Since hydraulic conductivity significantly influences the compression and deformation characteristics of granular terrains, this study examines the variations in permeability (k20) of granular soils under one-dimensional compression. Two uniformly graded calcareous soil samples were tested: one with grain sizes of 9.50-12.70 mm, and another of 4.75-9.50 mm. Both samples were subjected to one-dimensional compression and constanthead permeability tests. Key soil properties affecting permeability (k20), including absorption (n), specific surface area (Ss), relative density (Dr), void ratio (e), uniformity coefficient (Cu), effective grain size (d10), and mean grain size (d50), were analyzed. The virgin compression line (VCL) of the soil samples was identified within an oedometric stress (sigma VCL) range of 4.00-14.00 MPa, where the rate of change in soil properties affecting permeability was most pronounced. As oedometric stress increased, the instantaneous absorption (ni) of the soil samples increased linearly, with a slope (alpha n) of 0.055-0.061. Similarly, the instantaneous specific surface area (Ss,i) of the soil samples increased linearly, with a slope (alpha s) of 1.229-1.388. In addition, practical equations were developed to predict the instantaneous relative density (Dr,i), instantaneous grain size distribution curve, and instantaneous permeability (k20,i) of granular soils under one-dimensional compression.

Analyzing the dynamic properties of an integrated system consisting of a box-girder bridge and a tunnel with a railway track is crucial for maintaining the structure's security, reliability, and operation. This inquiry is notably important because of its possible relevance to time-varying forces exterior forces, including vehicular and seismic loads, as well as the dynamic reaction of a moving train impacting the structure's connections. The interaction between these complex components under various loading conditions is crucial in determining the structure's behaviour and performance. Despite the critical importance of such analyses, previous studies have indicated a gap in the literature regarding the modal and dynamic analyses of integrated systems like the one under consideration. This research aims to fill this gap by focusing on the integrated structure's dynamic behaviour through comprehensive dynamic analyses. The primary aim of this investigation is to ascertain the dynamic response of the integrated system. The methodology employed in this study involves conducting dynamic analysis on the Finite Element Method model of the integrated system by ANSYS software. This approach allows a detailed examination of the structural response to different loading conditions and parameter variations. The study's outcomes are multifaceted and provide valuable insights into the dynamic response of the integrated structure. This finding underscores the importance of considering all integrated system components when analyzing its dynamic behaviour. Furthermore, the study evaluates the impact of various factors, such as vehicle speed, different loading conditions, damping ratio, and varying rock grades, on the structural response. Higher speeds were found to result in increased deformation, highlighting the significance of considering train speed in structural design and assessment. Additionally, the quality of the ground surrounding the Tunnel and beneath the railway line was found to have a substantial influence on deformation, velocity, acceleration, and stress levels. Notably, the study reveals that increasing the damping ratio significantly improves structural stability and performance, emphasizing the critical role of damping in designing resilient structures subjected to dynamic stresses from trains. This research contributes valuable insights into the dynamic analyses of the integrated structure comprising a box-girder bridge and a tunnel with a railway track, providing a comprehensive understanding of their behaviour under different loading conditions. This study's discoveries offer valuable suggestions for Tunnel, railway, and bridge engineers in identifying the most efficient design and maintenance strategy for this integrated structure. This work can be a foundation for future fatigue analysis of this integrated structure under dynamic vehicle load.

Using infrared thermography (IRT) has been proven as an effective technology for early damage detection within the superstructure/substructure of the ballasted railway tracks. Performing statistical processing and integrating principle component analysis (PCA) underpinned by extensive data sources of infrared imaging technology can effectively detect complex features exhibiting temperature variation. The present study employs these processing techniques on thermal images to investigate the drainage health of railway ballast layer using IRT technology. Specifically, clean and clay-fouled ballast specimens are prepared to study the effect of contamination/fouling in ballast layer (porous granular media) on water retention (indicated by water level) during severe rainfall intensity. IRT is utilized to monitor the water level as the indicator of ballast layer drainage health condition. Results show that the IRT image-processing technology confirms the capability of IRT for detecting water surface/water retention based on the thermal images captured from ballast specimen surface. In addition, an appropriate time for monitoring via IRT is after heavy rainfall upon which the water retention in the ballast layer can be more effectively detected. Particularly, presence of water and fouling material among ballast particles results in lower and more uniform surface temperature compared to dry or clean ballast specimens.

Concrete slab tracks help shield the supporting railway earth structure from external water ingress. However, the inevitable cracks that arise during its lifespan provide a pathway for water penetration, leading to changes in the degree of saturation of the underlying support. This can affect the dynamic response of the structure, however is challenging to model due to the computational requirements of three-phase unsaturated soil simulation. To address this, this paper presents two main novelties: 1) an efficient moving frame of reference approach for railway ballastless tracks on unsaturated earthworks subject to train loading, 2) new findings into the effect of degree of subgrade bed saturation on ballastless track dynamics. First the model is presented, including formulations for vehicle-track interaction and unsaturated subgrade dynamics. Considerations for numerical stability are then discussed and the model is validated, before investigating the role of subgrade bed saturation on pore water pressure and displacements. It is shown to have a high impact on pore water pressure generation, but a limited impact on deflections. The effect of train speed is then investigated and it is found that higher train speeds induce higher pore water pressures. Track irregularities are also investigated and it is found that they play an important role in pore water pressures.

Treating ballast and subgrade soil as an integrated unit for sampling and loading has proven to be an effective method for investigating the interaction between ballast and subgrade soil. Given that direct testing of specimens containing large ballast is constrained by the capabilities of standard laboratory equipment, adopting a model material of smaller size is recommended. Parallel gradation method is widely used for this purpose. This study performed an evaluation of parallel gradation method based on the response of ballast penetration into subgrade soil. Discrete element models were developed to simulate the penetration of crushed ballast, featuring three different parallel gradations, into subgrade soil. On this basis, dynamic triaxial simulations were conducted on these models. By comparing the macroscopic and mesoscopic mechanical characteristics at different scaling ratio, the applicability of the parallel gradation method for assessing ballast penetration into subgrade soil was evaluated. At the macroscopic scale, the scaling ratio of crushed ballast significantly influences the axial, volumetric, and lateral deformations observed during penetration into subgrade soil. Specifically, a smaller average grain size of ballast correlates with reduced deformations in these specimens. The penetration of crushed ballast into subgrade soil significantly increases the porosity of subgrade soil, particularly at the interface between ballast and subgrade. This increase in porosity is more pronounced with larger average grain sizes of ballast. At the mesoscopic scale, larger average grain sizes of ballast lead to more localized high contact forces and more significant stress concentrations. The parallel gradation method substantially affects the mechanical properties of ballast penetration into subgrade soil, at both macroscopic and mesoscopic scales. Therefore, a cautious approach is necessary when relying on this method for precise assessments.

Relevance. The surfaced of a gas pipeline, ballasted with weights, in a swamp qualifies as > and must be decommissioned. Aim. To establish the effect of the weight of weighting agents on a gas pipeline ascent in a swamp. The weight depends on the concentration of moles soluble in water, changes in the values of the physico-mechanical characteristics of the soil due to its watering, and the parameters of the gas pipeline operation. Objects. Sections of a gas pipeline, ballasted with weights, in a swamp in a watered area. Methods. Modeling the stress-strain state of a gas pipeline, ballasted with weighting agents, in a swamp by a one-dimensional rod system consisting of rods and their coupling nodes; integration by the Godunov orthogonal run method of a normal system of nonlinear ordinary differential equations describing the stress-strain state of the rods and compiling a solution of systems of algebraic equilibrium equations in the coupling nodes, taking into account the impact of weighting agents on stress-strain state. Results. The paper introduces the brief information on the surfacing of gas pipelines with weights installed on them. The authors have set and solved the problem of the stress-strain state of the of the gas pipeline consisting of the middle underwater part, ballasted with reinforced concrete weights, and the extreme flooded underground parts. The analysis of the stress-strain state of the gas pipeline established the following main reasons for its ascent: uneven unequal sedimentation of the base soil on the extreme parts, in which the pipe remains in a trench filled with soil; reducing the weight of weighting agents in water due to an increase in the specific gravity of water due to the growth of concentration of moles dissolved in water. The authors found the critical values of the operating parameters, at which the bulging of the pipe with an upward deflection arrow begins, preceding the ascent of the gas pipeline.

Climate change in recent decades has increased the frequency and intensity of extreme rainfall events, causing varied moisture contents in the ballasted track, which greatly challenges railway operation and track maintenance. Currently, most research about permanent deformation of fouled ballast are under dry condition or with a moisture content in the individual tested sample, which could not fully represent varied moisture conditions in the field induced by varying rainfall intensities. In this paper, permanent deformation of field-sourced fouled ballast under progressive wetting condition was investigated using large-scale triaxial cyclic tests. The results indicate that, with progressively rising water contents (0% to 12%), the fouled ballast sample maintained their stability; however, the rate of permanent strain increases to a peak value before experiencing a slight decline, aligning with classified shakedown ranges. This observed deformation features can be attributed to both the negative effect of suction loss under progressive wetting and the positive cyclic densification effect of coarse aggregates under repeated loading, an aspect that existing research have not elaborated on. To encapsulate the identified deformation characteristics, this study proposes and validates a new predictive model for the permanent deformation of fouled ballast capturing the feature of progressive wetting.

This paper presents laboratory and field test results on the use of tire cell track foundation (TCTF) consisting of an assembly of infilled rubber tires to reinforce capping material below the ballast layer. Large-scale cubical triaxial tests were carried out with two different infill materials (crushed basalt rockfill and recycled spent ballast) and they were subjected to varying cyclic loading magnitudes and frequencies. A multistage cyclic loading was performed with and without the inclusion of tire cell reinforcement, whereby the cyclic loading was applied in four different stages with 25,000 loading cycles in each stage. In the first two stages, the frequency was increased from 10 to 15 Hz for an equivalent axle load of 25 t. For the third stage, the axle loading was increased to 35 t with a frequency of 10 Hz, which was then increased to 15 Hz in the final stage. The results showed that the TCTF could reduce the vertical stress transmitted to the subgrade layer as well as curtail the vertical and lateral displacement of the ballast layer. The TCTF further stabilized the track without any significant reduction of the resilient modulus of the overlying ballast as the loading and frequency increased. Compared to a traditional track, the TCTF showed a reduction of 40.1% and 28.3% in the breakage index for the crushed latite basalt and spent ballast (i.e., recycled from ballast tips) infilling the tire cells, respectively. Test results confirm that the TCTF can significantly improve the overall track performance, and this could be mainly attributed to the increased confining pressure provided by the tire cell assembly, as well as the enhanced damping properties of the rubber tire inclusions. In addition, the concept of TCTF was tested using a fully instrumented track (20 m long) subjected to the passage of a 22-t locomotive with two fully loaded carriages. The trial was constructed within a maintenance yard for heavy haul rolling stock located in a western suburb of Sydney, Australia. Field measurements revealed that, compared to the standard track, the TCTF significantly reduces stress transfer to the subgrade soil. This ultimately mitigates excessive deformation and subgrade failure, making TCTF a sustainable solution for soft and weak subgrade soils despite initial settlement.

Mud pumping is an undesirable subgrade distress in ballastless high-speed railway, significantly affecting the ride comfort and posing a threat to train operation safety. In this study, a full-scale physical model of the ballastless slab track was developed. A rainfall simulator was installed, and various testing sensors were embedded in the trackbed to investigate the phenomenon of mud pumping in ballastless tracks. The results revealed a three-stage process for the intruded rainwater, including the initial vertical infiltration, the following horizontal infiltration, and the eventual roadbed saturation. A significant excess pore water pressure gradient (PWP) was created vertically in the roadbed due to the moving train loads. Similarly, a small longitudinal gradient was also observed. Both PWP gradients indicated the spatial migration of fine particles within the roadbed. The contact pressure distribution under the concrete base varied notably under different roadbed conditions. In the saturated state, the maximum dynamic soil stress, initially located at side of the concrete base transitioned toward the track center. The findings contribute to a deeper understanding of mud pumping mechanism in ballastless tracks.

Most of the world's railways are on ballasted track-a versatile and cost-effective support solution that can be traced back to the nineteenth century. In the twenty-first century, heavier and faster trains (freight and passenger) create higher loads and maintenance requirements. Ballast degradation becomes an important issue and solutions to increase time intervals between maintenance interventions are necessary. Some proposals involve the incorporation of elastic elements such as crumb rubber mixtures in the ballast. The crumb rubber reduces dilatancy and particle breakage. However, there is a lack of consensus on some key parameters. For example, the optimum percentage of crumb rubber in ballast is often given as 10%, which results in beneficial changes in the stiffness and energy absorption properties of ballast. However, some studies refer to 10% by volume, while others refer to 10% by weight. This leads to very different outcomes, as 10% by weight is nearly double 10% by volume of the soil particles. The paper analyses the influence of incorporating crumb rubber with two different sizes of particle, at 10% by weight and 10% by volume of mineral particles, into 1/3 scaled ballast. The addition of crumb rubber densifies the natural volumetric packing of 1/3 scaled ballast. The maximum (e(max)) and minimum (e(min)) void ratios decreased for all situations tested. This is explained in part by voids filling. Under cyclic loading, crumb rubber segregation was observed.