High-speed Railway Subgrade Research Articles

A full-section asphalt concrete waterproof sealing structure for the high-speed railway subgrade

PurposeThis study aims to investigate the service performances of a new full-section asphalt concrete waterproof sealing structure (FSACWSS) for the high-speed railway subgrade through on-site tracking, monitoring and post-construction investigation.Design/methodology/approachBased on the working state of the waterproof sealing structure, the main functional characteristics were analyzed, and a kind of roller-compacted high elastic modulus asphalt concrete (HEMAC) was designed and evaluated by several groups of laboratory tests. It is applied to an engineering test section, and the long-term performance monitoring and subgrade dynamic performance testing system were installed to track and monitor working performances of the test section and the adjacent contrast section with fiber-reinforced concrete.FindingsResults show that both the dynamic performance of the track structure and the subgrade in the test section meet the requirements of the specification limits. The water content in the subgrade of the test section is maintained at 8–18%, which is less affected by the weather. However, the water content in the subgrade bed of the contrast section is 10–35%, which fluctuates significantly with the weather. The heat absorption effect of asphalt concrete in the test section makes the temperature of the subgrade at the shoulder larger than that in the contrastive section. The monitoring value of the subgrade vertical deformation in the test section is slightly larger than that in the contrastive section, but all of them meet the limit requirements. The asphalt concrete in the test section is in good contact with the base, and there are no diseases such as looseness or spalling. Only a number of cracks are found at the joints of the base plates. However, there are more longitudinal and lateral cracks in the contrastive section, which seriously affects the waterproof and sealing effects. Besides, the asphalt concrete is easier to repair, featuring good maintainability.Originality/valueThis research can provide a basis for popularization and application of the asphalt concrete waterproof sealing structure in high-speed railways.

Performance of High Speed Railway Subgrade Strengthened by Long-Short Piles: Part II—Numerical Modelling

Performance of High Speed Railway Subgrade Strengthened by Long-Short Piles: Part II—Numerical Modelling

Performance of High Speed Railway Subgrade Strengthened by Long-Short Piles—Part I: Experimental Results

Performance of High Speed Railway Subgrade Strengthened by Long-Short Piles—Part I: Experimental Results

A constitutive model for cyclic densification of coarse-grained soil filler for the high-speed railway subgrade considering particle breakage

PurposeThis study aims to propose a semiempirical and semitheoretical cyclic compaction constitutive model of coarse-grained soil filler for the high-speed railway (HSR) subgrade under cyclic load.Design/methodology/approachAccording to the basic framework of critical state soil mechanics and in view of the characteristics of the coarse-grained soil filler for the HSR subgrade to bear the train vibration load repeatedly for a long time, the hyperbolic empirical relationship between particle breakage and plastic work was derived. Considering the influence of cyclic vibration time and stress ratio, the particle breakage correction function of coarse-grained soil filler for the HSR subgrade under cyclic load was proposed. According to the classical theory of plastic mechanics, the shearing dilatation equation of the coarse-grained soil filler for the HSR subgrade considering particle breakage was modified and obtained. A semiempirical and semitheoretical cyclic compaction constitutive model of coarse-grained soil filler for the HSR subgrade under cyclic load was further established. The backward Euler method was used to discretize the constitutive equation, build a numerical algorithm of “elastic prediction and plastic modification” and make a secondary development of the program to solve the cyclic compaction model.FindingsThrough the comparison with the result of laboratory triaxial test under the cyclic loading of coarse-grained soil filler for the HSR subgrade, the accuracy and applicability of the cyclic compaction model were verified. Results show that the model can accurately predict the cumulative deformation characteristics of coarse-grained soil filler for the HSR subgrade under the train vibration loading repeatedly for a long time. It considers the effects of particle breakage and stress ratio, which can be used to calculate and analyze the stress and deformation evolution law of the subgrade structure for HSR.Originality/valueThe research can provide a simple and practical method for calculating deformation of railway under cyclic loading.

Design and Application of High-speed Railway Subgrade Strong and Weak Current Isolation Cable Shaft

Design and Application of High-speed Railway Subgrade Strong and Weak Current Isolation Cable Shaft

Research on Cumulative Deformation Characteristics of Subgrade Filling under Cyclic Train Loading

The smoothness of high-speed railway is extremely strict. As an important part of the high-speed railway foundation, the subgrade structure has strict deformation requirements. It is necessary to ensure that the subgrade structure does not have plastic cumulative deformation under the long-term cyclic load of the train, which is the most critical geodynamic problem in high-speed railway subgrade. This paper studied the cumulative deformation characteristics of subgrade filling under cyclic train loading through the cyclic triaxial test, three types of accumulative plastic deformation trends, and the value of critical volume shear strain was discussed, which would provide the theoretical support for the dynamic design of high-speed railway.

Study on the frost heave behavior of the freezing unsaturated silty clay

The frost heave behavior of unsaturated soils is related to the water-vapor redistribution, whereas the water-vapor migration processes cannot be directly observed due to the limitations of measurement techniques. To reveal the frost heave behavior of the unsaturated silty clay, five specimens for unsaturated silty clay were prepared. One-side freezing tests for the five specimens were carried out under uniform conditions. The test durations are 12 h, 24 h, 48 h, 96 h, and 192 h, respectively, and the water content profiles in the freezing process were studied by testing final water content profile of each specimen as the profile at that time. The heat-water-vapor migration and frost heave behavior of the freezing unsaturated silty clay were interpreted. The results showed that the temperature variations can be divided into three stages (a sharply cooling stage, a slowly cooling stage, and a steady stage) according to the change rate of temperature, and the duration times of the first and the second stage are short. A mix migration of liquid water and water vapor in unsaturated soils can be experimentally determined during the freezing, and a thin ice forms at the top of the specimens due to the vapor migration and condensation. Meanwhile, the liquid water in unfrozen zone mainly migrates to frozen fringe, and segregated ice forms in the freezing unsaturated soil once enough water accumulates at the frozen fringe. In addition, the frost heave of the specimens is discrete under the uniform test conditions. We selected the relative error and absolute error of the frost heave as evaluation indexes, and further evaluated the repeatability of the test results. Evaluation results showed that the one-side freezing test results are repeatable, and it is an useful testing method to study the heat-water-vapor migration through one-side freezing tests with different test durations under uniform testing conditions. Moreover, the confusion that the frost heave mainly occurred in the top layer of high-speed railway subgrade was explicit solved by the behavior revealed in this paper.

Semi-automatic construction of pile-supported subgrade adjacent to existing railway

The rapid expansion of the high-speed railway network in China leads to an increasing number of connections between new constructed infrastructures and existing ones. The construction of the infrastructure extremely adjacent to existing high-speed railways significantly threaten the operation safety of the high-speed trains. To guarantee the operation safety of the existing high-speed railways in this sensitive zone, a developed Benoto pile-plank-supported subgrade and a set of specially designed construction equipment are proposed. A fiber-optical monitoring system for foundation deformation and structural internal forces is employed to provide a data basis for parameterization of the construction equipment. In this way, an integrated semi-automatic construction system is established. The application effect of the construction system is tested in a real construction project of a pile-supported subgrade adjacent to an existing high-speed railway track. In-situ measurement data reveal that the deformation of the existing high-speed railway subgrade can be well controlled.

Dynamic behaviors of coarse granular aggregates in high-speed railway subgrades

With the increase in the running speed and axle load of trains, there has been a greater demand for high-speed railway (HSR) subgrades. Coarse granular aggregates are suitable materials for the HSR subgrade filler. Hence, the study of the dynamic characteristics of coarse granular aggregates is important for the safe operation of trains. In this study, a dynamic triaxial test apparatus was used to investigate the dynamic features of these aggregates under different dynamic amplitudes, confining pressures, fine particle contents, and water contents. The characteristics of the hysteresis loops, dynamic resilient modulus, and cumulative plastic strain during the cyclic loading of the soil were studied. The results illustrate that the hysteresis loop becomes more compact with an increase in the dynamic stress amplitude. The changing law of the dynamic resilient modulus depends on factors such as fine particle content, confining pressure, dynamic amplitude, and water content. Meanwhile, the cumulative plastic strain features are influenced by the critical dynamic stress and applied dynamic stress under the corresponding conditions. Based on the experimental results, a prediction model for the cumulative plastic strain considering the stable, critical, and failure types was proposed. Thus, the plastic strain at more loading cycles can be predicted. These results can help in the design of subgrade structures and maintain the daily safe operation of the HSR.

Dynamic Triaxial Test and Microscopic Study of Solidified Muddy Soil With Different Mixing Ratios and Curing Ages

Aiming to explore the optimal mixture ratio and curing age of solidified muddy soil under dynamic load, the paper intends to investigate whether the solidified muddy soil can be used as filling of high-speed railway subgrade. Based on the dynamic triaxial test, the investigation measured the dynamic strain and dynamic elastic modulus of solidified muddy soil under different mix ratios and curing ages, and also observed the microscopic morphology of solidified muddy soil samples by using scanning electron microscope. The results show that the addition of cement and curing agent significantly increases the dynamic strength and elastic modulus of muddy soil, which effectively improve the dynamic characteristics of muddy soil. The curing effect of the curing agent is more obvious with the increase of the dosage of cement and curing agent under different mix ratio. The content of curing agent plays a leading role in the hydration reaction between cement, curing agent and soil particles. Additionally, in case of the same test conditions, when the ratio of cement mass to dry silt mass is 1:20, the ratio of diluent volume to dry silt mass is 1:20, with 28 days of curing age, its curing effect will reach the best.

Experimental study on ring shear properties of fiber-reinforced loess

With poor mechanical properties and engineering characteristics, loess soils alone cannot meet the requirements of high-speed railway subgrade and large-sized building foundations based on shear strength and bearing capacity. Therefore, it is necessary to improve the mechanical properties of loess. In soil reinforcement, encouraging outcomes have been achieved by using fibers as reinforcement material for its relatively low costs and the low environment impact results from this material. To investigate the mechanical properties and the reinforcement mechanism of fiber-reinforced loess, ring shear tests were performed on loess samples with varying polypropylene fiber contents (0%, 0.25%, 0.50%, 0.75%, and 1%) and moisture contents (12%, 14%, 16%, 18%, and 20%). Furthermore, the macroscopic structure and microscopic images of the shear plane of reinforced specimens were analyzed as well. The test results showed that firstly polypropylene fibers significantly improved the peak strength and the residual strength of loess, and the optimal fiber content and the optimal moisture content were found to be 0.5% and 16%, respectively. The theoretical relationships between the fiber content Fc, the moisture content Mc, the peak strength τ, and the residual strength τr of reinforced loess were quantitatively determined. In addition, the fiber reinforcement mechanism was revealed based on the macroscopic shear plane of fiber-reinforced loess and SEM microscopic images of the shear plane.

Long-term uplift of high-speed railway subgrade caused by swelling effect of red-bed mudstone: case study in Southwest China

A high-speed railway must support fast-moving vehicles and have strict low-deformation requirements. However, many high-speed railways encounter the problem of abnormal subgrade deformation caused by expansive rocks. In this study, the Neijiangbei station of the Chengdu-Chongqing high-speed railway in Southwest China, where the subgrade has undergone continuous and stable uplift during the construction and operation periods, was considered as an example. The Jurassic red-bed mudstone widely distributed in this area is a typical expansive rock, and its swelling effect is the main cause behind the uplift of the subgrade. Results of water-absorption tests, disintegration tests, and expansion tests indicate that the red-bed mudstone is characterized by easy disintegration, slow water absorption, and long-term swelling. A decoupling analysis method for the seepage and swelling of red-bed mudstone was proposed to simulate the water infiltration through the fissures and the temporal and spatial changes in the swelling. Using monitoring data, an inversion analysis of the high-speed railway subgrade uplift was conducted, and the subgrade deformation was predicted. The results suggest that the main changed area of the moisture-content field in the rock formation was a small area near the fissure layer. The moisture content of the mudstone increased rapidly in the first few years of infiltration and increased slowly over subsequent decades. Correspondingly, the subgrade uplift increased rapidly in the first few years after excavation owing to the swelling of the mudstone; thereafter, the growth rate decreased, but the subgrade uplift maintained long-term continuous growth for several decades.

Study on control measures of the influence of shallow buried tunnel excavation on the subgrade settlement of high speed railway in operation

A finite element model is established to study the settlement control technology of the ballastless track of high-speed railway under the shield of shallow buried tunnel. In particular, the reinforcement mechanism and construction control technology of the Metro Jet System (MJS) method for horizontal reinforcement under complex geological conditions (medium coarse sand and strong permeable layer) are discussed. The results showed that when the ground is not reinforced, the shield tunnel directly passes through the high-speed railway, and the settlement caused by the construction of the railway gene tunnel directly above the tunnel has greatly exceeded the limit of the settlement control standard. Due to the limitations of site, planning and construction conditions, the horizontal jet grouting pile of MJS construction method is selected as an auxiliary measure through comprehensive comparison. After the completion of the MJS construction, the maximum settlement of the subgrade is 30 mm, and the settlement of the high-speed railway subgrade is about 25 mm.

Liquid water–vapour migration tracing and characteristics of unsaturated coarse-grained soil in high-speed railway subjected to freezing and different load types

Unsaturated coarse-grained soil (CGS) is typically used as fillings in high-speed railway subgrade. Herein, the frozen depth, external water intake, water content distribution, liquid water migration height, and frost-heaving process were investigated in vapour migration and liquid water–vapour migration modes. Liquid water–vapour migration characteristics under gravity, static load, and dynamic load were compared. Vapour migration is dominant in the CGS external water intake; vapour affects the frozen zone of CGS specimens. The frost-heaving duration under dynamic load is longer than under gravity and static load. More attention should be paid to the frost heaving induced by vapour migration.

A deep learning forecasting method for frost heave deformation of high-speed railway subgrade

Deformation of high-speed railway subgrades, due to low temperatures, is a common phenomenon in cold regions. In winter, the uneven frost heave of subgrade soil would cause hazards to train safety. It is therefore necessary to estimate and predict the subgrade properties. Since the variation of frost heave is non-stationary over time, traditional time series analyses have difficulties where complex physical parameters are not available. In this study, we introduce two models based on deep learning technology to predict frost heave deformation of railway subgrade. These include the artificial neural network (ANN) and long-short term memory (LSTM) network, where we used data of four sections to build the ANN and LSTM. The experimental results of the LSTM model provided lower MAE and RMSE with different datasets. The prediction of three deep deformations for the K1959 + 580 and K1962 + 618 section with slight fluctuation in the data and the performance of the ANN with MAE is 0.0090‐–0.0660 and 0.0069‐–0.0201 of the LSTM models. In the K2005 + 948 and K2029 + 829 section, ANN and LSTM estimated the frost heave deformation with MAE of 0.0061‐–0.0681 and 0.0054‐–0.0309 for a more intense fluctuation on the deformation. Our findings suggest that the network topology of the LSTM model with 12 hidden neurons performs best with fewer parameters, with an average RMSE of 0.0210 mm and MAE of 0.0138 for all the training samples, indicating that the deep learning model has high precision in this scenario.

Reliability-based assessment of high-speed railway subgrade defect

In this paper, a dynamic response mapping model of the wheel-rail system is established by using the support vector regression (SVR) method, and the hierarchical safety thresholds of the subgrade void are proposed based on the reliability theory. Firstly, the vehicle-track coupling dynamic model considering the subgrade void is constructed. Secondly, the subgrade void area, the subgrade compaction index K30 and the fastener stiffness are selected as random variables, and the mapping model between these three random parameters and the dynamic response of the wheel-rail system is built by using the orthogonal test and the SVR. The sensitivity analysis is carried out by the range analysis method. Finally, the hierarchical safety thresholds for the subgrade void are proposed. The results show that the subgrade void has the most significant influence on the carbody vertical acceleration, the rail vertical displacement, the vertical displacement and the slab tensile stress. From the range analysis, the subgrade void area has the largest effect on the dynamic response of the wheel-rail system, followed by the fastener stiffness and the subgrade compaction index K30. The recommended safety thresholds for the subgrade void of level I, II and III are 4.01m2, 6.81m2 and 9.79m2, respectively.

Dynamic Response and Stability Analysis of High-Speed Railway Subgrade in Karst Areas

The increase in railway coverage significantly increased the railway mileage in karst areas. However, the fragile ecosystem in karst areas and weak mechanical performance in cavities cause hidden railway safety hazards. Even with the crucial stability and safety of railways in karst areas, there is only limited research conducted on the dynamic response of railway subgrade and the influence of hidden soil holes on the stability under different conditions. In this study, the Guizhou section of the Shanghai–Kunming high-speed railway was chosen as the research area. On-site monitoring and simulations using ABAQUS were performed to study the dynamic response of the subgrade under the dynamic load of a train. The influence of the soil hole, axle load, and vehicle speed on the dynamic response law and stability of the subgrade were considered based on the model rationality verification. Previous studies have demonstrated the considerable impact of soil holes on the dynamic response characteristics and stability of roadbeds. The ambient vibration frequency of the train was concentrated at 10–60 Hz. Under train load, the amplitude of the dynamic response parameters of each subgrade structural layer increased with the axle load; however, the increase in speed exhibited a greater impact on the vertical dynamic displacement and dynamic stress than on the dynamic acceleration, which affected the stability of the soil hole and roadbed. This study summarized the dynamic response characteristics of subgrade in karst areas under different conditions, thereby providing a design reference for high-speed railways in karst areas.

Research on the swelling mechanism of high-speed railway subgrade and the induced railway heave of ballastless tracks

The ballastless track has been a widely-used track form in high-speed railway (HSR), however, its application is seriously hampered by the railway heave, which is mainly caused by subgrade swelling. In order to identify the mechanism of HSR subgrade swelling and the rules of swelling-induced railway heave response, long-term longitudinal-continuous deformation monitoring and layered deformation monitoring over a heaving-affected site have been carried out. Furthermore, a coarse-grained soil oedometer was applied to explore the correlations between swelling pressure and swelling ratio of the subgrade filler and mudstone foundation to the on-site water content. With the aid of FLAC3D-PFC3D coupled numerical simulation, the influence of different swelling ratios for subgrade filler and mudstone foundation on the railway heave response of a double-block ballastless track under was analyzed. According to the field monitoring results, swelling deformation occurred in both the filler layer and subgrade layer of the heave section, and this combined action within the two layers resulted in railway heave displacement. Laboratory tests indicated that the swelling ratios of the subgrade filler and mudstone foundation under in-situ water content reached 0.205% and 3.325%, respectively. The swelling pressure and swelling ratio in the subgrade filler and mudstone foundation both followed a logistic function relationship with the water content. Numerical results showed that the railway heave amount followed Expassoc and Nelder distribution relationships with the swelling ratios of the subgrade filler and mudstone foundation, respectively. The research results could provide some reference value for the study on the swelling potential of expansive soils and the prediction of railway deformation in railway engineering.

Analysis on Stability of Edge Roadbed in Large Mined-Out Regions Where the High-Speed Railway Pass

At present, the research results on the stability and reinforcement range of the subgrade when the high-speed railway traverses the edge of a large goaf are still scarce. Taking Guinan high-speed railway traversing the edge of the mined-out area of the Dapan well as the research object, high-speed rail load transfer depth and height of goaf impact were analyzed, Researching the stability of high-speed railway subgrade and the reinforcement range of goaf. The results show that Mined-out edge cracks more obvious development, High-speed railway subgrade at the edge of the goaf is more harmful than when located directly above the goaf; On the No.1 well goaf, the overlap zone between the height of the caving fissure zone and the depth of influence of the high-speed railway load appears, but the height of the goaf in the extremely soft rock will extend to the surface; The high-speed railway subgrade is mainly affected by the residual deformation of the gob of the Dapan well. At last, the reasonable reinforcement range is given through the finite element numerical calculation.

Long-term dynamic stability of improved loess subgrade for high-speed railways

Loess material requires improvement before being used as a filler for the bottom layer of the subgrade bed and substructure of a high-speed railway. Currently, cement and lime are often used to improve loess in engineering. However, whether improved loess material and the solution of key problems of the different types of improved loess can meet the long-term dynamic stability requirements of the bottom layer of a high-speed railway subgrade needs further study. Dynamic triaxial tests on cement-improved (CI) and lime-improved (LI) loess specimens were conducted to study the cyclic shear strain threshold and critical dynamic stress and to evaluate the long-term dynamic stability of CI and LI loess as fillers for the bottom layer of a subgrade bed. The results showed that the two improved loess materials can meet the long-term dynamic stability requirements when used as the bottom layer of a high-speed railway subgrade. After comprehensive consideration, 5% cement or 6% lime is recommended, with the CI soil prioritised. Compared with the critical dynamic stress method, the dynamic shear strain evaluation method is a more systematic and comprehensive method for evaluating the long-term dynamic stability of roadbeds. The research results can provide a technical reference for subgrade filler selection and subgrade design in a loess area.