Proceedings of the 5th International Conference on Transportation Geotechnics (ICTG) 2024, Volume 6

Table of Contents

1. Fatigue Damage of Tram Track Slab in Subgrade Settlement Area Based on Damage-Finite Element Fully Coupled Method

   Jia Li, Yao Shan

   Abstract

   In order to explore the stiffness degradation of tram track slab caused by the combined action of tram load and uneven settlement, based on damage-finite element fully coupled method, a tram-subgrade coupling dynamic model was established, and the damage field evolution was introduced into the stress field of the concrete, the influence of uneven settlement wavelength, amplitude, and tram load on the fatigue damage accumulation of tram track slab concrete were investigated, then from the perspective of the tram track slab service condition, a control threshold for the tram track subgrade settlement was proposed. The results showed that uneven subgrade settlement will accelerate the damage of the tram track slab concrete; as the tram speed increased, the track slab service life gradually decreased, and the calculation results of damage-finite element fully coupled method can better reflect the mutual influence mechanism between the tram track slab damage and stress field, the fatigue damage mechanism of the track tram slab was revealed to a certain extent.

2. Development of a Monitoring System to Reduce Uncertainties in Assessing the Wind Loading of Pile Foundations for Railway Overhead Line Electrification Structures

   Oliver John, Anthony Blake, David Richards, William Powrie, Richard Stainton

   Abstract

   Electric traction is key to decarbonising railways, but there are challenges and uncertainties in the cost of electrification. Overhead line electrification (OLE) structures and their foundations have contributed to cost and programme overruns in the UK, in part owing to uncertainties in the structural loads transmitted to the foundations. Improved understanding of these structural loads, particularly the dynamic components from wind and train aerodynamic effects, is essential to reducing the cost and uncertainty associated with the design and construction of OLE structures and their foundations. This paper describes the initial development of a suite of instrumentation to record synchronised wind velocities, structural strains and accelerations on in-service OLE structures. The monitoring system aims to establish both the effects of wind loading for comparison with design code coefficients, and the structural dynamic response to trains passing at speed. Strain measurements at the base of the foundation and at the OLE cantilever connection will identify the structural loads transmitted into the foundation pile cap. Accelerometers will be used to assess the structural displacements caused by wind excitation of the structure along with exploring potential coupling between adjacent OLE structures. Key findings from a preliminary instrumentation deployment in a non-operational setting are presented and the implications for in-service field deployment at a variety of sites across the UK rail network are discussed, along with the implications of the improved understanding for geotechnical design.

3. Numerical Simulation of Full-Scale Cyclic Physical Model Design Based on On-Site Monitoring

   Chih-Ming Liao, Chihping Kuo, Kai-Jui Ho

   Abstract

   Maintaining the serviceability and safety of the railway transportation system is an essential national engineering project. Today, most railway systems still use ballast as the primary foundation. Frequent mud pumping occurs on the ballast foundation, which makes the railway system's safety and reliability questionable. It is immediately essential to explore the mechanism of mud pumping. If the key factors causing mud pumping can be clarified, it will significantly help reduce railway maintenance costs and improve reliability and safety in the future. Conducting a full-scale ballast foundation cyclic load test to simulate the mud pumping behavior and explore its development mechanism is critical research. To this end, this article will demonstrate using the train load measured on-site and numerical simulation methods to calibrate the model size for subsequent physical testing.

4. Coupled CFD-DEM Simulations of Particle And Fluid Behaviour During Early Stage of Filtration

   Yingyi Zhang, Adnan Sufian, Alexander Scheuermann

   Abstract

   Mud pumping in railways occurs when finer particles in the subgrade soils infiltrate through the overlying coarser ballast layer. The finer particle migration can lead to local settlement and cavities in the subgrade soils and consequently causes poor track performance. The micro-scale mechanisms of finer particles infiltrating into a coarser layer are investigated in this study using coupled Computational Fluid Dynamics and Discrete Element Method (CFD-DEM). The early stage of filtration was simulated at the micro-scale with a simplified system where assemblies comprising a base layer of finer particles underlying a filter layer of coarser particles, and an upward seepage flow perpendicular to the interface was employed to trigger base infiltration. Various filter-base size ratios along with different flow conditions were considered to investigate the influence of geometric and hydraulic conditions on infiltration. The simulation results of the fluid behaviours were validated by comparing the numerical, empirical and experimental results of hydraulic conductivity. The hydraulic conductivity of the infiltrated zone was also investigated, which highlighted the capability of CFD-DEM in investigating the hydraulic conductivity change induced by filtration.

5. Application of Mechanistic Formation Design Tools to Rail Maintenance Requirements

   Vincent Blanchet, Douglas Tun, Nay Win, Andy Doe

   Abstract

   For new and existing rail network forecasting maintenance intervention is an important aspect of the network’s overall operation, can offer an alternative to “run to failure” strategies and assist greatly with renewal programs. Recent progress implemented in mechanistic formation design is performance-based where the design is developed to achieve a cumulative plastic deformation and or a rail deflection based on a forecasted rail traffic, train loading and speed for a design life. This paper presents an application of the mechanistic formation design to assist in predicting formation performance over the design life and assist rail operator with maintenance forecast typically comprising tamping to maintain rail grade through the design life. This paper presents results for typical embankment heights and at grade conditions for typical heavy haul traffic loading. This can be applied to green field new projects but also to existing networks. The mechanistic formation design uses a Li and Selig Approach incorporating stress distribution estimated using three-dimensional finite element modelling of sleeper, ballast formation and subgrade.

6. Experimental and Numerical Study on Cyclic Loading of Railway Subgrade

   Aruni Abeywickrama, Buddima Indraratna, Cholachat Rujikiatkamjorn

   Abstract

   This paper explicates the cyclic behaviour of soft clay railway subgrade, which is prone to mud pumping using laboratory experiments. Actual field conditions are applied on the soil samples using the dynamic triaxial apparatus to simulate the railway subgrades subjected to different train loads and speeds. The objective of this paper is to serve the reader with a rigorous understanding about the different aspects of cyclic behaviour of soil such as the generation of excess pore water pressure, cyclic axial strain development and effect of drainage on mud pumping through these laboratory experiments. For instance, the mechanism and mitigation of mud pumping are still being queried. Therefore, an endeavour to understand the mechanism of mud pumping and its mitigation is also given through this research. Evidently, the dynamic triaxial test results can be exploited to crystallize the understanding in the mechanism of mud pumping and its mitigation. Finite element modelling was done to investigate the effectiveness of prefabricated vertical drains in mitigating mud pumping in railways.

7. Damage Evaluation and Protection Measurement of the Double-Column Pier Subjected to Explosion

   Wenyi Tian, Chaoyi Xia, Jinghui Jiang, Yanyang Pan, Lu Wang

   Abstract

   In this paper, a numerical model of the “explosive-air-pier” coupling system is established by using finite element (FE) method. Through the parametric studies, the dynamic responses of the reinforced concrete (RC) double-column piers under typical explosion cases are analyzed. Taking the scaled distance and the pier diameter as the input vectors and the structural residual load-carrying capacity as the output vector, the Radial Basis Function Neural Network (RBFNN) is trained to predict the damage index of the pier. The threshold curve of the pier damage level is fitted, by which it can be observed that the three critical scaled distances between the complete damage, the serious damage, the moderate damage and the slight damage are 0.7, 1.1, and 1.4 m/kg^1/3, respectively. To explore the effective wrapping mode to improve the structural explosion resistance, the numerical pier models reinforced by the Carbon Fiber Reinforced Polymer (CFRP) material are established. The analysis results indicate that the partial wrapping of the CFRP at the pier bottom is more economical and efficient in the anti-explosion prevention.

8. Triaxial Tests to Assess the Effects of Densification, Lateral Spreading and Grain Breakage on Settlement Behaviour of Full-Size Railway Ballast

   Rashid S. Abeid, Madhusudan B. N. Murthy, Taufan Abadi, David Milne, Joel Smethurst, William Powrie

   Abstract

   Predicting the rate of deterioration of ballasted track due to cumulative plastic settlement is a major challenge for railway infrastructure owners. For track on a stiff subgrade, more than 50% of the total deformation originates from the ballast through grain rearrangement (compaction), lateral spreading and possibly grain breakage. Despite much research, knowledge of the mechanisms by and extent to which these three processes contribute to permanent settlement is limited, and permanent settlement is still usually estimated empirically. This paper describes the rationale and initial results of triaxial tests on full-size granite railway ballast, carried out to investigate the relative importance of the processes responsible for ballast settlement. Specimens of full-size railway ballast 600 mm high and 300 mm in diameter were subjected to cycles of deviator stress between 10 kPa and 50, 100 or 200 kPa. Tests were carried out over up to 500,000 load cycles at a frequency of 3 Hz and an effective confining stress (cell pressure) of 30 kPa. For the ballast tested, grain rearrangement and lateral spreading were the dominant effects on the evolution of ballast permanent settlement. Grain breakage was insignificant except at the highest test load.

9. Particle Breakage Prediction of Coral Sand Using Machine Learning Method

   Xue Li, Wan-Huan Zhou, Chao Wang

   Abstract

   Understanding the mechanical behavior of granular materials is of paramount importance in various geotechnical applications. Coral sand, a naturally occurring sediment composed of broken coral fragments, plays a crucial role in marine engineering. However, characterizing and predicting the breakage behavior remain challenging due to its complex and heterogeneous nature. At current work, a set of one-dimensional compression tests were carried out considering varying initial conditions. Four machine learning (ML) algorithms (random forest, linear regression, fully connected neural network, and eXtreme Gradient Boosting) were adopted to predict particle breakage ratio. The initial loading stress, fines content, density state, grain size, coefficient of uniformity, and curvature coefficient were considered as variables for regression and classification. Relative particle breakage ratio was set as output feature. The dataset was divided into 25 and 75% as the test and training sets, respectively. Test results show that high stress, lower fines content, smaller relative density, and larger grain can lead to remarkable particle breakage. ML analysis suggests that both random forest and eXtreme Gradient Boosting achieved remarkable accuracy levels, exceeding 99%. However, linear regression, with a root mean squared error of 0.041, presented poor performance for particle breakage prediction. The developed approach can be used to evaluate the particle breakage with an acceptable breakage modeling accuracy.

10. Effect of Particle Shape Alterations Using Grinding Process on the Compaction Characteristics of Granular Subgrade Materials

    Toshiyasu Unno, Akari Nagoya, Ryo Sakamoto, Akiyoshi Kamura

    Abstract

    This study systematically scrutinized the influence of grain shape modification on the compaction characteristics of granular subgrade materials commonly employed in roadbed and subgrade construction. The process involved conducting compaction tests on granular crushed stones whose shape was altered through the grinding process facilitated by a granulating machine. As an initial step, the crushed stone was subjected to the grinding machine multiple times to induce changes in grain shape. This procedure resulted in crushed stone grains with fewer surface irregularities, smaller diameters, and a more circular shape tendency. Subsequently, image processing techniques were utilized to quantify these alterations in grain shape. Further, compaction tests were executed using a tamping method on the ground crushed stones, and their compaction characteristics were meticulously examined afterward. The results revealed no notable disparities in maximum dry density or optimal moisture content.

11. Feature Value Evaluation of Compaction Property of Fine Aggregate by Principal Component Analysis

    Akari Nagoya, Toshiyasu Unno, Ryo Sakamoto, Akiyoshi Kamura

    Abstract

    To improve the mechanical rationality of road pavement, it is essential to evaluate the compaction properties of the fine aggregate that constitutes the skeleton of the pavement as a soil element. Hence this study clarified the relationship between physical properties such as grain size distribution and compaction properties. To describe the compaction phenomenon of granular materials, the authors employed nine grain size feature values such as uniformity coefficient and fine fraction content, four water-related feature values including water content, and degree of saturation, wet density and compaction energy as feature values. Using these feature values based on the physical properties of fine aggregate, we attempted to perform feature analysis with Random Forest. The results show that the degree of compaction is highly correlated with the compaction energy and the degree of saturation. Based on the feature values, PCA is performed to clarify the feature values that affect the compaction properties.

12. An Overview of Single-Objective Optimization Models for Assessing the Performance of Railway Ballast Under Cyclic Loading

    Srinivas Alagesan, Buddhima Indraratna, Rakesh Sai Malisetty, Yujie Qi, Cholachat Rujikiatkamjorn

    Abstract

    The performance of railway ballast under repeated loading greatly influences the overall stability and durability of the track. It is mainly quantified in terms of induced plastic strain, resilient modulus, and ballast breakage index. Past laboratory and field investigations indicated that external loading conditions and intrinsic material properties of ballast such as coefficient of uniformity and mean particle size affect the deformations of ballast. Threshold ranges for geotechnical design parameters such as confining pressure, frequency, and ballast gradation are available in literature to optimize the service life of the ballast under cyclic loads mimicking actual field conditions. However, the proposed optimum range cannot be widely adopted for all the scenarios because every optimization model has constraints. Moreover, majority of the proposed empirical relationships developed to quantify the extent of ballast degradation were mostly derived from single-objective optimization studies. Therefore, this paper presents a comprehensive review of the existing single-objective models for predicting different ballast performance metrics. The relative advantages and shortcomings are discussed with their constraints for application to field problems.

13. Appropriate Domain Size for Footing Bearing Capacity Analysis Using Random Finite Element Method

    Gang Niu, Xuzhen He

    Abstract

    The utilization of random finite element method (RFEM) to make geotechnical prediction has gained popularity in recent decades. These stochastic analyses, which accounts for the spatial variability of soil, can more precisely reflect soil condition in the natural environment. This study discusses the required domain size for footing bearing capacity analysis with RFEM, which can be applied to many infrastructure designs such as road pavement, airport runway, shallow foundation of buildings and so on. Since the infrastructure sits on an unbounded ground, expanding the domain size in RFEM can enhance the accuracy of result. However, it is found that after a critical size, any larger domain size would not contribute to a significant improved accuracy. The appropriate domain size proposed in this study is not limited to a narrow set of parameters. Instead, it is applicable across a wide range of situations, including different combinations of material characteristics. The robustness of our finding is verified by many numerical simulations, which shows the reliability of the finding in diverse geotechnical scenarios.

14. A Review of Progressive Soil Deformation Occurring in Integral Bridge Approaches

    M. S. K. Hassan, D. S. Liyanapathirana, W. Fuentes, C. J. Leo, P. Hu

    Abstract

    Integral bridges are a relatively recent design concept in which there is structural continuity at the girder–abutment interface. Whilst this has led to numerous advantages, it has also resulted in performance complications. Amongst numerous drawbacks, cyclic deformations of the bridge deck due to daily and seasonal temperature changes result in two notable geotechnical issues: ratcheting of passive lateral pressures on the abutment wall and progressive soil deformation in the approaches. During the last two decades, considerable research efforts have been dedicated to developing an understanding of these phenomena. However, it is apparent that a majority of the attention has been focused on stress ratcheting. Further, there is not yet a review available that assesses the theoretical aspects of soil deformation in integral bridge approaches. Accordingly, this manuscript presents a critical review of the long-term behaviour of soil subsidence and upheaval observed from controlled analyses. Subsequently, the impact of design parameters, namely, bridge length and foundation design are discussed. The significance of diurnal cycles on soil deformation is then presented. Through this review, it is understood that the formation of the settlement trough can reach a limiting state. However, due to the sustained accumulation of plastic shear strains, upheaving may continue to propagate, even in subsequent cycles. Soil upheaval is particularly influenced by the abutment movement mode and daily thermal fluctuations. Collectively, data from available literature is yet insufficient to predict the long-term soil deformation response of integral bridges.

15. Proposed Methodology for Obtaining Ballast Layer Performance Indicators

    Jorge Rojas Vivanco, Pierre Breul, Aurélie Talon, Miguel Benz-Navarrete, Sébastien Barbier, Fabien Ranvier

    Abstract

    Although ballast layer can be characterized by different parameters, the literature notes the absence of global performance indicators of ballast in service. This article presents a methodology that proposes to obtain local performance indicators (based on the functions performed by the ballast layer) and global performance indicators (based on the combination of the above). The proposed methodology consists of three phases: (i) the first is the performance of a functional analysis (FA) for the identification of the key functions of the ballast layer, (ii) application of the failure mode and effects analysis (FMEA) for the creation of the failure trees of the functions identified in the previous phase, and (iii) application of data aggregation to combine the parameters and indicators in the form of a model to obtain the performance indicators. The results of performance indicators can be useful for the planning of corrective actions and in case of failures or defects to identify their causes. The methodology allows adapting the conditions and/or needs of each railway manager by modifying the failure modes and modifying the scales proposed for data aggregation.

16. Use of Digital Imaging for Capturing the Soil Collapse Mechanism Behind Abutments of Integral Bridges

    Justin Yenne, Dunja Perić

    Abstract

    Integral abutment bridges (IABs) offer numerous advantages, including increased resilience and reduced construction and life time maintenance costs, thus making them popular in the transportation industry. Nevertheless, the lack of expansion joints in IABs leads to challenges in thermal load transfer that impact short- and long-term behaviors of IABs. This study explores complex soil-structure interaction behind IABs abutments by testing a downscaled model of the existing integral bridge subjected to 100 cycles of thermal loading and using digital imaging correlation (DIC), a technique originating in fluid mechanics, to capture the evolution of the soil collapse mechanism responsible for the development of bridge approach settlement. Additional measurements show that the rate of collapse gradually decreases with increasing number of load cycles. The results highlight the intricate nature of soil-structure interaction and offer insights into the challenges posed by cyclic movements. The research contributes to advancing the knowledge of thermally induced soil-structure interaction in IABs through emphasizing the relevance of the underlying granular soil collapse for devising engineering solutions for improved performance of IABs.

17. Application of an Efficient Bayesian Back Analysis Framework for Settlement Prediction of Soft Soils: A Case Study

    Shan Huang, Jinsong Huang, Richard Kelly, Merrick Jones, A. H. M. Kamruzzaman

    Abstract

    This study aims to utilize a self-developed, high-efficient Bayesian back analysis framework to perform Class C prediction of the embankment constructed on soft soils. In this framework, the general simplified Hypothesis B method based on a one-dimensional elastic visco-plastic (1D EVP) model and bypassing the need to solve complicated partial differential equations, is applied to perform consolidation analysis. Also, a high-efficient sampling method, Bayesian updating with structural reliability method (BUS), is employed to solve the Bayesian back analysis problem. The Class C prediction of a trial embankment constructed at Ballina, New South Wales, Australia, is conducted using the monitoring surface settlement data. The obtained results demonstrate that the accurate long-term settlement prediction at surface can be obtained at early stages, which enables cost-effective outcomes.

18. Comparison of Bearing Behavior Between I-shaped and X-shaped Sleeper Using DEM Coupled Simulation

    Cheng Chen, Yuyan Tang, Hongyi Zhang, Yifei Sun

    Abstract

    A new type of X-shaped sleeper was developed to increase the lateral resistance compared to conventional I-shaped sleepers. A series of sleeper push-out test simulations using discrete element method (DEM) and multi-body dynamics (MBD) were carried out. The contact forces between the sleeper and different zones of the ballast layer were measured. The ballast particle movement and the disturbance of the subballast and subgrade during the sleeper push-out were investigated from the macro-view and micro-view. The results indicate that the lateral resistance of a single X-shaped sleeper was increased by approximately 22.4% compared to the double I-shaped sleepers. Moreover, the frictional resistance of sleeper base is relatively close for both, primarily related to the bottom area. Simultaneously, the V-fork arms of the X-shaped sleeper increase the total resistance between the sleeper sides and the ballast, nearly 2 times compared to the I-shaped sleepers. From the micro-view of the particle movement and contact force distribution, it proved that the disturbance area in the crib ballast for the X-shaped sleeper appears larger, with a greater number of crib ballast particles actively participating in impeding the lateral movement of the sleeper. Similarly, the stress distribution of subgrade indicates the active involvement of the bottom ballast and subgrade in sharing the lateral resistance of the track bed.