ObjectiveThe PLG (propulsion, levitation, and guidance) system of the superconducting electrodynamic maglev train features non-contact operation, low energy consumption, high speed and high reliability. It has become an important structural form of new generation high-speed maglev transportation system, holding great theoretical research significance and promising engineering application prospects. Therefore, it is necessary to conduct systematic and in-depth research on this system. MethodThe technical principles of the superconducting electrodynamic maglev train are introduced, and the circuit model of the PLG magnetic levitation system composed of superconducting and track coils are analyzed. Based on circuit and electromagnetic field theories, the energy method is adopted to calculate the PLG forces, including traction force, suspension force, and guidance force during train operation. In accordance with Neumann's formula, the numerical expression of mutual inductance between superconducting coils and track coils varying with train positions is derived, and a magnetic field-circuit-motion coupling model for the PLG maglev system is further established. With the coupling model, the inductive coupling factor between superconducting coils and track coils of the PLG system is investigated, along with the variation characteristics of multi-directional mutual inductance against the lateral displacement offset and vertical displacement of the train. The dynamic variation rules of PLG traction force, suspension force, and guidance force during train operation are also analyzed. Result & Conclusion The research results show that the PLG superconducting electrodynamic maglev system retains the characteristics of conventional superconducting electrodynamic maglev systems, and exhibits superior performance in terms of PLG.
ObjectiveAs a critical safety guarantee signal for metro train operation, the zero-speed signal is widely used in vital control circuits including traction authorization, vehicle door control, and emergency braking. The zero-speed signal fault may result in failures of key train control circuits, train delays, triggering passenger complaints, all severely impact the normal operation of trains on main lines. Therefore, research on reliable zero-speed signal control is of great necessity. MethodThe sources of zero-speed signals and their faults are analyzed, with a focus on their impact on traction authorization, vehicle door control and emergency braking. Furthermore, schemes to optimize the zero-speed signal output circuit and increase redundancy measures for the zero-speed control circuit are explored, as detailed below: installing a power-off delay relay at the zero-speed output source; adopting internal-unit OR logic and inter-unit AND logic for the zero-speed signal braking system; and adopting optimized design approaches for critical control circuits, including staggered arrangement for door zero-speed signals, series-then-parallel topology for traction authorization zero-speed signals, and parallel-then-series topology for emergency braking zero-speed signals. These optimization methods enable reliable zero-speed signal output and effective operation of the train's zero-speed control circuits. Result & Conclusion The proposed optimization methods have successfully applied to metro train projects in multiple regions, significantly reduced the probability of train rescue incidents caused by zero-speed signal faults, and improved service quality and operational efficiency, guaranteeing the safe operation of trains effectively.
ObjectiveTo improve the reliability of visible light communication-based metro train positioning technology in narrow and enclosed metro tunnel scenarios and make up for the deficiencies of existing train positioning methods, it is necessary to study the effects of irregular reflections of optical signals from tunnel inner walls and train running speed on positioning accuracy, and further to propose a train positioning method capable of achieving continuous positioning. MethodFirst, signal modulation technology is employed to encode and modulate the information to be transmitted, making it carry the position data of the tunnel lighting lamps. An irregular channel model for visible light communication that conforms to actual conditions is established. Next, a fingerprint database is established using the light intensity characteristics of transmitting light sources to build a mapping relationship between train position coordinates and signal strength features. Meanwhile, the KNN (k-nearest neighbor) algorithm is used to match train position information with signal strength, thereby achieving train positioning. Finally, a Kalman filter algorithm is applied to optimize the positioning results. The effectiveness and feasibility of the proposed method are verified based on actual line data and equipment parameters from Chengdu Metro Line 1. Result & Conclusion When the train runs in a straight line at a constant speed of 40 km/h, the average positioning error of the proposed method is 1.8 m. When the train runs at variable speeds with the maximum speeds of 20 km/h, 100 km/h and 180 km/h respectively, the average positioning error is approximately 2.0 m. The positioning results meet the requirements of the CBTC (communication-based train control) system.
[Objective]In water-rich weathered diorite strata,earth pressure balance(EPB)shield tunneling is prone to stratum water loss and water gushing.Therefore,it is necessary to study the water loss pathways and treatment measures for metro shield tunneling.[Method]Based on the Gangzicun Sta.-Huayuan Road Sta.shield tunnel section of Nanjing Metro Line 6,a research framework of"gushing characteristic analy-sis-water loss pathway identification-treatment measure evaluation"is established combined with stratum properties and field water loss conditions.Firstly,the gushing characteristics of the screw conveyor before and after the installation of water stop ring,as well as the evolution pattern of key tunneling parameters,including total thrust force,cutterhead torque and earth chamber pressure,are analyzed emphatically.Secondly,field tests are carried out to monitor the response pattern of pore water pressure with shield advancing after the water stop ring installation,and the water inflow in different sections is calculated to further clarify the specific water loss mode of the stratum.Finally,treatment measures for stratum water loss are discussed.[Result&Conclusion]After the installation of the water stop ring,water gushing is greatly alleviated and the fluctuation of earth chamber pressure weakened,while the total thrust increased.Since the stratum of the studied section presents high stability and low permeability coefficient,tunneling exerts limited influence on pore water pressure,and seepage is hardly to form in front of the excavation face.The water loss pathway is mainly the longitudinal seepage behind segment linings,which flows into the earth chamber through over-excavation gaps and triggers screw conveyor gushing.The permeability coefficient of moderately weathered diorite in fracture zones is high,where the water inflow is significantly greater than that in intact moderately weathered diorite.Therefore,water stop rings need to be installed more frequently to block water inflow.Installation of water stop rings and active drainage are effective measures to mitigate water loss during shield tunneling.
ObjectiveAs key factors affecting the axial impact performance (AIP) of cutting-type energy-absorbing tubes (CEAT), material fracture failure parameters directly determine the stability of axial impact force and the curling-separation mode of chips. Therefore, it is necessary to investigate the AIP of CEAT from the perspective of material fracture failure parameters. MethodTensile fracture tests are carried out on three typical notched specimens to obtain the fracture strain of the material under different stress states. Furthermore, the tensile fracture tests of the three specimens are simulated using finite element method, and the average stress triaxiality of the specimens is obtained. A material fracture failure model based on the Johnson-Cook model is fitted accordingly. Finite element simulations of axial impact on CEAT are conducted, and the accuracy of the model is verified by comparing simulation results with impact test data. On this basis, the effects of cutting depth and cutting width on the AIP of CEAT are further studied. Result & Conclusion The fitted Johnson-Cook material fracture failure model can effectively simulate the cutting-curl mode of CEAT, yielding stable and accurate cutting force. The peak cutting force and average cutting force are positively correlated with cutting depth; the average force increases by approximately 76.3 kN for every 0.4 mm increase in cutting depth. With the increase of cutting width, both the peak force and average force will rise, while the growth rate gradually decreases.
ObjectiveUrban rail transit vehicles face two prominent problems in the O&M (operation and maintenance）service stage：the low efficiency in data management during this stage, and the existence of information silos between different stages of the vehicle product life cycle. Therefore, it is necessary to conduct research on configuration management methods for the MRO (maintenance, repair, and operations) services of urban rail transit vehicles. MethodA set of configuration management methods tailored for urban rail transit vehicles is proposed. Firstly, by analyzing the vehicle diverse demands for MRO services in the O&M stage, the definitions of configuration objects, configuration correlations, and configuration attributes are clarified. On this basis, a three-tier configuration management system consisting of functional configuration, physical configuration and service configuration is designed, and a configuration evolution model for the O&M service stage is established. The proposed system can effectively organize, manage and control changes of vehicle service data, and realize the integration and interconnection of lifecycle data across all stages. Meanwhile, service data can be used to drive the O&M management, providing an accurate, comprehensive, and complete data foundation for the informatization and digitalization of services. Finally, the passenger compartment door of a certain train model is taken as an example to verify the support and traceability capabilities of the proposed configuration management system for product MRO services so as to demonstrate the effectiveness of the system. Result & Conclusion The established configuration management system realizes refined management of product MRO services, guarantees the consistency and change continuity of vehicle product data, and enables information interconnection and data invocation between the O&M, design and manufacturing stages, thereby greatly improving vehicle product service efficiency.
ObjectiveTo investigate the stage-wise effects of ultra-large-diameter shield undercrossing the existing rectangular mined tunnel structures, it is necessary to study the settlement behavior of existing tunnels. MethodBased on the interval shield project of Shanghai Suburban Railway Airport Link Line passing beneath the existing Metro Line 12, 94 settlement monitoring points are laid out. Using field monitoring, settlement variation characteristics of the existing tunnel at different construction stages are analyzed with field-measured settlement data. Meanwhile, numerical simulation via FLAC3D software is employed to investigate the stage-wise settlement rules and structural lateral displacement laws of the existing tunnel under different slurry and grouting pressures. Result & Conclusion The existing double-track tunnel presents distinct deformation responses in three major construction stages, i.e. before, during and after shield undercrossing. Variations both in slurry pressure during cutterhead penetration and in grouting pressure during shield tail passage can induce more prominent deformation responses of the existing tunnel. The differential settlement between the double-track tunnels first increases and then decreases, and the stage-wise turning point occurs around the moment when the shield tail departs from the overlapping area. The uneven lateral displacement of existing tunnel structure induced by shield undercrossing project mainly occurs when the shield machine passes through.The maximum lateral displacement appears near the center point of the undercrossing, accounting for 90% of the final displacement, and in the opposite direction of the shield tunnelling advancement.
ObjectiveAccurate prediction of shield attitude is crucial for the tunnel axis deviation control and guarantee of finished tunnel quality. Existing purely data-driven prediction methods fail to consider multivariate spatial dependencies, showing deficiencies in feature extraction capacity. Therefore, further research on shield attitude prediction methods is necessary. MethodsA PIFE-LSTM (physics-informed feature enhancement long short-term memory) model is proposed. Starting from the mechanism by which the shield thrust system influences attitude changes, the model extracts thrust vectors (including resultant thrust and thrust application point) in the feature engineering stage to characterize the spatial distribution of thrust forces. These thrust vectors are used as enhanced features to reinforce the physical orientation of the feature extraction process, and the LSTM model is used to capture the temporal dependencies of shield attitude. Measured data from the tunnel section between Longdong Avenue Station and Pudong Football Stadium Station of Shanghai Metro Line 21 are applied to the proposed model training and comparative verification. Result & Conclusion The introduction of thrust vectors effectively improves the model's capability to capture the nonlinear mapping relationships. Compared with the model without introduced thrust vectors, the determination coefficient increases by 0.06 and the mean absolute error decreases by 0.40 mm. Moreover, in comparison with other classical time-series prediction models, the PIFE-LSTM model, benefiting from its gating mechanism, effectively alleviates the vanishing gradient problem in long-sequence data processing and exhibits superior nonlinear fitting capability.
ObjectiveTo improve the intelligent O&M (operation and maintenance) level of urban rail transit signal systems and address prominent issues in traditional O&M modes such as data silos, inefficient retrieval, and excessive reliance on human expertise in fault analysis, it is necessary to conduct research on intelligent O&M and fault analysis methods for signal systems based on large models. MethodTaking the intelligent O&M of metro signal systems as the research object, an intelligent analysis system consisting of data layer, service layer, application layer, and interaction layer is constructed. Four core technologies, i.e. NLP (natural language processing), Text-to-SQL (structured query language), RAG (retrieval-augmented generation), and OCR (optical character recognition) are adopted. A full-process processing mechanism is established based on semantic alignment, dynamic SQL generation and correction, hybrid retrieval, and re-ranking. Experiments are conducted to compare different retrieval methods and their performances. Meanwhile, fault scenario application tests are conducted to systematically assess the performance of each retrieval method in tasks such as fault Q&A, table parsing, and status discrimination. Result & Conclusion Experimental results show that the Hybrid+reranker (hybrid+BGE-reranker-v2-m3 re-ranking model) method performs excellently in six typical Q&A tasks, its overall performance is also significantly improved compared with traditional keyword-based retrieval and rule-based matching retrieval. The constructed intelligent system can achieve automatic fault analysis, precise retrieval of O&M knowledge, and rapid generation of decision suggestions, providing technical solutions and practical support for the digital and intelligent O&M of urban rail transit signal systems.
ObjectiveTo realize interoperability between CTCS-2 (China Train Control System Level 2) and CBTC (communication-based train control) systems, it is necessary to study the layout of the shared control zone and the switching method of onboard equipment based on the vehicle-to-ground compatibility scheme. MethodFirst, according to the operating principles of CTCS-2 and CBTC systems as well as the layout rules of trackside signal equipment, five basic requirements for shared control zone arrangement and onboard equipment switching are proposed. Then, the shared control zone is set up by orderly superimposing the trackside equipment of the CTCS-2 and CBTC systems, and the switching procedure of onboard equipment within the zone is designed. On this basis, given that both CTCS-2 and CBTC systems are integrated with the ATO (automatic train operation) function, adaptive adjustment schemes for shared control zone arrangement and switching procedures are designed. Finally, taking the switching from CTCS-2+ATO to CBTC+ATO as an example, a practical line in the shared control zone is designed using an existing railway line, and both normal and abnormal onboard equipment switching scenarios are simulated and verified in this zone. Result & Conclusion The proposed method can support system switching not only for the vehicle onboard split-type and integrated-type equipment, but also for those with ATO function. Under unidirectional operation in railway sections, the proposed method can maintain the mutual independence between CTCS-2 and CBTC ground equipment to the greatest extent, thereby achieving safe and efficient cross-system operation between CTCS-2 and CBTC.
ObjectiveWhen a newly built metro tunnel in water-rich sand strata under-crosses an existing metro station, challenges such as obstacle removal from the existing station's retaining structure, deformation control of the existing station, and water and sand inrush during construction will be encountered. Therefore, it is necessary to study the design and construction schemes for obstacle removal. MethodBased on the project of Wuhan Metro Line 12 interval tunnel under-crossing the existing Yuanlin Road Station of Metro Line 4, the spatial crossing relationship and construction difficulties are analyzed. A retaining structure obstacle removal design and construction scheme for stations adjacent to the first Yangtze River terrace is proposed as follows: first, an obstacle removal shaft is constructed outside the existing station; next, the shaft is excavated down to the shield under-crossing elevation for horizontal freezing and obstacle clearing; then, after backfilling the obstacle removal shaft, shield under-crossing is conducted. Numerical simulation is adopted to analyze the impacts of shaft foundation pit excavation, frost heave and thaw settlement, and shield under-crossing on the existing station. Furthermore, numerical calculation results are compared with field monitoring data to verify the effectiveness of the proposed scheme. Result & ConclusionNumerical simulation analysis shows that the maximum settlement of Yuanlin Road Station of Metro Line 4 induced by obstacle removal shaft excavation is 3.2 mm, the maximum station uplift caused by ground freezing reinforcement is 2.5 mm, and the maximum settlement induced by shield under-crossing is 1.4 mm, all lower than the allowable deformation limits. The field measured settlement deformation data of the existing station is consistent with the result from numerical simulation, with a maximum measured station settlement of 3.5 mm, meeting deformation control standards. Therefore, the proposed design and construction scheme is safe and feasible.
[Objective]The rigid catenary serves as a key power supply component for urban rail transit and mountain railway trains.Sliding contact current collection between the rigid catenary and pantograph is critical to the stable and safe operation of electrified railways.With the continuous operation speed increase for urban rail transit and mountain railway trains,the adverse impact of rigid catenary locator offset on the current collection performance of the pantograph-ca-tenary system is becoming prominent.To guarantee stable current collection of the pantograph-catenary system,it is necessary to investigate the influence law of rigid catenary locator offset on pantograph-catenary contact force.[Method]A nonlinear finite element model of the rigid catenary and a lumped mass equivalent model of the pantograph are established.The penalty function method is adopted to construct the pantograph-catenary coupling model,which is further validated in accordance with railway industry standards.Studies are carried out on the influence of different locator offset values on the current collection performance of pantograph-catenary system under two typical train operating speeds,taking into account single-locator offset and multi-locator offset,as well as both the upward and downward offset directions.[Result&Conclusion]Rigid catenary locator offset exerts significantly aggravated adverse impact on the current collection performance of pantograph-catenary system as the train speed increases,while the impact remains relatively limited for offsets within±3 mm.For both single and multi-locator offset conditions,the upward and downward offsets produce roughly equivalent degrees of impact on the current collection performance.
ObjectiveFor the tunnel construction of large-span metro stations in hard rock, it is necessary to investigate the applicability and vibration effect characteristics of micro-vibration blasting method in order to improve the conventional blasting technique. MethodBased on the underground project of Xietaizi Station on Chongqing Metro Line 18, a three-dimensional tunnel numerical model is established with finite difference software to simulate the blasting excavation process. An optimized micro-vibration blasting method is proposed, the monitoring points are arranged on the ground above the blasting area, and the vibration velocity and vibration frequency at ground measuring points are monitored and measured. Thus, the blasting vibration monitoring data are obtained and then compared with numerical simulation results for verification. Result & ConclusionThe optimized micro-vibration blasting method can reduce the number of blast holes, the single blasting charge mass and charge concentration, and block partial propagation pathways of blasting stress into the surrounding rock, thereby effectively mitigating the blasting vibration. Compared with the original blasting method, the optimized method reduces the vibration velocity at ground measuring points by more than 70% under the same excavation advance. This optimized method presents favorable adaptability for blasting excavation of large-span metro station tunnels in hard rock for urban environments.
ObjectiveTo control the variations of track/bridge forces and displacements induced by adding overtaking lines at existing elevated metro stations, it is necessary to carry out comparative research on different layout schemes of CWR (continuously welded rails). MethodTaking the scenario of adding overtaking lines on both sides of an existing elevated metro station, and replacing the original four-span simply supported beams with four-span continuous beams in situ as the research object, five CWR layout schemes in three categories are arranged, i.e. installing REJ (rail expansion joint) on straight and diverging turnout tracks, installing REJ only on diverging turnout tracks, installing buffer rails on both the straight and diverging turnout tracks, installing buffer rails only on the diverging turnout tracks, and adopting CWT (continuously welded turnout). A refined calculation model for beam-track interaction on the bridge turnout is established using the finite element method. The rails and bridge main structures are simulated with beam elements, while fasteners, spacer-iron force-transmitting components, rail joints, and fixed bridge pier bearings are simulated using combinations of nonlinear and linear spring elements. Key indicators such as the temperature difference between bridge and rail, longitudinal resistance of fasteners, resistance of rail joints, resistance of REJ, and turnout geometric parameters are incorporated in the model to reproduce the force transmission pattern under temperature expansion/contraction conditions. For the five CWR schemes, the rail expansion/contraction force, turnout displacement, force on the force-transmitting component at the switch rail heel, and longitudinal force on the existing piers are calculated respectively, and the effects of each scheme on the track, bridge piers and abutments are compared. Result & Conclusion Installing REJ on straight and diverging turnout tracks reduces the forces and displacements of the turnout, but increases the forces on the existing piers. Installing REJ only on diverging turnout tracks is favorable to control the pier forces, but increases the turnout forces and displacements. The scheme of installing buffer rails on both the straight and diverging turnout tracks is better for turnout forces and displacements than that only installing buffer rails on the diverging turnout tracks, but the latter can improve the running smoothness on the straight turnout track. The forces and displacements of the CWT are largest, yet featuring the best smoothness and more complicated maintenance. Except for the scheme with expansion joints on both the straight and diverging turnout tracks, all other schemes need to consider the effect of switch machine displacement and strengthen the force-transmitting design at the switch rail heel.
ObjectiveIn recent years, frequent pantograph-catenary faults have posed severe challenges to the operation safety of urban rail transit. Improving pantograph-catenary interaction and keeping it in a stable state have become key research focuses in the industry, which requires further in-depth study. MethodTaking one line of Guangzhou Metro as the research object, the train traction characteristic curve is optimized by adjusting the traction motor’s switching point between the constant torque and constant power regions. The acceleration performance, equivalent main circuit current and total operation energy consumption are compared through laboratory simulation before and after optimization. Furthermore, specific sections on the main line are selected to measure the train operating speed, traction force, traction current and the total energy consumption before and after optimization, and the optimized traction characteristic curve is applied to all trains on the line. Under normal passenger-carrying operation, the average wear rate of the train carbon strips and the energy consumption per hundred vehicle-kilometers over a certain period of time are statistically counted to comprehensively evaluate the practical effect of the improvement strategy. Result & Conclusion After implementing the improvement strategy, the average wear rate of the carbon strips of all trains on the certain Guangzhou Metro line decreases from 1.12 mm to 0.81 mm per 10 000 km, representing a reduction of 27.7%. The energy consumption per 100 vehicle-kilometers drops from approximately 180 kWh to 176 kWh, a decrease of about 2.2%. Without compromising train operation efficiency or raising overall operation energy consumption, the proposed strategy significantly reduces the wear rate of pantograph carbon strips.
ObjectiveThe dynamic excavation of ultra-deep foundation pits will impose impacts on adjacent existing metro stations, leading to structural deformation or settlement of the stations, and even endangering structural safety and disrupting normal metro operation. Accordingly, it is necessary to formulate a reasonable reinforcement scheme during excavation to mitigate the above-mentioned impacts on existing stations. MethodBased on the ultra-deep foundation pit project adjacent to an existing metro station of Chengdu Metro Line 18, three grouting reinforcement schemes targeting horizontal deformation control, vertical deformation control and overall deformation control are proposed. Numerical simulation is adopted to compare and analyze ground settlement and structural deformation responses of the existing station under different reinforcement schemes, and field monitoring data are used to verify the reinforcement effect. Result & Conclusion Before adopting reinforcement measures, the maximum ground settlement at the midpoint of the foundation pit long side reached 18.70 mm, and the differential settlement of the existing station standard section was 4.67 mm. With the adoption of the L-shaped grouting reinforcement scheme for overall deformation control, the maximum ground settlement decreased to 6.38 mm, a reduction of as much as 65.89%, and the differential settlement of the existing station standard section dropped to 1.57 mm, representing a 66.42% reduction. Numerical simulation results are in good agreement with field monitoring data, demonstrating that the L-shaped grouting reinforcement scheme can effectively restrain stratum deformation and structural settlement induced by the ultra-deep foundation pit projects adjacent to existing metro stations.
ObjectiveIncorporating permanent magnets into the onboard electromagnets enables the formation of hybrid suspension electromagnets in the permanent magnet electromagnetic hybrid suspension (hereinafter abbreviated as PMEHS) technology. This technology relies on permanent magnets to provide the majority of the levitation force and realizes dynamic adjustment of the levitation force using coil windings. Thereby, it can significantly reduce the energizing current of the electromagnets and cut down their energy consumption and heat generation, showing great developmental potential. To further promote the application of PMEHS technology in urban rail transit, it is necessary to study its current development status and technical challenges of.MethodRelevant researches on PMEHS conducted by domestic and foreign universities and research institutions are reviewed. Taking China, the United States, Japan and other countries with advanced maglev technologies as examples, the R&D and optimal design of hybrid suspension electromagnets are elaborated, and the engineering application status of hybrid suspension technology in urban rail transit is described as well. Based on the analysis of research achievements and current technical status worldwide, the key technical challenges confronted by PMEHS technology are summarized. Result & ConclusionThe United States, Japan and other countries have initiated researches on hybrid suspension technology in an earlier time, but the technology promotion and commercialization are relatively slow, remaining still at the stage of prototype design and experimental research. Through technological optimization, China has developed multiple generations of PMEHS test vehicles with practical engineering application value, stepping into the stage of engineering verification and application. Nevertheless, the introduction of permanent magnets in hybrid suspension can easily lead to increased control difficulty of the suspension system and the magnetic levitation sticking phenomenon, which are the key technical challenges to be solved in the engineering application of PMEHS.
ObjectiveTo solve the problem of seasonal abnormal wear of pantograph carbon strips on Chengdu Metro Line 9 trains and ensure the service life of equipment and operational safety, it is necessary to study the causes of the abnormal wear and corresponding rectification measures. MethodFirstly, the abnormal wear of carbon strips on Chengdu Metro Line 9 trains is systematically reviewed, and the influencing factors of wear are analyzed from three aspects: pantograph-catenary contact pressure, carbon strip material, and catenary current. Secondly, the effect pattern of ambient temperature and humidity on carbon strip wear is emphatically analyzed. Finally, based on the analysis results, targeted rectification measures for seasonal abnormal wear are proposed from optimizing the pantograph-catenary coordination state, applying lubricating grease, and humidifying the tunnel three aspects, thereby forming a systematic and comprehensive improvement plan for the seasonal wear. Result & Conclusion The research results show that there is a significant negative correlation between ambient humidity and carbon strip wear rate. When the ambient humidity falls below the critical value, the carbon strip wear rate will increase abnormally. By implementing comprehensive rectification measures such as catenary preventive inspection and grinding, carbon strips chamfering, and tunnel humidification, the carbon strip wear rate decreases from 5.76 mm/10 000 km before rectification to 3.10 mm/10 000 km, with a reduction of 46%. The proposed rectification measures can keep the carbon strip wear rate within a safe threshold, so as to ensure the safe and stable operation of trains.
[Objective]Current researches on slurry pressure calculation theories are fragmented,mainly focusing on the application of a single specific calculation theory or analyzing only one type of geological condition,without systematic comparison and summary.Accordingly,it is necessary to conduct a systematic engineering comparative analysis of calculation theories for the slurry pressure at shield tunnel excavation faces.[Method]A calculation theory for the above-mentioned slurry pressure is proposed.To investigate the adaptability of different theories under various stratum conditions,field data are collected from multiple shield tunnels that traverse differing strata,and on-site monitoring of slurry pressure values during tunnelling is carried out.Given the complexity and low efficiency of manually calculating full-line excavation face slurry pressure for shield tunnels,a MATLAB program is developed to rapidly compute the theoretical values derived from the proposed theory.Measured slurry pressure values are then comparatively analyzed against the theoretical calculated values.Meanwhile,numerical models for diverse working conditions are established using the finite difference software FLAC3D,and the adaptability of the proposed calculation theory is verified through simulation analysis.Finally,division intervals of stratum permeability for water-soil separated pressure calculation and water-soil combined pressure calculation are obtained in combination with the permeability coefficients of the strata shield tunnels traverse.[Result&Conclusion]For the sandy and gravel strata under shallow-buried conditions,the Rankine active earth pressure calculation theory is recommended.For the clay strata under shallow-buried conditions,a three-dimensional wedge mode calculation theory based on the full-soil column theory is suggested.For the sandy strata under deep-buried conditions,Terzaghi's loosening earth pressure calculation theory is preferred,and for the clay strata in same conditions,a three-dimensional wedge mode calculation theory built upon the above Terzaghi's calculation is advised.Water-soil separated pressure calculation is recommended for sandy strata with a permeability coefficient greater than 1×10-3 cm/s,whereas water-soil combined pressure calculation is preferred for clay strata with a permeability coefficient lower than 6×10-6 cm/s.
ObjectiveAt present, the rail transit systems in many Chinese cities are at a critical stage of rapid network expansion. On the one hand, the total volume, structure, and characteristics of rail transit network passenger flow are continuously evolving; on the other hand, the historical passenger flow data under the same network configuration are relatively limited, which brings new difficulties and challenges to passenger flow forecasting and analysis. Therefore, it is necessary to conduct research on the inbound/outbound passenger flow forecasting methods for urban rail transit stations under changing network conditions. MethodBased on multi-source correlation data analysis, the influencing factors of passenger flow forecasting are systematically extracted from two dimensions, i.e. the same network condition and the changed network condition. Considering the actual rapid changes of rail transit network structure, historical characteristic days of passenger flow patterns are first identified. Then, a network change coefficient and a natural growth coefficient are introduced to perform weighted corrections on passenger flows, and the exponential smoothing method is adopted to synthesize the multi-day corrected passenger flows. Based on the proposed forecasting method that takes network changes into account, a case study is carried out on Nanchang Metro. Result & Conclusion Under the condition of rapid network changes, the proposed method can effectively utilize historical data resources from different network stages, overcome the limitation of insufficient historical data under the same network configuration, thus resolving the difficulty that large-scale data-driven learning methods failing for network passenger flow forecasting. The forecasting errors for both inbound and outbound passenger volumes are within 9%. Compared with traditional forecasting methods, the proposed one exhibits higher accuracy and better applicability.
