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Über dieses Buch

This book includes keynote presentations, invited speeches, and general session papers presented at the 7th International Symposium on Environmental Vibration and Transportation Geodynamics (formerly the International Symposium on Environmental Vibration), held from October 28 to 30, 2016 at Zhejiang University, Hangzhou, China. It discusses topics such as the dynamic and cyclic behaviors of soils, dynamic interaction of vehicle and transportation infrastructure; traffic-induced structure and soil vibrations and wave propagation; soil-structure dynamic interaction problems in transportation; environmental vibration analysis and testing; vehicle, machine and human-induced vibrations; monitoring, evaluation and control of traffic induced vibrations; transportation foundation deformation and deterioration induced by vibration; structural safety and serviceability of railways, metros, roadways and bridges; and application of geosynthetics in transportation infrastructure. It is a valuable resource for government managers, scientific researchers, and engineering professionals engaged in the field of geotechnical and transportation engineering.

Inhaltsverzeichnis

Frontmatter

Evaluating Fatigue Resistance of FRP-Strengthened RC Bridge Decks Subjected to Repeated Wheel Load

One of the major causes of road infrastructure failure is traffic-induced fatigue of bridge superstructures, in particular concrete bridge deck panels Deterioration of steel reinforced concrete (RC) bridge decks a result of aging and fatigue is on the rise in many developed countries including Japan. This paper presents experimental work done in investigating traffic-induced fatigue mechanism of a normal RC bridge deck and the strengthening by fiber-reinforced polymer (FRP) sheets to extend fatigue life. Discussion is focused on experimental observations and development of a stress-passage (S-N) relationship that provides estimation to the fatigue life of deck as a result of FRP strengthening. Within the scope of study, the strengthening by FRP has proven to be a viable and relatively simple solution in salvaging RC bridge decks suffering from moderate level of fatigue damage, with fatigue life up to 28 times longer than that without strengthening.

Hwa Kian Chai, Hiroshi Onishi, Shigeyuki Matsui

Vibration Measurements for the Control of Damaged and Repaired Railway Tracks

The damage detection and repair control have become important tasks for ballast and slab tracks. Measurements which compare the damaged and the repaired status of the same track section at different times, or which compare a damaged and an intact track section at the same time, have been successfully performed at some sites in Germany with slab tracks and ballast tracks and compared with the theoretical behavior of intact and damaged tracks. The loss of contact between the sleeper and the plate, between the plate and the base layer, and some problems with soft or weakened soil have been analysed. The observed results, changes in the time histories of displacements and velocities due to train passages and in the transfer functions (compliances) due to hammer impacts, are encouraging that these measurements can be used to detect track damage. In addition, calculations with the combined finite-element boundary-element method have been used to confirm the conclusions about intact or damaged railway tracks.

Lutz Auersch, Samir Said

2D and 2.5D Responses of Long Underground Tunnels to Moving Train Loads: A Comparison Study

In this paper, a comparative study is conducted for the responses of soil-tunnel systems to moving train loads using the 2D and 2.5D finite/infinite element approaches, considering the effects of train speed, rail roughness and floating slab. Specific account is taken of the wheel-rail interaction forces. The following are the major findings of the numerical studies: (1) For all the cases studied, the soil response predicted by the 2D approach is always higher than the 2.5D approach. (2) The 2D result based on plane strain condition can be regarded as the limit of the 2.5D analysis with infinite train speed for smooth rails. (3) The 2D frequency response function (FRF) is contributed by frequencies of the whole range of the half space, but less sensitive to variation in roughness frequencies, while the 2.5D FRF is concentrated around the frequencies of rail roughness. In summary, the 2D approach saves a huge amount of computation time, due to the use of relatively smaller system matrices. But the 2.5D approach is more realistic in that it can cope with wave transmission along the tunnel axis.

Y. B. Yang, Xujie Liang, Hsiao-Hui Hung, Yuntian Wu

Out-of-Plane Parametric Resonance of Arches Under an In-Plane Central Harmonic Load

Arches have been widely used in infrastructures such as bridges. This paper presents an experimental investigation of the out-of-plane dynamic instability of shallow circular arches under an in-plane central concentrated harmonic load owing to parametric resonance. The effects of central concentrated weight and the amplitude of the periodic load on the out-of-plane dynamic instability of arches are also investigated. It is found that as the weight increases, the bandwidth of the critical frequency region for out-of-plane dynamic instability decreases. It is also found that the bandwidth of the critical frequency region increases with an increase of the amplitude of the harmonic load. It is shown that the curve of the excitation frequency vs. amplitude of out-of-plane resonance bends toward the low frequency region and that the “traction” out-of-plane instability may occur owing to the “amplitude” perturbation.

Airong Liu, Hanwen Lu, Yong-Lin Pi, Youqing Huang, Jing Li

Surface Vibration of a Layered Saturated Ground Subjected to an Embedded Moving Load

The dynamic response of a layered poroelastic ground subjected to a buried moving load is analyzed by using the Fourier transform and the TRM method. Soil is idealized as a fully saturated poroelastic medium obeying Biot’s theory. A modified hysteretic damping model is introduced to describe the visco-elastic behavior of the soil. Using the Fourier transform and the inverse Fourier transform, the integral form solutions for dynamic response of a layered saturated half-plane under a buried moving load are obtained. When the layered half-plane is reduced to a homogeneous poroelastic half-plane, the results obtained in this paper are in good agreement with the published paper. At last, the vibration characteristics of three different cases in both frequency domain and time domain are investigated. And the influence of depth, speed and frequency of the buried load was also discussed by some numerical examples.

Anfeng Hu, Yijun Li, Bo Sun, Kanghe Xie

Vibration Impact of Freight Train on the Tunnel Base Rock Mass

The tunnel base diseases threaten the safety of the heavy haul railway operation, one important reason is the effect of freight train vibration load. In this paper, based on the Huojialiang Tunnel on Shen-Shuo Railway Line, a dynamic-finite-element model including the rail, the tunnel structure and the rock mass was established to analysis the vibration influence on the tunnel base rock mass. The simulated 25t axle-load freight train load was applied on the sleepers. The results showed that the rock mass within 6.8 m away from tunnel invert was obviously influenced by the train vibration load. But to the rock mass just under the center of tunnel invert, the range of influence was expanded to 10 m. The rock mass out of the above range was less impacted by the freight train load.

Bin Li, Xiaojing Sun, Zhongsheng Tan, Chang Yu

Establishment of Finite Element Model for Wide Steel Box-Girder Bridge by Modal Test

Accurate finite element model of wide steel box-girder bridge is very important for evaluation of structural dynamic performance and structural design. In this paper, a sophisticated finite element model is presented for the wide steel box-girder bridge, modal tests in various stages of construction are carried out based on the field ambient vibration, stochastic subspace identification and peak picking of the average normalized power spectral densities are used to identify the bridge’s dynamic characteristics. Numerical simulation compared with the test result shows that the FEM established in this paper is quite accurate.

Boqiang Xiao, Weiping Xie, Haiqing Liu, Xiaoyu Cao

Study on the Vibration of Geosynthetic Reinforced Cushion in Pile Supported Embankment

The vibration of geosynthetic-reinforced cushion in pile supported embankment due to high-speed train load is theoretically investigated in this paper. The cushion is considered as an elastic sheet on viscoelastic foundation. The high-speed train load is assumed as a dynamic load made up of a stationary load and three sinusoidal loads. An analytical solution of the vibration response of cushion due to high-speed train load is obtained. Numerical examples are given to analyze the vibration characteristics of cushion and the effect of the train speed, Young’s modulus and thickness of cushion on the displacement response. The results show that the displacement response of cushion increases as the train speed increases. The peak value of displacement increase steeply with the decrease of damping. Furthermore, the influence of high-frequency load on the displacement decreases with the increase of the train load and damping. Properly increasing the Young’s modulus and thickness of cushion can effectively reduce the displacement of cushion.

Changjie Zheng, Xuanming Ding, Lubao Luan, Hui Yu

Strength and Deformation Behavior of Roadbed Aggregate by Large-Diameter Triaxial Test

Graded aggregates are widely used in the roadbed of high-speed railway, and its strength and deformation play a decisive role in determining the long-term service stability of railway. In this paper, aggregates with different gradation were tested by large-diameter triaxial testing apparatus. The influence of some key parameters, such as gradation, compaction degree and loading level on aggregate specimen’s strength and deformation behaviors are discussed based on the test data. The characteristics of particle breakage are presented. Based on experimental results, the graded aggregates which content of more coarse particles, when the compaction degree reach a certain extent, its strength has little relation with its compaction degree, for the graded aggregates which content of less coarse particles, only when the compaction degree is relatively high that can give full play to its strength. The graded aggregates which has a good gradation, resulting in little particle breakage. However, the specimen which has a relatively uniform size, results in more particle breakage. At a certain compaction degree, the amount of particle breakage obvious increase with the increase of confining pressure. It can be found that the volumetric strain caused by particle breakage cannot be neglected in the total volumetric strain of the gravel, especially in the case of relatively high confining pressure, the ratio of 10% can be achieved.

Dongdong Sun, Xuecheng Bian, Wei Li

Spatial Rotations of Principal Stress Axes in Infrastructures on High-Speed Railway

The rotations of principal stress axes are special phenomenon induced by moving loads and deep excavations. It plays a significant role in the deformation calculation. The characteristics of the rotations of principal stress axes in semi-infinite foundation caused by a moving constant pressure are studied and the influences of surface wave on the characteristics are analyzed. The three dimensional elaborately numerical model for infrastructures including embankment, embankment-bridge transition zone and tunnel on high-speed railway are developed. The nonlinear factors such as material nonlinearity, generated geometry nonlinearity and contact nonlinearity are incorporated in the adopted models. The elastic recovery and radiation damping of infinite domain are reflected using three dimensional viscoelastic static-dynamic unified artificial boundaries. The dynamic behaviors of the infrastructures on high-speed railway under moving impulse pressures are investigated. The results indicate that the principal stress axes rotate in XY, XZ and YZ plane synchronously and continuously, the rotation in YZ plane predominate for embankment, embankment-bridge transition zone and tunnel. The rotations of principal stress axes at lower depth are greatly affected by surface waves generated by the interactions of P-wave and S-wave, the influence of surface wave on soil elements decreases with the increasing of depth. Stress concentrations occur near the transition zone due to the existing of large free surfaces. The rotation modes in infrastructures on high-speed railway are much more complicated than those in semi-infinite foundation. The rotations of principal stress axes can only be correctly obtained through wave motion analyses.

Fuchun Xue

Field Measurement and Analysis of Ground Vibration Induced by High-Speed Train

In situ test data for ground vibration of high-speed railways is valuable but scarce. Chinese researchers used to cite test results from European countries to verify their numerical model, owing to the lack of open access to in situ data. To remedy this shortage, this paper presents field measurements of ground vibrations induced by high-speed trains at a site on the Qin-Shen Line in China. The free field vibrations at different distances from the track center during the passage of a high-speed train at a speed varying from 230 to 250 km/h are measured. The recorded vertical accelerations are analyzed both in the time and the frequency domains. The periodic exciting action of the train wheel-set can be identified in the vertical acceleration time-history when the test site is close to (e.g. 3.5 m away from) the track centerline. Vertical acceleration generally attenuates with distance from the track centerline, but a vibration boom occurs at the distance of 12 m. The effect of both P and S waves cannot be neglected in the vicinity of the track, while R waves begin to dominant beyond the distance of 15 m. In addition, an important frequency in the acceleration spectrum of the ground vibration is the fundamental axle passage frequency (25.6–27.8 Hz). The test results could be available to peer researchers for verification of their numerical models, and meanwhile act as a complementary material to currently scarce in situ tests results.

Guangyun Gao, Juan Chen, Jian Song, Jun Yang, Shaofeng Yao

Micro-analysis of Ballast Angularity Breakage and Evolution by Monotonic Triaxial Tests

Ballast particle angularity breakage may occur even under relatively lower stress compared with breakage, which leads to ballast degradation and fines accumulation. The degradation evolution and results have huge influence on potential recycling, reusable, and renewable design and operations. In the paper, the ballast angularity reduction under monotonic triaxial tests was studied, with different confining pressure including 10, 30 and 60 kPa. A simplified DEM model was developed to investigate the ballast particle angularity reduction and fines accumulation. The ballast particles were modeled by irregular clusters, where the small spheres were attached to the center sphere to simulate the angularity, as well as the fines after fracture. Results in DEM present a good coincidence with test data, and the presented irregular cluster was able to capture the degradation behavior of ballast angularity subject to loading. This paper demonstrates that ballast angularity reduction and fines accumulation increases with confining pressure increasing, which plays an important role in governing ballast degradation and recycling.

Guixian Liu, Guoqing Jing, Dong Ding, Xiaoyi Shi

Shaking Table Experiment on Soil-Micropile Interaction of Semi-integral Abutment Bridge

Based on a semi-integral abutment bridge employing micropiles under approach slabs, shaking table experiments have been conducted. Via shaking table experiments, dynamic responses, soil-micropile interaction and dynamic p-y curves are investigated. Experimental results shows that natural frequency of soil-micropile system is 8.38 Hz, the maximal bending moment distribution is highly affected by excitation frequency as well as pile displacement distribution. In addition, dynamic p-y skeleton curves are presented.

Haimin Qian, Yizhou Zhuang, Yun Chen

Dynamic Shakedown Analysis for Anisotropic Material Under Traffic Moving Loading

Shakedown solution is widely used to analyze elastic-plastic behaviors of structures in pavement design. It is an effective way to predict the maximum admissible load (termed ‘shakedown limit’) against excessive rutting in flexible pavements. However, previous research is concerned with shakedown theorem under traffic loads without the influences of anisotropy. This paper has firstly proposed numerical analysis for anisotropic material under traffic moving load, based on Melan’s lower bound shakedown theory. An anisotropic Finite Element–Infinite Element (FE–IE) model with a user subroutine in ABAQUS is proposed to calculate the dynamic response of elastic stress against load moving speeds. Shakedown limits for an anisotropic half-space pavement system under traffic moving loads at various speeds are investigated. It is found that the shakedown limit decreases when the load moving speed increases towards the Rayleigh wave speed of the pavement for isotropic half-space system. For cross-anisotropic half-space system, Poisson’s ratio only leads to negligible effect on shakedown limit. Furthermore, the shakedown limit rises with the increasing cohesion ratio c v /c h , but it reaches maximum value when cohesion ratio is larger than a specific value. And the maximum shakedown limit rises slightly with the increase of moving speed below Rayleigh wave speed.

Han Lin, Jiangu Qian, Yonggang Wang

Field Test Study on Influence of Undercrossing Construction on Safety of Existing High-Speed Railway

The construction of high-pressure jet grouting pile has a compacting effect, when the construction is close to bridge pier and abutment and other structures, it will cause lateral deformation and vertical settlement of the structures. High-speed railway is a premium risk source, and its operation safety must be guaranteed during the construction undercrossing it. However, in China, there has not been any construction experience about undercrossing an operating high-speed railway previously. To ensure safety of the construction undercrossing BeiJing-TianJin Inter-city Railway, the field test study are conducted. The conclusions of the field study are as follows: (1) The construction under three working conditions all has some influence on lateral deformation and vertical settlement of the structures, but it is safe and controllable according to the test data; (2) Relatively, Case 2 has greater influence than Case 1 and Case 3. Therefore, it should be given more attention during construction; (3) Lateral deformation is more sensitive than vertical settlement during the construction undercrossing the high-speed railway, and it should be intensively monitored.

Hong Xiao, Xing Ling, Song Lv

Field Test and Analysis on Subway Train Induced Vibration

With the development of society and the high-speed growing of urban population, traffic jam is becoming an increasing seriousness to people’s normal life. Subway construction as a result can be an efficient means to solve this problem. However, vibration induced by subway’s operation can seriously affect the structure of subway tunnel and the environment around it. So, getting into a thorough research of the environmental vibration response becomes an important issue. This paper introduces a field vibration test on Ningbo subway tunnel at different spots of track slab and tunnel lining, compares the vibrating performance at different spots. Then the propagating and damping properties of vibration are analyzed.

Hongming Liu, Jing Hu, Xuecheng Bian

Discrete Element Simulation Study of Contact Pressure Distribution Between Sleeper and Ballasts

With the rapid development of economics in China, High-speed railway plays an increasingly important role in public transport. The accompanying more rigorous design criteria requires further understanding into the behavior of track bed. Compared with experimental studies, it is more economical and more efficient to develop a model to conduct the research. In this paper, a discrete element simulation has been performed for assessment of the contact pressure distribution between railway sleeper and railway ballasts under static loads. The ballasts in the simulation are modeled by discrete spheres with rolling friction and static friction. In order to represent the deformable property, the sleeper is modeled using a layer of spheres which are connected by bonds based on the Timoshenko beam theory. Results from the model show that the contact pressure distribution between the sleeper and ballast layer follows a double-peak pattern. This pressure distribution is compatible with the results of an experimental research in railway sleeper. Although the model still needs to be elaborated and calibrated further, this work adds to the understanding of the behavior of sleepers used in service.

Huahan Chen, Xuecheng Bian

Seismic Response Analysis of Cylindrical Hollow Pier Based on Morison Equation

In order to realize the hydrodynamic pressure in numerical simulation, the hydrodynamic pressure is converted to added mass based on the Morison equation, which is imposed on outermost node of three-dimensional finite element model of bridge piers. The proposed method, the relevant literature method and fluid element method are used to analysis the effect of seismic response of bridge pier which considering hydrodynamic pressure action. The numerical results show that the calculated results of the 3 methods are in good agreement. The influence of outer water on the seismic response of circular bridge hollow pier is studied by this proposed method and fluid element method, the research shows that the proposed method is suitable for study of seismic response analysis of hollow bridge piers, with good calculation accuracy.

Huaxi Lu, Zhenwei Zhou

Experimental Study on Vibration Decay Rate Characteristics and Improvement for Beijing Metro

Measured decay rates(DR) [1] provide an estimation for track dynamic properties along rails. To entirely estimate the vibration propagation behaviors of tracks for Beijing metro, DR measurements of different track structure forms are carried out. Including standard track with DTVI2 fasteners un/installed with rail dampers, Egg fastening system track un/installed with rail dampers, and ladder track. All the test results are compared with the suggested lower limits of TSI-NOI [2] and shown as: (1) Installing with rail dampers can improve the DR characteristics for tracks in some frequency bands; (2) Some bad wheel/rail contact may be induced by the deficiencies of DR characteristics at some frequencies of tracks; (3) Comparing with lower limits of TSI-NOI may conduct the optimization of track structure.

Jialiang Chen, Weining Liu, Weifeng Liu

Numerical Analysis of Dynamic Stress Response to Moving Load Using Infinite Element and Visco-elastic Boundary

Finite element method provides a competitive way to get access to dynamic stresses subjected to moving loads on the ground. To get reasonable prediction of dynamic stresses using numerical methods, it’s important to choose a proper boundary condition, which can minimize the influence caused by the reflection of the stress waves at the boundary. This paper presents three-dimensional simulations of moving loads of different velocities using two different boundary conditions, infinite element boundary (IEB) and visco-elastic boundary (VEB), based on commercial finite element code ABAQUS. The results show that maximum dynamic stresses are remarkably affected by the velocity of the moving loads. The maximums of dynamic stresses increase slowly with an increasing velocity at first and then rapidly grow when the moving velocity is closer to the Rayleigh wave speed. The comparison of predicted dynamic stresses using these two different boundary conditions and the analytical results shows that at a relative low velocity (less than 70% of the Rayleigh wave speed), both boundary conditions’ results match the numerical solutions well. As the velocity increases (over 70% of the Rayleigh wave speed), the numerical predictions deviate from the analytical results, however, the IEB gives better results because of the simplicity of its coefficients selection.

Jiangu Qian, Jingliang Zhang, Zhiguo Lin

DEM Modeling of Vane Shear Test in Cohesive Solids

The vane shear test is used for obtaining the unstrained shear strength of cohesive soil in civil engineering. In present work, discrete element method (DEM) has been applied to build a numerical model to simulate the vane shear test. EDEM is a powerful DEM software, and it provides a cohesive contact model called Hertz-Mindling with JKR. In this literature, Hertz-Mindling with JKR contact model is chosen for the contact between soil particles. Comparing the results of simulation with the results of laboratory test, we can see that the torque changing with the rotation angle is qualitatively similar to the laboratory test. It proves that the numerical model is reasonable to simulate the vane shear test. And we can get the results about how the torque changes with the rotation angle.

Jiawei Xu, Xuecheng Bian

Dynamic Stresses in Embankment and Ground Caused by HST with the Considering of Track Irregularity

Scientific design of a railway track formation requires an understanding of the dynamic stresses in embankment and ground. To study the dynamic stress, the time-history of stress, and the stress development with train speed are essential, especially in embankment. This study investigates the dynamic stresses both in embankment and ground, by means of a high-efficient 2.5D track-embankment-foundation numerical model. Based on China’s first high speed railway, a 2.5D ballast track model is established. In order to study the effect of track irregularity, the track irregularity PSD of U.S. railways is adopted to the ballast track model. The in situ test results of ballast railways collected from predecessor’s research are summarized and normalized to compare with the 2.5D numerical results under different grades of track irregularity. Based on the comparison, a preliminary division of the irregularity of track running state can be made. Track irregularity of a new built railway was less than six grade track irregularity PSD of U.S. railways. But for some diseased lines or longtime operation lines, track irregularity were in an extremely serious condition, even larger than first grade track irregularity PSD of U.S. railways. The numerical results also shows that the amplification of dynamic stresses caused by track irregularity is limited at low speed stage (≤100 km/h), and at high speed stage, the dynamic stresses show a multiple increase. The track irregularity also cause deeper transmission and wider influence area in embankment and ground. Larger dynamic stress will caused a larger deformation in embankment and track structure which aggravate track irregularity in turn.

Jing Hu, Xiang Duan, Xuecheng Bian, Jianqun Jiang

Soft Soil Performances Under Combined Static and Cyclic Loading

Mechanical properties of soft clays under combined static and cyclic stresses are experimental tested. The sensitivity of static stress and cyclic stress is examined in terms of the total and cyclic excess pore pressures and axial strains. Results show that total excess pore pressures and total axial strains generally depend on combined stress ratio. For a given combined stress ratio, the cyclic excess pore pressures and cyclic axial strains are largely determined by the cyclic stress ratio. A modified soil model is proposed to incorporate the effect of initial static shear stress together with the cyclic loading and is verified with the test data. Parametric analyses indicate that more severe degradation during cyclic loading can be expected even for a lower cyclic stress ratio given a higher combined stress ratio. For a fixed combined stress ratio, the total cyclic stress ratios and total axial strains are highly influenced by the cyclic degradation parameters.

Jing Ni, Xueyu Geng, Yi Wei, Yin Zhu

Micro-vibration Measurement and Analysis of High-Tech Electronics Workshop in Guangzhou

High-tech electronics workshop typically has stringent requirements for micro-vibration control, so as to ensure the proper operation of the installed vibration-sensitive facilities. Based on a micro-vibration measurement on a high-tech electronics workshop in Guangzhou, China, this paper reports the test data, presents a systematic and detailed summary of issues related to vibration data processing, and analyzes the transformation of the vibration characteristics when the anti-vibration techniques enhances. The results show that, the one-third octave band spectral has great advantages in representing vibration data of high-tech buildings. With the enhancement of the anti-vibration techniques, the vibration amplitudes in all of the three directions decrease both in time-history and one-third octave band spectral and finally become roughly the same; and the dominant high-frequency component disappears, while the relative low-frequency component takes the leading role in all the three directions.

Juan Chen, Guangyun Gao, Jian Song, Wei Zhang

Theoretical Solutions for Static and Dynamic Shakedown of Cohesive-Frictional Materials Under Moving Loads

Shakedown theory can serve as a theoretical basis for the design of pavements and railways against long-term residual settlements. Based on the static and dynamic lower-bound shakedown theorems, this paper presents theoretical shakedown solutions for a plane strain cohesive-frictional half-space under a repeated moving load. The medium is described as a Mohr-Coulomb material. A self-equilibrated residual stress field which fully satisfies yield and boundary conditions is introduced to calculate the lower-bound shakedown limit. The dynamic effect of the moving load is considered using analytical solutions of the dynamic elastic stress fields in the half-space. It is found that the two-dimensional static shakedown limits agree with previous literatures. Surface traction has a negative influence on the shakedown limit. Particularly, when large surface sliding is considered, the shakedown limit is actually controlled by the shear stress distribution rather than the normal pressure. The dynamic shakedown limit is very close to the static solution when the load moving speed is very slow. And it is reduced as the load moving speed is increased towards the wave propagation speed in the semi-infinite medium. A material with a high friction angle is more vulnerable to the rise of the load moving speed in terms of the percentage of the shakedown limit reduction from the static solution. The theoretical results in paper can be used to benchmark numerical shakedown solutions.

Juan Wang, Shu Liu, Xiaojun Tang

Influences of Subgrade Bed Structure on Dynamic Responses of Railway Subgrade Under Train Loading: Field Testing Case Study

To explore the influences of subgrade bed structure (i.e. the upper part of railway subgrade) on subgrade dynamic responses under train loading, and thus to optimize the design of railway subgrade, this paper presents field tests of cyclic loading for railway subgrade with four different subgrade bed structures (say, different thickness and stiffness). The considered comparisons of subgrade dynamic responses includes the distribution of dynamic stress in railway subgrade, the elastic deformation and dynamic stiffness of subgrade, and the cumulative plastic deformation on subgrade surface. Test results indicate that, the increase of the thickness or stiffness of subgrade bed promotes the attenuation of dynamic stress in subgrade. The more the attenuation of dynamic stress in subgrade, the smaller the accumulative deformation of subgrade. An optimized subgrade dynamic stiffness requires comprehensive matching of both the thickness and stiffness of the layer structures of railway subgrade.

Junhua Xiao, Chengyu Liu, Ye Shengyu, Binglong Wang

A Study on Unsaturated Dynamic Constitutive Model Under Cyclic Loading for Western Sichuan Talus Mixed Soil

Settlement and deformation problems in the Western Sichuan area often occur in embankments consisting of mixed soil including sandy gravel and clay particles. Soil-accumulated deformation under traffic loads could be described by establishing a dynamic constitutive model under cyclic loading. This study elaborates on an unsaturated dynamic constitutive model for mixed soil within the framework of the elastic–plastic bounding surface model combined with a real description of the unsaturated soil collapsible performance loading–collapse (LC) yield curve based on the mapping rule of a mobile mapping origin. This study also considers the two main influencing factors of unsaturated state and fine particle content for talus mixed soil and takes the classic modified Cambridge model as a plastic potential equation. The comparisons between the experimental results and the model simulations show that the elaborated model is capable of describing the unsaturated loess behaviors under static and cyclic loading and predicting the phenomenon of hysteretic properties during both loading and unloading. The model parameters can be obtained through fitting or routine experimentation results.

Kai Cui, Yongkui Li

Study on Mitigation Measures to the Vibration of Vehicle-Track System

With the development of urban rail transit, more and more environmental problems come out, especially the impact of vibration and noise induced by transit lines on people who live around metro viaducts. In order to improve the vibration condition of bridge and surrounding buildings, most mitigation measures are applied without considering vehicle vibration. The past research has shown that these measures tended to enlarge the vibration of rail or vehicles. Aiming at improving this situation, a numerical finite element model of Wheel-Track-Bridge coupling system is built in this article. Vibration characteristics of bridge, wheels and rail can be obtained to validate the previous research results. Comparison of vibration levels of the whole system with different track structure stiffness, it is proved that lowering fastener stiffness can only reduce the vibration of bridge but enlarge that of rail and wheels. This paper proposal a new method to weaken the vibration of both bridge, rail and wheels simultaneously. The conceptualization of dynamic vibration absorber was put forward to absorb vibration of the whole system of elevated lines. A simplified two dimensional model was built to test mitigating vibration performance of this kind of absorber. After numerical analysis, the results indicated that dynamic vibration absorber would decrease vibration level of bridge effectively while not enlarge the vibration level of rail. Its mass and stiffness are the principal parameters related to its working property and is also where the key lies in designing this component.

Li Zhou, Yanyun Luo, Yan Liu, Qiutong Li

Experimental Study on Vibration Reduction Effect of New Anti-vibration Bearing

In this paper, a new anti-vibration bearing is proposed to mitigate vertical train-induced vibrations to improve the vibration environment around the elevated urban rail transit. A scale model test is carried out to verify the vibration reduction effect of a new anti-vibration bearing. Test result shows that vibration amplitudes of new anti-vibration bearing at the upper and lower plates are smaller than those of steel bearing while the electromagnetic vibrator is working on the test model. The whole insertion loss of anti-vibration bearing is 13.49 dB, which is 5.32 dB larger than that of steel bearing. For most frequency components, the new anti-vibration bearing can reduce more vibrations than the steel bearing in the vertical direction. Therefore, this kind of bearing is effective to isolate the vertical vibration.

Liangming Sun, Weiping Xie, Xu Liang

Study on Evaluation Index of Environmental Vibration Induced by Urban Transit

Index to evaluate environmental vibration induced by urban rail transit are VLzmax and VLmax. Confused calculating methods of evaluation index have affected plan and design of subway line. Influence of overlapping coefficient and frequency weighting curve on VLzmax is researched in this paper. The study found that when the overlapping coefficient is 3/4, the result of VLzmax is stable basically. Frequency weighting curve in ISO 2631-1:1997 considering the effect of rail transit vibration on human health, comfort and perception, which is recommended for the amendments on the GB10070-88 Standard. Calculating methods of linear averaging, peak hold have significant influence on the VLmax result, which could affect the evaluating result. In order to ensure the reliability of evaluation results, peak hold method should be adopted as the calculating method.

Linlin Du, Weining Liu, Weifeng Liu, Meng Ma

Bridge Structure-Borne Noise of Concrete Trough-Girder Beam and Its Influence Factors

In order to investigate the structure-borne noise of trough-girder beam and its influence factors, a 30.0 m simply-supported concrete trough-girder beam is simulated by a means of hybrid FEM-IBEM method. Firstly, the combination of SIMPACK and ANSYS simulation method is adopted to obtain the wheel/rail exciting force. Then, we can calculate the vibration response and structure noise of the trough-girder beam under the action of train load. Finally, the influence height of web on trough-girder beam structure-borne noise is probed into. The research results show that: the dominate frequency ranges of trough-girder beam structure-borne noise is 20.0–80.0 Hz, respectively, the peak frequency of noise is 63.0 Hz. The structure-borne noise decreases with the increase of web height, and the influences of the far sound field is the more obvious. Research results can provides a theoretical reference for optimum design of trough-girder beam structure vibration and noise reduction.

Linya Liu, Feng Zeng, J. D. Yau, Quanmin Liu

Measurement and Evaluation of Freight Train-Induced Ground Vibrations

With the substantial increase in transportation of goods on railway, the problem of ground-borne vibration induced by freight trains has received increasing interest in the recent years. To learn the vibration characteristic of freight train-induced vibrations and evaluate its vibration impact on human being, in this paper, an in situ experiment was carried out in the suburb of Beijing. The vibrations induced by both freight and passenger trains were considered. Then, a new vibration descriptor was presented to describe the received vibration energy from the passage of trains at sensitive locations. Results show that, the freight train induces obviously larger vibrations in low frequency ranges below 10 Hz and longer vibration duration which is an important factor to the annoyance to residents nearby. Compared to maximum Z-vibration level, vibration exposure level can better describe and evaluate the freight train-induced ground vibrations.

Meng Ma, Wenbin Wang, Xiaojing Sun

Dynamic Stress Distribution of Arbitrarily Arranged Deep Cavities Subjected to Incident Plane P Waves by Multiple Scattering Method

Based on the elastic wave propagation and scattering theories, it is introduced acoustical and electromagnetical multiple scattering solutions. With wave function expansion and coordinates translation methods, it is solved the every order of scattering complex coefficients with boundary conditions. The iteration relation of high order to lower order of scattering coefficients is established, the multiple scattering wave and total wave field are determined as well. It is innovatively calculated the elastic wave multiple scattering and dynamic stress response problems of arbitrarily arranged deep cavities subjected to incident P waves. The numerical example shows the value of Dynamic Stress Concentration Factor (DSCF) which the cavities group is arranged as hexagon is approximately the same as the ones linearly arranged meanwhile the separation between cavities is narrower than the former one.

Miaomiao Sun, Huajian Fang, Shimin Zhang, Xinjiang Wei

Earth Pressures of the Buried HDPE Pipe Subjected to Ground Subsidence

The High density polyethylene (HDPE) pipe is widely used in the municipal drainage system due to its merits of light weight, low cost and chemical resistance. The fractures of the buried HDPE pipe caused by the ground subsidence are common occurrence in engineering practice. Many methods for calculation of the earth pressure at the top of the pipe during the construction phase are available, while the method for estimating the earth pressure of the pipe subjected to the ground subsidence is limited. In this study, full-scale model tests are established to explore the distribution of earth pressure around the HDPE pipe subjected to the ground subsidence. HDPE pipes with two inside diameters of 200 and 400 mm are used in the model tests. Movable bottom plates of the model box are designed to generate the ground subsidence. The earth pressure cells are installed at three different profiles along the longitudinal direction of the pipes. The results demonstrate that the soil arching is triggered along both the longitudinal and cross-sectional directions of the pipe subjected to the ground subsidence. The earth pressure at the top of the pipe experiences an overall increase with lowering down the bottom of the model box.

Min Zhou, Yanjun Du, Fei Wang

Semi-analytical Solution for the Dynamic Response of a Cylindrical Structure Embedded in a Homogeneous Half-Space

This paper addresses the dynamic response of an infinitely long cylindrical structure embedded in an elastic half-space. The structure has a circular cross-section and its axis is parallel to the half-space surface. Excitation can be incident body waves or forces applied on the surface of the half-space and/or the structure. The model can be used to assess the integrity of structures when acted upon by seismic waves, to predict ground-borne vibration due to circulation of vehicles, and to infer about the safety of vehicles during earthquake events. Because the half-space and the structure surfaces possess different symmetries, the solution is not straightforward. In order to circumvent this difficulty, the physical domain is conformally mapped onto an auxiliary domain with a cylindrical symmetry, in which the free surface of the half-space and the surface of the structure are located at concentric cylindrical surfaces. The solution of the original boundary value problem is finally obtained by solving a set of algebraic equations. Truncation of the summation over circumferential modes is needed in the numerical implementation. Convergence tests, validations and comparisons of stresses and motions for two- and three-dimensional cases are presented and discussed as well as the advantages and disadvantages of the proposed method. Additionally, the effect of the presence of the tunnel is analysed by considering a limiting case of the half-space with just a cylindrical cavity of the same radius as the outer radius of the tunnel.

Mingjuan Zhao, Karel N. van Dalen, João M. Barbosa, Andrei V. Metrikine

Evaluation of Environmental Vibration in the Surrounding Building Caused by the Punching Machine

To assess the vibration influence of punching machine to surrounding buildings, a field test is carried out in a certain mold punching company. After analyzing the intensity of vibration source, Z vibration level (VLZ) and other indicators, the vibration comfort of the buildings is evaluated according to the requirement of standards. Their results show that the operation of the punching machine causes the vertical vibrations in second and third floors for a three-story lightweight steel construction which is 75 m far from the punch machine to be out of limits while the ground floor not. And then they make the staff of these floors uncomfortable. It is indicated that the influence of punching machine to the light steel structure building should be taken into consideration the location, and if necessary, countermeasures should be taken to reduce such effects.

Pengfei Zuo, Liangming Sun, Weiping Xie

Dynamic Behavior of Vehicle-Slab Track in the Condition of Subgrade and Culvert Transition Settlement

It is a common phenomenon for the settlement in the area of subgrade and culvert transition. Based on the theory of vehicle-track coupling dynamics, the vehicle-slab track-subgrade and culvert transition model was established. And the influence of different settlement types and values on vehicle-slab track dynamics behavior was studied. The results show that: (1) Settlement deformation of the subgrade and culvert transition area has great influence on the safety and stability of train and the vibration of the track structure. When the settlement occurs in different positions which include front of the transition section, transition area and culvert area, the maximum dynamic response arises in transition area and culvert area. (2) When the cosine settlement occurs in the transitional section of the subgrade and culvert, the bigger the amplitude is, the deeper the influence on the wheel rail dynamics index and track structure vibration is. (3) When the bending angle deformation occurs in the subgrade and culvert transition section, the greater the bending angle changing rates are, the bigger derailment coefficient and the wheel load reduction of the vehicle are, and the lower of driving safety and the stability of vehicles are.

Xiaopei Cai, Yongwang Kai, Chuangchuang Ren, Liangwu Guo, Qian Miao

Preliminary Analysis of the Interaction Between Tunnel and Soil by the 2.5D FEM-BEM Method

In this paper, both the full space and the half space 2.5 dimensional finite element-boundary element model is established for modeling the coupled tunnel and soil. The tunnel wall is modeled by using finite element method and the soil is modeled by using boundary element method. We also calculate the response of the tunnel model by using the exact solution. In order to illustrate the rationality of the model, we compared that to the result which we detected at the free boundary with a single point harmonic load. The response of tunnel and soil in the full space and the half space are analyzed.

Qingsong Feng, Shiyue Liu, Xiaoyan Lei

DEM Simulation of Simplified Railway Embankment Under the Effect of Train-Induced Dynamic Load

With the rapid development of high-speed railway over the world in recent years, more and more researchers are focused on the strength, stiffness and stability of the embankment. It’s more and more popular to use the discrete element method (DEM) to study cemented granular materials (e.g. rocks and concrete). This paper verified the Timoshenko beam bond model (TBBM) presented by the University of Edinburgh, then compared the bending and dynamic response of a simply supported beam under the effects of moving load with the analytical prediction. It’s ideally suited to use DEM to model the railroad ballast layer considering the naturally discrete inhomogeneous structure. A simplified railway embankment model composed of equal-sized ballast particles was built and the loading response of the simplified embankment was then investigated. The results show the feasibility of modeling train-induced dynamic load through adding moving load to railway track made up with the bonded particles. This paper presents one way to take the discrete features of the ballast layer and the characteristics of railway track into consideration in the same DEM framework at the same time. Apart from that, the mechanical characteristics of the ballast layer and the interactions between the ballast and railway track can be easily studied.

Qiusheng Gu, Xuecheng Bian, John P. Morrissey

Vibration Isolation of In-filled Trench in Layered Ground Under High-Speed Train Load with Track Irregularity

A 2.5D train-track-ground FEM model is developed to analyze the vibration mitigation effectiveness of in-filled trench in layered ground under high-speed train loadings. The train load including the track irregularity is deduced by simplifying the track as an Euler-Bernoulli beam resting on a visco-elastic layered sub-grade. By simulating the in-filled trench as a heteroplasmon in a half-space, the 2.5D finite element formulas are derived by employing the fast Fourier transform. The vibration isolation effectiveness of in-filled trench on ground under train dynamic load at different speeds is analyzed. Then the effects of the width and depth of the in-filled trench are analyzed in detail. The results show that the vibration isolation effect of in-filled trench is better for moving trains at high speed than that at normal speed. In addition, increasing the depth and width of the in-filled trench improves the vibration isolation effectiveness under moving train load.

Qiwei Zhang, Guangyun Gao, Jian Song

Computation Model for Structure-Borne Noise from Railway Bridge with CLD

With the increase of running speed and axel load of trains, the structure-borne noise emanating from the railway bridges is more and more serious. The constrained layer damping can achieve an obvious reduction of vibration and noise of the treated structure in a wide frequency range by means of dissipating the vibration energy owing to damping layer’s shear deformation. Based on the train-track-bridge coupled vibration, modal strain energy method and statistical energy analysis, a theoretical model for calculating the vehicle-induced vibration and noise of the railway bridge with constrained layer damping is presented. The vibration and noise of the (32 + 40 + 32) m steel-concrete composite bridge before and after constrained layer damping installation is simulated. The structure-borne noise radiated by the bridge in the whole analysis frequency range is reduced significantly. The sound pressure level at the field point which is 30 m to the track centerline in horizontal direction and 1.5 m to the ground in vertical direction is reduced by 4.3 dB(A).

Quanmin Liu, Xiaozhen Li, Xun Zhang

Comparison of Crane Induced Vibration on Steel Structural Levels in High-Tech Factories Using FEA and Experiments

A finite element model was developed to simulate the crane induced vibration on the steel structural levels of high-tech factories, in which the mesh includes two-node beam elements to simulate building members and rails, four-node plate elements to simulate building floors, spring-damper and moving wheel elements to simulate the crane. In addition, the rail irregularities, which is the major vibration source for moving cranes, were also included in the finite element analysis. The finite element results were then compared with the experimental measurements to investigate the accuracy of the numerical model, and the comparison result indicates a good agreement. Thus, it is helpful to perform parametric studies using this correct finite element model to understand the behavior of vibration induced by the crane moving on the high-tech factory.

S. H. Ju, H. H. Kuo, S. W. Yu

The Analysis of Unsaturated Ground Vibration Induced by Train Loading by 2.5D FEM

Two kinds of numerical models for unsaturated porous medium are used to simulate the unsaturated ground vibration induced by train loading, to study the influences of saturation on ground vibration and to discuss the differences of the two numerical models. The first numerical model is two phases model that derives from the Biot theory of saturated porous medium and uses modified compression modulus of water to take soil saturation into consideration. The second numerical model is three phases model and is deduced from the mass conservative equations and momentum conservative equations for the solid, water and air. The governor equations of the two kinds of numerical models are transformed into wave number and frequency domain by Fourier transform to adopt 2.5D finite element method (FEM) of solving those numerical models. The train loading and Euler beam dynamic equations for track are also transformed to wave number and frequency domain in 2.5D FEM model. Differences on the vibration frequency and amplitude are observed for the two kinds of model which may contribute to the scattering and reflecting by air in the three phases numerical model. Finally the ground vibration of layered unsaturated subgrade is studied and results show that the vibration at track center is controlled by superstratum. While for ground vibration far away the track the superstratum controls the high frequency spectrum and the subjacent layer effects the low frequency spectrum.

Shaoyi Li

Study of Infiltration into Partially Saturated Clay Soil Railway Embankment

This paper will involve using commercial software Vadose/W to model this process and using a variable flow boundary at the ground surface to represent infiltration by rainfall into partially saturated clay soil railway embankment. To investigate the influence that variations in rainfall and soil water properties, such as the saturated soil permeability, the rate of progression of the wetting front, and the implications this may have for continued slope stability. Suitable parameters and boundary conditions for the FEA model has been assumed base on the currently existing field data. Further improvements of currently existing railway embankments will be suggested to decrease the probability of slope failure caused by the rainfall infiltration of into partially saturated soil railway embankment.

Taifeng Li, Qianli Zhang, Degou Cai, Jianping Yao, Feng Chen

Experimental and Numerical Study on Structural Vibration Response of Buildings Along the Subway Tunnel

With the development of urban rail transit, people pay much more attention to the vibration of building along subway lines. The vibration of subway lines not only affects people’s normal life, but also has a lot of damage on the building structure. Doing lots of research on the vibration response of buildings is significant to vibration control. In this paper, a set of field tests measuring the vertical vibration of tunnel wall and each floor of a three-story building along the subway line were carried out to analyze different vibration responses of tunnel wall and surrounding building with two kinds of stiffness fastener in the tunnel. In order to explore influences of varies of factors on vibration of vicinity buildings around the subway lines, this article has established a multi body dynamics model of vehicle-track and a 3-D FEM model of tunnel-soil-structure by ANSYS. On the basis of verifying the validity of the model, the vertical vibration of each floor under different train speed and fastener stiffness can be calculated. It can be concluded that the vertical vibration would be reduced with the decrease of fastener stiffness and the increase of train speed.

Tianqi Zhang, Yanyun Luo, Yan Liu, Qiutong Li, Jingzhi Liu

Evaluation of Liquefaction Potential of Saturated Sands Based on Resistivity Piezocone Penetration Testing—A Case Study

The liquefaction of saturated soils is a major concern for the earthquake damage of foundation. Due to the difficulty and cost constraint in obtaining high-quality undisturbed samples, in situ testing is commonly applied to evaluating the potential of soil liquefaction. At present, numerous methods based on the cone penetration test (CPT) have been developed, but none of them has been accepted to be the most reliable one. In high risk projects, a comprehensive evaluation based on various methods is usually adopted, and thus the research on new method to evaluate the liquefaction is still necessary. In this research the feasibility of using resistivity piezocone penetration test (RCPTU) for predicting liquefaction resistance is investigated. The resistivity of saturated silts and sands is measured using RCPTU at a test section of Suqian-Xinyi expressway. The study on combination of resistivity and soil behavior type index to directly calculate the cycle resistance ratio (CRR) is conducted with the CRR from Robertson modified liquefaction evaluation model as reference. The state parameter (Ψ) to directly calculate the cycle resistance ratio (CRR) is also analyzed. It is shown that the resistivity and soil behavior type index and the in situ state parameter (Ψ) are two good methods that used for effective evaluation of liquefaction potential of saturated soils.

Wei Duan, Guojun Cai, Haifeng Zou, Songyu Liu

Research on Computational Model of Large-Span Flexible Structures for Serviceability Assessment

Vibration serviceability of large-span flexible structures has been intensively investigated in last decades but still needs more effort. In this paper, we put a special concern on the computational model of large-span flexible structures for serviceability assessment based on experimental results of two large-span railway stations at different construction stages. The differences between the model for serviceability and the model for safety are clarified and the main influential factors that a computational model for vibration serviceability should consider are presented. Furthermore, the damping for serviceability is discussed based on laboratory test of a cantilever beam.

Wei He, Weiping Xie

Quantify the Size and Shape of Aggregate Particles Based on the Double Mirror Method

Particle size distribution and shape properties are known to significantly influence the mechanical properties, e.g. strength, permanent deformation and packing density, of aggregates. Image analysis is a more efficient and accurate approach to quantify the particle size and shape compared with the manual test. This paper introduces a double mirror method to obtain five views of an object, thus various size and shape properties, such as size, volume, flat and elongation ratio, sphericity, convexity, roundness and angularity index, are determined from these five silhouettes. The method has been tested in two different aggregate samples in the laboratory. The test results show that by using this method, the size and volume results are very close to manual measurements. Furthermore, the interrelationships of various particle shape properties, i.e. sphericity, convexity, roundness, flat and elongation ratio and angularity index, are investigated.

Wei Li, Huahan Chen, Zhangbo Wan, Xuecheng Bian

Study on Metro Environmental Vibration Influence and Vibration Isolation Effect of Isolation Trench

With the deepening of the urbanization process and the formation of the rail transit network, excessive vibration issues inside buildings caused by the urban rail transit operation increased. Vibration propagation isolation is one of the effective control measures for the over-standard vibration of nearby buildings. By the means of in situ test and analysis on Qingdao Jiayuan residential area, which near the Beijing Metro Daxing Line, the main reason of sensitive building vibration isolation caused by the metro is investigated. Then a three-dimensional dynamics simulation model is established, and the influence of isolation trench filling material on vibration reduction is analyzed. At last the rationalization proposal of vibration isolation measures is proposed to provide a reference for similar situation.

Wenbin Wang

Effects of One Weak Interlayer on Seismic Response of Municipal Solid Waste Landfill

Weak interlayers often exist in the municipal solid waste (MSW) landfills due to the dumping of urban sewage sludge with MSW and the use of soil covers, which have significant influences on the seismic response of landfills. Forty one dimensional (1D) landfill profile models subjected to different ground motion inputs and one weak interlayer with various depths and thicknesses in the MSW body were developed, and 1D frequency independent equivalent-linear method was used to explore the influences of the depth and thickness of one weak interlayer on the dynamic behavior of landfills. Considering the variation of unit weight and shear wave velocity of MSW with the buried depth, and selecting the rational dynamic parameters of MSW and soils, the horizontal acceleration and equivalent shear strain were calculated by the direct stiffness method of EDT (Elastodynamics Toolbox for MATLAB) software. The results showed the maximum value of horizontal acceleration happens about 10 m below of the weak interlayer. And the weak interlayer’s influence on the maximum horizontal acceleration of MSW body declines after it reaches a critical thickness. In addition to that, the equivalent shear strain at the weak interlayer decreases with the increase of weak interlayer’s thickness, and hence thin weak interlayers in the MSW body should be avoided.

Wu Gao, Xuecheng Bian, Yunmin Chen

Applications of Optical Fiber Sensing Technology in Monitoring of Geotechnical Structures

The geotechnical structures will be inevitably suffered from material degradation and structural performance deterioration during the in-service operation stage. In order to acquire the on-line structural responses of each phase at the structural whole life-cycle (construction, operation, reinforcement, and rehabilitation), the structural health monitoring (SHM) systems based on the optical fiber sensing technology have been broadly implemented on a variety of geotechnical structures. The optical fiber sensors have received great concerns and been widely used in long-term geotechnical engineering monitoring due to their inherent advantages such as small size, light weight, immunity to electromagnetic interference (EMI) and corrosion, and embedding capability. Various monitoring purposes make optical fiber sensors get great advances in the manufacture and installation techniques as well as the analytical methods and theories. In this paper, the sensing principles of different types of optical fiber sensors are introduced. The applications of optical fiber sensing technology in different fields of geotechnical engineering are presented. The feasibility, reliability and effectiveness of optical fiber sensors in structural monitoring applications through laboratory tests and field experiments are described.

X. W. Ye, T. Liu, Dan-Feng Zhang, Jun Li, Zhi-Feng Liu, Liang Zhang

Dynamic Interaction of Vehicle-Track Coupled System Under Different Patterns of Uneven Settlement

Ballastless track is wildly employed in high-speed railways as its high stability, low irregularity and low maintain cost. However, uneven settlement at the roadbed will impact the railway’s stability, passenger’s comfort and service life of the track. Amount of models are established to investigate the vibration under uneven settlement and suggest the control standard. However, their simplification about the interaction in settlement zone are unreasonable in some cases. In this research, a vertical vehicle-track coupled model is introduced, in which the vehicle is modeled as multi-rigid body and the track is modeled as multilayer plane beams. The model is validated by track vibration measured in Beijing-Tianjin Intercity Passenger Line. To simulate the vehicle-track interaction under uneven settlement accurately, the settlement is divided into three patterns. In contact pattern, the displacement of track-subgrade interface is assumed to be continuous in settlement zone, while in contact pattern the displacement is assumed to be discontinuous. And in partial contact model, the track-subgrade interface is consider to be partial contact in settlement zone and a proposed trail-iterate algorithm is adopted to correct the contact area and the contact force in each integral step during the calculation. Based on proposed model, the dynamic response in three patterns are introduced. Result shows that the conventional model will obviously overrate the dynamic responses when the settlement is in the scope of partial contact pattern and gapped pattern.

Xiang Duan, Jing Hu, Xuecheng Bian, Jianqun Jiang

Experimental Study of Ground Vibrations Induced by HST on an Embankment Section

As a safer and faster means of transportation, the high speed railway grows rapidly around the world. However, the vibrations generated by high speed train (HST) draw more and more attentions from the researchers. Moreover, the experimental investigations of HST induced ground vibrations simultaneously in three directions are rare. So, this paper studies the vertical, perpendicular and parallel ground vibrations on the Beijing-Shanghai high-speed railway through the field experiment. The characteristics of ground vibration accelerations in both time and frequency domains are then analyzed. Moreover, a further discussion about the results is presented. The results show that the vibration rules in three directions are similar. The vibration amplitudes of the surrounding ground attenuate with the distance from the track centerline. And an amplify zone of ground vibration is clearly observed at about 24 m from the center of the lines. The main vibration frequency is at the range from 20 to 50 Hz.

XiaoLei Zhang, ShiJin Feng, HongXin Chen, Lei Wang

Laboratory Measurements of the Dynamic Properties of Shanghai Clay

It is well agreed that the dynamic properties including the dynamic shear modulus and damping ratio play essential role in many dynamic geotechnical problems. In this paper, the dynamic properties of the typical Shanghai clay were determined by resonant column tests on 38 undisturbed samples obtained from 9 site investigations in Shanghai. The results showed that the dynamic small strain shear modulus G0 of the soil significantly depends on the void ratio and the effective confining pressure. Meanwhile, the ratio of shear modulus at a certain shear strain level to the small strain shear modulus G/G0 (i.e. modulus reduction curve) decreases and the damping ratio increases continuously as the shear strain increases, indicating the nonlinear behavior of clay under dynamic loading. Meanwhile, the modulus reduction curve and the damping curve are generally independent of the void ratio and the effective stress. Empirical equations were provided to predict the small strain shear modulus, the modulus reduction curve and damping ratio of Shanghai clay in practical engineering.

Xiaoqiang Gu, Lutong Lu, Jun Yang, Xiaofeng Wu

Research on Seismic Response Calculation Method for Rocking Column

Damage investigation showed that the rocking column structures, such as stone pillars and Petroleum cracking towers, are easier rock, even collapse, under big earthquake. Focusing on this type of rocking column structure, their seismic responses are analyzed, in which the soil-structure interaction is considered by contact elements. And the results of the calculation and shaking table test results were compared and analyzed. Research results showed that: (1) The frequency characteristics of the model established in this paper are consistent with the experimental data, which can be used for the subsequent transient analysis; (2) Although the calculation results in amplitude is slightly different with the test results, seismic response rules between calculated results and the experimental results are consistent each other z1on the whole, which indicates that the calculation method used in this paper is reasonable. The research results in the paper can provide some references for seismic design of rocking column structure.

Xin Zhou, Jun Hu, Guobo Wang

Effect of the Treated Soft Soil Thickness on the Settlement Characteristic of Overlapping Embankment

Many transport facilities are needed reconstruction and extension nowadays to meet the growing traffic demand. However, differential settlement between the new and old embankment may arise the pavement cracking or even damage for the newly filled embankment without reasonable control measures. In order to provide information for reducing settlement between new and old embankment, the settlement characteristic of overlapping embankment was investigated in this study. Based on a case history in practice, numerical analyses were carried out in this paper. Effect of soft soil thickness on the overall and differential settlement of overlapping embankment was analyzed. It can be obtained that the influence of treated soft soil thickness on the differential settlement of the banding embankment can be divided into three intervals. When the treated soft soil thickness is less than h1 = 2 m, the differential settlement varied very small with the thickness. When the treated thickness increased from h1 = 2 m to h2 = 5 m, the differential settlement increased significantly with the thickness. And when the treated thickness is greater than h2 = 5 m, both the differential and overall settlement of overlapping embankment are no longer increased significantly. The depth of the treated soft soil can be appropriately deeper than h2 = 5 m, and there is no need for deeper soft soil treatment. The investigation may provide the basis and reference for the differential settlement control of the overlapping embankment for similar cases.

Yun Dong, Huasheng Sun

Structure Noise Test of Rail Transit Box Beam and the Assessment of Environment Impacts

The harm to health can not be ignored which is caused by vibration of rail transit box beam under dynamic action of the train and by quadratic noise therein. This paper takes 32 m double concrete simply-supported box beam as the research object, compares the result of boundary element simulation and the measured data, and employs Japan’s low frequency noise limit curve to assess environmental impacts. The research indicates that the noise of the rail transit box beam ranges within 20–60 Hz. The low-order local vibration of the structure around the center frequency of 20 Hz is prone to being inspired and it causes peak value of noise radiation of box beam structure. It would be more effective to conduct noise-reducing process if the frequency of noise peak is given priority.

Yan Zhang

Soil Arching Effect in Piled Embankments Under Moving Shakedown Limit Loads

Most research conducted so far has investigated the behavior of soil arching in piled embankment under static loads, knowledge on their dynamic behaviors under transient loads of moving vehicles is rather limited in the literature, and therefore it deserves more research attention. This paper presented an investigation of the soil arching effect in the piled embankment under shakedown limit loads. A 3D FE model combined with Melan’s lower-bound shakedown theorem is firstly presented, in which the shakedown limits were calculated as the minimum shakedown multiplier among all layers of the piled embankment by means of a self-equilibrated critical residual stress field. It showed that the shakedown limit loads decreased with the increase of the frictional coefficient, which decreases by approximately 77% when increasing μ from 0.2 to 1.0. The shakedown limit loads for the condition of μ = 0 were then applied onto the surface of pavement as the external traffic loads, which moved at a speed of 60 km/h for 40 cycles. The settlement at the surface of the pavement was found to increase gradually within the first a few load cycles, and then approaches to approximately a steady value, indicating that the piled embankment in a shakedown status. Finally, the soil arching effect under the moving shakedown limit loads was investigated in terms of the settlement profile, vertical stress and earth pressure coefficient both under static and dynamic loads. It showed that the soil arching effect remained existed, while was significantly reduced under the shakedown limit loads.

Yan Zhuang, Kangyu Wang

Numerical Calculation of Reducing Negative Shaft Resistance of Group Piles with Asphalt Coats

In this paper, the finite difference software FLAC3D is used to simulate the reduction effect of asphalt coat pouring on piles of a bridge. The numerical simulation uses contact parameters to simulate the interaction of the coat between piles and soil. In several cases stack loads, distribution of axial forces along piles and settlements on the caps of piles are computed. The action of asphalt to reduce the negative shaft resistance is analyzed. The results show that the finite difference software FLAC3D can be used to simulate negative shaft resistance of group piles and reducing action of asphalt coats. Asphalts coats of group piles play roles of obviously covered curtain. The neutral point position of the corner pile is the lowest and the range of negative shaft resistances is the largest. The neutral point position of the center pile is the highest and the negative shaft resistance range of it is the least. These results answer to the practice engineering rules. This paper concludes that as stack loads increase, the neutral point position gradually moves downwards. The larger stack loads are, the more obvious reducing effect of negative shaft resistances and settlements on the caps of piles are. The conclusions offer guidance to the design and calculation of group piles.

Yanfen Wang, Yuangang Ma, Caojiong Lv

Performance of Conductive Plastic Vertical Drainage Board Under Vacuum Preloading Combined with Electro-osmotic Consolidation

The electro-osmosis consolidation method is efficient to drain water out of soft clay subgrade, but the corrosion of traditional metal electrode restricted its application. With the innovation of the composite conductive material, the conductive plastic was made into prefabricated electric vertical drainage (e-PVD) board to avoid electrode corrosion. The drainage ability from the top and bottom of the e-PVD board was analyzed. Furthermore, the performance of the e-PVD board among the vacuum preloading method (V-P), the vacuum preloading combined with electro-osmosis method (V-E) and the cathode straight drainage method (C-S) was contrasted. The results showed that the top drainage method (T-D) was preceding the bottom drainage method (B-D) in several aspects with the usage of e-PVD board. The discharge of soil treatment using V-E method was the largest, and the potential was the most stable, the shear strength and the settlement were both the largest. Moreover, the discharge of the C-S method was larger than V-E method in the initial eight hours. At a certain time, the C-S method can improve the mutual inhibition of the vacuum preloading and electro-osmosis at the anode in the traditional V-E method. The combination of the C-S method and V-E method can further increase the total discharge.

Yang Shen, Chenchen Qiu, Yande Li, Yanfeng You

Stiffness Degradation and Deformation Characteristics of Soft Clay Foundation Under the Train Loads

The hollow cylinder apparatus was used to simulate the stress paths induced in traffic-affected ground, a series of undrained shear tests were carried out. The inflection points on generalized shear strain curves were used to establish a damage criterion, which distinguished different damage characteristics under different stress levels. And the different deformation models can be concluded into three categories which are stable, critical, and destructive, respectively. Groups of tests were carried out to understand the effect of different initial deviator stress on soil shear stiffness, and analyze the variation of shear modulus with vibration times under different dynamic stress ratios. It is found that when dynamic stress level is low, the amplitude ratio a has little effect on the shear stiffness. When dynamic stress ratio level is high, for critical models, the rate of stiffness degradation increases with the increases of amplitude ratio a; for destructive models, the initial shear modulus increases with the increase of amplitude ratio a, soil structure is damaged, its stiffness degrades obviously with increase of vibrations. A prediction model was established for investigating the stiffness degradation pattern when initial deviator stress equals to zero, which provides theoretical supports for the future research on bearing capacity of soft clay foundations that are suffering from repetitive traffic loads.

Yang Shen, Wenhan Du, Baoguang Wang, Mingan Tao

Experimental Study on Bending-Torsional Coupled Modal Identification of Wide Viaduct

With the rapid development of urban traffic, the viaducts which have the advantage of covering smaller area and three-dimensional traffic capacity have become arteries for urban traffic. Due to the increasing width of the bridge deck, the problem of bending-torsional coupled vibration raised concern. In order to analysis the bending-torsional coupled mode, firstly a box girder finite element numerical example is applied to verify that the stochastic subspace identification method based on ambient vibration can effectively identify the bending-torsional coupled mode of the structure. At the same time it proves that the efficiency of the two ways, using lateral and vertical responses to identify parameters together or separately, is consistent. Then experimental modal identification is conducted on a viaduct, using separate identification method based on stochastic subspace identification. The results show that the bending-torsional coupled mode cannot be ignored for this kind of wide viaduct, which is referential for model updating and dynamic analysis.

Yanwu Fang, Weiping Xie, Chao Zhang, Liangming Sun

Lateral Ground Displacement Induced by EPB Tunneling in Ningbo Soft Clay

Ningbo is located in the east China coast where the soft clay is widely distributed, series of problems were encountered when the subways were constructed. The ground movements caused by the EPB (Earth Pressure Balanced) tunneling is one of the problems that do great damage to the structure adjacent to the tunnel. In order to better understand the performance of the EPB tunneling, a comprehensive monitoring section was installed and a lot of field tests were undertaken, and further the data were analyzed with the construction process. It was demonstrated by the results that with the EPB shield moving closer, reaching and leaving from the monitoring section, the soil would move outward, then inward and finally be steady. When the cutter face reached the monitoring section, the maximum lateral displacement 44 mm occurred in inclinometer tube 7 that is 4.5 m far away from the tunnel axis. The farther the inclinometer tube was from the tunnel, the smaller lateral displacement the soil had. In addition, the grouting was an important factor, therefore the grouting parameters including pressure, volume and opportunity must be handled and controlled cautiously. Finally, the disturbance boundary was predicted about 9 m far away from the tunnel axis, that was nearly 3 times of the tunnel radius. The study may help construction companies, designers, supervisors and other relevant researchers to understand the effect induced by EPB tunneling in Ningbo soft clay more clearly.

Yaohong Zhu, Fei Gao, Junneng Ye, Xuecheng Bian, Weian Lin, Yunmin Chen

Application of Distributed Optical Fiber Sensors for Monitoring Pavement Settlement

This paper presents a novel beam (namely large-settlement beam) applied for monitoring large settlement underground based on fiber Bragg grating (FBG) and Brillouin optical time domain analysis (BOTDA), which were primarily mounted on the beam surface for strain measurement. Calibration test was performed to validate the performance of the beam for monitoring large deflection (settlement) under a load/unload cycle. Strain data collected from FBG and BOTDA sensors agree fairly well under this load/unload cycle and the corresponding deflection calculated using finite difference method are in good agreement with measured data from Linear Variable Differential Transformers (LVDTs). The relative errors occurred during loading and unloading processes were also found to be maintained within a limited range. The errors occurred during unload process were slightly higher than that in loading process, this phenomenon is possibly attributed to the unrecoverable plastic deformation when large deflection occurs. The maximum deflection achieved in present test was around 110 mm so that the large-settlement is expect to be embedded as a settlement sensor under pavements, foundations, and dams for monitoring possible excessive settlement.

Yifan Zhang, Chengyu Hong, Yawen Zhang, Rafique Ahmed

Numerical Model of Widen Construct of Geogrid-Reinforced Pile-Supported Railway Embankment

Established a 3D detailed model to understand the loading features and deformation behavior of the geogrid-reinforced pile-supported (GRPS) high-speed railway embankment under the situations of normal service and widen construct. According to the model results, the embankment is distinguished into three areas: Coverage Area, Slope Area and Extent Area. In the Coverage Area, the topline of the embankment settles indifferently. While the settlement is obviously heavy, the lateral deformation initiates linearly. In the Slope Area, the settlement decreases rapidly and the lateral deformation reaches the maximum which strongly affect the bearing capacity of piles. The load produced by the mound during the construction of widen couples with the bended piles leading to further reduce of the bearing capacity. In the Extent Area, the settlement of the embankment fades away and there is nearly no tension but the piles bend causing the retreat of the bearing capacity. In order to control the lateral deformation of GRPS embankment, it should be ensured enough piles.

Yinan Wang, Xuecheng Bian

Effects of Inhomogeneous Subgrade Settlement to Aircraft Vibration and Its Control Standard

The runway in mountainous areas usually passes across different geological unit and has the form of filled and excavated subgrade. It is of great significance to study the effect of the runway settlement to aircraft vibration. An airplane taxiing model of six degree of freedom which can consider the effect of aerodynamic lift was established to research the influence of settlement amplitude, wavelength and taxiing velocity to aircraft vibration under typical settlement model of inhomogeneous subgrade. The results show that the impact coefficient for posterior main landing gear tire force and root mean square of weighed centroid acceleration increase linearly with the increase of settlement amplitude. Both values have the increasing tendency with the taxiing velocity increasing or the wavelength decreasing. Based on security and passenger comfort, the settlement control standard for inhomogeneous subgrade was proposed. The calculated results can have a positive significance to the settlement control or maintenance of runway in mountainous areas.

Yun Zhao, Daosheng Ling, Bo Huang

Experimental Study on Temperature Characteristics of CRTS I Twin-Block Ballastless Track

Ballastless track is a composite structure made of reinforced concrete materials, whose temperature characteristics can be easily influenced by ambient factors (air temperature and solar radiation). Based on an on-site test in Chengdu, temperature of track superstructure, air temperature and solar radiation intensity are obtained for CRTS I twin-block ballastless track. The relationship between ambient factors and temperature of track superstructure was conduct by the method of statistical analysis, the results show that temperature of track slab, and base plate, air temperature and solar radiation intensity all show a periodical change with the day. The average maximum difference between track slab’s temperature and air temperature is within 6 ℃, and the average difference between maximum and minimum temperature of base plate is only 1.34 ℃. The temperature gradient of track slab also shows a periodical change with the day. The maximum positive and negative temperature gradient of track slab are 92.12 and −28.55 ℃/m, and the average maximum of positive and negative temperature gradient are 50.58 and −14.56 ℃/m.

Zhangbo Wan, Rongshan Yang

Experimental Study on Subway Nearby Building’s Base Isolation by Sandbag Piles

Taking a subway nearby 5-story reinforced frame structure as a prototype, a 1/8 scaled model of building was established in laboratory to study the isolation performance of sandbag piles on subway-induced vertical and horizontal vibration inside buildings. The feasibility and effectiveness of human comfort inside the building model was verified. Testing results showed that: (1) the vertical stiffness of sandbag piles was much smaller than the upper structure, so the base isolation method by sandbag piles greatly improved the vertical human comfort; (2) the more layers the sandbag piles have, the better the vertical human comfort inside the building model can be; (3) due to low horizontal stiffness and large damping ratio of sandbag piles, the effectiveness on controlling subway-induced horizontal vibration in the building model was significant. By the design of similarity ratio for scaled model, It is proved that sandbag piles are feasible applied to increase the vertical and horizontal human comfort of subway nearby buildings.

Zheng Tao, Tao Sheng, Shanshan Hou, Yongjiang Guo, Jianchao Wang, Qiaoting Chen, Hongliang Jin

A Frequency Domain Solution to Vehicle Induced Vibration of Railway Bridges

The vibration of railway bridges excited by passing vehicles was traditionally assessed through the time domain simulation using vehicle–bridge dynamics interaction theory. In this paper, a frequency domain solution to the responses of the railway bridge was derived, where a series of hunting forces was taken as the external excitations. Three spectrums were defined in the frequency domain analysis. The unit modal spectrum is the Fourier transform of the mode shape of the bridge deck; the shifted modal spectrum is the result of shifting the unit modal spectrum by the hunting frequency; and the load sequence spectrum reflects the effect of truck arrangement in a train on the modal load of the bridge. The response spectrum of the bridge was found to be the product of shifted modal spectrum, load sequence spectrum and square of the bridge’s frequency response function. The lateral vibration of a rigid frame with two spans excited by passing hunting forces was analyzed using the proposed method.

Zhibin Jin, Shiling Pei, Yan Zhu, Xiaozhen Li

Dynamic Stability Analysis of Embankment Along the Qinghai-Tibet Railroad in Permafrost Regions

This paper firstly gives a introduction of real-time strong-motion observation tests which are carried out in a permafrost region of the Beilu River segment along the Qinghai-Tibet Railway, the real-time acceleration data at different part of embankment are collected when trains passing. The experiment shows that there is an obvious attenuation effect during the waveform transfer process from the shoulder to the slope toe. Based on the site test results, two different kinds of embankment are set up, which is a crushed-rock embankment and another is a plain-fill embankment. Then the field test data and dynamic finite element analysis method of two dimensions linearly equivalent were used to analyze the characteristics of dynamic transmission and displacement response of both types of embankments bearing the load of a train. The numerical results showed that vibration acceleration was decreased through the crushed-rock layer, which could improve the stability of the embankment construction. Also, the vibration settlement caused by train loading was decreased obviously in the crushed-rock layer, in which the maximum settlement displacement was only 0.81 mm, while that of the plain-fill embankment reached 1.87 mm. Moreover, the influences from underlying active layer on the dynamic stability of the plain-fill embankment at different seasons were analyzed. The amount of deformation at the same location in summertime is far more than that in wintertime.

Zhijian Wu, Wei Ma, Tuo Chen, Lili Wang

Numerical Investigation on Ground Vibrations Induced by High-Speed Train and Its Mitigation

In order to analyze the characteristic of environment vibration of ground during passages of train moving loads, study the influence of vibration to human body, a theoretical model of track-ground was presented by employing the 2.5-dimensional finite element numerical method, three different vibration isolation measures were set up in the model. ISO2631 was applied to evaluate the vibration of ground near or far from the track, without wave barriers or with them. At last, the optimization suggestions for geometric and physical parameters of wave barriers were raised.

Zhixiang Sun, Xuecheng Bian, Yunmin Chen

Effect of Metro Excavation on Soft Clay’s Displacement and Strength Behaviors Based on In-situ Tests

The excavations will affect the soil’s stress, which leads to the change of undrained shear strength in soil, thus posing an adverse influence on the service life of foundation-pit. To investigate the soil deformation and the strength, a metro excavations on-site test was carried out on the soft clay areas in Ningbo. And it is discovered that the influenced area of the excavations on the surrounding environment is 1.8 times of the excavation depth. Within the influenced area, the soil deformation grows greater as it approaches the diaphragm wall. And the maximum ratio of the deformation value to the excavation depth is 0.48%. While the damages to the vane shear strength become more significant as it approaches the diaphragm wall. And around the maximum soil deformation, the damages to soil structure and the strength are the most serious.

Zhuofeng Li, Junneng Ye, Weian Lin, Xuecheng Bian, Yunmin Chen

An Implicit-Explicit Transition Method for Settlement Prediction of High-Speed Railway Subgrade Under High-Cycle Load

The long-term settlement of high speed railway subgrade under high-cycle traffic loads is difficult to be calculated and predicted accurately. The implicit-explicit transition algorithm is an effective way to solve this problem, but the applicability of the proposed method is still to be verified, and there is room for improvement. In this paper, a boundary surface model is used as the constitutive model for the implicit computation. In the stage of explicit calculation, an improved empirical formula is proposed by synthesizing the correction index model and HCA model. And the implicit-explicit transition calculation process is realized through secondary development method in the finite element platform. On the basis of this, parameters of loading history and number of load steps are introduced, which can improve the accuracy of the calculation results. Through the simulation of a section of Shanghai Nanjing Intercity High Speed Railway, the predicted value is in good agreement with the measured data.

Zongqi Bi, Quanmei Gong, Zhuang Kang, Liushan Wang
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