Stationarity Intervals of Time-Variant Channel in High Speed Railway Scenario

The non-stationary behavior, caused by the train rmverrent, is the rmin factor for the variation of high speed railway channel. To measure the tirce-variant effect, the parameter of stationarity interval, in which the channel keeps constant or has no great change, is adopted based on Zhengzfiou- Xi＇an （Zhengxi） passenger dedicated line measurement with different train speeds. The stationarity interval is calculated through the definition of Local Region of Stationarity （LRS） under three train ve- locities. Furthermore, the time non-stationary characteristic of high speed pared with five standard railway channel is corn- Multiple-Input MultipleOutput （MIMO） channel models, i.e. Spatial Channel Model （SCM）, extended version of SCM （SCME）, Wireless World Initiative New Radio Phase II （WINNERII）, International Mobile Teleconmnications-Advanced （IMT-Advanced） and WiMAX models which contain the high speed moving scenario. The stationarity interval of real channel is 9 ms in 80% of the cases, which is shorter than those of the standard models. Hence the real channel of high speed railway changes more rapidly. The stationarity intervals of standard models are different due to different modeling methods and scenario def- initions. And the compared results are instructive for wireless system design in high speed railway.

Aerodynamic effects on a railway tunnel with partially changed cross-sectional area

The present study numerically explored the aerodynamic performance of a novel railway tunnel with a partially reduced cross-section.The impact of the reduction rate of the tunnel cross-section on wave transmissions was analyzed based on the three-dimensional,unsteady,compressible,and RNG k-εturbulence model.The results highlight that the reduction rate(S)most affects pressure configurations at the middle tunnel segment,followed by the enlarged segments near access,and finally the exit.The strength of the newly generated compression wave at the tunnel junction where the cross-section abruptly changes increases exponentially with the decrease of the cross-sectional area.The maximum peak-to-peak pressureΔP on the tunnel and train surface for non-uniform tunnels is reduced by 10.7%and 13.8%,respectively,compared with those of equivalent uniform tunnels.Overall,the economic analysis suggests that the aerodynamic performance of the developed tunnel prototype surpasses those conventional tunnels based on the same excavated volume.

In Situ Experiments on Supporting Load Effect of Large-span Deep Tunnels in Hard Rock

A section of the Nanliang high speed railway tunnel on Shijiazhuang-Taiyuan high-speed passenger railway line in China was instrumented and studied for its mechanical properties and performances. The cross section for the tunnel was300 m2and is classified as the largest cross section for railway tunnels in China. Through in situ experimental studies, mechanistic properties of the tunnel were identified, including the surrounding rock pressure, convergences along tunnel perimeter and safety of primary support and lining structure.Based on the field measured data, the surrounding rock pressure demand for large-span deep tunnel in hard rock is recommended as double peak type in the vertical direction and fold line type was recommended for horizontal pressure. The results suggested that Promojiyfakonov's theory was most close to the monitored value. Specific recommendations were also generated for the use of bolts in tunnel structures.Numerical simulation was used to evaluate the safety of the tunnel and it confirmed that the current design can satisfy the requirement of the current code.

Influence of interface crack on dynamic characteristics of CRTSⅢslab ballastless track on bridge

The damage of the self-compacting concrete in CRTSⅢslab ballastless track on bridge will lead to a partial void of the track slab,which will affect the comfort and safety of the train and the durability of the track slab and bridge structure.In order to study the impact of the interface crack on the dynamic response of CRTSⅢballastless track system on bridge,based on the principle of multi-body dynamics theory and ANSYS+SIMPACK co-simulation,the spatial model of vehicle-track-bridge integration considering the longitudinal stiffness of supports,the track structure and interlayer contact characteristics were established.The dynamic characteristics of the system under different conditions of the width,length and position of the interface crack were analysed,and the limited values of the length and width of the cracks at the track slab edge were proposed.The results show that when the self-compacting concrete does not completely void along the transverse direction of the track slab,the crack has little effect on the dynamic characteristics of the vehicle-track-bridge system.However,when the self-compacting concrete is completely hollowed out along the transverse direction of the track slab,the dynamic amplitudes of the system increase.When the crack length is 1.6 m,the wheel load reduction rate reaches 0.769,which exceeds the limit value and threatens the safety of train operation.The vertical acceleration of the track slab increases by 250.1%,which affects the service life of the track system under the train speed of 200 km/h.

Beam-track interaction of high-speed railway bridge with ballast track

Based on the construction bridge of Xiamen-Shenzhen high-speed railway(9-32 m simply-supported beam + 6×32 m continuous beam),the pier-beam-track finite element model,where the continuous beam of the ballast track and simply-supported beam are combined with each other,was established.The laws of the track stress,the pier longitudinal stress and the beam-track relative displacement were analyzed.The results show that reducing the longitudinal resistance can effectively reduce the track stress and the pier stress of the continuous beam,and increase the beam-track relative displacement.Increasing the rigid pier stiffness of continuous beam can reduce the track braking stress,increase the pier longitudinal stress and reduce the beam-track relative displacement,Increasing the rigid pier stiffness of simply-supported beam can reduce the track braking stress,the rigid pier longitudinal stress and the beam-track relative displacement.

Key Techniques for the Construction of High-Speed Railway Large-Section Loess Tunnels

The successful completion of the Zhengzhou-Xi＇an high-speed railway project has greatly improved the construction level of China＇s large-section loess tunnels, and has resulted in significant progress being made in both design theory and construction technology. This paper systematically summarizes the tech- nical characteristics and main problems of the large-section loess tunnels on China＇s high-speed railway, including classification of the surrounding rock, design of the supporting structure, surface settlement and cracking control, and safe and rapid construction methods. On this basis, the key construction tech- niques of loess tunnels with large sections for high-speed railway are expounded from the aspects of design and construction. The research results show that the classification of loess strata surrounding large tunnels should be based on the geological age of the loess, and be determined by combining the plastic index and the water content. In addition, the influence of the buried depth should be considered. During tunnel excavation disturbance, if the tensile stress exceeds the soil tensile or shear strength, the surface part of the sliding trend plane can be damaged, and visible cracks can form. The pressure of the surrounding rock of a large-section loess tunnel should be calculated according to the buried depth, using the corresponding formula. A three-bench seven-step excavation method of construction was used as the core technology system to ensure the safe and rapid construction of a large-section loess tunnel, following a field test to optimize the construction parameters and determine the engineering measures to stabilize the tunnel face. The conclusions and methods presented here are of great significance in revealing the strata and supporting mechanics of large-section loess tunnels, and in optimizing the supporting structure design and the technical parameters for construction.

Wireless Relay Communication on High Speed Railway：Full Duplex or Half Duplex？

In this paper,we introduce one full-duplex(FD) relaying transmission scheme for high speed railway and compare its ergodic capacity and outage performance with half-duplex(HD) relaying scheme. Both decode-and-forward(DF) amplify-and-forward(AF) relay modes are considered. Moreover,the carriage penetration loss(CPL) and the self-interference(SI) cancellation ratio are investigated. We derive the closed-form expressions for the outage probability and ergodic capacity of both HD and FD relay transmission schemes. It is shown that when CPL is larger than a certain level,the FD relay can achieve better performance in terms of capacity and keep the outage probability in a low level. It is also found that three factors: AF or DF modes,CPL and SI cancellation ratio,can have impact on capacity performance,and that CPL is one decisive factor. Our results can provide theoretical supports for development and deployment of future wireless communication systems on high speed railways.

Design of unballasted track bridges on Beijing——Tianjin intercity railway

Beijing-Tianjin intercity railway is the first newly-built passenger dedicated line with operating speed of 350 km/h in our country. During design,new ideas of bridge construction were carried out to ensure the requirements of safety,comfort and stability of the train under high-speed condition. At the same time,concepts of environmental adaptability,service to transportation and comprehensive benefits were observed. On the whole line,long-bridge schemes were adopted and the most advanced technologies of unballasted track were utilized on bridges,the length of which accounts for 87.7 % of the total line. The success of design and construction of the bridges on this rail has accumulated valuable experience for high-speed railway construction on a large scale in the future,and made it a marking,demonstrating,and model project to follow.

Wheel/rail dynamic interaction due to excitation of rail corrugation in high-speed railway

Characteristics of wheel-rail dynamic interaction due to the rail corrugation in a high-speed railway are analyzed based on the theory of vehicle-track coupled dynamics in this paper.Influences of the corrugation wavelength and depth on the wheel-rail dynamic performance are investigated.The results show that,under the excitation of a measured rail corrugation,the wheel-rail dynamic interaction of high-speed railway is enhanced obviously,and the high-frequency dynamic force between wheel and rail is generated,which has an obvious impact on the vibrations of the wheelset and rail,and little effect on the vibration of the frame and carbody.If the corrugation wavelength is shorter than the sensitive wavelength,the wheel-rail vertical force will increase with the growth of the corrugation wavelength,otherwise,it will decrease.However,the wheel-rail vertical force keeps increasing with the growth of corrugation depth.Furthermore,if the corrugation wavelength is shorter than the sensitive wavelength,the wheel-rail vertical force will increase with the decrease of the running speed,otherwise,it will decrease.It is also found that the critical wavelength of corrugation increases with the growth of the corrugation depth and the running speed,and the critical depth of corrugation is nonlinearly related to the sensitive wavelength.

Characteristics of a compression wave propagating over porous plate wall in a high-speed railway tunnel

A pressure wave is generated ahead of a high-speed train, while entering a tunnel. This pressure wave propagates to the tunnel exit and spouts as a micro-pressure wave, which causes an exploding sound. From the fact that the ballast track tunnel has smaller noise than the slab track tunnel, we have suggested a new inner tunnel model to decrease the noise of the micro-pressure wave, using the ballast effect. Experimental and numerical investigations are carded out to clarify the attenuation and distortion of propagating compression wave over porous plate wall in a model tunnel. Data shows that the strength of the compression wave and a maximum pressure gradient of the compression wave was weakened. These data shows the possibility of the present alleviative method using the porous plate wall in a tunnel.

Elastic-plastic seismic response of CRTS II slab ballastless track system on high-speed railway bridges

China railways track structure II (CRTS II) slab ballastless track on bridge is one kind of track structures unique to China. Its main bearing component of longitudinal force is the continuous base plate rather than rail. And the track-bridge interaction is weakened by the sliding layer installed between base plate and bridge deck. In order to study the dynamic response of CRTS II slab ballastless track on bridge under seismic action, a 3D nonlinear dynamic model for simply-supported bridges and CRTS II track was established, which considered structures such as steel rail, fasteners, track plate, mortar layer, base plate, sliding layer, bridge, consolidation, anchors, stoppers, etc. Then its force and deformation features under different intensities of seismic excitation were studied. As revealed, the seismic response of the system increases with the increase of seismic intensity. The peak stresses of rail, track plate and base plate all occur at the abutment or anchors. Both track plate and base plate are about to crack. Besides, the rapid relative displacement between base plate and bridge deck due to the small friction coefficient of sliding layer is beneficial to improve the seismic performance of the system. During the earthquake, a large vertical displacement appears in base plate which leads to frequent collisions between stoppers and base plate, as a result, stoppers may be damaged.

Analysis on the influencing factors of mechanical characteristics of jointless turnout group in ballasted track of high-speed railway

Turnouts are in close proximity to each other in the stations of high-speed railway.The stress and deformation of those turnouts which are laid nearby are influenced mutually and therefore those turnouts should be considered together.On the basis of finite element method,according to No.18 jointless turnout with swing nose frog in the ballasted track of high-speed railway,a finite element calculating model of jointless turnout group coupling the longitudinal,lateral and vertical directions is established.The influencing factors,for instance the number of turnouts,connection form,length of intermediate straight line and ballast bed longitudinal resistance,on the mechanical characteristics of turnout,transverse deformation of switch rail and range of rail temperature for laying turnout are analyzed in this paper.The results show that more turnouts result in more obvious interaction between them when the lengths of intermediate straight line are the same;more significant influence between the turnouts with the connection form of head-to-head is produced compared to that of head-to-end;from the perspective of statics,influence between turnouts could be ignored basically if the intermediate straight line is over 50 m;bigger longitudinal resistance of ballast bed leads to less influence between the turnouts.

Safety threshold of high-speed railway pier settlement based on train-track-bridge dynamic interaction

This paper presents a method to determine the safety threshold of bridge pier settlement in high-speed railways.An analytical expression of the mapping relationship between the pier settlement and the rail deformation is derived theoretically for the double block ballastless track-bridge system.By adopting the superposition of the track random irregularity and the rail deformation caused by the pier settlement as the excitation inputs,the variations of vehicle dynamics indices with pier settlement are comparatively analyzed.Then,the safety threshold of the bridge pier settlement is obtained according to the limit of vehicle running safety and ride comfort indices of the high-speed trains.Results show that the dynamics indices of different trains have different sensitivities to the pier settlement,and the train CRH2C is the most sensitive one among all the types of Chinese high-speed trains.When passing through the bridges in common span with pier settlement at the speed of 250–350 km/h,the trains suffer the low-frequency excitations,and the vertical acceleration of car body is most sensitive to the pier settlement of all the dynamics indices.When the car body vertical acceleration just exceeds the allowable limit,the critical settlement value is 23.4 mm,which is much bigger than the pier differential settlement limit in the current code for Chinese high-speed railways.