Fire safety in tunnels

In 2006 the European Parliament requested the author to conduct a study of tunnel safety and make recommendations to be considered with a view to implementation in the European Union. This had been spurred by the large number of serious tunnel fires which have occurred in Europe since 1995 and fire safety was the main concern. Following a ten-month project a report was published and made available on the web-site of the European Parliament in 2008. The full report, containing twenty five recommendations, is available and details are given in Ref. [A.N. Beard, D. Cope, Assessment of the Safety of Tunnels. Commissioned by the European Parliament via the committee on Science and Technology Options Assessment (STOA); report IP/A/STOA/FWC/2005-28/SC22/29. Published in February 2008 on the European Parliament web-site at www.europarl.europa.eu]. The recommendations are intended to help to increase tunnel safety in the European Union and, primarily, to help to move towards a common system of tunnel safety decision-making and risk assessment. This article gives an outline of the report and high-lights some aspects of the content. This is not meant to imply that aspects which are not high-lighted here are of lesser importance.     

现代公路隧道安全管理初探

我国公路建设迅速发展,公路隧道不断增加。由于处于封闭的环境中,隧道中一旦发生事故,特别是火灾,往往导致严重的人员伤亡和财产损失。因此隧道安全管理问题是面临的一个重要课题。在调查国内外相关研究资料的基础上,对公路隧道的安全管理方法进行了归纳总结,以便为我国公路建设和维护管理提供参考。     

Management of road tunnels: Construction,maintenance and lighting costs

This paper presents a life cycle cost analysis, which compares construction, maintenance, and lighting costs needed to manage a highway tunnel. As regards the decision making process, it often considers only construction costs. Instead even maintenance and lighting, especially related to road tunnels, cause important cash flows. Therefore, both construction and managing costs have to be planned, in order to assess the cheapest solution. The lighting system of a road tunnel must guarantee the visual guidance for users moving at design speed and without hazardous actions.In this case study, the authors designed the pavement according to Italian standards and the lighting system according to Italian and European technical rules (UNI and UNI EN standards). They used LED technologies to maximize energy saving and road safety. The examined case study shows the importance of the surface pavement material, since it may contribute to the inter-reflected light and reduce electric energy consumption.     

Impact of fire on tunnels in Hawkesbury sandstone

The majority of tunnels in Sydney, Australia are within near-saturated Hawkesbury sandstone. Crown support in these tunnels typically comprises permanent rockbolts, and shotcrete ranging in thickness from about 75 mm to 250 mm. Sidewalls are mostly exposed sandstone with occasional rockbolts, and, in places, a thin shotcrete skin for surface protection.Rock will quickly be exposed to high temperature in a tunnel fire where no, or a thin layer of shotcrete exists. Rock with thicker shotcrete may also be exposed where spalling of the shotcrete occurs.The phenomenon of spalling in fire has been widely researched for concrete and, to a lesser extent, shotcrete [e.g. Tatnall, P.C. 2002. Shotcrete in fires: effects of fibers on explosive spalling. Shotcrete, 10–12]. It is assessed as being primarily associated with steam pressures produced by evaporation of water in pores [Hertz, K.D. 2002. Limits of spalling of fire-exposed concrete. Fire Safety Journal 38, 103–116].This paper assesses, by means of laboratory and field tests, how exposed sandstone is likely to respond in a tunnel fire.It is concluded that substantial explosive spalling will occur early and at relatively low temperatures. This spalling could create dangerous conditions for rescue, and escaping personnel. However, beyond the zone of spalled sandstone there would be only minor structural impact on the rock mass.     

Numerical 3D simulation of a longitudinal ventilation system: Memorial Tunnel case

In this work, a numerical 3D simulation of a longitudinal ventilation system (LVS) is developed to analyze the fire behaviour inside a road tunnel. The numerical modelling reproduces the Memorial Tunnel, a two-lane, 853 m long road tunnel, used for experimental purposes. On this tunnel, 98 full-scale fire ventilation tests with different ventilation systems were conducted, constituting the first significant experimental approach to analyze fire incidents inside road tunnels. A total number of 24 reversible jet fans were installed in groups of three, nearly equally spaced over the length of the tunnel, and cantilevered from the ceiling of the tunnel.

The validation of a numerical model is developed in the present paper. For that purpose, the behaviour of the smoke generated during a fire incident inside a road tunnel is predicted and compared with previous experimental data collected in the Memorial Tunnel Project. The smoke evolution and the performance of the LVS is simulated with a commercial code, FLUENT, which allows 3D unsteady simulations of the Navier–Stokes equations for multispecies mixtures of gases. A sufficient mesh density was introduced for the spatial discretization in order to obtain accurate results in a reasonable CPU time. Hence, typical ratios between total number of cells and the overall tunnel length were employed in the modelling. As a result, good agreement was achieved in all the tested cases, defining an accurate methodology to predict the performance of a LVS in case of fire inside a tunnel.     

Design fire curves for tunnels

Various ways exist to represent a design fire curve for tunnels. These can include different fire growth rates or combinations of fire growth rates with constant levels of heat release rate (HRR) coupled to a decay period. This means that the curve has to be represented with different mathematical expressions for different time periods. A more convenient way is to describe the design fire curve with a single mathematical expression. Such a curve has been presented by the author (H. Ingason, Fire development in large tunnel fires, 8th International Symposium on Fire Safety Science, Beijing, China, 18–23 September 2005, pp. 1497–1508), but it does not include a constant HRR period. This paper presents a new, single exponential, design fire curve with a constant maximum HRR. A presentation of available design curves is given as well.     

A study on long tunnel smoke extraction strategies by numerical simulation

The performance of different smoke extraction strategies for a long vehicle tunnel was investigated for a 100 MW fire scenario. Computer modeling was used for the investigation with a numerical simulation method. The selection of single-point extraction (SPE) opening strategy versus multi-point extraction (MPE) opening strategy was analyzed. In the single-point extraction (SPE) opening strategy, the smoke spread was found to be contained between the fire site and the point of smoke extraction. This result was obtained when the tunnel air velocity reached the critical velocity for preventing back-layering of smoke. For multi-point extraction (MPE) strategies with more than one opening, the smoke spread to all the extraction openings. Moreover for MPE strategy, air velocities were found to be slower near the middle openings and could be less than the critical velocity. Distributions of smoke spread, CO, visibility and temperature were analyzed. It was found that visibility of smoke and temperature were the key factors for safe evacuation of the personnel in tunnel. The SPE system was found to be more effective than the MPE system for partial transverse ventilation systems.     

The inner lining system in Norwegian traffic tunnels

A number of different Water and Frost Protection Systems, or so-called inner linings, have during the years been introduced and tested in Norwegian road tunnels. At present a limited number of such systems have been approved by the Norwegian Public Roads Administration (NPRA). These systems will all be described in brief. A system based on pre-cast concrete segments will be described in details, including the installation procedure. Experience and limitations associated with this system will also be discussed. A basic design concept for using an inner lining as water and frost protection is that there is no interaction between the inner lining and the rock support. The rock support practise in Norwegian traffic tunnels will also be briefly described in this paper. Sprayed concrete and rock bolts are the main support measures. In-situ cast-in-place concrete lining is only used locally to solve severe stability problems.     

Influence of floor motions in wind tunnels on the aerodynamics of road vehicles

The effect of a moving floor on the flow around a simplified car with a typical fastback geometry is investigated. Two large-eddy simulations of the flows with stationary and moving floors are made and both instantaneous and time-averaged results are compared. It is found that the floor motion reduces drag by 8% and lift by 16%. Changes in the flow are found to be global but are largest close to the floor and on the rear slanted surface of the vehicle. The wake flow is found to be relatively insensitive to the floor movement, in agreement with previous experimental observations. The periodicity of the flow events is found to be dependent on whether the floor is moving. Power spectral density of both the lift and the drag contain only one dominant frequency peak when the moving floor is adopted as compared to scattered spectra in the stationary floor case. Changes in the qualitative picture of the flow are limited to the flow near the floor and on the slanted surface of the body. However, changes in the surface pressure on the body and the history of the flow show the need of a moving floor in experimental and numerical simulations.     

Study of smoke backlayering during suppression in tunnels

Full-scale suppression tests and Computational Fluid Dynamics (CFD) simulations were carried out to investigate the effect of Water-based Fixed Fire Fighting Systems (WFFFS) on the effectiveness of longitudinal ventilation systems in resisting smoke backlayering in tunnels. Test results show that WFFFS enables longitudinal ventilation systems to resist smoke backlayering with a lower velocity than the critical velocity for the same size of tunnel fire. Based on data obtained from the test program and the simulation program, a design method is proposed to estimate the velocity required to resist smoke backlayering in tunnels when WFFFS is active.     

Model-based airflow controller design for fire ventilation in road tunnels

This paper describes a new approach to design the proportional-integral-derivative (PID) controller of the longitudinal airflow velocity in road tunnels for fire situations. Our work shows clearly that the use of a proper model provides valid data for model-based tuning of tunnel controllers, which is demonstrated by real tunnel tests. The design uses the simplified mathematical model of airflow dynamics based on Bernoulli and continuity equations, which describe the airflow dynamics in one dimension. Optimizing controller parameters on site is very time consuming and this problem increases in the case of complex tunnels with several entrance and exit ramps, which typically have occurrences of traffic congestion. Our approach is based on the design of the controller through simulations, which use the mathematical model of airflow velocity in the tunnel. This approach spares a lot of work and time with the controller tuning within tunnel tests. Moreover, it can discover potential problems, which can occur during real instances of fire in the tunnel. The additional advantage of this approach is a possibility to simulate a scenario of errors and failures of some devices, which are important for reliable control of longitudinal airflow velocity. Although this approach is focused primarily on complex road tunnels, due to their complexity and significant time savings with the controller tuning, it can be also used for simpler tunnels with no ramps (usually highway tunnels) where the design of the airflow controller is not as complex compared to the case of road tunnels. This paper also includes a case study of the airflow controller design for the Blanka tunnel complex in Prague, Czech Republic, which is the largest city tunnel in Central Europe.     

公路隧道防排水施工质量控制

针对隧道施工中的渗漏水问题,着重阐述了公路隧道防排水工程施工的工艺要求和质量控制方法,对从事公路隧道施工的技术人员及施工管理人员,在隧道防排水工程施工的现场质量控制方面有一定的参考价值.     

高速公路隧道火灾探测技术比较及应用

本文简要介绍了高速公路隧道火灾报警系统中线性光纤分布式温度探测技术、双波长火焰探测技术、智能视频图像火灾探测技术的原理,分析比较了这三种典型技术的优缺点,并对公路隧道火灾探测技术的发展方向进行了探讨。     

Physical model tests and numerical simulation for assessing the stability of brick-lined tunnels

Nowadays, numerical modelling is increasingly used to assess the stability of tunnels and underground caverns. However, an analysis of the mechanical behaviour of existing brick-lined tunnels remains challenging due to the complex material components. In order to study the mechanical behaviour of the masonry in brick-lined tunnels, this paper reports a series of small scale physical tunnel model tests to represent the true behaviour of a real tunnel under extreme loading. Advanced monitoring techniques of laser scanning and photogrammetry are used to record tunnel deformation and lining defects. This investigation shows how these techniques may substitute or supplement the conventional monitoring procedures. Moreover, numerical analyses based on continuum and discontinuum approaches are carried out. The numerical results are compared with physical model tests to assess the overall stability of these tunnels. Predictions using numerical models under various conditions have also been carried out to show the mechanical behaviour of masonry tunnel and to quantify the influence of the boundary and loading conditions.     

火场人员疏散的虚拟现实模拟研究

虚拟现实技术的发展使得观察者能够借助计算机模拟增强对危险场景的理解与认识。本文针对火灾场景下的人员疏散,结合虚拟现实与数值模拟开发了原型系统AutoEscape。系统采用FDS对火场的发生发展进行模拟,基于GIS技术设计并实现了疏散计算引擎。在此基础上,构建了虚拟现实表现模块,结合数值模拟结果对场景各要素的分布状况及行为特征进行综合描述。应用实例表明,系统有助于观察者对火场人员疏散形成深入全面的认识,从而为应急疏散演习、消防救援指挥等提供虚拟训练环境。     

关于沈海高速公路拓宽工程的数值模拟研究

本文依托沈海高速公路泉厦段扩建工程,通过数值模拟分析公路扩建工程中新旧路基之间产生的差异沉降,得出直观清晰的模拟计算数据和图形。结果表明:在新路基产生的附加应力作用下,新旧路基存在差异沉降,需进行设计处理,以避免产生病害。同时,在新旧路基结合部,存在较大附加应力,需进行处理,以确保路基的稳定。     

The fire catastrophe in the Tauern Tunnel: experience and conclusions for the Austrian guidelines

A fire occurred in the Tauern Tunnel, Austria on 29 May 1999 and caused severe casualties and damage. This paper examines the damage in the tunnel and the remedial work carried out — with a particular emphasis on the additional safety equipment required in the tunnel. The Austrian guidelines for tunnel construction have been subsequently revised to improve the fire safety in tunnels.     

Experimental study on transverse smoke temperature distribution in road tunnel fires

To assess the impact of smoke on the ceiling in tunnel fires, the smoke temperature under the ceiling was studied experimentally with small-scale experiments. This study focused on the transverse smoke temperature distribution in road tunnel fires as the longitudinal one has been widely researched. Comparison for the transverse and longitudinal smoke temperature distributions near the fire was conducted and the difference was researched. A correlation determining the transverse smoke temperature distribution under the ceiling was developed by taking the fire location into account.     

Roughness evaluation in shotcrete-lined water tunnels with invert concrete based on cases from Nepal

Most of the existing roughness estimation methods for water tunnels are related to either unlined or concrete/steel-lined tunnels. With the improvement in shotcrete technology, advancement in tunneling equipment and cost and time effectiveness, future water tunnels built for hydropower projects will consist of rock support with the extensive use of shotcrete lining in combination with systematic bolting and concrete lining in the tunnel invert. However, very little research has been performed to find out tunnel surface roughness for shotcrete-lined tunnels with invert concrete, which is important in calculating overall head loss along the waterway system to achieve an optimum and economic hydropower plant design. Hence, the main aim of this article is to review prevailing methods available to calculate tunnel wall roughness, and to use existing methods of head loss calculation to back-calculate roughness of the shotcrete-lined tunnels with invert concrete by exploiting measured head loss and actual cross-sectional profiles of two headrace tunnels from Nepal. Furthermore, the article aims to establish a link between the Manning coefficient and the physical roughness of the shotcrete-lined tunnel with invert concrete and to establish a link between over-break thickness and physical roughness. Attempts are also made to find a correlation between over-break thickness and rock mass quality described by Q-system and discussions are conducted on the potential cost savings that can be made if concrete lining is replaced by shotcrete lining with invert concrete.