Heightening method for gravity dam with limited combination of rear upper

Abstract

A gravity dam heightening method with limited combination of a rear upper comprises the steps that a finite element numerical model of a dam body is established; setting the joint surface of the new concrete dam and the old concrete dam as an interface unit, and calculating the normal stress and shear stress of the interface unit in the whole process of the new concrete dam; dividing the joint surface into a plurality of parts, and calculating the total shear force, the total normal pressure and the total normal tension corresponding to each part; according to the total shearing force and the total normal pressure corresponding to each part, the key groove size corresponding to the part is obtained; according to the total normal tension and the total normal pressure corresponding to each part, the total area of the reinforcing steel bars corresponding to the part and the distance and the length of the reinforcing steel bars are obtained; in the dam body construction process, construction is conducted according to the key groove size of each part, the total area of reinforcing steel bars, the distance between the reinforcing steel bars and the length of the reinforcing steel bars; therefore, the old dam body and the new dam body achieve a certain combination (fitting) ratio.

Description

Technical Field

[0001] The present invention relates to the technical field of water conservancy projects, and particularly relates to a method for heightening a gravity dam with limited connection at the rear slope. Background Art

[0002] There are more and more projects for second or multiple heightening of existing dams. The heightening methods of gravity dams include six types: integral connection at the rear slope, separated connection at the rear slope, integral connection at the front slope, combined connection of the front slope and the rear slope, heightening by prestressed anchor cables, and direct heightening at the dam crest. Among them, integral connection at the rear slope and separated connection at the rear slope are the most common. To ensure the heightening effect, both common heightening methods need to take engineering measures to ensure that the bonding degree between the newly heightened dam body and the old dam body reaches the designed required state, that is, the two are connected as a whole or completely separated.

[0003] In the actual dam projects with integral connection at the rear slope for heightening, through on-site tests and simulation calculations, it is found that it is difficult to connect the new and old dam bodies as a whole by conventional engineering measures. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for heightening a gravity dam with limited connection at the rear slope, which can increase the bonding strength of the bonding surface between the new and old concretes and solve the problem that it is difficult to connect the new and old dam bodies as a whole or completely disconnect them.

[0005] To achieve the above purpose, the present invention adopts the following technical solutions:

[0006] A method for heightening a gravity dam with limited connection at the rear slope, the method comprising:

[0007] Establishing a finite element numerical model of the dam body, the dam body including a new concrete dam and an old concrete dam;

[0008] Setting the bonding surface between the new concrete dam and the old concrete dam as an interface element, and calculating the normal stress and shear stress of the interface element during the whole process of the new concrete dam;

[0009] Dividing the bonding surface into multiple parts, and calculating the total shear force, total normal pressure, and total normal tension corresponding to each part;

[0010] Obtaining the key groove size corresponding to each part according to the total shear force and total normal pressure corresponding to each part;

[0011] Obtaining the total steel bar area, the spacing and length of the steel bars corresponding to each part according to the total normal tension and total normal pressure corresponding to each part;

[0012] During the construction of the dam body, constructing according to the key groove size, total steel bar area, steel bar spacing, and length of each part;

[0013] Among them, the whole process includes the pouring stage and the operation stage.

[0014] In one embodiment, the step of "calculating the total shear force, total normal pressure, and total normal tension corresponding to each part" includes:

[0015] Calculating the maximum shear stress, maximum normal tensile stress, and maximum normal compressive stress of each of the interface units;

[0016] Summing up the maximum shear stresses of all the interface units corresponding to each part to obtain the total shear force corresponding to that part;

[0017] Summing up the maximum normal tensile stresses of all the interface units corresponding to each part to obtain the total normal pressure corresponding to that part;

[0018] Summing up the maximum normal compressive stresses of all the interface units corresponding to each part to obtain the total normal tension corresponding to that part.

[0019] In one embodiment, a full-process stress search method is adopted to search for the maximum shear stress, maximum normal tensile stress, and maximum normal compressive stress of each of the interface units.

[0020] In one embodiment, the key groove is an isosceles trapezoidal groove opened on the surface of the old concrete dam, the bottom side of the isosceles trapezoidal groove is equal in length to the two side edges, and the distance between two adjacent isosceles trapezoidal grooves is equal to the length of the bottom side;

[0021] The step of "determining the key groove size corresponding to each part according to the total shear force and total normal pressure corresponding to each part" includes:

[0022] Combining the total shear force and total normal pressure corresponding to each part;

[0023] Assuming that the resultant force is perpendicular to the upper side edge of the key groove, the angles of each side of the isosceles trapezoidal groove are obtained;

[0024] Obtain the shear-resistant area of the key groove according to the following formula;

[0025]

[0026] where A k lT is the shear-resistant area of the key groove corresponding to the kth part, τ f is the tensile strength of the concrete of the new concrete dam, T k is the total shear force corresponding to the kth part;

[0027] Obtain the shear-resistant length of the key groove based on the shear-resistant area;

[0028] The notch length of the keyway is equal to the shear resistance length.

[0029] In one embodiment, the step of "obtaining the total steel bar area, the spacing and the length of the steel bars corresponding to each part according to the total normal tensile force and the total normal pressure corresponding to each part" includes:

[0030] Obtain the total steel bar area according to the following formula:

[0031]

[0032] where A sk is the total area of the steel bars corresponding to the kth part, f s is the tensile strength of the steel bars, and N lk is the total normal tensile force corresponding to the kth part;

[0033] Obtain the spacing of the steel bars according to the following formula:

[0034] A f =πd f 2 / 4

[0035] A m =πd m 2 / 4

[0036]

[0037] where d m is the spacing of the steel bars, P f (l) is the stress of the internal steel bars of the concrete of the new concrete dam, Pm(l) is the tensile strength under the combined action of the steel bars and the concrete, E m is the elastic modulus of the concrete of the new concrete dam, E f is the elastic modulus of the steel bars, and d f is the diameter of the steel bars;

[0038] Calculate the length of the steel bars according to the following formula:

[0039]

[0040] where l is the length of the steel bars, and N pk is the total normal pressure corresponding to the part, and τ is the bond force of the concrete of the new concrete dam to the steel bars.

[0041] In one embodiment, the new concrete dam is cast in layers, and the method further includes:

[0042] Calculating the maximum temperature and the stable temperature stress of the concrete for each layer of casting by using the finite element numerical model;

[0043] Obtain the basic temperature difference of each layer of concrete according to the maximum temperature and the stable temperature of the concrete poured in each layer.

[0044] Obtain the allowable basic temperature difference of the concrete poured in each layer according to the basic temperature difference of the concrete poured in each layer.

[0045] Obtain the allowable maximum temperature according to the allowable basic temperature difference of the concrete poured in each layer and the stable temperature of the concrete poured in each layer.

[0046] Correspondingly,

[0047] In the construction of the dam body, set heat preservation measures according to the allowable maximum temperature corresponding to each layer of concrete.

[0048] In one embodiment, the step of "obtaining the basic temperature difference of each layer of concrete according to the maximum temperature and the stable temperature of the concrete poured in each layer" includes:

[0049] Calculate the basic temperature difference of the concrete poured in each layer according to the following formula:

[0050] ΔT i =T mi -T am

[0051] Wherein, ΔT i is the basic temperature difference of the concrete poured in the i-th layer, T mi is the maximum temperature of the concrete poured in the i-th layer, T am is the stable temperature of the concrete.

[0052] In one embodiment, "obtaining the allowable basic temperature difference of the concrete poured in each layer according to the basic temperature difference of the concrete poured in each layer"

[0053] Calculate the allowable basic temperature difference of the concrete poured in each layer according to the following formula:

[0054]

[0055] Wherein, is the allowable basic temperature difference of the concrete poured in the i-th layer, τ f is the tensile strength of the concrete, σ mi is the maximum tensile stress of the concrete poured in the i-th layer.

[0056] In one embodiment, the step of "obtaining the allowable maximum temperature according to the allowable basic temperature difference of the concrete poured in each layer and the stable temperature of the concrete poured in each layer" includes:

[0057] Calculate the allowable maximum temperature of the concrete poured in each layer according to the following formula:

[0058]

[0059] Among them, is the allowable maximum temperature of the concrete poured in the i-th layer.

[0060] The advantages of the present invention are as follows:

[0061] A method for heightening a rear-bonding finite-combined gravity dam provided by the present invention increases the bonding strength of the bonding surface between new and old concretes, so that a certain bonding (fitting) ratio is achieved between the new and old dam bodies to ensure the effect of combined stress between the new and old dam bodies. Description of the Drawings

[0062] Figure 1 is a schematic diagram of the main steps of a method for heightening a rear-bonding finite-combined gravity dam of the present invention;

[0063] Figure 2 is a schematic diagram of the effect of a finite element numerical model of the present invention;

[0064] Figure 3 is a schematic diagram of the structure of an interface element of the present invention;

[0065] Figure 4 is a schematic diagram of the structure of the four parts divided by an interface element of the present invention;

[0066] Figure 5 is a schematic diagram of the total shear force and total normal pressure of the four parts of an interface element of the present invention;

[0067] Figure 6 is a schematic diagram of the total normal tensile force of the four parts of an interface element of the present invention;

[0068] Figure 7 is a schematic diagram of the structure of a key groove of the present invention;

[0069] Figure 8 is a max-min nephogram of the tangential stress of an interface element of the present invention;

[0070] Figure 9 is a numerical simulation schematic diagram of the layered pouring of a new concrete dam of the present invention. Detailed Embodiment

[0071] The heightening of the rear-bonded finite-combined gravity dam is achieved by adopting a complete set of technologies for the combination of new and old dam bodies, including interface treatment measures (including interface trimming, roughening, and applying interface agents), load-transfer key groove structure measures, through-seam anchor bolts and grouting systems, temperature control measures, etc., to achieve a certain combination (fitting) ratio between the new and old dam bodies, so as to ensure the combined stress effect between the new and old dam bodies. The present invention mainly improves in three aspects: the key groove structure (load-transfer key groove) of the joint surface, the reinforcement layout (through-seam anchor bolts), and the temperature control, so as to increase the bonding strength of the joint surface between the new and old concretes. The following will describe in detail the method for heightening the rear-bonded finite-combined gravity dam provided by the embodiments of the present invention with reference to the accompanying drawings.

[0072] Refer to the attached Figure 1 , Figure 1 which are the main steps of a method for heightening a rear-bonded finite-combined gravity dam according to an embodiment of the present invention. As Figure 1 shown, the method for heightening the rear-bonded finite-combined gravity dam provided by this embodiment includes:

[0073] Step S1: Establish a finite element numerical model of the dam body.

[0074] Specifically, the dam body includes a new concrete dam and an old concrete dam. The old concrete dam is the dam body to be heightened, and the new concrete dam is the dam body to be increased on the old concrete dam. As Figure 2 shown, this embodiment adopts finite element simulation calculation. By establishing a numerical model, the process of pouring the new concrete dam on the old concrete dam is simulated.

[0075] Step S2: Set the joint surface between the new concrete dam and the old concrete dam as an interface element, and calculate the normal stress and shear stress of the interface element throughout the whole process of the new concrete dam.

[0076] Specifically, the whole process includes the pouring stage and the operation stage. During the pouring and operation processes, conditions such as temperature change and water level change need to be added to the finite element numerical model. In addition, to ensure that the interface element does not crack during the calculation process, a sufficiently large bonding strength needs to be set for the interface element. Figure 3 shown, is the interface element of this embodiment.

[0077] Step S3: Divide the joint surface into multiple parts, and calculate the total shear force, total normal pressure, and total normal tension corresponding to each part.

[0078] Specifically, the joint surface between the old concrete dam and the new concrete dam is divided into multiple parts, and the number of divisions is at least 3. Refer to the attached Figure 4 , this embodiment divides it into 4 parts. Among them, the steps of calculating the total shear force, total normal pressure, and total normal tension corresponding to each part include:

[0079] Step S31: Calculate the maximum shear stress, maximum normal tensile stress, and maximum normal compressive stress of each interface element.

[0080] In this embodiment, the full-process stress search method is adopted to search for the maximum shear stress, maximum normal tensile stress, and maximum normal compressive stress of each interface element.

[0081] Maximum shear stress: τ mi =max{|τ i | k}, k = 1, 2... maxstep;

[0082] Maximum tensile stress: σ mli =max{|σ li | k}, k = 1, 2... maxstep;

[0083] Maximum compressive stress: σ mpi =max{|σ pi | k}, k = 1, 2... maxstep

[0084] Where, |τ i | k is the shear stress of the i-th interface element at the k-th time step; |σ li | k is the normal tensile stress of the i-th interface element at the k-th time step. When the normal stress is compressive, |σ li | k =0.0; |σ li | k is the normal compressive stress of the i-th interface element at the k-th time step. When the normal stress is tensile, |σ pi | k =0.0. In the formula, i = 1, 2,... nej, and nej is the total number of interface elements of the joint surface.

[0085] Step S32: Sum up the maximum shear stresses of all interface elements corresponding to each part to obtain the total shear force corresponding to that part. That is, the total shear force is: In this embodiment, the total shear forces of the 4 parts are as Figure 5 shown.

[0086] Step S33: Sum up the maximum normal tensile stresses of all interface elements corresponding to each part to obtain the total normal pressure corresponding to that part. That is, the total normal pressure is: In this embodiment, the total normal pressures of the 4 parts are as Figure 5 shown.

[0087] Step S34: Sum up the maximum normal compressive stresses of all interface units corresponding to each part to obtain the total normal tensile force corresponding to this part. That is, the total normal tensile force is: In this embodiment, the total normal tensile forces of the 4 parts are as Figure 6 shown.

[0088] where k is the identifier of the divided part of the joint surface, k = 1, 2, 3, 4...; a i is the area of the i-th interface unit.

[0089] Step S4: Obtain the keyway size corresponding to each part according to the total shear force and total normal pressure corresponding to each part.

[0090] Specifically, the keyway is an isosceles trapezoidal groove opened on the surface of the old concrete dam. The bottom side of the isosceles trapezoidal groove is equal in length to the two side edges, and the distance between adjacent two isosceles trapezoidal grooves is equal to the length of the bottom side. In this way, by determining the length of one side and the angle of one vertex angle, the size of the keyway can be determined.

[0091] Specifically, determining the keyway size includes the following steps:

[0092] Step 41: Combine the total shear force and total normal pressure corresponding to each part;

[0093] Step 42: Assume that the resultant force is perpendicular to the upper side of the keyway, then the angles of each side of the isosceles trapezoidal groove can be obtained; as Figure 7 shown, P N is the resultant force of the total shear force and total normal pressure corresponding to this part. Assume that P N is perpendicular to the upper side of the keyway, so the angles of each side of the keyway can be determined.

[0094] Step 43: Obtain the shear-resistant area of the keyway according to the following formula;

[0095]

[0096] where A k lT is the shear-resistant area of the keyway corresponding to the k-th part, τ f is the tensile strength of the concrete of the new concrete dam, T k is the total shear force corresponding to the k-th part;

[0097] Step S44: Obtain the shear-resistant length of the keyway based on the shear-resistant area. Specifically, when calculating the stress of the joint surface, the max-min nephogram of the tangential stress of the joint surface can be obtained, as Figure 8As shown, it can be seen that the width of the area enclosed by the tangential stress lines here is basically the same. This width is determined during the dam body design and generally takes values within 18 meters to 20 meters. Therefore, by dividing the shear area by this width, the shear length of the keyway can be determined.

[0098] Step S45: The notch length of the keyway is equal to the shear length. As Figure 7 shown, the notch length of the keyway is L T .

[0099] Accordingly, through the above steps, the angles and lengths of each side of the keyway for each part can be determined, that is, according to the total shear force and total normal pressure corresponding to each part, the keyway dimensions corresponding to this part are obtained.

[0100] Step S5: According to the total normal tensile force and total normal pressure corresponding to each part, obtain the total cross-sectional area of the steel bars, the spacing and length of the steel bars corresponding to this part.

[0101] Specifically, the spacing of the steel bars is obtained according to the following formula:

[0102] A f = πd f 2 / 4

[0103] A m = πd m 2 / 4

[0104]

[0105] where d m is the steel bar spacing, P f (l) is the stress of the steel bars inside the concrete of the new concrete dam, which is obtained through tests. Pm(l) is the tensile strength under the combined action of the steel bars and concrete, which is obtained through tests. E m is the elastic modulus of the concrete of the new concrete dam, E f is the elastic modulus of the steel bars, d f is the diameter of the steel bars, which is determined according to the specification requirements during the on-site reinforcement of reinforced concrete.

[0106] The length of the steel bars is calculated according to the following formula:

[0107]

[0108] where l is the length of the steel bars, N pk is the total normal pressure corresponding to the said part, τ is the bond force of the concrete of the new concrete dam to the steel bars, τ is a constant value, which refers to the ability of the concrete to resist the slip of the steel bars and is usually expressed by the bond strength of the concrete.

[0109] Accordingly, through the above calculations, the area of the steel bars inserted in each part, the buried depth length of the steel bars, and the steel bar spacing can be obtained.

[0110] Step S6: Determine the allowable maximum temperature of the layered concrete of the new concrete dam.

[0111] As Figure 9 shown, the new concrete dam is poured in layers, and the height of the concrete poured in each layer is about 3 meters. During the pouring of each layer, heat preservation measures need to be set according to the allowable maximum temperature. The heat preservation measures include controlling the pouring temperature, water circulation during the construction period, and permanent heat preservation, etc., so as to ensure that the concrete temperature of each layer is less than the allowable maximum temperature.

[0112] Among them, the allowable maximum temperature of each layer is obtained according to the following steps:

[0113] Step S61: Use the finite element numerical model to calculate the maximum temperature and the stable temperature stress of the concrete poured in each layer.

[0114] Step S62: Obtain the basic temperature difference of the concrete in each layer according to the maximum temperature and the stable temperature of the concrete poured in each layer.

[0115] The basic temperature difference of the concrete poured in each layer is calculated according to the following formula:

[0116] ΔT i =T mi -T am

[0117] Among them, ΔT i is the basic temperature difference of the concrete poured in the i-th layer, T mi is the maximum temperature of the concrete poured in the i-th layer, and T am is the stable temperature of the concrete.

[0118] Step S63: Obtain the allowable basic temperature difference of the concrete poured in each layer according to the basic temperature difference of the concrete poured in each layer.

[0119] The allowable basic temperature difference of the concrete poured in each layer is calculated according to the following formula:

[0120]

[0121] Among them, is the allowable basic temperature difference of the concrete poured in the i-th layer, τ f is the tensile strength of the concrete, and σ mi is the maximum tensile stress of the concrete poured in the i-th layer.

[0122] Step S64: Obtain the allowable maximum temperature according to the allowable basic temperature difference of the concrete poured in each layer and the stable temperature of the concrete poured in each layer.

[0123] Calculate the allowable maximum temperature of the concrete poured in each layer according to the following formula:

[0124]

[0125] Wherein, is the allowable maximum temperature of the concrete poured in the i-th layer.

[0126] Step S7: During the construction of the dam body, construct according to the keyway dimensions, total steel area, steel bar spacing and length of each part, and during the process of layered construction of the new concrete dam, set thermal insulation measures according to the allowable maximum temperature corresponding to each layer of concrete.

[0127] By adopting the above-mentioned interface treatment (keyway), structural treatment (steel bars), and temperature control treatment measures, a high-rise structure of a gravity dam with limited combination at the back is formed, increasing the bonding strength of the bonding surface between the new and old concretes, and enabling a certain bonding (fitting) ratio between the old dam body and the new dam body.

[0128] The above is the preferred embodiment of the present invention and the technical principles applied. For those skilled in the art, any obvious changes such as equivalent transformation and simple replacement based on the technical solution of the present invention without departing from the spirit and scope of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for raising a rear-wall limited combined gravity dam, characterized in that: The method comprises: Establishing a finite element numerical model of a dam body, wherein the dam body includes a new concrete dam and an old concrete dam; The interface between the new concrete dam and the old concrete dam is set as an interface unit, and the normal stress and shear stress of the interface unit in the whole process of the new concrete dam are calculated; Dividing the joint surface into a plurality of parts, and calculating the total shear force, the total normal pressure and the total normal tension corresponding to each part; According to the total shear force and the total normal pressure corresponding to each of the parts, the keyway size corresponding to the part is obtained; According to the total normal tension and total normal pressure corresponding to each of the parts, the total area of ​​the steel bars corresponding to the part and the spacing and length of the steel bars are obtained; During the construction of the dam body, the construction is carried out according to the keyway size, total area of ​​steel bars, spacing and length of steel bars of each of the parts; The whole process includes a casting stage and an operation stage.

2. The method for raising the rear-side limited combined gravity dam according to claim 1, characterized in that: The steps for "Calculating the total shear force, total normal pressure, and total normal tension corresponding to each section" include: Calculating the maximum shear stress, the maximum normal tensile stress, and the maximum normal compressive stress of each interface unit; The maximum shear stresses of all interface units corresponding to each of the parts are summed to obtain the total shear force corresponding to the part; The maximum normal tensile stresses of all interface units corresponding to each of the parts are summed to obtain the total normal pressure corresponding to the part; The maximum normal compressive stresses of all interface units corresponding to each of the parts are summed to obtain the total normal tensile force corresponding to the part.

3. The method for raising the rear-side limited combined gravity dam as claimed in claim 2, characterized in that: The full-process stress search method is adopted to search out the maximum shear stress, the maximum normal tensile stress and the maximum normal compressive stress of each interface unit.

4. The method for raising the rear-side limited combined gravity dam according to claim 1, characterized in that: The keyway is an isosceles trapezoidal groove opened on the surface of the old concrete dam, the bottom side of the isosceles trapezoidal groove is equal to the two side sides, and the spacing between two adjacent isosceles trapezoidal grooves is equal to the length of the bottom side; The step of "determining the keyway size corresponding to each of the parts according to the total shear force and the total normal pressure corresponding to the part" comprises: summing the total shear force and the total normal pressure corresponding to each of said parts; Assuming that the resultant force is perpendicular to the upper side of the keyway, the angles of the sides of the isosceles trapezoidal groove are obtained; The shear area of ​​the keyway is obtained according to the following formula; Among them, A k lT is the shear area of ​​the keyway corresponding to the kth part, τ f is the tensile strength of the concrete of the new concrete dam, T k is the total shear force corresponding to the kth part; Obtaining a shear length of the keyway based on the shear area; The slot length of the key slot is equal to the shear resistance length.

5. The method for raising the rear-side limited combined gravity dam according to claim 1, characterized in that: The step of "obtaining the total area of ​​steel bars corresponding to each portion and the spacing and length of the steel bars according to the total normal tension and the total normal pressure corresponding to each portion" includes: The total area of ​​the steel bars is obtained as follows: Among them, A sk is the total area of ​​the steel bars corresponding to the kth part, f s is the tensile strength of the steel bar, N lk is the total normal tension corresponding to the kth said part; The spacing of the steel bars is obtained as follows: A f =πd f 2 / 4 A m =πd m 2 / 4 Among them, d m is the spacing between the bars, P f (l) is the stress of the steel bars inside the concrete of the new concrete dam, Pm(l) is the tensile strength of the steel bars and concrete, E m is the concrete elastic modulus of the new concrete dam, E f is the elastic modulus of the steel bar, d f is the diameter of the steel bar; The length of the steel bar is calculated as follows: Where l is the length of the steel bar, N pk is the total normal pressure corresponding to the part, and τ is the bond strength of concrete on the steel bars of the new concrete dam.

6. The method for raising the rear-side limited combined gravity dam according to claim 1, characterized in that: The new concrete dam is poured in layers, and the method further comprises: Calculating the maximum temperature and stable temperature stress of each layer of poured concrete using the finite element numerical model; According to the maximum temperature and stable temperature of each layer of poured concrete, the basic temperature difference of each layer of concrete is obtained; According to the base temperature difference of each layer of poured concrete, the allowable base temperature difference of each layer of poured concrete is obtained; Obtaining the maximum allowable temperature according to the allowable basic temperature difference of each layer of poured concrete and the stable temperature of each layer of poured concrete; Accordingly, During the dam body construction, thermal insulation measures are provided according to the maximum allowable temperature corresponding to each layer of concrete.

7. The method for raising the rear-wall limited combined gravity dam according to claim 6, characterized in that: The steps of "obtaining the basic temperature difference of each layer of concrete according to the maximum temperature and stable temperature of each layer of poured concrete" include: Calculate the base temperature difference of each layer of poured concrete according to the following formula: ΔT i =T mi -T am Where, ΔT i is the base temperature difference of the i-th layer of poured concrete, T mi is the maximum temperature of the concrete poured in the i-th layer, T am is the stable temperature of concrete.

8. The method for raising the rear-side limited combined gravity dam according to claim 7, characterized in that: "According to the base temperature difference of each layer of poured concrete, obtain the allowable base temperature difference of each layer of poured concrete" Calculate the allowable foundation temperature difference of each layer of poured concrete according to the following formula: in, is the allowable foundation temperature difference of the i-th layer of concrete poured, τ f is the tensile strength of concrete, σ mi is the maximum tensile stress of the concrete poured in the i-th layer.

9. The method for raising the rear-side limited combined gravity dam according to claim 8, characterized in that: The step of "obtaining the maximum allowable temperature according to the allowable basic temperature difference of each layer of poured concrete and the stable temperature of each layer of poured concrete" includes: The maximum allowable temperature of each layer of poured concrete is calculated as follows: in, is the maximum allowable temperature of the concrete poured in the i-th layer.

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