A systematic approach to radon shielding construction in underground projects

Abstract

The present invention discloses a systematic method for radon shielding construction of underground projects, including survey, diagnosis, test, construction, acceptance, and maintenance stages; through on-site survey and measurement of the internal dimensions of the underground project, the original radon exhalation rate, and the background radon concentration of the external environment; setting the target radon concentration of the underground project, estimating the target radon exhalation rate; calculating the radon shielding efficiency target value of the anti-radon layer, and determining the construction plan; carrying out experimental construction on the wall of a local area of ​​the underground project according to the construction plan; carrying out comprehensive construction according to the construction plan; conducting an overall verification of the radon shielding effect of the underground project, and if the overall verification is unqualified, it is necessary to conduct a local verification of the radon shielding effect of the underground project; formulating the engineering use instructions and maintenance plan. The embodiment of the present invention carries out full-process planning of the entire radon shielding project, and optimizes the construction plan through on-site survey and testing, thereby realizing the scientificity, systematicness, and effectiveness of radon shielding of underground projects.

Description

Technical Field

[0001] The present invention relates to the field of radiation protection and environmental protection, and more specifically to a systematic method for radon shielding construction in underground engineering. Background Art

[0002] radon( 222 Rn) is a radioactive inert gas that mainly comes from the surrounding materials. 238 The decay products of U are: 226 Ra, 226 The radon formed by Ra decay is continuously released from the pores of the material into the surrounding air in the form of gas. 218 Po and 214 Po will combine with tiny particles in the air in solid form. When these particles are inhaled into the human body, they will stay in the lung tissue for a long time. 218 Po and 214 Po is a short-lived daughter. The radiation dose generated by their continuous decay can easily cause canceration of lung tissue cells, ultimately leading to lung cancer.

[0003] Underground projects are often surrounded by mountain rocks and soil. 226 Radon formed by Ra decay escapes into the surrounding air through cracks and gaps, which is the main reason for the increase of radon concentration in the air of underground projects. Underground projects are generally several meters or even hundreds of meters deep underground, surrounded by rock mass, and accompanied by a large amount of groundwater leakage. This relatively closed and humid environment is very easy to form radon accumulation, and the rock mass itself has a high radon precipitation, which makes the radon concentration inside underground projects much higher than that of general indoor environments. Studies have shown that the annual average radon concentration of 243 underground projects in the country is as high as 2482Bq·m -3 , of which more than 200 Bq·m -3 27% of the total -3 When measuring the radon concentration in 12 national defense projects in my country, it was found that the average radon concentration was 2702 Bq·m -3 , up to 5000Bq·m -3 , which is the national control standard 400Bq·m -3 The high radon environment in underground projects poses a huge threat to the health of internal workers. Therefore, it is necessary to carry out research related to the management of high radon environment in underground projects.

[0004] The "Control Requirements for Indoor Radon and Its Progeny" (GB / T 16146-2015) recommends that indoor radon concentrations above 300 Bq·m -3Radon shielding measures, including shielding radon sources, should be considered; when the indoor radon concentration is higher than 1000 Bq·m -3 It is recommended to take permanent radon reduction measures, such as shielding radon sources and foundation modification. The Technical Code for Radon Prevention and Control in Civil Buildings (JGJ / T349-2015) clearly states that indoor radon concentrations above 400 Bq·m -3 When the radon concentration is high, measures such as strengthening natural ventilation or mechanical ventilation, shielding radon sources (anti-radon coatings) should be taken to reduce the radon concentration.

[0005] Shielding radon sources means covering the inner surface of the entire enclosure wall of the underground project with one or more layers of radon-proof materials to cut off all ways for radon to enter the internal space of the project from the rock mass. This is an effective way to solve the problem of radon entry from the source. If the radon source shielding of underground projects is to achieve a better shielding effect, the entire enclosure wall needs to be wrapped for protection. The project is large in quantity and high in cost. Therefore, it is necessary to verify the radon-proof effect of the construction plan before large-scale construction.

[0006] The prior art includes methods for designing and testing construction technology for underground coating anti-radon projects in an integrated "detection-diagnosis-control" mode, as well as design plans for underground radon gas protection rooms, involving the selection, use, construction methods and radon concentration monitoring of anti-radon materials, and the linkage control of radon content detection systems and fresh air systems to reduce radon concentrations in underground projects.

[0007] However, most radon shielding plans are limited to describing the construction technology, process and post-construction acceptance of radon shielding. The formulation of construction technology lacks data support, and there is little consideration of optimizing and verifying the construction technology before large-scale construction. The construction plan is not systematic and is prone to problems such as poor radon reduction effect or excessive project cost, which need to be solved urgently. Summary of the invention

[0008] In order to reduce the construction risk of underground engineering radon shielding projects, improve the overall efficiency of engineering construction, and reduce construction costs while ensuring the radon reduction effect of the project, the present invention provides a systematic method for underground engineering radon shielding construction.

[0009] In order to achieve the above object, the present invention comprises the following steps:

[0010] S1. Survey phase

[0011] On-site survey of the concrete support of underground projects, measurement of the structural dimensions of underground projects, and point-by-point measurement of the original radon exhalation rate of underground project walls and the background radon concentration of the external environment;

[0012] S2. Diagnosis stage

[0013] Set the target radon concentration for underground projects and estimate the target radon exhalation rate;

[0014] Calculating a target value of radon shielding efficiency of the anti-radon layer based on the estimated value of the target radon exhalation rate and the measured value of the original radon exhalation rate;

[0015] Determining a first construction plan according to the radon shielding efficiency target value, the concrete support conditions and the size of the underground engineering structure;

[0016] S3. Experimental Phase

[0017] Carry out experimental construction on the walls of local areas of the underground project according to the first construction plan Carry out experimental construction on the walls of local areas of the underground project according to the construction plan;

[0018] Measuring the radon exhalation rate of the wall after the experimental construction, and comparing the measurement result with the target radon exhalation rate;

[0019] If the measurement result is not greater than the target radon exhalation rate, the first construction plan is the final construction plan;

[0020] If the measurement result is greater than the target radon exhalation rate, the first construction plan is optimized until the experimental construction and verification are repeated and the measurement satisfies that the radon exhalation rate is not greater than the target radon exhalation rate, and a second construction plan is formed as the final construction plan;

[0021] S4. Construction phase

[0022] Carry out comprehensive construction of the underground project in accordance with the final construction plan that meets the requirements;

[0023] S5. Acceptance stage

[0024] After the construction is completed, the radon shielding effect of the radon shielding project shall be verified, including overall verification and local verification;

[0025] Verify the radon shielding effect of the underground project as a whole, select several representative rooms or areas in the underground project, use a radon detector to measure the radon concentration, and compare it with the target radon concentration;

[0026] If the measured value is not greater than the target radon concentration, the overall verification is qualified; and there is no need to conduct local verification of the radon shielding effect of the underground project;

[0027] If the measured value is greater than the target radon concentration, the overall verification fails; local verification of the radon shielding effect of the underground project is required;

[0028] S6. Maintenance phase

[0029] According to the final construction plan, formulate the engineering operating instructions and maintenance plan, distribute them to the user unit, and coordinate with the construction party to carry out subsequent maintenance work.

[0030] Furthermore, the radon exhalation rate is measured by:

[0031] A radon collecting cover is placed on the surface to be tested and the four sides of the radon collecting cover are sealed. After the radon collecting cover is sealed, the mathematical model of the radon concentration change in its internal space is expressed by the following formula:

[0032]

[0033] Where: C(t) is the radon concentration at time t, Bq·m -3 ; J0 is the radon exhalation rate of the surface to be tested, Bq·m -2 ·h -1 ; h is the depth of the radon hood, m; V is the volume of the radon hood, m 3 ;K is the leakage rate of radon in the radon collecting hood, which is regarded as a constant, Bq·h -1 When the radon in the external environment leaks into the radon collecting cover, K is a positive number. When the radon in the radon collecting cover leaks into the external environment, K is a negative number. λ is the decay constant of radon, λ=0.00756h -1 ;

[0034] The initial conditions of the experiment are: at t = 0, C(t = 0) = C0; C0 is the initial radon concentration in the radon collecting hood, hereinafter referred to as the initial radon concentration, Bq·m -3 ; Substituting the initial conditions into equation (1), we can obtain:

[0035]

[0036] Let J represent the measured surface radon exhalation rate of the surface to be measured, Bq·m -2 ·h -1 , expressed as:

[0037]

[0038] When the sealing performance of the radon collecting cover is good, the radon leakage rate K in the radon collecting cover can be ignored; the radon exhalation rate J of the surface to be measured is replaced by the measured radon exhalation rate J0, and substituted into formula (2), the result is:

[0039]

[0040] Use the equal time interval method, that is, measure the radon concentration once at the same interval; obtain the radon concentration measurement data C at each fixed interval i and its corresponding uncertainty σ i , use the least squares method to get the measured radon exhalation rate J:

[0041]

[0042] Furthermore, the target radon exhalation rate is estimated by:

[0043] The indoor radon concentration change model is expressed by the following formula:

[0044]

[0045] Where: C(t) is the radon concentration at time t, Bq·m -3 ; C b is the background radon concentration in outdoor air, Bq·m -3 ; J is the surface radon exhalation rate of the inner surface of the room wall, hereinafter referred to as radon exhalation rate, Bq·m -2 ·h -1 ;λ is the decay constant of radon,λ=0.00756h -1 ; S is the radon release surface area, m 2 ; V is the free space volume for indoor radon to diffuse freely, m 3 ; R is the ratio of fresh air volume to free space volume per unit time, expressed as the number of air changes per unit time, h -1 ; D is the reverse diffusion coefficient of indoor radon, which refers to the coefficient of indoor air radon diffusion into the wall, h -1 ;

[0046] Assume that the initial indoor radon concentration is C a , Bq·m -3 ; e Defined as the equivalent decay constant, λ e =λ+R+D,h -1 ; Formula (5) is solved to get:

[0047]

[0048] After the preset time, the increase and decrease of indoor radon concentration will be equal, and the indoor radon concentration will remain at a stable level, which is called stable radon concentration C. stable , the radon concentration is the stable radon concentration; that is, t→∞, the stable radon concentration C is obtained from formula (6): stable The calculation formula is:

[0049]

[0050] The influence of radon's own decay and its own back-diffusion effect on the indoor radon concentration is ignored; therefore, λ e =λ+R+D≈R; Formula (7) is simplified to:

[0051]

[0052] After the radon shielding project is completed, the target radon concentration of the underground project under the normal operation of the ventilation system is set to Cm ; According to formula (8), C m It is expressed as:

[0053]

[0054] In the formula, R m It represents the air change rate of underground engineering under normal operation of ventilation system, h -1 ; J m is the target radon exhalation rate, Bq·m -2 ·h -1 ; C' b is the background radon concentration of the external environment of the underground project, Bq·m -3 ;

[0055] The target radon exhalation rate J is obtained by solving formula (9): m The estimation formula is:

[0056]

[0057] J m is the estimated result of the target radon exhalation rate.

[0058] Furthermore, the radon shielding effect of the underground project is verified as a whole, that is, the radon reduction effect of the radon shielding project is evaluated. The specific steps include:

[0059] ① Determine the verification object: select several representative rooms or areas in the underground project as the verification object; for underground projects composed of multiple rooms, each independent room should be used as the verification object; for underground projects composed of a whole large area, the area should be divided into several small areas according to the area, and each small area should be used as the verification object; for tunnel-type underground projects, it should be divided into several small areas according to the length, and each small area should be used as the verification object;

[0060] ② Determine the ventilation volume: adjust the ventilation rate of the verification object and stabilize it at R m , maintained for at least the preset duration;

[0061] ③ Determine the measurement time: Use a radon detector to measure the radon concentration of the verification object. The measurement point is located at the center of the ground in the room or area, at a preset height; the measurement cycle is set to a, and the measurement is continuous for 24 hours:

[0062] ④Evaluate the radon reduction effect: average the measured radon concentration data and record it as C P , Bq·m -3 ; If C P ≤C m , it means that after the construction plan is implemented, the radon concentration of the verification object can meet the target requirements; if C P >Cm , it means that after the implementation of the construction plan, the radon concentration of the verification object cannot meet the target requirements, and measures should be taken to improve the radon shielding project of the target room.

[0063] Furthermore, the radon shielding effect of underground projects is locally verified, that is, the radon prevention effect of radon shielding projects is evaluated, including:

[0064] The radon-proof layers around the underground project, on the ground and on the top are divided into several small square areas according to the area, and the center position of each small square area is taken as the measurement point; in addition, all abnormal positions on the radon-proof layer of the underground project are taken as measurement points; the radon exhalation rate of the measurement points is measured using the radon exhalation rate measurement method; assuming that the radon exhalation rate of one of the points is J Z , Bq·m -2 ·h -1 ; If J Z ≤J m , J m is the target radon exhalation rate, then after the construction plan is implemented, the radon exhalation rate of the point can meet the target requirement; if J Z >J m , if the radon exhalation rate of the point cannot meet the target requirements after the implementation of the construction plan, local repair, reinforcement and sealing measures shall be taken to deal with the point.

[0065] Furthermore, the calculation formula of the radon shielding efficiency target value is:

[0066] The target value μ of the radon shielding efficiency of the anti-radon layer can be calculated using the following formula:

[0067]

[0068] In the formula, J m is the target radon exhalation rate, Bq·m -2 ·h -1 ; J y is the original radon exhalation rate, Bq·m -2 ·h -1 .

[0069] It can be seen from the above technical scheme that, compared with the prior art, the present invention discloses a systematic method for the construction of radon shielding in underground projects, which integrates "survey-diagnosis-testing-construction-acceptance-maintenance" into one, and plans the entire process of the radon shielding project. Through on-site surveys and tests, the construction plan is optimized, thus realizing the scientificity, systematicness and effectiveness of radon shielding in underground projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0071] Figure 1 A flow chart of a systematic method for radon shielding construction in underground engineering provided by the present invention;

[0072] Figure 2 A schematic diagram of the radon exhalation rate measurement principle provided by the present invention;

[0073] Figure 3 This is a diagram of the physical model of underground engineering in the embodiment provided by the present invention. DETAILED DESCRIPTION

[0074] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0075] First, the terms used in the embodiments of the present invention are explained:

[0076] Underground engineering refers to artificially excavated buildings and structures deep below the ground or inside mountains, including civil air defense projects, national defense projects, mountain or underground tunnels, etc.

[0077] Radon shielding for underground projects refers to covering the surrounding areas, ground and top surfaces of underground projects with one or several layers of anti-radon materials in order to shield the radon from spreading from the rock wall into the underground projects.

[0078] The underground project was in a bare hole state before the construction of the radon shielding project, that is, the surrounding areas, ground and top surfaces were all supported by concrete.

[0079] When an underground project is in a bare hole state, the materials, density, water content, degree of fragmentation and other factors on its surroundings, ground and top surfaces are the same.

[0080] The ventilation system of the underground project is designed as a mechanical fresh air system, which means that when it is in operation, it can input external ambient air into the project to achieve ventilation; when the ventilation system is in operation, the fresh air flow rate can be controlled as needed.

[0081] When the radon shielding project of the underground project is accepted, its ventilation system has been installed and is capable of operation.

[0082] The anti-radon layer refers to the sum of anti-radon materials covering the inner surface of underground projects in radon shielding projects.

[0083] The radon-proof effect in the embodiment of the present invention is intended to evaluate whether the radon exhalation rate of the radon-proof layer in the embodiment of the present invention meets the requirements.

[0084] The radon reduction effect is intended to evaluate whether the radon concentration inside the underground project meets the requirements after the radon shielding project is completed in the embodiment of the present invention.

[0085] The target radon concentration refers to the artificially set control target for the radon concentration of the underground project.

[0086] The target radon exhalation rate refers to the artificially set control target for the radon exhalation rate around, on the ground and on the top surface of the underground project.

[0087] The original radon exhalation rate refers to the radon exhalation rate around the underground project, on the ground and on the top surface before the construction of the radon shielding project.

[0088] The embodiment of the present invention obtains a large amount of on-site measurement data through pre-construction surveys, selects construction materials and processes based on the data and control target requirements, and optimizes the construction plan by conducting local verification tests before full construction.

[0089] During the acceptance of radon shielding projects, we first conduct an overall verification by measuring the radon concentration. For some rooms or areas that fail the overall verification, we then conduct local verification by measuring the radon exhalation rate. We then perform local repairs and improvements on some locations that do not meet the requirements until the room or area meets the target requirements.

[0090] The embodiment of the present invention discloses a systematic method for radon shielding construction in underground engineering, such as Figure 1 As shown, the following steps are included:

[0091] S1. Survey phase

[0092] On-site survey of the concrete support of underground projects, measurement of the structural dimensions of underground projects, and point-by-point measurement of the original radon exhalation rate of underground project walls and the background radon concentration of the external environment;

[0093] S2. Diagnosis stage

[0094] Set the target radon concentration for underground projects and estimate the target radon exhalation rate;

[0095] Calculating a target value of radon shielding efficiency of the radon protection layer based on an estimated value of the target radon exhalation rate and a measured value of the original radon exhalation rate;

[0096] Determine the first construction plan based on the radon shielding efficiency target value, concrete support conditions and underground engineering structure dimensions;

[0097] S3. Experimental Phase

[0098] Carry out trial construction on the walls of local areas of the underground project according to the first construction plan;

[0099] The radon exhalation rate of the wall after the experimental construction was measured and the measurement results were compared with the target radon exhalation rate;

[0100] If the measurement result is not greater than the target radon exhalation rate, the first construction plan is the final construction plan;

[0101] If the measurement result is greater than the target radon exhalation rate, the first construction plan is optimized until the experimental construction and verification are repeated and the measurement satisfies that the radon exhalation rate is not greater than the target radon exhalation rate, and a second construction plan is formed as the final construction plan;

[0102] S4. Construction phase

[0103] Carry out comprehensive construction of the underground project in accordance with the final construction plan that meets the requirements;

[0104] S5. Acceptance stage

[0105] After the construction is completed, the radon shielding effect of the radon shielding project shall be verified, including overall verification and local verification;

[0106] Verify the radon shielding effect of the underground project as a whole, select several representative rooms or areas in the underground project, use a radon detector to measure the radon concentration, and compare it with the target radon concentration;

[0107] If the measured value is not greater than the target radon concentration, the overall verification is qualified; there is no need to conduct local verification of the radon shielding effect of the underground project;

[0108] If the measured value is greater than the target radon concentration, the overall verification fails; local verification of the radon shielding effect of the underground project is required;

[0109] S6. Maintenance phase

[0110] According to the final construction plan, formulate the engineering operating instructions and maintenance plan, distribute them to the user unit, and coordinate with the construction party to carry out subsequent maintenance work.

[0111] This method is applied to underground projects; for example, when building an underground parking lot, it is necessary to ensure that the radon concentration in the parking lot is lower than a certain target value.

[0112] First, a survey phase is needed to conduct on-site surveys of the concrete support conditions of underground projects, measure the structural dimensions of underground projects, and conduct point-by-point measurements of the original radon emanation rate of the underground project walls and the background radon concentration of the external environment, to provide a basis for the subsequent formulation of construction plans.

[0113] Next, a diagnostic phase is required to set the target radon concentration of the underground project under normal ventilation system conditions in the future, and use the calculation formula to estimate the target radon exhalation rate. Based on the estimated value of the target radon exhalation rate and the measured value of the original radon exhalation rate, the radon shielding efficiency target value of the anti-radon layer is calculated. Taking into account the radon shielding efficiency target value, the construction cost and construction difficulty of the radon shielding project, a suitable construction plan is selected, including but not limited to the materials, specifications, and construction technology of the anti-radon layer (such as the number of covering layers of the anti-radon board, the number of spraying times of the anti-radon paint layer, the sealing treatment of the anchor rod, etc.).

[0114] Then, a test phase is required, and test construction is carried out on the walls of local areas of the underground project according to the materials and processes in the construction plan. The radon exhalation rate of the wall after the test construction is measured according to the radon exhalation rate measurement method described in the embodiment of the present invention to verify the radon prevention effect of the plan; if the measurement result meets the target requirements, the full construction phase is entered; if not, the construction plan is modified and improved, and the test construction and verification are carried out again until the target requirements are met and the final construction plan is determined.

[0115] Next, the construction phase needs to be carried out to carry out comprehensive construction according to the construction plan.

[0116] Finally, an acceptance stage is required. After the overall completion, the radon shielding effect of the radon shielding project needs to be verified, which is divided into overall verification and local verification.

[0117] Conduct overall verification, that is, evaluate the radon reduction effect of the radon shielding project. Under normal ventilation system conditions, select several representative rooms or areas in the underground project, use a radon meter to measure their radon concentrations, and compare them with the target radon concentration to evaluate whether they meet the requirements. If the measured value is not greater than the target radon concentration, the overall verification of the room or area is qualified; if the measured value is greater than the target radon concentration, the overall verification of the room or area is unqualified.

[0118] If the room or area fails the overall verification, it is necessary to conduct a local verification, that is, to evaluate the radon protection effect of the radon shielding project. The radon exhalation rate of the room or area is measured at a point-by-point basis and compared with the target radon exhalation rate to evaluate whether its radon protection effect meets the target requirements; for the points that do not meet the target requirements, the reasons are analyzed, and relevant plans are formulated to carry out repair and acceptance work.

[0119] Rooms or areas that pass overall verification do not require local verification.

[0120] Finally, based on the construction materials, technology and underground engineering environment, the engineering instructions and maintenance plan are formulated and distributed to the user unit, and the construction party is coordinated to carry out subsequent maintenance work.

[0121] The calculation process in each of the above steps is described below:

[0122] 1. Radon exhalation rate measurement in step S1

[0123] The radon exhalation rate is measured by the local static method in the embodiment of the present invention. A radon collecting cover is placed on the surface to be measured, and the radon collecting cover is sealed around to collect the radon released from the surface. The measuring instrument is connected to the radon collecting cover through an air path, and then the radon measuring instrument is used to continuously monitor the change of radon concentration in the radon collecting cover over time. The principle is as follows: Figure 2 As shown. It is assumed that the radon exhalation rate of the surface to be measured will not change during the measurement, and the radon is evenly distributed in the radon collecting cover after precipitation, and the back diffusion effect is not considered during the measurement process. Under the condition of unchanged environmental conditions, the radon concentration in the internal space of the radon collecting cover depends on the radon exhalation rate of the surface to be measured. By establishing a model relationship between the two, the surface radon exhalation rate is converted after data fitting.

[0124] After the radon collecting cover is sealed, the mathematical model of the radon concentration change in its internal space can be expressed by the following formula:

[0125]

[0126] Where: C(t) is the radon concentration at time t, Bq·m -3 ; J0 is the radon exhalation rate of the surface to be tested, Bq·m -2 ·h -1 ; h is the depth of the radon hood, m. The depth of the radon hood used in this method is 0.14 m; V is the volume of the radon hood, m 3 ;K is the leakage rate of radon in the radon collecting hood, which is regarded as a constant, Bq·h -1 When the radon in the external environment leaks into the radon collecting cover, K is a positive number. When the radon in the radon collecting cover leaks into the external environment, K is a negative number. λ is the decay constant of radon, λ=0.00756h -1 .

[0127] The initial conditions of the experiment are: at t = 0, C(t = 0) = C0; C0 is the initial radon concentration in the radon collecting hood, hereinafter referred to as the initial radon concentration, Bq·m -3 Substituting the initial conditions into equation (1), we obtain:

[0128]

[0129] Let J represent the measured surface radon exhalation rate of the surface to be measured, Bq·m-2 ·h -1 , expressed as:

[0130]

[0131] When the sealing performance of the radon collecting cover is good, the radon leakage rate K in the radon collecting cover can be ignored. Substituting the measured radon exhalation rate J0 of the surface to be measured with the measured radon exhalation rate J into formula (2), we get:

[0132]

[0133] The radon concentration is measured once at the same interval using the equal time interval method. In this paper, the measurement cycle is set to 1h, and the cumulative measurement time is set to 6h, and the hourly radon concentration measurement data (C1, C2...C6) and its uncertainty (σ1, σ2...σ6) are obtained. The measured radon exhalation rate J is obtained using the least squares method:

[0134]

[0135] 2. In step S2, the target radon exhalation rate is estimated:

[0136] The indoor radon concentration change model can be expressed by the following formula:

[0137]

[0138] Where: C(t) represents the radon concentration at time t, Bq·m -3 ; C b Represents the background radon concentration in outdoor air, Bq·m -3 ; J is the surface radon exhalation rate of the inner surface of the room wall, hereinafter referred to as radon exhalation rate, Bq·m -2 ·h -1 ;λ is the decay constant of radon,λ=0.00756h -1 ; S is the radon release surface area, m 2 ; V is the volume of free space where indoor radon can diffuse freely, m 3 ; R refers to the ratio of fresh air volume to free space volume per unit time, usually expressed as the number of air changes per unit time (1h), h -1 ; D is the reverse diffusion coefficient of indoor radon, which refers to the coefficient of indoor air radon diffusion into the wall, h -1 .

[0139] Assume that the indoor radon concentration at the initial time is C, Bq·m -3 ; e Defined as the equivalent decay constant, λ e =λ+R+D,h -1 . Formula (5) can be solved as:

[0140]

[0141] When the time is long enough, the increase and decrease of indoor radon concentration will be equal, and the indoor radon concentration will remain at a stable level, which is called stable radon concentration C. stable , the radon concentration mentioned in the embodiment of the present invention refers specifically to the stable radon concentration. That is, t→∞, the stable radon concentration C can be obtained from formula (6): stable The calculation formula is:

[0142]

[0143] For general civil buildings, the indoor ventilation rate is faster than the decay rate of radon itself (λ is the decay constant of radon, which is 0.00756h -1 ) is more than two orders of magnitude greater. For the ventilation system of the underground project described in the embodiment of the present invention, its ventilation rate is higher than that of general civil buildings, so the embodiment of the present invention ignores the effect of radon's own decay on the indoor radon concentration. Similarly, the reverse diffusion effect of indoor radon is also ignored here.

[0144] The embodiment of the present invention ignores the influence of radon's own decay and its own back diffusion effect on the indoor radon concentration. Therefore, λ e =λ+R+D≈R. Formula (7) can be simplified as:

[0145]

[0146] After the radon shielding project is completed, the target radon concentration of the underground project under the normal operation of the ventilation system is set to C m According to formula (8), C m It can be expressed as:

[0147]

[0148] In the formula, R m It represents the air change rate of underground engineering under normal operation of ventilation system, h -1 ; J m is the target radon exhalation rate, Bq·m -2 ·h -1 ; C' b is the background radon concentration of the external environment of the underground project, Bq·m -3 .

[0149] The target radon exhalation rate J is obtained by solving formula (9): m The estimation formula is:

[0150]

[0151] J m is the estimated result of the target radon exhalation rate.

[0152] 3. In step S5, the overall verification of the radon shielding effect:

[0153] After the radon shielding project described in the embodiment of the present invention is completed, under the condition of normal operation of the ventilation system, several representative rooms or areas in the underground project are selected, and the radon concentration is measured using a radon detector, and compared with the target radon concentration to evaluate whether it meets the requirements. The specific steps are as follows:

[0154] ① Determination of verification objects. Select several representative rooms or areas in the underground project as verification objects. For underground projects composed of multiple rooms, each independent room should be used as a verification object; for underground projects composed of a whole large area, the area should be divided into several small areas according to the average area, and each small area should be used as a verification object; for tunnel-type underground projects, it should be divided into several small areas according to the average length, and each small area should be used as a verification object.

[0155] ② Determination of ventilation volume. Adjust and stabilize the ventilation rate of the verification object at R m , maintain for at least 24h.

[0156] ③ Determination of measurement time. Use a radon detector to measure the radon concentration of the verification object. The measurement point is located at the center of the room or area at a height of 1.5m. The measurement cycle is set to 1h, and the measurement is continuous for 24h.

[0157] ④ Evaluation of radon reduction effect. The average of the measured radon concentration data is recorded as C P , Bq·m -3 If C P ≤C m , it means that after the construction plan is implemented, the radon concentration of the verification object can meet the target requirements. P >C m , it means that after the implementation of the construction plan, the radon concentration of the verification object cannot meet the target requirements, and measures should be taken to improve the radon shielding project of the target room.

[0158] 4. In step S5, local verification of radon shielding effect:

[0159] The radon-proof layers around the underground project, on the ground and on the top are divided into several small square areas according to the average area, and the center of each small square area is taken as the measurement point. In addition, all abnormal positions on the radon-proof layer of the underground project (including but not limited to positions with protrusions such as anchor rods, cracks and damage, etc.) are taken as measurement points. The radon exhalation rate measurement method described in the embodiment of the present invention is used to measure the radon exhalation rate of the measurement point. Assume that the radon exhalation rate of one of the points is J Z , Bq·m-2 ·h -1 If J Z ≤J m (J m is the target radon exhalation rate, Bq·m -2 ·h -1 ), it means that after the construction plan is implemented, the radon exhalation rate of the point can meet the target requirements; if J Z >J m , it means that after the implementation of the construction plan, the radon exhalation rate of the point cannot meet the target requirements, and measures such as local repair, reinforcement and sealing should be taken to deal with the point.

[0160] 5. Calculation of radon shielding efficiency target value

[0161] The target value μ of the radon shielding efficiency of the anti-radon layer can be calculated using the following formula:

[0162]

[0163] In the formula, J m is the target radon exhalation rate, Bq·m -2 ·h -1 ; J y is the original radon exhalation rate, Bq·m -2 ·h -1 .

[0164] Example:

[0165] An underground project is now a bare hole, with concrete support on all sides, ground and top surfaces. The structural dimensions are as follows: Figure 3 As shown in the figure, the section of the arch top is an arc with an arc angle of 90°, and the area of ​​its gate is negligible. The underground project plans to use radon shielding to permanently reduce radon. The underground project plans to use a mechanical fresh air system. In the future, under normal operating conditions, the fresh air volume will be 2000m 3 ·h -1 , the ventilation rate is about 0.17h -1 .

[0166] The systematic method for radon shielding construction of underground engineering proposed by the present invention is applied to the radon shielding engineering of the above-mentioned underground engineering, and the specific steps are as follows:

[0167] S1. Survey phase

[0168] After on-site investigation, Figure 3 As shown, the free space volume of the underground project is 13645m 3 The radon exhalation rate area is about 3974m 2. Ten points (referred to as point set D) on the original wall of the underground project were selected to measure the radon exhalation rate. The original radon exhalation rate measurement results are shown in Table 1. Five points in the external environment of the underground project were selected, and the measurement results are shown in Table 2. The arithmetic mean of the background radon concentration is 16.88 Bq·m -3 .

[0169] Table 1 Measurement results of original radon exhalation rate of underground projects

[0170]

[0171]

[0172] Table 2 Measurement results of external environment radon concentration

[0173]

[0174] S2. Diagnosis stage

[0175] The target radon concentration for underground projects under normal ventilation system operation is set at 30 Bq·m -3 The free space volume of the underground project is 13645m 3 The radon exhalation rate area is about 3974m 2 In the future, under normal operating conditions of the fresh air system, the ventilation rate will be about 0.17h -1 Using formula (10), the target radon exhalation rate under normal ventilation system operation in the future is 7.65 Bq·m -2 ·h -1 The average value of the original radon exhalation rate (156.39 Bq·m -2 ·h -1 ), using formula (11) to estimate, the target value of radon shielding efficiency of the anti-radon layer is about 95.11%.

[0176] Taking into account the target value of radon shielding efficiency, the construction cost and construction difficulty of the radon shielding project, it was decided to adopt Construction Plan A of ordinary cement mortar layer + water-based anti-radon coating layer; the thickness of the cement mortar is 5cm, and the anti-radon coating is sprayed once; Construction Plan A forms an overall wrapping for the underground project to ensure the airtightness of radon protection.

[0177] S3. Experimental Phase

[0178] According to the materials and processes in construction plan A, three points were selected from point set D (their original radon exhalation rates were 153.46 Bq·m -2 ·h -1 、161.30Bq·m -2 ·h -1 、168.12Bq·m-2 ·h -1 ), and experimental construction was carried out on its original wall. The radon exhalation rate at three points after construction was measured according to the radon exhalation rate measurement method described in the embodiment of the present invention, and the results were 10.21 Bq·m -2 ·h -1 、11.21Bq·m -2 ·h -1 、13.74Bq·m -2 ·h -1 After construction, the radon exhalation rates at the three locations were all greater than the target radon exhalation rate (7.65 Bq·m -2 ·h -1 ), it is judged that construction plan A cannot meet the target requirements and the plan needs to be optimized.

[0179] Construction Plan A was optimized to form Construction Plan B. In Construction Plan B, the relevant materials were replaced, ordinary cement mortar was replaced with polymer cement mortar, water-based anti-radon coating was replaced with airtight emulsion polymer, and the number of spraying was changed to 2 times.

[0180] According to the materials and processes in construction plan B, three points were selected from point set D (their original radon exhalation rates were 155.08 Bq·m -2 ·h -1 、158.32Bq·m -2 ·h -1 、163.20Bq·m -2 ·h -1 ), and experimental construction was carried out on its original wall. The radon exhalation rate of the wall at three points after construction was measured according to the radon exhalation rate measurement method described in the embodiment of the present invention, and the results were 5.40 Bq·m -2 ·h -1 、6.18Bq·m -2 ·h -1 、6.65Bq·m -2 ·h -1 After construction, the radon exhalation rates of the three wall locations were all lower than the target radon exhalation rate (7.65 Bq·m -2 ·h -1 ), and judge that construction plan B can meet the target requirements.

[0181] The radon shielding efficiency μ of construction plan B was calculated using formula (11), and the obtained μ were 96.51%, 96.10%, and 95.93% respectively.

[0182] S4. Construction phase

[0183] The entire underground project is fully constructed according to the construction plan B diagnosed in step S2.

[0184] S5. Acceptance stage

[0185] Open the ventilation system of the underground project, adjust it and stabilize it in normal operation for 24 hours. At this time, the internal air exchange rate of the underground project is 0.17h -1 .

[0186] Along the inner axis of the underground project, from inside to outside, a measurement point was set every 16m, with a total of 3 measurement points at a height of 1.5m. The radon concentration was measured using a radon detector, with a measurement cycle of 1h and continuous measurement for 24h. The arithmetic average of the measurement results showed that the average radon concentrations of the 3 measurement points were 37.32Bq·m -3 40.48 Bq·m -3 43.16Bq·m -3 , which are greater than the target radon concentration (30 Bq·m -3 ), indicating that the overall verification of the radon shielding project of the underground project failed.

[0187] The radon-proof layers around the underground project, on the ground and on the top are divided into several small square areas according to their average area. The center position of each small square area and all abnormal positions (including 4 protrusions such as anchor rods and 2 cracks) are taken as measurement points, totaling 40 measurement points. The radon exhalation rate measurement method described in the embodiment of the present invention is used to measure the radon exhalation rate. The measurement results show that the radon exhalation rate of 37 points is less than the target radon exhalation rate (7.65 Bq·m -2 ·h -1 ), and the radon exhalation rates of the other three points were 180.23 Bq·m -2 ·h -1 、175.24Bq·m -2 ·h -1 、154.21Bq·m -2 ·h -1 , one of which was the protruding part of the anchor rod, and two were the cracks of the anti-radon layer coating. Cause analysis: The air tightness of the anti-radon layer was reduced at the protruding part and crack of the anchor rod, resulting in abnormal radon precipitation. Measures taken: Repair and strengthen the sealing of all the protruding parts and cracks of the anchor rod in the anti-radon layer of the underground project.

[0188] Using the radon shielding effect overall verification method described in the embodiment of the present invention, the radon shielding effect of the underground project was verified again at the above three radon concentration measurement points. The measurement cycle was set to 1 hour and the measurement was continued for 24 hours. The measurement results were arithmetic averaged, and the average radon concentrations of the three measurement points were 26.18 Bq·m -3 、28.53Bq·m -3 、29.20Bq·m -3, which are all less than the target radon concentration (30 Bq·m -3 ), indicating that the radon shielding project of the underground project has been verified as qualified as a whole.

[0189] S6. Maintenance phase

[0190] According to the construction materials and process characteristics of construction plan B, formulate the engineering use instructions and maintenance plan. Among them, according to the characteristics of the outer surface of the anti-radon layer (the material is an airtight emulsion polymer), formulate corresponding use and maintenance rules and precautions, for example: pay attention to protecting the outer surface of the anti-radon layer during work and check it regularly. Once cracks or damage are found, they should be repaired in time to prevent its airtightness from being reduced. After the engineering use instructions and maintenance plan are formulated, they should be distributed to the user unit in a timely manner to coordinate the construction party to do a good job in subsequent maintenance.

[0191] In view of the high radon concentration in underground projects, the present invention collects a large amount of data on-site and optimizes and verifies the construction process before large-scale construction. The construction plan is highly systematic, integrating "survey-diagnosis-test-construction-acceptance-maintenance" into one, and plans the entire radon shielding project throughout the entire process, thus achieving the scientificity, systematicness and effectiveness of radon shielding in underground projects.

[0192] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0193] The above description of the disclosed embodiments enables one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A systematic method for radon shielding construction in underground engineering, characterized in that: The following steps are involved: S1. Survey phase On-site survey of the concrete support of underground projects, measurement of the structural dimensions of underground projects, and point-by-point measurement of the original radon exhalation rate of underground project walls and the background radon concentration of the external environment; S2. Diagnosis stage Set the target radon concentration for underground projects and estimate the target radon exhalation rate; Calculating a target value of radon shielding efficiency of the anti-radon layer based on the estimated value of the target radon exhalation rate and the measured value of the original radon exhalation rate; Determining a first construction plan according to the radon shielding efficiency target value, the concrete support conditions and the size of the underground engineering structure; S3. Experimental Phase Carry out trial construction on the walls of local areas of the underground project according to the first construction plan; Measuring the radon exhalation rate of the wall after the experimental construction, and comparing the measurement result with the target radon exhalation rate; If the measurement result is not greater than the target radon exhalation rate, the first construction plan is the final construction plan; If the measurement result is greater than the target radon exhalation rate, the first construction plan is optimized until the experimental construction and verification are repeated and the measurement satisfies that the radon exhalation rate is not greater than the target radon exhalation rate, and a second construction plan is formed as the final construction plan; S4. Construction phase Carry out comprehensive construction of the underground project in accordance with the final construction plan that meets the requirements; S5. Acceptance stage After the construction is completed, the radon shielding effect of the radon shielding project shall be verified, including overall verification and local verification; Verify the radon shielding effect of the underground project as a whole, select several representative rooms or areas in the underground project, use a radon detector to measure the radon concentration, and compare it with the target radon concentration; If the measured value is not greater than the target radon concentration, the overall verification is qualified; and there is no need to conduct local verification of the radon shielding effect of the underground project; If the measured value is greater than the target radon concentration, the overall verification fails; local verification of the radon shielding effect of the underground project is required; S6. Maintenance phase According to the final construction plan, formulate the engineering instructions and maintenance plan, distribute them to the user unit, and coordinate the construction party to carry out subsequent maintenance work; Wherein, in step S1, the radon exhalation rate is measured by: A radon collecting cover is placed on the surface to be tested and the four sides of the radon collecting cover are sealed. After the radon collecting cover is sealed, the mathematical model of the radon concentration change in its internal space is expressed by the following formula: Where: C(t) is the radon concentration at time t, Bq·m -3 ; J0 is the radon exhalation rate of the surface to be tested, Bq·m -2 ·h -1 ; h is the depth of the radon collection cover, m; V is the volume of the radon collection cover, m 3 ;K is the leakage rate of radon in the radon collecting hood, which is regarded as a constant, Bq·h -1 When the radon in the external environment leaks into the radon collecting cover, K is a positive number. When the radon in the radon collecting cover leaks into the external environment, K is a negative number. λ is the decay constant of radon, λ=0.00756h -1 ; The initial conditions of the experiment are: at t = 0, C(t = 0) = C0; C0 is the initial radon concentration in the radon collecting hood, Bq·m -3 ; Substituting the initial conditions into equation (1), we can obtain: Let J represent the measured surface radon exhalation rate of the surface to be measured, Bq·m -2 ·h -1 , expressed as: When the sealing performance of the radon collecting cover is good, the radon leakage rate K in the radon collecting cover can be ignored; the radon exhalation rate J of the surface to be measured is replaced by the measured radon exhalation rate J0, and substituted into formula (2), the result is: Use the equal time interval method, that is, measure the radon concentration once at the same interval; obtain the radon concentration measurement data C at each fixed interval i and its corresponding uncertainty σ i , use the least squares method to get the measured radon exhalation rate J: Where i is a positive integer greater than 0; it represents the number of measurements; In step S2, the target radon exhalation rate is estimated by: The indoor radon concentration change model is expressed by the following formula: Where: C(t) is the radon concentration at time t, Bq·m -3 ; C b is the background radon concentration in outdoor air, Bq·m -3 ; J is the surface radon exhalation rate of the inner surface of the room wall, Bq·m -2 ·h -1 ;λ is the decay constant of radon,λ=0.00756h -1 ; S is the radon release surface area, m 2 ; V is the free space volume for indoor radon to diffuse freely, m 3 ; R is the ratio of fresh air volume to free space volume per unit time, expressed as the number of air changes per unit time, h -1 ; D is the reverse diffusion coefficient of indoor radon, which refers to the coefficient of indoor air radon diffusion into the wall, h -1 ; Assume that the initial indoor radon concentration is C a , Bq·m -3 ; e Defined as the equivalent decay constant, λ e =λ+R+D,h -1 ; Formula (5) is solved to get: After the preset time, the increase and decrease of indoor radon concentration will be equal, and the indoor radon concentration will remain at a stable level, which is called stable radon concentration C. stable , the radon concentration is the stable radon concentration; that is, t→∞, the stable radon concentration C is obtained from formula (6): stable The calculation formula is: The influence of radon's own decay and its own back-diffusion effect on the indoor radon concentration is ignored, so λ e =λ+R+D≈R; Formula (7) is simplified to: After the radon shielding project is completed, the target radon concentration of the underground project under the normal operation of the ventilation system is set to C m ; According to formula (8), C m It is expressed as: In the formula, R m It represents the air change rate of underground engineering under normal operation of ventilation system, h -1 ; J m is the target radon exhalation rate, Bq·m -2 ·h -1 ; C' b is the background radon concentration of the external environment of the underground project, Bq·m -3 ; The target radon exhalation rate J is obtained by solving formula (9): m The estimation formula is: J m is the estimated result of the target radon exhalation rate.

2. A systematic method for radon shielding construction in underground engineering according to claim 1, characterized in that: Verify the radon shielding effect of underground projects as a whole, that is, evaluate the radon reduction effect of radon shielding projects. The specific steps include: ① Determine the verification object: select several representative rooms or areas in the underground project as the verification object; for underground projects composed of multiple rooms, each independent room should be used as the verification object; for underground projects composed of a whole large area, the area should be divided into several small areas according to the area, and each small area should be used as the verification object; for tunnel-type underground projects, it should be divided into several small areas according to the length, and each small area should be used as the verification object; ② Determine the ventilation volume: adjust the ventilation rate of the verification object and stabilize it at R m , maintained for at least the preset duration; ③ Determine the measurement time: Use a radon detector to measure the radon concentration of the verification object. The measurement point is located at the center of the ground in the room or area, at a preset height; the measurement cycle is set to a, and the measurement is continuous for 24 hours: ④Evaluate the radon reduction effect: average the measured radon concentration data and record it as C P , Bq·m -3 ; If C P ≤C m , it means that after the construction plan is implemented, the radon concentration of the verification object can meet the target requirements; if C P >C m , it means that after the implementation of the construction plan, the radon concentration of the verification object cannot meet the target requirements, and measures should be taken to improve the radon shielding project of the target room.

3. A systematic method for radon shielding construction in underground engineering according to claim 1, characterized in that: Local verification of the radon shielding effect of underground projects, that is, evaluation of the radon shielding effect of radon shielding projects, including: The radon-proof layers around the underground project, on the ground and on the top are divided into several small square areas according to the area, and the center position of each small square area is taken as the measurement point; in addition, all abnormal positions on the radon-proof layer of the underground project are taken as measurement points; the radon exhalation rate of the measurement points is measured using the radon exhalation rate measurement method; assuming that the radon exhalation rate of one of the points is J Z , Bq·m -2 ·h -1 ; If J Z ≤J m , J m is the target radon exhalation rate, then after the construction plan is implemented, the radon exhalation rate of the point can meet the target requirement; if J Z >J m , if the radon exhalation rate of the point cannot meet the target requirements after the implementation of the construction plan, local repair, reinforcement and sealing measures shall be taken to deal with the point.

4. A systematic method for radon shielding construction in underground engineering according to any one of claims 1 to 3, characterized in that: The calculation formula of the radon shielding efficiency target value is: The target value μ of the radon shielding efficiency of the radon protection layer is calculated using the following formula: In the formula, J m is the target radon exhalation rate, Bq·m -2 ·h -1 ; J y is the original radon exhalation rate, Bq·m -2 ·h -1 .

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