Performance-based shield tunnel longitudinal evacuation spacing toughness evaluation method

Abstract

The invention relates to a shield tunnel longitudinal evacuation interval toughness evaluation method based on performance, and the method comprises the following steps: calculating the number of people needing to be evacuated at each evacuation exit, calculating the supply rate of each evacuation exit in unit time, the personnel safety evacuation time, the residence time, the total evacuation time, and the calculation of the number of casualties. By referring to the acceptable risk number of the tunnel fire accident, when the casualty number is smaller than the acceptable risk number, the risk can be considered to be within an acceptable range, and tunnel facilities do not need to be adjusted; when the number of casualties is larger than the acceptable risk number, evacuation facilities in the tunnel need to be optimized and adjusted. The method has the beneficial effects that the limitation of the traditional static design is broken through by introducing a traffic flow wave propagation model (quantitative retention number of people) and a dynamic supply and demand matching algorithm (demand rate-supply rate time-varying analysis), and a scientific, self-adaptive and risk-controllable solution is provided for the shield tunnel evacuation exit spacing.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of tunnel evacuation risk analysis, and in particular to a performance-based evaluation method for longitudinal evacuation spacing resilience of shield tunnels. BACKGROUND

[0002] At present, the determination of the longitudinal evacuation spacing of traditional shield tunnels is mostly based on experience or simple specification requirements, lacking comprehensive consideration of various complex factors in the evacuation process. In terms of evacuation risk analysis, existing methods often only focus on a single indicator, such as only considering evacuation time, without incorporating multi-dimensional factors such as evacuation efficiency, personnel casualties, and material allocation into a unified evaluation system. This one-sided evaluation method cannot fully reflect the real performance of the tunnel evacuation system in emergency situations such as fires.

[0003] In addition, in the calculation of evacuation-related parameters such as residence time, evacuation time, and casualty number, existing technologies have the problem of insufficient precision. For residence time, the actual traffic conditions such as the number of lanes and traffic flow waves are not fully considered in the impact on vehicle congestion and personnel residence; the calculation of evacuation time also fails to accurately cover various aspects such as personnel response and crowd congestion; in the estimation of casualty number, the analysis of extreme conditions such as high-temperature smoke, toxic gas, visibility, and smoke exhaust system failure is not comprehensive enough.

[0004] Therefore, there is an urgent need to develop a research method that can comprehensively consider multi-dimensional factors, accurately evaluate the performance of shield tunnel evacuation, and scientifically determine the longitudinal evacuation spacing resilience, which is of great significance for improving the safety and emergency management level of shield tunnels. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a performance-based evaluation method for longitudinal evacuation spacing of shield tunnels, comprising the following steps:

[0006] Step 1: Calculate the number of people P to be evacuated at each evacuation port according to the number of tunnel lanes, the evacuation spacing of the tunnel longitudinal evacuation staircase, and the estimated values of the traffic state density before and after the fire, the traffic volume of the traffic state, the proportion of each type of vehicle in the congested section, the vehicle length, the number of vehicles stranded in the congested section, and the vehicle spacing. I ;

[0007]

[0008]

[0009] w - wave speed (km / h);

[0010] K1, K2 – Traffic flow density (pcu / km) before and after the fire; Q1, Q2 – Traffic flow (pcu / h) for the two traffic flow states before and after the fire, where a positive wave velocity indicates forward direction and a negative wave velocity indicates backward direction; K1 and Q1 use historical data (such as the average value of weekday morning rush hour); or assume normal traffic flow conditions through simulation models. K2 and Q2 collect congestion density and flow in real time through an emergency sensor network; or assume that the fire causes lane closures and calculate the percentage decrease in remaining lane capacity.

[0011] L—Length of traffic flow segment (km);

[0012] X m —Weighted values ​​(m) for different vehicle lengths within the tunnel;

[0013] p i —The composition ratio of the i-th type of vehicles on the congested road section; p i Based on the tunnel design traffic volume forecast, the vehicle type composition ratio for the long-term projected year is predicted based on the maximum daily average traffic volume, provided by the design unit.

[0014] n i — The length (m) of the i-th type of vehicle in the congested section;

[0015] N C —Number of vehicles stranded on the congested section of road;

[0016] J C —Distance between vehicles in congested areas (m); According to traffic safety regulations, when a motor vehicle is traveling at 60 km / h, the distance between vehicles should be 60 meters. Different vehicle speeds correspond to different distances. C .

[0017] D – Number of lanes in the tunnel;

[0018] f i —The load factor of the i-th type of vehicle (where f) i ∈(0,1], considering the most unfavorable conditions, the full load factor is taken as 1);

[0019] h i —The passenger capacity (people) of the i-th type of vehicle;

[0020] P – Number of people evacuated (persons);

[0021] P1—Number of people to be evacuated from each evacuation point;

[0022] J—Evacuation distance of the longitudinal evacuation staircase in the tunnel (m);

[0023] Step 2: Find the evacuation capacity of the evacuation opening, i.e., the flow coefficient Q, according to the width b of the tunnel design evacuation opening and the evacuation spacing J of the longitudinal evacuation stairs in the tunnel. l , calculate the number of people S supplied within the unit time t d of the evacuation opening, S = t d * b * Q l ;

[0024] According to "Fire Protection Design of Highway Underwater Tunnels", the evacuation spacing J ≤ 250 m. Through evacuation experiments, the average evacuation capacity of the stairs is 33.3 ± 4.1 people / min, and the outlet flow rate reaches the maximum in the case of a 0.8 m door width. Therefore, this invention adopts an effective width of 0.8 m, and the flow rate Ql of the evacuees passing through the evacuation opening is 0.6 people / (m·s). When the evacuation spacing and the width of the evacuation opening are determined, the number of people passing through each evacuation opening within the unit time is fixed, that is, the supply rate S of each evacuation opening within the unit time is fixed, which is equal to the product of the unit time, the width of the evacuation opening, and the flow coefficient.

[0025] Step 3: Calculate the personnel safe evacuation time T(A);

[0026]

[0027] Q —— combustion scale HRR (MW);

[0028] V —— longitudinal wind speed (m / s);

[0029] Step 4: When the number of people to be evacuated is less than the number of people supplied, calculate the residence time T (delay) , evacuation time T and casualty number R;

[0030] T (delay) = 0;

[0031]

[0032] If T ≤ T(A), then R = 0;

[0033] If t 12 ≤ T(A) < T, then R = [T ― T(A)]Q l ;

[0034] L max —— actual walking path length (m) from the farthest vehicle in the tunnel to the nearest evacuation opening;

[0035] V a —— walking speed (m / s)

[0036]

[0037] V i—— Average evacuation speed (m / s) of different personnel types;

[0038] m i —— Proportion of different personnel types;

[0039] When the number of people demanded is not less than the number of people supplied, calculate the retention time T (delay) , evacuation time T and number of casualties R;

[0040]

[0041] If T ≤ T(A), then R = 0; if t 12 ≤ T(A) < T, then R = [T ― T(A)]Ql;

[0042] Step 5, referring to the acceptable risk number of tunnel fire accidents, when the number of casualties is less than the acceptable risk number, it can be regarded that the risk is within the acceptable range and there is no need to adjust the tunnel facilities; when the number of casualties is greater than the acceptable risk number, it is necessary to optimize and adjust the evacuation facilities in the tunnel.

[0043] Preferably, optimize and adjust the spacing and quantity of evacuation exits to seek the evacuation plan with the highest evacuation efficiency and the least damage.

[0044] Preferably, in step 1, represents the number of vehicles closely arranged per kilometer of road, with the unit of pcu / km, (pcu = passenger car unit, standard vehicle equivalent number), Q1 = K1V c , V c is the speed of motor vehicles before the fire; After the fire occurs, when all lanes are completely blocked, Q2 = 0, and when some lanes are open to traffic, 1000 is the unit conversion coefficient, used to convert "headway" (unit: meter, m) to "vehicle density" (unit: pcu / km, standard vehicle equivalent number / km). Through the speed V c ’ related: Q2 = K2 × V c ’;

[0045] If the speed of motor vehicles V c ’ after the fire can be estimated (such as the speed limit of 5 - 10 km / h during evacuation), then Q2 can be deduced from K2. If it is completely blocked (V c ’ = 0), then Q2 = 0, and at this time K2 only reflects the static density.

[0046] Preferably, the formula for calculating the number of people P to be evacuated from the tunnel in step 1 is obtained through the following steps: According to the wave velocity formula of the traffic flow model, the wave velocity is expressed as the ratio of the traffic flow volume before and after the fire to the traffic flow density before and after the fire, with the unit being km / h, so the length L of the traffic flow wave section can be calculated; determine the length of various types of vehicles, the composition ratio of various types of vehicles, the distance between vehicles before and after the congested section, the number of lanes in the tunnel, the passenger capacity of various types of vehicles, and the full load coefficient, and then calculate the number of vehicles Nc stuck in the congested section caused by the traffic flow wave and the number of people P to be evacuated from the tunnel;

[0047] The wave velocity formula for the traffic flow fluid model is shown in equation (1).

[0048]

[0049] In the formula, w is the wave velocity (km / h); K1 and K2 are the traffic flow densities before and after the fire (pcu / km); Q1 and Q2 are the traffic volumes before and after the fire (pcu / h). A positive wave velocity indicates a forward direction, and a negative wave velocity indicates a backward direction.

[0050] The method for calculating the length of the traffic flow wave section is as shown in equation (2).

[0051]

[0052] The weighted average value Xm for different vehicle lengths is given by equations (3) and (4).

[0053]

[0054] In the formula, X m The weighted values ​​for different vehicle lengths within the tunnel, m; p i n represents the proportion of the i-th type of vehicles in the congested road segment; i Let m be the length of the i-th type of vehicle in the congested section.

[0055] The number of vehicles stranded on the congested section, Nc, is as shown in equation (5).

[0056]

[0057] In the formula, N C The number of vehicles stranded on the congested section of road; J C denoted as: ...

[0058] The total number of people, P, to be evacuated from the tunnel is calculated using equation (6).

[0059]

[0060] In the formula, f i Let f be the load factor of the i-th type of vehicle (where f is the load factor of the i-th type of vehicle). i ∈(0,1], considering the most unfavorable condition, the full load factor is taken as 1); h i Let p be the passenger capacity of the i-th type of vehicle, in people; i N represents the proportion of the i-th type of vehicles in the congested road segment; C The number of vehicles stranded on the congested section of road is [number].

[0061] Distribute all the people to be evacuated evenly in the tunnel, and calculate the number of people P1 to be evacuated at each evacuation point as shown in equation (7).

[0062]

[0063] In the formula, P is the total number of people to be evacuated (persons); P1 is the average number of people to be evacuated at each evacuation exit (persons); and J is the evacuation distance of the longitudinal evacuation staircases in the tunnel (m).

[0064] Preferably, the acceptable risk threshold in step 5 is obtained through the following steps: (1) Accident data collection and processing: Collect data on highway tunnel fire accidents, tunnel operating mileage and number of tunnels, and traffic accident statistics in my country, and calculate the annual mortality rate of tunnel fire accidents, the annual frequency of tunnel fire deaths, and the annual mortality rate of traffic accidents. (2) Risk aversion coefficient setting: Set different risk aversion coefficients k according to the severity of the accident. Set the risk aversion coefficient k of 1 for general and major tunnel fire accidents with 1 to 10 deaths to 1; set the risk aversion coefficient k of 2 for major and particularly serious tunnel fire accidents with 10 or more deaths to 1. Set -k as the slope of the FN curve. (3) FN curve intercept calculation: The risk threshold is used to characterize the acceptable or tolerable cumulative death frequency of tunnel fire accidents. The threshold calculation formula is as follows: In the formula, EV represents the expected average number of deaths, and N represents the number of deaths in a single tunnel fire. M This represents the upper limit of the estimated number of deaths in a single tunnel fire accident; the annual traffic accident mortality rate is used as the expected average number of deaths EV1, and the annual tunnel fire accident mortality rate is used as the expected average number of deaths EV2. (4) Construction of the FN curve: The risk threshold C is used as the intercept F of the acceptable standard curve and the tolerable standard curve in the FN curve. The formula for calculating the intercept is as follows: In the formula, F NThe frequency of accidents in a single fire accident in a tunnel where more than N people die is represented. When N=1, F1=C. The acceptable risk threshold C1 and the tolerable risk threshold C2 are the intercepts of the acceptable curve F1 and the tolerable curve F'1. Based on different risk aversion coefficients k, the acceptable risk standard curve and the tolerable risk standard curve are constructed. (5) Definition of risk area: Based on the unacceptability of the public to the consequences of particularly serious tunnel fire accidents, the consequence control value of 30 people and the consequence limit value of 100 people are set. The consequence control line and the consequence limit line are drawn. Based on the acceptable risk curve, the tolerable risk curve, the consequence control line and the consequence limit line, the acceptable risk area, the tolerable risk area and the risk reduction area (ALARP) are divided.

[0065] The beneficial effects of this invention are as follows: By introducing a traffic flow wave propagation model (quantifying the number of stranded people) and a dynamic supply and demand matching algorithm (time-varying analysis of demand rate and supply rate), this invention breaks through the limitations of traditional static design and provides a scientific, adaptive, and risk-controllable solution for the spacing of evacuation exits in shield tunnels. Attached Figure Description

[0066] Figure 1 A graph showing the relationship between the limit tolerance time and temperature in a high-temperature environment;

[0067] Figure 2 This is the F / N curve, representing the social risk standard for tunnel fires in my country. Detailed Implementation

[0068] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this disclosure.

[0069] Terminology Explanation

[0070] The dwell time refers to the time spent waiting to enter the evacuation staircase after the last evacuee in the evacuation zone arrives at the evacuation exit. Because evacuation staircases have limited capacity and narrow passageways during tunnel fires, typically only allowing one person to pass at a time, a large number of people may crowd at the evacuation exit while waiting to enter the staircase. During this waiting period, there is a high risk of injury or death due to smoke inhalation. Therefore, the dwell time at the evacuation exit is studied.

[0071] The length of a traffic flow wave segment is determined when traffic density changes due to road or traffic conditions, creating a propagation of traffic flow waves. The speed at which these vehicle waves move along the road is called the wave speed. In a tunnel, if a sudden fire occurs ahead, vehicles upstream of the fire source are forced to slow down and stop, causing subsequent vehicles to gradually slow down as well, increasing the density and creating a traffic flow wave. The length of the traffic flow wave segment is the product of the ratio of the difference in traffic volume before and after the fire to the difference in traffic density, multiplied by 60 seconds after the fire. This allows determination of the congestion length upstream of the fire in the tunnel, and the number of vehicles can be obtained based on the distribution of stranded vehicles.

[0072] Example 1

[0073] Step 1: Determine the number of people to be evacuated, P: The dwell time of the people to be evacuated is most affected by the number of lanes and the traffic wave. Calculate the length of the traffic wave segment L based on the wave speed w and wave duration, which is the congestion length of vehicles upstream of the accident. Using the vehicle length weighted average Xm, further calculate the number of vehicles Nc stranded in the congested segment caused by the traffic wave. Determine the number of people to be evacuated, P, based on passenger capacity and load factor.

[0074] Step 2: Determine the passage capacity of the evacuation exit, i.e., the flow coefficient Q, based on the designed evacuation exit width b and the evacuation spacing J of the longitudinal evacuation stairs in the tunnel. l Calculate the evacuation exit time t. d The number of people supplied within the system is S, where S = t d *b*Q l ;

[0075] Step 3: Calculate the safe evacuation time T(A);

[0076] Step 4: Calculate the number of casualties:

[0077] Analyze the impact of high-temperature smoke, toxic gases, and visibility on the human body. Taking into account extreme situations such as damage to the smoke exhaust system and free spread of smoke, if the available safe evacuation time is greater than or equal to the evacuation time, then everyone can safely pass through the evacuation exit; if the available safe evacuation time is less than the evacuation time, then some people will be unable to pass through the evacuation exit, resulting in casualties. In this case, calculate the number of casualties R.

[0078] Step 5: Establish an evacuation performance evaluation model based on supply and demand. By analyzing the model operation mode of the number of casualties, evacuation time and dwell time in the evacuation performance, the output results are quantified. Based on the F / N curve of my country's tunnel fire social risk standard, the quantified evacuation performance is compared with the risk acceptable standard. Accordingly, the spacing between tunnel evacuation exits is adjusted according to the key indicators to determine the best evacuation plan and the optimal spacing between evacuation exits.

[0079] Specifically, step 1 includes: determining the number of people to be evacuated, P.

[0080] Step 11: Inside the tunnel, a sudden fire occurs ahead, forcing vehicles upstream of the fire to slow down and stop, causing congestion for following vehicles. When traffic flow density changes due to changes in road or traffic conditions, a traffic wave propagates within the traffic flow. The speed at which this traffic wave moves along the road is called the wave speed. Based on the wave speed formula of the traffic flow model, assuming the traffic wave propagates within the road at a speed of w, we have the following equation:

[0081]

[0082] In the formula, w is the wave speed, km / h; K1 and K2 are the traffic flow density before and after the fire, pcu / km; Q1 and Q2 are the traffic flow rates before and after the fire, pcu / h.

[0083] A positive wave velocity indicates a forward direction, while a negative wave velocity indicates a backward direction.

[0084] This represents the number of closely packed vehicles per kilometer of road, expressed in pcu / km (pcu = passenger car unit, standard vehicle equivalent). Q1 = K1V c V c The speed of the vehicle before the fire; When all lanes are completely blocked after a fire, Q2 = 0; when some lanes are open to traffic, 1000 is a unit conversion factor used to convert "vehicle headway" (unit: meters, m) to "vehicle density" (unit: pcu / km, standard vehicle equivalents / km). This is based on the vehicle speed V. c 'Relationship: Q2 = K2 × V' c ';

[0085] If the speed of the motor vehicle after the fire is V c If the speed limit during evacuation is 5-10 km / h, then Q2 can be calculated from K2. If there is a complete blockage (V... c If '=0), then Q2=0, and at this time K2 only reflects the static density.

[0086] Step 12: According to the "Highway Tunnel Design Code, Volume II: Traffic Engineering and Ancillary Facilities," the response time of fire detectors in tunnels should not exceed 60 seconds. Assume that the detectors alarm 60 seconds after a fire occurs, the tunnel entrance closes, and vehicles continue to enter during this period, causing increased vehicle density and extreme road congestion within the 60-second traffic flow segment. After 60 seconds, vehicles can no longer enter, the traffic flow stops, and vehicle speed returns to zero. Calculate the length L of the traffic flow segment based on the wave velocity w and the wave duration.

[0087]

[0088] In the formula, L is the length of the traffic flow wave section, in km.

[0089] Step 13: Based on the length of the traffic flow wave segment, determine the length of the traffic congestion upstream of the accident after the fire, take the weighted average Xm for different vehicle lengths, and obtain the number of vehicles in the wave segment based on the distribution of vehicle congestion, etc.

[0090]

[0091] In the formula, Xm is the weighted value for different vehicle lengths within the tunnel, in meters (m); p i n represents the proportion of the i-th type of vehicles in the congested road segment; i Let m be the length of the i-th type of vehicle in the congested section.

[0092] This study considers the different driving conditions of vehicles within the tunnel and predicts the vehicle ratio based on the tunnel's purpose. According to the "Terminology and Definitions for Motor Vehicles and Trailers" and the "Chinese Vehicle Classification Standard," the dimensions and passenger capacity of different vehicle types are specified. Relevant data is shown in Table 1 below.

[0093] Table 1 Classification of Vehicle Sizes in Tunnels

[0094]

[0095] Step 14: Given the weighted average length Xm of different vehicle types and different vehicle proportions, the number of vehicles Nc stranded in the congested section caused by traffic flow can be calculated.

[0096]

[0097] In the formula, N C The number of vehicles stranded on the congested section of road; J C denoted as: ...

[0098] Step 15: The number of people to be evacuated from the tunnel is related to the passenger capacity and load factor of different types of vehicles. Therefore, the number of people to be evacuated from the tunnel, P, is:

[0099]

[0100] In the formula, fi is the load factor of the i-th type of vehicle (where fi∈(0,1], and the load factor is taken as 1 under the most unfavorable conditions); hi is the passenger capacity of the i-th type of vehicle, in people; N C Let pi be the number of vehicles stranded on the congested road section; pi is the proportion of the i-th type of vehicles in the congested road section.

[0101] Step 2: Determine the passage capacity of the evacuation exit, i.e., the flow coefficient Q, based on the designed evacuation exit width b and the evacuation spacing J of the longitudinal evacuation staircases in the tunnel. l Calculate the evacuation exit time t. d The number of people supplied within the system is S, where S = t d *b*Q l

[0102] Calculate arrival rate

[0103] The arrival time of evacuees at the evacuation exit is calculated from a micro perspective, divided into 30-second intervals, to determine the number of people entering the evacuation exit in each time period, i.e., the arrival rate (considered as the demand rate). The number of people allowed to evacuate per unit time at the evacuation exit is the supply rate, which is affected by the exit width and evacuation distance.

[0104] According to the "Fire Protection Design of Underwater Highway Tunnels", the spacing between evacuation exits L ≤ 250m. Evacuation experiments showed that the average evacuation capacity of the staircase is 33.3 ± 4.1 people / min, with the maximum flow velocity at the exit when the door width is 0.8m. Therefore, this invention uses an effective width of 0.8m, resulting in a flow rate of 0.6 people / s through the evacuation exit.

[0105] Specifically, step 2 includes: determining the number of people to be evacuated, P1, and then calculating the number of people allowed to be evacuated per unit time at the evacuation point as the supply number.

[0106] Referring to the evacuation time calculation method for the building center and Saburo Horiuchi in the Japanese evacuation time algorithm, the evacuation time T1 is calculated as follows:

[0107] T1 = Max(t) 11 ,t 12 (7)

[0108]

[0109] In the formula, T1 is the evacuation time, in seconds; t 11 The time for all evacuees to queue through the evacuation exit, s;t 12 The time it takes for the evacuee furthest from the evacuation exit to reach the exit is s; P is the number of evacuees, people; w is the effective width of the evacuation exit, m; L X+Y denoted as walking distance (m), and v as the average speed of evacuees (m / s). The formula uses 1.5 as the flow coefficient, derived experimentally. X and Y are the lateral and longitudinal components of the evacuee's position in the building's planar coordinate system.

[0110] The above formula may have two possible outcomes, as shown in Table 2:

[0111] ①t 11 >t 12When the time it takes for all evacuees to queue through the evacuation exit is greater than the time it takes for the evacuee furthest from the exit to reach it, the evacuation time should be taken as t. 11 That is, T1 = t 11 ;

[0112] ①t 11 <t 12 If the time taken for all evacuees to queue through the evacuation exit is less than the time taken for the evacuee furthest from the exit to reach it, then the evacuation time should be taken as t. 12 That is, T1 = t 12 .

[0113] Table 2 Evacuation Time Scenarios and Physical Significance

[0114]

[0115] Saburo Horiuchi's calculation method only considers t 11 >t 12 In the case of t 12 The refugee furthest from the evacuation exit reaches the evacuation exit, which implies that at this point there are already (1.5∑w×t) 12 After the evacuation of 1,500 people, there are still (P-1.5∑w×t) remaining. 12 Since 1,000 people are blocking the evacuation exit and waiting, the remaining time for these people to complete the evacuation is P(P-1.5∑w×t). 12 ) / 1.5∑w seconds.

[0116] This invention studies shield tunnels where, due to the lack of lateral evacuation routes and the distance between evacuation exits exceeding 100 meters, evacuees can only escape via longitudinal staircases. During traffic flow, passengers disembark and proceed to the nearest evacuation exit. For efficient calculation, all evacuees (P) are evenly distributed throughout the tunnel to determine the number of people (P) requiring evacuation at each exit. I .

[0117]

[0118] In the formula, P represents the total number of people to be evacuated; P I J represents the average number of people to be evacuated from each evacuation exit (in people); J represents the evacuation distance of the longitudinal evacuation staircases in the tunnel (in meters).

[0119] Specifically, step 3 includes: calculating the safe evacuation time T(A).

[0120] Based on a comprehensive review of numerous authoritative research papers and accident investigation reports, the primary cause of casualties in fires is not burns from flames or extreme temperatures, but rather two fatal factors: first, the inhalation of large amounts of toxic gases released during combustion, leading to suffocation and respiratory system damage; and second, the intense heat radiation at the fire scene causing rapid heat loss and hypothermia. In tunnel fires, temperature, visibility, and toxic gases are all significant factors affecting safe evacuation. Understanding these factors helps determine whether safe evacuation is possible.

[0121] Step 31: The effects of high-temperature flue gas on the human body:

[0122] Fire is essentially an exothermic chemical reaction, inevitably leading to a rise in ambient temperature. The high temperatures in a fire can cause physical exhaustion, panic, and limited mobility in evacuees, consuming a significant amount of energy. If drastic temperature changes exceed the human body's tolerance limits, it will seriously threaten their lives and health. Granee provided the relationship between the maximum tolerance time for healthy men in high-temperature environments and temperature; Zhou Yongdi modified this formula based on the influence of air humidity and individual differences in tolerance.

[0123]

[0124] In the formula: t is the limit tolerance time, min; Tk is the air temperature, °C.

[0125] Line graph of extreme tolerance time versus temperature in high-temperature environments, such as... Figure 1 As shown.

[0126] Step 32, The effects of toxic gases on the human body:

[0127] The smoke produced by a fire is complex in composition, typically containing CO, CO2, HCN, NO2, NH3, etc. Among them, CO is the most dangerous. When CO combines with more than 50% of the hemoglobin in the blood, it causes severe hypoxia in the brain and central nervous system. Even if a lethal concentration is not inhaled, hypoxia can cause headaches and weakness, restricting movement and making it difficult to escape the fire, as shown in Table 3.

[0128] Table 3 CO concentration and exposure symptoms

[0129]

[0130] Step 33: The Impact of Visibility on the Human Body: After a fire breaks out, due to the special structure of tunnels, smoke is difficult to expel, and its accumulation and diffusion significantly reduce visibility. This not only slows down the evacuation speed and makes people easily disoriented, but also exacerbates psychological stress, causing panic and chaos, forcing evacuees to proceed cautiously to avoid collisions with obstacles or falling into dangerous areas. According to standards, if visibility at eye level along an evacuation route is less than 10 meters during a fire, it is considered a dangerous situation, as shown in Table 4.

[0131] Table 4 Personnel visibility limit

[0132]

[0133] Step 34. Calculate the available safe evacuation time for a fire based on the influence of temperature, visibility, and toxic gases:

[0134] The available safe evacuation time refers to the time window during which environmental conditions can still ensure the safe evacuation of personnel from the occurrence of a fire until they are evacuated to a safe location. It is affected by various factors, but after the tunnel is opened and in operation, this time value is fixed.

[0135] T(A) = G(Q, V, i, L.pcu, O) (12)

[0136] Where: T(A) is the available safe evacuation time, s; Q is the combustion scale HRR, MW; V is the longitudinal wind speed, m / s; i is the longitudinal slope of the tunnel; L is the number of lanes; pcu is the traffic volume; O is the management level.

[0137] In the case of a tunnel fire, temperature, visibility, and toxic gases significantly affect the safe evacuation of personnel. Among them, the fire combustion scale HRR and the longitudinal wind speed V have the most crucial impact on the available safe time for a tunnel fire. When evaluating the evacuation plan in this invention, extreme situations are considered, that is, the smoke exhaust system in the tunnel is damaged and the smoke spreads freely. Since the vehicles downstream of the accident point can quickly drive out of the tunnel, while the personnel in the upstream vehicles need to get off and go to the evacuation exits for evacuation, other factors affecting the available safe time can be comprehensively considered in the fire combustion scale HRR and the longitudinal wind speed V. Therefore, the available safe evacuation time T(A) can be characterized as follows:

[0138]

[0139] Specifically, step 4 includes:

[0140] Step 41. The number of people to be evacuated is less than the number of people provided,

[0141] The residence time T (delay) = 0;

[0142] The evacuation time

[0143] If T ≤ T(A), then the number of casualties R = 0;

[0144] If t 12 ≤ T(A) < T, then the number of casualties R = [T - T(A)]Q l ;

[0145] Where L max — The actual walking path length (m) from the farthest vehicle in the tunnel to the nearest evacuation exit; Va —Walking speed (m / s); Vi—Average evacuation speed (m / s) for different personnel types; m i —Percentage of different personnel types;

[0146] Step 42: When the number of people to be evacuated is not less than the number of people supplied,

[0147] Duration of stay

[0148] Based on the US NFPA 130 standard, the UK SFPE Handbook recommendations, and the age distribution of the urban population in different countries, the evacuation speed and proportion values ​​for different personnel types are shown in Table 5, thus yielding the average evacuation speed v:

[0149] Table 5. Proportion of Different Types of Personnel and Evacuation Speed

[0150]

[0151]

[0152] In the formula, Vi represents the average evacuation speed (m / s) for different personnel types; m i The percentage of different personnel types.

[0153] Based on the characteristics of tunnel fire evacuation, the evacuation time T in a shield tunnel is divided into two parts: one is the time t taken for the evacuee furthest from the evacuation exit to disembark and reach the longitudinal evacuation staircase of the shield tunnel. 12 Secondly, the time t that the evacuee spent waiting at the evacuation exit to enter the evacuation staircase due to the large number of evacuees and congestion was significant. 13 That is, the evacuation time T1 of the shield tunnel is:

[0154] T1 = t 12 +t 13 (15)

[0155]

[0156] In the formula, T1 is the evacuation time of the shield tunnel, in seconds; t 12 The time s;t is the time it takes for the evacuee furthest from the evacuation exit to reach it. 13 For the time it takes for stranded personnel to enter the evacuation staircase, s; Q l Flow coefficient (evacuation exit capacity), people / second; L max , where is the actual walking path length from the farthest vehicle in the tunnel to the nearest evacuation exit, in meters; v is the average speed of evacuees, in meters per second.

[0157] Since people do not start evacuating immediately when a fire breaks out and most will experience confused and panicked reactions, the required evacuation time TRSET for people to evacuate generally includes three stages: T alarm 、T response and T move . Therefore, on this basis, the evacuation time should also add T alarm 、T response . It has been proposed in the previous text that the response time of the fire detector in the tunnel should not be greater than 60s. Therefore, T alarm is taken as 60s; According to the "SFPE Fire Protection Engineering Handbook" in the United States, after people perceive the occurrence of a fire and have various instinctive reactions, there will be a certain delay in the time to start evacuating, as shown in Table 6:

[0158] Table 6 Evacuation start delay time T response

[0159]

[0160] There is a fire automatic alarm system installed in the shield tunnel. Therefore, the type of the alarm system is W1. The evacuating personnel are in a sober state but are not familiar with the building, evacuation measures, etc. Therefore, Tresponse is taken as 120s, and Talarm + Tresponse = 180s.

[0161] Total evacuation time

[0162] If T ≤ T(A), then the number of casualties R = 0;

[0163] If t 12 ≤ T(A) < T, then the number of casualties R = [T - T(A)]Q l ;

[0164] Specifically, step 5 includes:

[0165] The steps of constructing the acceptable standard curve include:

[0166] ① Interval of 1 - 10 people (general and relatively large accidents): According to the expected value EV1 of the acceptable average number of deaths and the accident cumulative frequency formula, calculate the acceptable risk threshold C1, which is used as the intercept F1 of the acceptable standard curve. Based on the risk aversion coefficient k = 1, determine the slope of the acceptable curve to be -1, and complete the construction;

[0167] ② Interval of 10 - 100 people (major and especially major accidents): According to the acceptable standard curve in the interval of 1 - 10 people, calculate the accident cumulative frequency F10 when the number of deaths is 10. Based on the risk aversion coefficient k = 2, determine the slope of the acceptable curve to be -2, and complete the construction;

[0168] The steps of constructing the tolerable standard curve include:

[0169] ① 1-10 people range (general and major accidents): Based on the expected average number of tolerable deaths EV2 and the accident cumulative frequency formula, the acceptable risk threshold C2 is calculated and used as the intercept F'1 of the tolerable standard curve. Based on the risk aversion coefficient k=1, the slope of the acceptable curve is determined to be -1, and the construction is completed.

[0170] ② 10-100 people range (major and extremely serious accidents): Calculate the cumulative frequency F'10 of accidents with 10 deaths based on the tolerable standard curve for the 1-10 people range, and determine the slope of the tolerable curve to be -2 based on the risk aversion coefficient k=2, thus completing the construction.

[0171] The risk areas are specifically divided as follows:

[0172] (1) Acceptable risk area: including the area enclosed by the acceptable risk curve, the horizontal and vertical coordinate axes and the consequence control line, located to the left of the consequence control line;

[0173] (2) Risk Minimum Area (ALARP): The area enclosed by the acceptable risk curve, the tolerable risk curve, the vertical axis, and the consequence control line, located to the left of the consequence control line;

[0174] (3) Unacceptable risk area: The area above the risk tolerance curve;

[0175] (4) Key risk monitoring area: The area enclosed by the acceptable risk curve and the consequence control line, located to the right of the consequence control line;

[0176] (5) Key risk control area: The area enclosed by the acceptable curve of major and particularly serious accident risk, the tolerable curve of major and particularly serious accident risk, the consequence control line and the consequence limit line, located between the consequence control line and the consequence limit line.

[0177] This invention derives an evacuation performance evaluation model through supply and demand analysis. By analyzing different evacuation plans, the time required to evacuate all people to be evacuated and the casualty situation are obtained. Based on this, the evacuation performance is evaluated, and the optimal evacuation plan and the optimal distance between evacuation exits are determined.

[0178] In tunnel fires, evacuation staircases are crucial facilities for ensuring the safe escape of personnel. To ensure that the evacuation plan is reasonable and effective, the location of the fire is considered to be the midpoint of the tunnel section, and the number of available evacuation staircases is determined accordingly.

[0179] After the incident, vehicles downstream of the fire source could leave, but vehicles upstream were delayed due to the fire obstructing traffic flow. Therefore, an assessment and evacuation plan was developed for personnel within the upstream band of the incident site.

[0180] Considering the different driving conditions of vehicles in the tunnel, the proportion of vehicles can be predicted according to the purpose of the tunnel. Based on the proportion of vehicles and passenger capacity in the tunnel, the number of people to be evacuated in the tunnel can be calculated by formula.

[0181] The arrival time of evacuees at the evacuation exit is calculated from a micro perspective, divided into 30-second intervals, to determine the number of people entering the evacuation exit in each time period, i.e., the arrival rate (considered as the demand rate). The number of people allowed to evacuate per unit time at the evacuation exit is the supply rate, which is affected by the exit width and evacuation distance.

[0182] According to the "Fire Protection Design of Underwater Tunnels for Highways," the spacing between evacuation exits J ≤ 250m. Evacuation experiments showed that the average evacuation capacity of the staircase is 33.3 ± 4.1 people / min, with the maximum flow velocity at the exit when the door width is 0.8m. Therefore, this invention adopts an effective width of 0.8m, resulting in a flow rate of 0.6 people / s through the evacuation exit.

[0183] The total evacuation time is analyzed using supply and demand, which is the time it takes for all personnel within the traffic flow band to evacuate to the evacuation staircase. The capacity of the evacuation exits is considered as supply, and the personnel arrival rate is considered as demand, thus utilizing the demand rate and supply rate analysis.

[0184] When evaluating evacuation plans for tunnel fires, the primary consideration is to minimize the number of casualties. Since the number of casualties is closely related to evacuation time, the shorter the evacuation time, the fewer the number of casualties. Therefore, evacuation time performance is the second consideration, and the dwell time is the third consideration. Finally, by combining these factors, the best evacuation plan is evaluated.

[0185] Based on the acceptable risk standard and social risk, Wang Qirui proposed an acceptable standard definition for the social risk of tunnel fires: within the current construction and operation level of the tunnel industry and the framework of fire safety policies and regulations, and on the premise of aligning with the safety objectives of decision-making departments and the public's willingness to accept risk, the frequency and consequence thresholds of tunnel fire fatalities are formulated. Based on this, an F / N curve for my country's tunnel fire social risk standard is constructed, as shown in the figure. Figure 2 As shown, it adopts a combination of objective risk statistical analysis and subjective risk perception survey. Based on the F / N curve initially constructed based on accident statistics and risk perception survey, the starting point of the F / N curve is set as 1 death, and the acceptable intercept is determined to be 10. -5 This means that the maximum acceptable frequency of tunnel fires resulting in one or more deaths per kilometer of tunnel per year is 10. -5 The consequences of 30 deaths are set as the control threshold for the F / N curve. Based on this, key monitoring areas and key control areas are established on the basis of the acceptable risk area and the ALARP area. The consequences of 100 deaths are set as the limit threshold for the F / N curve. Once the number of deaths exceeds 100, the risk will be intolerable.

[0186] In practical applications, referring to the standard that the acceptable number of casualties in a tunnel fire accident is 30 people, when the number of casualties is less than 30, the risk is within an acceptable range and no adjustment to the tunnel facilities is required; when the number of casualties is greater than 30, the evacuation facilities in the tunnel need to be optimized and adjusted, such as reducing the spacing between the tunnel evacuation staircases and increasing the number of evacuation exits, so as to effectively divert the evacuation of people and thus significantly reduce the evacuation pressure on each tunnel entrance.

[0187] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A performance-based evaluation method for longitudinal evacuation spacing of shield tunnels, characterized in that, The method comprises the following steps: step 1, calculating the number of people P to be evacuated at each evacuation port I ; K1, K2 are the density of traffic flow before and after the fire, pcu / km; Q1, Q2 are the traffic flow of the two traffic flow states before and after the fire, pcu / h; p i is the proportion of the i-th type of vehicle constituting the blocked road section; n i is the length of the i-th type of vehicle constituting the blocked road section; J C is the distance between vehicles before and after the congestion road section, which is a safe driving distance selected according to the vehicle speed; D is the number of lanes in the tunnel; f i is the full load factor of the ith type of vehicle, taken as 1;h i is the passenger capacity of the ith type of vehicle; J is the evacuation spacing of the longitudinal evacuation stair of the tunnel; Step 2, according to the tunnel design evacuation port width b and the evacuation spacing J of the longitudinal evacuation stair of the tunnel, find the evacuation port traffic capacity, i.e. the flow coefficient Q l , calculate the number of people S supplied by the evacuation port in unit time t d , S=t d *b*Q l ; Step 3, calculate the occupant safety evacuation time T(A); Q is the fire size HRR; Step 4, when the number of people to evacuate is less than the number of people to be supplied, calculate the remaining time T (delay) , evacuation time T and the number of casualties R; T (delay) = 0; If T < T(A), then R = 0; if T(A) < T < T, then R = [T - T(A)]Q 12 l ;​ L max is the actual walking path length from the farthest vehicle in the tunnel to the nearest exit; V a is the walking speed; V i is the average horizontal evacuation speed of different personnel types; m i is the proportion of different personnel types; When the number of people to be evacuated is not less than the number of people to be supplied, the remaining time T is calculated (delay) , the evacuation time T, and the number of casualties R. If T < T(A), then R = 0; if T(A) < T < T, then R = [T - T(A)]Q 12 l ;​ Step 5, when the number of casualties is greater than the acceptable risk number, the evacuation facilities in the tunnel need to be optimized and adjusted, otherwise, the tunnel facilities do not need to be adjusted.

2. The method of claim 1, wherein, S = 30 * 0.8 * Q l .

3. The method of claim 1, wherein, In step 1, represents the number of closely arranged vehicles per kilometer of road, Q1=K1V c , V c is the speed of motor vehicles before the fire; After the fire, when all lanes are completely blocked, Q2=0, when some lanes are open, J C is the distance between vehicles before and after the congested section.

4. The method of claim 1, wherein, Step 5, the acceptable risk threshold is obtained by the following steps: (1) Accident data collection and processing: Collect highway tunnel fire accident data, tunnel operation mileage and tunnel operation quantity data, and traffic accident statistical data, calculate the tunnel fire accident annual mortality rate, the tunnel fire accident annual frequency and the traffic accident annual mortality rate; (2) Risk aversion coefficient setting: According to the severity of the accident, set different risk aversion coefficients k, set the risk aversion coefficient k corresponding to the general and larger tunnel fire accidents with the number of deaths between 1 and less than 10 as 1; Set the risk aversion coefficient k corresponding to the major and especially major tunnel fire accidents with the number of deaths of 10 and above as 2, and set-k as the slope of the F-N curve; (3) F-N curve intercept calculation: the risk threshold is used to represent the acceptable or tolerable cumulative death frequency of tunnel fire accidents, and the threshold calculation formula is In the formula, EV represents the expected value of the average number of deaths, N represents the number of deaths in a single tunnel fire accident, and N M represents the estimated upper limit value of the number of deaths in a single tunnel fire accident. Take the traffic accident annual mortality rate as the expected value EV1 of the acceptable average number of deaths, and take the tunnel fire accident annual mortality rate as the expected value EV2 of the tolerable average number of deaths. (4) F-N curve construction: the risk threshold C is taken as the intercept F of the acceptable standard curve and the tolerable standard curve in the F-N curve, and the calculation formula of the intercept is In the formula, F N represents the frequency of accidents with N or more deaths in a single fire accident tunnel, when N = 1, F1 = C, the acceptable risk threshold C1 and the tolerable risk threshold C2 are the intercept F1 of the acceptable curve and the intercept F'1 of the tolerable curve, and the risk acceptable standard curve and the risk tolerable standard curve are constructed according to different risk aversion coefficients k. (5) Risk area definition: According to the public's unacceptable consequences of especially major tunnel fire accidents, set the consequence control value to 30 and the consequence limit value to 100, draw the consequence control line and the consequence limit line, and divide the risk acceptable area, the tolerable area and the risk as low as possible area according to the risk acceptable curve, the risk tolerable curve, the consequence control line and the consequence limit line.

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