Underground Railway Tunnels Research Articles

Review of the experience in utilising waste heat from the metro

The exhaustibility of traditional fossil energy sources is leading to the increasing use of unconventional energy sources. One of the most promising areas of alternative energy is the use of low-potential ground energy to heat buildings and structures for various purposes using a heat pump. The subway generates a significant amount of heat, especially when trains are braking, stopping on platforms and picking up speed when they start moving from the station. Thus, to combat the rise in temperature in tunnels and stations, a complex ventilation system is designed, including shafts, fans, and under-platform exhaust. In modern Ukrainian subways, the ventilation system is designed to cope with the rising temperatures in tunnels and stations. This traditional approach results in high energy consumption for running fans and ignores the possibility of using the extracted heat above ground in buildings. Techniques such as lining underground railway tunnels with heat exchanger segments, installing a heat exchanger in a subway ventilation shaft, installing geothermal heat pumps next to a subway tunnel, installing energy piles, energy baffle walls, energy platforms, and introducing absorption pipes into tunnel segments can provide an alternative solution to cool tunnels and the surrounding ground, and transfer the resulting heat to neighbouring buildings for heating. This would also have the benefit of reducing energy consumption for tunnel ventilation. This article discusses the possibility of using waste heat from underground railway systems as a source of low-potential energy to provide heat to, for example, adjacent buildings. Various technologies for utilising waste heat from underground railway tunnels that have already been implemented or whose models are technically and economically feasible are presented.

A parametric study of the train-induced vibration of a single pile near an underground railway tunnel

A particular concern in ground-borne vibration is the extent to which the construction of a foundation affects the vibration field from an existing railway tunnel. This paper presents the results of a parametric study of this ‘added-pile effect’ using a numerical model that captures the dynamic behaviour of a single pile located near a circular tunnel, excited by vibration due to wheel-rail roughness. The added-pile effect is characterised for a range of scenarios in terms of the vertical pile-head insertion gain over the frequency range most associated with human perception. The results highlight two underlying mechanisms that determine the pile-head response and how these are governed primarily by the pile length, the soil-pile stiffness ratio, and the relative position of the pile and tunnel. It is also shown that the addition of a representative building, in the form of a semi-infinite column, does not significantly change the pile-head response.

Risk modelling and simulation of thermal safety in underground railway tunnel surrounding

The temperature of surrounding rock of the underground railway tunnel is increasing year by year. This slowly changing thermal hazard not only has a prominent impact on the stability of tunnel surrounding structures, but also deteriorates the tunnel thermal environment, so the formation of the thermal hazard should be investigated. In this work, the thermal hazard model of tunnel surrounding rock was established under the superposition of ground atmospheric temperature wave and tunnel wind flow temperature wave. The corresponding simulation software was developed to estimate the thermal hazards. This dual periodic temperature boundary model (DPTB) was also investigated in comparison with the single periodic temperature boundary (SPTB) model that simplified the periodic ground atmospheric temperature to a constant. The results show that the overlying rock layer of the tunnel is more affected by the superposition of double periodic temperature waves, and its temperature will be significantly higher in autumn. For the calculation example, the average annual heat storage in the surrounding rock under the DPTB is 41,775 kJ/m2, reduced by 432 kJ/m2 compared to the SPTB. The average temperature rise in the shallow surface surrounding rock over 25 years under the DPTB is about 2.04 °C, which is 0.48 °C lower than that of the SPTB. These calculation results provide a reference for the thermal hazards control in underground railway tunnels.

Hybrid analytical-numerical modelling of ground vibrations from moving loads in a tunnel embedded in the saturated soil

The dynamic response of a floating-slab track and underground railway tunnel embedded in saturated soils under moving loads are investigated by a hybrid analytical-numerical method. The tunnel is modelled as thin cylindrical shell surrounded by saturated soil of infinite radial extent. A two-layered beam structure is used to model the floating-slab track. In the continuous floating-slab track, the slab is an infinitely long Euler–Bernoulli beam while in the discontinuous one, the slabs are modelled as a periodic structure consisting of beams of finite length. The coupled equations of the tunnel-soil system are solved in the frequency-wavenumber domain with the aid of Fourier transform and Fourier decomposition. The track structure and tunnel-soil model are coupled by force and displacement continuity conditions at the tunnel invert. Numerical results for the track, tunnel and soil responses are presented for a moving point and train load. It is found the critical velocity of a track-tunnel-soil system approaches the shear wave speed of the soils. The natural frequencies of the track have significant influence on the soil displacement and pore pressure. Furthermore, an increase of the soil permeability leads to a decrease of the displacement as well as the pore pressure in the free field.

Nonlinear seismic analysis of a train-tunnel-soil system and running safety assessment of metro vehicles

Since earthquakes would pose a serious threat to the safety of underground railway tunnels and subway trains, the seismic analysis of the subway tunnel and the metro train is essential for earthquake-resistant design and construction. This presented study aims to investigate the transient response of a train-tunnel-soil coupled system under various load conditions, and assess running safety of the moving train. Firstly, a simulation model of the train-tunnel-soil system was established, considering interactions between soil and tunnel, rail and train. Secondly, the numerical approaches employed in this paper were verified, and the tunnel-soil model was validated with the available test data. Finally, the nonlinear seismic response of the train-tunnel-soil system is investigated, and running safety indices of the subway vehicle are evaluated. Moreover, the effect of train speed and earthquake intensity on the running safety of the metro train is assessed. The numerical results reveal that compared to the moving-train load, the effect of earthquake action on the dynamic response of the subway tunnel is more prominent, resulting in a significant increase of the wheel-rail force and acceleration of the railway vehicle. Both earthquake loads and train speed have an impact on running safety indices, while the earthquake intensity has a more significant effect on the safety index of the metro vehicle. Moreover, it is worth noticing that with respect to the designed operational speed of 90 km/h for Nanjing Metro Line 10, the ability of the metro train to withstand earthquake excitation is no more than a maximum acceleration of 0.2 g.

Three-dimensional analytical model for vibrations from a tunnel embedded in an unsaturated half-space

An analytical model for predicting the vibrations from an underground railway tunnel embedded in an unsaturated half-space is proposed. The tunnel lining is modeled as an infinite Flugge cylindrical shell, and the unsaturated soil is modeled as a three-phase medium comprising solid grains and pores containing water and air. By using the transformation properties between the plane wave functions and the cylindrical wave functions, the model is coupled based on the boundary conditions. The developed model is validated by comparison with existing tunnel models, and the effect of saturation on the dynamic response of the tunnel–soil system is demonstrated through a case study.

Evaluation of the soil layering and soil lens effect on the ground-borne vibrations induced by twin metro tunnels

This study aims to examine the effects of surrounding soil layers and furthermore lens properties on induced vibrations by underground railway twin tunnels and comparing with the single tunnel. First, the predicted models for the vibration of the underground tunnel(s) are verified against in situ measurements. The tunnel(s) are assumed to be located in two-layer soil, and the influence of upper soil layer thickness, elastic modulus, and soil layers’ inclination angle (for three values of 5, 10, and 15 degrees) on surface vibrations are investigated. Furthermore, the influence of the presence of soft and stiff soil lens with various thicknesses in several levels respect to the tunnel(s) and the effect of the inclination angle of the soil lens (for two values of 5 and 15 degrees) on the surface vibrations is examined. The results indicate that the layered region around the single and twin tunnels increases the vibrations level up to 10 dB respect to the uniform soil layer. Also, the effect of soil lens with larger thickness is remarkable. The maximum inclination angle of 15 degrees for soil layers and soil lens respectively cause in 9 and 5 dB increase in the surface vibrations level.

Experimental study on hybrid precast tunnel segments reinforced by macro-synthetic fibres and glass fibre reinforced polymer bars

Increasing the popularity of using fibres in precast structures has brought questions about their usability in segmental tunnel linings as an alternative to the conventional reinforced lining. Most prior studies have already revealed that the replacement of conventional steel reinforcement is possible with steel fibres. However, the usability of macro-synthetic fibres (MSFs) as reinforcements in precast tunnel segments is still unclear and one of the controversial questions to be answered. As such, this study aims to evaluate the structural applicability of using polypropylene (PP) MSFs in precast tunnel segments by means of an experimental program on full-scale specimens. Within this framework, totally fourteen full-scale precast tunnel segments of Mecidiyekoy – Mahmutbey underground railway tunnel in Istanbul/Turkey characterized by four different reinforcement cases were analysed: i) typical conventional steel reinforcement; ii) the combination of MSFs and conventional reinforcement; iii) the combination of MSFs and glass fibre reinforced polymer (GFRP) rebars; and iv) MSFs only. Flexural tests were carried out to compare the flexural behaviour of specimens at the allowable crack opening width, while point load tests were conducted to observe the structural performance of precast tunnel segments under the effect of design thrust forces. The experimental results showed that the combination of MSFs and GFRP could be an innovative solution for precast tunnel segments in case of using a suitable quantity that satisfied the project requirements. Although PP fibres exhibited adequate spalling and splitting stress control, it is observed that they could not overcome high flexure forces without using reinforcement bars at a low volume of fractions. Thus, more comprehensive studies need to perform on GFRP + MSFs segments because of having the advantages of corrosion resistance in the presence of an aggressive surrounding environment.

Sprayed concrete lining versus traditional hand-mining at Bank station upgrade, London, UK

Three new adits were required between existing underground railway platform tunnels on the Bank station capacity upgrade project in London, UK. Normally they would have been built by traditional hand-mining techniques with temporary support from within the platform tunnels. An innovative solution, involving a mechanised sprayed concrete lining with an optimised external support system, was developed as an alternative for two of the adits. Compared to hand-mining it provided greater working space, minimised hand excavation and manual handling, kept the railway operational and reduced the programme and costs.

A methodology based on 2.5D FEM-BEM for the evaluation of the vibration energy flow radiated by underground railway infrastructures

In this paper, a comprehensive numerical approach for modelling track/tunnel/soil systems in the context of ground-borne railway-induced vibration problems considering a full-space model of the soil is proposed. All the approach is formulated in the wavenumber-frequency domain and it consists of a coupled finite element–boundary element model of the tunnel/soil system, a semi-analytical model of the track, a multibody model for the vehicle and a model for the vibration propagation in the soil based on semi-analytical solutions of a cylindrical cavity in a full-space. This comprehensive approach has been developed with the aim of computing the vibration energy flow radiated upwards by underground railway tunnels. An axisymmetric formulation to deal with circular underground railway tunnels is included in the approach in order to improve the computational speed of the methodology. This formulation can also be used for other types of railway tunnels if a circular boundary of the boundary element mesh is considered. Since this methodology uses finite elements to model the tunnel structure, its modelling detail is higher than the previously developed methodologies dedicated to compute the vibration energy flow radiated by underground railway infrastructures, since they are based on semi-analytical modelling of the tunnel structure. The present methodology has been specifically designed to be used in general assessment studies about ground-borne underground railway-induced vibrations where decisions on the type of track and/or the application of mitigation measures at the source, as soft rail-pads, under-ballast or under-slab mats, have to be made. Moreover, this methodology can be used for the study of the vibration radiation patterns of railway tunnels.

Opportunities for Integrating Underground Railways into Low Carbon Urban Energy Networks: A Review

Cities demand vast amounts of energy for their everyday operation, resulting in significant degradation of energy in the form of heat in the urban environment. This leads to high cooling requirements in cities, while also presenting the opportunity to reuse such waste heat in order to provide low-carbon heating for buildings and processes. Among the many potential energy sources that could be exploited in urban areas, underground railway tunnels are particularly attractive, as the operation of the trains produce considerable amounts of heat throughout the year. This paper reviews how secondary energy sources in urban areas can be integrated into heating and cooling networks, with emphasis on underground rail tunnels. This involves investigating potential urban waste heat sources and the existing state-of-the-art technologies that could be applied to efficiently recover this secondary energy, as well as analyzing how district heating and cooling networks have been a key mechanism to allow for a smooth transition from current fossil fuel based to future low-carbon energy sources.

RELIABILITY MODEL AND CRITICAL FACTORS IDENTIFICATION OF CONSTRUCTION SAFETY MANAGEMENT BASED ON SYSTEM THINKING

Safety is a key objective of construction management, but construction safety management is complex due to various types of technical and management factors. If critical factors can be identified and corresponding measurements can be adopted, it will be more direct and effective to improve safety performance. In this paper, by using the system thinking method, construction safety management is considered as a system and decomposed into six subsystems and related management factors. The fuzzy fault tree analysis method was used to build a reliability analysis model and reveal the failure probabilities of factors in the safety organization management subsystem. Through a questionnaire survey conducted in Wuhan, China, the pivotal importance degrees and average occurrence probabilities of basic factors are figured out. On the basis of that, nine critical factors of the safety organization management subsystem are identified and corresponding improvement measurements are proposed. More, a case study of Hangzhou underground railway tunnel collapse accident in 2008 is conducted, which verifies that the framework of construction safety management based on system thinking can be a useful tool for identifying faults or failure reasons of construction safety management.

A Methodology Based on Structural Finite Element Method-Boundary Element Method and Acoustic Boundary Element Method Models in 2.5D for the Prediction of Reradiated Noise in Railway-Induced Ground-Borne Vibration Problems

This work is focused on the analysis of noise and vibration generated in underground railway tunnels due to train traffic. Specifically, an analysis of noise and vibration generated by train passage in an underground simple tunnel in a homogeneous full-space is presented. In this methodology, a two-and-a-half-dimensional coupled finite element and boundary element method (2.5D FEM-BEM) is used to model soil–structure interaction problems. The noise analysis inside the tunnel is performed using a 2.5D acoustic BEM considering a weak coupling. The method of fundamental solutions (MFS) is used to validate the acoustic BEM methodology. The influence of fastener stiffness on vibration and noise characteristic inside a simple tunnel is investigated.

Combining cooling of underground railways with heat recovery and reuse

The paper concerns the recovery and use of secondary/waste heat and identifies secondary heat sources in London of 71 TWh i.e. c10% more than demand. London Underground (LU) railway tunnels generate significant quantities of low grade heat. There is also a requirement for active cooling to reverse the long term trend of rising tunnel temperatures. A novel combined cooling and heat recovery scheme for LU tunnels, utilising existing ventilation shafts, was proposed. Recovered heat was upgraded using a heat pump, for reuse in a local district heating network (DHN). A new model was developed to investigate the thermodynamic performance, economic feasibility and potential carbon savings available. It was concluded that the system could simultaneously provide 900 kW of cooling to the tunnel, and after upgrading to 70 °C, approximately 1.1 MW of heat, which could be used as a source for a DHN. The model predicted that this could be carried out economically and could deliver massive carbon and cost savings. With 200 ventilation shafts in London, >360,000 tonnes of carbon could be saved annually, while generating revenues of £40,000,000. Applying this technology to 50% of 150 metro systems worldwide would enable more than 27 million tonnes of carbon savings.

Overview of research on fire safety in underground road and railway tunnels

In the past two decades, the interest in fire safety science of tunnels has significantly increased, mainly due to the rapidly increasing number of tunnels built and the catastrophic tunnel fire incidents occurred. This paper presents an overview of research on fire safety in underground road and railway tunnels from the perspectives of fire safety design. The main focuses are on design fires, structural protection, smoke control and use of water-based fire suppression systems. Besides, some key fire characteristics, including flame length, fire spread, heat flux and smoke stratification, are discussed.

Benchmark solution for vibrations from a moving point source in a tunnel embedded in a half-space

A closed-form semi-analytical solution for the vibrations due to a moving point load in a tunnel embedded in a half-space is given in this paper. The tunnel is modelled as an elastic hollow cylinder and the ground surrounding the tunnel as a linear viscoelastic material. The total wave field in the half-space with a cylindrical hole is represented by outgoing cylindrical waves and down-going plane waves. To apply the boundary conditions on the ground surface and at the tunnel–soil interface, the transformation properties between the plane and cylindrical wave functions are employed. The proposed solution can predict the ground vibration from an underground railway tunnel of circular cross-section with a reasonable computational effort and can serve as a benchmark solution for other computational methods. Numerical results for the ground vibrations on the free surface due to a moving constant load and a moving harmonic load applied at the tunnel invert are presented for different load velocities and excitation frequencies. It is found that Rayleigh waves play an important role in the ground vibrations from a shallow tunnel.

Enhancing the piston effect in underground railway tunnels

The air flows induced by train movement in tunnels can be used for the purposes of underground railway ventilation. The magnitude of such air flows depends strongly upon the blockage ratio (the ratio of the train and tunnel cross-sectional areas) of the train. This study investigates the impact on the generated air flows due to the alteration of the aerodynamic resistance of the train, as a means of varying the blockage ratio. The alteration in aerodynamic resistance was achieved by using an aerofoil at a variety of different angles of inclination. A two-dimensional computational fluid dynamics model of a train travelling through a tunnel was developed and validated using experimental data from literature. This model was then used to investigate the influence of an aerofoil upon the volume of displaced air and the effect upon the aerodynamic work done by the train (work done by the train due to air drag). The results of this study show that ventilating air flows can be increased by 3% using an aerofoil at a fixed angle of 10° without increasing aerodynamic work. Through using a combination of different angles during different phases of train motion, a maximum increase in air displacement of 8% can be achieved, while not increasing the aerodynamic work done by the train. This equates to the train generated air displacement delivering an extra 1.6m3s-1 of air supply during the period of train motion.

Occupational Exposure to Respirable Dust, Respirable Crystalline Silica and Diesel Engine Exhaust Emissions in the London Tunnelling Environment.

Personal 8-h shift exposure to respirable dust, diesel engine exhaust emissions (DEEE) (as respirable elemental carbon), and respirable crystalline silica of workers involved in constructing an underground metro railway tunnel was assessed. Black carbon (BC) concentrations were also assessed using a MicroAeth AE51. During sprayed concrete lining (SCL) activities in the tunnel, the geometric mean (GM) respirable dust exposure level was 0.91mg m(-3), with the highest exposure measured on a back-up sprayer (3.20mg m(-3)). The GM respirable crystalline silica concentration for SCL workers was 0.03mg m(-3), with the highest measurement also for the back-up sprayer (0.24mg m(-3)). During tunnel boring machine (TBM) activities, the GM respirable dust concentration was 0.54mg m(-3). The GM respirable elemental carbon concentration for all the TBM operators was 18 µg m(-3); with the highest concentration measured on a segment lifter. The BC concentrations were higher in the SCL environment in comparison to the TBM environment (daily GM 18-54 µg m(-3) versus 3-6 µg m(-3)). This small-scale monitoring campaign provides additional personal data on exposures experienced by underground tunnel construction workers.

High-resolution geological maps of central London, UK: Comparisons with the London Underground

This study presents new thickness maps of post-Cretaceous sedimentary strata beneath central London. >1100 borehole records were analysed. London Clay is thickest in the west; thicker deposits extend as a narrow finger along the axis of the London Basin. More minor variations are probably governed by periglacial erosion and faulting. A shallow anticline in the Chalk in north-central London has resulted in a pronounced thinning of succeeding strata. These results are compared to the position of London Underground railway tunnels. Although tunnels have been bored through the upper levels of London Clay where thick, some tunnels and stations are positioned within the underlying, more lithologically variable, Lower London Tertiary deposits. Although less complex than other geological models of the London Basin, this technique is more objective and uses a higher density of borehole data. The high resolution of the resulting maps emphasises the power of modelling an expansive dataset in a rigorous but simple fashion.

Conceptual Issues Regarding the Development of Underground Railway Laser Scanning Systems

Mobile Laser Scanning (MLS) systems are widely applied for spatial data collection and support applications in many aspects. In recent years, MLS technology had been introduced to railway applications and greatly enhanced the spatial detail and efficiency when compared to traditional approaches. However, the advance of MLS technology is not completely applied to railway environment. Typical MLS systems rely on integrated navigation through the use of Inertial Navigation Systems (INS) and Global Navigation Satellite Systems (GNSS) for geo-referencing, while operation under long-term GNSS outages or even GNSS-free environments, such as underground railway or long tunnels, remains a challenging issue due to the degraded operation of standalone inertial navigation. Commercial MLS systems usually employ high performance inertial measurement units (IMU) and various strategies to manage GNSS outages, but GNSS components are still necessary prior to and after experiencing the loss of GNSS signals. To tackle the problem of permanent GNSS outages, alternative methods are introduced to replace the GNSS and so allow the use of MLS systems in GNSS-free underground railway environments. Such approaches encourage the MLS systems to be developed into the Underground Railway Laser Scanning (URLS) systems, which may provide several alternative operational functions for the management of underground railway operation.