Research purposes: The Quzhou-Lishui Railway, located on the northwestern side of the Kuocang Mountains in Zhejiang Province, is a typical mountain railway characterized by frequent high-steep slopes and rockfall hazards. This study focused on the stability of high-steep bank slopes and the side and heading slopes at tunnel portals along the Songyang-Lishui section, as well as the impact risk of rockfalls on portal areas. Limit equilibrium and numerical analysis methods were used to analyze slope stability, while discontinuous deformation analysis was adopted to evaluate rockfall movement,providing a theoretical basis for subsequent engineering design and construction.
Research conclusions: (1) The initial risk level of the Laozhuxi Bridge abutment slope is high and targeted treatment measures need to be taken to reduce the risk level. Under gravity alone the slope is stable, but when both gravity and pore water pressure are considered, it bocomes unstable. The critical slope angle of the abutment slope is 60°, indicating that the bridge abutment should be constructed on bedrock below the 60° slope line. (2) Among the 11 tunnel entrances and exits of the eight tunnels along the entire line, two are classified as high risk, three as moderate risk, and six as low risk. After implementing targeted measures, the residual risks are reduced to a low and acceptable level. (3) Rockfall simulations at six portals with high rockfall risk show that most rocks roll down the slope without stopping, while some bounce off the ground as rolling,and their trajectories are likely to cross tunnel openings, thereby posing a threat to tunnel construction and operational safety.(4) The slopes at the entrances of Ma'anshan and Zhoutan tunnels are unstable, while the slopes at the exit of Ma'anshan tunnel and the entrances of Yangshan and Songyin tunnels are stable. (5) These results provide a reference for the stability analysis of high-steep slopes and the assessment of rockfall hazards in similar mountain railways.

Research purposes: Under thermal cycling, the earth pressure behind integral abutments changes significantly and exhibits a ratcheting effect, causing the actual pressure to far exceed the design value. Therefore, based on pseudo-static tests of integral abutment-pile-soil interaction with EPS, this study further investigates the distributions of earth pressure behind the abutment and along the pile, examines the influence of EPS thickness, proposes a calculation method for the EPS-dependent earth pressure reduction coefficient, and compares the “m” method with the “p-y” curve method.
Research conclusions: (1) Installing EPS behind the abutment significantly affects the mechanical behavior of the integral abutment-pile-soil system. Increasing EPS thickness effectively slows the growth of earth pressure behind the abutment and shifts its maximum value from the abutment base to around the mid-height. (2) The lateral earth pressure on the pile decreases approximately linearly with increasing EPS thickness. At the same embedment depth, the pressure decreases as EPS thickness increases. (3) Based on the test results, a method is proposed for calculating the attenuation coefficient of earth pressure behind the abutment considering EPS thickness. (4) For lateral pile pressure, the distribution predicted by the “m” method differs markedly from the test results, whereas the “p-y” curve method gives a closer distribution. However, both methods show large deviations in peak pressure, requiring further study. (5) The findings can provide guidance for EPS design behind integral abutments, earth pressure reduction calculations, and pile foundation force analysis.

Research purposes: Most of the existing heavy haul railways in China adopt ballasted track structure. The strengthening measures of ballasted track structure in existing and new heavy haul lines are very important to ensure the safety and reliability of railway operation. The purpose of this study is to analyze the failure mechanism of heavy haul railway ballast track, and explore its influence on rail, fasteners and sleepers, sleeper pads, ballast beds, etc., so as to take targeted strengthening measures.
Research conclusions: (1) High-strength and wear-resistant rails are used, and continuously welded rails are laid in one go. (2) On the basis of the size of the type III sleeper, appropriately increasing the height and width of the sleeper is beneficial to reduce the dynamic stress of the ballast bed, the vertical acceleration of the sleeper, and the ballast pulverization. (3) Under heavy traffic conditions, the application of high-stiffness under-sleeper pads is recommended to enhance track structural stability and optimize maintenance operations. (4) It is more conducive to the stress of the track structure by laying elastic sleepers and using ballast cushion in the rigid foundation section. (5) In the transverse weak section of the track structure, rail supports, transverse resistance devices and high-strength elastic strip should be installed. In the weak section of turnout on ballasted bridge, beam limit piles should be added. In the section subject to long-term braking and starting, it is advisable to gradually replace the existing ballast with optimally graded ballast and strengthen observation. (6) The research results can provide reference for the design, construction, operation and maintenance of ballasted track structure in heavy haul railway.

Research purposes: To meet the engineering application requirements of 600 km/h high-speed maglev transportation technology, studies are carried out on the allowable limits of track irregularities for high-speed maglev trains through refined rigid-flexible coupled multi-body dynamics simulation analysis. By analyzing the causes of irregularities in conventional high-speed maglev tracks and clarifying the classification and evaluation indicators of track irregularities, a high-speed maglev vehicle system dynamics model and an irregularity parametric model are established, studying the dynamic response of the maglev vehicle operating at 600 km/h under irregularity excitation.
Research conclusions: (1) The 600 km/h maglev train is more sensitive to the long wave part of track irregularities during operation. A polynomial approximation fitting method is used to combine the simulated track spectrum with the long wave part of HSR ballastless track irregularities, creating a 300 m wavelength irregularity. (2) The acceleration and stability indicators of the train body change significantly with increasing wavelength, while the acceleration of the suspension frame and electromagnet, as well as the suspension guide gap, exhibit no obvious change. (3) The maglev track vertical installation limit of 1.032 m on the stator surface can be appropriately relaxed with a tolerance of ±0.8 mm, and the horizontal installation limit of 3.096 m on the guide surface can be relaxed with a tolerance of ±2 mm. (4) The research results can provide a reference for the formulation of relevant standards and regulations for China's 600 km/h high-speed magnetic levitation transportation system.

Research purposes: The CRTS Ⅱ slab ballastless track on the Shanghai-Kunming high-speed railway faces typical defects such as mortar layer separation, wide and narrow joint damage, inclined cracks in the supporting layer, or base plate damage after long-term service. Traditional manual inspection suffers from low efficiency, fragmented data, and insufficient quantitative capability. To enhance the intelligent perception and health management level of the service state of operational railway tracks, this paper constructs a multi-modal collaborative detection system that integrates high-definition images, structured light, and 3D laser point clouds. It employs an RT-DETR and Canny cascade model to achieve high-precision identification of apparent cracks, utilizes the projection slicing algorithm to analyze mortar layer separation, and employs 3D point cloud semantic segmentation and ICP registration to calculate the adjustment amount of fasteners. An intelligent perception system for service state is constructed, enabling quantitative analysis of the full-section service state of CRTS II slab ballastless track.
Research conclusions: (1) A multi-source fusion intelligent detection system that integrates images, structured light, and 3D point clouds has been constructed, breaking through the limitations of traditional manual inspection and single-sensing methods. With a detection efficiency of 10 km/h, it achieves automatic quantitative analysis of the service status of the entire track section. (2) A complete set of high-precision detection technologies for typical track defects has been formed, with a crack identification error of 0.31 mm and a gap detection error of 0.26 mm. The fastening adjustment detection achieves millimeter-level accuracy, meeting the precision requirements for high-speed rail track operation and maintenance. (3) The applicability and reliability of this technical system have been verified through engineering applications. The research results can effectively support precise detection of track defects, scientific assessment of status, and intelligent decision-making for operation and maintenance, enhancing the intelligence and refinement level in the operation and maintenance of high-speed railway ballastless tracks.

Research purposes: In urban rail transit, underground stations with stabling sidings generally exceed 500 m in length, leading to problems such as large construction scope, high investment, and severe disturbance to the urban environment. Due to geometric constraints, conventional single turnouts and their combinations cannot further shorten the length of auxiliary lines, which has become an industry bottleneck that limits the compression of station length. Targeting this scenario and focusing on the core demand of auxiliary line shortening, this research develops a new symmetrical two-way turnout. It encompasses the structural design, parameter determination, strength optimization and numerical safety verification, forming a turnout scheme adapted to modern metro engineering. The proposed turnout effectively shortens the station auxiliary lines, thereby reducing station excavation scale, saving engineering investment, and lowering construction difficulty and project risks. Consquently, it resolves the layout difficulty of metro stations with stabling sidings in confined urban spaces.
Research conclusions: (1) The new turnout can replace conventional single turnouts and realize smooth connection between the main line and stabling siding without setting a reverse curve. It effectively shortens the length of auxiliary lines, and features strong adaptability, low construction difficulty and minor environmental impact. (2) The core parameters and structural strength of the turnout fully comply with the current metro design specifications and safety operation requirements, with sufficient safety reserve. (3) Verified by the engineering application of Harbin Metro Line 3, the turnout can effectively shorten the length of auxiliary lines, save civil construction investment, and maintain stable and reliable performance in long-term operation. (4) The research results can be directly applied to the design of urban rail transit stations with stabling sidings, and also provide technical reference for the research and development of special turnouts for similar rail transit projects.

Research purposes: In China, the absence of a unified design specification for the dynamic amplification factor (DAF) of long-span half-through railway arch bridges has led to a conservative "bridge-specific analysis" strategy in engineering practice. This necessitates performing detailed dynamic time-history analysis for each individual bridge, significantly increasing computational costs and prolonging the design cycle. Moreover, the overly conservative approach may result in design redundancies, which hinders both economic efficiency and standardization in the development of this bridge type. Therefore, establishing a dedicated design formula for the DAF of such bridges carries substantial theoretical and practical importance.
Research conclusions: (1) The DAF of long-span half-through railway arch bridges exhibits a monotonically increasing exponential relationship with a normalized variable constructed from bridge span, the first two vertical natural frequencies, and train operating speed. (2) Through systematic validation of data samples, the fitted formula for the DAF proposed in this paper demonstrates high fitting accuracy within the sample range, and the resulting design equation effectively covers all data points with zero outliers. (3) This study establishes a design formula for the DAF of such bridges, providing a reliable theoretical basis for the design of long-span railway arch bridges and offering significant value for engineering applications.

Research purposes: To investigate the temperature field distribution of concrete box arch ribs in long-span deck arch bridges in western mountainous regions, clarify the vertical temperature gradient characteristics and their longitudinal variation along the arch rib, and to establish a vertical temperature gradient calculation formula suitable for the climatic conditions of this region, this paper studied the temperature field of typical arch ribs sections such as the arch springing and quarter-span, based on temperature monitoring data from the Meixi River Grand Bridge. The measured temperature distribution and the attenuation pattern of the vertical temperature gradient across various arch rib sections were systematically analyzed, considering the shielding effect of the deck system on longitudinal temperature distribution. Furthermore, a semi-empirical regression formula was introduced to establish a vertical temperature gradient model for box arch ribs without flanges, and its applicability and accuracy were verified with multi-period monitoring data.
Research conclusions: (1) The vertical temperature difference decreased gradually from the arch springing to the crown under the influence of the deck system, with the amplitude reducing from 5.1 ℃ to 0.6 ℃. (2) The overall distribution pattern was consistent across sections: the gradient was higher from the top slab to the web, while the variation between the web and bottom slab was relatively mild. (3) The exponential calculation model accurately captured the temperature distribution along the section height, with recommended parameter sets of (T₀, α) = (5.4, 0.55) and (3.9, 0.5) for the springing and quarter-span sections, respectively. Validation in other periods showed a maximum error of only 0.2 ℃, demonstrating high accuracy and generalization capability of the model. (4) The results provide a reference for analyzing temperature effects and structural design of long-span arch bridges and contribute to improving calculation methods and parameter selection for temperature loads of deck arch ribs in China's bridge design codes.

Research purposes: The high-temperature environment in high-geothermal tunnels deteriorates the construction conditions, reduces construction efficiency, and affects the durability of concrete. Moreover, the generated thermal stress can cause cracking and deformation of the surrounding rock and support, which has adverse effects on structural safety and rock stability. Therefore, the thermal stress in high-geothermal tunnels is an issue that must be addressed. Taking into account the dynamic changes in temperature during the construction process, temperature stress analysis is carried out based on the two-dimensional thermoelastic theory and superposition principle.
Research conclusions: (1) An elastic solution for the thermal stress in high-geothermal tunnels considering the construction process is derived. And the spatio-temporal evolution laws of the additional stress and displacement caused by temperature changes are obtained. (2) In a high-geothermal tunnel, the additional displacement is directed inward. Its magnitude peaks at an intermediate radius and then decays radially. It grows steadily with time, yet remains far smaller than the excavation deformation driven by in-situ stress and gravity. (3) The additional radial stress induced by temperature variation is mainly tensile. It increases with time, rises to a maximum, and then declines along the radial direction. As the temperature-adjustment ring expands, this stress peak migrates deeper into the surrounding rock. (4) The additional circumferential stress is much larger than the additional radial stress and is discontinuous at the interface between the support and the surrounding rock. In the support area, the additional circumferential stress is tensile stress before the application of the thermal insulation layer. After that, as the temperature rises, it turns into compressive stress. (5) The research conclusion has certain guiding value for the analysis of structural safety and surrounding rock stability of high-geothermal tunnels.

Research purposes: To effectively control the excavation deformation of deep buried tunnel surrounding rock, it is necessary to conduct research on the synergistic bearing effect of surrounding rock and support considering the influence of support structure types. Relying on the Fu-Xie section tunnel engineering of Chongqing Rail Transit Line 18, the mechanical model of tunnel composite lining is established. Based on the principle of convergence-constraint method, analytical solutions for the displacement of surrounding rock and support reaction force are derived. The accuracy of the theoretical model is verified by comparing it with numerical solutions. Finally, the radial displacement changes of surrounding rock and the transmission law of support reaction force under unsupported and supported conditions are discussed, and the synergistic bearing process and effect of surrounding rock-composite lining structure are evaluated.
Research conclusions: (1) The minimum errors between the analytical solution and numerical simulation regarding the surrounding rock deformation and the initial support reaction force are 5.3% and 0.4%, respectively, which verifies the accuracy of the composite lining theoretical model and its analytical solution. (2) During the synergistic bearing process, the initial support plays a major role in constraining the deformation of the surrounding rock. After the initial support is applied, the maximum deformation of the surrounding rock is reduced by 18%, and the secondary lining hardly bears the deformation. The initial support bears most of the surrounding rock load, while the secondary lining only bears an average of 0.16% of the load. (3) The evaluation indicator for the synergy degree is defined, and the utilization rate of tunnel support performance gradually increases with the increase of section angle (with the section angle at the arch waist position being 0°). The utilization rate of initial support performance is much higher than that of the secondary lining. (4) The results of this study can be used for the design of support systems during the excavation process of deep buried tunnels.

Research purposes: Effective prevention and control of large deformation disasters in soft rock is crucial for the smooth construction of long and large tunnels. Based on the concept of mutual coordination between active reinforcement of surrounding rock and deformation energy release, an approach of active-yield support is proposed. This article investigates the characteristics and effects of the active-yield support, its utility and rationality, as well as the reasonable composition of the active-yield support system and its field application, through support effect analysis, numerical simulation, and field test.
Research conclusions: (1) Active-yield support possesses two major functions: "active support" and "yield support". In addition to providing immediate radial active support force, it should also exhibit good yield functionality. (2) The effectiveness of active support is reflected in its ability to improve the cohesion of surrounding rock, effectively enhancing its self-supporting capacity. Furthermore, the improvement of both the cohesion and elastic modulus of surrounding rock can enhance the control over its deformation. (3) The rationality of active-yield support lies in the fact that the implementation of active support provides a more sufficient "release interval" for subsequent "yielding". (4) This article proposes an active-yield support system, centered around active-yield anchor cables and combined with conventional preliminary support (steel frame + shotcrete). Based on this, the experimental section verifies that the active-yield support system exhibits excellent deformation control capabilities and yield functionality. (5) The research findings provide significant guidance for understanding different support modes for tunnels with large deformations in soft rock, as well as for selecting appropriate support modes.

Research purposes: The disease phenomena in the LSS Tunnel on the Nanning-Kunming Passenger Railway initially manifested as invert bulging, gradually developing into invert arch and filling layer cracking, concrete corrosion with sanding and siltation, as well as cracking and spalling of the parallel heading sidewalls. As time progresses, the lengths of the bottom bulges in each section tend to extend toward both ends, and the degree of concrete corrosion gradually becomes more severe, affecting railway operational safety.To investigate the causes of the hazards, the degree of the concrete corrosion, and its development trends, successive geological drilling, well television, geophysical surveys, in-situ stress testing, experiments, and specialized studies were employed. Through a method of elimination, it was determined that the primary controlling factors of the hazards were small deformations induced by high in-situ stress and concrete corrosion caused by sulfates.
Research conclusions: (1) The hazards in Sections 1-3 are primarily caused by the upward extrusion effect of gently dipping strata at tunnel invert under high geostress environments, and secondarily by the invert arching due to high groundwater levels and dynamic train loads, as well as by construction-related structural defects such as insufficient thickness and inadequate curvature of invert arch that failed to effectively resist and suppress initial structural deformation. (2) The hazards in Sections 4-11: During the initial phase (2017-2019), the primary cause is the upward extrusion effect of the fragmented rock mass at the tunnel bottom under high-stress environment, combined with local construction defects in the tunnel bottom structure failing to effectively resist and suppress initial deformation, resulting in micro-level deterioration of the tunnel bottom structure. Secondary factors include sulfate (SO₄^2-) erosion from groundwater and expansion reactions from concrete containing gypsum aggregate upon water exposure, leading to concrete expansion-induced bulging and reduced strength. During the post-construction phase (2020-present), the primary cause of deformation is the continuous corrosion of concrete,producing large amounts of sulfate corrosion products such as gypsum, ettringite, and monosulfate, leading to concrete volume expansion and bulging. The presence of gypsum and anhydrite in concrete aggregates accelerate the corrosion rate and severity. Secondary causes include construction defects in tunnel base structures, reduced early-age concrete strength, and the upward extrusion effect of fractured rock mass under high geostress, all of which exacerbate deformation development. (3) Based on the causes of the diseases and the degree of concrete corrosion, it is recommended to consider engineering measures such as water drainage at the tunnel bottom, corrosion protection for concrete, and reconstruction of the invert arch. (4) The research methods and findings provide valuable references for the investigation and prevention and control of engineering hazards under similar geological conditions.

Research purposes: Aiming at the matching problem of design parameters for the seven-span section insulator in a railway catenary system under the contact wire and messenger wire tension combination of 25 kN + 20 kN, this paper conducts static mechanics and pantograph-catenary dynamic simulation studies on catenary. By establishing simulation models of seven-span section insulator catenary with different design parameters, the static mechanical parameters, dynamic pantograph-catenary characteristics and load distribution laws of registration devices are analyzed. The key design parameters of seven-span section insulator for high-tension catenary are systematically identified. This study aims to provide a theoretical basis for the design, construction, operation & maintenance of high-tension catenary section insulator in new construction or speed-up reconstruction projects of mixed passenger-freight and heavy-haul railways.
Research conclusions: (1) When a newly built 200 km/h mixed passenger-freight railway is reserved for speed-up to 250 km/h, adopting a tension combination of 25 kN + 20 kN for the contact wire and messenger wire can effectively reduce reconstruction costs in the later speed-up stage. (2) With the contact wire and messenger wire tension combination of 25 kN + 20 kN, the span between conversion poles of the seven-span section insulator of the catenary is 40 m, the anchor lift of the contact wire is 0.43 m, and the distance from the end of the sectionalizing insulator to the registration point is 4 m. The lengths of the neutral section and the dead zone can meet the requirements of the train operation scheme of the line. The neutral section structure can satisfy the dynamic clearance under the maximum lift of the pantograph. The forces at each registration point and the gradient of the dropper can meet the requirements of component performance and the operation and maintenance regulations. (3) The scheme of five consecutive 40 m spans (40 m + 40 m + 40 m + 40 m + 40 m) between conversion poles of the seven-span articulated neutral section is applicable to the dynamic performance requirements of pantograph-catenary system at the operation speed of 200 km/h with the rated contact suspension tension of 20 kN + 15 kN, and also meets the dynamic performance requirements at 250 km/h with the rated tension of 25 kN + 20 kN. (4) The research results can be applied to the design, construction, operation and maintenance of seven-span section insulator for mixed passenger-freight railways and high-speed railways with a rated contact suspension tension of 25 kN + 20 kN.

Research purposes: To systematically evaluate the structural impact and multi-dimensional restructuring effects of introducing high-speed rail (HSR) into a major aviation hub's ground access system, this paper establishes a six-dimensional framework encompassing "network structure, passenger flow structure, spatial scope, transport organization, facility layout, and coordination mechanism." Through this framework, it systematically analyzes the chain-type restructuring effects of HSR integration at Xi'an Xianyang International Airport. Firstly, by analyzing the current bottlenecks in the ground transportation system of Xi'an Xianyang International Airport and its competitive-cooperative dynamics within the regional air network, the strategic necessity for HSR integration is clarified. Subsequently, a multi-scenario forecasting model is constructed to quantitatively analyze the long-term evolution of passenger volumes and shifts in modal share following HSR access. Finally, the value of HSR to the hub is comprehensively evaluated from multiple dimensions, including transport efficiency, hinterland expansion, and resource allocation. Based on this, pathways for optimizing the integrated transport system and strategies for coordinated operation are proposed. This research not only provides direct decision-making support for the planning and implementation of large-scale comprehensive transport hubs but also offers systematic methodological guidance and practical references for promoting air-rail integrated development in similar regional hubs.
Research conclusions: (1) The network structure has transformed from a highway and rail terminal into a comprehensive hub deeply integrated into the national high-speed rail network, intercity rail network and urban rail transit system, forming an efficient multi-modal corridor. (2) The passenger flow structure has shifted to an intensive new pattern with rail transit as the backbone, high-speed rail as a cross-regional artery, and highways as a supplement. (3) The service scope has expanded from Xi'an urban area to the Guanzhong Plain Urban Agglomeration and wider regions, promoting the airport's upgrading from a "city airport" to a "regional core comprehensive transportation hub". (4) Transport organization and facility layout need to be optimized accordingly. In particular, the "soft reconstruction" of the coordination mechanism is required to break industrial barriers, establish an integrated operation and service system, and unleash the efficiency of air-rail intermodal transport. (5) The introduction of high-speed rail has triggered a multi-level chain reconstruction ranging from physical connection and operation mode to spatial expansion and institutional coordination. This study provides a systematic analytical framework and practical reference for the planning and performance improvement of similar air-rail hubs.

Research purposes: The twisted roof on the ground of Shenzhen Dayun Hub adopts steel structures, which forms a twisted combination spatial force structure system through straight and Y-shaped columns, circular tube main beams, inverted trapezoid secondary beams, and a central inverted triangle spatial truss. The structural members are arranged with ups and downs, bends and twists. And these members have significant differences in force compared to conventional spatial structures, especially their stability performance is unclear. Therefore, this article focuses on studying the stability of the roof structure, revealing its special instability mechanism, and proposing stability design suggestions.
Research conclusions: (1) Based on the analysis of the overall force characteristics of the members, the hub roof is defined as a twisted spatial grid structure. (2) Through eigenvalue buckling analysis and nonlinear buckling analysis, the stability and bearing capacity of the twisted spatial grid structure are studied, and it is determined that this type of structure does not have elastic ultimate bearing capacity and has good stability performance. (3) Through direct analysis and full process buckling analysis, the safety of high length cantilever columns for the roof with slenderness ratios exceeding the limit is verified. (4) The research results provide necessary basis for the design of the twisted steel structure roof for Shenzhen Dayun Hub, and offer references for the design of similar spatial grid structures.

Research purposes: As an important carrier of integrated transport-tourism development, tourist rail transit is experiencing rapid development driven by policy support and market demand. It differs fundamentally from conventional rail transit in terms of service objects and functional characteristics. Starting from the connotation and classification of tourist rail transit, this paper analyzes its typical characteristics and proposes the technical roadmap and future development directions from an overall design perspective, aiming to provide technical support for the scientific planning and high-quality construction of tourist rail transit.
Research conclusions: (1) Tourist rail transit is a new type of rail transit system oriented around tourism and sightseeing, creating unique experiences for tourists through rail transport. It can be classified into three categories: dedicated tourist lines within scenic area, multi-functional tourism-transport corridor routes, and pure tourism sightseeing lines. (2) Tourist rail transit exhibits typical characteristics including significant functional differences, distinctive passenger flow distribution patterns, stringent economic requirements, prominent landscape integration demands, and high expectations for comfort and experiential quality. (3) The overall design of tourist rail transit should be approached from four dimensions: conducting comprehensive integrated planning, reasonably determining project functional positioning, emphasizing economic orientation, and effectively enhancing tourist experience. (4) The research findings provide a guiding direction for the design of tourist rail transit and support its development.

Research purposes: Traditional mechanical ventilation systems suffer from poor thermal comfort and high energy consumption. To tackle these issues, direct evaporative cooling (DEC) ventilation systems have been adopted in urban rail transit projects in Lanzhou, Urumqi and other similar cities. This study identified the key factors influencing the operational performance of metro DEC ventilation systems and proposed an innovative time-segmented control strategy for humidity regulation and energy conservation, which adjusts the spray mode of DEC units in different time periods. Through experimental analysis, the interrelationships among the air temperature and humidity at the inlet and outlet of DEC units, the indoor thermal environment parameters of metro stations, and the operating power of system equipment were tested and analyzed. The results verified the reliability and significant energy-saving effect of the proposed time-segmented spray adjustment strategy.
Research conclusions: (1) The DEC ventilation system can maintain the supply air temperature within the range of 16 ℃ to 18 ℃, demonstrating a significant capacity to regulate the ambient temperature in station public areas. The system ensures high stability in temperature and humidity control, with temperature fluctuations kept within ±1 ℃ and relative humidity variations not exceeding ±10%. (2) Top spraying is the key water distribution method affecting unit performance. When the top spray system in the filler zone is activated, the direct evaporative cooling efficiency can generally reach over 85%. (3) Under various spraying modes, the optimal operating frequency of the system fan at the best working condition is 40 Hz. By regulating the fan frequency and the spraying mode, the system's operational energy consumption can be significantly reduced. (4) The time-segmented spray control strategy proposed in this study—regulating the on/off status of the front spray system and employing top spraying, combined front-and-top spraying, front spraying or no spraying at different times—effectively mitigates the issue of high relative humidity in public areas. This strategy is applicable to urban rail transit DEC cooling systems. (5) The outcomes of this research provide valuable references for the operational control design and management of DEC technology in urban rail transit ventilation and cooling systems.

Research purposes: To address design-demand deviations arising from inaccurate vibration source intensity characterization and insufficient understanding of spatial variability in vibration attenuation along transmission paths, this study analyzes over 700 vehicle-induced vibration datasets from multiple urban rail transit lines in China. It identifies the discrete nature of source intensity, proposes a refined measurement method, quantifies the spatial variability of vibration attenuation, and provides parameters for train-induced vibration prediction and control, thereby mitigating both under-reduction, which leads to social complaints, and over-reduction, which results in engineering waste.
Research conclusions: (1) Repeated measurements reveal significant discreteness in vibration source intensity. The moving average method with a recommended window width of 20 effectively approximates the overall stable vibration level. (2) Vehicle-induced vibration propagates to sensitive points through three attenuation stages, with the attenuation varying both across stages within the same section and across different track bed types within the same stage. (3) The effect of track vibration reduction measures is lower at ground level than at tunnel walls, therefore, appropriate safety margins should be incorporated when tunnel wall results are used to guide design. (4) The findings provide reference for the environmental assessment and vibration reduction design of underground rail transit lines.

Research purposes: The plateau region has environmental characteristics such as low air pressure and large temperature difference, the concrete of infrastructure suffers from severe shrinkage and cracking. This article conducted field experiments using the same raw materials and mix proportions in high-altitude areas (71 kPa) and low altitude areas (101 kPa) to study the effects of EA, SAP and SRA on the drying shrinkage deformation of cement mortar.
Research conclusions: (1) The decrease in air pressure will increase the drying shrinkage rate of cement mortar. Compared with normal pressure conditions, the drying shrinkage rate of cement mortar under low air pressure increases by 13.4% at 7 d of age and 64.5% at 28 d of age. (2) The reason for the more severe cracking phenomenon of cement-based materials under low-pressure conditions is that the water loss is faster, the porosity increases, especially the increase of capillary pores between 10-50 nm, and the negative pressure of internal pores is greater. (3) Under low atmospheric pressure, EA, SAP, and SRA can reduce the drying shrinkage rate of cement mortar. Among them, the combination of 0.1% SAP and 0.5% SRA has the best effect, with a reduction of 30.8% in the drying shrinkage rate of cement mortar. (4) The results can provide reference for improving the crack resistance of concrete in extreme high-altitude environments.