Full-scale experiment and CFD simulation on smoke movement and smoke control in a metro tunnel with one opening portal

Three full-scale model experiments were conducted in a unidirectional tube, which is a part of a metro tunnel with one end connected to an underground metro station and the other end opened to outside in Chongqing, PR China. Three fire HRRs, 1.35 MW, 3 MW and 3.8 MW were produced by pool fires with different oil pan sizes in the experiments. Temperature distributions under the tunnel ceiling along the longitudinal direction were measured. At the same time, CFD simulations were conducted under the same boundary conditions with the experiments by FDS 5.5. In addition, more FDS simulation cases were conducted after the FDS simulation results agreed with the experimental results. The simulation results show that the smoke temperature and the decay rate of the temperature distribution under the tunnel ceiling along the longitudinal direction increase as HRR increases. The smoke exhausts effectively from the tunnel under mechanical ventilation system, whether the emergency vent is activated as a smoke exhaust or an air supply vent. The operation mode of the mechanical ventilation system depends on the evacuation route.     

Studies on buoyancy driven two-directional smoke flow layering length with combination of point extraction and longitudinal ventilation in tunnel fires

This paper investigates the buoyancy-driven smoke flow layering length (both upstream and downstream) beneath the ceiling with combination of point extraction and longitudinal ventilation in tunnel fires. A theoretical model is developed based on previous back-laying model with only longitudinal ventilation, with modified actual heat release rate, as well as modified upstream and downstream opposing longitudinal air flow velocities by the induced flow velocity due to point extraction. Experiments are carried out in a reduced scale model tunnel with dimensionless of 72 m×1.5 m×1.3 m. A LPG porous gas burner is used as fire source. The smoke flow layering length both upstream and downstream are identified based on temperature profiles measured along the ceiling, for different experiment conditions. CFD simulations with FDS are also performed for the same scenarios. Results show that with combination of point extraction and longitudinal ventilation, the smoke flow layering length is not symmetric where it is longer downstream than that upstream. The upstream smoke layering length decreases, while the downstream layering length increases with increase in longitudinal ventilation velocity; and they both decrease with increase in point extraction velocity. The predictions by the proposed theoretical model agree well with the measurements and simulation results.     

The evacuation safety analysis of fire scenarios in the entire acoustic barriers of elevated Mass Rapid Transit System

The entire acoustic barrier is similar to a tunnel for the elevated Mass Rapid Transit (MRT) System. Current smoke ventilation designs for the elevated MRT system have no precedent standards to follow, and therefore are all designed based on experience. For the entire acoustic barrier design in the MRT system in Taiwan, this research used FDS to simulate fires under the compartments with different heat release rates and varying number of compartments in varying lengths of entire acoustic barriers. The effects of the smoke layers produced by the fires on the evacuation of the personnel were observed. This research used a 1000 m entire acoustic barrier without smoke vent for discussion, and it was discovered that evacuation proved to be ineffective when the heat release rates were 10, 20, 30 and 40 MW. However, under circumstances where openings of different sizes were used at the top of the barriers, or changes were made to the heat release rates, or alterations were made to the number of passengers and compartments, a formula was developed in which all passengers could be evacuated under these varying circumstances; and this formula can be used as reference during the designing of natural ventilation vents in acoustic barriers for elevated MRT systems.     

Upgrading the Arlberg tunnel to current safety standards

Austrian road tunnels within the Trans-European Road Network (TERN) must fulfil the requirements of the Directive 2004/54/EC (European Commission, 2004) not later than April 2019. This regulation has to be applied to all tunnels in the TERN with a length of more than 500 m, whether they are in operation, under construction or at design stage, and aims at ensuring a minimum level of safety for road users. One of the main features of this directive is the requirement for providing an egress possibility to a safe environment every 500 m throughout the whole tunnel.The Arlberg road tunnel has a length of some 15.5 km and is in operation for more than 35 years. It is a single tube tunnel operated with bi-directional traffic, but carries a quite low traffic volume. Hence, the construction of a second tube is not really cost effective. Currently the tunnel is equipped with a transversal ventilation system with remotely controlled smoke extraction dampers providing smoke extraction every 100 m. The maximum distance between egress possibilities to a save environment is some 1500 m. Due to the high costs of a construction of a second tube or a parallel running escape gallery, a novel solution was found. The existing fresh air duct will be used as safe escape way between the existing egress possibilities. This solution has big impacts on the ventilation system and on the requirements for thermal structure protection of the new egress ways, i.e. the fresh air duct. In order to overcome this problem, massive changes in the ventilation design have to be performed, accompanied by the installation of a high-pressure water-mist system for structure protection.     

Simulating longitudinal ventilation flows in long tunnels: Comparison of full CFD and multi-scale modelling approaches in FDS6

The accurate computational modelling of airflows in transport tunnels is needed for regulations compliance, pollution and fire safety studies but remains a challenge for long domains because the computational time increases dramatically. We simulate air flows using the open-source code FDS 6.1.1 developed by NIST, USA. This work contains two parts. First we validate FDS6’s capability for predicting the flow conditions in the tunnel by comparing the predictions against on-site measurements in the Dartford Tunnel, London, UK, which is 1200 m long and 8.5 m in diameter. The comparison includes the average velocity and the profile downstream of an active jet fan up to 120 m. Secondly, we study the performance of the multi-scale modelling approach by splitting the tunnel into CFD domain and a one-dimensional domain using the FDS HVAC (Heating, Ventilation and Air Conditioning) feature. The work shows the average velocity predicted by FDS6 using both the full CFD and multi-scale approaches is within the experimental uncertainty of the measurements. Although the results showed the prediction of the downstream velocity profile near the jet fan falls outside the on-site measurements, the predictions at 80 m and beyond are accurate. Our results also show multi-scale modelling in FDS6 is as accurate as full CFD but up to 2.2 times faster and that computational savings increase with the length of the tunnel. This work sets the foundation for the next step in complexity with fire dynamics introduced to the tunnel.     

CFRP strengthened openings in two-way concrete slabs – An experimental and numerical study

Rehabilitation and strengthening of concrete structures with externally bonded fibre reinforced polymers (FRPs) has been a viable technique for at least a decade. An interesting and useful application is strengthening of slabs or walls where openings are introduced. In these situations, FRP sheets are very suitable; not only because of their strength, but also due to that they are easy to apply in comparison to traditional steel girders or other lintel systems. Even though many benefits have been shown by strengthening openings with FRPs not much research have been presented in the literature.In this paper, laboratory tests on 11 slabs with openings, loaded with a distributed load are presented together with analytical and numerical evaluations. Six slabs with openings have been strengthened with carbon fibre reinforced polymers (CFRPs) sheets. These slabs are compared with traditionally steel reinforced slabs, both with (four slabs) and without openings (one slab). The slabs are quadratic with a side length of 2.6 m and a thickness of 100 mm. Two different sizes of openings are used, 0.85 × 0.85 m and 1.2 × 1.2 m.The results from the tests show that slabs with openings can be strengthened with externally bonded CFRP sheets. The performance is even better than for traditionally steel reinforced slabs. The numerical and analytical evaluations show good agreement with the experimental results.     

Predicting the structural response of a compartment fire using full-field heat transfer measurements

Inverse heat transfer analysis (IHT) was used to measure the full-field heat fluxes on a small scale (0.9 m×0.9 m×0.9 m) stainless steel SS304 compartment exposed to a 100 kW diffusion flame. The measured heat fluxes were then used in a thermo-mechanical finite element model in Abaqus to predict the response of an aluminum 6061-T6 compartment to the same exposure. Coupled measurements of deflection and temperature using Thermographic Digital Image Correlation (TDIC) were obtained of an aluminum compartment tested until collapse. Two convective heat transfer coefficients, h =35 W/m²-K and h =10 W/m²-K were examined for the thermal model using the experimentally measured heat fluxes. Predictions of the thermal and structural response of the same compartment were generated by coupling Fire Dynamics Simulator (FDS) and Abaqus using the two values for h, h =35 W/m²-K and h from convection correlations. Predictions of deflection and temperature using heat fluxes from IHT and FDS with h=35 W/m²-K agreed with experimental measurements along the back wall. The temperature predictions from the IHT-Abaqus model were independent of h, whereas the temperature predictions from the FDS-Abaqus model were dependent on h.     

Automatic fire detection in road traffic tunnels

Fire detection experiments in a road traffic tunnel were performed in the Runehamar test tunnel 5th–8th March 2007. The Runehamar test tunnel is a full profile road traffic tunnel, 1.65 km long, located outside Åndalsnes, Norway. The goal was to examinate smoke and heat detection systems to determinate what kind of principle best suited for detecting a fire in an early stage. The systems were tested during small Heptane pool fires, varying between 0.16 m² and 1 m², giving heat release rates from 0.2 MW to 2.4 MW accordingly, and one car fire of about 3–5 MW, and with wind conditions varying from 1.1 m s^?1 to 1.6 m s^?1. The size of the fires, were designed to be in the range from impossible to difficult to detect. The results were conclusive. Earliest detection of a car fire, fire starts inside, was by smoke detection given fixed limits (3000 μg m^?3). With open pool fires, or immediate flames, continues fibre optical heat detection systems was faster given the limits 3 °C/4 min.     

Determination of dynamic model parameters of smoke detectors

A simple model for the dynamic response of point-type smoke detectors is described. The model is based on two independent parameters: the characteristic length and the static response threshold. Experimentally determined values of the parameters for six commonly used point-type smoke detectors are reported. In the tests the free stream flow velocity was varied in the range of 0.2–0.8 m/s and the rate of rise of smoke density in the range of 0.1–2 dB/ms. The model parameters were determined from the experimental data by using the least squares fitting with regularisation. The characteristic length was found to vary in the range of 2–10 m indicating a smoke entry time constant in the range of 10–50 s at a flow rate of 0.2 m/s typical of smouldering fires. The response of photoelectric detectors was described by the model reasonably well. In the case of ionisation detectors, significant deviations were found. A method of using the model in fire safety engineering calculations is also presented.     

Influence of traffic force on pollutant dispersion of CO,NO and particle matter (PM2.5) measured in an urban tunnel in Changsha,China

Environmental safety issues and ventilation problems caused by the construction of urban tunnel have increasingly been attracting people’s attention. Previous studies in China have mainly focused on vehicle emissions and ventilation control technologies in road tunnels, resulting in a research gap on urban tunnel ventilation engineering design. Therefore, a detailed monitoring investigation was conducted from May 22 to June 2, 2013 in Changsha Yingpan Road Tunnel, China. The study aim was to measure the traffic characteristics, air velocity and the carbon monoxide (CO), nitrogen oxides (NO_x) and fine particulate matter (PM_2.5) concentrations in this tunnel, which has two lanes per bore and multiple ramps. Measurement results show that during the workday morning peak, the maximum traffic flow was 1560 passenger-car-unit/h per lane with vehicle speed around 33.6 km/h in the eastbound tunnel, the average air velocity was 3.07 m/s, and the proportion of the light-duty vehicles (LDV) was 97.3%. Under the traffic force (not open fan), the CO and NO average concentrations at the main tunnel outlet were 20.3 ppm and 1.65 ppm, respectively. The gas pollutant concentrations are effectively controlled within the multiple-ramps tunnel and the design air volume flow is noticeably reduced. The traffic air flow was found to provide 32.5% of the required air volume to dilute NO_x in blocked traffic condition (vehicle speed of 10 km/h). In addition, the PM_2.5 concentration is mainly affected by the value of background outside the tunnel. The result can provide a quantitative assessment method to support pollutant concentration control and contribution of requested air volume by traffic flow in urban complex structure tunnel.     

Experimental study on smoke movement leading to glass damages in double-skinned façade

Fire hazard of the new architectural feature – double-skinned façade was examined experimentally. Full-scale burning tests on part of the design feature were carried out in a facility developed in a remote area in Northeast China. A total of eight tests were performed to demonstrate how the depth of cavity of a double-skinned façade affects the smoke movement. Surface temperature and heat flux received on the test panels are presented. Cracking patterns found on the glass panels are also observed. The measured results would give the possible smoke movement pattern inside the air cavity.By examining the results for cavity depth of 0.5, 1.0 and 1.5 m, it is found that a deeper cavity might give better safety under the scenario studied. The outer glass panel would be broken rapidly for the cavity of 0.5 m deep. Double-skinned façade with a cavity of 1.0 m deep appeared to be very risky as glass panels above broke most among the different cavity depths. The inner glass panel might be broken before the outer panel. This would give an undesirable outcome.Other separation distances of the two skins should be further examined to give optimum design of cavity depth. Other factors affecting flame and smoke movement should be further investigated.     

Numerical simulation of air ventilation in super-large underground developments

Recent advancements in engineering technology have enabled the construction of super-large underground engineering projects in China. Currently, the ventilation requirements and standards of normal-size underground spaces are used for super-large underground excavating engineering projects in China. For example, the minimum air velocity of 0.15 m/s is the standard velocity for normal-size underground spaces; however, this value is also used as the required air velocity for diluting underground contaminants in super-large underground developments. This paper aims to examine the minimum ventilation requirements for super-large underground developments (S > 100 m²). A three-dimensional computational domain representing a full-scale underground space has been developed. The pertinent parameters such as dust concentration, smoke density, oxygen concentration and air temperature have been simulated. The results show that at some specific underground conditions, the ventilation air velocity of 0.15 m/s is sufficient to control the dust level, provide required oxygen concentration and maintain the air temperature at acceptable levels during development; however, it is not sufficient to bring the CO concentration below an acceptable safe limit. This must be considered by the ventilation system designers of super-large underground developments.     

Performance analysis of a solar-assisted ground-source heat pump system for greenhouse heating: an experimental study

This study investigates the performance characteristics of a solar-assisted ground-source (geothermal) heat pump system (SAGSHPS) for greenhouse heating with a 50 m vertical 32 mm nominal diameter U-bend ground heat-exchanger. This system was designed and installed in the Solar Energy Institute, Ege University, Izmir (568 degree days cooling, base: 22 °C, 1226 degree days heating, base: 18 °C), Turkey. Based upon the measurements made in the heating mode from the 20th of January till 31st of March 2004, the heat extraction rate from the soil is found to be, on average, 57.78 W/m of bore depth, while the required borehole length in metre per kW of capacity is obtained as 11.92. Design practices in Turkey normally call for U-bend depths between 11 and 13 m/kW of heating. The entering water temperature to the unit ranges from 8.2 to 16.2 °C, with an average value of 14 °C. The greenhouse air has a maximum day temperature of 31.05 °C and night temperature of 14.54 °C with a relative humidity of 40.35%. The heating coefficient of performance of the heat pump (COP_HP) is about 2.00 at the end of a cloudy day, while it is about 3.13 at the end of sunny day and fluctuates between these values in other times. The COP values for the whole system are also obtained to be 5–20% lower than COP_HP. The clearness index during experimental period is computed as average 0.56. At the same period, Cucumus sativus cv. pandora F₁ was raised, and product quality was improved with the climatic conditions in the designed SAGSHPS. However, experimental results show that monovalent central heating operation (independent of any other heating system) cannot meet the overall heat loss of the greenhouse if the ambient temperature is very low. The bivalent operation (combined with other heating system) can be suggested as the best solution in Mediterranean and Aegean regions of Turkey.     

Safe velocity of on-fire train running in the tunnel

The safety of a running train on fire in a tunnel is a key issue for rescue operations, and the train velocity is mainly related to its safety. In this study, the relationship between the wind velocity and heat release rate (HRR), temperature field around the train, and flame/smoke pervasion rule were investigated under the conditions of variable train velocity, fire location, and fire source location. Beijing Metro was considered as a typical example, in which the safe velocity was estimated to be ∼41.83 km h⁻¹. Assuming the occurrence of fire at the center of the train, the numerical simulations of the flow field using the sliding grid of CFD were performed for a full-scale tunnel under different HRRs. When the fire source reached to the target section, the velocities of all the monitoring points rapidly increased. The velocities increased as the train tail arrived at the target section. The velocities at the measuring points increased with the increase in height, excluding the value of the position with a distance of 0.025 m from the tunnel ceiling. The average temperature and concentration of smoke in the annular space between the train and tunnel ceiling had the minimum values when the running train on fire moved with a speed of 45 km h⁻¹. Thus, the safe velocity of a subway train on fire should be managed between 41.83 km h⁻¹ and 45 km h⁻¹.     

Assesment of clay bricks compressive strength using quantitative values of colour components

This study was conducted to assess the relationships among firing temperature, colour components and compressive strength of bricks. Lightness (L*) and chromaticity (a* and b*) of 10 replicated brick samples fired at temperatures 700–1050 °C in steps of 25 °C under free access of air, were measured with a colorimeter, which uses an L* a* b* colour space. Increasing firing temperature significantly increased the compressive strength of bricks. The values of L* slightly increased with firing temperature up to around 800 °C then decreased as temperature increased further. The values of b* and a* increased with increasing firing temperature up to around 900 °C then rapidly decreased with further increases in firing temperature. A negative relationship occurred between each of L*, a*, and b* and compressive strength. Compressive strength was adequately described by colour components of L* and b* by linear regression equations (R² = 0.87 for L*, and R² = 77 for b*). However, the relationship occurred between a* and compressive strength was quite poor. It was concluded that the numerical values of colour components of L* and b* may be used to predict and judge the compressive strength of bricks. However, the method can not be generalized before its calibrated with different raw materials under different firing conditions.     

Experiments of evacuation speed in smoke-filled tunnel

Among tunnel fire safety strategies, evacuation speed in smoke, which is the basic evacuation performance characteristic, is one of the most important factors when assessing safety. An evacuation experiment in a full-scale tunnel filled with smoke has been done in order to clarify the relation between extinction coefficient up to Cs = 1.0 m⁻¹, which includes Cs = 0.4 m⁻¹ as a Japanese road tunnel fire prevention standard, and evacuation speed. The maximum, minimum and mean values of normal walking speeds are almost constant regardless of the extinction coefficient. As for the emergency evacuation speeds, the maximum speed is largely influenced by extinction coefficient, decreasing rapidly from 3.55 m/s at Cs = 0.30 m⁻¹ to 2.53 m/s at Cs = 0.75 m⁻¹ while the minimum and mean speeds are almost constant with a slight decrease as Cs increases. The maximum evacuation speed trends in the present experiments and those in Frantzich and Nillson (2003, 2004) and Fridolf et al. (2013), lie on the same decreasing logarithmic curve as a function of extinction coefficient.     

Smoke concentrations inside and outside of a corridor-like enclosure

This work presents smoke measurements and correlations inside and outside of a corridor-like enclosure fires in order to determine the effects of burning on smoke concentrations inside and outside the enclosure. Thirty eight experiments were performed in a three metre long corridor-like enclosure having a cross section 0.5 m×0.5 m, door like openings in the front panel and a gaseous burner located near the closed end. Smoke concentrations were measured at two locations inside the enclosure and also in the exhaust duct of a hood collecting the fire gases from the enclosure. It was found that smoke concentration in the exhaust duct decreased whereas smoke concentration inside the enclosure increased after the flames started moving towards the opening and external burning occurred. This increased smoke concentration inside the enclosure was caused by reversion of the flow pattern inside the enclosure after the flames moved past a point towards the opening. Namely, the flow pattern changed direction behind the flame front in the sense that hot gases in the upper layer were travelling backwards towards the closed end of the corridor thus contributing to smoke increase inside the enclosure. This change of flow pattern was confirmed in all experiments by bidirectional probe velocity measurements in the upper and lower layer as well as by oxygen concentrations and temperature measurements inside the enclosure. These results are useful for CFD validation and specifically applicable for assessing smoke hazards in corridor fires in buildings where smoke concentrations can be much larger than anticipated owing to leakage to adjacent rooms behind a moving flame front.     

Longitudinal ventilation for smoke control in a tilted tunnel by scale modeling

Longitudinal ventilation systems are commonly installed in new tunnels in large cities of the Far East including Mainland China, Hong Kong and Taiwan. Many tunnels are found in big cities and some of them are inclined at an angle to the horizontal. However, smoke movement in tilted tunnels is not fully understood. In some of the tunnels, the ventilation system was designed based on presumed smoke movement pattern without experimental demonstration. Smoke movement pattern in a tilted tunnel model was studied by using a scaled model. A 1/50 tunnel model of length 2 m with adjustable angle to the horizontal was constructed by transparent acrylic plastics. A small 0.097 kW propanol pool fire was used as the heat source combined with burning pellets generating smoke. A fan placed at the upstream end was used to create longitudinal ventilation. Different ventilation rates were set using a transformer to control or adjust the fan speed. Experiments were performed with the tunnel angle varying up to 30° to the horizontal. Effect of smoke screens was also studied. The observed smoke movement patterns indicated that the shape of the buoyant plume inside the tunnel depends on the tilted angle. Smoke would flow along the tunnel floor due to gravity. The bending angle of the plume depends on the tunnel angle. Tunnel inclined at greater angles to the horizontal would give larger amount of smoke flow. Smoke movement pattern for a tilted tunnel with smoke screens was observed to be very different from some design projects. All results will be reported in this paper.     

On-line airflow pattern measurement in ventilated buildings

Comfort, productivity and quality of life of living beings are strongly influenced by the physical properties of their microenvironment. To guarantee an optimal microenvironment, the supply and distribution of fresh air must be controlled. Therefore, on-line airflow pattern measurement and control are crucial elements. A new concept of an airflow pattern sensor, based on the measurement of the temperature distribution at air inlet, was tested and validated in two test installations at different scale. The sensor allowed a prediction of the airflow pattern centreline with a maximum deviation of 0.22 m at 1.5 m from inlet and a deviation of 0.53 m at 3.5 m from inlet. Integrating this sensor in climate control equipment will improve the distribution of fresh air within the ventilated space.     

Construction of a large-section long pedestrian underpass using pipe jacking in muddy silty clay: A case study

This paper presents a case study of constructing a large-section long pedestrian underpass using pipe jacking method in Nanjing, China. The underpass, having a width of 7 m and a height of 4.3 m, was jacked 94.5 m in muddy silty clay under a busy roadway with 6.2 m overburden soil, meanwhile it traverses above the existed shield metro tunnels with just 4.5 m from the underpass bottom to tunnel vault. This paper introduced the design and construction schemes of this project in detail. A pre-construction three dimensional numerical simulation was conducted to investigate the responses of the roadway and metro tunnels to pipe jacking construction. Based on the simulation results, the field monitoring program was proposed, and the tunnels deformation and ground settlement were constantly monitored. The field performances of the metro tunnels and roadway were analyzed according to the monitoring data. In the jacking process, the micro-underbreak method was adopted. In order to decrease the tunnels uplift and ground settlement, the actual volume of soil conveyed out from soil chamber to ground surface was kept 95–98% of theoretical soil volume cut by cutter head. In general, this project is completed successfully without taking any additional time and money-consuming deformation control measures. The ground traffic and underneath metro runs well during the whole construction process.