A Simulation Method for Crack Resistance of Dam Concrete in High-Altitude and Cold Regions

Abstract

This invention relates to the field of hydraulic engineering technology and discloses a simulation method for crack resistance of dam concrete in high-altitude and cold regions. The method includes establishing a three-dimensional finite element model of the dam body, dam section, and foundation, and dividing it into constraint zones; obtaining the adiabatic temperature rise, autogenous volumetric deformation, elastic modulus, and creep of low-heat silicate cement concrete under low-temperature curing conditions, constructing a material constitutive model, and assigning corresponding material zones; applying boundary conditions for the high-altitude and cold environment and construction process, including air temperature correction conditions considering the solar radiation temperature rise effect and water temperature boundary conditions based on the reservoir's stable stratification characteristics; and performing sequential coupling simulation calculations of the temperature field and stress field to obtain crack-sensitive areas. This invention solves the problem of inaccurate simulation results caused by directly applying medium-heat cement models in existing technologies, accurately reflecting the hardening and heating laws of low-heat cement in cold environments, improving the accuracy of temperature and stress field simulation calculations in high-altitude and cold regions, and providing a reliable basis for crack prevention in engineering projects.

Description

Technical Field

[0001] This invention relates to the field of water conservancy engineering technology, specifically to a simulation method for crack resistance of dam concrete in high-altitude and cold regions. Background Technology

[0002] As hydropower development in my country extends to high-altitude and cold regions, the temperature control and crack prevention of large-volume concrete faces increasingly stringent challenges. Low-heat silicate cement, due to its characteristics such as low heat of hydration and stable strength growth in later stages, is gradually becoming the preferred cementing material for hydraulic dams in high-altitude and cold regions.

[0003] Currently, simulation analysis and crack resistance evaluation methods for the temperature stress field of dam concrete are mainly based on the physical and mechanical properties of traditional intermediate-heat silicate cement. Existing technologies typically utilize finite element software, combined with conventional adiabatic temperature rise models, elastic modulus growth models, and creep models, to simulate and calculate the temperature and stress fields during the dam construction and operation periods, and to formulate temperature control standards such as the maximum allowable temperature.

[0004] However, when directly applying the mature simulation system for medium-heat cement to low-heat cement concrete dams in high-altitude and cold regions, there is a lack of quantitative models for the time-varying thermodynamic parameters of low-heat cement concrete under high-altitude and cold curing conditions. The early-age hydration heat release rate, autogenous volume deformation (micro-expansion characteristics), creep, and mechanical strength development patterns of low-heat cement concrete are fundamentally different from those of medium-heat cement. Especially in the complex environment of low temperature and strong radiation in high-altitude and cold regions, the evolution of these characteristics of low-heat cement is still unclear, making it impossible to accurately assign values ​​in existing simulation calculations. Using the calculation parameters for medium-heat cement will lead to distorted simulation results, failing to accurately assess the crack-resistant advantages of low-heat cement, and failing to accurately identify the actual cracking risk areas of the dam body, making it difficult to formulate effective temperature control and crack prevention measures for the engineering site. Summary of the Invention

[0005] In view of this, the present invention provides a simulation method for crack resistance of dam concrete in high-altitude and cold regions to solve the problems mentioned in the background art.

[0006] This invention provides a simulation method for crack resistance of dam concrete in high-altitude and cold regions, comprising the following steps: A three-dimensional finite element model including the dam body, dam section, and foundation is established, and concrete constraint zones are divided in the three-dimensional finite element model; The adiabatic temperature rise, autogenous volumetric deformation, elastic modulus and creep of low-heat silicate cement concrete under preset low-temperature curing conditions were obtained, and a material constitutive model was constructed based on the obtained values. The material constitutive model is assigned to the corresponding concrete material partition in the three-dimensional finite element model; On the three-dimensional finite element model after the material constitutive model is applied, boundary conditions simulating the environment and construction process in high-altitude and cold regions are applied; the boundary conditions include at least the air temperature correction condition considering the temperature rise effect of solar radiation and the water temperature boundary condition based on the reservoir operation characteristics. Perform sequential coupled simulation calculations of temperature and stress fields from the construction period to the initial operation period to obtain the temperature field distribution, stress field distribution, and crack-prone areas of the dam concrete.

[0007] Beneficial Effects: This method, by establishing a three-dimensional finite element model and applying boundary conditions specific to cold environments, combined with the specific time-varying thermodynamic parameters of low-heat cement under preset low-temperature curing, solves the technical problem of inaccurate simulation results in cold regions caused by directly applying medium-heat cement models in existing technologies. Because the hydration rate of low-heat cement is temperature-sensitive, the actual internal temperature field evolution of dams in cold regions differs significantly from that under normal-temperature curing. Directly using normal-temperature curing parameters for simulation would incorrectly overestimate the early-age hydration heat rate and underestimate the micro-expansion compensation effect, leading to overestimation of stress calculation results. This scheme, through low-temperature parameter modeling, accurately reflects the hardening and heat generation laws of low-heat cement in cold environments. Specifically, this scheme introduces solar radiation temperature rise correction and reservoir water temperature boundaries. In cold regions, the large diurnal temperature range and strong solar radiation mean that neglecting solar radiation would lead to underestimation of the tensile stress calculation results on the dam surface, thus overlooking the risk of surface cracks. Furthermore, without considering water temperature stratification, it is impossible to accurately calculate the cold impact stress on the upstream face of the dam after impoundment. Based on the accurate inputs described above, the temperature envelope and tensile stress envelope obtained from subsequent coupled simulations can precisely locate sensitive areas such as the downstream surface of strongly constrained regions, providing reliable target points for crack prevention in engineering projects. This application can improve the accuracy and engineering reference value of simulation calculations of temperature and stress fields in low-heat cement concrete dams in cold regions.

[0008] In some embodiments, the boundary conditions simulating a high-altitude, cold region environment include: Obtain corrected monthly average air temperature and ground temperature data for the project location; In the upstream and downstream surfaces of the dam body and the boundary conditions of the storage area, a preset temperature increment is added to the monthly average temperature to simulate the solar radiation temperature rise effect in the plateau region.

[0009] Beneficial Effects: This scheme refines the simulation accuracy of high-altitude and cold environments. Although temperatures are low in high-altitude and cold regions, solar radiation is intense. Without this correction, the concrete surface in the simulation model dissipates heat too quickly, resulting in calculated surface tensile stresses that are lower than the actual values, leading engineers to misjudge the necessity of surface insulation. Specifically, this scheme compensates for the thermodynamic effect of the actual concrete surface temperature being higher than the air temperature due to strong solar radiation in high-altitude areas by adding a heat increment to the monthly average air temperature. This avoids surface stress calculation deviations caused by simplified boundary conditions and improves the accuracy of predicting the risk of surface cracks on the upstream and downstream surfaces of the dam and the surface of the dam.

[0010] In some embodiments, the water temperature boundary condition based on reservoir operating characteristics includes: Based on the stable stratification characteristics of the reservoir, monthly water temperature data distributed along the water depth during the reservoir's operation period are calculated and input as the temperature boundary conditions for the upstream face of the dam after impoundment.

[0011] Beneficial Effects: Reservoirs in high-altitude and cold regions are mostly stable stratified types, with the reservoir bottom water temperature remaining at around 4℃ year-round, while the dam body interior can reach 20-30℃ due to hydration heat. This huge temperature gradient is a significant factor leading to upstream face cracking. This scheme uses monthly, depth-based water temperature distribution calculated based on the reservoir's stable stratification characteristics as boundary conditions, providing accurate thermal load input and ensuring that the maximum tensile stress peak induced by the low temperature in deep water can be captured during coupled stress calculations. Compared to using fixed water temperature or coarse estimation methods, this approach can accurately simulate the cooling impact of the low temperature in deep water on the upstream face of the dam after impoundment and the induced longitudinal tensile stress, thus more accurately assessing the risk of cracking in the underwater portion of the upstream face of the dam during the initial operation phase.

[0012] In some embodiments, the material constitutive model includes at least: an adiabatic temperature rise model that varies with age, an autogenous volumetric deformation model, an elastic modulus growth model, and a creep model; The self-generated volumetric deformation model is configured to output positive volumetric strain increments during the first 7 to 28 days of the concrete's curing period. The creep rate function in the creep model satisfies the condition that, under the stress level of 30% of the compressive strength at 7 days of age, the calculated creep rate is not less than 45 × 10⁻⁶. 6 / MPa.

[0013] Beneficial effects: This scheme specifically optimizes the adiabatic temperature rise model, autogenous volumetric deformation model, elastic modulus growth model, and creep model for low-heat cement. Autogenous volumetric deformation outputs positive strain within 7-28 days, simulating the unique MgO or crystal expansion reaction of low-heat cement. In strongly constrained regions, this micro-expansion generates compressive stress, offsetting the tensile stress generated by subsequent temperature drop and shrinkage. The creep degree is not less than 45 × 10⁻⁶. -6 / MPa, because low-heat cement has low early strength but high creep, it means that under the same temperature drop load, concrete can release more stress through viscous flow. Such models can automatically release some of the temperature tensile stress in simulation, thereby avoiding misjudging low-heat cement dams as being in a high-risk state of cracking, and providing a basis for relaxing temperature control standards on site and saving engineering costs.

[0014] In some embodiments, the boundary conditions of the simulated construction process include dynamically simulating the layered pouring process, the inter-layer interval time, and the various phases of water cooling processes performed by the cooling water pipe network deployed within the dam body.

[0015] Beneficial effects: By dynamically simulating the entire process of layered pouring, intermittent and multi-stage cooling water circulation, the temperature during construction can be precisely adjusted to accurately capture the local stress concentration problem at the interlayer interface caused by improper interlayer intervals or unreasonable water circulation parameters, thereby guiding the optimization of construction operations and preventing cracking of horizontal construction joints.

[0016] In some embodiments, the simulation of the layered casting process includes: Different pouring layer thicknesses and inter-layer intervals are defined according to the concrete constraint zones; The strong constraint region uses the first layer thickness, while the weak constraint region or free region uses the second layer thickness, which is greater than the first layer thickness.

[0017] Beneficial effects: This scheme defines the pouring layer thickness based on the differentiating zones of the constrained areas. Under the premise of ensuring temperature control safety in the strongly constrained areas, it allows for a thicker pouring layer in the free areas to accelerate the construction progress, which is conducive to balancing construction speed and crack prevention safety.

[0018] In some embodiments, the boundary conditions simulating a high-altitude, cold region environment further include: The third type of heat exchange boundary parameter is the equivalent surface heat dissipation coefficient, which is applied to the permanently exposed surface of the dam and the surface of the winter construction site.

[0019] Beneficial effects: By applying heat exchange parameters of an equivalent surface insulation layer to the boundary conditions, the effect of insulation measures on reducing surface temperature gradients and decreasing surface tensile stress can be quantitatively evaluated. By changing the equivalent heat dissipation coefficient of the third type of boundary conditions, the degree of weakening of heat exchange between the concrete surface and the atmosphere after the insulation board is pasted is simulated. This helps to accurately design insulation schemes in cold regions, preventing surface cracking caused by cold waves and avoiding the difficulty of internal heat dissipation due to excessive insulation.

[0020] In some embodiments, the step of dividing the concrete confinement zone specifically includes: For the riverbed dam section, based on the length L of the long side of the cast block, the range of 0-0.2L above the foundation surface is defined as the strongly constrained zone, the range of 0.2L-0.4L is defined as the weakly constrained zone, and the range greater than 0.4L is defined as the free zone. For steep slope dam sections, all concrete below the slope crest elevation is defined as a strongly constrained zone.

[0021] Beneficial effects: By defining strong constraint zones and weak constraint zones for riverbed dam sections and steep slope dam sections respectively, the strength of the foundation constraints on different parts of the dam body can be accurately determined. This ensures that parameters such as the foundation elastic modulus ratio and autogenous volume deformation effect can be correctly applied according to the constraint state in subsequent stress calculations, avoiding the misjudgment of free areas as high-risk areas and resulting in unnecessary over-temperature control.

[0022] In some embodiments, after the step of performing sequential coupling simulation calculations of the temperature field and stress field, the method further includes: Extract the maximum temperature envelope and maximum tensile stress envelope of the dam body throughout the entire construction process; Output the highest temperature value of the dam body and the maximum principal stress value of the foundation constraint zone corresponding to the low-heat silicate cement concrete. This value is used to compare with the corresponding value when using medium-heat silicate cement concrete. Identify and output the crack-sensitive areas of the dam body, which include the location of the strongly constrained area within a preset depth range near the downstream face.

[0023] Beneficial effects: By outputting the envelope diagram of maximum temperature and tensile stress and directly comparing the numerical differences between low-heat cement and medium-heat cement, the crack resistance advantage of low-heat cement can be quantitatively expressed, which helps to demonstrate the performance of low-heat cement in reducing maximum temperature and reducing constraint stress during the engineering design stage.

[0024] In some embodiments, after the step of identifying and outputting the dam body crack-sensitive area, the method further includes: With the goal of controlling cracking risk, a multi-condition simulation sensitivity analysis was conducted on at least one of the construction parameters, namely pouring temperature, pouring layer thickness, cooling water supply scheme and surface insulation measures. Based on simulation results, output the maximum allowable temperature control standards for low-heat silicate cement concrete dams in high-altitude and cold regions, as well as the recommended values ​​for pouring temperature by season.

[0025] Beneficial effects: Based on the simulation results, multi-condition sensitivity analysis and optimization are carried out to generate an economical and efficient temperature control and crack prevention scheme applicable to high-altitude and cold regions. This scheme reduces cooling energy consumption, shortens the interlayer interval time, and increases the upper limit of the pouring temperature, thereby reducing the construction difficulty under the harsh natural conditions of high-altitude and cold regions, while ensuring that the dam does not develop through-cracks. Attached Figure Description

[0026] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0027] Figure 1 This is a schematic diagram of the overall model of section 12 of the arched dam in this embodiment of the invention; Figure 2 This is a schematic diagram of the dam body model of section 12 of the arched dam in this embodiment of the invention; Figure 3 This is a schematic diagram of the overall model of the steep slope dam section #19 in this embodiment of the invention; Figure 4 This is a schematic diagram of the dam body model of the steep slope dam section #19 in this embodiment of the invention. Figure 5 This is a three-dimensional schematic diagram of the material zoning of the arch crown dam section in an embodiment of the present invention; Figure 6 This is a schematic diagram of the horizontal and vertical cross-sections of the material partitioning of the arch crown dam section in an embodiment of the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] The following is combined Figures 1 to 6 The following describes embodiments of the present invention.

[0030] According to an embodiment of the present invention, a method for simulating crack resistance of dam concrete in high-altitude and cold regions is provided, comprising the following steps: S1. Establish a three-dimensional finite element model and divide it into constraint partitions: A three-dimensional finite element model including the dam body, dam sections, and foundation is established, and concrete constraint zones are divided within the three-dimensional finite element model. Specifically, in implementing this step, the dam structure design drawings and geological exploration data of the target high-altitude hydropower project are first used to perform preprocessing modeling using finite element analysis software. A three-dimensional solid model including typical dam sections and foundations is then established. Typical dam sections include arched dam sections and steep slope dam sections; see [reference needed]. Figures 1 to 4 The established model should be a three-dimensional solid model that can reflect the interaction between the dam body and the foundation. The geometric dimensions, material interfaces, and structural features of the model should accurately represent the dam body, dam sections, and foundation.

[0031] Based on this, the model is meshed, and in subsequent steps, the detailed concrete constraint zones are assigned as model attributes to the corresponding element sets so that the constraint effect of the foundation rock mass on the deformation of concrete at different elevations and locations can be considered in stress calculations.

[0032] In some embodiments, the step of dividing the concrete confinement zones specifically includes: for riverbed dam sections, based on the long side length L of the cast-in-place block, the range of 0-0.2L above the foundation surface is defined as a strongly confined zone, the range of 0.2L-0.4L is defined as a weakly confined zone, and the range greater than 0.4L is defined as a free zone; for steep slope dam sections, all concrete below the slope crest elevation is defined as a strongly confined zone. Defining strongly confined and weakly confined zones for riverbed and steep slope dam sections respectively precisely locks in the strength of foundation constraints on different parts of the dam body, thereby ensuring that parameters such as the foundation elastic modulus ratio and autogenous volumetric deformation effect can be correctly applied according to the constraint state in subsequent stress calculations, avoiding misjudging the free zone as a high-risk zone and causing unnecessary over-temperature control.

[0033] In particular, during mesh generation, local meshing is performed in strongly constrained areas, on the dam surface, and near orifices to ensure the calculation accuracy of temperature gradients and stress concentration areas.

[0034] S2. Obtain the parameters of low-heat cement under low-temperature curing and construct a material constitutive model: The adiabatic temperature rise, autogenous volumetric deformation, elastic modulus and creep of low-heat silicate cement concrete under preset low-temperature curing conditions were obtained, and a material constitutive model was constructed based on the obtained values; the preset low-temperature curing conditions were a temperature range of -5℃ to 10℃.

[0035] In specific embodiments, the material constitutive model includes at least: an adiabatic temperature rise model that varies with age, an autogenous volumetric deformation model, an elastic modulus growth model, and a creep model; For the adiabatic temperature rise model, the functional relationship between the adiabatic temperature rise and age is expressed as a hyperbola:

[0036] in, Age The adiabatic temperature rise over time, in °C; For the final adiabatic temperature rise value, 18-22℃ is selected based on the mix proportion and low-temperature curing conditions; , where is the concrete age in days (d); n is the hydration heat release rate parameter, taken as 2.5-3.5d.

[0037] For the autogenous volumetric deformation model, the functional relationship between autogenous volumetric deformation and age is expressed using an exponential decay type:

[0038] in, Age The autogenous volumetric strain at time, in units of ×10⁻⁶; The final value of the self-generated volumetric deformation is taken as a positive value of 30-60×10-6 under the preset low-temperature curing conditions; The concrete age is expressed in days (d). The expansion rate coefficient is taken as 0.10-0.18 d. -1 b is the decay coefficient in the later stage of expansion, taken as 0.005-0.015 d -1 This function allows the autogenous volumetric deformation to maintain a positive volumetric strain increment in the early stage (7 to 28 days of age), and then gradually stabilizes, in order to simulate the micro-expansion chemical prestress generated in low-heat cement during the middle stage of hydration reaction.

[0039] The self-generated volumetric deformation model was configured to output positive volumetric strain increments during the first 7 to 28 days of concrete curing; that is, to simulate the micro-expansion chemical behavior of low-heat cement in the middle of the hydration reaction. This expansion is typically in the range of tens of micro-strains, but is sufficient to produce considerable chemical prestress.

[0040] For the elastic modulus growth model, the functional relationship between the elastic modulus and age is expressed as an exponential function:

[0041] in, Age The elastic modulus at time , expressed in GPa; The final elastic modulus is taken as 30-38 GPa under the preset low-temperature curing conditions; d represents the concrete age in days (d); c is the elastic modulus growth rate coefficient, which decreases as the curing temperature decreases, and is taken as 0.08-0.15 d under low-temperature curing conditions. -1 .

[0042] For the creep model, the creep degree is expressed using a logarithmic empirical function:

[0043] in, For loading age is Hold load until time The creep at time, in units of ×10⁻⁶ / MPa; The creep reference value is taken as 18-25×10-6 / MPa; The loading period is in days (d). The load duration is expressed in days (d); the creep development index is taken as 0.25-0.40 under low-temperature curing conditions.

[0044] The creep function in the creep model satisfies the condition that, under the stress level of 30% of the compressive strength at 7 days of age, the calculated creep degree is not less than 45 × 10⁻⁶. 6 / MPa. This quantitative indicator establishes the boundary of the high creep characteristics of low-heat cement at early age in numerical terms, providing a reasonable reference for stress relaxation calculations in simulations.

[0045] This scheme specifically optimizes the adiabatic temperature rise model, autogenous volumetric deformation model, elastic modulus growth model, and creep model for low-heat cement. The autogenous volumetric deformation outputs positive strain within 7-28 days, simulating the unique MgO or crystal expansion reaction of low-heat cement. In strongly constrained regions, this micro-expansion generates compressive stress, offsetting the tensile stress generated by subsequent temperature drop and shrinkage. The creep degree is not less than 45 × 10⁻⁶. -6 / MPa, because low-heat cement has low early strength but high creep, it means that under the same temperature drop load, concrete can release more stress through viscous flow. Such models can automatically release some of the temperature tensile stress in simulation, thereby avoiding misjudging low-heat cement dams as being in a high-risk state of cracking, and providing a basis for relaxing temperature control standards on site and saving engineering costs.

[0046] Unlike existing technologies that use material parameters under normal temperature or standard curing conditions, this invention conducts material performance tests on low-heat silicate cement concrete under simulated actual environmental temperatures in cold regions. Specifically, multiple typical low-temperature curing chamber environments, such as -5℃, 0℃, 5℃, and 10℃, can be set up to monitor the low-heat cement concrete specimens over a long period. This allows for the acquisition of adiabatic temperature rise curves, autogenous volumetric deformation curves, compressive / tensile strength growth curves, elastic modulus growth curves, and creep curves at different ages. These data, measured under low-temperature conditions, reflect characteristics such as the slowdown in cement hydration rate and the evolution of micro-expansion effects. Based on these measured data, regression analysis or neural network fitting is used to establish a multi-field coupled material constitutive model, including an adiabatic temperature rise model, an autogenous volumetric deformation model, an elastic modulus growth model, and a creep model. This provides material input that conforms to actual cold-region conditions for subsequent simulation calculations.

[0047] S3: Assign the material constitutive model to the corresponding concrete material partitions in the 3D finite element model. After completing the finite element mesh generation and the mathematical expression of the material constitutive model, this step links the two. Specifically, based on the design grade partitioning diagram of the dam concrete (e.g., different pouring areas divided according to strength grade or impermeability grade), the specific time-varying thermodynamic parameter model under low-temperature curing constructed in step S2 is assigned to the corresponding element set in the model established in step S1. Thus, during simulation calculations, the concrete at different elevations and in different partitions of the dam can utilize the correct thermal and mechanical evolution laws according to its actual material category, avoiding calculation errors caused by using a single material parameter for the entire dam section.

[0048] S4. Apply boundary conditions for high-altitude and cold environments and construction processes: On the three-dimensional finite element model after the material constitutive model is applied, boundary conditions simulating the environment and construction process in high-altitude and cold regions are applied; the boundary conditions include at least the air temperature correction condition considering the temperature rise effect of solar radiation and the water temperature boundary condition based on the reservoir operation characteristics.

[0049] The boundary conditions for simulating high-altitude and cold-region environments include: S401: Obtain corrected monthly average air temperature and ground temperature data for the project site; based on years of measured statistical data from meteorological stations near the project site, a monthly average air temperature variation sequence representing typical hydrological years can be compiled.

[0050] S402: A preset temperature increment is added to the monthly average air temperature in the upstream and downstream surfaces and the boundary conditions of the dam body to simulate the temperature rise effect of solar radiation in plateau regions. In practice, this preset temperature increment can be taken as 3℃. Through this correction, an equivalent comprehensive temperature load that integrates the effects of air temperature and radiation is applied to the surface nodes of the simulation model, thereby accurately reflecting the actual temperature rise of the concrete surface due to the absorption of solar shortwave radiation.

[0051] This approach refines the simulation accuracy for high-altitude, frigid environments. While temperatures are low in these regions, solar radiation is intense. Without this correction, the concrete surface in the simulation model would dissipate heat too quickly, resulting in calculated surface tensile stresses that are lower than the actual values, leading engineers to misjudge the necessity of surface insulation. Specifically, this approach compensates for the thermodynamic effect of the actual concrete surface temperature being higher than the air temperature due to strong solar radiation at high altitudes by adding a heat increment to the monthly average air temperature. This avoids surface stress calculation errors caused by simplified boundary conditions and improves the accuracy of predicting the risk of surface cracks on the upstream and downstream surfaces of the dam and the dam's surface.

[0052] After obtaining the geothermal data in step S401, a third type of heat exchange boundary condition can be applied to the top surface of the bedrock. By defining the equivalent heat dissipation coefficient of the bedrock surface, the heat exchange process between the bedrock and the atmospheric environment during construction is realistically simulated, thereby avoiding the problem of distorted calculation of the concrete temperature gradient near the foundation surface due to neglecting the heat exchange of the bedrock.

[0053] In the specific implementation plan, to determine the monthly comprehensive equivalent temperature, daily measured data from long-term meteorological observation stations near the project site (with a continuous observation period of no less than 10 years) will be obtained, including daily average temperature, daily maximum temperature, daily minimum temperature, sunshine duration, and total solar radiation. Statistical analysis will be performed on the above data to compile a monthly average temperature series representing a typical hydrological year. (Where m = 1, 2, ..., 12 represents the month).

[0054] Based on this, the monthly comprehensive equivalent temperature is calculated using the following formula. The temperature value applied as a first or third type boundary condition to the concrete surface of the dam body (upstream and downstream surfaces and the surface of the dam):

[0055] in, is the comprehensive equivalent temperature of month m, in °C; is the multi-year average temperature of month m, in °C. This represents the increase in temperature due to solar radiation, expressed in °C.

[0056] In this embodiment, The value is determined comprehensively based on factors such as the latitude and altitude of the project site. For plateaus and surrounding high-altitude areas, this increment can be selected within the range of 2-5℃. In the absence of detailed radiation observation data, the following empirical scheme can be used to determine the value: Areas with an altitude of 2000-3000m: Set at 2-3℃; Areas with an altitude of 3000-4000m: Take 3-4℃; Areas above 4000m altitude: Set the temperature to 4-5℃.

[0057] In this embodiment, the altitude of the project site is approximately 3200m. Take 3℃.

[0058] Of course, with detailed data on solar radiation, a more precise estimate can be made using the following empirical formula:

[0059] in, The average daily total solar radiation intensity on the concrete surface in month m is expressed in W / m². 2 ; The solar radiation absorption coefficient of the concrete surface is taken as 0.5-0.6 for the dam surface concrete. The convective heat transfer coefficient of the concrete surface is taken as 15-25 W / (m²) under wind speed conditions of 2-4 m / s. 2 ℃); To account for the overall reduction factor of long-wave radiation heat dissipation at night, a value of 0.6-0.8 is taken.

[0060] When calculating using the above-mentioned refined method, The final value should be the arithmetic mean of the calculation results for each month.

[0061] In the finite element model, boundary conditions are applied in the following ways, depending on the different stages of the construction or operation phase: For the upstream and downstream surfaces and storage area during the construction period (belonging to the third type of boundary condition): the above comprehensive equivalent temperature The ambient temperature, along with the surface's equivalent heat dissipation coefficient, is applied to the corresponding nodes.

[0062] For the permanently exposed surface of the dam body during operation (belonging to Class I or Class III boundary conditions): It can be used as a first-type temperature boundary condition on a node, or as a medium temperature input in a third-type boundary condition.

[0063] The above scheme incorporates the thermal effect of strong sunlight on concrete surfaces in plateau regions into the simulation calculation, thereby accurately reflecting the actual distribution of the surface temperature field.

[0064] In a specific embodiment, the boundary conditions for simulating a high-altitude, cold region environment further include: applying a third type of heat exchange boundary parameter corresponding to the equivalent surface insulation layer to the permanently exposed surface of the dam and the surface of the winter construction area. The third type of heat exchange boundary parameter includes the equivalent surface heat dissipation coefficient. Specifically, based on the thermal conductivity and thickness of the insulation material to be used on site, such as a 5cm thick extruded polystyrene board, the equivalent convective heat transfer coefficient of the surface is calculated using the equivalent heat conduction formula, and the original bare surface heat dissipation coefficient is replaced on the model surface at the corresponding construction stage.

[0065] By applying equivalent surface insulation layer heat exchange parameters to the boundary conditions, the effect of insulation measures on reducing surface temperature gradient and mitigating surface tensile stress can be quantitatively evaluated. By changing the equivalent heat dissipation coefficient of the third type of boundary condition, the degree of weakening of heat exchange between the concrete surface and the atmosphere after the insulation board is pasted is simulated. This helps to accurately design insulation schemes in cold regions, preventing surface cracking caused by cold waves and avoiding the difficulty of internal heat dissipation due to excessive insulation.

[0066] S403: Calculate the monthly water temperature data along the water depth during the reservoir's operation period based on the reservoir's stable stratification characteristics; The water temperature boundary conditions based on reservoir operation characteristics include: calculating and inputting monthly water temperature data distributed along water depth during the reservoir's operation period, based on the reservoir's stable stratification characteristics, as the temperature boundary conditions for the upstream face of the dam after impoundment. Numerical simulation algorithms or empirical formulas for reservoir water temperature can be used to pre-calculate the temperature field distribution curves along elevation and depth in different months, based on reservoir capacity, inflow, meteorological conditions, and operation scheduling. Subsequently, in the finite element software, this temperature function, varying along elevation and time, is applied as a first-type boundary condition, i.e., a forced temperature boundary, to the nodes on the upstream face of the dam below the impoundment level.

[0067] Because reservoirs in high-altitude and cold regions are mostly of the stable stratified type, the water temperature at the bottom of the reservoir remains at around 4℃ year-round, while the temperature inside the dam body can reach 20-30℃ due to hydration heat. This huge temperature gradient is a significant factor leading to upstream face splitting. For reservoirs in high-altitude and cold regions, due to their large regulating capacity and relatively weak water flow, the reservoir water temperature exhibits a seasonally stable stratification characteristic in the vertical direction. This embodiment uses reservoir water temperature stratification discrimination parameters. Perform the following judgment:

[0068] in, The length of the reservoir is in meters (m). This represents the average annual inflow, in cubic meters (m³). 3 / s; The effective storage capacity of the reservoir is expressed in meters (m). 3 ; The acceleration due to gravity is taken as 9.81 m / s². 2 ; The average water depth of the reservoir is expressed in meters (m).

[0069] when When <0.1, the reservoir exhibits strong stratification; 0.1≤ When ≤1.0, it is a weakly stratified type; When the value is greater than 1.0, it is a fully mixed type.

[0070] After determining that the reservoir is a stable stratified type, the vertical water temperature distribution in front of the dam is estimated using an empirical method based on the principle of heat balance, according to the following formula:

[0071] in, The water temperature in month m, at a depth z from the reservoir surface, is expressed in °C. The reservoir surface water temperature in month m is expressed in °C and can be estimated based on local temperature data. In this embodiment, the average temperature of each month is taken plus 1-3 °C. z is the vertical depth from the reservoir surface, expressed in meters. This is the water temperature decay index along depth; for stratified reservoirs, this coefficient ranges from 0.015 to 0.030 m. -1 Values ​​can be taken within a range.

[0072] Reservoirs in high-altitude and cold regions typically exhibit a stable stratified structure, with the reservoir bottom water temperature remaining consistently at a low level of 4–6°C year-round. In specific calculations, the constant temperature of the reservoir bottom water can be incorporated. When the water depth exceeds a certain limit depth The constant boundary conditions afterwards. That is: When calculated < At that time, take = .

[0073] In this embodiment, Take 4.5℃.

[0074] In the absence of actual measured water temperature data, monthly reservoir surface water temperature The following formula can be used to adjust the local monthly average temperature. Conversion:

[0075] in, This is the correction value for the deviation between the water surface temperature and the air temperature in the m-th month. This value is affected by factors such as sunshine and wind speed, and is usually between -1 and 3℃.

[0076]

[0077] Based on the above method, 12 water temperature profiles were calculated for the monthly (January to December) water depth distribution along the dam front during the reservoir operation period (each profile contains a set of water temperature values ​​at different elevation nodes from the reservoir surface to the reservoir bottom).

[0078] In the finite element simulation model, the aforementioned water temperature data is applied as the first type of temperature boundary condition for nodes at various water depths on the upstream face of the dam after impoundment. Specifically, for each node on the upstream face of the dam below the water level after impoundment, water temperature profile data is retrieved based on its elevation and the month corresponding to the current calculation time, and the corresponding... The value is set as the forced temperature value of the node. For nodes in the variable water level zone, the temperature boundary conditions of the node are dynamically updated according to the monthly water level changes of the actual operation and scheduling line of the reservoir (water temperature boundary is applied when there is water, and air temperature boundary is applied when there is no water).

[0079] Using the above methods, this scheme can accurately simulate the cold impact of deep-water low temperature on the upstream face of the dam after impoundment and the induced tensile stress along the river, thereby more accurately assessing the risk of cracking in the underwater part of the upstream face of the dam during the initial stage of operation.

[0080] This scheme uses monthly, depth-based water temperature distribution calculated based on the reservoir's stable stratified characteristics as boundary conditions to provide accurate thermal load input, ensuring that the maximum tensile stress peak induced by the low temperature in deep water can be captured during coupled stress calculations. Compared to using fixed water temperature or coarse estimation methods, this scheme can accurately simulate the cooling effect of the low temperature in deep water on the upstream face of the dam after impoundment and the induced longitudinal tensile stress, thereby more accurately assessing the risk of cracking in the underwater portion of the upstream face of the dam during the initial stage of operation.

[0081] When applying boundary conditions, it is necessary not only to define the thermal and displacement constraints around the foundation and on the bottom surface, but more importantly, to apply dynamically changing environmental loads to the surfaces of the dam body that come into contact with the atmosphere and water. For example, on the air temperature boundary, the measured atmospheric temperature cannot be simply input; the surface radiation warming effect caused by strong solar radiation on the plateau must be superimposed. On the water temperature boundary, the water surface temperature cannot be estimated solely based on the water temperature; instead, a water temperature field distribution function covering the entire depth and all time periods must be introduced.

[0082] In a specific embodiment, the parameters of the cooling water pipe network are optimized in the boundary conditions of the simulated construction process. Specifically, in the established finite element model, cooling water pipe units can be arranged according to the actual construction organization design. For example, the horizontal and vertical spacing of the cooling water pipes can be increased from the commonly used 1.0m×1.5m in conventional medium-heat cement construction to 1.5m×1.5m, and simulation calculations can verify whether the temperature control requirements can still be met after increasing the spacing. At the same time, in the simulation of water cooling parameters, based on the characteristics of low-heat cement concrete with low heat generation and slow rate, the water temperature for the first, middle, and second phases of water cooling is specifically optimized: during the summer construction period, compared with the medium-heat cement scheme, the standard water temperature for water cooling can be increased by 2°C to 4°C. This adjustment is reflected in the simulation model as an increase in the boundary conditions of the cooling water temperature. By performing temperature field simulations that include the above optimized parameters, the cooling curve inside the dam can be accurately predicted, and the energy-saving and consumption-reducing benefits of increasing the water temperature and increasing the pipe spacing can be quantitatively evaluated.

[0083] Perform sequential coupled simulation calculations of temperature and stress fields from the construction period to the initial operation period; obtain the temperature field distribution, stress field distribution, and cracking risk sensitive areas of the dam concrete.

[0084] S5. Post-processing and analysis: S501: Extract the maximum temperature envelope and maximum tensile stress envelope of the dam body throughout the entire construction process; the temperature envelope reflects the highest temperature experienced by each point inside the dam body in history, serving as the basis for verifying the allowable maximum temperature standard; the tensile stress envelope reflects the maximum tensile stress level borne by each point in history, which is an important basis for judging whether cracking has occurred.

[0085] S502: Outputs the highest temperature value of the dam body and the maximum principal stress value of the foundation confinement zone corresponding to low-heat silicate cement concrete. This value is used to compare with the corresponding value when using medium-heat silicate cement concrete. Specifically, by establishing a parallel comparison simulation model, the specific numerical advantages of the low-heat cement scheme in reducing temperature peaks and reducing tensile stress in the confinement zone are quantitatively evaluated.

[0086] S503. Identify and output the crack-sensitive areas of the dam body. The crack-sensitive areas include the location of the strong constraint zone near the downstream face within a preset depth range.

[0087] By outputting the envelope diagram of maximum temperature and tensile stress and directly comparing the numerical differences between low-heat cement and medium-heat cement, the crack resistance advantage of low-heat cement can be quantitatively expressed, which helps to demonstrate the performance of low-heat cement in reducing maximum temperature and reducing constraint stress during the engineering design stage.

[0088] In a specific simulation analysis example, this method was applied to compare the arch crown section of an ultra-high arch dam in a high-altitude, cold region, yielding quantitative advantages of the low-heat cement scheme compared to the traditional medium-heat cement scheme. Within the strongly constrained foundation zone, the highest internal temperature of the dam body using low-heat silicate cement concrete was reduced by approximately 4°C compared to the simulation results using medium-heat silicate cement concrete. Simultaneously, the maximum principal tensile stress in this region due to temperature changes and foundation constraints was reduced by approximately 0.5 MPa compared to the medium-heat cement scheme. This stress reduction effect verifies the effectiveness of low-heat cement in reducing the cracking risk of dams in high-altitude, cold regions.

[0089] S6. Regarding the optimization of the temperature control scheme: S601: With the goal of controlling cracking risk, perform multi-condition simulation sensitivity analysis on at least one of the following construction parameters: pouring temperature, pouring layer thickness, cooling water circulation scheme, and surface insulation measures. For example, for pouring temperatures of 12℃, 14℃, and 16℃, calculate the influence curves of each temperature on the maximum temperature and maximum stress to obtain the upper temperature limit that can be relaxed for low-heat cement concrete without causing stress to exceed the limit.

[0090] S602: Based on simulation results, output the zoned maximum allowable temperature control standards and seasonal pouring temperature recommendations for low-heat silicate cement concrete dams in high-altitude and cold regions. The output will include a detailed temperature control design parameter table, listing the maximum allowable temperature limits for different constraint zones in summer and winter, the recommended pouring temperature range, and the corresponding cooling water parameters.

[0091] Based on the simulation results, multi-condition sensitivity analysis and optimization were carried out to generate an economical and efficient temperature control and crack prevention scheme applicable to high-altitude and cold regions. This scheme aims to reduce cooling energy consumption, shorten interlayer interval time, and increase the upper limit of pouring temperature while ensuring that the dam does not develop through-cracks, thereby reducing the construction difficulty under the harsh natural conditions of high-altitude and cold regions.

[0092] In a specific embodiment, the boundary conditions for simulating the construction process include dynamically simulating the layered pouring process, the inter-layer interval time, and the cooling process of each stage performed by the cooling water pipe network deployed within the dam body. Using finite element software, concrete elements at corresponding elevations are activated layer by layer according to the actual construction schedule, and the initial pouring temperature and hydration heat generation load of that layer of concrete are applied simultaneously upon activation. For the cooling water pipes, discrete linear elements or equivalent negative heat source algorithms can be used, and different water temperatures, flow rates, and durations are set according to the first, middle, and second phase cooling schemes.

[0093] By dynamically simulating the entire process of layered pouring, intermittent and multi-stage cooling water circulation, the temperature during construction can be precisely adjusted to accurately capture local stress concentration problems at the interlayer interface caused by improper interlayer intervals or unreasonable water circulation parameters, thereby guiding the optimization of construction operations and preventing cracking of horizontal construction joints.

[0094] In a specific embodiment, the simulation of the layered casting process includes: Different pouring layer thicknesses and inter-layer intervals are defined according to the concrete constraint zones; The first layer thickness is used in the strongly constrained zone, while a second layer thickness greater than the first layer is used in the weakly constrained or free zone. For example, a thin layer of 1.5m can be used in the strongly constrained zone to facilitate heat dissipation, while a thick layer of 3.0m can be used in the free zone to accelerate the ascent. The corresponding interlayer interval can also be set differently according to the stress development requirements.

[0095] This scheme defines the pouring layer thickness based on the different constraints of the zones. While ensuring the temperature control safety of the strongly constrained zone, it allows for a thicker pouring layer in the free zone to accelerate the construction progress, which is beneficial to balancing construction speed and crack prevention safety.

[0096] This embodiment provides a simulation method for crack resistance of dam concrete in high-altitude and cold regions. By establishing a three-dimensional finite element model and applying boundary conditions specific to the high-altitude and cold environment, combined with specific time-varying thermodynamic parameters of low-heat cement under preset low-temperature curing, it solves the technical problem of inaccurate simulation results in high-altitude and cold regions caused by directly applying the model of medium-heat cement in existing technologies. Because the hydration rate of low-heat cement is temperature-sensitive, the actual internal temperature field evolution of dams in high-altitude and cold regions differs greatly from that under normal temperature curing. If normal temperature curing parameters are directly used for simulation, the early-age hydration heat rate will be overestimated and the micro-expansion compensation effect underestimated, leading to overestimation of stress calculation results. This scheme uses low-temperature parameter modeling to realistically reflect the hardening and heat generation laws of low-heat cement in cold environments. Specifically, this scheme introduces solar radiation temperature rise correction and reservoir water temperature boundary. High-altitude and cold regions have large diurnal temperature differences and strong solar radiation. Ignoring solar radiation will lead to underestimation of the tensile stress calculation results on the dam surface, thus overlooking the risk of surface cracks. Without considering water temperature stratification, the cold impact stress on the upstream surface of the dam after impoundment cannot be accurately calculated. Based on the accurate input described above, the temperature envelope map and tensile stress envelope map obtained from the subsequent coupled simulation can accurately locate sensitive areas such as the strongly constrained region near the downstream surface, providing reliable target points for crack prevention in engineering projects. The dam concrete crack resistance simulation method provided in this embodiment can improve the accuracy and engineering reference value of the simulation calculation of temperature and stress fields of low-heat cement concrete dams in high-altitude and cold regions.

[0097] In the specific implementation plan, the No. 12 arch crown dam section and the No. 19 steep slope dam section of a certain dam were selected as typical dam sections.

[0098] The finite element calculation model of section 12 of the arch crown dam is as follows: Figure 1 and Figure 2 As shown, the maximum bottom width of the dam section along the river is 54.0m, and the spacing between transverse joints is 18m. The overall mesh size of the model is 40200 elements and 50787 nodes. In the figure, the direction along the river is the X direction, the transverse direction is the Y direction, and the vertical direction is the Z direction.

[0099] For riverbed dam sections, the concrete within a height of 0.4L above the foundation surface of the dam section or cast-in-place block (L is the length of the long side of the cast-in-place block, the same below) is the foundation-constrained zone concrete, of which the 0~0.2L range is the strongly constrained zone concrete, and the 0.2L~0.4L range is the weakly constrained zone concrete. The strongly constrained zone range for the arched dam section is from 2955m to 2964m elevation, the weakly constrained zone range is from 2964m to 2976m elevation, and the area above 2976m elevation is the free zone. Boundary conditions for temperature field calculation of the arched dam section: the bedrock perimeter and bottom surface are adiabatic boundary conditions, and the top surface of the bedrock (excluding the foundation surface) is a third-type boundary condition; the upstream and downstream faces of the dam are third-type boundary conditions during construction, and first-type boundary conditions after impoundment. The effect of solar radiation is considered on the upstream and downstream faces, calculated as air temperature plus 3℃. Boundary conditions for stress field calculation: the bottom surface is triaxially constrained, and the remaining surfaces are free boundaries.

[0100] The finite element calculation model of the steep slope dam section #19 is as follows: Figure 3 and Figure 4 As shown, the horizontal joint spacing of the dam section is 20m, the maximum bottom width is about 53m, the model has 87424 grid elements and 108438 nodes. In the figure, the direction along the river is the X direction, the direction across the river is the Y direction, and the vertical direction is the Z direction.

[0101] For steep slope dam sections, the concrete below the slope crest elevation is considered strongly constrained concrete, the area from 0 to 0.2L above the slope crest is also considered strongly constrained concrete, and the area from 0.2L to 0.4L is considered weakly constrained concrete. The strongly constrained zone of the steep slope dam section extends from 2987m to 3047m elevation, the weakly constrained zone extends from 3047m to 3056m elevation, and the area above 3056m elevation is a free zone. Boundary conditions for temperature field calculation in the steep slope dam section: the bedrock perimeter and bottom surface are adiabatic boundary conditions, the top surface of the bedrock (excluding the foundation surface) is a third-type boundary condition; the upstream and downstream faces of the dam are third-type boundary conditions during construction, and first-type boundary conditions after impoundment. The effect of solar radiation is considered on the upstream and downstream faces, calculated as air temperature plus 3℃. Boundary conditions for stress field calculation: the foundation bottom surface is triaxially constrained, and the remaining surfaces are free boundaries.

[0102] The calculations used comparative data for ordinary materials and low-heat silicate cement concrete materials, as shown in the table below:

[0103] See dam body material zoning Figure 5 and Figure 6 In the simulation model, the dam concrete is divided into three material zones: Zone I, Zone II, and Zone III. Each zone is configured with different strength grades based on its location's stress characteristics and durability requirements: Zone III uses C18040W12F300 concrete, mainly placed in areas subject to strong water flow erosion and freeze-thaw cycles, such as the upstream water level fluctuation zone, the area around the orifice, and the downstream surface; Zone I uses C18035W10F300 concrete, placed in large-volume areas within the dam body; Zone II uses C18030W10F300 concrete, placed in areas with lower stress levels, such as within the foundation or in the upper free zone of the dam body.

[0104] In step S3, when assigning the material constitutive model to the corresponding partition, values ​​are assigned based on the parameters provided in the data table. Specifically, the time-varying parameters such as elastic modulus, ultimate tensile strength, allowable crack stress, adiabatic temperature rise, thermal conductivity, specific heat, and unit weight corresponding to each partition are input into the element set of the corresponding partition in the finite element model. The aforementioned data table provides a complete parameter comparison for both ordinary cement and low-heat cement.

[0105] Taking Zone III as an example, the elastic modulus of low-heat cement concrete at 7 days is 23.2 GPa, which increases to 39.2 GPa at 180 days, and the final value reaches 41.9 GPa, which is about 39.7% higher than the final value of 30 GPa of ordinary cement. When subjected to shrinkage deformation due to later temperature drop, the higher elastic modulus can provide the dam body with stronger resistance to restraint stress.

[0106] The allowable crack resistance stress is a crack resistance evaluation index calculated from the elastic modulus and ultimate tensile value. Although the allowable tensile stress of low-heat cement concrete is slightly lower than that of ordinary cement at the very early age of 7 days, it surpasses it from 28 days onwards. In Zone III, the allowable crack resistance stress of low-heat cement at 28 days is 1.27 MPa, exceeding that of ordinary cement (1.23 MPa); by 180 days, the allowable crack resistance stress of low-heat cement reaches 2.04 MPa, far exceeding that of ordinary cement (1.89 MPa); Zones II and I show the same trend. This indicates that in the most dangerous stage of water cooling to the arch sealing temperature in the second phase, the crack resistance safety margin of low-heat cement has significantly exceeded that of ordinary cement.

[0107] The thermal conductivity of low-heat cement is 7.6 kJ / (m·h·℃), lower than that of ordinary cement (8.2); its specific heat is 0.90 kJ / (kg·℃), lower than that of ordinary cement (0.95). The lower thermal conductivity helps slow the heat loss rate from the concrete surface, forming a natural protective layer during sudden temperature drops; the lower specific heat means less heat is required per unit volume of concrete to rise or fall, which helps reduce the absolute internal temperature rise. This, combined with the lower-heat characteristics resulting in a flatter adiabatic temperature rise curve, effectively reduces the maximum internal temperature of the dam.

[0108] In the early stages, low-heat cement exhibits low heat release during hydration and slight expansion, resulting in a structure under compression. In the later stages, the allowable crack-resistant stress increases significantly, providing a sufficient material performance basis for optimizing the temperature control scheme. In practical implementation, the pouring temperature can be reasonably relaxed, the water temperature can be increased, and the spacing between cooling water pipes can be expanded to reduce construction energy consumption and difficulty while ensuring the dam's crack prevention safety.

[0109] Although embodiments of the invention have been described in conjunction with the accompanying drawings, those skilled in the art can make various modifications and variations without departing from the spirit and scope of the invention, and such modifications and variations all fall within the scope defined by the appended claims.

Claims

1. A dam body concrete anti-cracking simulation method for high-cold regions, characterized in that, Includes the following steps: A three-dimensional finite element model including the dam body, dam section, and foundation is established, and concrete constraint zones are divided in the three-dimensional finite element model; The adiabatic temperature rise, autogenous volumetric deformation, elastic modulus and creep of low-heat silicate cement concrete under preset low-temperature curing conditions were obtained, and a material constitutive model was constructed based on the obtained values. The material constitutive model is assigned to the corresponding concrete material partition in the three-dimensional finite element model; On the three-dimensional finite element model after the material constitutive model is applied, boundary conditions simulating the environment and construction process in high-altitude and cold regions are applied; the boundary conditions include at least the air temperature correction condition considering the temperature rise effect of solar radiation and the water temperature boundary condition based on the reservoir operation characteristics. Perform sequential coupled simulation calculations of temperature and stress fields from the construction period to the initial operation period to obtain the temperature field distribution, stress field distribution, and crack-prone areas of the dam concrete.

2. The simulation method for crack resistance of dam concrete in high-altitude and cold regions according to claim 1, characterized in that, The boundary conditions for simulating a high-altitude, cold region environment include: Obtain corrected monthly average air temperature and ground temperature data for the project location; In the upstream and downstream surfaces of the dam body and the boundary conditions of the storage area, a preset temperature increment is added to the monthly average temperature to simulate the solar radiation temperature rise effect in the plateau region.

3. The simulation method for crack resistance of dam concrete in high-altitude and cold regions according to claim 1, characterized in that, The water temperature boundary conditions based on reservoir operation characteristics include: Based on the stable stratification characteristics of the reservoir, monthly water temperature data distributed along the water depth during the reservoir's operation period are calculated and input as the temperature boundary conditions for the upstream face of the dam after impoundment.

4. The simulation method for crack resistance of dam concrete in high-altitude and cold regions according to claim 1, characterized in that, The constitutive model of the material includes at least: an adiabatic temperature rise model that varies with age, an autogenous volumetric deformation model, an elastic modulus growth model, and a creep model; The self-generated volumetric deformation model is configured to output positive volumetric strain increments during the first 7 to 28 days of the concrete's curing period. The creep rate function in the creep model satisfies the condition that, under the stress level of 30% of the compressive strength at 7 days of age, the calculated creep rate is not less than 45 × 10⁻⁶. 6 / MPa.

5. The simulation method for crack resistance of dam concrete in high-altitude and cold regions according to claim 1, characterized in that, The boundary conditions for simulating the construction process include dynamically simulating the layered pouring process, the inter-layer interval time, and the cooling process carried out by the cooling water pipe network deployed in the dam body at each stage.

6. The simulation method for crack resistance of dam concrete in high-altitude and cold regions according to claim 5, characterized in that, The simulation of the layered casting process includes: Different pouring layer thicknesses and inter-layer intervals are defined according to the concrete constraint zones; The strong constraint region uses the first layer thickness, while the weak constraint region or free region uses the second layer thickness, which is greater than the first layer thickness.

7. The simulation method for crack resistance of dam concrete in high-altitude and cold regions according to claim 1, characterized in that, The boundary conditions for simulating a high-altitude, cold region environment also include: The third type of heat exchange boundary parameter is the equivalent surface heat dissipation coefficient, which is applied to the permanently exposed surface of the dam and the surface of the winter construction site.

8. The simulation method for crack resistance of dam concrete in high-altitude and cold regions according to claim 1, characterized in that, The steps for dividing the concrete confinement zones specifically include: For the riverbed dam section, based on the length L of the long side of the cast block, the range of 0-0.2L above the foundation surface is defined as the strongly constrained zone, the range of 0.2L-0.4L is defined as the weakly constrained zone, and the range greater than 0.4L is defined as the free zone. For steep slope dam sections, all concrete below the slope crest elevation is defined as a strongly constrained zone.

9. The simulation method for crack resistance of dam concrete in high-altitude and cold regions according to claim 1, characterized in that, After performing the sequential coupling simulation calculations of the temperature field and stress field, the following steps are also included: Extract the maximum temperature envelope and maximum tensile stress envelope of the dam body throughout the entire construction process; Output the highest temperature value of the dam body and the maximum principal stress value of the foundation constraint zone corresponding to the low-heat silicate cement concrete. This value is used to compare with the corresponding value when using medium-heat silicate cement concrete. Identify and output the crack-sensitive areas of the dam body, which include the location of the strongly constrained area within a preset depth range near the downstream face.

10. The simulation method for crack resistance of dam concrete in high-altitude and cold regions according to claim 9, characterized in that, Following the step of identifying and outputting the sensitive areas of dam cracking, the method further includes: With the goal of controlling cracking risk, a multi-condition simulation sensitivity analysis was conducted on at least one of the construction parameters, namely pouring temperature, pouring layer thickness, cooling water supply scheme and surface insulation measures. Based on simulation results, output the maximum allowable temperature control standards for low-heat silicate cement concrete dams in high-altitude and cold regions, as well as the recommended values ​​for pouring temperature by season.

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