster management,and innovative construction methods.This paper reviews the application and methodologies of intelligent testing equipment,including cone penetration testing(CPT)devices,soil resistivity testers,and intelligent rebound testers,in subgrade engineering.It examines the operating principles,advantages,limitations,and application ranges of these tools in subgrade testing.Additionally,the paper evaluates the practical use of advanced equipment from both domestic and international perspectives,addressing the challenges encountered by various instruments in realworld applications.These devices enable precise,comprehensive testing and evaluation of subgrade conditions at different stages,providing real-time data analysis and intelligent early warnings.This supports effective subgrade health management and maintenance.As intelligent technologies continue to evolve and integrate,these tools will increasingly enhance the accuracy,efficiency,and sustainability of subgrade monitoring.展开更多
Understanding the reinforcement effect of the newly developed prestressed reinforcement components(PRCs)(a system composed of prestressed steel bars(PSBs),protective sleeves,lateral pressure plates(LPPs),and anchoring...Understanding the reinforcement effect of the newly developed prestressed reinforcement components(PRCs)(a system composed of prestressed steel bars(PSBs),protective sleeves,lateral pressure plates(LPPs),and anchoring elements)is technically significant for the rational design of prestressed subgrade.A three-dimensional finite element model was established and verified based on a novel static model test and utilized to systematically analyze the influence of prestress levels and reinforcement modes on the reinforcement effect of the subgrade.The results show that the PRCs provide additional confining pressure to the subgrade through the diffusion effect of the prestress,which can therefore effectively improve the service performance of the subgrade.Compared to the unreinforced conventional subgrades,the settlements of prestressreinforced subgrades are reduced.The settlement attenuation rate(Rs)near the LPPs is larger than that at the subgrade center,and increasing the prestress positively contributes to the stability of the subgrade structure.In the multi-row reinforcement mode,the reinforcement effect of PRCs can extend from the reinforced area to the unreinforced area.In addition,as the horizontal distance from the LPPs increases,the additional confining pressure converted by the PSBs and LPPs gradually diminishes when spreading to the core load bearing area of the subgrade,resulting in a decrease in the Rs.Under the singlerow reinforcement mode,PRCs can be strategically arranged according to the local areas where subgrade defects readily occurred or observed,to obtain the desired reinforcement effect.Moreover,excessive prestress should not be applied near the subgrade shoulder line to avoid the shear failure of the subgrade shoulder.PRCs can be flexibly used for preventing and treating various subgrade defects of newly constructed or existing railway lines,achieving targeted and classified prevention,and effectively improving the bearing performance and deformation resistance of the subgrade.The research results are instructive for further elucidating the prestress reinforcement effect of PRCs on railway subgrades.展开更多
Purpose–Salt rock from salt lakes can serve as a cost-effective material for subgrade filling,as demonstrated in projects like the Qarhan Salt Lake section of the Qinghai-Tibet Railway and the Qarhan Salt Lake sectio...Purpose–Salt rock from salt lakes can serve as a cost-effective material for subgrade filling,as demonstrated in projects like the Qarhan Salt Lake section of the Qinghai-Tibet Railway and the Qarhan Salt Lake section of the G215 Highway.This state-of-the-art paper aims to summarize the engineering properties of salt rock filling and present the advances of its utilization.Design/methodology/approach–This paper collects and analyzes laboratory and field data of salt rock filling from previous studies to present a comprehensive analysis of the engineering properties and utilization of salt rock fillings.Findings–Salt rock primarily contains minerals such as halite and glauberite,which contribute to its unique phase-changing behavior under varying environmental conditions,impacting its mechanical properties.Salt rock filling shrinks when in contact with vapor or unsaturated brine and expands under cooling or evaporation.Its use is particularly recommended for arid regions,with specific restrictions depending on the structure type.This paper discusses suggested countermeasures to mitigate these issues,as well as key quality acceptance indices for salt rock filling compaction.Moisture content after air-drying is recommended as a crucial parameter for construction quality control.Originality/value–This review aims to support future research and engineering practices in salt rock subgrade applications.展开更多
To mitigate the sand burial of highways in sandy regions,a separated subgrade design was widely adopted in the embankments of high-grade highways,but the problem of sand deposition on subgrade slopes and pavements sti...To mitigate the sand burial of highways in sandy regions,a separated subgrade design was widely adopted in the embankments of high-grade highways,but the problem of sand deposition on subgrade slopes and pavements still happens frequently.Based on the theory of wind-sand two-phase flow,this paper constructed a three-dimensional model of the separated subgrade,the wind-sand flow transport law around the subgrade with varying median strip widths and concave depths was simulated by Fluent software.After comparison and analysis of seven subgrade models,the flow field distribution,wind speed horizontal variation,and erosion-deposition characteristics were investigated.The findings are as follows:(1)The width of the median strip in the separated subgrade had significant influences on the wind-sand flow.The smooth passage of wind-sand flow over the road surface was facilitated with the increase of the median strip width.However,sand deposition in the median strip happened.It can lead to secondary sand damage of downwind subgrade and increase the work load of road sand removal for subsequent maintenance.(2)The obstruction to airflow and sand accumulation was aggravated with greater concave depth of the median strip.Therefore,it is advisable to minimize the concave depth of the median strip in case of more sand damage.(3)A median strip width exceeding 12 m(possibly without guardrails)for an integral embankment without enough road land is recommended.Conversely,median strip width of over 40 m for separate subgrade with unrestricted land is suggested.(4)In the case of sand deposition in the existing separated subgrade,the median strip can be filled by sand deposition or other materials,then was covered with gravel to form a flat ground like Gobi smooth surface,which can let the wind-blown sand flow pass through the subgrade section without sand deposition.展开更多
Purpose–The deformation of the roadbed is easily influenced by the external environment to improve the accuracy of high-speed railway subgrade settlement prediction.Design/methodology/approach–A high-speed railway s...Purpose–The deformation of the roadbed is easily influenced by the external environment to improve the accuracy of high-speed railway subgrade settlement prediction.Design/methodology/approach–A high-speed railway subgrade settlement interval prediction method using the secretary bird optimization(SBOA)algorithm to optimize the BP neural network under the premise of gray relational analysis is proposed.Findings–Using the SBOA algorithm to optimize the BP neural network,the optimal weights and thresholds are obtained,and the best parameter prediction model is combined.The data were collected from the sensors deployed through the subgrade settlement monitoring system,and the gray relational analysis is used to verify that all four influencing factors had a great correlation to the subgrade settlement,and the collected data are verified using the model.Originality/value–The experimental results show that the SBOA-BP model has higher prediction accuracy than the BP model,and the SBOA-BP model has a wider range of prediction intervals for a given confidence level,which can provide higher guiding value for practical engineering applications.展开更多
Real-time assessment of subgrade compaction quality poses a significant challenge in the implementation of intelligent compaction(IC).Current compaction evaluation models are confined to specific scenarios and lack ro...Real-time assessment of subgrade compaction quality poses a significant challenge in the implementation of intelligent compaction(IC).Current compaction evaluation models are confined to specific scenarios and lack robustness.This study proposes a subgrade compaction strategy that utilizes a heterogeneous dataset to estimate compaction quality across diverse scenarios while maintaining model accuracy.Field compaction tests are conducted in four distinct scenarios,considering various construction parameters.Compaction models are developed using several machine learning algorithms.The datasets are thoroughly assessed in terms of quality,diversity and similarity.The proposed model exhibits good performance in new scenarios by incorporating an additional 5%e8%of new data for retraining.The model's generalization capability is enhanced by conducting a limited number of field tests,which are labor-saving and time-efficient.The model's accuracy consistently improves across diverse scenarios and optimal algorithms.The proposed compaction strategy adopts a physics-and-data dual-driven approach,aimed at practical engineering applications and guiding the compaction procedure.展开更多
Foamed concrete has been used to address the issue of differential settlement in high-speed railway subgrades in China.However,to enhance crack resistance,reinforcement is still necessary,and further research is requi...Foamed concrete has been used to address the issue of differential settlement in high-speed railway subgrades in China.However,to enhance crack resistance,reinforcement is still necessary,and further research is required to better understand the performance of foamed concrete in subgrade applications.To this end,a series of tests—including uniaxial compres-sive and dynamic triaxial tests—were conducted to comprehensively examine the effects of basalt fiber reinforcement on the mechanical properties of foamed concrete with densities of 700 and 1000 kg/m3.Additionally,a full-scale model of the foamed concrete subgrade was established,and simulated loading was applied.The diffusion patterns of dynamic stress and dynamic acceleration within the subgrade were explored,leading to the development of experimental formulas to calculate the attenuation coefficients of these two parameters along the depth and width of the subgrade.Furthermore,the dynamic displacement and cumulative settlement were analyzed to evaluate the stability of the subgrade.These findings provide valuable insights for the design and construction of foamed concrete subgrades in high-speed rail systems.The outcomes are currently under consideration for inclusion in the code of practice for high-speed rail restoration.展开更多
Purpose–This paper conducts a joint analysis of monitoring data in the hidden danger areas of railway subgrade deformation using a data-driven method,thereby realizing the systematic risk identification of regional h...Purpose–This paper conducts a joint analysis of monitoring data in the hidden danger areas of railway subgrade deformation using a data-driven method,thereby realizing the systematic risk identification of regional hidden dangers.Design/methodology/approach–The paper proposes a regional systematic risk identification method based on Bayesian and independent component analysis(ICA)theories.Firstly,the Gray Wolf Optimization(GWO)algorithm is used to partition each group of monitoring data in the hidden danger area,so that the data distribution characteristics within each sub-block are similar.Then,a distributed ICA early warning model is constructed to obtain prior knowledge such as control limits and statistics of the area under normal conditions.For the online evaluation process,the input data is partitioned following the above-mentioned procedure and the ICA statistics of each sub-block are calculated.The Bayesian method is applied to fuse online parameters with offline parameters,yielding statistics under a specific confidence interval.These statistics are then compared with the control limits–specifically,checking whether they exceed the pre-set confidence parameters–thus realizing the systematic risk identification of the hidden danger area.Findings–Through simulation experiments,the proposed method can integrate prior knowledge such as control limits and statistics to effectively determine the overall stability status of the area,thereby realizing the systematic risk identification of the hidden danger area.Originality/value–The proposed method leverages Bayesian theory to fuse online process parameters with offline parameters and further compares them with confidence parameters,thereby effectively enhancing the utilization efficiency of monitoring data and the robustness of the analytical model.展开更多
Biochar,a solid carbonaceous material produced by heating biomass in oxygen-free or low-oxygen conditions(pyrolysis),has been used in various applications,including wastewater treatment,carbon sequestration,and improv...Biochar,a solid carbonaceous material produced by heating biomass in oxygen-free or low-oxygen conditions(pyrolysis),has been used in various applications,including wastewater treatment,carbon sequestration,and improving soil fertility.However,very limited research has been performed to explore its feasibility to improve the expansive clay(EC)subgrade.In this study,fine-grained wood biochar derived from wood waste was used to stabilise and enhance the mechanical performance of the EC as road subgrade.A comprehensive series of geotechnical tests,including unconfined compressive strength(UCS),California bearing ratio(CBR),repeated load triaxial(RLT),and swelling-shrinkage tests,were conducted to investigate the engineering properties of expansive clay mixed with different contents of the fine-grained biochar(FGB)(i.e.0,1%,2%,3%,and 4%by weight of dry soil).Furthermore,X-ray diffraction(XRD),X-ray fluorescence(XRF),X-ray micro-CT,and thermogravimetric analysis(TGA)analyses were performed to study the microchemical modification of the EC-FGB mixtures.The results showed that adding FGB reduced the swelling and shrinkage potential while enhancing the mechanical properties of the EC.The micro-level analysis also supported the enhancement of the geotechnical performance of the EC resulting from the incorporation of FGB.According to the test results,2%FGB was considered the optimum content,increasing UCS,CBR,and resilient modulus by 31.1%,24.1%,and 31.5%,respectively,and decreasing the swell-shrinkage index by 7%.展开更多
The pile-plate structure has proven highly effective support for high-speed railway subgrades,particularly in poor geological conditions.Although its efficacy in non-frozen regions is well-established,its potential in...The pile-plate structure has proven highly effective support for high-speed railway subgrades,particularly in poor geological conditions.Although its efficacy in non-frozen regions is well-established,its potential in frozen regions remains underexplored.In seasonally frozen areas,F-T(freeze-thaw)cycles threaten subgrade stability,necessitating research on pile-plate structure’s behavior under such conditions.To address this challenge,a scaled model experiment was conducted on a silty sand foundation,simulating F-T cycles using temperature control devices.Key parameters,including soil temperature,frozen depth,and displacement,were systematically monitored.Results indicate that the bearing plate functions as an effective insulation layer,significantly reducing sub-zero temperature penetration.Additionally,the anchoring action of the piles mitigates frost heave in the foundation soil,while the plate middle restrains soil deformation more effectively due to increased constraint.The thermal insulation provided by the plate maintains higher soil temperatures,delaying the onset of freezing.By the end of each freezing stage,the vertical displacement in the natural subgrade is approximately 4 times greater than that beneath the pile-plate structure.Furthermore,the frost depth is about 1.3-1.4 times and 1.6-4.9 times greater than that measured below the plate edge and middle,respectively.These insights contribute to the development of more resilient designs for high-speed railway subgrades in seasonally frozen regions,offering engineers a robust,scientifically-backed foundation for future infrastructure projects.展开更多
Purpose-Conventional high-speed railways(HSR)subgrade design methods remain constrained by platformdependent drafting systems,leading to data interaction hindrances and redundant design processes.This study strives to...Purpose-Conventional high-speed railways(HSR)subgrade design methods remain constrained by platformdependent drafting systems,leading to data interaction hindrances and redundant design processes.This study strives to develop a digital earthwork design methodology that enhances design while reducing collaborative expenses.Design/methodology/approach-A novel digital subgrade design approach,utilizing sophisticated analysis and modeling tools customized for different subgrade elements,is put forward in this study.The methodology incorporates the following essential steps:(1)the advancement of digital analysis and modeling techniques for diverse subgrade components,including surfaces,filling,slopes,retaining structures,and foundation treatments;(2)the formulation of a digital design principle repository incorporating various slope protection combinations;(3)the establishment of a comprehensive digital design framework and process for subgrade cross-sections;and(4)the development and implementation of an open-source digital design system.Findings-The proposed method liberates subgrade design from the constraints of conventional drawing platforms,elevating efficiency,intelligence,and flexibility.The open software architecture and code have achieved over 60%efficiency gains in design workflows during its deployment on three major high-speed rail projects:the Baotou-Yinchuan HSR corridor,Shenyang-Baihe HSR network,and Weifang-Yantai HSR system.Originality/value-This paper introduces an innovative digital design methodology that enables modular and parametric design for railway subgrade sections.The proposed approach provides a digital base for the intelligent design and maintenance of the next-generation high-speed railway.展开更多
The sustainable geotechnical approach for addressing the challenges associated with clayey soils at construction sites involves the modification of these soils’mechanical and chemical characteristics using soil enhan...The sustainable geotechnical approach for addressing the challenges associated with clayey soils at construction sites involves the modification of these soils’mechanical and chemical characteristics using soil enhancement methods.The present study investigates the coupling effect of sandstone slurry waste(SSW)and calcium carbonate nanoparticle(CCN)as potential stabilizers to enhance the characteristics of clayey soil.A comprehensive investigation was conducted using compaction tests,plasticity index(PI)tests,California bearing ratio(CBR)tests,unconfined compressive strength(UCS)tests,and microstructural analyses of clayey soil,SSW and SSW-CCN-treated clay samples containing 5%,10%,15%,20%,25%,30%,and 35%SSW and 0.3%,0.6%,0.9%,1.2%,and 1.5%CCN mixed with clayey soil in different combinations of clay,SSW,and CCN.The findings reveal that incorporating 25%SSW with 0.9%CCN into clay soil results in an increase in the UCS from 132.2 kPa for untreated clayey soil without curing to 263 kPa after a 28-d curing period.Similarly,a rising trend in CBR results is observed up to 25%SSW addition in clay soil and up to 0.9%CCN addition in SSW-clay mixture.Initially,notable enhancements in UCS were attributed to a denser soil structure,followed by the formation of calcium–silicate–hydrate(CSH)gel,which intensified with prolonged curing.Gel patches were detected by scanning electron microscopy(SEM)in addition to particle aggregation.The results obtained from thermogravimetric analysis,Fourier transform infrared spectroscopy(FTIR),and X-ray diffraction(XRD)supported the presence of hydration products such as CSH.The experimental study indicates that SSW,in combination with CCN,offers a sustainable alternative to traditional soil stabilizers.展开更多
Subgrade frost heave in seasonally frozen ground can greatly influence the safety and smooth running of high-speed trains and the service performance of track structures.In this study,we used a static model to:(1)inve...Subgrade frost heave in seasonally frozen ground can greatly influence the safety and smooth running of high-speed trains and the service performance of track structures.In this study,we used a static model to:(1)investigate track-subgrade frost heave and develop a dynamic model of vehicle-track-subgrade frost heave;(2)explore the transfer relation between subgrade frost heave and track structure deformation;(3)examine the characteristics of interlayer debonding;(4)study the influence of subgrade frost heave on the dynamic response of vehicles in high-speed railways in seasonally frozen regions.A Fourier series was used to fit the frost heave waveform and simulate the behavior of subgrade uneven frost heave using data collected on-site.The results show:(i)The position of frost heave significantly affects the transfer of deformation to a slab track.The largest deformation of the track slab,with the amplitude transfer ratio reaching 20%,was recorded when the frost heave occurred near the joint of the base plate.(ii)At the same frost heave amplitude,long-wave frost heave causes smaller deformation and debonding of the track structure than short-wave frost heave.In the wavelength range of 10-30 m,the main frequency of the acceleration spectral density was concentrated between 3.5 and 3.7 Hz,with larger frost heave wavelengths producing smaller superposition on the vertical acceleration of the vehicle.(ii)The maximum wheel-rail force occurs when the front bogie passes the frost heave peak,with greater frost heave amplitudes producing greater wheel-rail force.From these results,we conclude there is a clear need to control the frost heave deformation of the track to reduce the dynamic response of the vehicle and in turn improve train operatSubgrade frost heave in seasonally frozen ground can greatly influence the safety and smooth running of high-speed trains and the service performance of track structures.In this study,we used a static model to:(1)investigate track`-subgrade frost heave and develop a dynamic model of vehicle`-track`-subgrade frost heave;(2)explore the transfer relation between subgrade frost heave and track structure deformation;(3)examine the characteristics of interlayer debonding;(4)study the influence of subgrade frost heave on the dynamic response of vehicles in high-speed railways in seasonally frozen regions.A Fourier series was used to fit the frost heave waveform and simulate the behavior of subgrade uneven frost heave using data collected on-site.The results show:(i)The position of frost heave significantly affects the transfer of deformation to a slab track.The largest deformation of the track slab,with the amplitude transfer ratio reaching 20%,was recorded when the frost heave occurred near the joint of the base plate.(ii)At the same frost heave amplitude,long-wave frost heave causes smaller deformation and debonding of the track structure than short-wave frost heave.In the wavelength range of 10-30 m,the main frequency of the acceleration spectral density was concentrated between 3.5 and 3.7 Hz,with larger frost heave wavelengths producing smaller superposition on the vertical acceleration of the vehicle.(iii)The maximum wheel`-rail force occurs when the front bogie passes the frost heave peak,with greater frost heave amplitudes producing greater wheel`-rail force.From these results,we conclude there is a clear need to control the frost heave deformation of the track to reduce the dynamic response of the vehicle and in turn improve train operations.ions.展开更多
The compaction quality of subgrade filler strongly affects subgrade settlement.The main objective of this research is to analyze the macro-and micro-mechanical compaction characteristics of subgrade filler based on th...The compaction quality of subgrade filler strongly affects subgrade settlement.The main objective of this research is to analyze the macro-and micro-mechanical compaction characteristics of subgrade filler based on the real shape of coarse particles.First,an improved Viola-Jones algorithm is employed to establish a digitalized 2D particle database for coarse particle shape evaluation and discrete modeling purposes of subgrade filler.Shape indexes of 2D subgrade filler are then computed and statistically analyzed.Finally,numerical simulations are performed to quantitatively investigate the effects of the aspect ratio(AR)and interparticle friction coefficient(μ)on the macro-and micro-mechanical compaction characteristics of subgrade filler based on the discrete element method(DEM).The results show that with the increasing AR,the coarse particles are narrower,leading to the increasing movement of fine particles during compaction,which indicates that it is difficult for slender coarse particles to inhibit the migration of fine particles.Moreover,the average displacement of particles is strongly influenced by the AR,indicating that their occlusion under power relies on particle shapes.The dis-placement and velocity of fine particles are much greater than those of the coarse particles,which shows that compaction is primarily a migration of fine particles.Under the cyclic load,the interparticle friction coefficientμhas little effect on the internal structure of the sample;under the quasi-static loads,however,the increase inμwill lead to a significant increase in the porosity of the sample.This study could not only provide a novel approach to investigate the compaction mechanism but also establish a new theoretical basis for the evaluation of intelligent subgrade compaction.展开更多
Purpose-The experiments of this study investigated the effect of the subgrade degree of saturation on the value of the stresses generated on the surface and the middle(vertical and lateral stresses).The objectives of ...Purpose-The experiments of this study investigated the effect of the subgrade degree of saturation on the value of the stresses generated on the surface and the middle(vertical and lateral stresses).The objectives of this study can be identified by studying the effect of subgrade layer degree of saturation variation,load amplitude and load frequency on the transmitted stresses through the ballast layer to the subgrade layer and the stress distribution inside it and investigating the excess pore water pressure development in the clay layer in the case of a fully saturated subgrade layer and the change in matric suction in the case of an unsaturated subgrade layer.Design/methodology/approach-Thirty-six laboratory experiments were conducted using approximately half-scale replicas of real railways,with an iron box measuring 1.5×1.031.0 m.Inside the box,a 0.5 m thick layer of clay soil representing the base layer was built.Above it is a 0.2 m thick ballast layer made of crushed stone,and on top of that is a 0.8 m long rail line supported by three 0.9 m(0.1×0.1 m)slipper beams.The subgrade layer has been built at the following various saturation levels:100,80,70 and 60%.Experiments were conducted with various frequencies of 1,2 and 4 Hz with load amplitudes of 15,25 and 35 kN.Findings-The results of the study demonstrated that as the subgrade degree of saturation decreased from 100 to 60%,the ratio of stress in the lateral direction to stress in the vertical direction generated in the middle of the subgrade layer decreased as well.On average,this ratio changed from approximately 0.75 to approximately 0.65.Originality/value-The study discovered that as the test proceeded and the number of cycles increased,the value of negative water pressure(matric suction)in the case of unsaturated subgrade soils declined.The frequency of loads had no bearing on the ratio of decline in matric suction values,which was greater under a larger load amplitude than a lower one.As the test progressed(as the number of cycles increased),the matric suction dropped.For larger load amplitudes,there is a greater shift in matric suction.The change in matric suction is greater at higher saturation levels than it is at lower saturation levels.Furthermore,it is seen that the load frequency value has no bearing on how the matric suction changes.For all load frequencies and subgrade layer saturation levels,the track panel settlement rises with the load amplitude.Higher load frequency and saturation levels have a greater impact.展开更多
The ultrasonic pulse velocity(UPV)correlates significantly with the density and pore size of subgrade filling materials.This research conducts numerous Proctor and UPV tests to examine how moisture and rock content af...The ultrasonic pulse velocity(UPV)correlates significantly with the density and pore size of subgrade filling materials.This research conducts numerous Proctor and UPV tests to examine how moisture and rock content affect compaction quality.The study measures the changes in UPV across dry density and compaction characteristics.The compacted specimens exhibit distinct microstructures and mechanical properties along the dry and wet sides of the compaction curve,primarily influenced by internal water molecules.The maximum dry density exhibits a positive correlation with the rock content,while the optimal moisture content demonstrates an inverse relationship.As the rock content increases,the relative error of UPV measurement rises.The UPV follows a hump-shaped pattern with the initial moisture content.Three intelligent models are established to forecast dry density.The measure of UPV and PSO-BP-NN model quickly assesses compaction quality.展开更多
With the change of seasons, the shear strength of saline soil subgrade filler will change with the change of external temperature, which will aggravate the adverse effects of seismic on the subgrade. To explore the in...With the change of seasons, the shear strength of saline soil subgrade filler will change with the change of external temperature, which will aggravate the adverse effects of seismic on the subgrade. To explore the influence of seismic action on the stability of saline soil subgrade under the influence of temperature on the strength of saline soil subgrade filler, this paper first carried out saline soil shear tests at different temperatures to obtain the influence of temperature on the shear strength of saline soil. Then, the temperature field of the saline soil subgrade was simulated, and then based on the subgrade isothermal stratification model and FLAC3D, the displacement and acceleration amplification effects of seismic action on the shady slope, sunny slope and subgrade of saline soil subgrade in different months were analyzed. The following conclusions were finally drawn: under the action of seismic, In the process of the change of subgrade temperature of Qarhan-Golmud Expressway between 7.7°C and 27°C, the change of saline soil cohesion is the main factor affecting the stability of subgrade slope, and the maximum and minimum values of subgrade surface settlement appear in September and June of each year,respectively. In August, the differences of settlement between the shady slope and the sunny slope shoulder of the subgrade were the largest, and the acceleration of the shady slope and the sunny slope and the inside of the subgrade changed most significantly in the vertical direction. Special attention should be paid to the seismic early warning in the above key months;In the range from both sides of the shoulder to the centerline of the roadbed,the acceleration amplification effect starts to increase significantly from about 3m from the centerline of the roadbed to the centerline, so it is necessary to pay attention to the seismic design of this range.展开更多
With the continuous development of China’s economy,the construction of roads and bridges work has put forward higher requirements.Due to various factors,the long-term use of roads and bridges will produce a settlemen...With the continuous development of China’s economy,the construction of roads and bridges work has put forward higher requirements.Due to various factors,the long-term use of roads and bridges will produce a settlement phenomenon.Therefore,it is crucial to address settlement issues during the construction of roads and bridges to ensure that the quality of subgrade and pavement construction meets national regulations.This paper introduces the harm of subgrade pavement subsidence,analyzes the causes of subgrade pavement deformation,and discusses the technical points of subgrade pavement construction,hoping to provide some reference for relevant practitioners.展开更多
The railway subgrades in the sandy areas act as an obstacle interfering wind-blown sand,causing sand erosion and sedimentation,which can disrupt the safe and stable operation of the railway system.Most previous studie...The railway subgrades in the sandy areas act as an obstacle interfering wind-blown sand,causing sand erosion and sedimentation,which can disrupt the safe and stable operation of the railway system.Most previous studies mainly focus on the flow field around railway subgrades,however,the real erosion and sedimentation patterns are rarely studied.This study aims to analyze the erosion and sand sedimentation patterns of wind-blown sand over the subgrades with different heights and steel rails using the ratio of the wall shear stress to the critical value of erosion shear stress.Results show that wind erosion near the top of the upwind slope of the embankment and the shoulder on the upwind side are more severe,and the severity increases with an increase in the height of the embankment.With the increase of wind velocity,sand sedimentation both on the windward and leeside of the subgrade decreases and wind erosion by reverse flow occur.This study indicates that railways in sandy areas should be constructed with a moderate subgrade height(4 m).展开更多
The improved granular mixtures are widely used as the fillings of railway 8ubgrade, and in order to investigate the effect of coarse grain content on granular mixtures, a series of field tests were conducted. The expe...The improved granular mixtures are widely used as the fillings of railway 8ubgrade, and in order to investigate the effect of coarse grain content on granular mixtures, a series of field tests were conducted. The experimental results indicate that the permeability coefficient increases significantly with the increment of granite gravel content, especially in the range of 60%-70%. Thcrc exists a coarse grain content limit defined as 53%-58.5% to reform the permeable granular skeleton. Beyond this limit, the permeable granular skeleton is efficiently formed, and the macro pores between the separate gravels are partially filled, which is the explanation lbr the permeability increase. The investigations indicate the subgrade resistance modulus （ks0, Ev2, and Evd） depends on the granite gravel content, and the resistance modulus increases significantly beyond granite gravel content of 50%. The skeletons of granitc gravel clayey sand mixture change in the long-term deformation objected to the train-induced dynamic load, which involves three main repeated and circular deformation stages. Generally, the long-time deformation is explained as the gravel crushing and filling the internal porous space with crushed gravel fragments. Through these investigations, the C40-G60 or C30-G70 is recommended as an optimum soil mixture for the good permeability and high resistance modulus.展开更多
基金supported by the National Natural Science Foundation of China for Distinguished Young Scholars(Grant No.42225206)National Natural Science Foundation of China(42207180,42477209,42302320).
文摘Subgrade engineering is a fundamental aspect of infrastructure construction in China.As the primary structural element responsible for bearing and distributing traffic loads,the subgrade must not only withstand the substantial pressures exerted by vehicles,trains,and other forms of transportation,but also efficiently transfer these loads to the underlying foundation,ensuring the stability and longevity of the roadway.In recent years,advancements in subgrade engineering technology have propelled the industry towards smarter,greener,and more sustainable practices,particularly in the areas of intelligent monitoring,disaster management,and innovative construction methods.This paper reviews the application and methodologies of intelligent testing equipment,including cone penetration testing(CPT)devices,soil resistivity testers,and intelligent rebound testers,in subgrade engineering.It examines the operating principles,advantages,limitations,and application ranges of these tools in subgrade testing.Additionally,the paper evaluates the practical use of advanced equipment from both domestic and international perspectives,addressing the challenges encountered by various instruments in realworld applications.These devices enable precise,comprehensive testing and evaluation of subgrade conditions at different stages,providing real-time data analysis and intelligent early warnings.This supports effective subgrade health management and maintenance.As intelligent technologies continue to evolve and integrate,these tools will increasingly enhance the accuracy,efficiency,and sustainability of subgrade monitoring.
基金supported by the National Natural Science Foundation of China(Grant Nos.51978672 and 52308335)the Natural Science Funding of Hunan Province(Grant No.2023JJ41054)the Natural Science Research Project of Anhui Educational Committee(Grant No.2023AH051170)。
文摘Understanding the reinforcement effect of the newly developed prestressed reinforcement components(PRCs)(a system composed of prestressed steel bars(PSBs),protective sleeves,lateral pressure plates(LPPs),and anchoring elements)is technically significant for the rational design of prestressed subgrade.A three-dimensional finite element model was established and verified based on a novel static model test and utilized to systematically analyze the influence of prestress levels and reinforcement modes on the reinforcement effect of the subgrade.The results show that the PRCs provide additional confining pressure to the subgrade through the diffusion effect of the prestress,which can therefore effectively improve the service performance of the subgrade.Compared to the unreinforced conventional subgrades,the settlements of prestressreinforced subgrades are reduced.The settlement attenuation rate(Rs)near the LPPs is larger than that at the subgrade center,and increasing the prestress positively contributes to the stability of the subgrade structure.In the multi-row reinforcement mode,the reinforcement effect of PRCs can extend from the reinforced area to the unreinforced area.In addition,as the horizontal distance from the LPPs increases,the additional confining pressure converted by the PSBs and LPPs gradually diminishes when spreading to the core load bearing area of the subgrade,resulting in a decrease in the Rs.Under the singlerow reinforcement mode,PRCs can be strategically arranged according to the local areas where subgrade defects readily occurred or observed,to obtain the desired reinforcement effect.Moreover,excessive prestress should not be applied near the subgrade shoulder line to avoid the shear failure of the subgrade shoulder.PRCs can be flexibly used for preventing and treating various subgrade defects of newly constructed or existing railway lines,achieving targeted and classified prevention,and effectively improving the bearing performance and deformation resistance of the subgrade.The research results are instructive for further elucidating the prestress reinforcement effect of PRCs on railway subgrades.
文摘Purpose–Salt rock from salt lakes can serve as a cost-effective material for subgrade filling,as demonstrated in projects like the Qarhan Salt Lake section of the Qinghai-Tibet Railway and the Qarhan Salt Lake section of the G215 Highway.This state-of-the-art paper aims to summarize the engineering properties of salt rock filling and present the advances of its utilization.Design/methodology/approach–This paper collects and analyzes laboratory and field data of salt rock filling from previous studies to present a comprehensive analysis of the engineering properties and utilization of salt rock fillings.Findings–Salt rock primarily contains minerals such as halite and glauberite,which contribute to its unique phase-changing behavior under varying environmental conditions,impacting its mechanical properties.Salt rock filling shrinks when in contact with vapor or unsaturated brine and expands under cooling or evaporation.Its use is particularly recommended for arid regions,with specific restrictions depending on the structure type.This paper discusses suggested countermeasures to mitigate these issues,as well as key quality acceptance indices for salt rock filling compaction.Moisture content after air-drying is recommended as a crucial parameter for construction quality control.Originality/value–This review aims to support future research and engineering practices in salt rock subgrade applications.
基金supported by the Third Xinjiang Scientific Expedition and Research Program-Investigation and Risk Assessment of Drought and Aeolian Disasters in Tarim River Basin(No.2021xjkk0300)the National Natural Science Foundation of China(No.62466056)the subject of'the technical scheme and application demonstration of sand disaster prevention and control of Xinjiang expressway to engineering practice,Xinjiang Transportation Investment(Group)Co.,Ltd.(No.XJJTZKX-FWCG-202401-0043).
文摘To mitigate the sand burial of highways in sandy regions,a separated subgrade design was widely adopted in the embankments of high-grade highways,but the problem of sand deposition on subgrade slopes and pavements still happens frequently.Based on the theory of wind-sand two-phase flow,this paper constructed a three-dimensional model of the separated subgrade,the wind-sand flow transport law around the subgrade with varying median strip widths and concave depths was simulated by Fluent software.After comparison and analysis of seven subgrade models,the flow field distribution,wind speed horizontal variation,and erosion-deposition characteristics were investigated.The findings are as follows:(1)The width of the median strip in the separated subgrade had significant influences on the wind-sand flow.The smooth passage of wind-sand flow over the road surface was facilitated with the increase of the median strip width.However,sand deposition in the median strip happened.It can lead to secondary sand damage of downwind subgrade and increase the work load of road sand removal for subsequent maintenance.(2)The obstruction to airflow and sand accumulation was aggravated with greater concave depth of the median strip.Therefore,it is advisable to minimize the concave depth of the median strip in case of more sand damage.(3)A median strip width exceeding 12 m(possibly without guardrails)for an integral embankment without enough road land is recommended.Conversely,median strip width of over 40 m for separate subgrade with unrestricted land is suggested.(4)In the case of sand deposition in the existing separated subgrade,the median strip can be filled by sand deposition or other materials,then was covered with gravel to form a flat ground like Gobi smooth surface,which can let the wind-blown sand flow pass through the subgrade section without sand deposition.
文摘Purpose–The deformation of the roadbed is easily influenced by the external environment to improve the accuracy of high-speed railway subgrade settlement prediction.Design/methodology/approach–A high-speed railway subgrade settlement interval prediction method using the secretary bird optimization(SBOA)algorithm to optimize the BP neural network under the premise of gray relational analysis is proposed.Findings–Using the SBOA algorithm to optimize the BP neural network,the optimal weights and thresholds are obtained,and the best parameter prediction model is combined.The data were collected from the sensors deployed through the subgrade settlement monitoring system,and the gray relational analysis is used to verify that all four influencing factors had a great correlation to the subgrade settlement,and the collected data are verified using the model.Originality/value–The experimental results show that the SBOA-BP model has higher prediction accuracy than the BP model,and the SBOA-BP model has a wider range of prediction intervals for a given confidence level,which can provide higher guiding value for practical engineering applications.
基金supported by the National Natural Science Foundation of China(Grant Nos.52038005 and 52278342)the Natural Science Foundation of Tianjin Municipal(Grant No.23JCJQJC00160).
文摘Real-time assessment of subgrade compaction quality poses a significant challenge in the implementation of intelligent compaction(IC).Current compaction evaluation models are confined to specific scenarios and lack robustness.This study proposes a subgrade compaction strategy that utilizes a heterogeneous dataset to estimate compaction quality across diverse scenarios while maintaining model accuracy.Field compaction tests are conducted in four distinct scenarios,considering various construction parameters.Compaction models are developed using several machine learning algorithms.The datasets are thoroughly assessed in terms of quality,diversity and similarity.The proposed model exhibits good performance in new scenarios by incorporating an additional 5%e8%of new data for retraining.The model's generalization capability is enhanced by conducting a limited number of field tests,which are labor-saving and time-efficient.The model's accuracy consistently improves across diverse scenarios and optimal algorithms.The proposed compaction strategy adopts a physics-and-data dual-driven approach,aimed at practical engineering applications and guiding the compaction procedure.
基金support for this research from the Fundamental Research Funds for the National Natural Science Foundation of China (Grant Nos. 51978588, 52078434, and 52368065)the China Scholarship Council (Grant No. 202107000077)UKRI Engineering and Physical Science ResearchCouncil (EPSRC) for the financial sponsorship of Re4Rail project (Grant No. EP/Y015401/1)
文摘Foamed concrete has been used to address the issue of differential settlement in high-speed railway subgrades in China.However,to enhance crack resistance,reinforcement is still necessary,and further research is required to better understand the performance of foamed concrete in subgrade applications.To this end,a series of tests—including uniaxial compres-sive and dynamic triaxial tests—were conducted to comprehensively examine the effects of basalt fiber reinforcement on the mechanical properties of foamed concrete with densities of 700 and 1000 kg/m3.Additionally,a full-scale model of the foamed concrete subgrade was established,and simulated loading was applied.The diffusion patterns of dynamic stress and dynamic acceleration within the subgrade were explored,leading to the development of experimental formulas to calculate the attenuation coefficients of these two parameters along the depth and width of the subgrade.Furthermore,the dynamic displacement and cumulative settlement were analyzed to evaluate the stability of the subgrade.These findings provide valuable insights for the design and construction of foamed concrete subgrades in high-speed rail systems.The outcomes are currently under consideration for inclusion in the code of practice for high-speed rail restoration.
基金supported by Science and Technology Research and Development Program Project of China State Railway Group Co.,Ltd.(award number:K2024X010).
文摘Purpose–This paper conducts a joint analysis of monitoring data in the hidden danger areas of railway subgrade deformation using a data-driven method,thereby realizing the systematic risk identification of regional hidden dangers.Design/methodology/approach–The paper proposes a regional systematic risk identification method based on Bayesian and independent component analysis(ICA)theories.Firstly,the Gray Wolf Optimization(GWO)algorithm is used to partition each group of monitoring data in the hidden danger area,so that the data distribution characteristics within each sub-block are similar.Then,a distributed ICA early warning model is constructed to obtain prior knowledge such as control limits and statistics of the area under normal conditions.For the online evaluation process,the input data is partitioned following the above-mentioned procedure and the ICA statistics of each sub-block are calculated.The Bayesian method is applied to fuse online parameters with offline parameters,yielding statistics under a specific confidence interval.These statistics are then compared with the control limits–specifically,checking whether they exceed the pre-set confidence parameters–thus realizing the systematic risk identification of the hidden danger area.Findings–Through simulation experiments,the proposed method can integrate prior knowledge such as control limits and statistics to effectively determine the overall stability status of the area,thereby realizing the systematic risk identification of the hidden danger area.Originality/value–The proposed method leverages Bayesian theory to fuse online process parameters with offline parameters and further compares them with confidence parameters,thereby effectively enhancing the utilization efficiency of monitoring data and the robustness of the analytical model.
基金supported by the Australian Research Council Training Centre for Whole Life Design of Carbon Neutral Infrastructure(Grant No.IC230100015).
文摘Biochar,a solid carbonaceous material produced by heating biomass in oxygen-free or low-oxygen conditions(pyrolysis),has been used in various applications,including wastewater treatment,carbon sequestration,and improving soil fertility.However,very limited research has been performed to explore its feasibility to improve the expansive clay(EC)subgrade.In this study,fine-grained wood biochar derived from wood waste was used to stabilise and enhance the mechanical performance of the EC as road subgrade.A comprehensive series of geotechnical tests,including unconfined compressive strength(UCS),California bearing ratio(CBR),repeated load triaxial(RLT),and swelling-shrinkage tests,were conducted to investigate the engineering properties of expansive clay mixed with different contents of the fine-grained biochar(FGB)(i.e.0,1%,2%,3%,and 4%by weight of dry soil).Furthermore,X-ray diffraction(XRD),X-ray fluorescence(XRF),X-ray micro-CT,and thermogravimetric analysis(TGA)analyses were performed to study the microchemical modification of the EC-FGB mixtures.The results showed that adding FGB reduced the swelling and shrinkage potential while enhancing the mechanical properties of the EC.The micro-level analysis also supported the enhancement of the geotechnical performance of the EC resulting from the incorporation of FGB.According to the test results,2%FGB was considered the optimum content,increasing UCS,CBR,and resilient modulus by 31.1%,24.1%,and 31.5%,respectively,and decreasing the swell-shrinkage index by 7%.
基金The authors express their gratitude to the financial support from National Key R&D Program of China(No.2023YFB2604001)National Natural Science Foundation of China(No.52478475,No.52378463 and No.52168066).
文摘The pile-plate structure has proven highly effective support for high-speed railway subgrades,particularly in poor geological conditions.Although its efficacy in non-frozen regions is well-established,its potential in frozen regions remains underexplored.In seasonally frozen areas,F-T(freeze-thaw)cycles threaten subgrade stability,necessitating research on pile-plate structure’s behavior under such conditions.To address this challenge,a scaled model experiment was conducted on a silty sand foundation,simulating F-T cycles using temperature control devices.Key parameters,including soil temperature,frozen depth,and displacement,were systematically monitored.Results indicate that the bearing plate functions as an effective insulation layer,significantly reducing sub-zero temperature penetration.Additionally,the anchoring action of the piles mitigates frost heave in the foundation soil,while the plate middle restrains soil deformation more effectively due to increased constraint.The thermal insulation provided by the plate maintains higher soil temperatures,delaying the onset of freezing.By the end of each freezing stage,the vertical displacement in the natural subgrade is approximately 4 times greater than that beneath the pile-plate structure.Furthermore,the frost depth is about 1.3-1.4 times and 1.6-4.9 times greater than that measured below the plate edge and middle,respectively.These insights contribute to the development of more resilient designs for high-speed railway subgrades in seasonally frozen regions,offering engineers a robust,scientifically-backed foundation for future infrastructure projects.
基金supported by the major project of China State Railway Group Co.,Ltd.(No.Q2023G020)the internal project of China Railway Design Cooperation(No.2023A0248002).
文摘Purpose-Conventional high-speed railways(HSR)subgrade design methods remain constrained by platformdependent drafting systems,leading to data interaction hindrances and redundant design processes.This study strives to develop a digital earthwork design methodology that enhances design while reducing collaborative expenses.Design/methodology/approach-A novel digital subgrade design approach,utilizing sophisticated analysis and modeling tools customized for different subgrade elements,is put forward in this study.The methodology incorporates the following essential steps:(1)the advancement of digital analysis and modeling techniques for diverse subgrade components,including surfaces,filling,slopes,retaining structures,and foundation treatments;(2)the formulation of a digital design principle repository incorporating various slope protection combinations;(3)the establishment of a comprehensive digital design framework and process for subgrade cross-sections;and(4)the development and implementation of an open-source digital design system.Findings-The proposed method liberates subgrade design from the constraints of conventional drawing platforms,elevating efficiency,intelligence,and flexibility.The open software architecture and code have achieved over 60%efficiency gains in design workflows during its deployment on three major high-speed rail projects:the Baotou-Yinchuan HSR corridor,Shenyang-Baihe HSR network,and Weifang-Yantai HSR system.Originality/value-This paper introduces an innovative digital design methodology that enables modular and parametric design for railway subgrade sections.The proposed approach provides a digital base for the intelligent design and maintenance of the next-generation high-speed railway.
文摘The sustainable geotechnical approach for addressing the challenges associated with clayey soils at construction sites involves the modification of these soils’mechanical and chemical characteristics using soil enhancement methods.The present study investigates the coupling effect of sandstone slurry waste(SSW)and calcium carbonate nanoparticle(CCN)as potential stabilizers to enhance the characteristics of clayey soil.A comprehensive investigation was conducted using compaction tests,plasticity index(PI)tests,California bearing ratio(CBR)tests,unconfined compressive strength(UCS)tests,and microstructural analyses of clayey soil,SSW and SSW-CCN-treated clay samples containing 5%,10%,15%,20%,25%,30%,and 35%SSW and 0.3%,0.6%,0.9%,1.2%,and 1.5%CCN mixed with clayey soil in different combinations of clay,SSW,and CCN.The findings reveal that incorporating 25%SSW with 0.9%CCN into clay soil results in an increase in the UCS from 132.2 kPa for untreated clayey soil without curing to 263 kPa after a 28-d curing period.Similarly,a rising trend in CBR results is observed up to 25%SSW addition in clay soil and up to 0.9%CCN addition in SSW-clay mixture.Initially,notable enhancements in UCS were attributed to a denser soil structure,followed by the formation of calcium–silicate–hydrate(CSH)gel,which intensified with prolonged curing.Gel patches were detected by scanning electron microscopy(SEM)in addition to particle aggregation.The results obtained from thermogravimetric analysis,Fourier transform infrared spectroscopy(FTIR),and X-ray diffraction(XRD)supported the presence of hydration products such as CSH.The experimental study indicates that SSW,in combination with CCN,offers a sustainable alternative to traditional soil stabilizers.
基金This work is supported by the National Key R&D Program of China(No.2021YFF0502100)the National Natural Science Foundation of China(Nos.52022085 and 52278461)+1 种基金the Sichuan Provincial Youth Science and Technology Innovation Team(No.2022JDTD0015)the Research and Development Program of China State Railway Group Co.,Ltd.(No.N2022G033),China.
文摘Subgrade frost heave in seasonally frozen ground can greatly influence the safety and smooth running of high-speed trains and the service performance of track structures.In this study,we used a static model to:(1)investigate track-subgrade frost heave and develop a dynamic model of vehicle-track-subgrade frost heave;(2)explore the transfer relation between subgrade frost heave and track structure deformation;(3)examine the characteristics of interlayer debonding;(4)study the influence of subgrade frost heave on the dynamic response of vehicles in high-speed railways in seasonally frozen regions.A Fourier series was used to fit the frost heave waveform and simulate the behavior of subgrade uneven frost heave using data collected on-site.The results show:(i)The position of frost heave significantly affects the transfer of deformation to a slab track.The largest deformation of the track slab,with the amplitude transfer ratio reaching 20%,was recorded when the frost heave occurred near the joint of the base plate.(ii)At the same frost heave amplitude,long-wave frost heave causes smaller deformation and debonding of the track structure than short-wave frost heave.In the wavelength range of 10-30 m,the main frequency of the acceleration spectral density was concentrated between 3.5 and 3.7 Hz,with larger frost heave wavelengths producing smaller superposition on the vertical acceleration of the vehicle.(ii)The maximum wheel-rail force occurs when the front bogie passes the frost heave peak,with greater frost heave amplitudes producing greater wheel-rail force.From these results,we conclude there is a clear need to control the frost heave deformation of the track to reduce the dynamic response of the vehicle and in turn improve train operatSubgrade frost heave in seasonally frozen ground can greatly influence the safety and smooth running of high-speed trains and the service performance of track structures.In this study,we used a static model to:(1)investigate track`-subgrade frost heave and develop a dynamic model of vehicle`-track`-subgrade frost heave;(2)explore the transfer relation between subgrade frost heave and track structure deformation;(3)examine the characteristics of interlayer debonding;(4)study the influence of subgrade frost heave on the dynamic response of vehicles in high-speed railways in seasonally frozen regions.A Fourier series was used to fit the frost heave waveform and simulate the behavior of subgrade uneven frost heave using data collected on-site.The results show:(i)The position of frost heave significantly affects the transfer of deformation to a slab track.The largest deformation of the track slab,with the amplitude transfer ratio reaching 20%,was recorded when the frost heave occurred near the joint of the base plate.(ii)At the same frost heave amplitude,long-wave frost heave causes smaller deformation and debonding of the track structure than short-wave frost heave.In the wavelength range of 10-30 m,the main frequency of the acceleration spectral density was concentrated between 3.5 and 3.7 Hz,with larger frost heave wavelengths producing smaller superposition on the vertical acceleration of the vehicle.(iii)The maximum wheel`-rail force occurs when the front bogie passes the frost heave peak,with greater frost heave amplitudes producing greater wheel`-rail force.From these results,we conclude there is a clear need to control the frost heave deformation of the track to reduce the dynamic response of the vehicle and in turn improve train operations.ions.
基金This work was supported by the National Key R&D Program‘Transportation Infrastructure’project(No.2022YFB2603400).
文摘The compaction quality of subgrade filler strongly affects subgrade settlement.The main objective of this research is to analyze the macro-and micro-mechanical compaction characteristics of subgrade filler based on the real shape of coarse particles.First,an improved Viola-Jones algorithm is employed to establish a digitalized 2D particle database for coarse particle shape evaluation and discrete modeling purposes of subgrade filler.Shape indexes of 2D subgrade filler are then computed and statistically analyzed.Finally,numerical simulations are performed to quantitatively investigate the effects of the aspect ratio(AR)and interparticle friction coefficient(μ)on the macro-and micro-mechanical compaction characteristics of subgrade filler based on the discrete element method(DEM).The results show that with the increasing AR,the coarse particles are narrower,leading to the increasing movement of fine particles during compaction,which indicates that it is difficult for slender coarse particles to inhibit the migration of fine particles.Moreover,the average displacement of particles is strongly influenced by the AR,indicating that their occlusion under power relies on particle shapes.The dis-placement and velocity of fine particles are much greater than those of the coarse particles,which shows that compaction is primarily a migration of fine particles.Under the cyclic load,the interparticle friction coefficientμhas little effect on the internal structure of the sample;under the quasi-static loads,however,the increase inμwill lead to a significant increase in the porosity of the sample.This study could not only provide a novel approach to investigate the compaction mechanism but also establish a new theoretical basis for the evaluation of intelligent subgrade compaction.
文摘Purpose-The experiments of this study investigated the effect of the subgrade degree of saturation on the value of the stresses generated on the surface and the middle(vertical and lateral stresses).The objectives of this study can be identified by studying the effect of subgrade layer degree of saturation variation,load amplitude and load frequency on the transmitted stresses through the ballast layer to the subgrade layer and the stress distribution inside it and investigating the excess pore water pressure development in the clay layer in the case of a fully saturated subgrade layer and the change in matric suction in the case of an unsaturated subgrade layer.Design/methodology/approach-Thirty-six laboratory experiments were conducted using approximately half-scale replicas of real railways,with an iron box measuring 1.5×1.031.0 m.Inside the box,a 0.5 m thick layer of clay soil representing the base layer was built.Above it is a 0.2 m thick ballast layer made of crushed stone,and on top of that is a 0.8 m long rail line supported by three 0.9 m(0.1×0.1 m)slipper beams.The subgrade layer has been built at the following various saturation levels:100,80,70 and 60%.Experiments were conducted with various frequencies of 1,2 and 4 Hz with load amplitudes of 15,25 and 35 kN.Findings-The results of the study demonstrated that as the subgrade degree of saturation decreased from 100 to 60%,the ratio of stress in the lateral direction to stress in the vertical direction generated in the middle of the subgrade layer decreased as well.On average,this ratio changed from approximately 0.75 to approximately 0.65.Originality/value-The study discovered that as the test proceeded and the number of cycles increased,the value of negative water pressure(matric suction)in the case of unsaturated subgrade soils declined.The frequency of loads had no bearing on the ratio of decline in matric suction values,which was greater under a larger load amplitude than a lower one.As the test progressed(as the number of cycles increased),the matric suction dropped.For larger load amplitudes,there is a greater shift in matric suction.The change in matric suction is greater at higher saturation levels than it is at lower saturation levels.Furthermore,it is seen that the load frequency value has no bearing on how the matric suction changes.For all load frequencies and subgrade layer saturation levels,the track panel settlement rises with the load amplitude.Higher load frequency and saturation levels have a greater impact.
基金supported by the National Natural Science Foundation of China (Grant Nos.52038005 and 52278342)Natural Science Foundation of Tianjin,China (Grant No.23JCJQJC00160).
文摘The ultrasonic pulse velocity(UPV)correlates significantly with the density and pore size of subgrade filling materials.This research conducts numerous Proctor and UPV tests to examine how moisture and rock content affect compaction quality.The study measures the changes in UPV across dry density and compaction characteristics.The compacted specimens exhibit distinct microstructures and mechanical properties along the dry and wet sides of the compaction curve,primarily influenced by internal water molecules.The maximum dry density exhibits a positive correlation with the rock content,while the optimal moisture content demonstrates an inverse relationship.As the rock content increases,the relative error of UPV measurement rises.The UPV follows a hump-shaped pattern with the initial moisture content.Three intelligent models are established to forecast dry density.The measure of UPV and PSO-BP-NN model quickly assesses compaction quality.
基金supported by a grant from the Gansu Provincial Department of Natural Resources Science and Technology Innovation Talent Cultivation Project (2022-09)the geological disaster prevention projects of Gansu Provincial Bureau of Geology and Mineral Resources(2022-09)Natural Science Foundation of Gansu province(No.22JR5RA326)。
文摘With the change of seasons, the shear strength of saline soil subgrade filler will change with the change of external temperature, which will aggravate the adverse effects of seismic on the subgrade. To explore the influence of seismic action on the stability of saline soil subgrade under the influence of temperature on the strength of saline soil subgrade filler, this paper first carried out saline soil shear tests at different temperatures to obtain the influence of temperature on the shear strength of saline soil. Then, the temperature field of the saline soil subgrade was simulated, and then based on the subgrade isothermal stratification model and FLAC3D, the displacement and acceleration amplification effects of seismic action on the shady slope, sunny slope and subgrade of saline soil subgrade in different months were analyzed. The following conclusions were finally drawn: under the action of seismic, In the process of the change of subgrade temperature of Qarhan-Golmud Expressway between 7.7°C and 27°C, the change of saline soil cohesion is the main factor affecting the stability of subgrade slope, and the maximum and minimum values of subgrade surface settlement appear in September and June of each year,respectively. In August, the differences of settlement between the shady slope and the sunny slope shoulder of the subgrade were the largest, and the acceleration of the shady slope and the sunny slope and the inside of the subgrade changed most significantly in the vertical direction. Special attention should be paid to the seismic early warning in the above key months;In the range from both sides of the shoulder to the centerline of the roadbed,the acceleration amplification effect starts to increase significantly from about 3m from the centerline of the roadbed to the centerline, so it is necessary to pay attention to the seismic design of this range.
文摘With the continuous development of China’s economy,the construction of roads and bridges work has put forward higher requirements.Due to various factors,the long-term use of roads and bridges will produce a settlement phenomenon.Therefore,it is crucial to address settlement issues during the construction of roads and bridges to ensure that the quality of subgrade and pavement construction meets national regulations.This paper introduces the harm of subgrade pavement subsidence,analyzes the causes of subgrade pavement deformation,and discusses the technical points of subgrade pavement construction,hoping to provide some reference for relevant practitioners.
基金financially supported by the Fellowship of the China Postdoctoral Science Foundation(2021M703466)the Natural Science Foundation of Gansu Province,China(20JR10RA231)+1 种基金the Basic Research Innovation Group Project of Gansu Province,China(21JR7RA347)Special Funds for Guiding Local Scientific and Technological Development by the Central Government(22ZY1QA005)。
文摘The railway subgrades in the sandy areas act as an obstacle interfering wind-blown sand,causing sand erosion and sedimentation,which can disrupt the safe and stable operation of the railway system.Most previous studies mainly focus on the flow field around railway subgrades,however,the real erosion and sedimentation patterns are rarely studied.This study aims to analyze the erosion and sand sedimentation patterns of wind-blown sand over the subgrades with different heights and steel rails using the ratio of the wall shear stress to the critical value of erosion shear stress.Results show that wind erosion near the top of the upwind slope of the embankment and the shoulder on the upwind side are more severe,and the severity increases with an increase in the height of the embankment.With the increase of wind velocity,sand sedimentation both on the windward and leeside of the subgrade decreases and wind erosion by reverse flow occur.This study indicates that railways in sandy areas should be constructed with a moderate subgrade height(4 m).
基金Project(51378514)supported by the National Natural Science Foundation of China
文摘The improved granular mixtures are widely used as the fillings of railway 8ubgrade, and in order to investigate the effect of coarse grain content on granular mixtures, a series of field tests were conducted. The experimental results indicate that the permeability coefficient increases significantly with the increment of granite gravel content, especially in the range of 60%-70%. Thcrc exists a coarse grain content limit defined as 53%-58.5% to reform the permeable granular skeleton. Beyond this limit, the permeable granular skeleton is efficiently formed, and the macro pores between the separate gravels are partially filled, which is the explanation lbr the permeability increase. The investigations indicate the subgrade resistance modulus （ks0, Ev2, and Evd） depends on the granite gravel content, and the resistance modulus increases significantly beyond granite gravel content of 50%. The skeletons of granitc gravel clayey sand mixture change in the long-term deformation objected to the train-induced dynamic load, which involves three main repeated and circular deformation stages. Generally, the long-time deformation is explained as the gravel crushing and filling the internal porous space with crushed gravel fragments. Through these investigations, the C40-G60 or C30-G70 is recommended as an optimum soil mixture for the good permeability and high resistance modulus.
