High-speed Railway Embankment Research Articles

Experimental and Numerical Study on Lightweight-Foamed-Concrete-Filled Widened Embankment of High-Speed Railway.

To study the performance of lightweight foamed concrete (LWFC) in widened embankments of high-speed railways, this study first conducted numerous strength, permeability, and water immersion tests to investigate the mechanical properties and water resistance of LWFC with designed dry densities of 550, 600, and 650 kg/m3. Secondly, a field test was performed to analyze the behavior of the deformation and the internal pressure within the LWFC-filled portions. Furthermore, a parametric study via numerical modeling was performed to investigate the effects of four key factors on the performance of the LWFC-filled, widened embankments. Results showed that LWFC possesses adequate bearing capacity and impermeability to meet high-speed railway embankment widening requirements. However, water seepage reduces LWFC strength. The additional pressure from LWFC filling increases initially but then decreases once dehydration occurs. The settlement induced by LWFC accounted for 71% of the total filling height, which is only 37.5% of the total settlement after construction. The parametric study results show that the maximum settlement of widened and existing portions induced by LWFC was 46.3-49.6% and 48.3-53.2% of those induced by traditional fillers due to the LWFC's lower density as well as their better self-supporting ability. Making an appropriate reduction in the thickness of the retain wall installed against the LWFC-filled widened embankment of the high-speed railway generates a few variations in the lateral deformation of the wall. Furthermore, the effects of the pile offset on the deformation of the LWFC-filled embankment were more sensitive compared to the diameter of the piles.

Water accumulation unrelated to ice segregation near the freezing front during soil freezing: Implications for frost heave in high-speed railway embankments and ground ice formation

Investigating water migration in frozen ground is crucial for understanding the hydrothermal dynamics of frozen soil, which is central to frozen soil engineering (e.g., frost heave) and permafrost environments (e.g., ground ice formation). Previous studies have mostly focused on water migration related to ice segregation in frost-susceptible soils, but less on water migration that is independent of ice segregation in non-frost-susceptible soils. Using a novel layer-scanning method based on the nuclear magnetic resonance (NMR) techniques, the water migration dynamic was observed during the freezing of non-frost-susceptible loess under different drainage conditions (with or without water drainage). Results showed an apparent phenomenon of water migration to the freezing front (TFF) (layer L7) (i.e., water accumulation that is independent of ice segregation) occurred in the early freezing stage of non-frost-susceptible soils under no draining water conditions. The traditional water migration mode is related to ice segregation, a new water migration (including upward and downward) mechanism was proposed to reveal this water accumulation unrelated to ice segregation at TFF. The water accumulation at the freezing front is independent of ice segregation, and is attributed to 9% volume expansion due to pore ice formation in the frozen zone, causing water migration downward TFF; while the decrease of the pore volume of the unfrozen zone (being compressed) accounts for the water migration upward TFF. Investigation into whether ice segregation exists and different modes of water migrations (depending on ice segregation or not) will be greatly helpful for exploring the mechanisms of micro frost heave in the high-speed railway embankments and the thick-layered ground ice formation.

The Influence of Asphalt Concrete Underlayment on Slope Stability of the Ballasted High-speed Railways

In recent years, a hot mix asphalt layer, known as an underlayment, has been replacing granular sub-ballast in high-speed and heavy haul tracks, aiming to overcome the limitations of traditional ballasted railways. However, there is a lack of literature regarding the impact of this layer on the slope stability of railway embankments. Ensuring the safety of trains and track availability requires a thorough understanding of embankment slope stability. Hence, this study examined the influence of the underlayment. layer on slope stability in ballasted high-speed railway embankments. Using Slope/W software, twelve embankment models with 2H:1V and 1.5H:1V slopes were analyzed. Half the number of the models were traditional ballasted, while the others incorporated the underlayment layer. Different heights (3, 6, and 8m) were simulated to evaluate the effect on slope stability for both slope levels and track cross-sections. The analysis focused on gravitational force and neglected the increase in pore water pressure. Safety factors for slope slipping surface were used to quantify stability. The findings revealed that the underlayment layer enhances slope stability by 8% to 31% in high-speed railway embankments. However, the degree of improvement decreases with increasing embankment height, and steeper slopes benefit more from the underlayment layer compared to gentler slopes. While these results are promising, further research is needed to investigate the impact of varying pore water pressure on asphaltic tracks.

Long-term freeze–thaw cycle behavior of high-speed railway embankment in frozen soil regions and its effects on train-track dynamic interaction system

The high-speed railway embankment built in cold regions has a long-term freeze–thaw cycle behavior, and the frost heave of soil will inevitably affect the smoothness of the track structure laid on the embankment, resulting in the deterioration of the train running performance and the dynamic behavior of the ballastless track system. This work is motivated by the research to investigate the long-term freeze–thaw behavior of the embankment in frozen soil regions and its effects on the train-track dynamic interaction system. Based on this motivation, the temperature-deformation field model of the embankment and the train-track dynamic interaction model (TTDIM) are established as an integrated model. The additional track irregularity triggered by the frost heave deformation of the embankment is regarded as the excitation source in the TTDIM to achieve the co-analysis of two sub-models. Through an illustrative example, the evolution characteristics of the freeze–thaw cycle behavior of embankment is fully revealed. Moreover, the effects of time-varying frost heave deformation of embankment on the performance of train-track interaction are quantified from the aspect of representative responses and safety evaluation indexes. This paper provides a valuable model and research thought reference for the analysis and assessment of the performance of train-track interaction under the long-term freeze–thaw cycles of the embankment in frozen soil regions.

Dynamic Axle Load Effects on High-speed Railway Embankment: Pore Pressure and Deformation in Varied Subsoils

Dynamic Axle Load Effects on High-speed Railway Embankment: Pore Pressure and Deformation in Varied Subsoils

Integrating life-cycle environmental impact and costs into geotechnical design

Construction and infrastructure projects account for a large share of global greenhouse gas emissions. Included in these projects are geotechnical engineering works, which cause environmental impact and costs throughout their life cycle. In the geotechnical design process, the geotechnical engineer often has design choices where different methods and materials can be used. If assessments of environmental impact and costs were to be integrated into the geotechnical design process, the geotechnical work could be made more sustainable. As a result of this, there is a need for research on integrating the assessments of environmental impact and costs into the geotechnical design process. This paper, therefore, presents a methodology showing how life-cycle assessment and life-cycle cost analysis could be integrated into the geotechnical design process. The presented methodology is then illustrated in a practical example for assessing the climate impact and costs of high-speed railway embankment fill methods.

Experimental and analytical investigation on frost heave characteristics of coarse-grained soils under closed and open systems

Coarse-grained soil is widely used in the seasonal frozen soil region as subgrade filler. However, substantial frost heave has been observed in coarse filler in high-speed railway embankments. To investigate the frost heave characteristics of the coarse-grained soil in a deep seasonal frozen soil zone, indoor tests were carried out under water supply and no water supply conditions. The effect of water, fineness, and temperature on frost heave behavior is studied experimentally. The relationship between the freezing rate and frost heave of coarse-grained soils was analyzed. The results show that the freezing process of the filler can be divided into the rapid cooling stage, phase transition stage, slow freezing stage, and freezing stability stage. In the closed system, the increase of the fine-grained soil does not affect the cooling process, while the moisture content significantly affects the whole process. In the opened system, both the fine-grained soil content and the ambient temperature affect the cooling process. When the ambient temperature decreased from −5°C to −15°C, the duration of the phase transition stage decreased by almost 17 h, whereas when the fine-grained soil content increased from 2.7 to 16%, the duration of the phase transition stage increased by only 5 h. In both opened and closed systems, the development of the frost heave is closely related to the cooling process. Approximately 95% of frost heave occurs during the phase transition stage and slow freezing stage. Frost heave develops most rapidly in the phase transition stage, with approximately 85% of the frost heave amount occurring in this stage.

Soft Soil Behavior Under High-Speed Railway Embankment Loading Using Numerical Modelling

Soft Soil Behavior Under High-Speed Railway Embankment Loading Using Numerical Modelling

Experimental Study on Improvement Effects of Completely Weathered Phyllite Using Red Clay and Cement for High-Speed Railway Embankments

Completely weathered phyllite (CWP) has the characteristics of difficult compaction, low shear strength after compaction and large settlement after construction. The traditional improvement method using a single agent of red clay or cement for CWP satisfies the subgrade requirements for ordinary railway, but cannot meet the requirements of immediate strength and long-term post-construction settlement of high-speed railway at the same time. A series of experimental investigations were undertaken for the blended CWP soils, with three additives used. The first additive was red clay, the second was cement and the third was a combination of both red clay and cement at various portions. Results of consolidation test and shear strength test carried out for the treated CWP soils show that: 1) The effect of cement on improving the compression modulus of CWP is much better than that of red clay; 2) The settlement of an embankment of 10 m high formed by blended soil of CWP with 3% cement can be controlled within 15 mm, while the settlement will be 25.15 mm for the same embankment of blended soil of CWP with 40% red clay; 3) The shear strength and ultimate bearing capacity of CWP improved by red clay are much better than those of 5% cement; 4) The ultimate bearing capacity of CWP improved by 40% red clay is 3.42 times of that by 3% cement and 2.95 times by 5% cement. Furthermore, the bearing capacity of CWP when improved by red clay can meet railway subgrade requirements immediately after compaction, while cement improved CWP needs a curing time of 1 day or longer. This is an impediment to rapid construction process. The improvement mechanism of red clay is mainly filling effect and grading improvement effect, while the improvement mechanism of cement is mainly hardening reaction, which produces high strength material to cement. It is found that 40% red clay and 3% cement treated CWP, which is considered to be optimum, can meet the subgrade requirements of both immediate bearing capacity and long-term post-construction settlement for the high-speed railway.

Structures and Settlement Control of Yujingshan High-Speed Railway Tunnel Crossing Massive Rockfill in a Giant Karst Cave

The Yujingshan high-speed railway tunnel crosses a giant cavern system with a 108 × 104 m3 volume chamber and an 18 km long underground river. The massive project, which lasted three years, was eventually awarded the “Overcoming the Challenges” award by the International Tunneling and Underground Space Association (ITA) in 2020. However, since the cave chamber was filled with large-scale rockfill, structural settlement is a non-negligible problem. This paper presents the unique structures of a bridge supporting railway tracks wrapped by tunnel lining and the settlement control of the Yujingshan tunnel crossing massive rockfill in the giant cave. The geological characteristics and design considerations are systematically introduced. A three-dimensional coupling discrete element method (DEM) and finite difference method (FDM) numerical model and 13 months of long-term settlement monitoring were conducted to evaluate the settlement behavior. The results indicate that the morphology of cavern and internal deposits caused the whole rockfill to migrate to the lower left. The tunnel structure consequently developed a significant inclined settlement. The continuous construction load would increase the settlement value by 31.4%. The bottom reinforcement of steel-pipe pile with grouting could effectively inhibit settlement and differential settlement. Considering the simulation results, the tunnel bottom had greater settlement than the limit standard for high-speed railway embankment, which means this special structure form is reasonable for operation. Meanwhile, the monitoring results show that the tunnel bottom settlement in D3K279+891~D3K279+947 had not performed an apparent convergence trend after 13 months. Further structural monitoring and compensation grouting should be actively considered for operation maintenance.

Evaluating the heating performance of a novel heating two-phase closed thermosyphon (HTPCT) in high-speed railway embankments of seasonally frozen regions

Evaluating the heating performance of a novel heating two-phase closed thermosyphon (HTPCT) in high-speed railway embankments of seasonally frozen regions

Improving the pressuremeter approach for settlement calculation under high-speed railway embankments

Consolidation settlement under embankment is often calculated using the oedometric approach. However, engineers tend to conduct these calculations in clays based on in situ test results including the pressuremeter measurements. The pressuremeter method is based on Menard's rheological coefficient, enabling to shift from the pressuremeter modulus to the oedometric one. This relationship has demonstrated some prominent success when estimating consolidation settlements within a defined stress domain. This paper addresses improvements in this method for settlement calculation in overconsolidated terrain. For this purpose, the authors suggest two expressions for the rheological coefficient based on back-calculation together with a linear and nonlinear multiple regression. The results indicate that using the rheological coefficients proposed in this study gives settlements approximating the measured ones compared to the rheological coefficients reported in the literature. The authors have also established an adjusting coefficient to be introduced as part of the common pressuremeter settlement expression for approximating the measured values on-site.

Coupled hydraulic-mechanical-air simulation of unsaturated railway embankment under rainfall and dynamic train load

Performance evaluation of the embankment subject to climate change and dynamic train loads is important to the safety of high speed railway (HSR). In this study, based on an elasto-plastic unsaturated soil model, a coupled hydraulic-mechanical-air finite element analysis method is proposed, which integrates the analysis under rainfall condition and the analysis under dynamic load in one numerical simulation. A finite element analysis program called DBLEAVES-X is improved from its previous version (DBLEAVES) to consider the hydraulic-mechanical-air coupled behavior in unsaturated soils under dynamic condition. In order to verify the feasibility of the proposed method, a reduced-scale model test was first simulated. The calculating results showed that the measured displacement and acceleration can be well reproduced by the proposed method. Analyses on the effect of rainfall conditions, train loads and embankment materials were then conducted for a full scale prototype model of typical HSR embankment. The results of the analyses show that higher intensity of rainfall infiltration increases the risk of local failure. A higher train speed and heavier train axle load result in larger displacements. The frequency of the acceleration response is only influenced by the train speed. The embankment performance worsens with the degradation of the embankment material. Preceding rainfall condition results in a larger displacement of the track slab after the dynamic load is applied.

Numerical stability analysis of piled embankments reinforced with ground beams

Rigid piles are extensively used to support high-speed railway embankments resting on soft ground, and ground beams are structural elements at ground level to connect adjacent pile caps to improve the stability of pile-supported embankments. In this study, a validated three-dimensional numerical model of piled embankment was developed based on a well-documented centrifuge test, where the Mohr–Coulomb tension crack model was adopted for capturing the brittle failure behavior of concrete piles. The results showed that concrete piles are subject to a serious bending failure within the clay layer when the overlying embankment collapses. By introducing the ground beams in conjunction with rigid piles, the resultant displacement of the improved area was markedly decreased and the pile failure mode was changed. The combination of concrete piles and ground beams results in a synergistic effect. According to the mechanical response of individual piles, the foundation soil was divided into the extension-bending, bending, bending-compression, and compression zones to elucidate the reinforcement mechanism related to ground beams. A proper arrangement of ground beams was ultimately obtained based on the localized slip resistance performance of the improved ground. Overall, this research contributes to the knowledge of piled embankment performance evaluation and may further extend the practical application of ground beams.

Spatial Variation of Ground Vibrations in Ballasted High-Speed Railway Embankments

Transit of high-speed trains in ballasted railway tracks leads to generation and propagation of ground vibrations onto buildings proximate to railway lines through the track embankment and native subsoil. These vibrations amplify through the building structure, causing deformations in the buildings and distress to the residents. The spatial variation of train-induced vibrations in the ballasted railway embankments is characterized for the high-speed train speeds from 160 to 200 km/h. Variation of PPVs in the embankment strata at different speeds, during the transit of train wheels on the track in single and multiple wheel load configurations, are presented. It is ascertained that faster train speeds induce strong ground vibrations in upper embankment strata and slower trains induce large ground vibrations in the strata below track subgrade. The results from the present study also point out that strong vibrations persist in the track embankment, even after a train wheel has traversed a distance of 15 m ahead of a given location in the track. Mitigation of these ground vibrations can avoid potential hazards due to track defects like flying ballasts, hanging sleepers and mud pumping resulting from strong ground motions.

Silt and Clay with Low Liquid Limits as Fill Materials for High-Speed Railway Embankments in China

Silt and clay with low liquid limits do not qualify as fill materials for high-speed railway (HSR) according to Chinese standard {TB, 10001 (2016)}. The present paper proposes using these materials as fillings for HSR embankments in an attempt to reduce the costs of exploiting and transporting qualifying fill materials. Our proposal of using silt and clay with low liquid limits is rooted in German standards {DIN,18196 (2006)} and {Ril, 836(1999)} and Japanese standards {ISBN 13: 9784621046692 (1999)}, and is preliminarily verified by operation experiences of the Zhengzhou–Xi'an HSR as well as other types of projects. On the basis of proven practices, a design cross-section for an HSR embankment constructed in from silt and clay with low liquid limits area is recommended combined with corresponding engineering measures.

Amplification of Vibrations in High-Speed Railway Embankments by Passive Ground Vibration Barriers

The objective of the present study is to characterise the dynamic response of ballasted railway embankments subject to high-speed train loads, for the track conditions with and without inclusions of geofoam in-filled trenches next to the embankments for passive isolation of ground vibrations. Full-scale models of the ballasted railway track sections were developed for the simulation of high-speed train transit. Although vibration isolation trenches have been characterised as a suitable method for attenuation of ground-borne railway vibrations propagating away from the track, the results from the present study signify that the embankments supporting the railway track are subject to augmented levels of vibrations, due to reflection of ground vibrations from the soil–trench interface back into the embankment. In-filling of trenches with EPS (expanded polystyrene) geofoam of high buffer stiffness results in stronger reflection of ground vibrations back into the railway embankment. Augmented levels of track vibration are also estimated, when geofoam with higher densities are used for in-filling the trench. Deployment of vibration isolation trenches with higher depths result in stronger reflection of ground vibrations as well, especially when the trench is deployed at locations farther from the track. In general, amplification of vibrations in the railway embankment is higher when the trains transit at faster speeds. Reflection of vibrations by the passive vibration isolation trenches is inevitable, and hence, it is recommended that rail pads or under-sleeper pads shall be used in conjunction with the passive trenches for limiting the amplification of vibrations in the embankment.

Comparative Analysis of Design Parameters for High-Speed Railway Earthworks in Different Countries and a Unified Definition of Embankment Substructure

This paper compares design specifications and parameters for high-speed railway (HSR) earthworks in different countries (i.e., China, France, Germany, Japan, Russia, Spain and Sweden) for different track types (i.e., ballasted and ballastless), and for different design aspects (i.e., HSR embankment substructure, compaction criteria, width of the substructure surface, settlement control, transition section, and design service life). Explanations for differences in HSR implementation among different countries are provided and reference values of the design parameters are obtained. In an attempt to unify different types of HSR substructures around the world, a widely applicable definition of the stratified embankment substructure based on the practices adopted in different countries is proposed. The functions and requirements of each functional layer (i.e., the blanket layer, frost protection layer and filtering layer) are summarized.

Modelling frost heave in unsaturated coarse-grained soils

Coarse-grained soils were considered not susceptible to frost heave. However, substantial frost heave has been observed in unsaturated coarse fills in high-speed railway embankments. Recent experimental results in the literature show that vapour transfer has a considerable influence on the frost heaving of coarse-grained soil. However, vapour transfer has rarely been considered in modelling frost heave. This study presents a new frost heave model that considers vapour transfer and its contribution to ice formation. An updated computer program (PCHeave) is developed to account for the vapour transfer in unsaturated coarse-grained soils, where the rigid ice theory is applied to initiate ice lens formation in the frozen fringe. The results of the proposed model are compared with laboratory test results, which show reasonable agreement. The frost heave data monitored in 2013–2014 along the embankment of the Harbin–Dalian Passenger Dedicated Railway are also used to validate the proposed model. The prediction of the model agrees well with the measured results of frost heave and frost depth. This indicates that the proposed model can reasonably reflect the process of frost heave caused by vapour transfer in unsaturated coarse-grained soils.

A frost heave model of unsaturated coarse-grained soil considering vapour transfer

Substantial frost heave has been observed in coarse fills in high-speed railway embankments. These coarse fills have low fine contents and very low water content. The groundwater table is located below the coarse fills. The coarse fills were considered not susceptible to frost heave. Recent experimental results in the literature showed that vapour transfer has a considerable influence on the frost heaving of unsaturated coarse-grained soil. But vapour transfer has been rarely considered in the modelling of frost heave. This study presents a new frost heave model with considering vapour transfer and its contribution to ice formation. The rigid ice theory is applied to initiate an ice lens formation in the frozen fringe. An updated computer programme PCHeave is developed by considering the vapour transfer. The results of the proposed model are compared with laboratory test results, which show reasonable agreement. The prediction of the model agrees well with the measured frost heave and frost depth, which indicates that the proposed model can reasonably reflects the process of frost heave in unsaturated coarse soil.