High-speed Train Loads Research Articles

Assessment of the Dynamic Behaviors of Submerged Floating Tunnel Under a High-Speed Train Loading

Submerged floating tunnels (SFTs) are innovative structural solutions to waterway crossings and are more economical compared to the conventional structures such as cable-supported bridges, underground tunnels or immersed tunnels. The dynamic behaviors of SFT under real train loads is the primary design requirement of an SFT, However, it is not investigated using realistic train models. In this study, the China-star high-speed train is used to evaluate the dynamic displacements, internal forces and cable tensions of SFT. The tunnel is modeled by FEM, the cables are modeled by elastic catenary cables, and ocean waves and currents are modeled by Airy’s wave theory. The SFT displacements, bending moments and cable tensions were significantly influenced by moving trains. The SFT experienced extreme vertical displacements and there was a large drop in the minimum cable tensions. The mooring cables were slacked both by magnitudes and speed of the moving trains, which should be avoided for the safety of SFT. This study recommends the additional buoyancies for the stability of SFT subjected to high speed trains.

Effects of suffosion-induced contact variation on dynamic responses of saturated roadbed considering hydro-mechanical coupling under high-speed train loading

Recent experience of high-speed railway in operation has indicated that the hydro-mechanical coupling effect under dynamic loads from high-speed train may lead to excessive pumping of fine particles in saturated roadbed surface layer. This can result in large variations of contact condition between track and subgrade structure layers while study on this issue remains scare. Based on the theory of fluid dynamics in porous medium and the vehicle-track-subgrade coupling vibration theory, a numerical model is established to evaluate the dynamic responses of saturated roadbed surface resulting from the contact condition variation under the high-speed train load considering the hydro-mechanical coupling effects. A concept of three contact types (fully continuous contact, vibration contact and contact loss) is proposed and three contact shape forms (rectangular, cosine and elliptical shapes) simplified for describing contact damaged zones are compared in terms of dynamic responses (stress, pore water pressure, seepage velocity) evaluated. Also, time-frequency analysis is performed to investigate the influence of contact variation on dynamic responses of roadbed surface in aforementioned contact types. Results show that this progressive development of contact damage can pose extra great stress and pore-water pressures in roadbed and a critical length of contact loss zone is suggested.

Importance of load frequency in applying cyclic loads to investigate ballast deformation under high-speed train loads

Railway ballast is now subjected to dynamic train loads with higher frequency components due to the continue increase of the train speed. However, the effect of load frequency on ballast permanent deformation was ignored in most laboratory tests. This study aims to clarify the importance of load frequency in applying cyclic loads to investigate the ballast permanent deformation under high-speed rail loading conditions. A three-dimensional discrete element model was established using clumps with realistic ballast particle shapes and validated with a laboratory test. Numerical simulations were then conducted with the validated DEM model to study the ballast deformation behavior. The simulated ballast deformation under high-speed train loads and that under cyclic loads with different load frequencies were compared to demonstrate the quantitative discrepancy between them. The results from this study confirm that under high-speed rail loading scenarios, the load frequency has significant influence on ballast permanent deformation and there is significant importance to take the effect of the load frequency into account when investigating the permanent deformation of high-speed railway ballast by applying cyclic loads. It is recommended to apply the cyclic loading with the same amplitude to the high-speed train load and with the frequency equivalent to the passing frequency of the train’s wheelbase to the ballast in laboratory tests so as to obtain quantitative ballast deformation results by using one load cycle to simulate two axle loads of a train.

Dynamic responses of non-ballast track structures subjected to high-speed train loads at the welded rail joint

This paper presents a numerical study on the dynamic responses of the non-ballast track structures under the high-speed train load that is excited by the rail irregularity at the welded rail joint. In this study, a multi-body dynamics model with 10 degrees of freedom is built to model a high-speed vehicle and a finite element model is established to simulate the non-ballast track. A mathematical model is also given to characterize the geometry of the local rail irregularity at the welded rail joint. By coupling the high-speed vehicle model and the track model and taking the mathematical model of the welded rail joint as an input, the dynamic responses of the non-ballast track structures under a rail vehicle running at a high speed are simulated and discussed in this paper. The wheel/rail force and the rail and slab vibration acceleration are investigated to demonstrate the significant dynamic effects on the track structures due to the welded rail joint.

Investigation of track settlement and ballast degradation in the high-speed railway using a full-scale laboratory test

This paper presents a full-scale laboratory test for investigating the track settlement and ballast degradation of the ballasted track–subgrade system on the high-speed railways. The test was carried out on a full-scale test platform with a ballasted track–subgrade system constructed exactly according to the construction standards of high-speed railways in China. In this test, four million cycles of cyclic loads simulating repeated high-speed train loads with an axle load of 140 kN were applied to the ballasted track–subgrade system through a specialized loading system. The vertical displacement and settlement of the rail, the sleepers and the subgrade at various sections and depths were recorded during the test. The test results show that the settlement of the high-speed railway ballasted track is very less. A logarithmic model was proposed for predicting the settlement of the high-speed railway ballasted track by fitting the measured data. Moreover, some painted ballast samples were embedded into the tested track to investigate the ballast degradation. After the test, it was found that more than 80% of the painted ballast grains remained intact and less than 20% were degraded. Four different ballast degradation phenomena were observed: corner or edge breakage, surface scratch, surface crack and the production of fine particles. The test results indicate that the high-speed railway ballasted tracks in China are very stable and the settlement is less under long-term cyclic loads, which could significantly benefit the track geometry and the railway maintenance work.

Study on Water Pressure and Velocity in Cracks of Slab Track

The essence of slab track damage under the coupling effect of train load and water is a coupled hydro-mechanical (HM) fracture, and the core technology is the water pressure calculation. Finite element software ANSYS and CFX are used to analyze the water pressure and speed of slab track cracks under high speed train loads. The results show that, the maximum water pressure appears at the crack tip under loading, and decreases along the crack. The value of water pressure is proportional to load amplitude, square of loading frequency and inversely proportional to crack aperture. On the contrary, the maximum water velocity appears at the crack mouth, and increases along the crack. The value of velocity is proportional to load amplitude, proportional to loading frequency, and inversely proportional to crack aperture. The presented theory can be applied to the stress study of slab track water crack.

NUMERICAL MODELLING OF RAILWAY EMBANKMENTS FOR HIGH-SPEED TRAIN CONSTRUCTED ON SOFT SOIL

Recently, several mass rapid transit projects have been launched to improve the logistics of trade in Thailand. The railway construction projects linked from Bangkok will be a challenging task for civil engineers since they are located on soft ground conditions. Consequently, an understanding of geomaterial properties and subsoil conditions is important in the design phase. This paper presents a numerical study of railway embankment behaviour when constructed on soft soil. Simplified finite-element modelling was performed to predict stability and deformation characteristics of railway embankments under high-speed design requirements. The construction materials, including ballasts and subgrade soils were selected and tested to characterise their engineering properties. It was found that existing railway embankment conditions exhibit a large degree of movement under a high-speed train load. The study recommends improvements of subgrade conditions, using methods such as cement stabilisation to enhance stability and reduce settlement of the railway embankments.

Evaluation on the dynamic performance of bridge approach backfilled with fibre reinforced lightweight concrete under high-speed train loading

In China, high-speed rails are often constructed over bridges in the region of soft soils. Differential settlement could occur in the foundation soils between bridge abutment and approach embankment that causes “bumps” to affect the smoothness at the end of a bridge. A three-dimensional finite element model is developed to investigate the use of fibre reinforced lightweight concrete in the transition zone of bridge approach for high-speed railways. Time-frequency analysis is performed using the method of Fast Fourier transform. The sensitivity analysis of rail speed, density of backfills, and the structural type of the trapezoidal shaped transition zone is conducted.

Hydrodynamic Pressure and Velocity Distributions in the Interlayer Crack of Ballastless Track under High-Speed Train Load: A Theoretical Analysis

In the abundant rain or poor drainage areas, there will be serious water damage existing in the interlayer of ballastless track. The essence of water damage of ballastless track is a dynamic development process of damage shape under the combined action of train load, hydrodynamic pressure, and flow velocity. In view of the distribution characteristics of hydrodynamic pressure and flow velocity in the interlayer crack of ballastless track under the high-speed train load, the simplified mechanics model for water and composite slab with interfacial crack is proposed in accordance with the water damage characteristics of ballastless track. Based on the conservation of mass and momentum theorem, the analytical expressions of water pressure and velocity in the saturated water crack were deduced. Similarly, the analytical expressions of water pressure and velocity in the unsaturated water crack were deduced by adding the state equation of ideal air. Considering that the water does not flow back timely, the analytical expressions of water pressure and velocity in another kind of unsaturated water crack were deduced. The results show that the hydrodynamic pressure and flow velocity in the interlayer crack are synthetically determined by multiple influencing factors such as fluid viscosity, load characteristic, crack shape, absolute pressure at the crack mouth, and initial volume of the air in the crack, and there is an intersecting phenomenon between influencing factors. When there is a small amount of air at the crack tip, the pressure and velocity distribution in the crack can be divided into three parts in terms of air-water interface and stagnation point. When the crack is filled with water, the hydrodynamic pressure tends to decrease along the direction of the crack mouth, and the distribution along the whole crack approximates to a cubic polynomial curve. Similarly, the flow velocity increases along the direction of crack mouth, and the distribution along the whole crack approximates to a quadratic polynomial curve.

Dynamic Behavior of Masonry Arch Bridge under High-Speed Train Loading: Veresk Bridge Case Study

AbstractThis paper studies the dynamic behavior of one of the oldest masonry arch bridges of the Iranian railway network, the Veresk bridge, located in the Mazandaran province of Iran. To do so, th...

Analysis of the influence of train load characteristics on the water damage of slab tracks

High-speed train load is one of the main factors that causes the failure of a slab track and is also the direct cause for producing water pressure in the cracks. Hence, choosing the right loading method is the key to analyze the water damage of slab tracks. In order to identify the distribution characteristics of the vertical force acting on the slab track, the analytic expression of fastener load was derived, and the field test was conducted to verify the theoretical model. According to the distribution characteristics of fastener load and the area of crack filled with water, the loading method was presented to analyze the water damage of slab tracks, and the influence of loading characteristics on the hydrodynamic pressure and crack propagation was analyzed. The results show that the distribution of fastener load in the main affected zone approximately accords with the Gaussian distribution under the single wheel load. When under the action of double wheels, the superimposed effect makes the second derivative of the loading function to increase by 99.93%. The superimposed effect of three or more wheels is less than 1% and can be ignored. Considering that the hydrodynamic pressure is highly sensitive to the second derivative of loading function, the load applied on the track slab should be in the form of a bogie, and different loads should be applied step by step based on the time series. The distribution of hydrodynamic pressure along the crack is approximately equal to the cubic polynomial, and the pressure peak appears at the crack tip. Also, the pressure is proportional to the square of the running speed of the train. In the region with abundant rainwater and a poor drainage system, reducing the train speed and taking timely measures such as grouting can effectively reduce the water damage of slab tracks.

Study on Deduction and Extend of High-speed Train Load Spectrum

Study on Deduction and Extend of High-speed Train Load Spectrum

Settlement mechanism of piled-raft foundation due to cyclic train loads and its countermeasure

In this paper, numerical simulation with soil-water coupling finite element-finite difference (FE-FD) analysis is conducted to investigate the settlement and the excess pore water pressure (EPWP) of a piled-raft foundation due to cyclic high-speed (speed: 300km/h) train loading. To demonstrate the performance of this numerical simulation, the settlement and EPWP in the ground under the train loading within one month was calculated and confirmed by monitoring data, which shows that the change of the settlement and EPWP can be simulated well on the whole. In order to ensure the safety of train operation, countermeasure by the fracturing grouting is proposed. Two cases are analyzed, namely, grouting in No-4 softest layer and No-9 pile bearing layer respectively. It is found that fracturing grouting in the pile bearing layer (No-9 layer) has better effect on reducing the settlement.

Settlement of Soft Clay Subgrade Under Coupled Effects of Vibration Frequency and Dynamic Stress Ratio Caused by High-Speed Train Loads

Settlement regularity of soft clay subgrade under cyclic principal stress rotation caused by high-speed train loads is investigated. In laboratory tests, it is found that, with increasing vibration frequency at a fixed dynamic stress ratio, the increase of axial plastic cumulative strain in saturated soil is restricted at mid-high frequencies (0.5-2 Hz), and the changes in pore-water pressure are not evident. Combined with the empirical settlement formula and analysis of the dynamic amplification equation of German standard, a simplified settlement calculation method accounting for resonance is obtained.

Iterative Method for Predicting Uneven Settlement Caused by High-Speed Train Loads in Transition-Zone Subgrade

Uneven subgrade settlement associated with rail deflection occurs mainly in the bridge–embankment transition zones of high-speed railways. An iterative method of computation is proposed for studying such uneven settlement in these zones. A vehicle–track–subgrade model is used to investigate the vehicle–track interactions and the deviator stress field of the transition zone, and a soil cumulative plastic strain model is used to obtain the deterioration process of uneven settlement in the transition zone. Results indicate that uneven settlement caused by train loads in the transition zone tends to plateau at 40,000 repeated load applications. Sub-grade settlement changes abruptly in the first measured 5 m, as well as from 25 to 30 m from the abutment; these two regions should be adequately strengthened and should receive more attention for track maintenance.

Mechanical behaviour of piled-raft foundations subjected to high-speed train loading

In this paper, settlement of piled-raft foundation for high-speed train is considered systematically. It is observed in a case study that the railway settled significantly due to the cyclic train loading after a one-month trial operation. As traditional methods such as empirical methods or numerical simulation based on primitive constitutive models are unable to properly interpret the settlement mechanism, a sophisticated model-based numerical simulation, using a soil-water coupled finite element (FE)-finite difference (FD) hybrid algorithm, is conducted to investigate the mechanism of the settlement of the piled-raft foundation and excess pore water pressure (EPWP) of soft soils caused by the cyclic train loading. In order to demonstrate the performance of this numerical simulation, the calculated results are compared with the data recorded in the one-month trial operation and the reliability of the proposed numerical method is confirmed. The newly proposed numerical method is also used to predict the long-term settlement and the change in the EPWP during a one-year period. The predicted results suggest that without proper treatment, more serious settlement would have occurred, which is unacceptable in engineering terms.

Remote monitoring for a high-speed railway subgrade structure state in a mountainous area and its response analysis

High-speed railway engineering in mountainous areas suffers from occasional poor geological conditions, rugged topography, and complex hydrographic conditions. It is an important means of ensuring its safe operation to conduct real-time remote monitoring and analysis of the subgrade structure condition. Through analysing the stress characteristics of the mountainous subgrade, a complete monitoring system has been built and a corresponding software platform for datum acquisition and analysis has also been developed. After selecting a typical mountainous high-speed railway subgrade located in Hunan Province as the test section, the real-time monitoring of the subgrade structure in a static settling period, joint commissioning period, and an operational period was conducted and the primary condition datum was obtained. It is found that the dynamic response parameters have relatively slow attenuation velocities and the influencing depth of the high-speed train loads was about 4–5 m; when the structural state of the mountainous subgrade is healthy, subgrade deformations are small and, compared with the dynamic response datum of the subgrade in plain areas, the dynamic response of the mountainous high-speed railway subgrade was consistent. However, the long-term dynamic response and deformation of such mountainous subgrades still needs to be monitored, and analysed, continually.

A METHOD FOR THE EXTRACTION OF LONG-TERM DEFORMATION CHARACTERISTICS OF LONG-SPAN HIGH-SPEED RAILWAY BRIDGES USING HIGH-RESOLUTION SAR IMAGES

Natural causes and high-speed train load will result in the structural deformation of long-span bridges, which greatly influence the safety operation of high-speed railway. Hence it is necessary to conduct the deformation monitoring and regular status assessment for long-span bridges. However for some traditional surveying technique, e.g. control-point-based surveying techniques, a lot of human and material resources are needed to perform the long-term monitoring for the whole bridge. In this study we detected the long-term bridge deformation time-series by persistent scatterer interferometric synthetic aperture radar (PSInSAR) technique using the high-resolution SAR images and external digital elevation model. A test area in Nanjing city in China is chosen and TerraSAR-X images and Tandem-X for this area have been used. There is the Dashengguan bridge in high speed railway in this area as study object to evaluate this method. Experiment results indicate that the proposed method can effectively extract the long-term deformation of long-span high-speed railway bridge with higher accuracy.

A METHOD FOR THE EXTRACTION OF LONG-TERM DEFORMATION CHARACTERISTICS OF LONG-SPAN HIGH-SPEED RAILWAY BRIDGES USING HIGH-RESOLUTION SAR IMAGES

Abstract. Natural causes and high-speed train load will result in the structural deformation of long-span bridges, which greatly influence the safety operation of high-speed railway. Hence it is necessary to conduct the deformation monitoring and regular status assessment for long-span bridges. However for some traditional surveying technique, e.g. control-point-based surveying techniques, a lot of human and material resources are needed to perform the long-term monitoring for the whole bridge. In this study we detected the long-term bridge deformation time-series by persistent scatterer interferometric synthetic aperture radar (PSInSAR) technique using the high-resolution SAR images and external digital elevation model. A test area in Nanjing city in China is chosen and TerraSAR-X images and Tandem-X for this area have been used. There is the Dashengguan bridge in high speed railway in this area as study object to evaluate this method. Experiment results indicate that the proposed method can effectively extract the long-term deformation of long-span high-speed railway bridge with higher accuracy.

Study on the subgrade deformation under high-speed train loading and water–soil interaction

It is important to study the subgrade characteristics of high-speed railways in consideration of the water–soil coupling dynamic problem, especially when high-speed trains operate in rainy regions. This study develops a nonlinear water–soil interaction dynamic model of slab track coupling with subgrade under high-speed train loading based on vehicle–track coupling dynamics. By using this model, the basic dynamic characteristics, including water–soil interaction and without water induced by the high-speed train loading, are studied. The main factors-the permeability coefficient and the porosity-influencing the subgrade deformation are investigated. The developed model can characterize the soil dynamic behaviour more realistically, especially when considering the influence of water-rich soil.