Research purposes: In response to the problems caused by the collapse of red bed soft rock subgrade along the railway, such as slurry, mud, and foundation settlement, the Jurassic red bed soft rock in the central and eastern Sichuan Basin was taken as the research object. Referring to the climate and environmental background conditions of the study area, an external disturbance resistance test was carried out under dry wet cycle conditions. Through quantitative analysis of multiple indicators of the disintegration process, the disintegration characteristics of red bed soft rock under dry wet cycle effects were explored, and the differences in the disintegration of red bed soft rock in different strata were clarified. The evolution law of disintegration rate with cyclic dry wet was identified.
Research conclusions: (1) The variation pattern of the content of disintegrated particles with the increase of dry-wet cycles in the disintegration resistance test can be divided into three stages: the rapid reduction stage of coarse particles, the stable stage of intermediate particles, and the continuous increase stage of fine particles. (2) There are significant differences in the particle content and disintegration of red bed soft rocks in different regions, with the order of disintegration strength being Neijiang> Suining> Dazhou. (3) The disintegration law of red-bed soft rock shows that as the number of dry-wet cycles increases, the disintegration resistance index, disintegration ratio, and standard basic entropy decrease continuously, while the small particle index increases continuously. As the number of wet-dry cycles increases, the disintegration rate decreases continuously, the content of large particles decreases, while the content of small particles continues to increase, and the disintegration gradually reaches stability. (4) The research results can provide a reference and theoretical basis for railway route selection and disaster prevention of red-layer soft rock subgrade.

Research purposes: In northern China, concrete structures not only face freeze-thaw cycles but also suffer from abrasion caused by sediment and gravel during flood seasons, leading to significant durability degradation. Adding high-strength, high-modulus fibers can effectively improve durability. This study investigated the concrete used in a high-speed railway bridge in northern China. By incorporating calcium sulfate whisker (CSW), freeze-thaw and abrasion tests were conducted on C40 and C60 CSWC, and the effects on durability were analyzed.
Research conclusions: (1) Incorporating CSW significantly improved the freeze-thaw and mechanical properties of CSWC. (2) The optimal surface performance under freeze-thaw and abrasion occurred with 5 kg/m³ of CSW. (3) A plastic microstrain-based freeze-thaw damage model was established to predict frost resistance durability. (4) The research results can provide a theoretical basis for the improvement of concrete durability, and have guiding significance for the practical application of CSWC in cold regions of northern China.

Research purposes: The Chongqing to Guiyang corridor is the backbone section of the Baotou-Haikou and Lanzhou-Guangzhou high-speed rail corridors, as well as the railway corridor of New International Land-sea Trade Corridor in western China. Currently, it consists of the Chuanqian Line and the Yugui Line, facing issues such as capacity constraints and low transportation quality. Therefore, it is necessary to conduct a systematic study on diversion and alternative construction schemes.
Research conclusions: (1) Combining road network planning and project positioning, this paper predicts the annual traffic volume of the corridor, and analyzes that the diversion schemes for passenger and freight transportation face problems such as insufficient transportation capacity on related routes, long detour distances, and low transportation quality, making them all infeasible. Therefore, new railway lines need to be constructed. (2) The construction schemes propose three options: adding a second line to Chuanqian, maintaining the status quo for Yugui and building a new passenger and freight line, maintaining the status quo for Chuanqian and Yugui while constructing a new high-speed railway, and maintaining the status quo for Chuanqian and Yugui while building a new high-speed railway. The final recommendation is to construct a new high-speed railway that meets planning policy requirements, transportation quality, and economic benefits. (3) The research ideas and methods can provide reference and inspiration for similar projects.

Research purposes: The development degree of rail transit has become a symbol of modernization and plays a key role in national economic development and social stability. Among them, the safety and reliability of traction power supply systems have gradually become the focus of public attention. The dynamic matching of catenary and pantograph in the power supply system is the key to ensure the smooth current collection of the locomotive. However, the high-frequency vibration caused by frequent alternating contact force can loosen components of the catenary, especially in high-speed railway operation, coupled with mechanical vibration and wind-induced vibration of trains. Therefore, the anti-loosening of equipment and components is an essential requirement for safety and reliability. The purpose of this paper is to analyze the comprehensive ability of catenary structure, equipment, connection mode between parts, failure mode of threaded connection, and matrix collapse. Through qualitative investigation, quantitative test, theoretical calculation, and finite element comparative simulation calculation, the technical performance of thread fastening and anti-loosening is compared and analyzed, and the anti-loosening ability is evaluated and the new technology for simple, long-term, and controllable thread connection is proposed.
Research conclusions: (1) The proportion of carbon steel or carbon steel M16 and above bolts and nuts with added elements used in the overhead contact system is about 40%, but the control of tightening torque and the evaluation of anti-loosening performance are often ignored. (2) The anchor bolts of the inverted cone must be tightened accurately to allow the adhesive to detach from the body and produce expansion and compression, to better play their role. Therefore, precise control of tightening torque is an important safety indicator. (3) Through the analysis of the relationship between loosening torque and tightening torque, it is concluded that it is not necessary to completely prevent loosening as long as the loosening torque is greater than the tightening torque. Improper handling can lead to thread adhesion and jamming. Accurate control of tightening torque is the key to truly preventing loosening. (4) Precision torque control type anti-loosening nut achieves the most precise torque value with the simplest operation, ensuring reliable connection, controllable indicators, energy saving, and efficiency enhancement, and is more suitable for high-altitude operations on high altitudes. (5) The research results are mainly applied to bolt tightening and anti-loosening of contact network equipment, structures, and components.

Research purposes: In the process of conducting discrete element-based simulation analysis of the interaction between shield machines and sandy cobblestones, there is a mismatch between the actual sandy cobblestone parameters and the simulation parameters of the discrete element method. To address this issue, it is necessary to conduct physical and simulation tests on the sandy cobblestones from the actual construction stratum of the Ganguan Station-Qiandaohu Street Station (referred to as Gan-Qian Section) section of Line 3 of the Shenyang Metro. By taking the angle of repose as the response value, Plackett-Burman and Box-Behnken experimental designs were carried out to calibrate the simulation parameters required for discrete element simulation analysis, providing a basis for the simulation analysis of the interaction between shield machines and sandy cobblestones.
Research conclusions: (1) Physical experiments measured the particle size distribution, the density of 1 719 kg/m³, and the accumulation angle of 38.68°. (2) Plackett-Burman experimental design, and screened out the factors that have a significant influence on the accumulation angle of sand gravel: sand gravel-sand gravel static friction coefficient, sand-gravel-sand gravel rolling friction coefficient, sandstone-shield machine rolling friction coefficient (3) Box-Behnken experimental design, establish a regression model between the accumulation angle and the significance factor, and the inverted optimal simulation parameters are: the static friction coefficient of sand pebble is 0.599, the rolling friction coefficient of sand pebble-sand pebble is 0.195, and the rolling friction coefficient of sand pebble-shield machine is 0.033. (4) The research results can be applied to the discrete element simulation analysis of shield tunneling machines.

Research purposes: The Jiujiawan landslide is a rare landslide geological disaster that caused damage and suspension of high-speed railway since the construction of high-speed railway in China, and it will surely have a far-reaching impact on the geological alignment selection in the construction of high-speed railway. The study of the characteristics and causes of this landslide will help the technical workers have a deep understanding of the high slopes along the high-speed railway and their potential risks, and provide valuable experience for the prevention and control of similar geological disasters in the future.
Research conclusions: (1) Jiujiawan landslide is a new landslide formed by the instability of natural slope, and it is a natural disaster that occurs suddenly under the combined effect of extreme heavy rainfall and man-made activities on high steep slopes of mudstone sandwiched with gypsum rock. (2) The long-term leakage of the irrigation canal at the foot of the slope is the main reason why the landslide was able to continue to slide forward on the river terrace for three days and travel more than a hundred meters after being sheared out from the foot of the slope and ultimately caused damages to the bridges of Lanzhou-Xinjiang High-speed Railway. (3) The research results can be applied to the selection of railway schemes in mountainous areas to avoid the risk of the line being subjected to landslides and geological hazards.

Research purposes: The permafrost on the Qinghai-Tibet Railway is gradually degraded due to the global temperature rise, which brings many technical problems to railway safety operation and related railway construction in the plateau cold region. By collecting and analyzing the changes in temperature, precipitation, ground temperature, and frozen soil upper limit of meteorological stations along the Qinghai-Tibet Railway, the characteristics of climate and frozen soil changes along the Qinghai-Tibet Railway under the condition of temperature rise of the Qinghai-Tibet Railway are analyzed. The research results aim to provide theoretical support for the engineering maintenance and engineering construction in the plateau cold area under warming conditions.
Research conclusions: (1) In the past 20 years, the warming rate of the Qinghai-Tibet Plateau has reached 0.64 ℃/ 10 a, and the precipitation has increased at a rate of 16.8 mm/10 a. (2) The temperature along the Qinghai-Tibet Railway is influenced by altitude and dimensions, with an average temperature value of -5.9 ℃~-2.7 ℃. The annual average precipitation has shown an increasing trend from 1996 to 2022, an increase of 75~86 mm compared to 1976 to 1995. (3) The ground temperature in the permafrost region of the Qinghai-Tibet Railway in 2022 has increased by 0.06~0.21 ℃ compared to 2007, and the temperature at the north and south ends of the permafrost has increased by 0.04 ℃~0.17 ℃. The freezing index along the route ranges from 1.5 to 5.6. (4) The research results can provide theoretical support and technical reference for the construction of road projects in plateau cold areas and the disposal of existing engineering diseases.

Research purposes: As the center of gravity of railroad construction gradually shifts to the southwest region, deep valley long-span bridges are widely used in complex and dangerous areas. Aiming at the problems of many potential risk factors and limited accuracy of traditional assessment methods for deep valley span bridges, we take a deep valley span bridge in Southwest China as the research object, establish a risk identification and optimization system based on the Delphi method (DELPHI) versus the work-risk decomposition method (WBS-RBS) and carry out the risk assessment research based on the fuzzy hierarchical analysis method (FAHP) coupled with the results of the risk matrix method (LS) to improve the accuracy and rationality of the evaluation results from both risk identification and assessment.
Research conclusions: (1) The WBS-RBS is optimized by DELPHI, which can comprehensively and accurately identify potential risk sources, and the RBS risk decomposition structure system is determined based on the optimized 206 RBM identification results. (2) Adopting three-value coupling calculation to derive the risk degree to identify the significant risk sources can avoid the influence of single-value chance on the assessment results, and identify seven major risk sources, such as equipment quality defects, personnel working without safety measures, and equipment fixing connection is not secure. (3) In addition to the seven major risk sources, in order to improve the rigor of the assessment process, the unreasonable preparation of the construction program and flooding as a single-value risk source still need to be focused on. (4) The research in this paper can provide theoretical support and methodological reference for the safety risk evaluation of deep valley long-span bridges.

Research purposes: In the process of importing High-speed railway ( HSR ) construction technology, the difference of chord offsets (DoCOs) method was introduced in China Railway for representing profile/alignment irregularities. Nevertheless, there are some controversies about DoCOs’ effects on track state evaluation and maintenance operation instruction, so DoCOs’ serviceability in track maintenance should be ascertained. To address the underlying mechanism of this issue, this paper starts with the correlation between DoCOs and car body acceleration and evaluates DoCOs’ reflection capability about vehicle dynamic response using correlation coefficient and normalized mutual information. Then in view of DoCOs’ state space description, discusses track deformation representing capability of DoCOs and addresses the instruction capability for maintenance operation, which employed track deformation state-space representation and observability analysis. On this basis, compares track irregularities representing the capability of mid-chord offset (MCO) and difference of chord offsets.
Research conclusions: (1) There is a weak correlation between 5 m/30 m or 150 m/300 m DoCOs and car body accelerations, and no evidence indicates that a nonlinear mapping structure exists. (2) Since the state space of 5 m/ 30 m or150 m/ 300 m DoCOs is not complete observable, it is difficult to instruct the maintenance from DoCOs. (3) MCO’s unobservable states are quite a few compared with DoCOs’ in the track deformation state-space representing, and it could be complete observable taking some supplementary observations, moreover, MCOs are strongly correlated with car body accelerations, all these characteristics are more propitious to evaluate the track states and instruct the maintenance operation. (4) These conclusions illuminate the serviceability problem of DoCOs existing in HSR track evaluation and maintenance and could present a theoretical foundation for selecting representation indices for track irregularities.

Research purposes: In order to investigate the mechanical performance of UHPC layer in the negative moment zone of small span continuous frame bridges, the crack resistance ability, rotation ability and ultimate bearing capacity of the joint were investigated by using the real bridge scaling model. Based on ABAQUS finite element software, the numerical simulation and parameter analysis of the test model were carried out to explore the effects of key parameters such as UHPC layer length, thickness and reinforcement ratio on mechanical performance of the negative moment joints of the frame bridges.
Research conclusions: (1) The UHPC layer of frame bridge joint has a high cracking stress (6.56 MPa). In the normal use stage, the UHPC layer effectively inhibits the formation and development of cracks in the negative bending moment zone, and improves the overall cracking resistance of the structure. (2) Increasing the reinforcement ratio of UHPC layer can effectively improve the flexural bearing capacity of frame bridge joints, but will reduce the cracking resistance of UHPC surface layer. (3) The crack resistance and load bearing capacity of frame bridge joint increases with the increase of UHPC layer thickness. (4) On the premise that both the UHPC layer and the UHPC-NC interface have good crack resistance, it is the most economical to set the UHPC layer between the zero points of the negative bending moment of frame bridge. (5) The research results put forward a high performance joint design method for the negative moment zone of small span continuous frame bridge, which can provide an effective reference for similar bridge design.

Research purposes: The Peck formula is one of the important methods for studying tunnel surface settlement. Its prediction results are mainly affected by parameters such as settlement groove width i and formation loss rate η, and due to the strong regional characteristics of each parameter, the parameter values vary greatly in different regions. Therefore, this paper takes the double line shield tunnel in the sedimentary strata of Kunming Lake as the research object, explores the variation rules and value distribution of each parameter, and finally obtains a surface settlement prediction formula for the double line tunnel applicable to the region, filling the research gap in China.
Research conclusions: (1) Due to the influence of the right line leading, the fitting degree of the Peck formula on the left line has decreased. (2) i is directly proportional to the tunnel depth z and can be characterized by the settlement groove width coefficient k. Its correlation with the weighted compression modulus E is weak. (3) η is positively correlated with z, negatively correlated with grouting rate g, and has little regularity with E. (4) The double line tunnel surface settlement prediction formula takes the leading tunnel k₁ [0.23,0.68], η₁ [0.31%, 1.66%], and the following tunnel k₂ [0.21,0.58], η₂ [0.31%, 1.79%]. (5) The rationality of the formula was verified by the measured data of a certain line, and the predicted results were basically consistent with the actual settlement, both located between the upper and lower limits. At the same time, based on the maximum settlement of the upper limit curve, it can be roughly judged whether the predicted settlement value exceeds the engineering warning, which can provide reference for safe construction of similar tunnels.

Research purposes: This paper uses the analytic hierarchy process (AHP) to study the evaluation and selection of railway hub schemes for newly built lines. By introducing concepts such as weight, membership degree, and consistency, based on fuzzy mathematical concepts, the relative superiority degree of each scheme is determined under evaluation criteria such as overall layout, transport indicators,technical indicators, and operational indicators. With the goal of maximizing the total relative superiority degree of each scheme, a hierarchical structure model is constructed. The scores of each scheme are quantitatively calculated using Matlab programming, and the optimal scheme is determined through comprehensive scores.
Research conclusions: (1) By introducing the concept of systems engineering and transforming qualitative analysis methods into quantitative calculations for comprehensive comparison of all factors, the traditional list evaluation method can effectively overcome the disadvantage of being greatly influenced by subjective factors.(2) Taking the introduction of Nantong-Suzhou-Jiaxing-Ningbo high speed railway into Jiaxing railway hub as an example, the AHP analytic hierarchy process was used to analyze and verify various schemes, and the results were consistent with traditional evaluation schemes, indicating that this evaluation method has good applicability.(3) The research results have reference value for decision-making on the introduction of railway hub schemes for future planning of new lines.

Research purposes: Frequent falling blocks in high-speed rail tunnels can cause serious economic losses and even casualties. The intensification effect of high-speed train aerodynamic load in the crack may be an important reason for the crack expansion and eventually the formation of falling block. In order to prevent falling block accidents in high-speed railway tunnels and strengthen tunnel disease control, the intensification effect of aerodynamic load in lining cracks should be studied. In this study, based on Fluent software, finite volume method (FVM) and Pressure-Based solver are used to simulate the aerodynamic pressure in crack space by unsteady viscous k-ε turbulence model considering the compressibility of air. Using this model, the temporal and spatial characteristics of the aerodynamic loads of circumferential, inclined and longitudinal cracks are discussed. The spectrum characteristics of aerodynamic pressures are analyzed, and the effects of crack length, width, depth and vehicle speed on the aerodynamic loads of crack surface are analyzed.
Research conclusions: (1) The pressure wave enters the circumferential crack space instantaneously, and the pressure wave enters the inclined and longitudinal crack space procedurally. (2) The peak value of circumferential crack pressure is 5.32 times of the input pressure. The peak pressure values of inclined and longitudinal crack are only 79.5% and 64.9% of the corresponding values of circumferential crack, respectively. (3) The PSD of the aerodynamic pressure of the circumferential crack is 4.04 and 1.54 times higher than the value of longitudinal and inclined cracks on average. (4) The crack length and width have limited influence on the peak pressure of crack surface. The crack depth and the peak pressure meet the linear function relation, and the speed and the peak pressure meet the power function relation of 2.303 3. (5) The research findings can provide references for the design of high-speed rail tunnels, and the assessment and repair of cracks within the tunnels.

Research purposes: To study the vibration and noise response of steel-concrete continuous composite beam bridges under railway heavy loads, a railway steel-concrete continuous composite beam bridge with a span of (40+50+40) m on a certain passenger dedicated line was used as the engineering background to conduct on-site testing of structural vibration and noise. The valid data for 16 trains of different formations under operating conditions has been recorded, with train speeds ranging from 160 to 210 km/h. Based on the valid data, the characteristics of vibration and noise of railway composite beam bridges were analyzed and discussed. This research can provide data reference for the research and engineering application of acoustic and vibration response of railway composite structure bridges.
Research conclusions: (1)The results showed that the dominant frequency range of vehicle-induced vibration of the composite bridge was 30 to 2 000 Hz, the peak frequency of vertical vibration of the bridge appeared at 100 Hz, and the peak frequency of transverse vibration of the bridge appeared at 63 Hz. (2) The dominant frequency range of A-weighted sound pressure level at each field point in the test was 63 to 1 250 Hz. (3) The local vibration response of the steel web in the steel-concrete composite bridge was prominent, and the acceleration effective value can reach 6 to 10 m/s², significantly higher than the vertical and transverse vibration of the bridge. (4) The noise pressure level of the railway boundary field point can reach 75 to 78 dB(A). (5) The research results can provide measured data support for railway steel-concrete composite beam bridge engineering and research.

Research purposes: To verify the feasibility of applying textile reinforced concrete (TRC) to bridge strengthening, this paper investigates the flexural performance of TRC strengthening old hollow slab beams based on four-point bending tests in the field to address the problems of inadequate load carrying capacity and large deflection of in-service reinforced concrete (RC) bridge main beams.
Research conclusions: (1) The specimens mainly suffer from the failure modes of fracture of the textile, relative slip of the textile and the matrix, local debonding and interlaminar peeling, and the load carrying capacity is increased by 9.09%~30.3% by TRC reinforcement. (2) TRC reinforcement reduces the deflection of hollow slab beams by 8.4% to 26.8%, effectively improving their stiffness and limiting the development of cracks, but reducing ductility by 13.8% to 31.9%. (3) The optimum textile lap length obtained from this test is 400 mm. (4) The load carrying capacity of TRC reinforced hollow slab beams is calculated, and the theoretical value is in good agreement with the test value. (5) The research results have certain guiding significance for the application of TRC in the strengthening of bridge projects.

Research purposes: Large unstable soil slope has the characteristics of long deformation duration, high concealment of deep displacement and great damage of instability. According to the results of displacement monitoring and the engineering geological environment conditions of slope, the deformation characteristics of slope are studied, the displacement change mechanism is analyzed, and the deformation trend and stability of slope are comprehensively evaluated.
Research conclusions:(1) According to the analysis of surface displacement monitoring data, the horizontal displacement of slope at different positions has obvious difference, the leading edge is the largest, and the trailing edge is the smallest. (2) According to the analysis of deep displacement monitoring data, the slope is in creep deformation stage. There are two potential sliding surfaces, shallow layer and bottom layer. The shallow sliding surface buried depth of 3~10 m is about 6 m on average, the deep sliding surface is located at the soil-rock interface, buried depth of 25~51 m, and the shallow layer displacement is greater than the deep layer. (3) Comprehensive analysis of surface displacement and deep displacement monitoring data shows that slope deformation has seasonal and multi-layer characteristics, and creep deformation is in a continuous development state and an aggravating trend. (4) The research results can provide reference for the stability evaluation of large-scale soil slopes.

Research purposes: Rockburst disasters are most prominent in the construction of deep-buried high-ground stress hard rock tunnels, and the clear influence of the main factors affecting the occurrence of rockbursts is of great significance for the prediction and prevention of rockburst disasters. This paper takes a new mountain TBM tunnel in southwest China as the engineering background, based on the summary analysis of the conditions of rock explosion, based on the FLAC3D software to establish a numerical model of the TBM tunnel boring, analyze the impact of the ground stress and the strength of the surrounding rock on the propensity to rock explosion; and then use the game combination of empowerment-gray correlation analysis to determine the degree of influence of different factors on the propensity to rock eruption.
Research conclusions:(1) High energy storage brittle rock mass, sufficient energy source, and engineering excavation unloading are the conditions for the occurrence of tunnel rockburst. (2) Rockburst propensity increases gradually with the increase in depth of burial. Lateral pressure coefficient <1.0, the side wall of the largest rock explosion tendency; lateral pressure coefficient >1.0, the arch (arch bottom) at the largest rock explosion tendency. With the increase in lateral pressure coefficient, the arch and arch shoulder rock explosion propensity gradually increased, and the side wall rock explosion propensity gradually decreased. (3) The rockburst tendency increases slightly with an increase in cohesion. When the internal friction angle is small, the rockburst tendency increases with the increase of the internal friction angle, but the larger the internal friction angle, the smaller the influence on the rockburst tendency. (4) The degree of influence of different factors on the rockburst propensity is burial depth > internal friction angle > lateral pressure coefficient > cohesion. (5) The results of this study can provide support for the determination of influencing factors of rockburst prediction in high-ground stress tunnels and also provide a reference for the prevention and control of rockburst disasters.

Research purposes: The structure of the subway station is buried deep underground, once it is damaged by an earthquake, disaster prevention, rescue, and post-disaster repair will be very difficult, and will cause huge economic losses and casualties. Improving the earthquake resilience of subway stations is an important guarantee for sustainable development. This paper aims to propose a simple and practical method for evaluating the seismic toughness of subway stations, which can be used to evaluate the seismic toughness of typical subway stations under different site conditions and provide a decision basis for improving the toughness of subway stations.
Research conclusions: (1) The seismic toughness evaluation method not only considers the structural part but also considers the non-structural components, which is more reasonable and real. (2) The seismic vulnerability curves of subway station structures provided in this paper are more comprehensive and practical, considering the situations of underground two-storey single-span, two storey double-span, and two-storey triple-span in class Ⅰ, Ⅱ, and Ⅲsites, respectively. (3) With the increasing number of subway station spans, the overtaking probability decreases under different damage states, and the station tends to be safe; As the stratum decreases from the Class Ⅰ site to the Class Ⅲsite, the overrunning probability becomes larger under different damage states, and the station tends to be dangerous. (4) The results of this paper can be used to evaluate the seismic toughness of subway stations.

Research purposes: The mortar void disease of ballastless track directly affects the operating speed and running performance of high-speed railway line. Taking a six-span simply supported girder bridge-CRTS Ⅱ type ballastless track system and the CRH2C, CRH3 and CRH380A high-speed EMUs as the research object, the modal analysis of the ballastless track-bridge submodel is carried out based on ANSYS to obtain the overall mass, stiffness and damping matrix. Combined with HBMAT command and PYTHON language, the overall matrix is transformed into sparse matrix and imported into multi-body dynamics software together with node degree of freedom mapping file. Based on wheel-rail contact relationship, a dynamic model of track-bridge coupling system considering mortar void is finally established and verified. With the Chinese track spectrum as the initial irregularity, the track deformation caused by pier settlement based on the general representation model of bridge-rail developed by the author is the additional irregularity. Considering the randomness of fastener stiffness, mortar elastic modulus and pier settlement, the Box-Behnken method was used to design the test points based on Design-Expert software, coupled dynamics model calculation is carried out respectively to evaluate the running performance of CRH2C, CRH3 and CRH380A under different mortar void conditions and mechanical parameter randomness.
Research conclusions: (1) The established dynamics model of train-track-simply-supported beam bridge coupling system is in good agreement with the calculation results of the literature model. (2) Under the same mortar void condition, the influence on the safety index is CRH380A>CRH2C>CRH380A, and the influence on the comfort index is CRH2C>CRH3>CRH380A, the influence on the stability index of the three types of trains is basically the same. (3) After considering the randomness of parameters, the index values of safety, comfort and stability indexes are all fluctuate up and down, and the control limits of each index are upper and lower limits boundary values. Taking the upper limit boundary value as the control limit is safer and more reliable than not considering parameter randomness. (4) The research results can provide some reference for the design and checking calculation of high-speed railway simply supported girder bridge.

Research purposes: To investigate the seismic response characteristics of the bridge-track-catenary system under different longitudinal resistances, a sophisticated simulation model was established, taking the example of a 7× 32 m double-track simply supported box girder installation. The influence of longitudinal resistance on the seismic response of each component in the system was explored, the response characteristics of different components under various seismic waves were analyzed, and the impact of the catenary structure on the track-bridge system was also revealed.
Research conclusions: (1) The longitudinal resistance significantly affected the stress on steel rails and the longitudinal deformation of fasteners. Moreover, the implementation of a ballastless track system notably reduced the deformation of fasteners at the piers while increasing the stress on rails at both ends of the bridge piers. Under the action of El-Centro seismic wave, the longitudinal deformation of fasteners under longitudinal resistance of ballastless rail fasteners is 16.7% and 15.0% lower than that under ballasted track and small resistance fasteners respectively. (2) The seismic response of the catenary structure and the bridge structure showed minor sensitivity to longitudinal resistance. (3) Under different longitudinal resistances, the impact of El-Centro wave on the bridge structure and track structure was greater than that of the Taft wave. Specifically, under the El-Centro seismic wave, the bridge stress was 9.6% higher for smaller fastenings and 7.4% higher for the ballast track compared to the ballastless track. (4) The presence of the catenary structure influenced the overall stiffness of the system. Considering the catenary, the bridge stress and the bottom shear force of the bridge piers significantly increased. It is recommended that during the design of high-speed railway bridges in seismic regions, the influence of the catenary structure should be taken into account. (5) The research results can provide reference for the seismic design of the track structure on the bridge.

Research purposes: Surrounding rock classification is a key parameter to be determined in the design and construction of railway tunnels. With the in-depth implementation of China's railway "going out" strategy, it is often difficult for Chinese design engineers and international consultants to reach a consensus on the selection and application of tunnel surrounding rock classification methods, thus affecting the smooth development of overseas projects. In order to study the correlation between Chinese standard BQ method and the international mainstream Q value method and RMR method, the three surrounding rock classification methods, BQ method, Q value method and RMR method, were summarized and compared, and a number of representative railway tunnels at home and abroad were selected to use the above three methods to classify the surrounding rock on the tunnel face of the same chainage, and the classification results were compared and analyzed in combination with other literature research results.
Research conclusions: (1) Q value method and RMR method both have advantages and disadvantages in practical engineering applications, and the determination of site surrounding rock grade should be combined with the Chinese standard BQ method to reach a conclusion. (2) The relationship between [BQ] value and Q value conforms to exponential function, the relationship between [BQ] value and RMR value conforms to linear relationship, and the relationship between Q value and RMR value conforms to logarithmic function. (3) In terms of the difference of research results on the relationship between BQ method, Q value method and RMR method in different literatures, the relationship between Q value and RMR value is the smallest and most widely used, followed by the relationship between [BQ] value and RMR value, and the relationship between [BQ] value and Q value is the largest. (4) This paper establishes a corresponding relation table between the Chinese standard BQ method, the international Q value method and the RMR method for the classification of surrounding rock grades. In the case that the BQ method cannot be applied to the classification of surrounding rock grades, the table can help Chinese design engineers to understand and select the surrounding rock supporting system. The research results will be conducive to the mutual learning and integration between BQ method, international Q value method and RMR method. It has certain guiding significance for overseas tunnel engineering design and construction.

Research purposes: A reasonable estimation of anchor plate's pulling capacity is an important guarantee to maintain the stability of anchor plate foundation. This paper focused on the inclined strip anchor plate buried in the soil slope stratum, constructed an asymmetric pulling failure mechanism of anchor plate under the limit state, and assumed that the soil failure hypothesis follows the nonlinear strength criterion and its non-correlated flow law. Based on the failure mechanism, the analytical expressions of the ultimate pulling capacity of anchor plate and the failure surface equation of soil above the anchor plate were derived by using the upper limit method and variational principle, and the influence of each parameter on the pulling capacity of anchor plate was systematically studied.
Research conclusions:（1）The analytical expressions of the ultimate uplift bearing capacity of the anchor plate and the failure surface equation of the soil above the anchor plate were derived, and the effectiveness of the analysis method was verified by comparison with the existing literature results.（2）The failure range of soil above the inclined anchor plate presents a certain asymmetric feature. As the angle of anchor plate increases, the failure range of soil gradually shifts to the downward slope. Soil failure range is positively correlated with soil dilatancy coefficient and initial cohesion, and negatively correlated with nonlinear coefficient, unit weight and surface load.（3）The embedment depth ratio of anchor plate, embedment angle, surface inclination angle, soil cohesion and dilatancy coefficient have significant effects on the uplift bearing capacity of anchor plate and the uplift failure range of soil, which should be paid attention to in engineering design to realize the optimal layout of anchor plate foundation and the effective use of bearing capacity.

Research purposes: The railway line selection has a wide range of areas, multiple influencing factors, and strong multidisciplinary comprehensiveness. The research and development of intelligent line selection is difficult, and the efficiency and effectiveness of its application have not yet reached widespread promotion. The intelligent railway line selection system is developed, key and difficult points are identified to break through them step by step, new perspectives are proposed on path planning, local optimization, human-machine interaction, etc., in order to supplement and improve existing theoretical methods, and improve the efficiency and quality of line selection design.
Research conclusions: (1) Conducting system research and development through three steps: channel search, scheme optimization, and human-machine collaboration, and fully reusing automatic vertical section design as the basic function, can significantly reduce research and development difficulty and improve research and development efficiency. (2) A method for automatically exploring terrain in large scenes is proposed to obtain high cost areas for bridges and tunnels, and to construct a triangulation cost graph based on the boundary feature lines of the areas, which can improve search adaptability and accuracy. (3) Based on Dijkstra's shortest path search algorithm, automatic path planning can greatly improve search efficiency and effectiveness. (4) Adaptive optimization of horizontal and vertical lines, real-time linkage of horizontal and vertical lines, and system fusion based GIS line selection can flexibly meet practical needs and enhance system applicability. (5) The research results can provide reference for the development of intelligent line selection systems for railways and highways.

Research purposes: The Wuhan-Yichang section of the Shanghai-Chongqing-Chengdu Railway, as a key section of China's "Eight Verticals and Eight Horizontals" high-speed railway network, is an important intercity channel between the Wuhan urban agglomeration and the Yichang-Jingzhou-Jingmen urban agglomeration. Through the research, it is planned to achieve the scientific introduction of the Shanghai-Chongqing-Chengdu Railway into the Jingmen region and rationally determine the route alignment and station layout scheme of the introduction of the Shanghai-Chongqing-Chengdu Railway into the Jingmen region.
Research conclusions: (1) Based on the current situation of railways in Jingmen area, coordinated urban planning and the direction of Shanghai-Chongqing-Chengdu Railway and Xiangyang-Jingmen-Jingzhou Railway, combined with the pre measurement of passenger train pairs in Jingmen area, five schemes for introducing railway routes into Jingmen area are proposed. (2) By analyzing the route direction and length, engineering investment, station location, transportation organization, adaptability to urban planning, difficulty of project implementation, and social impact, a reasonable layout of the route plan is selected. (3) The introduction plan to the north of the city has the advantages of a straight route, good station conditions, flexible operation, low investment, and easy implementation. It also helps to enhance the radiation and driving ability of Jingmen to surrounding cities. Therefore, it is recommended. (4) The research results can provide reference and guidance for the planning and site selection of similar new railway hubs.

Research purposes: Elastic modulus is a key parameter to analyze the mechanical properties of concrete structures. In the design of prestressed concrete structures, the elastic modulus of concrete is usually directly used to simplify the calculation, but this method ignores the influence of prestressed reinforcement and ordinary reinforcement. The purpose of this study is to explore the actual influence of prestressed reinforcement and ordinary reinforcement on the elastic modulus of prestressed concrete beams through theoretical analysis and experimental verification, and to propose an analytical formula for the elastic modulus of beams based on the principle of equal equivalent stiffness. ANSYS Workbench software is used to simulate the elastic modulus of the beam under different reinforcement conditions, and the accuracy and reliability of the model are verified by experiments.
Research conclusions: (1) The reinforcement ratio of prestressed reinforcement and ordinary reinforcement has a significant effect on the elastic modulus of prestressed concrete beams, and there is a linear relationship between them. (2) With the increase of reinforcement ratio, the elastic modulus of the beam is obviously improved. When the reinforcement ratio is 3%, the elastic modulus of the beam is 27.3% higher than that of the concrete. When the reinforcement ratio is 5%, it is increased by 44.3%. (3) The research results can be applied to the design optimization of prestressed concrete structures. Considering the influence of reinforcement on the elastic modulus, it can significantly reduce the error in the structural calculation and improve the safety and economy of the project.

Research purposes: To improve the deformation capacity and construction efficiency of center columns in assembled subway stations, a mortise-and-tenon prefabricated column end connection was proposed. In this paper, ABAQUS finite element software was used to analyze the damage mode, force mechanism and seismic performance of prefabricated column end connections, and to compare the difference in dynamic response between assembled subway stations with mortise-and-tenon prefabricated column end connections and cast-in-place subway stations under seismic action.
Research conclusions: (1) The tenon-bolt column end joints have better load carrying capacity, deformation capacity, and energy dissipation capacity, and better seismic performance. (2) Compared with cast-in-place subway stations, the structural interstory displacement angle of the assembled subway station with tenon-bolt column end joints increases slightly, but the tensile damages of the center columns and the connection of the top base plate with the side walls are smaller. (3) The design of tenon-bolt joints effectively enhances the center columns and the connection of top base plate with side walls by releasing some of the column bottom constraints, which effectively improves the safety of the center column and enhances the collapse resistance of the structure. (4) The results of this paper have reference value for the application and promotion of dry prefabricated column end connections in subway stations.

Research purposes: Against the backdrop of utilizing existing railway resources for the development of suburban (commuter) railways, this study aims to improve the operational efficiency of suburban railways to meet passenger travel demands. By analyzing passenger behavior under different arrival patterns, a traffic allocation method for suburban railways under a mixed arrival pattern is proposed. Based on the "national ownership of lines, co-management by national and local railways" model, a multi-objective optimization model is constructed, which comprehensively considers passenger travel time, operational costs, and local government costs. The model is solved using a genetic particle swarm optimization algorithm to optimize train scheduling plans.
Research conclusions: (1) Empirical analysis of peak morning passenger flow data from a suburban railway line shows that the constructed optimization model for suburban railway scheduling can significantly improve operational efficiency. (2) The model shortens total passenger travel time by 34.8% during peak morning hours, reduces railway operational costs by 10.2%, decreases local government costs by 11.5%, and saves 10% on vehicle acquisition costs. (3) The results of this study can be applied to project planning decisions and operational optimization for suburban railways utilizing existing railway resources.

Research purposes: Due to the complexity, sequence, space and openness of investment consumption factors in subway construction projects, the existing fixed investment control mode has far failed to meet the requirements of investment randomness and nonlinear evolution, and it is urgent to reform the subway investment control management mode. Therefore, this paper comprehensively uses BIM, Python technology, fuzzy mathematics, BP neural network, acquired value theory and PDCA cycle method to build an intelligent prediction and control method for subway construction investment.
Research conclusions: (1) The basic database of subway construction investment is established, and the cause and countermeasure database of subway project investment is constructed. (2) Using SPSS factor analysis, rough set theory, fuzzy mathematics combined with BP neural network, the overall construction objective of the whole line is obtained. (3) Integrated PDCA cycle and acquired value theory carry out dynamic investment optimization control for key control projects, significantly improving the overall management efficiency and level of the project. (4) The computer aided intelligent control software for subway construction investment was established and applied in Chengdu subway construction example. (5) The research results can provide a feasible plan for the investment control of the entire subway line construction.

Research purposes: At present, research on double shield TBM is mainly focused on equipment selection and construction technology under squeezing geological conditions both domestically and internationally. However, there is relatively little research on the design of pipe segment structures. In order to make up for the lack of research in this area, based on the temporal and spatial effects of TBM tunnel construction, the focus was on the calculation method of deformation pressure of double shield TBM tunnel segments in squeezing ground.
Research conclusions: (1) By using a genetic creep model, the temporal effects of surrounding rock deformation were simulated and integrated into the longitudinal deformation curve of the tunnel, thus forming a method for calculating the longitudinal deformation curve of the tunnel that takes into account the temporal and spatial effects. In addition, the advanced deformation in the first stage was also considered and a formula for the characteristic curve of surrounding rock was constructed based on the equivalent excavation diameter. (2) Using the elastic theory of thick walled cylinders, a stiffness calculation formula for pipe segment gravel composite support was derived, and an expression for calculating the critical elastic modulus was established. (3) Based on the principle of convergence constraint analysis, the formulas for the combined support force and displacement were derived, further forming a calculation method for the deformation pressure of pipe segments. Finally, the accuracy of the deformation pressure calculation method was verified through practical engineering cases. (4) The research result can be applied to the design of TBM tunnel segment structure in squeezing ground.

Research purposes: Aiming at the station layout such as the swallow tail tunnel, the short effective length of station track and the multi-line parallel lines in the project of using the existing Northeast Ring Railway in Beijing Railway Hub to build the second line to run suburban trains, the several schemes about interface design are analyzed and researched for the signal cable channel reservation, integrated grounding setting scheme, trackside signal equipment cable into the cable channel, remote LEU settings in the swallow tail tunnel, signal equipment settings of station track, and the cable channel settings of existing multi-line parallel lines, and the design scheme suitable for the implementation of the project is proposed.
Research conclusions: (1)The interface design scheme of signal engineering for swallow tail tunnel proposed in this paper can reduce the cross of strong and weak electricity, improve the grounding effect, reduce the influence of trackside signal equipment cable into the cable channel on other professions, realize the different physical path connection of remote LEU. (2)The signal equipment settings of station track proposed in this paper can reduce the length of the station track while avoiding adjacent line interference. (3)The cable channel settings of multi-line parallel lines proposed in this paper can meet the operational requirements of separate ownership and the maintenance of different lines. (4)The research results proposed in this paper have engineering feasibility, which can be selected and referred for similar projects.

Research purposes: Portland cement was the main cementitious material for railway concrete. In order to study the performance of anti-cracking cement and improve the anti-cracking performance of plateau railway bridge pier concrete from the perspective of cement, the differences between anti-cracking cement and general silica cement in working performance, hydration performance, mechanical properties, drying shrinkage properties and anti-cracking properties were systematically compared, and a comparative test was carried out in the solid pier. Through the study of the internal temperature and strain change law of pier concrete, the effect of cement on crack resistance of the plateau bridge pier concrete is evaluated comprehensively.
Research conclusions: (1) Compared with general silica cement, the water requirement of crack resistant cement is lower, the hydration rate slows down and the hydration heat decreases in the early stage, the hydration activity decreases in the early stage, and the strength decreases slightly in the early stage, but the strength develops stably and exceeds that of general silica cement in the late stage. The bending ratio of crack resistant cement at the same age is obviously higher than that of general silica cement, showing better toughness. (2) The dry shrinkage rate of concrete prepared with anti-cracking cement is significantly lower than that of general silicon cement, and the anti-cracking property of concrete is significantly improved. (3) The application of crack resistant cement in pier concrete can reduce the core temperature of pier concrete, the temperature peak of core can be reduced by 5.0 ℃, and the strain of core concrete and surface concrete can be significantly reduced, the strain of core can be reduced by 50%, and the strain of surface concrete can be reduced by 40%, thus improving the crack resistance of plateau pier concrete. (4) The application of crack resistant cement can be used as an effective means to improve the crack resistance of railway bridge pier concrete.

Research purposes: Aiming at the road traffic problems confronted by the open-cut method of subway station construction in the water-rich sandy pebble layer, this paper relies on the successful project of Chengdu subway station construction in water-rich sandy pebble layer for the first time using the concealed excavation method to carry out a study on the key technology of concealed excavation method, indicating the key technology of the concealed excavation guide hole setting and its excavation sequence, the way of over-advanced pre-strengthening of the strata, the type of initial support, the steel pipe columns with permanent-temporary combination, and the arched cover buckling arch and so on, and clarifying the feasibility of the shallow buried large span metro station with water-rich sandy pebble layer for the first time. The feasibility of using the concealed excavation method for the first time in the construction of the shallow buried large-span subway station in water-rich sand and pebble layer was clarified.
Research conclusions: (1) Based on the concept of modular tunneling approach, with the pre-support of tube curtain with large rigidity, the basic principle of the pilot tunnel is clarified, and then multiple pilot tunnels are adopted in the construction of steel pile pillars, tunnel roofs. The underground excavation of metro stations with large spans and shallow buried depth can be realized. (2) The precise control of construction accuracy and stratum disturbance of tube curtains with large rigidity plays a key role in the control of stratum settlement. The corresponding basic construction principle is accurate positioning, timely correction, not enough slagging, strict control of over-digging, low-speed drilling at the beginning, and then even speed drilling. (3) Based on the passive bearing properties of initial support, grid steel has a relatively better economic effect and construction convenience, the overall flexural stiffness after shotcrete increases to nearly 8 times. The corresponding stiffness of grid steel is larger than H plate steel after shotcrete. So, grid steel should be adopted as far as possible. (4) In the center pilot tunnel, the snakelike middle column embedded with inverted L-shaped steel plate at the top can realize the effective connection of the lining structure on both sides and the effective horizontal force transmission. The hydraulic reverse circulation drilling machine can meet the need for high-precision permanent steel pipe pillar construction within a small headroom. (5) This paper can provide a reference for the similar project in the sand and gravel stratum in the future.

Research purposes: The complex geological conditions and fragile environment in mountainous areas make the construction of railway tunnels arduous in terms of environmental protection, soil and water conservation, etc. It is imperative to reduce the disturbance of tunnel construction to the regional environment and balance the relationship between tunnel construction and environmental stability. To clarify the key nodes of green coordinated development of "tunnel-environment" and formulate targeted strategies to reduce the adverse impact of tunnel construction on the regional environment, an analysis method of key green elements of "tunnel-environment" in mountain railway based on a multi-layer coupling network model is proposed.
Research conclusions: (1) Based on clarifying the interaction relationship of the "tunnel-environment" in mountain railway, build an element system that includes tunnel green, interface, and environmental elements. Using the multi-layer coupling network model, each element is abstracted as the node of the network at different levels, and the organic relationship of each node in and between the network layers is established, which can establish the basis for the quantitative expression of the interaction relationship of the "tunnel-environment". (2) Taking a railway tunnel engineering in a mountainous area as an example, the network node importance assessment method is used to identify seven key green elements: tunnel section size, tunnel excavation length, tunnel blasting mode, tunnel ventilation mode, tunnel lining waterproof design, tunnel grouting and water plugging, tunnel ventilation equipment layout, which should be optimized and controlled. (3) The research results are in line with the engineering practice, and verify the applicability of the model, which can provide a basis for determining the key points to reduce the stress effect of railway tunnel construction in mountainous areas on the regional environment.

Research purposes: The Quaternary cover layer in the Chengdu area is thick, overlying the red soft rock strata, with a variety of rock and soil types. The unique geological environment has given rise to numerous geotechnical engineering problems, which have constrained the planning and construction of Chengdu rail transit. Through a series of geotechnical engineering practices in Chengdu rail transit construction, this paper systematically analyzes the geological characteristics and causes of various problems and proposes targeted geotechnical investigations of key points and corresponding prevention and control measures.
Research conclusions: (1) The Chengdu rail transit is mainly located in the central part of the Sichuan Basin, which belongs to the Minjiang River watershed. Its geological structures are mainly box-shaped Longquan Mountain anticline, and the basic seismic intensity is Grade Ⅶ. (2) The Chengdu Plain is widely distributed with thick Quaternary Holocene System (Q₄) and Pleistocene System (Q₃) clay, pebbles, and sand layers, while the cover layers on the hilly and low mountain areas are thinner. The underlying bedrock is the Cretaceous System (K) and Jurassic System (J) red lacustrine sedimentary mudstone, sandstone, etc., with thin layers of gypsum and calcareous halite commonly found in the mudstone. (3) The study area has diverse rock and soil types, and the Chengdu rail transit construction faces large-grained high-strength floating pebbles, lenticular sand layers, Ya'an gravel layers, gypsum-containing formations, shallow gas, red mudstone, composite formations, and hydrogeological problems. The paper provides a detailed explanation of the engineering geological characteristics, geotechnical investigations key points, and control measures for each problem. (4) The research results have reference and guidance significance for the construction of the fifth phase of the Chengdu rail transit and the second phase of the Chengdu suburban railway network.

Research purposes: This paper established a three-dimensional numerical analysis model of 'bedrock-cover layer-subgrade' that can consider the features of fault creep activity, analyzed the deformation characteristics of subgrade structure under the action of fault creep dislocation, and clarified the action mode and sensitivity of various chief influencing factors on subgrade deformation, such as fault movement mode, creep amount, thickness of overlying soil.
Research conclusions: (1) Different creeping modes of active faults lead to different deformation characteristics of subgrade surface and slope, in particular, the near-fault slope under the action of strike-slip shows obvious 'middle bulging'. (2) Under the action of dip-slip fault dislocation there is a critical creep amount and critical overburden thickness that make the subgrade irregularity range tend to be stable. (3) The increase of strike-slip displacement obviously aggravates the lateral displacement of the subgrade and the 'middle bulging' of a near-fault slope, while the sufficient thickness of overburden will obviously smooth the above lateral deformation. (4) Those analysis results can provide a reference for the deformation control of railway subgrade under the background of fault dislocation.

Research purposes: In response to the requirement of signal system switching between the CTCS signal system and the CBTC signal system for the cross-line operation of trains in suburban railways, the technical routes of different signal system switching are analyzed and studied in terms of the advancement of technical routes, conformity of specifications and so on, the switching locations of different signal system switching are compared and analyzed in terms of safety of switching locations, division of dispatching boundaries for different type of railways and so on, and the applicability of each technical scheme of different signal system switching for cross-line operation to the construction of different projects is systematically clarified.
Research conclusions: (1) The technical route that the systematic structure and communication interface of the CTCS signal system and CBTC signal system are completely independent and should be adopted in the project that will be constructed soon, such as the project of running suburban trains in the Beijing Railway Hub Northeast Ring Railway. (2) The technical route that the CTCS signal system is independent, and the CBTC signal system adds new conversion equipment using the existing communication interface of the CTCS signal system and CBTC signal system, and the technical route that systematic structure of the CTCS signal system and CBTC signal system remains unchanged and system equipment of CTCS signal system and CBTC signal system increases the communication interface can be applied in construction projects after completing the preconditions of project implementation such as certification and licensing and so on. (3) The technical route of systematic structure and communication interface of the CTCS signal system and CBTC signal system are completely integrated is the development direction of the signal system, which can be applied in long-term projects. (4) The stopping at junction stations of different types of railways should be selected to complete the different signal system switching for cross-line operation in the project. (5) The research results proposed in this paper can provide a reference for the design and construction of other suburban railway projects.

Research purposes:With the continuous promotion and application of Building Information Model (BIM) in railway station building engineering, a large amount of basic digital assets will be formed after the completion of the project. Therefore, it is necessary to study new technical methods to improve the reuse rate of BIM basic data assets, solve the problems of large component resources, and the difficulty of data expansion in downstream users of the model, and achieve efficient utilization of BIM results, forming a railway passenger station digital base, and providing a basic data service platform for comprehensive business applications of digital twins.
Research conclusions:(1) Based on BIM model, a railway passenger station data base is built using a visualization engine platform and relational database, to achieve digital delivery of 3D design results. (2) From the perspective of geometric and non geometric data processing, a lightweight development application of the system based on the digital analog separation technology route has been developed. (3) Through engineering application practice, the feasibility and completeness of this technical solution have been verified, which can support downstream users to expand and extend business functions using model data information.

Research purposes: Surface defects of steel rails are important hidden dangers for safe operation of railway traffic, accurate detection of surface defects on steel rails is crucial. The complex environment in which steel rails are in service may cause them to be contaminated with stains, at the same time, the shape of rail defects is often inconsistent. To address the problems of false detection due to stains and difficulty in accurate detection due to different shapes of defects in rail surface defect detection, an improved YOLOv7-based rail surface defect detection method is proposed.
Research conclusions: (1)The problem of false detection of stains was overcome by constructing the dataset with images of rails containing stains as negative samples, with the use of label differences to enable the network to learn features that distinguish between defects and stains. (2)YOLOv7 was improved by deformable convolution with an embedded channel attention mechanism. That was, the deformable convolution replaced the fixed convolution by adding a bias to the convolution sampling points to enhance the network's ability to adapt to the geometric deformation of defects. At the same time, the channel attention mechanism was embedded in the network, and its feature of weighting different channel features made the network focus on the defect features, thus enhancing the defect feature extraction ability. (3) The effectiveness and feasibility of the proposed method was demonstrated by loading the rail surface defect dataset onto the constructed improved YOLOv7 network for end-to-end rail surface defect detection. (4) The research can provide a new method for intelligent detection of rail surface defects.

Research purposes: Expansive soil foundation is widely distributed in China, and its strength decreases significantly after immersion. The swelling and shrinkage deformation caused by water absorption and loss is repeated, and the engineering hazard is extremely high. The existing railway and highway subgrade diseases are very prominent. The problems of expansive soil slope stability and subgrade slurry overflow have been solved. The deformation of ordinary railway and highway subgrade has also been well controlled, but its settlement control standard is 20~30 cm. High-speed railway uses millimeter level deformation as the control standard. The construction of high-speed railway subgrade on an expansive soil foundation must solve two technical problems: the expansion arch deformation of road cuts and low embankments, and the settlement deformation of high embankments.
Research conclusions:(1) The expansion amount of natural expansive soil foundation after water immersion is significantly greater than the limit value of ballastless track railway maintenance. The flexible filling body of the roadbed has a good buffering effect on the expansion and contraction deformation of expansive soil. (2) During the construction period, the natural expansive soil foundation filling the roadbed can achieve more than 80% of the total settlement, and the composite foundation reinforcement treatment can exceed 90%. When the filling height on the overconsolidated expansive soil foundation is not high, the total settlement of the reinforced foundation and the natural foundation is relatively small. (3) Embankment-type cutting structure should be adopted for expansive soil foundation and low embankment engineering, with all roadbed areas replaced and drainage measures strengthened. Small diameter and small spacing CFG piles should be used for foundation reinforcement. Shallow layers of 4~6 meters should be reinforced for general embankments, and settlement calculation analysis should be conducted for high embankment foundation treatment based on general soil foundation. (4) This research result can provide a useful reference for the construction of high-speed railways on expansive soil foundations.

Research purposes: The increase of heavy-haul train axle load enhances the dynamic stress at different depths of the subgrade, leading to more and more serious subgrade issues such as mud pumping. In this paper, a series of refined model tests were carried out to study the characteristics of mud pumping of saturated silty clay subgrade under the heavy-haul train load. The influence of cyclic loading amplitude and loading frequency on the axial strain, excess pore water pressure, and fine particles migration characteristics of the sample was analyzed.
Research conclusions: (1) The cyclic loading amplitude has a significant impact on the characteristics of mud pumping from silty clay subgrade. As the cyclic loading amplitude increases, axial strain and excess pore water pressure rise, intensifying mud pumping. (2) The loading frequency has a certain influence on the characteristics of subgrade mud pumping. In general, higher loading frequencies decrease the final axial strain and excess pore water pressure, reducing mud pumping quality post-test. The increased frequency can't accelerate the mud pumping severity, but can shorten the duration of mud pumping. (3) Under cyclic loading, the excess pore water pressure gradient drives the migration of fine particles in the subgrade soil, resulting in mud pumping. (4) The research results can provide a reference for the treatment of the mud pumping issues in the heavy-haul train subgrade.