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ScienceDirect Procedia Engineering 165 (2016) 214 – 223

15th International scientific conference “Underground Urbanisation as a Prerequisite for Sustainable Development”

Innovative engineering solutions for improving operational safety and efficiency of subways with two-way tunnels Vladimir Maslak a, Dmitry Boytsov a, Andrey Danilov a, Elena Levina a, Semen Gendlerb,* a

Open Joint-Stock Company "Research and Survey Institute Lenmetrogiprotrans", Russia a Saint Petersburg Mining University, Russia

Abstract The paper considers the problems of improving the operational safety of the two-way tunnel subway under weather conditions characteristic of Russian megapolises. A significant difference is indicated between annually mean, monthly mean and extreme outdoor air temperatures affecting thermodynamic parameters of the intra-subway atmosphere in Russia and foreign countries having subways. Comparative characteristics are given for the factors determining temperature regimes of the subway lines with single-way and two-way tunnels in case conventional ventilation schemes are used. The paper also describes alternative ventilation schemes involving constructive elements widely used for venting motor-road tunnels. Based on specific initial data, calculations have been performed whose results characterize temperature distribution in running single-way and two-way tunnels vented by using the ventilation scheme comprising vent ducts and air recirculation. The efficiency of the two-way tunnel ventilation scheme comprising a ventilation duct and air recirculation has been justified. Mathematical simulation of the dynamics of smoke propagation in case of a fire in tunnels and at stations has been accomplished. Efficiency of the emergency ventilation scheme comprising a vent duct in smoke protection of the fire evacuation passages for people and in smoke removal has been proved. The paper presents such station complex layout solutions that, contrary to historical prototypes, imply integrating the station ventilation and smoke removal systems into the general structure of the station space-planning solutions so that they are in close vicinity of all the designed passenger flows with retention of the comfortable space necessary for passengers. 2016The TheAuthors. Authors. Published by Elsevier Ltd.is an open access article under the CC BY-NC-ND license ©2016 © Published by Elsevier Ltd. This (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the 15th International scientific conference “Underground Peer-review under theSustainable scientific committee of the 15th International scientific conference “Underground Urbanisation as a Urbanisation as aresponsibility Prerequisiteoffor Development. Prerequisite for Sustainable Development

* Corresponding author. Tel.: +7-812-328-86-23. E-mail address: [email protected]

1877-7058 © 2016 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the scientific committee of the 15th International scientific conference “Underground Urbanisation as a Prerequisite for Sustainable Development

doi:10.1016/j.proeng.2016.11.793

Vladimir Maslak et al. / Procedia Engineering 165 (2016) 214 – 223

Keywords: Subway, two-way tunnel, temperature, air, vent duct, train, fire, smoke removal.

1. Introduction The use of two-way subway running tunnels has become possible due to creation of large-diameter tunnel boring machines enabling tunneling at the 10 to 15 m depth in densely populated megapolis districts without damaging the ground surface and negatively affecting the condition of buildings and structures. Analysis of the international practice in subway construction evidences that construction of two-way tunnels leads to cost reduction by approximately 20-30% with respect to conventional single-way tunnels and also to reduction of the work schedule. Another positive aspect of subway lines with two-way tunnels is creation of more favorable (as compared with single-way tunnels) conditions for people evacuation from dangerous zones in emergencies because in this case their walking speed is higher and the maneuver space is larger. The most widespread type of lines with two-way tunnels is shallow station complexes with a two-way railway in the station center and two platforms at the station periphery (Fig. 1).

Fig.1. Subway stations with peripheral passenger platforms (Saint Petersburg, Moscow) .

A specific feature of space-planning solutions for stations at the two-way tunnel lines is such arrangement and zoning of passenger and service areas as to ensure optimal operation of utility systems providing safe exploitation of the stations. For instance, communication channels of the station ventilation and smoke removal systems occupy the isolated central zone and are directly connected to the passenger platforms. One of the main utility systems supporting the subway operation is the ventilation system whose functioning should sustain creation of normative air parameters in running tunnels and at stations under standard conditions and also realization of emergency modes guaranteeing safe escape of people in emergency situations (e.g., fires) and subsequent elimination of the emergency (fire extinguishing). 2. Temperature regimes of the subway tunnels with typical-scheme ventilation As the domestic and foreign experience shows, subway lines may comprise both single- and two-way tunnels. One of the possible ventilation schemes of single-way tunnels implies supplying the tunnels with outdoor air through a running-line plenum shaft, air motion towards the stations, and removal of a portion of air to the surface through the station exhaust vent shaft (Fig. 2) [3].

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3

6

3

1

6

5 2

4

4

9

7

Station I

10

7

Station I

8

Fig. 2. Ventilation scheme for single-way subway tunnels (1 – plenum running vent shaft; 2 – plenum fan; 3 – station exhaust vent shaft; 4 – exhaust fan; 5 – outdoor air; 6 – exhaust air; 7 – circulation air; 8 – the mixture of outdoor and circulation air; 9 – train running direction; 10 – running tunnels).

The amount of air passing through the tunnels will be approximately equal to the sum of the air flow rate provided by the fans and that created by the train piston effect and depending (other factors being equal) on the interstation section length, train length, and train speed [3]. The circulation flows accumulate a portion of heat emitted into the air from trains and other energy sources. This causes the following facts: in summer, heat accumulated in the circulation flows causes extra increase in the air temperature jointly with other heat sources, while in winter the situation is reversed. Positive-temperature circulation air is being mixed with cold outdoor air fed into the tunnels through the running-line shafts. As a result, the tunnels are supplied with air whose initial temperature exceeds significantly the outdoor air temperature. To estimate the effect of circulation air flows on the subway thermal regime, a series of calculations were performed according to the method presented in [1]. The outdoor air temperature was assumed to correspond to the Moscow and Saint Petersburg climate characterized by the annually mean temperature not higher than 40С and outdoor air temperature in the coldest winter month lower than -70С to -100С [5]. The following initial data were also used in calculation: The length of the interstation semi-section of 1030 m, flow rate of the outdoor air fed to the interstation section of 36 m3/s, circulation air flow rate of 25 m3/s, the heat source power of 1140 kW. Calculations for the ventilation system presented in Fig. 1 are shown in Fig. 3.

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15 10

Air temperature, 0С

5 0 -5

0

200

400

600

800

1000

-10 -15 Distance from the interstation section center, m

-20 -25 -30

Fig.3. Air temperature distribution throughout the interstation semi-section length: In venting single-way tunnels at the outdoor air temperature of -250С (blue dashed line) and -130С (blue dash-and-dot line); in venting two-way tunnels at the outdoor air temperature of -250С (dark-blue solid line) and -130С (dark-blue dashed line).

The Fig. 3 plots show that the mixture of outdoor and circulation air decreases to - 30С at the outdoor air temperature of -130С. In the case of extremely low outdoor air temperature of -250С, temperature at the junction of the vent shaft approaching the running-line shaft and tunnel can decrease to -120С. The station air temperatures are 12 0С and 6 0С, respectively. If the two-way subway lines are vented according to the same scheme as single-way tunnels, fresh air is fed to the tunnel through the shafts located in the center of the interstation section at the approximately equal distances from the neighboring stations, while the outgoing flow is extracted from the subway structures through the vent shafts (Fig. 4). 6

3 4

1

3

6

5 8

2

4

Station I

7

Station I

7

9 8 Fig. 4. Ventilation system for a two-way subway tunnel (1 – plenum vent shaft of the interstation section; 2 – plenum fan; 3 – station exhaust vent shaft; 4 – exhaust fan; 5 – outdoor air; 6 – exhaust air; 7 – exhaust air; 8 – train running direction; 9 – the running tunnel).

However, contrary to the case of parallel single-way tunnels where air passes through the running tunnels mainly due to the train piston effect, the main sources of draught in the two-way tunnels are fans installed in the ventilation units of the running-line and station shafts. Another difference of aerodynamics of a two-way tunnel from that of

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single-way tunnels is the absence of air (circulation) flows initiated by trains running in the opposite directions. Therefore, in subways with two-way running tunnels, air-assimilated heat is extracted together with air through the station shafts (except for heat loss into the soil surrounding the tunnel). In summer, this causes a certain decrease in the station air temperature with respect to single-way tunnel subways. In winter, the air temperature will decrease both at the air intake into the running tunnel and at the stations. In countries with hot climate with the annually mean air temperature exceeding 100С and positive winter temperature where two-way tunnels are exploited (Madrid, Rome, London, Turin), this fact provides a positive result by making it possible to reduce the amount of air fed by fans in order to support the necessary temperature regime. At the same time, calculations show that at weather conditions of Moscow and Saint Petersburg where two-way tunnels are being planned to be constructed, supplying the two-way tunnel with air having temperature equal to that of the outdoor air will cause not only freezing of the tunnel parts adjacent to the stations (which is characteristic also of relatively short single-way tunnels) but also the station temperature decrease to below zero at the outdoor temperatures inherent to the coldest five days (see Fig. 3). Thus the automatic appliance of all the engineering solutions well-proved in operating two-way tunnel subways in hot climate to meteorological conditions of Moscow and Saint Petersburg will cause violation of the station sanitary/hygienic standards and, probably, failures in the water-drainage system. Another significant disadvantage of the above-considered two-way tunnel ventilation scheme is the difficulty of activating emergency ventilation (e.g., in fire). In a standard ventilation system, the emergency venting mode is typically provided by joint operation of fans mounted in the interstation section and station shafts. As experience shows, their aerodynamic characteristics meeting the requirements of general dilution ventilation do not guarantee proper management of emergency operation. Hence, either extra fans should be installed to provide emergency ventilation or the general dilution ventilation fans should have efficiency and pressure margins. In addition, the standard ventilation scheme implies the motion of combustion products and evacuating people flow within the same space, which makes impossible preventing the influence of critical hazardous fire factors on people until their evacuation is accomplished. As a result, it becomes necessary to construct emergency exits from the interstation sections to the ground surface every 500-700 m. 3. Temperature regimes of two-way tunnels in operating modes involving alternative ventilation schemes Under the vast majority of Russian weather conditions, conventional ventilation schemes for two-way tunnels may require in winter artificial heating of outdoor air prior to feeding it into the interstation section shaft accesses. This can reduce the advantages of using two-way tunnels. A possible alternative method for increasing the temperature of air fed into the tunnel is creating artificial circulation flows as in single-way tunnels. In this case, the source of circulation is not running trains but fans mounted in the station complexes. One of the possible two-way tunnel ventilation schemes able to create artificial air circulation implies a special vent duct to be installed at the tunnel crown (false ceiling). Though such a constructive element is widely used in motor-road tunnel vent systems to remove motor transport exhaust gas and fire fumes and smoke, it has not been yet used in two-way tunnel subways both in Russia and abroad. Involving such a ventilation duct into subway ventilation systems enables creation of a circulation loop between the station and interstation section central part due to feeding warm air into the ventilation duct directly from the station. Essentially, the proposed technical solution stipulates organization in winter controllable circulation flows that will participate in the microclimate formation. At that, the circulation air and cold outdoor air may be mixed directly in the station complex, namely, in the plenum chamber. Fig. 5 presents a schematic diagram of this solution for tunnel ventilation. Cold outdoor air is fed by the fans into the plenum chamber where it is mixed with warm air coming from the station. The air flow that is a sum of the inflow and circulation air flows is directed into the vent duct and passes through it to the center of the interstation section where it is released through the tunnel and then can move in the opposite directions to the neighboring stations. While air moves through the tunnel towards stations, its temperature grows due to heat generated by moving trains and other energy sources. As a result of heat exchange with the vent duct surface, a portion of heat is transferred through the surface to the air moving in the duct. This also promotes the temperature

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growth. Thus the heat from moving trains and energy sources will be used in the proposed engineering solution for both heating the outdoor air in the station complex and its additional heating in the vent duct.

Fig. 5. Schematic diagram of the ventilation system for two-way subway running tunnels operating in winter (1 – two-way tunnel; 2 – subway stations; 3 – vent duct; 4 – exhaust ventilation shaft of the station; 5 - plenum ventilation shaft of the station; 6 – plenum fan; 7 - recirculation fan (valve); 8 – cold outdoor air; 9 – warm tunnel air; 10 – exhaust fans; 11 – inclined airway).


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10 Distance from the station, m 5

0 0

200

400

600

800

1000

-5

-10

Fig. 6. Air temperature distribution throughout the interstation semi-section in venting two-way tunnels with recirculation: For the outdoor air temperature of -250С (blue solid line – vent duct temperature, yellow dash-and-dot line – tunnel temperature) and of -130С (yellow solid line – vent duct temperature, red dotted line – tunnel temperature); the zero distance is the station position, the 1030-m distance –is the point of the vent duct air release into the tunnel).

The estimates obtained showed that utilization of partial air recirculation during the periods of low outdoor air temperatures ensures positive air temperatures at the stations even when the outdoor air temperature falls to -250С. When the outdoor air temperature is higher than -130С, air temperature in the vent duct and in the tunnel itself becomes positive. The ventilation scheme illustrated in Fig. 5 can be also realized without air circulation. In this case, the vent duct is supplied with only cold outdoor air that moves through the duct to the point of release into the tunnel, being heated due to heat exchange with the tunnel air whose temperature is higher. Fig. 7 presents the calculations of air temperature distribution in the vent duct and tunnel at the above-mentioned initial data.

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10 5

Distance from the station, m


0 0

200

400

600

800

1000

-5 -10 -15 -20 -25 -30

Fig. 7. Air temperature distribution throughout the length of the interstation semi-section in venting the two-way tunnels at the outdoor air temperature of -250С (blue solid line – vent duct temperature, yellow dash-and-dot line – tunnel temperature) and of -130С (yellow solid line – vent duct temperature, red dotted line – tunnel temperature); the zero distance is the station position, the 1030-m distance is the point of the vent duct air release into the tunnel).

Analysis of the calculations shows that temperatures meeting sanitary/hygienic requirements guarantying safe operation cannot be ensured at the stations and in a significant part of running tunnels within the temperature ranges under consideration. When the ground-surface air temperature is positive, only outdoor air is fed into the vent duct through the station ventilation shaft. The air is released into the tunnel through the open valves arranged along the tunnel length and can move after that through the tunnel towards the neighboring stations and be extracted to the ground surface by exhaust fans through the exhaust station shafts and inclined airways of the station. 4. Efficiency assessment for alternative emergency ventilation schemes of two-way tunnels. Venting of the vent duct in the emergency mode makes it possible to improve (relative to the standard ventilation scheme) the efficiency of measures for protecting the people evacuation routes against smoke arising in fire. This is possible due to removing toxic combustion products through the vent duct and plenum shaft via open valves located at the left and right from the staying flaming train that is the fire source (Fig. 8). In this case, smoke is removed only by fans related to the vent duct. The smoked tunnel zone can be limited to the section between two valves nearest to the fire source for the time period necessary to evacuate people from the tunnel, start fire localization and extinguishing, and organize sufficiently fast removal of the combustion products from the tunnel. Fig. 9 confirms this conclusion by presenting the results of calculating the fire and smoke spread dynamics with a program code [4].

Fig. 8. Schematic diagram of the subway two-way running tunnel ventilation in fire (12 – fire fumes; 13 – flaming train).


Since the smoke intake apertures equipped with valves are arranged along the vent duct at the 100-m intervals, the problem of finding the nearest to the fire source valves to be opened is not difficult. If in the interstation section of a two-way tunnel there are several moving trains simultaneously, the described antismoke ventilation system with restricted smoked zone ensures safety of the tunnel parts where trains have been stopped. The classical longitudinal ventilation scheme can hardly ensure this safety. To remove smoke directly from stations, an independent ventilation system is used, which comprises: abovetrack vent ducts equipped with valves removing smoke from the platform hall upper zone; the vestibule pressurization fans designed to create in the evacuation routes stable air flows in the direction opposite to that of people evacuation;

Fig. 9. Smoke from fire in a running tunnel for the fire durations of 600 s, 1200 s, and 3600 s.

Smoke protection screens designed to prevent the combustion product propagation from the station platform hall to the vestibules at the early stage of fire. The screens will be mounted in front of stair flights leading towards the vestibules. All these measures allow localization of the smoke layer in the station upper part. This prevents combustion product spread for the time necessary to evacuate people from the station platform hall to a safe place. The efficiency of smoke removal from stations with the proposed ventilation system has been confirmed by mathematically simulating the dynamics of fire hazardous factors propagation [4]. The simulation results are given in Fig. 10.

Fig. 10. Smoke from fire at the station in 600 s after the fire beginning.

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5. Schematic layouts of station complexes for implementing alternative ventilation schemes Contrary to historical prototypes, the station complex layouts were designed taking into account the general process engineering systems operating over the entire subway line. For instance, the station ventilation and smoke removal system is integrated into the general structure of the station space-planning solutions so as to be in the close vicinity of all the designed passenger flows, the space necessary for passengers' comfort remaining free. The specific feature of the space-planning solutions is modular character of all the station complex structures, including isolation of the station vent ducts into a separate compartment. The station layout optimization is based on clearly zoning and adapting all the spaces around the passenger zones so as to allow creation of communication ducts, shafts, and process room modules (Fig. 11). This layout solution is characterized by a number of advantages enabling impressive and balanced architectural decoration of the station. The main advantages are: - the absence of special decoration of the communication ducts and utilities on the level of platforms, passages and vestibules due to their peripheral arrangement; the fact that utilities are located beyond the passenger zones and do not hinder creation of an integral architectural and artistic compositions.

Fig. 11. Station complex layout solutions (Moscow, Saint Petersburg).

Thus, the use of a vent duct for air supply to and extraction from the tunnels allows denying of constructing ventilation units in the interstation sections and building them at the stations. If the subway line is constructed in a densely populated megapolis districts, this results in significant reduction of costs for arranging construction sites for the interstation section ventilation shafts, re-laying the utilities (electric energy supply lines, water and heat supply lines, sewerage system), compensation of environmental damage, and alienation of expensive land. According to a conservative estimate, cost saving in constructing one kilometer of a subway route free of neartunnel structures is 700 thousand rubles relative to the variant with the conventional ventilation scheme. 6. Conclusion The novel engineering solutions developed by the Research and Survey Institute "Lenmetrogiprotrans" for subway lines embodiment with two-way tunnels are based on constructing a duct mounted along the two-way tunnel length in its upper part and separated from the main cross-section with an impermeable partition.


As compared with conventional engineering solutions implying air supply into the tunnel through the interstation section ventilation shafts, the version with a vent duct in the ventilation system allows denying of installing the interstation section ventilation units, which is especially important in case of megapolis subways, enables considerable improvement (relative to the standard emergency ventilation) of the efficiency of people protection against smoke in the fire evacuation routes and of smoke removal both from the tunnel and stations, and makes it possible to heat the outdoor air by mixing with a portion of warm station air when the outdoor air temperature is lower than 150С to -100С. Layout solutions for station complexes that, contrary to historical prototypes, enable integration of the station ventilation and smoke removal systems into the general structure of the station space-planning solutions so that, being in the close vicinity of all the predicted passenger flows, they provide free space necessary for the passengers' comfort. References [1] S.G. Gendler, Thermal regimes of underground structures, LGI Publishing House, Leningrad, 1987. [2] E.M. Yushkovsky, Air circulation in the subway ventilation systems with different venting schemes. Shaft and mine ventilation. Issue 8, LGI Publishing House, Leningrad, 1981, pp 104-111. [3] V.Ya. Tsodikov, Subway ventilation and heat supply systems, Nedra, Moscow, 1975. [4] Fire Dynamic Simulation (Version 5), Technical Reference Guide. Vol. 1: Mathematical Model, NIST Special Publication 1018-5, Washington, 2007. [5] SP 131.13330.2012. Climate science in building. Revised edition of SNiP 23-01-99*(Rev. 2), Official publication, Russia Minregion, Moscow, 2012.

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