Subway Structure Research Articles

ON ONE METHOD FOR CALCULATING THE STRESS-DEFORMED STATE OF ESCALATOR TUNNELS

In the article, based on the finite element method, the main stages of the study of free oscillations are given, since the separation of normal coordinates in the system of differential equations of vibrations of structures is possible only with constant global stiffness and damping matrices of the system. The method of calculating the stress-strain state of the subway escalator tunnel structure under the influence of both constant and seismic loads, as well as with a special combination of loads, is given in order to scientifically substantiate the design and construction of its lining made of monolithic reinforced concrete in Almaty, which allows, in general, to obtain significant economic efficiency compared with the traditional method of lining made of cast-iron tubing. A comparative analysis of the stress-strain state of the lining is performed from the main combination of loads, seismic impact and a special combination of operational loads. The authors proposed a finite element design scheme of the lining and the surrounding soil massif. The analysis of the distribution of vertical displacements in the tunnel lining is carried out on the basis of the application of the dynamic theory of seismic resistance for building structures of special responsibility.

Improvement of Automatic Measurement Evaluation System for Subway Structures by Adjacent Excavation.

This study evaluated the structural stability of subway structures based on adjacent excavations by comparing automatically measured and numerically analyzed data. The reliability of the automated measurement methodology was evaluated by first applying probability statistical analysis to the measured results and then comparing these results with the numerically analyzed results. An improvement in the calculation method evaluation system, including the method of processing and analysis of the automatically measured data of subway structures through the average value of probability density, was proposed. As a result of the field measurement and numerical analysis, the measured results of tunnel displacement and track deformation exhibited some differences. However, it was determined that the construction stage and location where the maximum values of the tunnel displacement and track deformation occurred had similarities.

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.

Rationale for the Use Of Radonometry to Identify the Areas of Tectonic Faults During the Passage of Subway Tunnels in Dnipro

Purpose. The article is aimed to substantiate the choice of the most effective method of geophysical research within the metropolis for more accurate mapping of fault zones in erupted rocks for the purposes of 2nd stage subway construction in the city of Dnipro. Methodology. Practical and organizational measures for radonometry for seismotectonics during the 2nd stage construction of the city subway were developed in detail, which in case of continued mining operations in the ravine-beam system contributes to further safe operation of the facility. Findings. Based on the analysis and evaluation of all profile studies conducted in the city in different years, one of the emanation methods was chosen – radonometry, and the method for its implementation was proposed, which provides dense urban development and complex tectonic structure of the region (fault zones) to obtain the necessary quality characteristics of soil incision. Originality. This paper for the first time provides a rationale for radonometry to identify fault zones in erupted rocks and assess their activity within the city. Practical value. The given technique is recommended for ensuring seismically safe conditions of drilling and blasting works during the passage of mine workings, which will ensure the maximum construction speed. In the future, these studies may be required when creating a ventilation system for underground structures of the 2nd stage of the city subway. Also, the radonometry results can be taken into account when placing elements of geotechnical (deformation) monitoring systems, both in tunnels and other deep-seated subway structures, and in buildings and structures. Clarification of the position of fault zones with the assessment of their activity can directly affect the choice of certain methods of measuring the deformation parameters of the observed objects, facilitate the choice of means of tunnel processing, highlight their qualitative or quantitative parameters.

Stability evaluation of existing subway structure by adjacent excavation in urban tunnelling

Stability evaluation of existing subway structure by adjacent excavation in urban tunnelling

Environmental impact analysis for the construction of subway stations: Comparison between open-excavation and underground-excavation scheme

The excessive environmental impacts from the construction of subway infrastructure have become a concern for operators who are keen on continuing to lower the environmental footprint, but the factors affecting the impacts are yet to be fully identified. Excavation scheme is the governing factor in subway construction, not only because it prescribes the ensuing construction procedures, but it also epitomizes the design philosophy towards the interaction between the subway structure and city environment. In this paper, a comparative assessment is made among the fifteen mid-point environmental impacts from the two major excavation schemes in subway construction, i.e. the open-excavation (OE) and underground-excavation (UE) scheme. The case station provides a perfect example for such a comparison as it consists of both OE and UE section at the same buried depth. GHG emissions are identified as the largest contributor after normalization. However, GHG emissions are not representative for the overall impacts. The UE section is responsible for more impacts per area than that of OE section in all the investigated categories. The gap between the two sections is attributable to the extra reinforcement procedures that protect the surrounding infrastructure from adverse settlement. Though the underground environment limits the use of construction machines, the UE construction involves more on-site impacts because it requires 11.79 times the labor used in the OE section. Based on the results, the adaptability of the two methods was discussed, considering the life-cycle performance and their interaction with the city environment.

Numerical analysis of the impact of foundation excavation on the immediately adjacent subway station

The excavation adjacent to an existing subway station is a high-risk project during the underground engineering, which has an inevitable impact on the subway structure to affect the safety of train operation. This Paper studies the excavations adjacent to a subway station on its both sides. A 3D numerical simulation with finite element code MIDAS GTS/NX is conducted to analyze the proposed excavations’ impact on the subway station as well as the accessory structure. The deformation law and the corresponding technical measures to contain the deformation of station structure are proposed afterwards, which could be a guideline for the design and construction of similar projects.

Failure mechanism of subway structure with different central columns based on Daikai Station

The central columns of the Daikai Station in Kobe City were severely damaged due to Hanshin earthquake in the year 1995, leading to serious ground collapse. To evaluate the behavior of underground structures, the finite element model of Daikai Station was established using ABAQUS, and benchmarked against the measured data. Furthermore, the central column was replaced by concrete-filled steel tube (CFST) column to illustrate the response under the earthquake action. Results show that the central column of the station is one weak part of structure. Compared with the ordinary reinforced concrete (RC) structures, using CFST central column can enhance the overall rigidity of the structure and greatly improve the seismic performance of the underground structures.

Study on the influence of deep foundation pit excavation on adjacent metro structure

The excavation of deep foundation pit will have an adverse impact on the existing adjacent subway structure, which is affected by a series of factors such as subway structure, foundation pit depth and excavation construction process. Based on the excavation of a deep foundation pit adjacent to a subway station in Tianjin, through three-dimensional numerical calculation and analysis, it is concluded that after the excavation of the foundation pit, the structure of the subway station has local settlement, local floating and small horizontal displacement. According to the numerical results, the corresponding hazard sources are put forward, and the monitoring and early warning pre-values of hazard sources are given, in which the reference value of floating wind pavilion is about 1.3cm, the reference value of settlement value at the entrance and exit of subway station is about 6mm, the maximum horizontal displacement of diaphragm wall is about 7cm, and the maximum settlement outside pit is about 5cm. The results of this paper provide a basis for engineering risk points, and provide operational guidelines for monitoring risk points.

Research on earthquake damage mechanism of a subway station structure based on centrifuge shaking table tests and numerical analysis

During the 1995 Kobe earthquake, the Daikai subway station witnessed serious collapse, which attracted the attention of people to the earthquake damage response of the subway structure. To study the earthquake failure mechanism of a subway station structure, two comparative dynamic centrifuge tests were performed. During the centrifuge tests, many important physical quantities cannot be directly monitored with appropriate instruments due to many limitations, such as extremely small model structures, extremely high collection frequency and complex centrifugal environment. To study the earthquake failure mechanism of a subway station structure in depth, an extended analysis of model tests was performed by means of numerical model. Finally, the earthquake failure mechanism was summarized in detail based on the numerical analysis.

Seismic response characteristics of multi-story subway station through shaking table test

A series of shaking table tests were carried out to investigate the seismic response characteristics of a multi-story subway station. Dynamic responses, including accelerations of the soils and the underground structure, layer drift, dynamic earth pressure, and lateral deformation of soils were recorded and analyzed. Several seismic characteristics of multi-story subway station structures are figured out. It is found that in addition to the racking deformation, the rotation vibration is observed for the multi-story subway station subjected to acceleration waves. From the viewpoint of frequency, the low-frequency component and high-frequency component of the acceleration response of the subway station represent the translation and rotation component of the multi-story subway structure, respectively. In addition, the rotation vibration of the deep-depth structure leads to the local squeezing and detachment from the surrounding soils alternately at both top and bottom ends of the sidewalls. This results in the hump-shaped distribution of dynamic earth pressure. The racking deformation of the multi-story subway station has a linear relationship with the dynamic earth pressure at a certain area along the sidewall, where the top of hump-shaped distribution of dynamic earth pressure is.

Evolution of loading paths in a heterogeneous soil mass during the foundation pits’ construction

This article shows the construction of loading paths for the soil mass points using the example of a phased construction of the subway structure underground part. The solution to the problem was obtained by the finite element method using a PC PLAXIS 2D. The graphs of changes in the points’ stress state in coordinates p’/q are shown.

Analysis on the Influence of Shaft and Cross Passage Turn to the Main Line of Ingate under Different Construction Schemes

In the weak stratum, the construction of ingate is a key technical problem at the place where the shaft and cross passage turn to the tunnel. Based on Lanzhou Metro, the corresponding changes to the construction plan of the ingate of the section tunnel were made. Finite element software is used to carry out three-dimensional modeling and design of subway shaft, cross passage, and tunnel structures in connected sections. The influence of the two construction schemes on surface settlement, deformation, and stress of tunnel support structure and stress conversion of ingate are compared, as well as the fitting degree between numerical simulation results and field monitoring data. Finally, the optimal scheme and key points of construction control are determined. The results show that the optimization scheme has obvious advantages in the control of surface settlement and the deformation of shaft and cross passage support. However, the difference between the stress and deformation of the tunnel supporting structure and the original plan is not obvious. Since the project focuses on shaft, cross passage, and tunnel connection section, the changed construction scheme is better.

Combined Effect of Stray Current and Sustained Compressive Loading on Chloride Transport in Concrete

As with the leakage of stray current in the surrounding medium, the chloride transport in concrete is influenced by the stray current and loading of the subway structure. This paper presents the results of the experimental study on the chloride transport properties of concrete under the combined action of stray current and sustained compressive loading. First, an experiment was setup to explore the chloride transport in the subway structure as the concrete specimen embedded with steel under test current and study the influence of the existence of steel on the chloride transport profiles in concrete under stray current. Then, to investigate the combined effect of stray current and loading on the chloride transport properties, an improved experiment was designed with stray current and sustained compressive loading. The chloride transport profiles were measured, respectively, subjected to different stray currents and compressive stress levels. The experimental results indicated that stray current and sustained compressive loading have a significant influence on the chloride transport properties of concrete, and the loading threshold existed as the turning point of the chloride transport rate. Based on the experimental data and migration theory, the prediction model of chloride transport in concrete under stray current and sustained compressive loading was established and verified by the experimental measurements, and the steel corrosion‐induced cover cracking was studied, and the comparison indicated that the numerical results were consistent with the experimental results.

Vibration Characteristics of Subway Tunnel Structure in Viscous Soil Medium

Based on research on subway tunnels in a viscous soil medium, this paper establishes the vibration equation of a tunnel structure by using the theory of moderately thick cylindrical shells and the method of wave propagation. The soil around the tunnel is represented in simplified form as an isotropic viscoelastic medium to obtain the equation of motion of the soil, and the vibration control equation of the tunnel under the influence of viscous soil is obtained by coupling. By numerical calculations, the variation trends in the natural vibration frequency of the tunnel and attenuation affected by soil viscosity under different modes are given. Furthermore, the influences of the tunnel radius, wall thickness, and length on the vibration characteristics of a tunnel structure in viscous soil are discussed. This study will provide a reference for the design of subway vehicles and the antivibration design of subway tunnel structures.

Numerical Simulation of the Daikai Station Subway Structure Collapse due to Sudden Uplift during Earthquake

AbstractThe Daikai Station subway structure in Japan completely collapsed during the Hyogoken-Nanbu earthquake that occurred on January 17, 1995. Based on the numerical results obtained by two-dime...

Research on the impact of building blasting vibration on the safety of adjacent subway structures

When using controlled blasting technology to demolish a building, the blasting vibration caused by the blasting process may harm the surrounding structure of the blasting area. To study the influence of blasting vibration on the adjacent subway structure, this paper takes the blasting demolition of a building in Chengdu as an example, analyzes the load during the blasting process, establishes the stratum-structure and load-structure finite element models of the subway structure, and simulates the dynamic response process of the structure, and then studies the safety impact of blasting demolition vibration on the adjacent subway structure. Studies have shown that: under the blasting construction scheme in this paper, the impact of blasting vibration on the subway structure is within a safe and controllable range.

Deformation Detection Method of Mine Tunnel Based on Mobile Detection System.

Subway structure safety detection is an important method to ensure the safe operation of trains. Efficient, high-precision, and automatic tunnel clearance detection is the key to ensure safe operations. This study introduces a mobile tunnel scanning system that integrates a scanner, an inertial measurement unit (IMU), and a rail car. Global Navigation Satellite System (GNSS) time and system hardware calibration are used to synchronize time and space information of the system; the attitude and speed are corrected using the control points from the tunnel to improve the accuracy of absolute positioning. The section coordinate system is converted using the control points and system calibration parameters to complete the tunnel clearance inspection, and the distance between the nearest point of the section and the clear height of the vault is given. Taking Fengxi Road’s Bashan tunnel section of Chongqing Metro Line 5 as an example, the overall system accuracy was tested. The accuracy of chord line measurements was within 1 mm, the internal coincidence accuracy of repeated measurements of the vault clear height was 1.1 mm, the internal coincidence accuracy of repeated measurements of the closest gauge point was 4.8 mm, and the system calibration accuracy was approximately 2 mm. Compared with the existing scheme, the system combines absolute measurement and relative measurement mode to judge the structural safety of tunnel section from multiple angles, high precision, and high efficiency.

TO THE PROBLEM OF DETERMINING AIR VELOCITY FIELD IN TUNNEL STRUCTURES OF A SUBWAY LINE USING CIRCULAR MODELS AS A METHOD OF TOPOLOGICAL DECOMPOSITION

Underground subway structures represent crowded public areas; therefore, they are subject to high requirements for maintaining the standard microclimate parameters at stations and in tunnels, including the content of suspended dust in the air. To maintain dust concentration within specifications, it is proposed to use air filters installed in station ventilation connections in the stream of air from the piston effect of trains. To study the piston effect by aerogasdynamic computational methods, a method is proposed for the topological decomposition of a subway line - transition froma complete linear model to a closed circular model by isolating several lines and closing them into a circle, which allows reducing the size of discrete model of the design section, while maintaining the influence of neighboring lines and stations as well as calculation accuracy. As a result of a numerical experiment, the parameters of transient air distribution from the piston effect of trains and the structure of air stream at the places of filter installation are determined for further study of their geometric, structural and operational parameters.

Seismic response of irregular underground structures under adverse soil conditions using shaking table tests

A series of large-scale shaking table tests were performed to investigate the seismic response of an underground subway structure with irregular sections in adverse soil conditions (soft and liquefiable sites). Emphasis is placed on the influence of the adverse soil conditions on the response of the irregular underground structures and over areas of soil-structure interface, involving buildup of pore pressures and resulting large deformations. The results indicate that the seismic responses of the structure and the soil were sensitive to input motions with richer low-frequency components. The seismic damage of the underground structure was more significant in the soft site as compared with that in the liquefiable site. The liquefiable site worked as a natural seismic isolation system for the underground structure, significantly reducing the damage potential to the model structure. Under the action of a strong earthquake, the horizontal displacement response of the liquefiable site sharply increased compared with that of the soft site. With respect to the structure response, the interlayer displacement of the structure in the soft site was approximately twice that in the liquefiable site. The lateral deformation of the structure was greater in the soft site and the interior structure column was more prone to damage. Correspondently, the peak and the residual strains in the structural components in the soft site were higher than those in the liquefiable site were. The results provided insights into the site effects of adverse soil conditions on the seismic response of underground structures, especially on the seismic damage process and the failure mechanisms of the structure members.