Numerical analysis of factors affecting the range of heat transfer in earth surrounding three subways

In order to examine the factors which affect the range of heat transfer in earth surrounding subways, FLAC3D was adopted in this study to analyze these factors, under different conditions, in a systematic manner. When we compare these numerical tests, the results show that the main factors, affecting the heat transfer range are the thermal properties of the surrounding earth, the initial ground temperature and the temperature in the tunnel. The heat transfer coefficient between air and linings has little effect on the temperature distribution around the tunnel. The current results can provide a reference for improving the thermal environment in subways and optimizing the design of subwav ventilation and air conditioning.

Elevated levels of the pollutant PM2.5 in crowded subways of cities with high COVID-19 related mortality-when COVID-19 went underground

Background:Recent literature indicates that the pollutant,particulate matter PM2.5,may have an impact on COVID-19 related infection and mortality.Genes coding for SARS-CoV-2 has been found adherent to PM2.5 and possibly the COVID-19/PM2.5 complex may be involved in the transmission and the exacerbation of COVID-19 infection.PM2.5 levels in deep underground subways have been found up to 90 times higher than roads closer to the surface.Method:The levels of PM2.5 were retrieved from literature assessing particulate matter PM2.5 measured on subway platforms in two groups of cities.These cities were differentiated by the COVID-19 population percentage mortality rate(0.007%vs 0.19%)(P<0.0004).Data regarding the number of stations,length of the networks(km)and the annual ridership were also obtained from literature related to underground commuting.Results:The population percentage mortality related to SARS-CoV-2 infection correlated significantly for both minimum(P<0.01)and maximum(P<0.00001)levels of PM2.5.The cities’subways with low COVID-19 mortality had minimum platform PM2.5 levels of 27.4(SD+/-17.2μg/m3)compared to 63.4μg/m3(SD+/-10.8μg/m3)in cities with high SARS-CoV-2 associated mortality(P<0.01).Subway maximum levels of PM2.5 in cities with low COVID-19 mortality was 53.4μg/m3(SD+/-21.8μg/m3)while that of underground networks with high COVID-19 mortality had maximum platform PM2.5 levels of 172.1μg/m3(SD+/-98μg/m3)(P<0.001).Conclusion:Underground networks may have inherent characteristics accelerating spread of SARSCoV-2 infection and consequent mortality.The highly elevated levels of PM2.5 in overcrowded subways with extensive reach,may have acted as a co-factor to disseminate the pandemic in a number of metropolises.

Subways and the Diffusion of Knowledge:Evidence from China

This paper aims to examine the role of the subway network,a typical form of transportation within urban areas,on innovation and knowledge diffusion.Applying the differece-in-diferences strategy and spatial analysis,we used 1,332 newly opened stations in China from 2000 to 2013 as a quasi-experiment to identify the local effects of subway expansions.Results suggested that by reducing communication costs and increasing opportunities for interaction,subway construction would bring growth at the district level.Knowledge dissemination would become more active after new stations open.Micro-level results showed that these positive impacts were highly localized;that is,only those firms located within lkm around stations benefited from the new subway.Moreover,new subways facilitated the flow of knowledge from station to station and assisted.firms in acquiring knowledge from more distant technology clusters conveniently.

Assessment of the Influence of Tunnel Settlement on Operational Performance of Subway Vehicles

In the realm of subway shield tunnel operations,the impact of tunnel settlement on the operational performance of subway vehicles is a crucial concern.This study introduces an advanced analytical model to investigate rail geometric deformations caused by settlement within a vehicle-track-tunnel coupled system.The model integrates the geometric deformations of the track,attributed to settlement,as track irregularities.A novel“cyclic model”algorithm was employed to enhance computational efficiency without compromising on precision,a claim that was rigorously validated.The model’s capability extends to analyzing the time-history responses of vehicles traversing settlement-affected areas.The research primarily focuses on how settlement wavelength,amplitude,and vehicle speed influence operational performance.Key findings indicate that an increase in settlement wavelength can improve vehicle performance,whereas a rise in amplitude can degrade it.The study also establishes settlement thresholds,based on vehicle operation comfort and safety.These insights are pivotal for maintaining and enhancing the safety and efficiency of subway systems,providing a valuable framework for urban infrastructure management and long-term maintenance strategies in metropolitan transit systems.

Automatic Sensing and Detection for Subway Tunnel Pathologies

Subway tunnels often suffer from surface pathologies such as cracks,corrosion,fractures,peeling,water and sand infiltration,and sudden hazards caused by foreign object intrusions.Installing a mobile visual pathology sensing system at the front end of operating trains is a critical measure to ensure subway safety.Taking leakage as the typical pathology,a tunnel pathology automatic visual detection method based on Deeplabv3+(ASTPDS)was proposed to achieve automatic and high-precision detection and pixel-level morphology extraction of pathologies.Compared with similar methods,this approach showed significant advantages and achieved a detection accuracy of 93.12%,surpassing FCN and U-Net.Moreover,it also exceeded the recall rates for detecting leaks of FCN and U-Net by 8.33%and 8.19%,respectively.

Sustainable Urban Mobility: (A)Synchrony between Subway Systems

The present study analyses the differences between the subways systems of two cities, Lisbon (Portugal) and Brasília (Brazil), verifying the extent to which their subway systems are spatially integrated with the respective urban fabric-which would promote a better synchrony in terms of economy and sustainability. For interpreting the data, the methodology and tools of the Theory of the Social Logic of Space were used, by means of axial maps, researching the relationship between the constructed and empty (public spaces) areas of the urban structures. Based on the findings, meaningful differences between the subway systems and the configuration of urban spaces were observed, as a product of specific design matrixes. In Lisbon, the mobility associated to the subway seems to be encouraged by the integration of the system with the potential for movement provided by the urban tissue (making the secondary centralities articulated with the subway stations more dynamic). In Brasilia, however, there are several difficulties for such mobility, due to the predominant role of the empty spaces in the city which weakens the gathering potential of such areas, despite the fact that such articulation with secondary centralities is also present there.

Construction Technology of Pile Foundation for Subway Tunnel Crossing Bridge

Urban infrastructure has become more complex with the rapid development of urban transportation networks.In urban environments with limited space,construction of facilities like subways and bridges may mutually influence each other,especially when subway construction requires passing under bridges.In such cases,pile foundation replacement technology is often necessary.However,this technology is highly specialized,with a lengthy and risky construction period,and high costs.Personnel must be proficient in key technical aspects to ensure construction quality.This article discusses the technical principle,construction process,and core technology of pile foundation replacement,along with the application of this technology in subway tunnel crossing bridge projects,supported by engineering examples for reference.

Discussion on Construction Technology of Subway Tunnel Expansion under Bridge Foundation

As the urban populations grow,the number and size of subway construction projects are increasing while also meeting higher construction standards.So,subway construction projects must have a better understanding of construction technology.This article focuses on the construction technology of the subway tunnel expansion under the bridge foundation.By analyzing the engineering characteristics of the bridge foundation and using a project as an example,this article provides a detailed discussion of the construction process of tunnel expansion under a bridge foundation.This article aims to serve as a reference for subway tunnel construction in China to ensure the key points of construction technology are understood,thus improving construction quality and laying a solid technical foundation for the sustainable development of urban rail engineering.

To Topple Trees for Subways or Not?

The tall trees in Nanjing,capital city of east China’s Jiangsu Province,are an amenity local people boast about.In1928,in order to commemorate Sun Yat-sen,founder o the Kuomintang,hundreds

Functional Characteristics of Beijing Subway Stations Based on POI Data:Taking Beijing Metro Line 6 as An Example

Urban subway station is a key node related to urban social,political,economic and cultural activities.There are some differences in the location,function orientation,land use and flow characteristics of different types of stations in the city.This paper mainly used Tyson’s edge,kernel density analysis,chart analysis and other methods to classify the functional types of 412,393 POI data of 26 stations along Metro he results showed that the spatial distribution of Beijing Metro Line 6 was mainly divided into 3 categories,subway stations were divided into 4 categories.Among them,type A sites were divided into composite and single types,and the distribution characteristics of the 6 types of sites were quite different.Based on the qualitative and quantitative analysis of POI point data,this method can quickly classify and analyze the characteristics of stations along Line 6 in Beijing,which also has theoretical and practical value for the planning of urban subway lines.

Monitoring Study of Long-Term Land Subsidence during Subway Operation in High-Density Urban Areas Based on DInSAR-GPS-GIS Technology and Numerical Simulation

During subway operation,various factors will cause long-term land subsidence,such as the vibration subsidence of foundation soil caused by train vibration load,incomplete consolidation deformation of foundation soil during tunnel construction,dense buildings and structures in the vicinity of the tunnel,and changes in water level in the stratum where the tunnel is located.The monitoring of long-term land subsidence during subway operation in high-density urban areas differs from that in low-density urban construction areas.The former is the gathering point of the entire urban population.There are many complex buildings around the project,busy road traffic,high pedestrian flow,and less vegetation cover.Several existing items requiremonitoring.However,monitoring distance is long,and providing early warning is difficult.This study uses the 2.8 km operation line between Wulin Square station and Ding’an Road station of Hangzhou Subway Line 1 as an example to propose the integrated method of DInSAR-GPS-GIS technology and the key algorithm for long-term land subsidence deformation.Then,it selects multiscene image data to analyze long-termland subsidence of high-density urban areas during subway operation.Results show that long-term land subsidence caused by the operation of Wulin Square station to Ding’an Road station of Hangzhou Subway Line 1 is small,with maximumsubsidence of 30.64 mm,and minimumsubsidence of 11.45 mm,and average subsidence ranging from 19.27 to 21.33 mm.And FLAC3D software was used to verify the monitoring situation,using the geological conditions of the soil in the study area and the tunnel profile to simulate the settlement under vehicle load,and the simulation results tended to be consistent with the monitoring situation.

A practical framework for performance-based reliability analysis of subway stations based on a faultestructure combined system

It is necessary to pay particular attention to the uncertainties that exist in an engineering problem to reduce the risk of seismic damage of infrastructures against natural hazards.Moreover,certain structural performance levels should be satisfied during strong earthquakes.However,these performance levels have been only well described for aboveground structures.This study investigates the main uncertainties involved in the performance-based seismic analysis of a multi-story subway station.More than 100 pulse-like and no pulse-like ground motions have been selected.In this regard,an effective framework is presented,based on a set of nonlinear static and dynamic analyses performed by OpenSees code.The probabilistic seismic demand models for computing the free-field shear strain of soil and racking ratio of structure are proposed.These models result in less variability compared with existing relations,and make it possible to evaluate a wider range of uncertainties through reliability analysis in Rtx software using the Monte Carlo sampling method.This work is performed for three different structural performance levels(denoted as PL1ePL3).It is demonstrated that the error terms related to the magnitude and location of earthquake excitations and also the corresponding attenuation relationships have been the most important parameters.Therefore,using a faultestructure model would be inevitable for the reliability analysis of subway stations.It is found that the higher performance level(i.e.PL3)has more sensitivity to random variables than the others.In this condition,the pulse-like ground motions have a major contribution to the vulnerability of subway stations.

An experimental study on fire characteristics of urban complex underground space based on BIM

Compared with the space on the ground,if there is a fire in the urban complex underground space,the loss will be greatly harmful.In addition,the complex underground space is usually connected with other large space areas and densely populated.Once a fire occurs in the complex underground space,it will cause huge property losses and casualties.In order to reduce the risk of fire,it is necessary to deeply understand the development rules and characteristics of fire in the complex underground space of the city.This article has mainly carried on the following work:(I)A particularly complex model of the multi‐storey subway station was built.On this basis,three groups of comparative experiments were conducted to study the effects of fire power,fire location and smoke control system on fire development,and the conclusion that fire location is the most important factor for fire development was obtained;(II)In order to explore the entire space fire and the local space fire,CFD(Computational Fluid Dynamics)is used to build a large‐size fire model and a small‐size fire model respectively;(III)Multiple detector data as temperature slices were built,and it is expected to make full use of the simulation data to deduce the important index of fire location in the early stage of fire.All of the works in this paper will provide reference experimental data for the prevention and firefighting of a sudden fire in the complex underground space.

Performance of the suspension method in large cross-section shallow-buried tunnels

Large cross-section tunnel construction induces ground surface settlements, potentially endangering both subterranean projects and nearby above-ground structures. A novel tunnel construction method, known as the suspension method,is introduced in this paper to mitigate surface settlement. The suspension method employs vertical tie rods to establish a structural connection between the initial tunnel support system and the surface steel beam, thereby exerting effective control settlements. To analyze the performance of the proposed method, systematic numerical simulations were conducted based on the practical engineering of Harbin Subway Line 3. The surface settlement and vault settlement characteristics during construction are investigated. The results show a gradual increment in both surface and vault settlement throughout the construction process, culminating in a stabilized state upon the completion of construction.In addition, compared to the double-side drift method and the Cross Diaphragm Method(CRD) method, the suspension method can obviously reduce the surface settlement and vault settlement. Moreover, the surface settlements and the axial force of tie rods were continuously monitored during the construction process at the trial tunnel block.These specific monitoring measurements are illustrated in comparison to numerical analysis results. The monitored results show great agreement with the numerical predictions, confirming the success of the project. This research can serve as a valuable practical reference for similar projects, offering insights and guidance for addressing ground surface settlements and enhancing construction safety in the domain of large cross-section tunneling.

Classification of Beijing Line 10 Subway Living Circle Based on Multi-source Big Data

In the first-tier cities,subway has become an important carrier and life focus of people’s daily travel activities.By studying the distribution of POIs of public service facilities around Metro Line 10,using GIS to quantitatively analyze the surrounding formats of subway stations,discussing the functional attributes of subway stations,and discussing the distribution of urban functions from a new perspective,this paper provided guidance and advice for the construction of service facilities.

Functional Characteristics of the Surrounding Area of Beijing Metro Line 5 Based on POI Data

As an important urban infrastructure,rail transit not only has transportation function,but also has a close connection and harmonious development with the surrounding urban space.Taking Beijing Metro Line 5 as an example,each station of Beijing Metro Line 5 was analyzed by GIS software and Echarts chart based on POI data.The functions of subway site type were divided into main function,secondary function and no significant function,and various types of sites within the main functional characteristics of urban functions were discussed in details.The paper presents a new method for identifying urban functional features,which can be applied to not only other metro stations in Beijing but also the same type of cities.Moreover,it lays a foundation for the research of rail transit subway stations and their related researches.

Passengers gathering-scattering analysis at the corners of subway stations

During both daily operation and emergency evacuation,the corners of walking facilities in subway stations play an important role in efficient circulation.However,the effectiveness of the corner is difficult to assess.In this paper,a method of passenger gathering and scattering analysis based on queueing models was proposed to investigate the corner performance in subway stations.Firstly,we constructed a set of state spaces of passenger flow according to passenger density and proposed the state transition model of passenger flow.Moreover,the model of passenger flow blocking and unblocking probability were also presented.Then,to illustrate the validity of the method and model,several passenger gathering-scattering scenarios and were simulated to verify the influence of passenger distribution and facility width on passenger walking,and the blocking probability,throughput,and expected time were also analyzed under various widths of the target corridor and arrival rates.Results showed that the proposed model can reproduce the trend of walking parameters changing and the self-organizing phenomenon of'faster is lower'.With the increase of arrival rates of passengers,walking speeds of passengers decrease and the expected walking time is prolonged,and the blocking probability sharply increased when the arrival rate exceeded 7 peds/s.In addition,with change of width of the target facility,efficiency of capacity of walking circulation facility fluctuated.With the width of the target corridor enlarged by 10%,the steady state of passenger flow was less crowded.Therefore,corridor width is critical to the circulation efficiency of passengers in subway stations.The conclusions will help to develop reasonable passenger flow control plans to ease the jam and keep passengers walking safely.

Study on the Principle Model and Simplification of Subway Station Itemized Energy Consumption

Owing to the constant modernization and urbanization of China,most cities have subways,and the total power consumption of subway stations has been rising,which contradicts with China’s green goals.In this regard,energy consumption indicators for major energy use projects in subway stations should be established,comprehensive evaluation and detailed research on the current situation of subway operation should be conducted,and specific energy-saving measures should be taken from a diversified perspective.It is crucial to systematically sort out the principle of sub-item energy consumption in subway stations,and practice and explore the specific simplification measures of the principle model of sub-item energy consumption,so as to lay a solid foundation for achieving the goal of reducing energy consumption of subway stations.

Assessment of the Safety Impacts of a Pit Construction on the Neighboring Subway

In order to study the impact of pit excavation on the adjacent existing subway structure,the safety impact assessment of a project was carried out using project under construction near the subway as the engineering background.The results show that the new pit construction will produce some additional deformation on the existing subway interval structure,the deformation values are within the permissible range for safe operation.Through analysis of the results,the risk point rating of the pit adjacent to the interval is level 2.In general,the impacts of the pit construction on the neighboring subway structure are less than the specification limits.

基于视频图像块模型的局部异常行为检测

为提高视频监控下局部异常行为检测的准确性和快速性,文中提出一种基于视频图像块模型的局部异常行为检测方法。该方法首先进行基于梯度直方图的视频图像块提取和基于时空相关性的视频图像块优化;然后,对视频图像块进行基于张量投票的正常行为模型学习和基于时空相似性的异常行为模型学习;最后,依据学习结果进行视频图像块的局部异常行为检测,确定异常区域并进行有效的标记。在通用UCSD数据集和Subway数据集上的实验结果表明,文中所提方法能有效提高局部异常行为检测的准确性和检测的效率。