Search Results (15)

The span of pile foundations beneath metro depots typically ranges from 10 to 20 m, exhibiting a notably large span. This structural characteristic results in the pile foundations bearing a more concentrated upper load, while the interstitial soil between the piles bears minimal force. Concurrently, global climate change and enhanced urban greening initiatives have led to a significant increase in rainfall in northwest China, a region traditionally characterized by arid and semi-arid conditions. This climatic shift has precipitated a continuous rise in groundwater levels. Furthermore, the extensive distribution of collapsible loess in this region exacerbates the situation, as the rising groundwater levels induce loess collapse, thereby adversely affecting the mechanical behavior of the pile foundations. In light of these factors, this study utilized the pile foundations of a metro depot in Xi’an as a prototype to conduct static load model tests under conditions of rising groundwater levels. The experimental results reveal that the load–settlement curve of the pile foundations in the absence of groundwater exhibited a steep decline with distinct three-stage characteristics, and the ultimate bearing capacity was determined to be 5 kN. When the groundwater level is situated below the loess stratum, the settlement of both the pile foundations and the foundation soil, as well as the axial force, skin friction, and pile tip force, remains relatively stable. However, when the groundwater level rises to the loess stratum, there is a significant increase in the settlement of the pile foundations and foundation soil. Negative skin friction emerges along the pile shaft, and the bearing type of the pile foundation transitions gradually from a friction pile to an end-bearing pile. The influence range of the pile foundation on the settlement of the foundation soil is approximately three times the pile diameter. Full article

Many cities around the world are developing over-track buildings above metro depots to achieve efficient and economical land use. However, the vibrations generated by frequent train operations have a significant impact on the over-track buildings. Therefore, the analysis and control of vibrations at metro depots are of great importance. This paper focuses on the train-induced vibration propagation law and the application of vibration isolation trench measures of the over-track building in the metro depot. To this end, a typical metro depot is taken as the research object. The train-track model, used for simulating wheel-rail force, and the track-soil-building model, used for predicting structural response, are established, respectively. Then, the vibration response of the over-track building of the metro depot is explored, and the effects of vibration isolation measures of the open trench and infilled trench in the metro depot are studied. The results show that the train-induced vibration excitation of the metro is mainly concentrated in the range of 1 to 80 Hz, and the predominant frequency range of the floor vibration is 25 to 50 Hz. The vibration response of the floor is mainly affected by the stiffness. The larger the floor area, the smaller the vertical natural frequency, and the wider the range between the train vibration excitation areas, the more prone to resonance. In addition, the vibration isolation effect of the open trench is better than that of the infilled trench. The primary factor affecting the vibration isolation performance of open trenches is their depth; the influence of trench position and width on the vibration isolation performance is weaker compared to the depth. In the predominant frequency range of floor vibration, the overall vibration isolation effect of the flexible infilled trenches is better than that of the rigid infilled trenches. The main factor affecting the vibration isolation effect of the infilled trenches is the impedance ratio of the material. Among the six kinds of filling materials selected in this paper, the barrier effect of gravel is the worst, and the barrier effect of foam is the best. Using the measure of a foam infilled trench, Z-vibration levels of floors can be reduced by 8.6–13.9 dB. Full article

This study presents a probabilistic prediction method for train-induced vibrations by combining a deep neural network (DNN) with the mixture density model in a cascade fashion, referred to as the DNN-RMDN model in this paper. A benchmark example is conducted to demonstrate and evaluate the prediction performance of the DNN-RMDN model. Subsequently, the model is applied to a case study to investigate and compare the uncertainties of train-induced vibrations in the throat area and testing line area of a metro depot. After training, the model is capable of accurately predicting the probability density function (PDF) of train-induced vibrations at different distances from the track and at different frequencies. Utilizing the predicted PDF, probabilistic assessments can be performed to ascertain the likelihood of surpassing predefined limits. By employing a mixture density model instead of a single Gaussian distribution, the DNN-RMDN model achieves more accurate prediction of the PDF for train-induced vibrations. The proposed probabilistic assessment framework can effectively assist in vibration screening during the planning phase and in selecting and designing vibration mitigation measures of appropriate levels. Full article

Urban land resources are scarce in China. To utilize land effectively and economically, many cities are developing over-track buildings above metro depots. The vibration from the entrance and exit lines of metro depots under an over-track platform would significantly impact over-track buildings. To study the influence of train vibration in the throat area of a metro depot on over-track buildings, a simulation model was established using a finite element method. The reasonability of the simulation method and parameter settings was verified through comparing the vibration simulation results with vibration test results in the throat area of a metro depot. Furthermore, the impact of parameters of over-track platform and building on indoor vibration induced by a train was quantitatively studied. According to simulation results, a prediction model was developed to predict the impact of train vibration on over-track buildings in metro depots. From the perspective of architectural planning and design, this study provides a theoretical and technical basis for the prevention and control of indoor vibrations in over-track buildings of urban metro depots. Full article

In view of the problem that vibration of superstructures under vibration loads of metro trains causes, this research used a metro depot and superstructure project as its background and proposed a numerical simulation method based on the impedance analytical model and finite element model to simulate and predict the vibration and secondary noise response of subway trains affecting multi-story buildings at different locations on the ground and in the superstructure. The method’s accuracy was verified using real measurement data. The research shows that vibrations generated by subway operations vertically at lower floors remain relatively unchanged, then slowly attenuate before increasing near the top floors. Mitigation measures should primarily address four aspects: rails, fasteners, sleepers, and roadbed. The adverse effects of vibration can be controlled by reducing the excitation intensity of the vibration source, attenuating vibrations along the propagation path, and isolating vibrations in the foundation and interior of the building. This research method can quickly and accurately predict the vibration and noise conditions of superstructure properties and provide support for vibration and noise reduction in practical engineering. Full article

Metro transit construction has begun to develop rapidly in northwest China because of the acceleration of urbanization. Accordingly, metro depots are also regarded as an essential auxiliary facility for stopping, operation, and maintenance of trains. Meanwhile, many commercial buildings are constructed over metro depots to improve the utilization rate of land due to the increasingly scarce urban land resources, known as transit-oriented development (TOD). These buildings have a large covered area and transfer concentrated loads to the bases. Therefore, pile bases under metro depots have the bearing characteristics of undertaking large concentrated loads, while lesser loads are placed on the soil between the adjacent pile bases. Additionally, the main ground in northwest China is collapsible loess, so the collapsibility should also be considered. Based on the above background, this research performed static loading tests with and without immersion in a reduced scale of adjacent pile bases under a metro depot in Xi’an. The remolding process of natural loess could destroy its structure and the anisotropy of natural loess could also affect the test results. Therefore, four kinds of artificial collapsible loess with different mass ratios of barite powder, kaolin, river sand, cement, industrial salt, and calcium oxide were made by the free-drop method. This method could make the artificial loess simulate the structure of natural loess reasonably. Then, the artificial loess with the most similar properties to intact loess was selected by comparison. Finally, static loading tests with this artificial loess were implemented. The results showed that the ultimate bearing capacity was 4.5 kN. At the same time, the axial force decreased along depth, since the pile shaft friction was positive, and the load sharing ratio of pile tip force increased to 0.58 when the load exceeded 4.5 kN in the situation without immersion; the settlement of pile bases increased significantly after immersion, while the negative shaft friction occurred at the depth of −8 cm~−35 cm, and the load sharing ratio of pile tip force reached 0.92. Full article

When urban subway trains run in the depot, they can cause vibration and noise, which affects the safety and reliability of the structure under the track, and these transmits to the over-track buildings and often trouble passengers and staff. This paper established a coupling model of a track–metro depot–over-track building based on the structural finite element method and analyzed vibration response and then summarized the vibration transmission and distribution characteristics as the speed changes. The results show that, at train speeds of 20 km/h and 5 km/h, the Z-vibration level difference between the two at the rail is nearly 20 dB, and the vibration can be reduced by 17.9% at most. The difference between the two on the 9 m platform is 6–8 dB and 5–14 dB on the 16 m platform, and the vibration can be reduced by 17.7% at most. The difference between the two in the over-track building is 3–11 dB, and the vibration can be reduced by 13.0% at most. The vibration has the highest energy within a range of 2 m radiating from the center of the line, reaching a maximum of 118.5 dB. The vibration shows a ring-shaped distribution, and the ring-shaped distribution is more pronounced as the train speed increases. In the horizontal direction of the track line, the vibration energy distribution is within a range of −4 m to 11.5 m from the track line. In the longitudinal direction of the track line, the ring-shaped distribution of vibration energy exhibits a periodic pattern. The results provide a reference for the vibration control of the over-track buildings. Full article

Creating new multimodal infrastructure in an existing transport network of an urban city is a challenging process. The responsible transport authorities have to pay special attention to the details regarding the accessibility and effectiveness of the new development, to avoid travelers’ confusion and network congestion. The subject of this paper is the assessment and optimization of the traffic network in the surroundings of the new multimodal depot of Thessaloniki’s future metro system with the use of the microsimulation software PTV VISSIM (version 2022). Five different scenarios were developed in collaboration with the city’s transport authority and evaluated into two stages, beginning with the whole traffic network, and then continuing with the analyzed intersections separately. The evaluation is based on Key Performance Indicators (KPIs), which were extracted by the software. According to the results of the base case scenario, the network functions satisfactorily, with slight delays. Regarding the future network, the operation of the new hub will strongly increase the traffic demand, while the proposed traffic network adjustments by the local authorities seem to cause significant delay problems. This paper aims to highlight the importance of using modeling tools during the design phase of a new infrastructure to create efficient, accessible, and sustainable infrastructures that enhance the public transport system. Full article

To predict and control the train-induced vibration in depot buildings, a case study of the depot of Tianjin Metro, Line 5, was conducted. The platform of the depot has been constructed and is in use, and the construction of over-track buildings has not been completed. Firstly, an in situ measurement was performed to obtain the train loads and validate the numerical model. Secondly, a finite element model of the track–soil–depot structure was established. The train was simplified as a series of two spring-mass models and the train load was simulated using the measured rail acceleration. The calculated results were validated by the measurement data. To predict the vibration responses of the over-track building to be built, a sub-system of the over-track building was added to the numerical model. Finally, the vibration control effect of vibration isolation bearings was discussed. The results indicate that vibrations exceeded guideline limits without mitigation measures in some rooms of the over-track building. The dominant frequency of the building floors is 31.5 Hz. Vibration isolation bearings effectively mitigated the vibrations, and the IL reached approximately 7–15 dB at about 31.5 Hz. Full article

The superstructure of the metro depot is not only convenient for traffic but also solves the land-use problem. However, the construction of the superstructure comes after the metro depot has been put into normal operation. The foundation of the depot is bound to produce secondary settlement. Based on the calculation method of the friction-end bearing pile of Mindlin’s solution in the specification, the superstructure construction project above the Beijing Guogongzhuang metro depot is taken as the basis. Under certain conditions, the settlement of the pile foundation under the action of secondary load and the influence on the track structure are calculated. Moreover, the finite element analysis software ANSYS 18.0 is used to establish the analysis model of the construction of the superstructure of the applied depot. The results show that the influence of the pile foundation settlement produces a certain additional influence on the surrounding tracks, and the maximum value locates at the center of the bearing platform and gradually decreases outward. Under the conditions of informative construction, uniform loading of the structure and control of the construction process, local bias loads and uneven settlements are avoided. The impact of the construction on the track can be effectively controlled, and the impact on the structure can be kept within the allowable limits. By comparing this instance with a number of similar superstructure projects in Beijing, this study shows that the overall risk of this type of project can be controlled and can provide a technical reference for similar superstructure projects on top of a metro depot construction in the future. Full article

In this paper, anomaly detection of wheel flats based on signal processing and deep learning techniques is analyzed. Wheel flats mostly affect running stability and ride comfort. Currently, domestic railway companies visually inspect wheel flats one by one with their eyes after railway vehicles enter the railway depots for maintenance. Therefore, CBM (Condition-Based Maintenance) is required for wheel flats resolution. Anomaly detection for wheel flat signals of railway vehicles using Order analysis and STFT (Short Time Fourier Transform) is studied in this paper. In the case of railway vehicles, it is not easy to obtain actual failure data through running vehicles in a university laboratory due to safety and cost issues. Therefore, vibration-induced acceleration was obtained using a multibody dynamics simulation software, SIMPACK. This method is also proved in the other paper by rig tests. In addition, since the noise signal was not included in the simulated vibration, the noise signal obtained from the Seoul Metro Subway Line 7 vehicle was overlapped with the simulated one. Finally, to improve the performance of both detection rate and real-time of characteristics based on existing LeNet-5 architectures, spectrogram images transformed from time domain data were proceeded with the LeNet deep learning model modified with the pooling method and activation function. As a result, it is validated that the method using the spectrogram with a deep learning approach yields higher accuracy than the time domain data. Full article

Taking the frame-supported shear wall structure of a 102.1 m high metro depot as the test object, the structure has obvious vertical irregularity, and a quasi-static test was carried out on the structural model with the scale of 1/5. The damage development and strain of the structure were observed by applying displacement loads under different seismic actions, and the experimental phenomena and measured data were analyzed. The results show that the safety performance of the structure meets the seismic requirements of the MCE (Maximum considered earthquake) condition. Under the action of load, a reasonable damage mechanism is formed in which the components above the transfer story crack first and those below the transfer story crack later, which is in line with the design concept of “the performance objective of the bottom frame structure is higher than that of the upper shear wall structure”. The transfer plate is mainly subjected to shear deformation, the possible shear failure of the transfer plate should be avoided by reasonable design. Due to the large height difference between the first floor and the second floor, the structure may be adversely affected, so it is necessary to make the yielding floor appear in the bottom strengthening part above the transfer story. Under the SLE (Service level earthquake) and DBE (Design based earthquake) conditions, the bottom frame of the structure is mainly subjected to elastic deformation. Under the MCE (Maximum considered earthquake) condition, the bottom frame of the structure causes a lot of damage, increases energy consumption and decreases stiffness, which further proves that “the performance goal of the bottom frame structure is higher than that of the upper shear wall structure”. Full article

As a sustainable mode of metro-development strategy, transit-oriented development (TOD) is rapidly growing to finance the transport infrastructure investment. The main negative consequence of constructing residential buildings directly over metro depots is railway-induced vibration, that may affect structural serviceability. The residents may feel uncomfortable, as the metro trains start running very early in the morning and finish daily operations very late at night. In order to evaluate the level of human comfort subject to the special situation, a case study was provided in this paper. Directed by the academic review, there were four common comfort evaluation methods, with difference indexes to describe the influence of vibrations. Therefore, a measurement campaign was conducted and both acceleration and velocity sensors were simultaneously installed at the same measurement points, to reduce the influence of the conversion accuracy. The results show that there are certain differences between the evaluation methods in assessing the vibration comfort, but considering the most adverse effects together, the over-track building at this particular TOD-developed depot can ensure that 90% of the occupants would not be highly annoyed by the vibrations. The main negative effect on human comfort at the TOD depot is that the high-level vibrations would cause interruptions in sleep. Among them, the vibrations in this case would affect the rest of 17% of the occupants in the bedrooms on the seventh floor, and make it difficult for 9% of the occupants to fall asleep. Therefore, the evaluation index was suggested to consider more factors related to sleep difficulties and awake threshold values. Full article

Over-track buildings above metro depots have become common in megacities due to urban land shortages. The transmission of vibrations into the over-track buildings during routine train operations has the potential to adversely impact the occupants in terms of perceptible vibration and noise. There is a need to quantify the potential impacts before construction for planning and design purposes. Train-induced vibration measurements were carried out on a six-story over-track building at the Luogang metro depot in Guangzhou, China, which is located adjacent to the tracks. The measurements were used to develop a data-driven cascaded state-space model, which can be applied to planned over-track buildings located in track areas to predict and assess whether train-induced vibrations would adversely affect the buildings’ future occupants. Vibration levels in the platform of the building’s columns were used as inputs to the models, thereby avoiding the complexity of modeling the transfer behavior of the platform. The predicted vibration levels corresponded with measurements in the existing building. This comparison validated the use of the model for future residential buildings where the predictions indicate that the impacts on its occupants will be within the applicable criteria. Full article

In order to improve train operation planning from the two perspectives of enterprise operating costs and passengers’ travel time, this paper proposes an integrated optimization model of three sub-problems, namely line planning, timetabling and rolling stock allocation for urban railway transit lines based on passengers’ travelling demands and the constraints of the urban rail line. The model features dwelling time at stations, turnaround operations at terminal stations, entering/exiting depot operations and an assignment for passengers’ travelling flow. We propose a solution method based on a metaheuristic method that simulates annealing to generate an optimal solution for the overall problem using MATLAB. Finally, we use the example of Xi’an metro line one to demonstrate the performance of the model. Full article