A method for controlling thermal stress of dam body considering temperature difference in irrigation area and development of concrete elastic modulus

Abstract

The present invention provides a dam body temperature stress control method that takes into account the temperature difference in the irrigation area and the development of the concrete elastic modulus, that is, before the second-stage cooling of the concrete, the temperature stress of the concrete at the end of the second-stage cooling and water supply is predicted based on the existing temperature data and the change of the concrete elastic modulus, and the stress calculation is used to determine whether the upper irrigation area concrete should be supplemented with water before the lower irrigation area is cooled, and the temperature reduction range of the supplementary water cooling is obtained, and finally the stress of the lower irrigation area concrete is optimized by adjusting the temperature of the upper irrigation area concrete before the second-stage cooling of the lower irrigation area. Advantages of the present invention: effective application of temperature monitoring data, more flexible regulation of concrete temperature, more accurate control of concrete temperature stress, and significant effect of temperature control and crack prevention measures.

Description

Technical Field

[0001] The present invention relates to a method for controlling concrete temperature stress, and more specifically, to a method for controlling concrete temperature stress by taking into account the influence of concrete elastic modulus history and temperature difference of concrete in an upper tank area on concrete temperature stress. The present invention belongs to the technical field of temperature control and crack prevention in concrete arch dam construction. Background Art

[0002] Since ancient times, "no dam is not cracked". In order to prevent concrete dams from cracking, a series of temperature control and crack prevention measures need to be formulated. Concrete temperature stress is an important basis for formulating concrete temperature control and crack prevention measures. At present, the calculation methods of concrete temperature stress mainly include formula method and influence line method. "Concrete Arch Dam Design Code" (DL / T 5346-2006), "Concrete Arch Dam Design Code" (SL282-2018) and "Hydraulic Concrete Temperature Control Construction Code" (DL / T 5787-2019) all stipulate the calculation method of concrete temperature stress under the condition of uniform temperature field cooling of foundation concrete. The contents are as follows:

[0003] 1. The Code for Design of Concrete Arch Dams (DL / T 5346-2006) stipulates that the temperature stress of the uniform temperature field of the foundation concrete can be estimated by the constraint coefficient method, that is:

[0004]

[0005] Where:

[0006] Δσ x It represents the temperature stress of the uniform temperature field of the foundation concrete; x represents the direction along the river;

[0007] K p is the stress relaxation coefficient of concrete, which is approximately 0.5;

[0008] E C is the elastic modulus of concrete;

[0009] R is the basic constraint coefficient. At the contact surface between concrete and rock, when the elastic modulus of concrete E C Approximately equal to the bedrock elastic modulus E r When Ec≠Er, R takes the value in Table 1; when Ec≠Er, R takes the value in Table 2; the R value above the foundation surface is converted in proportion;

[0010] ΔT is the basic temperature difference;

[0011] α represents the linear expansion coefficient of concrete;

[0012] μ represents the Poisson's ratio of concrete.

[0013] Table 1 Basic constraint coefficient (Ec=Er)

[0014]

[0015] Table 2 Basic constraint coefficient (Ec≠Er)

[0016]

[0017] 2. The Code for Design of Concrete Arch Dams (SL282-2018) stipulates that the influence line method is used to calculate the temperature stress of the uniform temperature field cooling of the foundation concrete. The specific method is to calculate the temperature stress σ1 caused by the difference between the pouring temperature and the stable temperature and the temperature stress σ2 caused by the hydration heat temperature drop respectively. The temperature stress σ of the uniform temperature field cooling of the foundation concrete is calculated by superposition according to formula (2), that is:

[0018] σ=σ1+σ2 (2)

[0019] in,

[0020]

[0021] Where:

[0022] K p is the stress relaxation coefficient of concrete, which can be taken as 0.5 in the absence of test data;

[0023] R is the basic constraint coefficient, when the concrete elastic modulus E c When the elastic modulus of concrete is close to that of bedrock, R is taken according to Table 1. c When it is not equal to the elastic modulus Er of the bedrock, R shall be taken according to Table 2, and the R value above the foundation surface can be converted in proportion;

[0024] E c is the elastic modulus of concrete, MPa;

[0025] μ is the Poisson’s ratio of concrete;

[0026] α is the linear expansion coefficient of concrete, 1 / ℃

[0027] T f is the stable temperature of the concrete dam body, ℃.

[0028] T P is the pouring temperature of concrete, ℃.

[0029] The temperature stress σ2 caused by the temperature drop of hydration heat can be calculated based on the temperature difference of the maximum temperature rise envelope diagram of the hydration heat of each layer of the foundation block, and calculated by the influence line method according to formula (4):

[0030]

[0031] In the formula

[0032] T(y): Temperature value at stress calculation point y, ℃.

[0033] A y (ξ): indicates the influence coefficient of the normal stress generated by adding a pair of unit loads P = 1 at y = ξ on the calculation point y, which can be obtained by Figure 1 and Figure 2 Get value;

[0034] T(ξ): represents the temperature at y=ξ, °C.

[0035] Δy: represents the increment of y, m;

[0036] l: The long side dimension of the casting block, m.

[0037] 3. The "Construction Specification for Temperature Control of Hydraulic Concrete" (DL / T 5787-2019) stipulates that the calculation method for temperature stress of uniform temperature field cooling of foundation concrete is:

[0038] Considering the different internal temperatures of concrete during the initial pouring and the later cooling, the temperature stress σσ of the uniform temperature field of foundation concrete can be calculated according to formula (5):

[0039]

[0040] Normal concrete state:

[0041]

[0042]

[0043] M=0.001E (8)

[0044] Roller compacted concrete status:

[0045]

[0046]

[0047] M=0.001E (11)

[0048] Where:

[0049] A1: Hydration heat temperature difference influence coefficient, select (6) or (9) for calculation according to the concrete state;

[0050] A2: Casting temperature difference influence coefficient, select (7) or (10) for calculation according to the concrete state;

[0051] E1: elastic modulus of concrete in the middle of late cooling, unit: MPa;

[0052] E2: elastic modulus of concrete at the end of late cooling, unit: MPa;

[0053] E: basic elastic modulus, unit: MPa, if less than 20000MPa, it shall be considered as 20000MPa;

[0054] α: linear expansion coefficient, unit: m / ℃;

[0055] ΔT r : Hydration heat temperature difference, unit: ℃, specific value is as follows Figure 3 The temperature difference between the peak temperature and the pouring temperature is shown.

[0056] ΔT p : Casting temperature difference, that is, the difference between the concrete casting temperature and the temperature at the end of the later cooling (that is, the casting temperature minus the temperature at the end of the later cooling, which can be a negative value), unit: ℃, specific values ​​are as follows Figure 3 As shown;

[0057] L: the length of the longest side of the casting block, unit: m;

[0058] ΔG: Equivalent self-volume deformation, unit: m.

[0059] The aforementioned specifications propose calculation methods for the temperature stress of the uniform temperature field cooling of the foundation concrete. Although the calculation methods of various specifications are different, the proposed methods do not consider the change history of the concrete elastic modulus. However, the development process of concrete temperature stress is closely related to the development history of concrete elastic modulus. If the development and change history of concrete elastic modulus is not considered, the calculated concrete temperature stress value cannot truly reflect the change of concrete stress. The concrete temperature control and crack prevention measures formulated based on this are not rigorous and scientific, and the temperature control and crack prevention effect is not ideal.

[0060] In addition, the various calculation methods proposed in the aforementioned specifications are only applicable to calculating the temperature stress of concrete under the condition of uniform temperature field cooling of foundation concrete. However, in the actual concrete pouring process, the temperature field is not cooled uniformly. The cooling method is to cool in multiple tank areas along the elevation direction of the dam body. That is, the temperature fields of different tank areas and adjacent tank areas are different, and the temperature field cooling conditions inside the concrete in different areas are different. In particular, the temperature difference of the concrete in the upper tank area will affect the temperature stress of the concrete in the lower tank area.

[0061] The concrete cooling process is divided into the first phase cooling and the second phase cooling. Many high dams also carry out mid-term cooling and temperature control between the first phase cooling and the second phase cooling. The purpose of the first phase cooling is to reduce the temperature and reduce the temperature stress. The purpose of the mid-term cooling is to reduce the temperature of the dam body to the target temperature so that the dam body will not crack due to the large temperature difference between the upper and lower irrigation areas during the second phase cooling. The purpose of the second phase cooling is to reduce the dam body to the target temperature so that the transverse joints are opened for grouting to meet the integrity requirements of the arch dam. Although both the first phase cooling and the second phase cooling have cooling target temperatures, the temperature of the dam body before the second phase cooling is often difficult to predict and control in advance due to the long-term heat release of concrete after pouring, the small heat release and the possible adjustment of the construction period. Therefore, it is necessary to adjust the temperature of the dam body before the second phase cooling to prevent the large temperature difference between the upper and lower irrigation areas from causing cracks.

[0062] At present, with the development of intelligent temperature control, the data during the concrete pouring process are recorded in detail, which provides conditions for the accurate calculation of concrete temperature stress. With the rapid development of intelligent temperature control technology, the temperature difference of concrete in adjacent tank areas is also controllable, which also lays the foundation for accurately calculating concrete temperature stress by considering the influence of the temperature difference of concrete in adjacent tank areas on the temperature stress of the entire concrete dam body. Summary of the invention

[0063] In view of the above reasons, an object of the present invention is to provide a dam body temperature stress control method taking into account the temperature difference in the irrigation area and the development of the concrete elastic modulus.

[0064] To achieve the above purpose, the present invention adopts the following technical scheme: a dam body temperature stress control method considering the temperature difference of the irrigation area and the development of the concrete elastic modulus, characterized in that: before the second stage cooling of the concrete, the temperature stress of the concrete at the end of the second stage cooling and water passing is predicted according to the existing temperature data and the change of the concrete elastic modulus, and by stress calculation, it is judged whether the upper irrigation area concrete should be supplemented with water passing before the lower irrigation area is cooled by water passing and the temperature reduction range of the supplementary water passing is obtained, and finally the stress of the lower irrigation area concrete is optimized by adjusting the temperature of the upper concrete of the irrigation area before the second stage cooling of the lower irrigation area. The specific method is:

[0065] S1. Considering the change history of concrete elastic modulus, calculate the foundation temperature stress σ of the concrete dam body before the second stage cooling b ;

[0066] Before the second stage cooling of the concrete dam body, the concrete age is t n When [0,t n ] The time period is divided into n periods, where the start time of the i-th period is t i-1 , the end time is t i, when i = 1 and t0 = 0, the temperature stress increment of the basic temperature difference stress at a point inside the concrete in the i-th period is:

[0067]

[0068] Where: t ki =0.5(t i-1 +t i ); E(t ki ) is t ki The concrete elastic modulus at the moment; R is the basic constraint coefficient, α is the concrete linear expansion coefficient, μ is the concrete Poisson's ratio, ΔT i t i Temperature increment during a period; K p is the stress relaxation coefficient of concrete, which is approximately 0.5;

[0069] Before the second stage cooling, the concrete age is t n When the foundation temperature stress σ b for:

[0070]

[0071] S2. Considering the influence of the upper tank area concrete on the temperature stress of the lower tank area concrete, calculate the temperature difference temperature stress σ of the concrete dam body before the second phase cooling s ;

[0072] Before the second stage cooling, when the concrete pouring age of the upper tank area is t m When [0,t m ] The period is divided into m periods, where the start time of the jth period is t j-1 The end time is t j , when j = 1 and t0 = 0, the temperature stress increment of the upper tank area concrete on the lower tank area concrete in the jth period is:

[0073]

[0074] Where: t kj =0.5(t j-1 +t j );E s (t kj ) is t kj The elastic modulus of the concrete in the upper tank area at the moment; R is the basic constraint coefficient, α is the linear expansion coefficient, μ is the Poisson's ratio, ΔT j t j The temperature difference increment between the concrete in the upper irrigation area and the concrete in the lower irrigation area during the period; K p is the stress relaxation coefficient of concrete, which is approximately 0.5;

[0075] The age of concrete pouring in the upper mixing tank area is t m When the concrete in the lower tank area is poured, the temperature stress generated by the concrete pouring in the upper tank area is:

[0076]

[0077] S3, n is taken as k times the number of days of concrete age before the second stage cooling. The temperature stress of the foundation temperature difference and the temperature difference between the upper and lower layers during the concrete age is calculated in equal time periods. When the following conditions are met, the foundation temperature stress σ b and the temperature stress of the irrigation area s Satisfy the calculation accuracy conditions:

[0078]

[0079] S4. Calculate the stress increment formed by the second stage cooling according to the final elastic modulus of concrete and the target cooling temperature:

[0080]

[0081] Where: E s is the final elastic modulus of concrete; R is the basic constraint coefficient, α is the linear expansion coefficient of concrete, μ is the Poisson's ratio of concrete, ΔT bs The difference between the temperature before the second stage cooling and the design target temperature of the second stage cooling; K p is the stress relaxation coefficient of concrete, which is approximately 0.5;

[0082] S5. Before the second stage cooling of the concrete in the lower irrigation area is completed, assuming that no additional water cooling is performed on the concrete in the upper irrigation area, the calculated stress at the end of the second stage cooling of the concrete in the lower irrigation area is:

[0083] f=σ b +σ s +Δσ bs (18)

[0084] S5.1. If f≤σ0, there is no need to conduct additional water cooling on the concrete in the upper irrigation area before the second stage cooling of the concrete in the lower irrigation area begins;

[0085] S5.2. If f>σ0, it is necessary to supplement water cooling for the concrete in the upper irrigation area before the second stage cooling of the concrete in the lower irrigation area begins; at the end of the supplementary water cooling, the influence of the concrete in the upper irrigation area on the temperature stress of the lower irrigation area is:

[0086]

[0087] Where: E s is the final elastic modulus of concrete; R is the basic constraint coefficient, α is the linear expansion coefficient of concrete, μ is the Poisson's ratio of concrete; ΔT ssTo supplement the decrease in upper concrete temperature; K p is the stress relaxation coefficient of concrete, which is approximately 0.5; adjust the temperature of the upper concrete layer in the irrigation area so that σ b , σ s , Δσ bs and ΔT ss The sum is less than or equal to the allowable tensile strength of concrete σ0. At the end of the second stage cooling, the stress should meet the following criteria:

[0088] σ b +σ s +Δσ bs +Δσ ss ≤σ0 (20)

[0089] Where: σ0 is the allowable tensile strength;

[0090] According to equations (18) and (19) and considering that a large decrease in the temperature of the upper concrete layer may lead to an increase in its own stress and a delay in the construction progress, the temperature decrease of the upper irrigation area concrete after supplementary water cooling is:

[0091] BRIEF DESCRIPTION OF THE DRAWINGS

[0092] Figure 1 For E c =E R Temperature stress influence line of concrete casting block;

[0093] Figure 2 For E c =E R / 2 concrete casting block temperature stress influence line;

[0094] Figure 3 Typical cooling process line of concrete casting block considering post-cooling;

[0095] Figure 4 The invention discloses a method for regulating the temperature of concrete in an upper irrigation area before the second-stage cooling of concrete in a lower irrigation area. DETAILED DESCRIPTION

[0096] The structure and features of the present invention are described in detail below in conjunction with the accompanying drawings and embodiments. It should be noted that various modifications can be made to the embodiments disclosed herein, and therefore, the embodiments disclosed in the specification should not be regarded as limiting the present invention, but are merely examples of embodiments, the purpose of which is to make the features of the present invention obvious.

[0097] The present invention predicts the temperature stress of concrete at the end of the second-stage cooling and water circulation according to the existing temperature data and the change of concrete elastic modulus before the second-stage cooling of concrete, judges whether the concrete of the upper irrigation area should be supplemented with water circulation before the water circulation cooling of the lower irrigation area through stress calculation, and obtains the temperature reduction range of the supplementary water circulation cooling, and finally optimizes the stress of the concrete of the lower irrigation area by adjusting the temperature of the upper concrete of the irrigation area before the second-stage cooling of the lower irrigation area.

[0098] The dam body temperature stress control method considering the temperature difference in the irrigation area and the development of the concrete elastic modulus disclosed in the present invention not only considers the change process of the concrete elastic modulus, but also considers the influence of the temperature difference of the concrete in the adjacent tank area, especially the upper tank area, on the concrete temperature stress. The specific method is:

[0099] 1. Considering the change history of concrete elastic modulus, calculate the foundation temperature stress σ of the concrete dam body before the second stage cooling b .

[0100] Before the second stage cooling of the concrete dam body, the concrete age is t n When [0,t n ] The time period is divided into n periods, where the start time of the i-th period is t i-1 , the end time is t i (When i=1, t0=0), the basic temperature difference stress at a point inside the concrete is the temperature stress increment Δσ in the i-th period bi for:

[0101]

[0102] Where: t ki =0.5(t i-1 +t i ); E(t ki ) is t ki The concrete elastic modulus at that moment; R is the basic coefficient (according to Table 1 or Table 2), α is the concrete linear expansion coefficient, μ is the concrete Poisson's ratio, ΔT i t i Temperature increment during a period; K p is the stress relaxation coefficient of concrete, which is approximately 0.5.

[0103] Before the second stage cooling, the concrete age is t n When the foundation temperature stress σ b for:

[0104]

[0105] 2. Considering the influence of the upper tank area concrete on the temperature stress of the lower tank area concrete, calculate the temperature difference temperature stress σ of the filling area before the second phase cooling of the dam body s .

[0106] Concrete dams, especially concrete arch dams, require grouting of transverse joints to ensure the integrity of the dam body. To ensure the smooth grouting of joints, the concrete dam needs to be cooled after pouring so that the transverse joints can be stretched before grouting. At present, joint grouting is carried out step by step in multiple dam blocks along the elevation direction. The grouting area at the same time is a tank area. The concrete blocks in the tank area need to be cooled to the grouting temperature first, which causes the upper tank area concrete to produce a certain constraint stress on the lower tank area concrete.

[0107] When the age of concrete pouring in the upper tank area is t m When [0,t m ] The period is divided into m periods, where the start time of the jth period is t j-1 The end time is t j (When i=1, t0=0), the temperature stress increment of the upper tank area concrete on the lower tank area concrete in the jth period is:

[0108]

[0109] Where: t kj =0.5(t j-1 +t j );E s (t kj ) is t kj The elastic modulus of the concrete in the upper tank area at the moment; R is the foundation constraint coefficient (according to Table 1 or Table 2), α is the concrete linear expansion coefficient, μ is the concrete Poisson's ratio; ΔT j t j The temperature difference increment between the concrete in the upper irrigation area and the concrete in the lower irrigation area during the period; K p is the stress relaxation coefficient of concrete, which is approximately 0.5.

[0110] The age of concrete pouring in the upper mixing tank area is t m When the concrete in the lower tank area is poured, the temperature stress generated by the concrete pouring in the upper tank area is:

[0111]

[0112] 3. The value of n is k times the number of days of concrete age before the second stage cooling. The temperature stress of the foundation temperature difference and the temperature difference between the upper and lower layers during the concrete age is calculated in equal time periods. When the following conditions are met, the foundation temperature stress σ b and the temperature stress of the irrigation area s Satisfy the calculation accuracy conditions:

[0113]

[0114] 4. According to the final elastic modulus of concrete and the target cooling temperature, calculate the stress increment formed by the second stage cooling:

[0115]

[0116] Where: E s is the final elastic modulus of concrete; R is the basic constraint coefficient (values ​​are taken according to Table 1 or Table 2), α is the linear expansion coefficient of concrete, μ is the Poisson's ratio of concrete, ΔT bs The difference between the temperature before the second stage cooling and the design target temperature of the second stage cooling; K p is the stress relaxation coefficient of concrete, which is approximately 0.5.

[0117] 5. Before the second stage cooling of the concrete in the lower irrigation area is completed, assuming that no additional water cooling is performed on the concrete in the upper irrigation area, the calculated stress at the end of the second stage cooling of the concrete in the lower irrigation area is:

[0118] f=σ b +σ s +Δσ bs (18)

[0119] If f≤σ0, there is no need to conduct additional water cooling on the concrete in the upper irrigation area before the second stage cooling of the concrete in the lower irrigation area begins.

[0120] If f>σ0, it is necessary to supplement water cooling for the upper irrigation area concrete before the second stage cooling of the lower irrigation area concrete begins. At the end of the supplementary water cooling, the influence of the upper irrigation area concrete on the temperature stress of the lower irrigation area is:

[0121]

[0122] Where: E s is the final elastic modulus of concrete; R is the basic constraint coefficient (according to Table 1 or Table 2), α is the linear expansion coefficient of concrete, μ is the Poisson's ratio of concrete; ΔT ss To supplement the decrease in upper concrete temperature; K p is the stress relaxation coefficient of concrete, which is approximately 0.5.

[0123] Adjust the temperature of the upper concrete layer in the irrigation area so that σ b , σ s , Δσ bs and ΔT ss The sum is less than or equal to the allowable tensile strength of concrete σ0. At the end of the second stage cooling, the stress should meet the following criteria:

[0124] σ b +σ s +Δσ bs +Δσ ss ≤σ0 (20)

[0125] Where: σ0 is the allowable tensile strength.

[0126] According to equations (18) and (19) and considering that a large decrease in the temperature of the upper concrete layer may lead to an increase in its own stress and a delay in the construction progress, the temperature decrease of the upper irrigation area concrete after supplementary water cooling is:

[0127]

[0128] Advantages of the present invention:

[0129] The present invention provides a dam body temperature stress control method that takes into account the temperature difference in the irrigation area and the development of the concrete elastic modulus, that is, before the second phase cooling of the concrete, the temperature stress of the concrete at the end of the second phase cooling and water supply is predicted based on the existing temperature data and the change of the concrete elastic modulus, and the stress calculation is used to determine whether the upper irrigation area concrete should be supplemented with water supply before the lower irrigation area is cooled, and the temperature reduction range of the supplementary water supply is obtained, and finally the stress of the lower irrigation area concrete is optimized by adjusting the temperature of the upper irrigation area concrete before the second phase cooling of the lower irrigation area. Effectively applying temperature monitoring data, more flexible regulation of concrete temperature makes the control of concrete temperature stress more accurate, and the temperature control and crack prevention measures are effective.

[0130] Finally, it should be noted that the above-described embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some or all of the technical features thereof may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A dam body temperature stress control method considering the temperature difference in the irrigation area and the development of concrete elastic modulus, characterized by: Before the second stage cooling of concrete, the temperature stress of concrete at the end of the second stage cooling water flow is predicted based on the existing temperature data and the change of concrete elastic modulus. Through the calculation of stress, it is judged whether the concrete in the upper irrigation area should be supplemented with water flow before the lower irrigation area is cooled by water flow and the temperature reduction range of the supplementary water flow is obtained. Finally, the stress of the concrete in the lower irrigation area is optimized by adjusting the temperature of the upper concrete in the irrigation area before the second stage cooling of the lower irrigation area. The specific method is as follows: S1. Considering the change history of concrete elastic modulus, calculate the foundation temperature stress σ of the concrete dam body before the second stage cooling b ; Before the second stage cooling of the concrete dam body, the concrete age is t n When [0,t n ] The time period is divided into n periods, where the start time of the i-th period is t i-1 , the end time is t i , when i=1 and t0=0, the temperature stress increment of the basic temperature difference stress at a point inside the concrete in the i-th period is: Where: t ki =0.5(t i-1 +t i ); E(t ki ) is t ki The concrete elastic modulus at the moment; R is the basic constraint coefficient, α is the concrete linear expansion coefficient, μ is the concrete Poisson's ratio, ΔT i t i Temperature increment during a period; K p is the stress relaxation coefficient of concrete, which is approximately 0.5; Before the second stage cooling, the concrete age is t n When the foundation temperature stress σ b for: S2. Considering the influence of the upper tank area concrete on the temperature stress of the lower tank area concrete, calculate the temperature difference temperature stress σ of the concrete dam body before the second phase cooling s ; Before the second stage cooling, when the concrete pouring age of the upper tank area is t m When [0,t m ] The period is divided into m periods, where the start time of the jth period is t j-1 The end time is t j , when j = 1 and t0 = 0, the temperature stress increment of the upper tank area concrete on the lower tank area concrete in the jth period is: Where: t kj =0.5(t j-1 +t j );E s (t kj ) is t kj The elastic modulus of the concrete in the upper tank area at the moment; R is the basic constraint coefficient, α is the linear expansion coefficient, μ is the Poisson's ratio, ΔT j t j The temperature difference increment between the concrete in the upper irrigation area and the concrete in the lower irrigation area during the period; K p is the stress relaxation coefficient of concrete, which is approximately 0.5; The age of concrete pouring in the upper mixing tank area is t m When the concrete in the lower tank area is poured, the temperature stress generated by the concrete pouring in the upper tank area is: S3, n is taken as k times the number of days of concrete age before the second stage cooling. The temperature stress of the foundation temperature difference and the temperature difference between the upper and lower layers during the concrete age is calculated in equal time periods. When the following conditions are met, the foundation temperature stress σ b and the temperature stress of the irrigation area s Satisfy the calculation accuracy conditions: S4. Calculate the stress increment formed by the second stage cooling according to the final elastic modulus of concrete and the target cooling temperature: Where: E s is the final elastic modulus of concrete; R is the basic constraint coefficient, α is the linear expansion coefficient of concrete, μ is the Poisson's ratio of concrete, ΔT bs The difference between the temperature before the second stage cooling and the design target temperature of the second stage cooling; K p is the stress relaxation coefficient of concrete, which is approximately 0.5; S5. Before the second stage cooling of the concrete in the lower irrigation area is completed, assuming that no additional water cooling is performed on the concrete in the upper irrigation area, the calculated stress at the end of the second stage cooling of the concrete in the lower irrigation area is: f=σ b +s s +Ds bs (18) S5.

1. If f≤σ0, there is no need to conduct additional water cooling on the concrete in the upper irrigation area before the second stage cooling of the concrete in the lower irrigation area begins; S5.

2. If f>σ0, it is necessary to supplement water cooling for the concrete in the upper irrigation area before the second stage cooling of the concrete in the lower irrigation area begins; at the end of the supplementary water cooling, the influence of the concrete in the upper irrigation area on the temperature stress of the lower irrigation area is: Where: E s is the final elastic modulus of concrete; R is the basic constraint coefficient, α is the linear expansion coefficient of concrete, μ is the Poisson's ratio of concrete; ΔT ss To supplement the decrease in upper concrete temperature; K p is the stress relaxation coefficient of concrete, which is approximately 0.5; adjust the temperature of the upper concrete layer in the irrigation area so that σ b , σ s , Δσ bs and ΔT ss The sum is less than or equal to the allowable tensile strength of concrete σ0. At the end of the second stage cooling, the stress should meet the following criteria: s b +s s +Ds bs +Ds ss ≤σ0 (20) Where: σ0 is the allowable tensile strength; According to equations (18) and (19) and considering that a large decrease in the temperature of the upper concrete layer may lead to an increase in its own stress and a delay in the construction progress, the temperature decrease of the upper irrigation area concrete after supplementary water cooling is:

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