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

Table of Contents

1. Frontmatter

2. A Coupled CFD-DEM Approach to Examine Clogging Behaviour of Granular Medium by Fines

   Thao Doan, Buddhima Indraratna, Thanh T. Nguyen, Cholachat Rujikiatkamjorn

   Abstract

   Clogging is one of the prevalent problems that cause severe damage in the performance, functionality and longevity of granular medium used in geotechnical structures such as filters and stone columns. Despite the growing interest in clogging phenomena, there is a limited number of studies investigating the microscale mechanisms of clogging when fines are flowing into the porous medium under the influence of fluid flow. In this respect, this study aims to employ an advanced numerical approach where the discrete element method (DEM) to model discrete soil particles is combined with computational fluid dynamics (CFD) to model fluid flow governed by Navier–Stokes equations. The numerical results show different patterns of migration and accumulation of fine particles in the given porous media (i.e., stone column) depending on the associated properties of soil and fluid. A set of critical factors that control the clogging potential are also investigated in detail including the influence of hydraulic gradient and characteristics of coarse medium such as its particle sizes. The innovation of this study is the exploration of the micromechanics of clogging, which has not been addressed thoroughly before.

3. Effect of Principal Stress Rotation on Plastic Strain Accumulation in Granular Materials

   Sajjad Vaseghi, Daichao Sheng, Jayantha Kodikara, Hadi Khabbaz

   Abstract

   Unbound granular materials (UGMs) are utilized in flexible pavements to serve mainly as subgrade materials, offering the necessary support for the imposed traffic loads. Although the likelihood of subgrade strength failure under traffic loads is minimal, its permanent deformation is more critical. The repeated load triaxial (RLT) test is a widely employed method for assessing the accumulated permanent deformation in unbound granular materials (UGMs) in their lifetime. Nevertheless, there have been challenges in establishing a direct correlation between the results obtained from RLT tests and the actual deformation measured in full-scale pavements. The primary reason for the disparity is the incapability of RLT-based designs to account for the rotation of principal stresses imposed by the application of shear stress coming from the movement of vehicles. In order to examine how the rotation of principal stress affects the formation of plastic strain in UGMs, various experiments were conducted in the present study. These experiments include different levels of cyclic stress ratio (CSR) and cyclic shear stress ratio (CSSR) using a hollow cylinder apparatus (HCA). The results obtained from the HCA tests were compared to those obtained from the RLT, and it was discovered that incorporating the principal stress rotation significantly amplified the permanent deformation of the unbound granular materials (UGMs). This indicates that incorporating the influence of principal stress rotation is essential for ensuring a proper and accurate design that can effectively address the deformation behavior of the pavement layers.

4. Dem Study on the Dynamic Performance of a Fouled Ballasted Track Under Repeated Traffic Loading

   Jing Chen, Buddhima Indraratna, Jayan S. Vinod, Ngoc Trung Ngo, Yangzepeng Liu

   Abstract

   The fouling of ballast, resulting from upward intrusion of subgrade slurries, coal or other mineral ore dislodging from passing freight traffic, and the accumulation of debris among ballast grains, has been extensively reported as the primary cause for numerous disastrous railroad incidents. This paper presents a numerical study to examine the deformation and degradation responses of a coal-fouled ballasted track upon repeated traffic loading using the discrete element modeling (DEM). A particle degradation model considering Weibull statistics in tandem with a granular medium size effect is developed and employed to capture the continuous corner abrasion of angular ballast. The model had been calibrated by comparing the predicted shear stress–strain response with laboratory data obtained from large-scale direct shear testing. A series of cubical shear test simulations have been carried out to examine the dynamic performance of ballast assemblies with various coal fouling contents under cyclic loading. The results show that an increase in fouling content exacerbates the sleeper settlement, while decreasing the resilient modulus and the particle breakage in ballasted bed. Ballast beneath the sleeper experiences significant breakage compared to the crib ballast, and the extent of damage is mitigated with depth. Rigorous microscopic analysis is also presented in terms of interparticle contacts and contact network anisotropy of the ballast assembly. The micromechanical examinations show that the decrease in ballast breakage observed in fouled assemblies is predominantly attributed to the inevitable decrease in interparticle pressures as effected by the coating of ballast aggregates by the coal fines.

5. Numerical Analysis for Ballasted Rail Tracks: Coupled DEM-FEM Approach

   Trung Ngo, Buddhima Indraratna

   Abstract

   Ballasted tracks are essential for transporting goods and passengers between major urban areas and ports, but they suffer breakage, fouling and excessive deformation from repeated train loads. This study investigates the effect of loading and frequency on ballast deformation and degradation through lab tests and numerical modelling. A coupling model based on the finite element method and discrete element method is introduced to predict load-deformation behaviour. DEM represents ballast grains, while FEM models the subgrade, accounting for their interactions. The model is applied to analyze a Singleton, Australia track, with numerical results compared to field data for validation.

6. Barrier Systems to Protect Critical Transportation Infrastructure from Impact-Induced Ground Vibrations

   Abhinav Raj, Nitish Jauhari, Amarnath Hegde

   Abstract

   Critical transportation infrastructure includes the vast network of highways, railways, utilities, buildings and stations. The unwanted vibrations induced due to man-made activities, e.g. dynamic compaction, drop hammers and pile driving, propagate through the soil media and affect infrastructure amenities. Therefore, an attempt has been made in the current study to limit the propagation of these unwanted vibrations from reaching the critical infrastructure. The efficacy of the single and dual barriers constructed between the vibration source and the infrastructural amenities has been investigated using numerical techniques. A finite element model was developed using ABAQUS to simulate vibrations induced due to impact loads. The excitation force generated due to impact load was modelled as a pulse in the developed numerical model. Initially, the model was validated with the published literature and thereafter used to investigate the influence of the depth, width, location and number of barriers on the isolation efficacy. The results indicated that the depth of the barriers was the most influential parameter in mitigating the vibrations. The optimum depth and width for the single open barrier were observed as 1.0L_R and 0.1L_R, respectively, where L_R is the Rayleigh wavelength. However, the depth requirement for the dual barriers was significantly lesser than the single barriers. The average amplitude reduction ratio for the dual open barriers of a depth of 0.4L_R was recorded as low as 0.22.

7. Numerical Modelling of Jointed Rock Foundation Under Heavy Haul Train Loading

   Majid Jazebi, Buddhima Indraratna, Rakesh Sai Malisetty, Cholachat Rujikiatkamjorn

   Abstract

   Railways are an important lifeline for mining and industrial based economy such as Australia. Railway tracks traverse a number of difficult terrains across the country such as jointed sandstone rock formations near Sydney region. In an economic point of view, it is necessary to reduce maintenance costs and improve the life span of railway tracks built on fractured or jointed sandstone. To address this issue, a numerical model is developed to simulate the behaviour of jointed rock under the passage of heavy-haul trains using FLAC 3D, and the response of a single joint under a moving axle load was simulated for simplicity. In this study, Barton and Choubey’s method for estimating shear strength of a rock joint was incorporated alongside the existing Coulomb frictional interface in FLAC 3D. The proposed method provides a practical approach to improve the Coulomb frictional interface by including Joint Roughness Coefficient. Further, this method also simulates the evolution of shear and normal stresses distinctly at different locations on the joint surface under train passage. Under a heavy haul train passage, the contours depicting normal stress and the related apparent friction angle are presented.

8. Molecular Dynamics Study on the Effect of Temperature and Water Content to the Mechanical Properties of Na-Montmorillonite

   Bonan Li, Yilin Gui, Miao Yu

   Abstract

   Sodium montmorillonite (Na-MMT) is the predominant active mineral in clays. It is very sensitive to environmental factors, especially changes in temperature and moisture content. However, there is a lack of comprehensive studies on how temperature and moisture content affect the structural properties of Na-MMT on a microscopic scale. In this study, molecular dynamics (MD) simulations were used to analyse the structural and micromechanical behaviour of Na-MMT. The aim is to investigate how different temperatures (from 200 to 700 K) and water contents (10, 20 and 30%) affect the mechanical properties of Na-MMT. The simulation results highlight several key points: (1) The movement and behaviour of water molecules change significantly due to the temperature increase, leading to interlayer swelling, which reduces the mechanical properties. (2) Na-MMT exhibits anisotropy, with mechanical properties in the y-direction being superior to those in the x and z directions with increasing temperature and water content. (3) It was found that the higher the degree of hydration, the worse the mechanical properties of Na-MMT, which is consistent with observations in practical engineering applications. This study deepens the understanding of the microscopic characteristics of Na-MMT and further investigates the microstructural changes associated with the swelling mechanism of bentonite.

9. A New Update Criteria of Verlet List for Geotechnical Dense Granular Materials Under Periodic Loading

   Shuchen Wang, Longlong Fu, Yongjia Qiu, Haonan Xi, Shunhua Zhou

   Abstract

   Discrete element method (DEM) based on graphic processing unit (GPU) is widely employed for investigating the responses of geotechnical dense granular materials under periodic or traffic loading. In most conventional GPU-based DEM, the maximum displacement of particles in the global coordinate system is considered as the criteria for updating Verlet list. Once the displacement exceeds the specified threshold, the Verlet list is updated. Although the particles experience considerable quasi-periodic displacement under periodic loading, the potential contact targets for most particles will not change during quite a few loading cycles. As a result, data between central processing unit (CPU) and GPU is transferred with an over-demanded high frequency and thus restrict the computational efficiency. In this study, we propose a criteria to improve the updates of Verlet list, in which the maximum displacement of particles in local particle coordinates system is used as the update criteria. The improved update criteria is plugged in the open source DEM software MUSEN. Then by simulating a previous laboratory full-scale half-sleeper model test, the performance of the proposed criteria is testified. The results show that the application of the proposed update criteria has no significant influence on the multi-scale responses of the ballast bed. Meanwhile, unnecessary updates of Verlet list resulting from only overall displacement of particles are effectively decreased. This indicates a potential way to improve the computational efficiency in GPU-based DEM for geotechnical dense granular materials under periodic loading.

10. Effect of Train-Induced Ground Vibrations on Liquefiable Soils

    Farbod Yarmohammadi, Katherina Ziotopoulou, Kostas Lontzetidis

    Abstract

    Rapid development of railway transportation in recent years has brought attention to the potential problems caused by train-induced vibrations. These problems include damaging the tracks, shaking and cracking the nearby buildings, and damaging the sensitive apparatus and therefore must be addressed when designing the railways. Another potential problem caused by the train-induced vibrations is the increase in the pore water pressures in the loose sandy layers located under the tracks. These excess pore pressures can potentially cause differential settlements in the underlying soil through different mechanisms and damage the railway system. This paper presents the results of finite element modellings developed in PLAXIS software studying this problem. PM4Sand constitutive model is used to capture the response of the loose sandy layer to the train-induced cyclic loads. Different train speeds are considered in the numerical simulations to study the effects of the frequency contents of the dynamic loads on the soil response. Additionally, the effect of the ground profile, including the depth, thickness, and relative density of the loose sand, is also investigated. The results of this study aim to help the researchers and engineers to better understand the problem and design the railway subgrade accordingly to reduce the long-term maintenance costs of the railway system.

11. Performance of Bounding Surface Plasticity in the Prediction of Progressive Soil Deformation in Integral Bridge Approaches

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

    Abstract

    The structural continuity of integral bridges has resulted in a long-term, cyclic interaction with the approach backfills leading to two crucial geotechnical consequences, passive lateral stress accumulation, and progressive soil deformation. To investigate these phenomena, numerical methods have been commonly used. However, it is apparent that a majority of utilized techniques are unable to capture the critical facets involved with cyclic loading conditions. Hence, this study presents a comparison of the performance of the widely utilized Mohr–Coulomb (MC) model to that of the bounding surface model proposed by Dafalias and Manzari in 2004 (DM04). Evaluations are made against settlement and lateral pressure data from a scaled physical model of an integral abutment. Results indicate that the MC model is an inappropriate choice, being unable to capture the accumulation of stresses and plastic strains. The DM04 model can reasonably simulate the stress ratcheting response. The propagation of the settlement trough is adequately predicted, particularly at latter cycles. However, the variation in the rate of change of maximum settlements with the progression of cycles is anomalous from typical behavior.

12. A Coupled Flow Deformation Model for Expansive Soil with Temperature Change

    Miao Yu, Yilin Gui, Les Dawes, Maziar Gholami Korzani, Bonan Li

    Abstract

    Expansive soils exhibit significant volume change when experiencing variation of temperature or moisture change. However, previous constitutive models on expansive soil mainly focus on hydraulic conditions, less attention on thermal field. This study delves into the thermo-hydro-mechanical behavior of expansive soils, crucial for applications such as nuclear waste disposal and thermal energy storage. A novel constitutive model, extended from bounding surface plasticity theory, is introduced to simulate the expansive soil behavior under various temperatures. A new approach on effective stress principle considering the effect of temperature is proposed. In this model, changes on suction and temperature are considered, which are in response to mechanical behaviors. Validated by temperature-controlled tests from (Tang et al. in Géotechnique 58:45–54 [1]), the proposed model shows potential in understanding the complex coupling of thermal, hydraulic, and mechanical processes in expansive soils, especially in cyclic environmental conditions.

13. Three-Dimensional Finite Element Modelling of Sealed and Unsealed Roads Considering Effects of Moving Wheel Loads

    Piyush Punetha, Sanjay Nimbalkar

    Abstract

    Accurate simulation of the response of sealed and unsealed roads to moving wheel loads is essential for improving the current understanding of their behaviour. A proper evaluation of the stress distribution within different pavement layers under moving loads is essential for their appropriate design. This article presents the findings of three-dimensional (3D) finite element (FE) analyses carried out on sealed and unsealed roads, taking into account the effects of moving wheel loads. A parametric study is conducted to investigate the influence of variables, such as the elastic modulus of pavement layers, on the performance of both sealed and unsealed roads. The results reveal that the peak values of vertical stress at the subgrade top under moving wheel load are more sensitive to the base modulus for the unsealed road than the sealed roads, which is due to the structural difference between the two road types. The results predicted using FE models are also compared with those from the approach commonly used by practising engineers. The findings from this study demonstrate the capability of 3D FE method in evaluating critical responses of sealed and unsealed roads under moving wheel loads, which are crucial for optimising their design.

14. Application of an Advanced Constitutive Model for Shakedown Analysis in Unbound Pavements

    Liuxin Chen, Javad Ghorbani, Troyee Tanu Dutta, Arooran Sounthararajah, Arjoon Moses Jesudasan, Jayantha Kodikara

    Abstract

    This study uses a cutting-edge constitutive model for analysing shakedown phenomena in unsaturated granular soils commonly used in lightly and moderately trafficked pavements. The primary source of structural support in these pavements comes from granular soils used in the subbase and the subgrade soil. This highlights the crucial role of accurately evaluating their mechanical properties for optimum design and use of materials. Our model successfully captures material kinematic hardening with memory and provides more accurate simulations of the hydro-mechanical shakedown in these soils under millions of load cycles. The model also addresses some key computational challenges associated with a large number of load cycles, such as potential numerical instability and a significant loss of accuracy. The model’s capabilities are showcased, highlighting its proficiency in simulating soil plastic deformations. This is particularly demonstrated in a novel laboratory test, the constant radial stiffness triaxial (CRST) test, designed to mimic traffic loading on unbound pavements. It is argued that this test better simulates the stress path encountered by road materials under moving traffic loads in the field than the traditional repeated load triaxial (RLT) test.

15. Performance Assessment of Existing Railway Track Subjected to Varying Train Speed

    Sujitha Soundararajan, Prishati Raychowdhury, Sanjay Nimbalkar

    Abstract

    With increasing population growth and rapid urbanization, a faster and heavier train network is being planned in India, aiming to reduce the travel time without compromising the passenger comfort. Since construction of new railway tracks for the intended high-speed trains involves economic, social, and other land acquisition related feasibility issues. Therefore, it is preferable to evaluate the existing tracks and recommend possible upgrades as a solution, given the aforementioned factors. The major objective of this study is to evaluate the performance of the existing railway track in terms of differential settlement when subjected to trains moving at varying speeds. The significance of varying speed of train is to assess the response of the track to accommodate mixed traffic conditions and high-speed trains. A two-dimensional finite element model has been developed in PLAXIS to simulate the rail-track-subgrade system subjected to the moving load. A full-scale rail-track in Rohtak-Gohana line located in the Northwestern region of India is considered as a case study for evaluation of the train-track system for varying train speeds. The developed model is validated with the field data available from the literature. The results show that the vertical settlement of the track gradually reduces with the inclusion of transition slab as the train moves from softer side to stiffer side. Furthermore, the densely compacted embankment shows a similar trend of vertical rail displacement for varying speed of the train.

16. Static and Dynamic Responses of Geosynthetic-Reinforced and Pile-Supported Embankment of High-Speed Railway

    Shun Liu, Xuecheng Bian, Chuang Zhao

    Abstract

    Soil arching plays a major role in geosynthetic-reinforced and pile-supported (GRPS) embankment by load transfer mechanism. For the purpose of understanding the static and dynamic behavior of GRPS embankment, a two-dimensional plane strain simplified finite element model (FEM) of pile-supported embankment was established to examine the soil stress distribution in depth and pile efficacy on the surface of piled foundation. Due to the transmission of stress waves, the distribution pattern of dynamic stress was different with that of static stress. Besides, stress waves were reflected greatly when they arrived at the surface of piled foundation, which caused the greater additional stress than that of static train loading, and the dynamic pile efficacy was smaller than the static pile efficacy. Factors of speed of moving train, elastic modulus of subsoil, and embankment height were examined and showed that the elastic modulus of subsoil was the most sensitive factor to pile efficacy, especially dynamic pile arching. Finally, the distribution pattern of dynamic stress in depth was determined by the height of superstructure of piled foundation. Below the critical height of embankment, the dynamic stress distribution was dominated by the reflection of stress waves, but, when the embankment height exceeded the critical height, the soil stress above the height of soil arching could be calculated by Boussinesq solution.

17. Investigating the Impact of Autonomous Vehicles on Pavement Structures: A 3D Finite Element Simulation

    Pratik Chaudhary, Sireesh Saride

    Abstract

    Autonomous vehicles (AVs) have stepped up efforts to become the automobiles of the future. In terms of productivity, AVs are superior to human-driven vehicles (HVs). Current road infrastructure is believed to be unsuitable for AVs; autonomous vehicles may pose different challenges to pavement structures as they are not engineered to accommodate such novel classes of vehicles. Using a 3D finite element model, the present study simulates the wheel load movement of an autonomous vehicle attempting to maintain its position in the centre of a given lane for safety and fuel efficiency reasons. The 3D model adopts as single wide wheel and takes into account the influence of tyre contact width and the contact tyre pressure on the road with different numbers of wheel passages. The results discuss the influence of speed on the development of road damage stress and strains at 40 and 80 kmph. In addition, a platoon strategy is proposed to reduce pavement damage and improve roadway durability.

18. Towards a New Soil Constitutive Model for Simulation of Road Barrier Piles

    Fatemeh Safari Honar, Negin Yousefpour, Nelson T. K. Lam, Jude S. Perera

    Abstract

    The interaction between soil and pile is an important factor in the performance assessment of roadside piled-barrier systems under vehicle collision. Previous studies have primarily focused on the structural aspects of the system in numerical simulations of full-scale crash tests, failing to consider the effect of soil nonlinear behaviour on roadside barrier crashworthiness. In this study, we first evaluate commonly used soil constitutive models in LS-DYNA for full-scale crash simulations. The primary goal is to assess the suitability of these models for simulating piled barriers under impact, highlighting the limitations. In the second part of the paper, we propose a new soil constitutive model developed based on the Mohr–Coulomb and FHWA constitutive models. This model can effectively represent critical soil features, including strain softening and strain rate effects, essential for more accurate soil-pile simulation under impact. The proposed soil constitutive model is validated through a series of triaxial test results in element scale and will be further developed to be used in boundary-value simulations.