钻爆法施工隧道空气质量现场测试

为明确钻爆法施工爆破后隧道的粉尘与有害气体分布情况,检验通风、防尘效果,分别利用风速仪、粉尘仪和气体检测仪对兰渝铁路四座高瓦斯隧道的风速、粉尘和有害气体进行现场测试。测试结果显示:穿山甲风机配合螺旋式风管的压入式通风的效果最好,采用这种配置通风20 min左右,掌子面附近的粉尘、SO₂等有害气体浓度即降至允许浓度以下,通风30 min左右CO浓度降至允许浓度以下。隧道内风速主要受断面大小、掘进长度和通风设备及其维护等影响,隧道断面对净化空气所需要的通风时间影响最大,风管漏风率次之,再次为通风长度。在确保设备维护和通风管理情况下,穿山甲风机高档配合螺旋风管可实现长距离通风。     

Effects of the solid curtains on natural ventilation performance in a subway tunnel

Solid curtains can be installed in subway tunnels for the promotion of air ventilation in ventilation ducts in association with the piston effect caused by a running train. With an aim to analyze the effects of solid curtains on duct ventilation performance in a subway tunnel, the current study adopts the tunnel and subway train geometries which are exactly the same as those in a previous model tunnel experiment, but newly incorporates two ventilation ducts connected vertically to the tunnel ceiling and two solid curtains placed at an upstream position of a duct near the tunnel inlet and at a downstream position of another duct near the tunnel outlet, respectively. A three-dimensional CFD model adopting the dynamic layering method for tracking the motion of a train, which was validated against the reported model tunnel experiment in a previous study, is employed to predict the train-induced unsteady airflows in the subway tunnel and in the ducts. The numerical results reveal that the duct ventilation performance in a subway tunnel strongly depends on the operation of the solid curtains. The suction mass flow of the air through the duct near the tunnel inlet and the exhaust mass flow of the air through the duct near the tunnel outlet are increased considerably in the case with the solid curtains in comparison with those in the case without the solid curtains.     

风管出口位置对隧道施工通风效果影响的研究

为研究风管出口位置对公路隧道施工通风效果的影响,利用流体力学软件Fluent,建立隧道三维模型并进行了数值模拟。通过分别对风管管口与工作面5种布设距离及4种布设形式下流场特性的对比,分析了管口与工作面距离及风管附壁程度对流速变化和有效射程的影响。并进一步探讨了风管出口不同位置对局部风阻压力的影响。模拟结果表明:在相同的入口速度条件下,风管附壁程度越高、距离工作面越近,射流速度变化梯度越大,通风效果越明显;风管管口离工作面越近引起的局部压力损失越大。     

Effects of twin tunnels construction beneath existing shield-driven twin tunnels

This paper presents a case of closely spaced twin tunnels excavated beneath other closely spaced existing twin tunnels in Beijing, China. The existing twin tunnels were previously built by the shield method while the new twin tunnels were excavated by the shallow tunnelling method. The settlements of the existing tunnels and the ground surfaces associated with the new tunnels construction were systematically monitored. A superposition method is adopted to describe the settlement profiles of both the existing tunnels and the ground surfaces under the influence of the new twin tunnels construction below. A satisfactory match between the proposed fitting curves and the measured settlement data of both the existing tunnels and the ground surfaces is obtained. As shown in a particular monitoring cross-section, the settlement profile shapes for the existing tunnel and the ground surface are different. The settlement profile of the existing structure displays a “W” shape while the ground surface settlement profile displays a “U” shape. It is also found that due to the flexibility of the segmental lining, the ground losses obtained from the existing tunnel level and the ground surface level in the same monitoring cross-section are nearly the same.     

Numerical analysis of different ventilation schemes during the construction process of inclined tunnel groups at the Changheba Hydropower Station,China

During the excavation process of underground caverns, the rational selection of the ventilation scheme is very important for the safety and health of construction workers. The flood discharge tunnel groups at the Changheba Hydropower Station are selected as a case to study the design of ventilation schemes in inclined tunnel groups; these groups are characterized by a gradient of approximately 10% and a complex intersecting relationship among the tunnels. The Computational Fluid Dynamics (CFD) method is used to simulate the fluid dynamics in tunnel groups when different ventilation schemes are employed. Four ventilation schemes with the same duct at different positions along the transverse section are formulated, and the scheme approaching the right side with most of the construction adits is adopted in engineering after a comparative analysis, as it offers a well-distributed velocity field and sufficient security distance. The study reveals that flow vortices appear in the tunnels with a long axis length ranging from 5 m to 20 m; the observation that the flow velocity on the transverse sections is away from the heading face indicates that a low-velocity area is always present in the vicinity of an air duct, and the security distance on the upstream side is 60% shorter than on the downstream side with the same air-blower when the tunnels have a 10% gradient. In addition, when the excavation distance rises 200 m, the ventilation condition in the tunnels, especially in the areas around tunnel intersections, is greatly improved by the completion of pilot tunnels and shafts in advance.     

基于FDS的公路隧道火灾可逆射流风机通风疏散研究

随着我国公路隧道从高速建设期转变为建设与管理并重期,可逆射流风机在隧道通风系统中得到广泛应用。为探究可逆射流风机在隧道火灾下通风运行方式对人员疏散的影响,依托广东山隧道,采用5,20 MW两种火源功率,研究不同射流风机运行方式下隧道中部区域烟气、温度、CO体积分数及能见度的变化特性。结果表明,自然风和射流风机的出口气流均会破坏烟气-空气分层结构。在隧道内部1 m/s纵向自然风的影响下,面对不同功率火源,射流风机运行模式与人员疏散方向应随之改变。     

Experimental studies on fire-induced buoyant smoke temperature distribution along tunnel ceiling

Twelve tests were conducted to study the distribution of smoke temperature along the tunnel ceiling in the one-dimensional spreading phase, two tests in a large-scale tunnel and the other ten in full scale vehicular tunnels. The fire size and the height above the floor, the tunnel section geometry and longitudinal ventilation velocity varied in these tests. Experimental results showed that when the fire size was larger, the smoke temperature below the ceiling was higher, but it decayed faster while traveling down the tunnel. The longitudinal ventilation velocity seemed to take much influence on the smoke temperature decay speed downstream. A “barrier effect” was shown for the smoke temperature distribution of the upstream back layering. The smoke temperatures measured were higher upstream than downstream before the “barrier”, and were much lower and decreased faster along the tunnel ceiling after the “barrier”. The temperature and the traveling velocity of the upstream smoke flow decreased largely when the longitudinal ventilation velocity increased a bit. The dimensionless excess smoke temperature distributions along the tunnel ceiling in all tests fell into good exponential decay. But the decay speed along the tunnel seemed to be much larger in the large-scale tunnel than that in full-scale tunnels. The measured data on ceiling jet temperature decay along the tunnel was compared with predictions of Delichatsios's model, a model built based on small-scale tests, with hydraulic diameter introduced. Results showed that Delichatsisos’ model over estimated the decay speed of ceiling jet temperature for the downstream flow. However, good agreement was achieved between the measured data and the model predictions for the upstream back layering. All the experimental data presented in this paper can be further applied for verification of numerical models, bench-scale results and building new models on ceiling jet temperature distribution.     

Analysis of the ventilation systems in the Dartford tunnels using a multi-scale modelling approach

The capabilities of the ventilation systems in the two road tunnels at Dartford (UK) are analysed using a multi-scale modelling approach. Both tunnels have complex semi-transverse ventilation systems with jet fans to control longitudinal flow. The construction and ventilation systems in the tunnels are described and the current emergency ventilation strategies are presented. The analysis includes a coupling of a 1D network model with 3D components, representing the operational jet fans, built using computational fluid dynamics. The jet fans were experimentally characterized on-site and the findings were compared to the model predictions. The predicted ventilation flows for each of the emergency ventilation strategies are presented and discussed. In cold-flow conditions, ventilation velocities significantly above 3 m/s can be generated throughout the tunnels. However, it is observed that 1/3 of the flow generated in the East tunnel is diverted from the tunnel up the extract shafts. The model was used to simulate various reduced fan combinations and thus the level of redundancy in each of the systems has been estimated. It is found that an acceptable level of ventilation may be produced in the West tunnel, even if several pairs of jet fans are disabled. In the East tunnel there is less redundancy, but an acceptable level of ventilation control can be maintained with one or two jet fans disabled.     

Numerical simulation of TBM construction ventilation in a long diversion tunnel

A three-dimensional Renormalization-group (RNG) k-ε model has been performed for forced ventilation to the working face of a long diversion tunnel, taking into account the effects of air leakage and the frictional resistance along the tunnel. The case study involves the working face during TBM construction of the Xinjiang 81 Daban long diversion tunnel, China. Analysis of the flow-field distribution and the pressure distribution near the working face and tunnel outlet revealed the relationships among the air leakage rate per 100 m, pressure difference at the air leakage port, and quantity of air in the air duct. The simulation results show that the air flux, velocity, and leakage rate gradually decrease along the tunnel. The air leakage rate per 100 m increases logarithmically along with pressure growth when the latter is limited within a certain pressure difference range. A low-pressure area can be found on the duct wall near the air leakage port, and the pressure inside the tunnel gradually decreases from the working face to the tunnel outlet; the velocity is relatively high near the leakage port, and is low in the tunnel. The simulated results were in good agreement with the experimental work by Cigdem Aydin and Hui-min Wang, and the simulated axial velocities of the tunnel were validated with the empirical value.     

Surface subsidence induced by twin subway tunnelling in soft ground conditions in Istanbul

Unlike the symmetrical surface settlement trough of a single tunnel which can be described using the Gaussian function, surface settlement over twin tunnels can be symmetric with respect to the mid-point between two tunnels or asymmetric. The paper reports the settlement troughs which developed when earth pressure balance (EPB) machines were used to excavate twin tunnels at shallow depth in the soft ground conditions beneath a developed part of Istanbul. An attempt is made to evaluate the effects of different factors on the surface subsidence. Detailed monitoring was undertaken when one tunnel was advanced ahead of the other and when only one tunnel was being driven. It was found that the shapes of the subsidence troughs over the two tunnels were different and varied with the excavation of the second/subsequent tunnel. It is concluded that changes in the subsidence trough are related to disturbance in the geo-material when an excavation is advanced ahead, as well as the nature and thickness of the overburden.     

狭长空间强扰动条件下热环境控制的数值模拟

本文针对一单侧开口,内部存在两股对称高温高速热射流且伴随多股扰动气流的狭长空间,采用全面纵向通风技术进行热环境控制、排除热污染。经数值模拟方法,得到了经济有效的全面通风临界断面风速为2．6m／s。另外,为改善局部有人区域及敏感壁面的温度,在热射流出口前端4m处设置射流风机,进行助推诱导,使排风温度提高约10～20K,提升了纵向通风的排热效果;并改善了相关人员呼吸区的温度场,使其平均温度下降约10K。     

隧道等截面通风系统均匀送风特性研究

针对地下建筑长大隧道均匀通风的工程需求,提出了一种基于通风均流器的等截面通风系统,为获得主风管风速、宽高比与通风系统送风均匀性的关系,采用CFD数值模拟分析方法对通风系统的送风均匀性和阻力性能进行了研究。研究发现,主风管风速为9.7 m/s时,各风口最低风速4.45 m/s,最高风速4.96 m/s,平均风速4.63 m/s,最大偏差7%,各风口风速标准差为0.16,等截面通风系统能实现均匀送风。通风均流器阀片角度恒定时,系统送风均匀性随着主风管风速的增大而小幅降低,各风口风速标准差范围为0.12～0.24;随着主风管宽高比的增加,各风口风速标准差波动范围为0.22～0.34,主风管风速、宽高比对系统送风均匀性影响较小。风速大于6.5 m/s时,通风均流器阻力系数ξ随着阀片角度β的增大而减小,与Re无关;阀片角度β一定时,通风均流器阻力系数ξ随主风管宽高比的增加而减小。     

The critical ventilation velocity in tunnel fires—a computer simulation

In ventilated tunnel fires, smoke and hot combustion products may form a layer near the ceiling and flow in the direction opposite to the ventilation stream. The existence of this reverse stratified flow has an important bearing on fire fighting and evacuation of underground mine roadways, tunnels and building corridors. In the present study, conducted by the National Institute for Occupational Safety and Health, a CFD program (fire dynamics simulator) based on large eddy simulations (LES) is used to model floor-level fires in a ventilated tunnel. Specifically, the critical ventilation velocity that is just sufficient to prevent the formation of a reverse stratified layer is simulated for two tunnels of different size. The computer code is verified by checking the computed velocity profile against experimental measurements. The CFD results show the leveling-off of the critical ventilation velocity as the heat release rate surpasses a certain value. At this critical ventilation, the ceiling temperature above the fire reaches a maximum for both tunnels. The velocity leveling-off can be explained from this observation. An extended correlation of Newman (Combust. Flame 57 (1984) 33) is applied to the temperature profiles obtained by CFD. At the critical ventilation, temperature stratification exists downstream from the fire. The computed critical ventilation velocity shows fair agreement with available experimental data taken from both horizontal and inclined fire tunnels. The CFD simulations indicate that the Froude modeling is an approximation for tunnel fires. The Froude-scaling law does not apply to two geometrically similar fire tunnels. The CFD results are compared with two simple theories of critical ventilation by Kennedy et al. (ASHRAE Trans. Res. 102(2) (1996) 40) and Kunsch (Fire safety J. 37 (2002) 67).     

Control of smoke flow in tunnel fires using longitudinal ventilation systems – a study of the critical velocity

The “critical velocity” is the minimum air velocity required to suppress the smoke spreading against the longitudinal ventilation flow during tunnel fire situations. The current techniques for prediction of the values of the critical velocity for various tunnels were mainly based on semi-empirical equations obtained from the Froude number preservation combining with some experimental data. There are a few uncertainties in the current methods of prediction of the critical ventilation velocity. The first is the influence of the fire power on the critical ventilation velocity. The second is the effect of the tunnel geometry on the critical velocity. Both problems lead to the issues of the scaling techniques in tunnel fires. This study addressed these problems by carrying out a series of experimental tests in five model tunnels having the same height but different cross-sectional geometry. Detailed temperature and velocity distributions in the tunnels have been carried out. The experimental results showed that the critical velocity did vary with the tunnel cross-sectional geometry. It was also shown clearly that there are two regimes of variation of critical velocity against fire heat release rate. At low rates of heat release the critical velocity varies as the one-third power of the heat release rate, however at higher rates of heat release, the critical velocity becomes independent of fire heat release rate. Analysis of the distribution of temperature within the fire plumes showed that there were two fire plume distributions at the critical ventilation conditions. The change of the fire plume distribution coincided with the change of the regime in the curves of the critical velocity against fire heat release rate. The study used dimensionless velocity and dimensionless heat release rate with the tunnel hydraulic height (tunnel mean hydraulic diameter) as the characteristic length in the experimental data analysis. It was shown that the experimental data for the five tunnels can be correlated into simple formulae which can be used for scaling. The new scaling techniques are examined by applying the scaling techniques to the present experimental results and three large-scale experimental results available in the public literature. A good agreement has been obtained. This suggests that the scaling techniques can be used with confidence to predict the critical ventilation velocity for larger-scale tunnels in any cross-sectional geometry. Comprehensive CFD simulations have been carried out to examine the flow behaviour inside the tunnels. Validation against the experimental results showed that the CFD gave slightly lower but satisfactory prediction of the flow velocity. However the temperature prediction in the fire region was too high. The findings from the CFD simulations supported the ones from experimental tests.     

海底隧道腐蚀环境下射流风机升压力衰减机理及计算方法研究

海底道路隧道内高湿度、富盐雾和多酸性气体的环境特征会加速腐蚀风机,进而使通风效果无法满足洞内环境控制标准。以厦门翔安海底隧道为依托对隧道内风机升压力展开现场测试,结合理论分析和Fluent滑移网格模型研究风机升压力计算公式和表面粗糙度与风机升压力的衰减关系。研究结果表明：单台射流风机升压力计算公式还应考虑风机自身性能损失折减系数η1;海底隧道腐蚀环境通过积垢沉淀、侵蚀和腐蚀效应增大风机叶片和流通部件的表面粗糙度,进而增大风流阻力,降低风机升压力;通过数值模拟得到基于表面粗糙度的风机升压力计算方法。研究结果揭示海底隧道腐蚀环境下风机升压力衰减机理并建立了计算方法,为同类型海底隧道通风系统设计提供参考。     

The Influence of Tunnel Geometry and Ventilation on the Heat Release Rate of a Fire

It has occasionally been observed that fires in tunnels appear to be significantly more severe than fires in the open air. A literature review has been carried out, comparing heat release data from fires in tunnels with heat release data from similar fires in the open air. A Bayesian methodology has been used to investigate the geometrical factors that have the greatest influence on heat release rate. It is shown that the heat release rate of a fire in a tunnel is influenced primarily by the width of a tunnel; a fire will tend to have a higher heat release rate in a narrow tunnel rather than in a wide tunnel. The observed relationship between heat release rate and tunnel width is presented. Results from a study investigating the variation of heat release rate with ventilation velocity for fires in tunnels are also presented. A method for making realistic estimates of the heat release rates of fires in tunnels, based on these results, is presented.     

CFD analysis of a realistic reduced-scale modeling equipped with axial jet fan

Typically, in the experimental scale road tunnel model, the air flow induced by ventilation system is provided by an external fan. In this paper, the authors have numerically simulated full and reduced-scale tunnel in order to evaluate the possibility to realize a reduced scale of a road tunnel model with a realistic ventilation system consisting of impulsive jet fans.In particular, two different types of longitudinal ventilation systems were considered, traditional and alternative. The last one was equipped with jet fans that have the inlet/outlet sections inclined at a fixed pitch angle (α=6°) toward the tunnel floor. The jet fan was simulated as a simple momentum source that provides a pressure rise (pressure drop) across them as a function of the outflow air velocity.The analyzed tunnel consists in a 800 m one directional bore with circular cross section 5.05 m radius; the jet fans were installed at 5.67 m from the floor. Furthermore a burning Heavy Good Vehicle (HGV), placed at 450 m far away the tunnel entrance, was considered. To simulate numerically the burning vehicle, the species transport equation combustion model with Eddy-Dissipation-Concept (EDC) model was adopted.In order to create a reduced-scale model from a full scale, Froude method was applied to preserve geometrical, kinematical and dynamical similitude. Temperature and axial velocity profiles, in different tunnel sections for both considered models (full and scaled) and ventilation systems, were provided. The numerical results showed a good agreement for the both ventilation systems.     

Effects of the ventilation duct arrangement and duct geometry on ventilation performance in a subway tunnel

This study has investigated numerically the effects of the ventilation duct number and duct geometry on duct ventilation performance in a subway tunnel. A three-dimensional numerical model using the dynamic layering method for the moving boundary of a train, which was validated against the model tunnel experimental data in a previous study, is adopted to simulate train-induced unsteady tunnel flows. For the tunnel and subway train geometries that are exactly the same as those used in the model tunnel experimental test, but with the ventilation ducts being connected to the tunnel ceiling, the three-dimensional tunnel flows are simulated numerically under five different ventilation duct numbers and two different duct geometries. The numerical results reveal that: (1) for a given total area of openings, the ventilation duct number has little influence on the total mass flow of the air sucked into the tunnel through the ventilation ducts while the total mass flow of the air pushed out of the tunnel through the ducts increases remarkably with the increase in the duct number; (2) with the increase of the distance between a specific ventilation duct and the tunnel inlet the suction mass flow through the duct decreases significantly while the exhaust mass flow through the duct increases greatly, i.e., the location of a specific duct has a strong impact on the total suction and exhaust mass flows through the ventilation duct; (3) as the linkage angle between the tunnel ceiling and the upstream side wall of a duct is changed from 90° to 45°, the size of the re-circulation area inside the duct is much reduced when the train approaches the duct and thus the amount of air pushed out of the duct is greatly increased (i.e. the exhaust effect through the duct is remarkably strengthened).     

近接隧道污染物窜流特性与通风能耗分析

采用三维壁面射流理论分析隧道洞口排污的射流特性,在此基础上建立近接隧道污染物窜流的理论模型,理论计算结果与已有研究试验数据吻合良好。在不考虑地形、环境风、交通流等影响时,窜流比φ主要受上下游隧道间距x与洞口水力直径D的影响,φ随x/D的增大而减小,为了控制窜流比在10%以下,x/D应大于25。理论计算表明:随着窜流比的增加,下游隧道的需风量增加,隧道通风能耗陡增;且需风量和能耗的增幅随窜流比的增大而增大。为抑制近接隧道需风量和通风能耗的增加,除了降低窜流比,还可采用竖井进行提前排污。     

Fire simulation in road tunnels

The catastrophic tunnel fires since the year 1999 and a series of accidents in some tunnels in the summer of 2001 triggered extensive discussions and proposals relating to tunnel safety. When a fire occurs in a tunnel, and in absence of sufficient air supply, large quantities of smoke are generated, filling the vehicles and any space available around them. Unless a strong flow is created and maintained, hot gases and smoke migrate in all directions. With a weak airflow, smoke forms a layer along the tunnel ceiling and can flow against the direction of forced ventilation, interfering with personal evacuation. This paper shows the results of a computer fire simulation in a tunnel and the results of this simulation: air velocity, air temperature and wall temperature in the case of fire. The simulation started before the emergency ventilation system is activated and continued with the fans activated to control the smoke.