Weathering steel has excellent resistance to atmospheric corrosion, but still faces complex environmental corrosion problems during long-term operation. This paper mainly studies the corrosion problem of weather resistant steel materials for railway freight car bodies with a load capacity of 70 tons.

The paper analyzes the corrosion characteristics of weather resistant steel materials for truck bodies through macroscopic and microscopic methods including metallographic microscopy, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Electrochemical analysis shows that the rust layer on the surface of weathering steel changes the surface state of the material, and also proves that weathering steel used in trucks undergoes electrochemical corrosion under atmospheric corrosion. At the same time, ion chromatography technology is used to study the corrosive ions mainly present in the residual liquid and foam solution inside the vehicle body.

The corrosion of truck body materials is mainly electrochemical corrosion, and the corrosion of door materials is more obvious than that of other parts. The corrosion products are mainly Fe oxides and hydroxides. There are high concentrations of Cl^- and SO42^- ions in the residual liquid and foam solution at the bottom of the freight car, which are the main factors causing corrosion of the railway freight car body.

The foam adhesive around the door panel is in a moist state for a long time, and corrosive ions will accelerate the electrochemical corrosion of the weather resistant steel material of the door panel. Therefore, the corrosion of the cargo door panel is more severe than other components.

Conventional high-speed railways (HSR) subgrade design methods remain constrained by platform-dependent drafting systems, leading to data interaction hindrances and redundant design processes. This study strives to develop a digital earthwork design methodology that enhances design while reducing collaborative expenses.

A novel digital subgrade design approach, utilizing sophisticated analysis and modeling tools customized for different subgrade elements, is put forward in this study. The methodology incorporates the following essential steps: (1) the advancement of digital analysis and modeling techniques for diverse subgrade components, including surfaces, filling, slopes, retaining structures, and foundation treatments; (2) the formulation of a digital design principle repository incorporating various slope protection combinations; (3) the establishment of a comprehensive digital design framework and process for subgrade cross-sections; and (4) the development and implementation of an open-source digital design system.

The proposed method liberates subgrade design from the constraints of conventional drawing platforms, elevating efficiency, intelligence, and flexibility. The open software architecture and code have achieved over 60% efficiency gains in design workflows during its deployment on three major high-speed rail projects: the Baotou-Yinchuan HSR corridor, Shenyang-Baihe HSR network, and Weifang-Yantai HSR system.

This paper introduces an innovative digital design methodology that enables modular and parametric design for railway subgrade sections. The proposed approach provides a digital base for the intelligent design and maintenance of the next-generation high-speed railway.

The indoor vibration compaction test (IVCT) was a key step in controlling the compaction quality for high-speed railway graded aggregate (HRGA), which currently had a research gap on the assessment indicators and compaction parameters.

To address these issues, a novel multi-indicator IVCT method was proposed, including physical indicator dry density (ρ_d) and mechanical indicators dynamic stiffness (K_rb) and bearing capacity coefficient (K₂₀). Then, a series of IVCTs on HRGA under different compaction parameters were conducted with an improved vibration compactor, which could monitor the physical-mechanical indicators in real-time. Finally, the optimal vibration compaction parameters, including the moisture content (ω), the diameter-to-maximum particle size ratio (R_d), the thickness-to-maximum particle size ratio (R_h), the vibration frequency (f), the vibration mass (M_c) and the eccentric distance (r_e), were determined based on the evolution characteristics for the physical-mechanical indicators during compaction.

All results indicated that the ρ_d gradually increased and then stabilized, and the K_rb initially increased and then decreased. Moreover, the inflection time of the K_rb was present as the optimal compaction time (T_lp) during compaction. Additionally, optimal compaction was achieved when ω was the water-holding content after mud pumping, R_d was 3.4, R_h was 3.5, f was the resonance frequency, and the ratio between the excitation force and the M_c was 1.8.

The findings of this paper were significant for the quality control of HRGA compaction.

The rapid development of China's railway construction has led to an increase in data generated by the high-speed rail (HSR) catenary system. Traditional management methods struggle with challenges such as poor information sharing, disconnected business applications and insufficient intelligence throughout the lifecycle. This study aims to address these issues by applying building information modeling (BIM) technology to improve lifecycle management efficiency for HSR catenary systems.

Based on the lifecycle management needs of catenary engineering, incorporating the intelligent HSR "Model-Data Driven, Axis-Plane Coordination" philosophy, this paper constructs a BIM-based lifecycle management framework for HSR catenary engineering.

This study investigates the full-process lifecycle management of the catenary system across various stages of design, manufacture, construction and operation, exploring integrated BIM models and data transmission methods, along with key technologies for BIM model transmission, transformation and lightweighting.

This study establishes a lossless information circulation and transmission system for HSR catenary lifecycle management. Multi-stage applications are verified through the construction of the Chongqing-Kunming High-Speed Railway, comprehensive advancing the intelligent promotion and high-quality development of catenary engineering.

MxV Rail conducted multiple single tie push tests (STPTs) between 2020 and 2023 to assess the changes in lateral tie resistance from tonnage accumulation, dynamic track stabilizers (DTS), tie type and ballast condition. High lateral tie resistance is necessary for preventing lateral misalignments and track buckles. Therefore, understanding how various factors affect the lateral tie resistance will aid in the development of track buckling risk assessments and ballast maintenance best practices.

The test involved tamping a section of track that consisted of both concrete and wood ties and then increasing the lateral tie resistance, using either tonnage during speed restrictions or a DTS. The STPTs and top-of-rail (TOR) elevation measurements were taken at multiple stages, including immediately after tamping and then after different tonnage increments or DTS. The results from this test were then added to a compiled measurement from previous tests, and the results from all the tests were used to develop general guidelines for ballast maintenance best practices and trade-off considerations.

The results showed multiple factors affect the lateral track strength and therefore the susceptibility to misalignments and track buckles. The disturbance from ballast tamping can reduce the lateral track strength by 20-80% (~45% median) and can be compacted from either tonnage (25-50% regain in strength after 0.1 m gross ton or MGT) or DTS (33-78% regain in strength). The amount of ballast (shoulder width and crib height), tie type and ballast characteristics all have a meaningful role in lateral track strength.

This paper is based on the testing programs conducted by authors at MxV Rail.

The precast concrete slab track (PST) has advantages of fewer maintenance frequencies, better smooth rides and structural stability, which has been widely applied in urban rail transit. Precise positioning of precast concrete slab (PCS) is vital for keeping the initial track regularity. However, the cast-in-place process of the self-compacting concrete (SCC) filling layer generally causes a large deformation of PCS due to the water-hammer effect of flowing SCC, even cracking of PCS. Currently, the buoyancy characteristic and influencing factors of PCS during the SCC casting process have not been thoroughly studied in urban rail transit.

In this work, a Computational Fluid Dynamics (CFD) model is established to calculate the buoyancy of PCS caused by the flowing SCC. The main influencing factors, including the inlet speed and flowability of SCC, have been analyzed and discussed. A new structural optimization scheme has been proposed for PST to reduce the buoyancy caused by the flowing SCC.

The simulation and field test results showed that the buoyancy and deformation of PCS decreased obviously after adopting the new scheme.

The findings of this study can provide guidance for the control of the deformation of PCS during the SCC construction process.

Salt rock from salt lakes can serve as a cost-effective material for subgrade filling, as demonstrated in projects like the Qarhan Salt Lake section of the Qinghai-Tibet Railway and the Qarhan Salt Lake section of the G215 Highway. This state-of-the-art paper aims to summarize the engineering properties of salt rock filling and present the advances of its utilization.

This paper collects and analyzes laboratory and field data of salt rock filling from previous studies to present a comprehensive analysis of the engineering properties and utilization of salt rock fillings.

Salt rock primarily contains minerals such as halite and glauberite, which contribute to its unique phase-changing behavior under varying environmental conditions, impacting its mechanical properties. Salt rock filling shrinks when in contact with vapor or unsaturated brine and expands under cooling or evaporation. Its use is particularly recommended for arid regions, with specific restrictions depending on the structure type. This paper discusses suggested countermeasures to mitigate these issues, as well as key quality acceptance indices for salt rock filling compaction. Moisture content after air-drying is recommended as a crucial parameter for construction quality control.

This review aims to support future research and engineering practices in salt rock subgrade applications.

The deformation of the roadbed is easily influenced by the external environment to improve the accuracy of high-speed railway subgrade settlement prediction.

A high-speed railway subgrade settlement interval prediction method using the secretary bird optimization (SBOA) algorithm to optimize the BP neural network under the premise of gray relational analysis is proposed.

Using the SBOA algorithm to optimize the BP neural network, the optimal weights and thresholds are obtained, and the best parameter prediction model is combined. The data were collected from the sensors deployed through the subgrade settlement monitoring system, and the gray relational analysis is used to verify that all four influencing factors had a great correlation to the subgrade settlement, and the collected data are verified using the model.

The experimental results show that the SBOA-BP model has higher prediction accuracy than the BP model, and the SBOA-BP model has a wider range of prediction intervals for a given confidence level, which can provide higher guiding value for practical engineering applications.

The paper aims to clarify the operation rationality of high speed trains (HSTs) under tunnel condition with the speed of 400 km/h through representative aerodynamic factors including running drag, eardrum comfort, carriages noise, aerodynamic loads on tunnel ancillary facilities and HST, micro-pressure waves, and then put forward engineering suggestions for higher speed tunnel operation based on the analysis.

Based on the field measurement data of CR400AF-C and CR400BF-J tunnel operation, correlations between each aerodynamic indicators with HST speed were established. By analyzing the safety reserve of aerodynamic indicators at 350 km/h and the sensitivity of each indicator to HST speed increasing and the indicators' formation mechanism, the coupling relationship between various indicators was obtained.

The sensitivity of different aerodynamic indicators to speed variation differed. The aerodynamic indicators representing flow field around HST showed a linear relationship with HST speed including noise, eardrum comfort, aerodynamic load on HST body. The positive aerodynamic load on tunnel auxiliary facilities and the micro-pressure wave at the entrance of the tunnel have the same sensitivity to the 3th-power relation of HST speed. The over-limit proportion of micro-pressure wave was the highest among the indicators, and aerodynamic buffering measures were recommended for optimization. The open tunnel pressure relief structure is recommended, while allowing trains to pass through the tunnel at an unconditional speed of 380 km/h.

Comprehensive evaluation of multiple aerodynamic indicators for HST tunnel operation with higher speeds was realized. The main engineering requirements to release aerodynamic effect were identified and the optimization scheme is proposed.

The study aims to build a high-precision longitudinal dynamics model for heavy-haul trains and validate it with line test data, present an optimization method for multi-stage cyclic brakes based on the model and conduct a multi-objective detailed evaluation of the driver's manipulation during cyclic braking.

The high-precision longitudinal train dynamics model was established and verified by the cyclic braking test data of the 20,000 t heavy-haul combination train on the long and steep downgrade. Then the genetic algorithm is employed for optimization subsequent to decoupling multiple cyclic braking procedures, with due consideration of driver operation rules. For evaluation, key manipulation assessments in the scenario are prioritized, supplemented by multi-objective evaluation requirements, and the computational model is employed for detailed evaluation analysis.

Based on the model, experimental data reveal that the probability of longitudinal force error being less than 64.6 kN is approximately 68%, 95% for less than 129.2 kN and 99.7% for less than 193.8 kN. Upon optimizing manipulations during the cyclic braking, the maximum reduction in coupler force spans from 21% ~23.9%. And the evaluation scores imply that a proper elevation of the releasing speed favors safety. A high electric braking force, although beneficial to some extent for energy-saving, is detrimental to reducing coupler force.

The results will provide a theoretical basis and practical guidance for further ensuring the safety and energy-efficient operation of heavy haul trains on long downhill sections and improving the operational quality of heavy-haul trains.