A method for evaluating freeze-thaw damage and predicting service safety of roller compacted concrete dam considering the influence of low temperature and low humidity maintenance

Abstract

This invention discloses a method for evaluating freeze-thaw damage and predicting service safety of roller-compacted concrete dams considering the effects of low-temperature and low-humidity curing. The method collects environmental and engineering parameters of the dam body in arid and cold regions, sets low-temperature, low-humidity, and coupled low-temperature and low-humidity curing regimes, prepares roller-compacted concrete specimens, and conducts freeze-thaw cycles, uniaxial compression, and triaxial compression tests. Based on mass loss, dynamic elastic modulus attenuation, strength loss, peak strain change, and confining pressure, a comprehensive freeze-thaw damage variable is constructed. A freeze-thaw damage evolution equation considering the effects of curing temperature and humidity is established, and the damage variable is introduced into the Ottosen constitutive model for parameter correction. Furthermore, through size effect, construction-period thermal damage, and dam stress state correction, the specimen dimensional parameters are converted to dam dimensional parameters. Combined with a finite element model, freeze-thaw damage simulation and service safety level evaluation of the dam body are conducted, enabling quantitative evaluation and service safety prediction of freeze-thaw damage in roller-compacted concrete dams in arid and cold regions, providing a technical basis for dam operation and maintenance and reinforcement decisions.

Description

Technical Field

[0001] This invention belongs to the technical field of durability evaluation of hydraulic concrete structures and dam safety prediction, specifically involving a method for evaluating freeze-thaw damage and predicting service safety of roller-compacted concrete dams that takes into account the effects of low-temperature and low-humidity curing. Background Technology

[0002] Roller-compacted concrete (RCC) dams have advantages such as fast construction speed, low cement consumption, low heat of hydration, and high degree of mechanization, and have been widely used in water conservancy and hydropower projects. However, in the cold and arid northwest region, RCC dams are often exposed to complex environments with low temperatures, low humidity, large diurnal temperature variations, and repeated freeze-thaw cycles during construction and service. Low-temperature and low-humidity curing affects the early hydration, pore structure development, and interfacial bonding quality of RCC, leading to significant differences in its subsequent freeze-thaw resistance and mechanical properties.

[0003] Existing methods for evaluating freeze-thaw damage to roller-compacted concrete mostly use the mass loss rate, dynamic elastic modulus, or compressive strength loss rate under standard curing conditions as evaluation indicators, focusing primarily on the impact of the number of freeze-thaw cycles on material properties. This type of method has the following shortcomings: First, it usually does not fully consider the deterioration effect of low temperature and low humidity curing history on the inherent properties of concrete in cold and arid regions, and the test environment is out of touch with the actual construction conditions. Second, it uses a single damage index, which cannot comprehensively characterize the damage evolution law under the coupling of quality, deformation, strength and three-dimensional stress after freeze-thaw. Third, the conclusions of indoor specimen tests are only applicable to the material level and are difficult to be converted to the actual dam body, and cannot reflect the spatial damage distribution differences caused by temperature gradient, layered construction and constraint stress of the dam body. Fourth, the existing concrete constitutive model does not couple the synergistic deterioration effect of early curing temperature and humidity and freeze-thaw cycle, and it is difficult to accurately describe the actual stress and deformation characteristics of dam bodies in cold and arid regions under the combined action of low temperature and low humidity curing and freeze-thaw cycle. In addition, the existing technology lacks a complete set of technical solutions from on-site environmental survey, indoor multi-condition test, damage modeling, dam body numerical simulation to safety classification, which makes it difficult for indoor test results to directly serve the decision-making of dam operation, maintenance and reinforcement.

[0004] Therefore, it is necessary to propose a method for evaluating freeze-thaw damage and predicting service safety of roller-compacted concrete dams that can simultaneously consider the history of low-temperature and low-humidity curing during construction, freeze-thaw cycles during service, complex stress states, and dam structural scale effects. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, the present invention aims to provide a method for evaluating freeze-thaw damage and predicting service safety of roller-compacted concrete dams that takes into account the effects of low-temperature and low-humidity curing. This method enables accurate characterization of the evolution of freeze-thaw damage in roller-compacted concrete dams in cold and arid regions and quantitative prediction of service safety throughout the entire life cycle. It provides scientific and precise technical support for durability assessment, disease prevention and control, and operation and maintenance decision-making of dams in cold and arid regions.

[0006] This invention is achieved through the following technical solution: A method for evaluating freeze-thaw damage and predicting service safety of roller-compacted concrete dams considering the effects of low-temperature and low-humidity curing includes the following steps: S1. Collect regional environmental and engineering parameters of the target roller-compacted concrete dam, and determine the specimen curing regime and freeze-thaw cycle regime based on the obtained parameters; S2. Prepare roller-compacted concrete specimens according to the actual mix proportion of the dam body. After the specimens are cured in groups according to the curing system established in step S1, conduct initial performance tests. S3. Conduct graded freeze-thaw cycle tests on the cured specimens and test damage indicators including specimen mass, dynamic elastic modulus, and apparent damage at each preset cycle node. S4. Conduct uniaxial compression and triaxial compression tests on the specimens after S2 and S3 treatments, and collect parameters. S5. Combining the test data of S3 and S4, a comprehensive freeze-thaw damage variable is constructed based on mass loss, dynamic elastic modulus decay, compressive strength decay, peak strain change and confining pressure influence, and a freeze-thaw damage evolution equation considering the influence of curing temperature, curing relative humidity and freeze-thaw cycle number is established. S6. Introduce the comprehensive freeze-thaw damage variables into the Ottosen constitutive model, and reduce and correct the key parameters of the model's compressive strength, tensile strength, and elastic modulus to obtain the freeze-thaw damage corrected constitutive parameters. S7. Introduce size effect correction factor, construction period thermal damage correction factor, and dam stress state correction factor to convert the specimen size comprehensive damage parameter into dam size damage parameter. S8. Establish a finite element numerical model of a roller-compacted concrete dam, import the modified constitutive parameters and dam body dimensional damage parameters, and calculate the dam body construction temperature field, creep stress field and freeze-thaw damage field under different service years in sequence to obtain the spatial distribution characteristics of dam body damage under different service years. S9. Based on the spatial distribution characteristics of dam damage under different service years and combined with safety evaluation indicators, the service safety status of roller-compacted concrete dams is graded and evaluated, and the service status of the dam body is divided into damage levels.

[0007] The present invention also has the following technical features: Preferably, the environmental and engineering parameters mentioned in step S1 include: ambient temperature during construction, relative humidity during construction, daily temperature difference and seasonal temperature changes, freeze-thaw cycle temperature range, annual number of freeze-thaw cycles, surface temperature changes of the dam body, concrete mix proportion of the dam body, dam body zoning, dam height, dam thickness and construction layer parameters, temperature control data during construction and monitoring data during operation. The maintenance system includes a standard maintenance group, a low-temperature maintenance group, a low-humidity maintenance group, and a low-temperature and low-humidity coupled maintenance group.

[0008] Preferably, the initial performance test in step S2 includes one or more of the following: mass, ultrasonic wave velocity, dynamic elastic modulus, compressive strength, or initial porosity characteristics test.

[0009] Preferably, the number of cycles in the graded freeze-thaw cycle test in step S3 is selected from multiple gradient conditions of 0, 25, 50, 75, 100, 150 and 200 cycles.

[0010] Preferably, the parameters mentioned in step S4 include stress-strain curve, peak stress, peak strain, elastic modulus, residual strength, failure strain, volumetric deformation, strength parameters under different confining pressure conditions, and failure mode.

[0011] Preferably, the comprehensive freeze-thaw damage variable mentioned in step S5 is determined by a combination of the mass loss rate, dynamic elastic modulus attenuation rate, compressive strength loss rate, peak strain change rate, and confining pressure influence coefficient, as expressed below: D=w 1 D m +w 2 D e +w 3 D f +w 4 D s +w 5 D c in, D m The damage component is based on the mass loss rate; D e The damage component is based on the decay of the dynamic elastic modulus; D f This is the damage component based on the decrease in compressive strength; D s The damage component is based on the peak strain variation; D c This represents the damage component based on the influence of confining pressure conditions. w 1. w 2. w 3. w 4. w 5 is the weighting coefficient, and w 1+ w 2+ w 3+ w 4+ w 5 = 1.

[0012] Furthermore, the curing temperature is introduced as a comprehensive freeze-thaw damage variable in step S5.T Maintenance of relative humidity H and number of freeze-thaw cycles N This enables a quantitative characterization of the freeze-thaw damage degree of roller-compacted concrete under the coupled effects of low-temperature and low-humidity curing, freeze-thaw cycles, and complex stress states, expressed as: D=F(T, H, N, σ) 3 ,m,E d ，f c , ε p ） in, T For maintenance temperature; H To maintain relative humidity; N This represents the number of freeze-thaw cycles. σ 3 represents the confining pressure in a triaxial compression test; m This refers to the quality loss rate; E d It is the dynamic elastic modulus; f c Compressive strength; ε p Peak strain; The freeze-thaw damage evolution equation is expressed as follows: in, D To incorporate freeze-thaw damage variables; T For maintenance temperature; H To maintain relative humidity; N This represents the number of freeze-thaw cycles. a(T, H) The damage development coefficient related to curing temperature and curing humidity; b The freeze-thaw damage evolution index; a(T, H） This can be further expressed as: in, a 0 represents the baseline damage coefficient under standard maintenance conditions; K T This is a temperature correction factor; K H This is the humidity correction factor; K TH This is the temperature-humidity coupling correction factor.

[0013] Preferably, the freeze-thaw damage correction constitutive parameter mentioned in step S6 is expressed as: in, f cD The compressive strength after freeze-thaw damage; f tD Tensile strength after freeze-thaw damage; E D The elastic modulus after freeze-thaw damage; f c0 Undamaged compressive strength; f t0 This represents the undamaged tensile strength. E 0 represents the undamaged elastic modulus; D To incorporate freeze-thaw damage variables; α c This is the compressive strength damage reduction factor. α t This is the tensile strength damage reduction factor. α E The elastic modulus damage reduction factor; when α c , α t , α E When the value is 1, it degenerates into a variable based on comprehensive freeze-thaw damage. D The linear reduction form.

[0014] Preferably, the dam body dimensional damage parameters mentioned in step S7 can be expressed as: D b = min[ 1, K s ·K t ·K σ ·D ] in, D b For freeze-thaw damage variables at the dam scale; D For indoor specimens, the comprehensive freeze-thaw damage variable is used. K s This is a size effect correction factor; Kt This is the correction factor for thermal damage during the construction period; K σ This is the correction factor for the stress state of the dam body.

[0015] Preferably, the damage levels described in step S9 are classified as follows: Level I: basically intact; Level II: minor damage; Level III: moderate damage; Level IV: severe damage; Level V: dangerous condition.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention takes the low temperature and low humidity maintenance conditions in cold and arid areas as a prerequisite influencing factor for the evaluation of freeze-thaw damage, which can simultaneously consider the deterioration of maintenance during construction and the freeze-thaw cycle effect during service, thus improving the matching degree between the test conditions and the actual engineering. (2) The present invention constructs a comprehensive freeze-thaw damage variable by integrating mass loss, dynamic elastic modulus decay, compressive strength decay, peak strain change and confining pressure effect, which can comprehensively characterize the damage degree of roller-compacted concrete under the combined action of low temperature and low humidity curing, freeze-thaw cycle and complex stress state. (3) This invention introduces the comprehensive freeze-thaw damage variables into the Ottosen constitutive model and reduces and corrects the strength and elastic modulus parameters, which is beneficial to describing the mechanical degradation characteristics of roller-compacted concrete after freeze-thaw damage. (4) This invention realizes the conversion of indoor specimen dimensional parameters to dam dimensional parameters through size effect, construction period thermal damage and dam stress state correction, and combines finite element simulation results to evaluate service safety level, which can provide technical basis for the operation and maintenance and reinforcement decision of roller-compacted concrete dams in cold and arid areas. Attached Figure Description

[0017] Figure 1 This is a flowchart of the overall process for evaluating freeze-thaw damage and predicting service safety of roller-compacted concrete dams according to the present invention. Figure 2 This is a flowchart of the low-temperature and low-humidity curing-freeze-thaw cycle-mechanical loading test of the present invention; Figure 3 This is a schematic diagram illustrating the construction of the comprehensive freeze-thaw damage variables in this invention; Figure 4 This invention presents a freeze-thaw damage evolution model and a schematic diagram of damage development relationships that take into account the effects of curing temperature and humidity. Figure 5 The flowchart for updating the parameters of the Ottosen constitutive model is modified for this invention; Figure 6 This is a schematic diagram illustrating the conversion of the specimen dimensional parameters to the dam body dimensional parameters according to the present invention; Figure 7 This is a flowchart of the numerical simulation of freeze-thaw damage in the dam body according to the present invention; Figure 8 This is a flowchart illustrating the safety level determination process for roller-compacted concrete dams according to the present invention. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to specific embodiments. These descriptions are for explanation purposes only and are not intended to limit the scope of the invention.

[0019] Example 1 Combined with appendix Figures 1 to 8This embodiment presents a method for evaluating freeze-thaw damage and predicting service safety of roller-compacted concrete dams considering the effects of low-temperature and low-humidity curing, including the following steps: S1. Collect regional environmental and engineering parameters of the target roller-compacted concrete dam, and determine the specimen curing regime and freeze-thaw cycle regime based on the obtained parameters; environmental and engineering parameters include: ambient temperature during construction, relative humidity during construction, daily temperature difference and seasonal temperature changes, freeze-thaw cycle temperature range, annual number of freeze-thaw cycles, surface temperature changes of the dam body, concrete mix proportion of the dam body, dam body zoning, dam height, dam thickness and construction layer parameters, temperature control data during construction and monitoring data during operation. The maintenance regimes include a standard maintenance group, a low-temperature maintenance group, a low-humidity maintenance group, and a low-temperature and low-humidity coupled maintenance group. The four maintenance regimes are as follows: standard maintenance at 20°C and 95% relative humidity, low-temperature maintenance at 5°C and 95% relative humidity, low-humidity maintenance at 20°C and 40% relative humidity, and low-temperature and low-humidity coupled maintenance at 5°C and 40% relative humidity.

[0020] S2. Prepare roller-compacted concrete specimens according to the actual mix proportion of the dam body. Cast cubic and cylindrical roller-compacted concrete specimens uniformly. The specimens are divided into four groups and cured in the corresponding constant temperature and humidity environment to the design age according to the curing system established in step S1. After the curing is completed, carry out initial performance tests. The initial performance tests include mass, ultrasonic wave velocity, dynamic elastic modulus, compressive strength and initial porosity characteristics. Record the initial basic parameters of each group of specimens.

[0021] S3. Conduct graded freeze-thaw cycle tests on the cured specimens, and detect damage indicators including specimen mass, dynamic elastic modulus, and apparent damage at each preset cycle node. The number of cycles in the graded freeze-thaw cycle test is selected from multiple gradient conditions of 0, 25, 50, 75, 100, 150, and 200 cycles. The overall test procedure is as follows. Figure 2 .

[0022] S4. Conduct uniaxial and triaxial compression tests on the specimens treated in S2 and S3, respectively. The confining pressure can be set to 0 MPa, 2 MPa, 4 MPa, 6 MPa, or determined according to the actual stress level of the dam body. Collect parameters, including stress-strain curves, peak stress, peak strain, elastic modulus, residual strength, failure strain, volumetric deformation, strength parameters under different confining pressure conditions, and failure mode.

[0023] S5. Combining the test data from S3 and S4, refer to... Figure 3The index coupling logic is used to construct a comprehensive freeze-thaw damage variable by weighting and combining multiple damage components. Based on the comprehensive freeze-thaw damage variable, a freeze-thaw damage evolution equation is established. The comprehensive freeze-thaw damage variable is determined by a combination of mass loss rate, dynamic elastic modulus attenuation rate, compressive strength loss rate, peak strain change rate, and confining pressure influence coefficient, and the expression is as follows: D=w 1 D m +w 2 D e +w 3 D f +w 4 D s +w 5 D c in, D m The damage component is based on the mass loss rate; D e The damage component is based on the decay of the dynamic elastic modulus; D f This is the damage component based on the decrease in compressive strength; D s The damage component is based on the peak strain variation; D c This represents the damage component based on the influence of confining pressure conditions. w 1. w 2. w 3. w 4. w 5 is the weighting coefficient, and w 1+ w 2+ w 3+ w 4+ w 5 = 1.

[0024] The weighting coefficients are determined based on the sensitivity of each damage component to the freeze-thaw degradation of roller-compacted concrete, its impact on the service safety of the dam, and the stability of the test data. Specifically, the compressive strength attenuation damage component and the dynamic elastic modulus attenuation damage component have a significant impact on the dam's bearing capacity and stiffness degradation, and are assigned higher weights. The peak strain change damage component, used to characterize the deformation degradation features after freeze-thaw damage, is assigned a medium weight. The confining pressure effect damage component, used to reflect changes in material strength response under complex stress states, is assigned a moderate weight. The mass loss damage component mainly reflects surface erosion and appearance degradation, with relatively low early sensitivity, and is assigned a lower weight. The weighting coefficients can be determined by combining engineering experience-based weighting with experimental sensitivity verification.

[0025] Incorporating curing temperature as a comprehensive variable of freeze-thaw damage T Maintenance of relative humidity H and number of freeze-thaw cycles N This enables a quantitative characterization of the freeze-thaw damage degree of roller-compacted concrete under the coupled effects of low-temperature and low-humidity curing, freeze-thaw cycles, and complex stress states, expressed as: D=F(T, H, N, σ) 3 ,m,E d ，f c , ε p ） in, T For maintenance temperature; H To maintain relative humidity; N This represents the number of freeze-thaw cycles. σ 3 represents the confining pressure in a triaxial compression test; m This refers to the quality loss rate; E d It is the dynamic elastic modulus; f c Compressive strength; ε p Peak strain; The freeze-thaw damage evolution equation is expressed as: in, D To incorporate freeze-thaw damage variables; T For maintenance temperature; H To maintain relative humidity; N This represents the number of freeze-thaw cycles. a(T, H) The damage development coefficient related to curing temperature and curing humidity; b The freeze-thaw damage evolution index; a(T, H) Represented as: in, a 0 represents the baseline damage coefficient under standard maintenance conditions; K T This is a temperature correction factor; K H This is the humidity correction factor; K TH This represents the temperature-humidity coupling correction coefficient. The Ottosen model parameters were corrected based on experimental results. The damage evolution modeling process is detailed below. Figure 4 .

[0026] S6. Introduce the comprehensive freeze-thaw damage variables into the Ottosen constitutive model, and reduce and correct the key parameters of compressive strength, tensile strength, and elastic modulus of the model to obtain the freeze-thaw damage corrected constitutive parameters. The parameter update process is as follows: Figure 5 As shown. The constitutive parameters corrected for freeze-thaw damage are expressed as: in, f cD The compressive strength after freeze-thaw damage; f tD Tensile strength after freeze-thaw damage; E D The elastic modulus after freeze-thaw damage; f c0 Undamaged compressive strength; f t0 This represents the undamaged tensile strength. E 0 represents the undamaged elastic modulus; D To incorporate freeze-thaw damage variables; α c This is the compressive strength damage reduction factor. α t This is the tensile strength damage reduction factor. α E The elastic modulus damage reduction factor; when α c , α t , α E When the value is 1, it degenerates into a variable based on comprehensive freeze-thaw damage. D The linear reduction form.

[0027] During model verification, the calculated stress-strain curves are compared with the experimental curves. When the peak strength error, peak strain error, and curve fitting error meet the set requirements, the model parameters are considered reasonable.

[0028] S7. Introduce size effect correction factors, construction period thermal damage correction factors, and dam stress state correction factors to convert the specimen dimensional comprehensive damage parameters into dam dimensional damage parameters. The parameter conversion process is as follows: Figure 6 As shown; Dam body dimensional damage parameters can be expressed as: D b = min[ 1, K s ·K t ·K σ ·D ] in, D bFor freeze-thaw damage variables at the dam scale; D For indoor specimens, the comprehensive freeze-thaw damage variable is used. K s This is a size effect correction factor; Kt This is the correction factor for thermal damage during the construction period; K σ This is the correction factor for the stress state of the dam body.

[0029] S8. Numerical simulation process for freeze-thaw damage to dam body as follows: Figure 7 As shown, a finite element numerical model of a roller-compacted concrete dam was established. Modified constitutive parameters and dam body dimensional damage parameters were imported, and the construction temperature field, creep stress field, and full-cycle freeze-thaw damage field of the dam body were calculated sequentially. Based on the surface temperature changes and freeze-thaw cycle characteristics of the dam body, the freeze-thaw depth and the freeze-thaw influence area were determined. The obtained modified Ottosen freeze-thaw damage constitutive parameters were input into the finite element numerical model to simulate freeze-thaw damage of the dam body under different service years. Damage distribution cloud maps of the entire dam after 10, 30, and 50 years of service were output, clearly identifying the damage depth and extent in weak areas such as the dam heel, dam toe, and interlayer construction joints. S9. Based on the spatial distribution characteristics of dam damage under different service years and combined with safety evaluation indicators, the service safety status of roller-compacted concrete dams is graded and evaluated. The service status of the dam body is divided into damage levels, and the judgment process is as follows: Figure 8 As shown. Safety evaluation indicators include: maximum freeze-thaw damage value; depth of damaged area; area of ​​damaged area; strength reduction factor; elastic modulus reduction factor; dam body anti-sliding stability safety factor; dam body stress exceeding limit area; crack propagation risk; degree of interlayer bond weakening.

[0030] Damage levels are classified as follows: Level I: Basically intact; Level II: Minor damage; Level III: Moderate damage; Level IV: Severe damage; Level V: Dangerous condition.

[0031] A roller-compacted concrete gravity dam project in the cold and arid region of Northwest my country was selected as the implementation object. The method described in this invention was used to calculate the degree of freeze-thaw damage of roller-compacted concrete under low temperature and low humidity curing conditions, and further completed the conversion of dam body dimensional parameters, numerical simulation of freeze-thaw damage, and determination of service safety level.

[0032] I. Basic Engineering and Testing Parameters A roller-compacted concrete dam is located in a cold and arid region. The dam is 80 m high, 8 m wide at the crest, and 62 m wide at the base, with each layer 2 m thick. The lowest winter temperature at the dam site is approximately -18 ℃, and the average annual relative humidity is approximately 40%–55%. Significant freeze-thaw cycles occur on the dam surface. The roller-compacted concrete specimens were prepared using an engineering mix design, and the material consumption per unit volume is shown in the table below. Cylindrical specimens, measuring Φ150 mm × 300 mm, were vibratory compacted. The curing and freeze-thaw conditions set for the experiment are shown in the table below. This group of specimens represents the damage state of roller-compacted concrete after service life freeze-thaw cycles under unfavorable curing conditions of low temperature and low humidity during the construction period in cold and arid regions.

[0033] II. Test Results After low-temperature and low-humidity curing and 100 freeze-thaw cycles, the following data were obtained from the test.

[0034] III. Calculation of Comprehensive Freeze-Thaw Damage Variables This embodiment uses mass loss rate, dynamic elastic modulus attenuation rate, strength loss rate, peak strain change rate, and confining pressure influence term to construct a comprehensive freeze-thaw damage variable. D The formula for calculating the comprehensive freeze-thaw damage variable is as follows: and: In this embodiment, considering the sensitivity of each damage component to freeze-thaw degradation and its impact on the dam's service safety, the weighting coefficients are determined by combining engineering experience-based weighting with experimental sensitivity verification. The weight values ​​are: ; 1. Mass loss damage component Substitute the data: The mass loss damage component is: 2. Damage component of dynamic elastic modulus Substitute the data: The damage component of the kinetic elastic modulus is: 3. Strength loss damage component Substitute the data: That is, the strength loss damage component is: 4. Damage component of peak strain variation Since the peak strain of the specimen increases after freeze-thaw damage, the following formula is used to characterize the deformation degradation: Substitute the data: That is, the damage component of peak strain variation is: 5. Confining pressure affects damage components Define the confining pressure enhancement factor as: The confining pressure enhancement factor before freeze-thaw is: The confining pressure enhancement factor after freeze-thaw is: The impact of confining pressure on the damage component is as follows: Substitute the data: The damage component affected by confining pressure is: 6. Calculation of comprehensive freeze-thaw damage variables Therefore, the comprehensive freeze-thaw damage variable of the roller-compacted concrete after low-temperature and low-humidity curing and 100 freeze-thaw cycles is: This indicates that the specimen is at a moderate level of freeze-thaw damage.

[0035] IV. Calculation of Freeze-Thaw Damage Evolution Equation This embodiment uses the following freeze-thaw damage evolution equation: in: Pick: The temperature correction factor is: The humidity correction factor is: The temperature and humidity coupling correction factor is: Model exponent is taken as: Substituting the curing temperature T=5℃ and curing humidity H=40% in this embodiment, we get: When the number of freeze-thaw cycles N When =100: That is, the model's calculated value is: Combined damage calculation value from the test D Compared to 0.267, the relative error is: This indicates that the established freeze-thaw damage evolution equation can effectively characterize the development law of freeze-thaw damage in roller-compacted concrete under low temperature and low humidity curing conditions.

[0036] V. Correcting the parameter updates of the Ottosen constitutive model Integrating freeze-thaw damage variables D The parameter update process for the roller-compacted concrete constitutive model is introduced. Material parameters before freeze-thaw cycles are as follows: Based on the experimental inversion, the strength reduction factor, tensile strength reduction factor, and elastic modulus reduction factor are respectively taken as follows: The compressive strength after freeze-thaw damage is: The tensile strength after freeze-thaw damage is: The elastic modulus after freeze-thaw damage is: Therefore, the input parameters of the Ottosen constitutive model are corrected as follows: The model parameter vector can be represented as: Right now: VI. Conversion of specimen dimensional parameters to dam body dimensional parameters Considering the differences between indoor specimens and actual dam bodies in terms of size effect, thermal damage during construction, and stress state of the dam body, the dimensional damage variables of the specimens are corrected.

[0037] The freeze-thaw damage variables at the dam scale are: Where: size effect correction coefficient Ks=1.08; Correction factor for thermal damage during construction period Kt =1.12; Dam stress state correction factor Kσ =0.95.

[0038] Substitute into the calculation: Therefore, the dam-scale damage variables in the freeze-thaw influence zone on the dam surface are: Further material parameters for the dam body dimensions were obtained: The output of the dam body dimensional parameters is: Dam body dimensional damage variables. ; Dam body dimensional compressive strength ; Modulus of elasticity at dam dimensions .

[0039] VII. Numerical Simulation of Freeze-Thaw Damage A two-dimensional finite element model of the dam body was established, adopting the plane strain assumption. The parameters of the dam body model are as follows: The simulation process includes: 1. Establish the geometric model of the dam body; 2. Generate a finite element mesh; 3. Input dam body dimensions and material parameters , , and the corrected Ottosen constitutive parameters; 4. Calculate the temperature field during the construction period; 5. Calculate the creep stress field; 6. Identify the freeze-thaw action zones on the dam surface; 7. Perform iterative updates to the damage field; 8. Output a cloud map showing the distribution of freeze-thaw damage to the dam body and the hazardous areas.

[0040] The simulation results are as follows: According to the damage cloud map, the freeze-thaw damage to the dam body is mainly concentrated in the water level fluctuation zone upstream of the dam body and the local surface area downstream. The damage in the internal core area is relatively small and no through-damage zone has been formed.

[0041] VIII. Service Safety Level Determination Construct a comprehensive safety evaluation scoring function: in: ; ; ; .

[0042] Substitute into the calculation: because: therefore: Continue calculation: Determine the security level according to the table below: In this embodiment: Therefore, the service safety level of the dam body is determined as follows: IX. Results Output As can be seen from the above embodiments, the present invention can calculate the comprehensive freeze-thaw damage variables of roller-compacted concrete based on low temperature and low humidity curing conditions, freeze-thaw cycle count, and mechanical test results, and further complete constitutive parameter correction, dam body scale conversion, numerical simulation, and service safety level output, thereby realizing the evaluation of freeze-thaw damage and service safety prediction of roller-compacted concrete dams in cold and arid regions.

Claims

1. A method for evaluating freeze-thaw damage and predicting service safety of roller-compacted concrete dams considering the effects of low-temperature and low-humidity curing, characterized in that, Includes the following steps: S1. Collect regional environmental and engineering parameters of the target roller-compacted concrete dam, and determine the specimen curing regime and freeze-thaw cycle regime based on the obtained parameters; S2. Prepare roller-compacted concrete specimens according to the actual mix proportion of the dam body. After the specimens are cured in groups according to the curing system established in step S1, conduct initial performance tests. S3. Conduct graded freeze-thaw cycle tests on the cured specimens and test damage indicators, including specimen mass, dynamic elastic modulus, and apparent damage, at each preset cycle node. S4. Uniaxial compression and triaxial compression tests were conducted on the specimens after S2 and S3 treatments to obtain the mechanical property parameters after freeze-thaw damage. S5. Combining the test data of S3 and S4, a comprehensive freeze-thaw damage variable is constructed based on mass loss, dynamic elastic modulus decay, compressive strength decay, peak strain change and confining pressure influence, and a freeze-thaw damage evolution equation considering the influence of curing temperature, curing humidity and freeze-thaw cycle number is established. S6. Introduce the comprehensive freeze-thaw damage variables into the Ottosen constitutive model, and reduce and correct the key parameters of the model's compressive strength, tensile strength, and elastic modulus to obtain the freeze-thaw damage corrected constitutive parameters. S7. Introduce size effect correction factor, construction period thermal damage correction factor, and dam stress state correction factor to convert the specimen size comprehensive damage parameter into dam size damage parameter. S8. Establish a finite element numerical model of a roller-compacted concrete dam, import the modified constitutive parameters and dam body dimensional damage parameters, and calculate the dam body construction temperature field, creep stress field, and freeze-thaw damage field under different service years in sequence to obtain the spatial distribution characteristics of dam body damage under different service years. S9. Based on the spatial distribution characteristics of dam damage under different service years and combined with safety evaluation indicators, the service safety status of roller-compacted concrete dams is graded and evaluated, and the service status of the dam body is divided into damage levels.

2. The method for evaluating freeze-thaw damage and predicting service safety of roller-compacted concrete dams considering the effects of low-temperature and low-humidity curing as described in claim 1, is characterized in that... The environmental and engineering parameters mentioned in step S1 include: ambient temperature during construction, relative humidity during construction, daily temperature difference and seasonal temperature changes, freeze-thaw cycle temperature range, annual number of freeze-thaw cycles, surface temperature changes of the dam body, concrete mix proportion of the dam body, dam body zoning, dam height, dam thickness and construction layering parameters, temperature control data during construction and monitoring data during operation. The maintenance system includes a standard maintenance group, a low-temperature maintenance group, a low-humidity maintenance group, and a low-temperature and low-humidity coupled maintenance group.

3. The method for evaluating freeze-thaw damage and predicting service safety of roller-compacted concrete dams considering the effects of low-temperature and low-humidity curing as described in claim 1, is characterized in that... The initial performance test described in step S2 includes one or more of the following tests: mass, ultrasonic wave velocity, dynamic elastic modulus, compressive strength, or initial porosity characteristics.

4. The method for evaluating freeze-thaw damage and predicting service safety of roller-compacted concrete dams considering the effects of low-temperature and low-humidity curing as described in claim 1, characterized in that, The number of cycles in the graded freeze-thaw cycle test described in step S3 is selected from multiple gradient conditions, including 0, 25, 50, 75, 100, 150 and 200 cycles.

5. The method for evaluating freeze-thaw damage and predicting service safety of roller-compacted concrete dams considering the effects of low-temperature and low-humidity curing as described in claim 1, characterized in that, The parameters mentioned in step S4 include stress-strain curve, peak stress, peak strain, elastic modulus, residual strength, failure strain, volumetric deformation, strength parameters under different confining pressure conditions, and failure mode.

6. The method for evaluating freeze-thaw damage and predicting service safety of roller-compacted concrete dams considering the effects of low-temperature and low-humidity curing, as described in claim 1, is characterized in that... The comprehensive freeze-thaw damage variable mentioned in step S5 is determined by a combination of the mass loss rate, dynamic elastic modulus attenuation rate, compressive strength loss rate, peak strain change rate, and confining pressure influence coefficient, as expressed below: D=w 1 D m +w 2 D e +w 3 D f +w 4 D s +w 5 D c in, D m The damage component is based on the mass loss rate; D e The damage component is based on the decay of the dynamic elastic modulus; D f This is the damage component based on the decrease in compressive strength; D s The damage component is based on the peak strain variation; D c This represents the damage component based on the influence of confining pressure conditions. w 1. w 2. w 3. w 4. w 5 is the weighting coefficient, and 0 ≤ w i ≤1, i =1, 2, 3, 4, 5 w 1+ w 2+ w 3+ w 4+ w 5 = 1, 0 ≤ D ≤1.

7. The method for evaluating freeze-thaw damage and predicting service safety of roller-compacted concrete dams considering the effects of low-temperature and low-humidity curing, as described in claim 6, is characterized in that... The curing temperature is introduced as a comprehensive freeze-thaw damage variable in step S5. T Maintenance of relative humidity H and number of freeze-thaw cycles N This enables a quantitative characterization of the freeze-thaw damage degree of roller-compacted concrete under the coupled effects of low-temperature and low-humidity curing, freeze-thaw cycles, and complex stress states, expressed as: D=F(T, H, N, σ) 3 ,m,E d ，f c , ε p ） in, T For maintenance temperature; H To maintain relative humidity; N This refers to the number of freeze-thaw cycles. σ 3 represents the confining pressure in a triaxial compression test; m This refers to the quality loss rate; E d It is the dynamic elastic modulus; f c Compressive strength; ε p Peak strain; The freeze-thaw damage evolution equation is expressed as follows: in, D To incorporate freeze-thaw damage variables; T For maintenance temperature; H To maintain relative humidity; N This represents the number of freeze-thaw cycles. a(T, H） The damage development coefficient related to curing temperature and humidity; b The freeze-thaw damage evolution index; a(T, H) Represented as: in, a 0 represents the baseline damage coefficient under standard maintenance conditions; K T This is a temperature correction factor; K H This is the humidity correction factor; K TH This is the temperature-humidity coupling correction factor.

8. The method for evaluating freeze-thaw damage and predicting service safety of roller-compacted concrete dams considering the effects of low-temperature and low-humidity curing as described in claim 1, characterized in that, The freeze-thaw damage correction constitutive parameters mentioned in step S6 can be expressed as: in, f cD The compressive strength after freeze-thaw damage; f tD Tensile strength after freeze-thaw damage; E D The elastic modulus after freeze-thaw damage; f c0 Undamaged compressive strength; f t0 This represents the undamaged tensile strength. E 0 represents the undamaged elastic modulus; D To incorporate freeze-thaw damage variables; α c This is the compressive strength damage reduction factor. α t This is the tensile strength damage reduction factor. α E The elastic modulus damage reduction factor; when α c , α t , α E When the value is 1, it degenerates into a variable based on comprehensive freeze-thaw damage. D The linear reduction form.

9. The method for evaluating freeze-thaw damage and predicting service safety of roller-compacted concrete dams considering the effects of low-temperature and low-humidity curing, as described in claim 1, is characterized in that... The dam body dimensional damage parameters mentioned in step S7 can be expressed as: D b = min[1, K s ·K t ·K σ ·D ] in, D b For freeze-thaw damage variables at the dam scale; D For indoor specimens, the comprehensive freeze-thaw damage variable is used. K s This is a size effect correction factor; Kt This is the correction factor for thermal damage during the construction period; K σ This is the correction factor for the stress state of the dam body.

10. The method for evaluating freeze-thaw damage and predicting service safety of roller-compacted concrete dams considering the effects of low-temperature and low-humidity curing as described in claim 1, characterized in that, In step S9, the maximum freeze-thaw damage value of the dam body is used. D b,max Depth of damage R d Damage area ratio A d Strength reduction factor η f Elastic modulus reduction factor η E and minimum anti-skid stability safety factor K min Construct a comprehensive scoring function for the input variables S And based on the comprehensive scoring function S The service status of the dam body is divided into levels I to V: level I is basically intact, level II is slightly damaged, level III is moderately damaged, level IV is severely damaged, and level V is in a dangerous state.

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