Subway Engineering Research Articles

Application and Vibration Reduction Properties of Prefabricated and Cast-in-Place Phononic-Like Crystal Polymer Concrete Track Bed in Subway Engineering

Application and Vibration Reduction Properties of Prefabricated and Cast-in-Place Phononic-Like Crystal Polymer Concrete Track Bed in Subway Engineering

Low frequency vibration reduction bandgap characteristics and engineering application of phononic-like crystal metaconcrete material

Metaconcrete, as a new type of composite material with vibration attenuation characteristics, is formed by replacing traditional coarse aggregates with a heavy metal core wrapped with an elastic soft coating and mixing with cement mortar. However, due to the high bandgap frequency and narrow bandgap width, it is greatly limited in the engineering application of low frequency vibration control. In order to broaden the range and number of elastic wave bandgap of metaconcrete materials and solve the problem of low frequency vibration, a novel three-component cement-based phononic-like crystal model is proposed based on local resonance theory, and phononic-like crystal metaconcrete vibration reduction material is developed accordingly. Secondly, the band structure, bandgap mechanism, and frequency response function of the phononic-like crystal metaconcrete are calculated and analyzed, and indoor tests of the phononic-like crystal metaconcrete are conducted. Finally, a phononic-like crystal metaconcrete subway track bed is prepared using the developed phononic-like crystal metaconcrete material, and applied to the practical subway engineerings to solve the low frequency vibration problem generated during subway operation. The results show that the phononic-like crystal metaconcrete opens 6 low frequency bandgaps in the frequency range of 200 Hz, and the attenuation values are mostly above 10 dB in the frequency range of the bandgap, and the attenuation effect is good. Meanwhile, the on-site monitoring results show that the phononic-like crystal metaconcrete subway track bed has good low frequency vibration reduction effect in the 200 Hz frequency range. The maximum value of the one-third octave insertion loss of the tunnel wall is 13.22 dB, the maximum vertical Z-vibration level difference of the tunnel wall is 5.052 dB, and the maximum vertical frequency division vibration level difference of the tunnel wall is 5.926 dB. The maximum value of the vertical frequency division vibration level difference in the frequency range of 4–200 Hz is 13.87 dB, and the average value is 5.74 dB. The relevant research results of this paper provide a new technical approach to solve the problem of low frequency vibration in subway engineering and other engineering construction, breaking through the traditional vibration reduction control technology of civil engineering structures, and providing new idea and method for long-term vibration reduction and application of engineering structures.

Research on 3D Visualization of Real Scene in Subway Engineering Based on 3D Model

As an urban infrastructure project, subway engineering exhibits the characteristics of large scale, trans-regional presence, and complex environmental conditions. The three-dimensional (3D) real scene of subway engineering aims to visually present the project features by creating a virtual environment in the 3D form by integrating numerous geographical scenes and entities. However, existing methods of geometric data integration and model visualization are insufficient for handling the diverse and heterogeneous data types encountered in this process. To address these challenges, this study proposes a framework for real-scene 3D visualization management in subway engineering, establishing a technical process of multi-source data integration for organizing 3D models within the scene, and developing a visualization display strategy that incorporates octree and level of detail principles for multi-scale hierarchical dynamic loading of 3D Scene. To validate the proposed method, a prototype system is developed with Geographic Information System (GIS) and Building Information Modeling (BIM) technology and applied to an actual subway project. The results demonstrate that this method ensures effective integration and management of data, enabling the display of real scenes in an integrated 3D model in a web environment.

Research on Groundwater Control Technology in Construction Based on Foundation Pit Construction Condition

With the rapid development of national economy and the restriction of urban construction land, high-rise buildings are mostly concentrated in urban centers. The construction and development of high-rise buildings promote the rapid development of deep foundation pit engineering, and the number and scale of foundation pit engineering are increasing day by day. In urban construction, a large number of high-rise buildings appear, and with the need of subway engineering and civil air defence works, deep foundation pit engineering in buildings is very common. In order to ensure the safe construction of deep foundation pit, groundwater must be controlled. If the groundwater is mainly phreatic water, vadose water or confined water with low water pressure, it should be blocked mainly. The specific technology is to construct a water-stop curtain around the foundation pit to stop the groundwater outside the foundation pit. If the groundwater is confined water with high pressure, measures should be taken to remove the water in the pit to prevent the foundation pit from surging. By analyzing the relationship between deep foundation pit engineering and groundwater, this paper summarizes the control methods of groundwater in deep foundation pit engineering.

Intelligent Electrical Engineering Automation on Account of Particle Swarm Optimization (PSO) Algorithm

Electrical engineering is closely related to people’s life. Many projects have proved that electrical engineering using PSO algorithm provides more convenient applications for people’s production and life, greatly improves people’s living standards, and makes people’s life and work more relaxed and valid. In many production fields, such as subway engineering, if advanced electrical engineering automation is adopted, the subway engineering can be carried out validly from start to finish, and the workload of workers can be greatly reduced. PSO algorithm further improves the automation performance of electrical engineering, and effectively breaks through the traditional electrical engineering operation mode, improve the operation efficiency. This text studies the concept and work flow of PSO algorithm, introduces the intelligent working principle and internal mechanism of electrical engineering. Data analysis, intelligent electrical engineering automation on account of PSO algorithm effectively improve the intelligent effect of electrical engineering automation.

Problems Existing and Related Countermeasures in the Construction Management of Subway Engineering

Problems Existing and Related Countermeasures in the Construction Management of Subway Engineering

Reduction of SO42− and Cl− migration rates and degradation of silica nanoparticles incorporated cement pastes exposed to co-existence of sulfate, chloride and electric fields

The reinforced concrete structures in subway engineering are generally subjected to combined exposure of chloride, sulfate and electric fields. Thus, it is necessary to reveal a way of enhancing corrosion resistance of concrete in this complicated environment condition. Although improvement of concrete properties by addition of nano silica is well known, how it can lead to the reduced transport rates of aggressive ions in the cementitious systems has not been systematically confirmed. In this work, the strengthening mechanism of nano-SiO2 on the erosion resistance of cement pastes was investigated in terms of water absorption, distribution of sulfate concentration, free chloride concentration and bound chloride concentration, ionic diffusion coefficients, crystalline phase composition, thermal gravimetric and Vickers hardness. The results indicated that the sulfate concentration exhibited a decreased trend with increasing the depth from exposed surface, while both free chloride and bound chloride concentrations first increased and then decreased gradually. The modification of silica nanoparticles on the cement pastes was remarkable, and 3% nano-silica admixed binary mixtures exhibited a significant reduction of the ionic migration rates and the accompany degradation. Moreover, replacement of 1% nano silica to cement due to pozzolanic reaction and nucleation effect dramatically led to the effective chloride capture near the exposed surface as a result of the declined porosity, which can be substantiated by X-ray diffraction and thermal gravimetric results. The results of this work are beneficial for establishment of a finer transport model in further research and provide a reference for monitoring and evaluation of durability of reinforced concrete structures serving in subway engineering.

Analysis and Prediction of Subway Tunnel Surface Subsidence Based on Internet of Things Monitoring and BP Neural Network.

With the acceleration of the urban development process and the rapid growth of China's population, the subway has become the first choice for people to travel, and the urban underground space has been continuously improved. The subway construction has become the focus of urban underground space development in the 21st century. During the construction of subway tunnels, the problem of surface settlement will inevitably be caused, and the problem of surface settlement will have a certain safety impact on the safe use of surface buildings. The impact of surface construction is predicted, so as to select the best construction technology and avoid the problem of surface subsidence to the greatest extent. On the basis of analyzing the principle of surface subsidence, this paper studies the optimal control strategy and process of subsidence in subway tunnel engineering. The research results of the article show the following. (1) The two sections of the pebble soil layer have basically the same subsidence trend. Among them, the first section has a larger settlement amplitude and both sides are steeper. The second section is mainly cobble clay soil. The pebble layer has good mechanical properties. If it can be well filled, its stability will be improved. The comparative analysis of the two sections shows that with the increase of the soil cover thickness, the maximum subsidence at the surface gradually decreases. The reason is that when the stratum loss is the same, the greater the soil cover thickness, the greater the settlement width. Sections 2 and 3 of a single silty clay have relatively close settlement laws, and the settlement changes on both sides of the tunnel are similar. (2) The surface subsidence caused by the excavation of the side hole accounts for more than 50% of the total surface subsidence, and the width of the settlement tank after the excavation of the side hole is increased by 8–10 meters compared with the excavation of the middle hole. (3) The prediction error of the BP neural network model proposed in this paper is the lowest among the four models, whether it is the prediction of the cumulative maximum surface subsidence or the location of the cumulative maximum surface subsidence, and the average relative error of the cumulative maximum surface subsidence is 3.27%, the root mean square error is 3.87, the average relative error of the location of the cumulative maximum surface subsidence is 7.96%, and the root mean square error is 21.06. In the prediction process of the cumulative maximum surface subsidence, the prediction error value of the Elman neural network is relatively large, and the GRNN generalized neural network and RBF neural network have no significant changes; in the process of predicting the position where the cumulative maximum surface subsidence occurs, the prediction error value of RBF neural network is maximum.

Probabilistic analysis of subway station excavation based on BIM-RF integrated technology

In the past decade, BIM technology has developed considerably, especially in the building industry. Although BIM technology has excellent potential in promoting information and digitization technology in the construction industry, its advantages still cannot be fully utilized during subway station excavations, and engineering computations based on complex theory cannot be well performed in the BIM technology. Particularly, with the rapid development of subway engineering and considering the great uncertainties in soil properties, it is necessary to improve the engineering management and risk assessment in construction process. In this paper, a BIM-RF integrated technology for performing probabilistic analysis of BIM-based subway station excavation based on random field theory (RF) is proposed to meet practical needs. Specifically, a three-dimensional parametric modeling method in Revit software is introduced. Then, a process of probabilistic analysis combined with RF theory for subway station excavation is presented. In the BIM-RF integrated framework, the necessary information for engineering computations is decoded from the BIM model; combined with the generated RF, a probabilistic analysis based on Monte Carlo simulations is performed to provide an engineering risk assessment. The BIM-RF integrated technology enables comprehensive engineering computations to be implemented in analyses of BIM-based subway station excavation and can improve the expandability of BIM technology.

A study of variables that affect the process of sulfate attack of cement‐based materials subjected to stray current

AbstractDurability is one of the most important considerations for subway structures. However, the cement‐based materials used in subway engineering can be jeopardized by sulfate and the stray current and therefore can be subjected to severe damage during service. This study aims to investigate the degradation process of cement‐based materials exposed to stray current and external sulfate. In particular, the effects of three key variables were evaluated: concentration of external sulfate solution, level of stray current and cement type. After exposure, the visual appearance, compressive strength, SO42− profiles and microstructure of cement‐based materials were analyzed. Moreover, the amounts of degradation products were measured to evaluate the influencing degree of different variables and further explain the degradation mechanisms. Experimental results of this study reveal that (a) sulfate attack was related to the external sulfate concentration, but the relation was changed due to the presence of stray current. One explanation is that sulfate ions can be quickly accumulated in the pores of cement‐based materials under the effect of stray current, which makes the chemical reaction of sulfate attack exchange from diffusion control to reaction control. (b) Stray current could accelerate external sulfate attack of cement‐based materials, and the greater the stray current, the more severe sulfate attack was induced. (c) Compared with P·I type cement, high sulfate resistant (HSR) cement showed a better resistance to external sulfate attack. (iv) And, the main degradation products, ettringite and gypsum, were observed in specimens after exposure. Additionally, stray current might induce the decomposition of ettringite. It should be paid more attention on the durability of cement‐based materials exposed to the coupled conditions of stray current and sulfate.

Vickers hardness distribution and prediction model of cement pastes corroded by sulfate under the coexistence of electric field and chloride

The durability of reinforced concrete structures in subway engineering is a continuing concern due to the long-term complications associated with the coexistence of sulfate, chloride and electric field. However, there remain challenges towards better characterizing the changes in the mechanical and durability of the influenced structures. In this study, the micro-Vickers hardness was measured to reflect the changes in the local mechanical properties of the cement pastes before and after sulfate erosion under the combined treatment of an electric field and chloride. The effect of the water-to-cement ratio, sulfate concentration, chloride concentration and current intensity on the Vickers hardness of cement paste was explored under the coupling effect of sulfate, chloride and electric field. Moreover, a Vickers hardness prediction model taking into account multiple factors was established by modifying the Logistic function. The results showed that increasing the water-cement ratio, the sulfate concentration and the current strength all led to a decrease in the Vickers hardness of the cement paste. Interestingly, an increase in the chloride concentration alleviated the sulfate-induced decrease in the Vickers hardness, indicating that the existence of chloride delayed the sulfate attack, which was substantiated by the XRD results. There was a good correlation between the Vickers hardness prediction model and the experimental data. Therefore, the developed model is able to predict the changes in the Vickers hardness of the cement paste under the changes in the above mentioned factors with a high confidence.

Experimental Study on Physical and Mechanical Properties of Sandy Cobble Strata of Beijing Subway

The aquifers of θ cobble stratum,⑦ cobble stratum and ⑨ cobble stratum are the main shallow aquifers affecting the construction of Beijing subway, and water inrush accidents often occur in the process of construction of Beijing subway. In addition, Beijing is located in a semi-arid area, the per capita water resources are less. In order to ensure the safety and protection of underground water resources in the construction of Beijing subway engineering, the typical soil samples of Beijing sandy cobble quifer were used for grain size distribution test, water content test and consolidation test. The results showed that the cobble accounted for 64.77% of the weight of the soil sample, the uniformity coefficient Cu=30.06 and the curvity coefficient Cc=0.32, which indicated that the soil was poorly graded; the water content of sand soil was 4.00%; the compression modulus of sand was 2.5~520 kPa. The test results can provide a scientific basis for remodeling the sandy cobble aquifers in Beijing subway and the simulation test of grouting water plugging and reinforcement the aquifers, and can also provide a reference for the evaluation of aquifers’ grouting effect.

Effects of Large-Scale Unloading on Existing Shield Tunnels in Sandy Gravel Strata

The influence of large-scale unloading of soil on existing metro tunnels is a difficult problem in the operation of Metro in sandy gravel strata. In order to predict and control the tunnel deformation and ensure the safety and normal operation of the metro, three-dimensional numerical models are proposed in this study. These models based on the line 5 of Chengdu subway engineering and the adjacent unloading projects analyze the deformation of existing metro tunnels under large-scale unloading of soil. The results show that the maximum bulge after unloading excavation of foundation pit is 11.1 mm, which is lower than the limit value of foundation pit uplift proved by relevant studies; the maximum deformation value of left tunnel is 9.56 mm, and that of right tunnel is 8.33 mm, which is less than the proposed 10 mm deformation control standard. In addition, the paper analyses the restraining effect of different reinforcement measures on soil deformation, such as advanced tubal curtains and horizontal beams, anti-floating anchor cables. The results show that the deformation of soil under different reinforcement measures is greater than the specified limits, while the comprehensive reinforcement measures can restrain the deformation of soil well. The numerical simulation results in this paper verify the effective reinforcement of comprehensive reinforcement measures for large-scale unloading in sandy gravel strata, which can provide reference experience for large-scale unloading excavation construction in similar sandy gravel strata.

Locally Resonant Periodic Wave Barriers for Vibration Isolation in Subway Engineering

Subway transportation is being promoted worldwide to effectively solve urban congestion. However, the vibration induced by subway traffic has caused a major adverse impact on building safety, precision instrument operation and human health. Wave barriers have been proven effective in mitigating ground vibration, whereas they have some limitations in achieving ideal attenuation zone and high efficiency to cover the low-frequency vibration in underground railway system. Based on locally resonant phononic crystals theory, this paper designs three-component locally resonant periodic wave barriers (LRPWBs), and investigates the effects of geometrical and material parameters on the bandgap features in detail. The band structures are calculated using improved plane wave expansion (IPWE), the transmission spectra and vibration modes are obtained by finite element method (FEM). The results indicate LRPWBs are able to give lower and wider bandgap to cover the main frequency of subway environment, which is proved by time and frequency domain analysis. For the bandgap mechanism, the local resonance features of LRPWBs result in the energy conversion between kinetic energy and elastic strain energy, thus the elastic wave energy is localized in resonance unit and then the locally resonant bandgap is created. In addition, the bandgap can be adjusted by carefully selecting proper geometrical and material parameters to actualize low-frequency broadband attenuation. Further studies about multi-oscillator system indicate that the appropriate combination of multiple LRPWBs are conductive to diverse and broad bandgaps. The investigations can provide inspiration for periodic wave barriers design in multi-frequency vibration attenuation field.

The Deterioration of Cement Mortar under the Coupled Conditions of Stray Current and Sulfate

Abstract Subway engineering often suffers varieties of corroding environments. This article investigated the effects of stray current and external sulfate coupled conditions on the deterioration of cement mortar. The cement mortar specimens suffered from one-dimensional sulfate attack. Simultaneously, a direct current electric field was applied to both ends of the specimen to simulate stray current. By contrast, a group of mortar specimens was immersed in the same concentration of sodium sulfate (Na2SO4) solution. In order to investigate the effect of stray current on the sulfate attack of cement mortar, the compressive strength of specimens was tested. In addition, the sulfate ions profile in the cement mortar specimen was tested. Corrosion products and the microstructure of specimens were investigated using x-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscope. Experimental results showed that stray current could exacerbate strength degradation and accelerate the sulfate ions’ migration into the cement mortar, which led to the number of total sulfate ions and free sulfate ions at the same depth being higher than that of the immersion group, and quantities of corrosion products (gypsum and ettringite) were also higher than those of the immersion group. In a word, the stray current aggravated the sulfate attack of cement mortar. Therefore, the durability of cement mortar exposed to the stray current and sulfate coupled conditions should be given more attention.

Research on Safety Measures of Shallow-buried and Undercut Tunnel

The application of mine method shallow burying and undercutting method in subway and tunnel engineering is becoming more and more significant, but shallow burying and undercutting method also has its own limitations: the shallow burying and undercutting method can easily cause the subsidence of nearby surface, there is a security threat to surrounding buildings, the instability of the tunnel inside, easy to cause the collapse of construction tunnels, endangering construction safety, so ensuring construction safety becomes the key to the project. By combining the examples of the Heyi River Tunnel in Quzhou, the project focuses on the safety measures of tunnel surrounding rock, and simulates tunnel excavation with BIM technology.

Research on Construction Risk Management of Underground Engineering Based on AHP-Fuzzy Comprehensive Evaluation Method

In order to strengthen the construction risk management of underground engineering projects, reduce the probability of accidents, and ensure that the underground engineering completes the construction tasks on schedule, the article relies on a certain subway engineering project to carry out research from the aspects of risk identification, risk factor analysis, and risk factor evaluation. The article adopts analytic hierarchy process and fuzzy comprehensive evaluation method to carry out risk factor evaluation weight analysis and risk system evaluation in the construction process, and then realize reasonable prediction and evaluation of construction risk factors. Finally, this essay sorts out the prevention and control measures of underground engineering construction risk management from five aspects of personnel, machinery, management, environment and technology, and then provides auxiliary decision-making for underground engineering construction risk management.

Recent Patents on Conical Pick and Flat Pick for Coal Mining

Background: Coal mining machines are the primary equipment used for the comprehensive mining of medium and thick coal seams. A shield machine is used to modify the geological structure of the soil, especially in urban subway tunnel engineering. The cutting and tunneling equipment have greatly improved the efficiency of coal seam mining and rock tunneling construction, but the consumption of picks in mining and tunneling is very high. Objective: In order to reduce the consumption of picks, it is necessary to obtain the change of temperature inside the pick in the process of cutting. Methods: This paper introduces a temperature measurement method to measure the temperature inside the conical and flat pick to provide a reference for the design and manufacture of picks. Results: The temperature measurement method used in flat and conical pick can obtain the temperature change inside the pick under the actual working condition, which has a considerable guiding significance to promote the development of coal mining. Conclusion: This study provides an important basis for the safety of mining operations and for prolonging the service life of picks. It has a strong innovation value and broad practicality.

Sensitivity Analysis of Flexural Strength Characteristics of Artificial Frozen Soil

In subway engineering, artificial frozen soil wall is often used as temporary supporting curtain for underground connecting passage, which bears the effect of upper pressure and lateral earth pressure. In the actual subway tunnel project, artificial frozen soil is generally under both compression and bending. Therefore, to evaluate the soil strength, both compressive strength index and tensile and bending strength index of frozen soil are required. The tensile strength index of frozen soil has a great influence on the design and construction of frozen soil engineering, so it is of great significance to study the tensile strength by testing the flexural strength of frozen soil.

Study on the Characteristics and Reduction Measures of Construction Waste Generated in Subway Engineering

In the process of urban modernization and rapid construction, the construction and reconstruction of large-scale construction projects such as subways, underground pipe corridors, and housing construction facilities are accompanied by a large amount of construction waste. A huge amount of construction waste not only occupies a large number of land resources, but also affects air quality, pollutes waters, destroys city appearance and environmental sanitation, and has potential safety hazards. In the long run, it also affects urban development space and shortens the city life cycle. At present, there are many shortcomings in China’s policy management, classification and measurement, reduction technology, transportation recovery, recycling and other aspects of construction waste. Especially from the source, there is a lack of research on the source characteristics of construction waste, which makes the quantitative quantification of various construction wastes impossible to achieve construction, accurate management, and control of waste. This study takes the urban subway construction project as the research object, through the field investigation, literature review and other methods, analyses the classification and source of underground construction waste by the project unit construction process as the framework, and analyses the corresponding construction waste according to the investigation and data collection. The reduction measures implemented.