Method for arranging dam crest formwork increasing area on core-wall rock-fill dam to control water storage cracking and earthquake response whip effect

Abstract

The invention discloses a method for arranging a dam crest formwork increasing area on a core-wall rockfill dam to control water storage cracking and an earthquake response whip effect, a formwork increasing rockfill area is arranged at the position 1 / 3-1 / 5 of the dam height below the dam crest, the filling standard is controlled by adopting double indexes of porosity and relative density, it is guaranteed that the formwork increasing rockfill area reaches the full compaction degree, and the dam crest formwork increasing area is arranged at the position 1 / 3-1 / 5 of the dam height. The crack of the core-wall rock-fill dam is controlled, the whip effect of earthquake response of the rock-fill dam is effectively reduced, and the method for controlling the crack of the dam and improving the anti-seismic safety performance is expected to be achieved.

Description

Technical Field

[0001] This invention belongs to the field of civil engineering, water conservancy and hydropower technology, specifically a method for controlling water storage cracking and the whiplash effect of seismic response by setting up a dam crest enhancement zone in a core rockfill dam. Background Technology

[0002] Rockfill dams with core walls are widely used today due to their advantages such as readily available materials, strong adaptability to terrain and geological conditions, and safety and economy. The "Design Code for Rolled Earth-Rockfill Dams NB / T 10872_2021" requires that the design of rockfill dams with core walls ensures coordinated deformation across different zones. However, in domestic rockfill dam engineering problems, cracking at the dam crest due to uncoordinated deformation across zones still accounts for approximately 39%, indicating that the zoning design standard system for rockfill dams with core walls still cannot meet the needs of engineering practice. The main causes of cracking at the dam crest in rockfill dams with core walls are:

[0003] (1) The Design Specification for Roller-Compacted Earth-Rock Dams NB / T 10872_2021 stipulates that the porosity index, which is related to both gradation and compaction work, should be used in the rockfill zone and transition zone. However, the relative density used in the filter zone and the compaction degree standard used in the core wall zone are mainly related to compaction work, making it difficult to intuitively judge the deformation coordination of the dam zones.

[0004] (2) Due to the complexity of the scaling effect, the finite element method currently widely used is also difficult to accurately predict the zonal deformation coordination of the dam.

[0005] (3) There is currently a lack of experience in designing deformation coordination for 300m-class ultra-high core rockfill dams, which increases the difficulty of designing dam body zonal deformation coordination. Theoretically, the problem of non-coordinated zonal deformation in core rockfill dams can be avoided by optimizing the zonal filling design standards and reducing the deformation gradient between different zonal zones to prevent harmful cracks in the dam body.

[0006] Meanwhile, both core-walled and face-faced rockfill dams exhibit a significant "whiplash effect" in their seismic response, with the most intense seismic response occurring in the crest region. Therefore, effectively reducing the seismic response of rockfill dams by utilizing standard dam construction design is a crucial aspect of their seismic safety. Summary of the Invention

[0007] To address the above technical issues, this invention proposes, under the premise of ensuring overall dam zonal deformation coordination, to establish a modulated rockfill zone with dual control of porosity and relative density in the dam crest region, where deformation coordination issues are prominent and seismic response is most severe. This zone serves as the filling or design standard for the modulated rockfill zone on the dam crest, ensuring that the modulated rockfill zone achieves sufficient compaction, controlling cracks in the core wall rockfill dam, effectively reducing the "whiplash effect" in the seismic response of the rockfill dam, suppressing water storage cracks on the dam crest, and improving seismic safety performance.

[0008] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0009] A method for controlling water storage cracking and the whiplash effect of seismic response by setting a dam crest enhancement zone in a rockfill dam includes the following steps:

[0010] S1. Set up a rockfill zone at a position 1 / 3 to 1 / 5 of the dam height below the dam crest;

[0011] S2. Determine the filling gradation: the maximum particle size is ≤600mm and ≤2 / 3 of the thickness of the compacted layer, and the mass percentage of particles with a particle size <5mm is between 10% and 30%.

[0012] S3. Determine the filling standard: Select the minimum porosity standard n of the rockfill material according to the "Design Specification for Rolled Earth-Rock Dams NB / T 10872_2021". d And calculate the minimum porosity standard n of the riprap. d Corresponding relative density compaction standard :

[0013] (1)

[0014] Where, n max To satisfy the condition that porosity equals n d The maximum porosity of the gradation; n min For porosity equal to n d The minimum porosity of the graded distribution;

[0015] S4. Based on the relative density compaction standard Dr in step S3, conduct indoor triaxial tests on scaled gradation samples to determine the constitutive model parameters of the dam material.

[0016] S5. A unified generalized plastic model of soil and rock is adopted as the constitutive model for the dam finite element calculation including the design scheme of the modulus-enhanced rockfill area. Three-dimensional finite element static and dynamic calculations of the dam including the modulus-enhanced rockfill area are performed. The formula for calculating the loading modulus of the unified generalized plastic model of soil and rock is:

[0017] (2)

[0018] In the formula, Indicates the plastic modulus at the time of loading. Indicates the reference stress. Indicates the average normal stress. The modulus factor reflects the influence of stress path. ,in,

[0019] These are the compression parameters for the isotropic compression curve;

[0020] The springback parameters are from the isotropic compression test.

[0021] m is a material parameter for coarse-grained soil, reflecting the degree of influence of confining pressure;

[0022] d represents the material parameters of the soil and rock;

[0023] This represents the ratio of shear dilatation stress of coarse-grained material under various confining pressures. , and These are material parameters, obtained through fitting via indoor experiments;

[0024] This represents the peak stress ratio of coarse-grained soil under various confining pressures. , and These are material parameters, obtained through fitting via indoor experiments;

[0025] Indicates the stress ratio;

[0026] S6. Verify the zonal deformation compatibility based on the finite element calculation results, specifically including the following sub-steps:

[0027] S61. Hydraulic fracturing conditions of the core wall: The deformation compatibility requirement is not met.

[0028] Core wall arch effect coefficient: The deformation compatibility requirement is not met.

[0029] In the formula, This refers to the splitting pressure, which is the hydrostatic pressure that causes hydraulic splitting. The minimum total principal stress of the soil; It is the tensile strength of the soil. This refers to the vertical stress of the soil. This refers to the dry density of the soil. The height of the soil column at the calculation point; S62. Repeat steps S1 to S5 until the deformation compatibility requirements are met.

[0030] S7. During construction, the minimum porosity standard for riprap shall be followed. d The relative density compaction standard Dr dual-control standard compacted the rockfill area on the dam crest.

[0031] Beneficial effects: This invention sets up a rockfill zone on the dam crest and uses the three-dimensional elastoplastic static-dynamic finite element method for core-wall rockfill dams to calculate the dam stress, deformation, and seismic response. Based on this, it suppresses water-retaining cracks on the dam crest and the seismic response on the dam crest, thereby increasing the dam's operational and seismic safety.

[0032] Specifically, in the three-dimensional elastoplastic static and dynamic finite element method, a unified generalized plastic model of soil and rock is used as the constitutive model, which is directly applied to the three-dimensional finite element static and dynamic calculation of dams that include the modified rockfill zone design. This method can completely reflect the overall stress and deformation of the dam after the participation of the modified rockfill zone in the same calculation, improving the relevance and reliability of the calculation results.

[0033] In one optional embodiment, the modulated rockfill zone is set at an elevation of more than 79% of the total dam height and has a relative density Dr ≥ 0.71.

[0034] Beneficial effects: It determines the filling standards for the rockfill area on the dam crest, ensuring that the rockfill material in the dam filling is fully compacted.

[0035] In an optional embodiment, in step S3, the maximum and minimum dry densities of different gradations within the envelope are determined by on-site density barrel tests. The gradation with the worst filling relationship within the envelope or the lower envelope is selected, which is the minimum porosity standard n for the riprap. d The required gradation.

[0036] In an optional embodiment, step S4 specifically includes the following sub-steps:

[0037] S41. Based on the gradation of the modulated rockfill area determined in step S1, scale down the rockfill area according to the scaling-down method in GB / T 50123-2019 Standard for Geotechnical Testing Methods.

[0038] S42. Use the relative density compaction standard determined in step S3. As a standard for preparing triaxial test specimens for indoor scaled gradation;

[0039] S43. Conduct indoor triaxial tests on the dam material in the reinforced rockfill area according to the procedure of GBT 50123-2019 Standard for Geotechnical Testing Methods to determine the constitutive model parameters of the dam material.

[0040] Beneficial effects: This invention introduces a scaled-down sample preparation method and combines it with a relative density compaction standard. By controlling the density of the indoor samples, it is ensured that the scaled-down samples are highly consistent with the actual material in the augmented rockfill area in terms of particle size distribution and compaction. This optimization scheme enables the model parameters obtained indoors to more accurately reflect the mechanical properties of the engineering materials and effectively reduces experimental errors caused by differences in particle size and inconsistent sample density.

[0041] In an optional embodiment, step S5 further includes a verification step for subsequent safety measures. Specifically, the verification method involves extracting the following key results under full-storage conditions during the water storage period:

[0042] A. Spatial distribution of minimum total principal stress in the core wall, used for verification of water splitting resistance of clay core wall;

[0043] B. The ratio of vertical stress in the core wall section to the self-weight of the overlying soil strip is used to calculate the arch effect coefficient of the core wall.

[0044] C. The cumulative settlement at each measuring point along the dam crest monitoring line is used for deformation and inclination calculation;

[0045] D. Permanent settlement and relative displacement of dam slope under seismic action are used for earthquake damage verification.

[0046] Beneficial effects: Extracting key results under full-storage conditions during the water storage period can provide direct data support for subsequent safety calculations and provide a basis for optimizing parameters in the modulated rockfill area.

[0047] In an optional embodiment, in step S5, the three-dimensional finite element static and dynamic calculation of the dam body uses the Rayleigh damping matrix:

[0048] (5)

[0049] in, Here is the instantaneous tangent stiffness matrix. Let a, b, be the initial stiffness matrix. The proportionality coefficient and b and They cannot occur simultaneously, so b0=0 is used in the calculation; the damping ratio of the dam material is taken as 5%.

[0050] Beneficial effects: By adopting the above-mentioned damping matrix setting method and introducing a 5% damping ratio of dam material, the energy dissipation behavior of dam material under seismic conditions can be effectively simulated, improving the accuracy and reliability of seismic response. It is especially suitable for nonlinear dynamic calculation of ultra-high core rockfill dams, and helps to accurately evaluate key indicators such as seismic subsidence and slippage in the dam crest area, providing support for structural optimization design and seismic safety.

[0051] In an optional embodiment, between steps S6 and S7, the method of deformation inclination is used to verify the cracking of the dam crest, as shown in the following formula:

[0052] (4)

[0053] In the formula: The inclination of the deformation is dimensionless. This indicates the angle between the line connecting the settlement points and the horizontal plane. These represent the cumulative settlement measured on a specific date. express , The horizontal distance between two points.

[0054] Beneficial effects: The deformation inclination method is introduced as the basis for judging cracks on the dam crest. A critical inclination value of 1% is set. When the transverse deformation inclination of the dam crest area exceeds this value, it is determined that there is a risk of cracking. This method can quickly identify high-risk crack areas and help optimize filling parameters and the setting of the modulus-enhanced rockfill area.

[0055] In an optional embodiment, in step S7 construction quality control, the compaction guarantee rate is ≥94.7%, and the content of particles with a diameter <5mm in the gradation test is controlled between 10% and 30%.

[0056] Beneficial effects: Strict control over compaction guarantee rate and fine particle content significantly improves the filling density and structural uniformity of the modulated rockfill area, reduces segregation and porosity during the filling process, effectively enhances the mechanical stability and deformation coordination of the dam crest area, reduces the risk of cracking during the impoundment period, permanent deformation after earthquakes and instability, and ensures the safety and reliability of dam operation.

[0057] In one optional embodiment, the modulated rockfill area is compacted by a vibratory roller of not less than 32t for not less than 10 passes, with a loose thickness of 1m and a water content of not less than 5%.

[0058] Beneficial effects: By adopting the above compaction process parameters, the compaction degree and uniformity of the fill material can be significantly improved while ensuring construction efficiency, forming a dense, high-strength, and well-coordinated modulated rockfill zone, effectively suppressing uneven settlement of the dam crest, reducing the risk of cracking, and improving the overall stability and seismic performance of the dam. Attached Figure Description

[0059] Figure 1 A flowchart illustrating the method for controlling water storage cracking and the whiplash effect of seismic response in a rockfill dam by setting up a dam crest enhancement zone according to the present invention;

[0060] Figure 2 This is a distribution map of the lateral dip values ​​of the dam crest on the left bank section during the full storage period for both schemes;

[0061] Figure 3 This is a distribution map of the lateral dip values ​​of the dam crest on the riverbed cross section during the full storage period for the two schemes;

[0062] Figure 4 This is a distribution map of the lateral dip values ​​of the right bank section of the dam crest during the full storage period for both schemes;

[0063] Figure 5 This is a diagram showing the longitudinal dip distribution of the dam crest at the dam axis during the full storage period for both schemes;

[0064] Figure 6 This is the finite element calculation scheme I for dams in this invention;

[0065] Figure 7 This is the finite element calculation scheme II for dams in this invention;

[0066] Figure 8 Mesh generation for finite element method (FEM) calculation of the dam;

[0067] Figure 9 The settlement distribution of the riverbed at section 0+310 during the completion of Scheme I;

[0068] Figure 10 The settlement distribution of the riverbed at section 0+310 during the completion of Scheme II;

[0069] Figure 11 Differential settlement of the riverbed at section 0+310, calculated for the completion period;

[0070] Figure 12 The differential settlement of the riverbed at section 0+310 is calculated for the full storage period;

[0071] Figure 13 The horizontal distribution of shear stress in the riverbed section 0+310 during the full storage period of Scheme I;

[0072] Figure 14 The horizontal distribution of shear stress in the riverbed section 0+310 during the full storage period of Scheme II;

[0073] Figure 15 The minimum principal stress and external water pressure of the core wall water-facing unit;

[0074] Figure 16 The distribution of the arch effect coefficient in the 0+310 section of the riverbed during the full storage period of Scheme I;

[0075] Figure 17 The distribution of the arch effect coefficient in the 0+310 section of the riverbed during the full storage period of Scheme II;

[0076] Figure 18 The upstream and downstream dip of the dam crest area during the full storage period;

[0077] Figure 19 Design seismic acceleration time history for the bedrock of the horizontal dam site along the river;

[0078] Figure 20 Seismic acceleration time histories were designed vertically to the bedrock of the dam site;

[0079] Figure 21 Design the seismic acceleration time history for the dam axis on the bedrock at the dam site;

[0080] Figure 22 The distribution of seismic acceleration response in the upstream and downstream directions of the dam in Scheme I;

[0081] Figure 23 The distribution of seismic acceleration response in the upstream and downstream directions of the dam in Scheme II;

[0082] Figure 24 The distribution of seismic subsidence after the earthquake at the dam in Scheme I;

[0083] Figure 25 The distribution of seismic subsidence after the earthquake at the Scheme II dam;

[0084] Figure 26 The percentage of earthquake subsidence at the dam height is distributed along the elevation.

[0085] Figure 27 The amplification factor of the dam's seismic acceleration response is distributed along the elevation.

[0086] Figure 28 This represents the most potentially dangerous slip arc on the upstream dam slope during the earthquake in Scheme I.

[0087] Figure 29 This represents the most potentially dangerous slip arc on the upstream dam slope during the earthquake scenario described in Scheme II.

[0088] Figure 30 This represents the potential most dangerous slip arc displacement on the upstream dam slope during the earthquake in Scheme I.

[0089] Figure 31 This represents the potential most dangerous slip arc displacement on the upstream dam slope during the earthquake event in Scheme II.

[0090] Figure 32 For fill gradation;

[0091] Figure 33 For filling standards and test results;

[0092] Figure 34 The results of the relative density test for the filling are shown. Detailed Implementation

[0093] The following examples will further illustrate the scaling method of the present invention, but the scope of protection of the present invention is not limited to these examples.

[0094] Invention principle: The following is a detailed explanation of the method for setting the filling standard of the dam crest rockfill area according to the present invention.

[0095] This invention proposes filling standards and construction parameters for rockfill zones with dual control of porosity and relative density, providing a basis for the construction and compaction quality control of rockfill material on the crest of the Lianghekou ultra-high core wall dam. Specifically, it includes the following steps:

[0096] (1) Location of the modulus-enhanced riprap area

[0097] An augmentation rockfill zone is set up at a position 1 / 3 to 1 / 5 of the dam height below the crest of the rockfill dam.

[0098] (2) Gradation of the modulated rockfill area

[0099] The gradation of the modulus-enhanced rockfill area must meet the following requirements: the maximum particle size should not exceed 2 / 3 of the thickness of the compacted layer to ensure that there is no obvious "wall effect" during vibratory compaction and to avoid the phenomenon of incomplete compaction; the mass percentage of particles with a diameter of less than 5mm should not be less than 5% to ensure a good particle skeleton inside the rockfill area after vibratory compaction.

[0100] (3) Filling standards for reinforced rockfill areas

[0101] According to the "Design Specification for Rolled Earth-Rock Dams NB / T 10872_2021", the minimum porosity standard n for the rockfill material is selected. d ;

[0102] For the rockfill gradation determined in step (2), a large density barrel test was conducted to determine the maximum and minimum dry density of different gradations within the envelope.

[0103] The worst gradation of the filling relationship within the envelope of the riprap is determined, which is the standard porosity n. d Minimum required gradation;

[0104] Using the results of large-density barrel tests, the standard porosity n was determined. d Minimum required maximum porosity n of gradation max and minimum porosity n min Using formula (1), the corresponding relative density compaction standard Dr is calculated.

[0105] (1)

[0106] (4) Conduct indoor triaxial tests on the design scheme of the modulated rockfill area to determine the calculation parameters of the dam material:

[0107] 41. Using the gradation of the modulated rockfill area determined in step (1), scale it down according to the scaling-down method in GB / T 50123-2019 Standard for Geotechnical Testing Methods;

[0108] 42. The relative density standard determined in step (3) shall be used as the standard for preparing triaxial test specimens for indoor scaled gradation.

[0109] 43. Conduct indoor triaxial tests on the dam material in accordance with the procedures of GB / T 50123-2019 Standard for Geotechnical Testing Methods to determine the constitutive model parameters of the dam material.

[0110] (5) Perform finite element calculations of the dam including the design scheme of the modulated rockfill area.

[0111] 51. The unified generalized plastic model of soil and rock recommended in the "Design Code for Concrete-faced Rockfill Dams NB / T 10871_2021" is adopted as the constitutive model for the finite element calculation of the dam, which includes the design scheme of the modulated rockfill area.

[0112] The stress-strain relationship of the dam material can be expressed as:

[0113] (2)

[0114] in: For the elasticity matrix, This refers to the direction of plastic flow during loading or unloading; Indicates the loading direction; The plastic modulus at the time of loading or unloading.

[0115] The plastic modulus at loading is:

[0116] (3)

[0117] In the formula, Indicates the plastic modulus at the time of loading. Indicates the reference stress. Indicates the average normal stress. The modulus factor reflects the influence of stress path. ,in, These are the compression parameters for the isotropic compression curve; is the rebound parameter of the isotropic compression test; m is the material parameter of the coarse-grained soil, reflecting the degree of influence of the confining pressure; d is the material parameter of the soil and rock. This represents the ratio of shear dilatation stress of coarse-grained material under various confining pressures. , and These are material parameters, obtained through fitting via indoor experiments;

[0118] This represents the peak stress ratio of coarse-grained soil under various confining pressures. , and These are material parameters, obtained through fitting via indoor experiments; Indicates the stress ratio.

[0119] 52. Incremental governing equations for three-dimensional finite element static and dynamic calculation of the dam body under seismic load:

[0120] (6)

[0121] In the formula: , and These represent the displacement, velocity, and acceleration increments of the node, respectively. This represents the increment of seismic acceleration. The structural mass matrix, Here is the tangent damping matrix of the structure. Let be the tangent stiffness matrix of the structure.

[0122] When calculating the time step increment The calculations can basically meet the accuracy requirements.

[0123] In equation (6), the structural tangential damping matrix, since the stiffness matrix changes with time in each calculation step, is expressed using Rayleigh damping as follows:

[0124] (7)

[0125] In the formula, Here is the instantaneous tangent stiffness matrix. The initial stiffness matrix is ​​given by a, b, and b0, which are proportionality coefficients and b and b0 cannot appear at the same time. The calculation takes b0=0. The damping ratio of the dam material in this invention is taken as 5%.

[0126] 53. Under full storage conditions during the water storage period, extract the following key results:

[0127] A. Spatial distribution of minimum total principal stress in the core wall, used for verification of water splitting resistance of clay core wall;

[0128] B. The ratio of vertical stress in the core wall section to the self-weight of the overlying soil strip is used to calculate the arch effect coefficient of the core wall.

[0129] C. The cumulative settlement at each measuring point along the dam crest monitoring line is used for deformation and inclination calculation;

[0130] D. Permanent settlement and relative displacement of dam slope under seismic action are used for earthquake damage verification.

[0131] The above results can provide direct data support for subsequent safety verification calculations and provide a basis for optimizing the parameters of the modulated rockfill area.

[0132] (6) Perform zoned deformation coordination calculations for the dam in the rockfill area design scheme.

[0133] 61. Perform water-resistant splitting cracking verification on the clay core wall; the method is as follows:

[0134] The condition for hydraulic fracturing is defined as follows: the sum of the soil's tensile strength and the minimum total principal stress is less than the hydrostatic pressure.

[0135] (8)

[0136] In the formula: This refers to the splitting pressure, which is the hydrostatic pressure that causes hydraulic splitting. The minimum total principal stress of the soil; Let be the tensile strength of the soil. If the tensile strength of the soil is very small, its influence can be ignored. Therefore, the conditions for hydraulic splitting can be obtained as follows:

[0137] (9)

[0138] 62. Perform core wall arch effect verification; the formula is as follows:

[0139] (10)

[0140] The strength of the core wall arch effect is characterized by the ratio of the vertical stress of the element to the self-weight of the soil strip above it, i.e., the core wall arch effect coefficient R.

[0141] In the formula: The thickness of the overlying soil; This is the theoretical earth pressure.

[0142] 63. If the requirements are not met, repeat steps (1) to (6) until the dam zonal deformation coordination requirements are met;

[0143] (7) Perform dam crest cracking and seismic damage calculations on the dam designed for the rockfill area.

[0144] 71. The deformation inclination method is used to check the cracks on the dam crest; the formula is as follows:

[0145] (11)

[0146] In the formula: The inclination of deformation is dimensionless. This indicates the angle between the line connecting the settlement points and the horizontal plane; These represent the cumulative settlement measured on a specific date. express , The horizontal distance between two points.

[0147] Let the critical failure slope of the soil be... If the slope is calculated If this is the case, then it is assumed that a shear failure surface will occur in that soil layer. In this invention... Take 1%.

[0148] 72. Verify typical earthquake damage such as permanent deformation and dam slope stability;

[0149] 73. If the requirements are not met, repeat steps (1) to (6) until the dam crest does not crack and there is no major earthquake damage.

[0150] (8) Quality control of filling in the modified rockfill area design scheme

[0151] Quality control of porosity and relative density in the filling and modulating zone of the dam crest is carried out to ensure that the dam crest does not crack and is free from major earthquake damage.

[0152] 81. Determine construction parameters:

[0153] An enhanced rockfill zone was established above the 2814m elevation of the dam. The gradation envelope of the enhanced rockfill zone was selected as follows: Figure 1 As shown, the mass percentage of particles smaller than 5mm is between 10% and 20%. The loose thickness of the riprap compaction layer is 1m, with 5% water added, and 10 passes are made using a 32t vibratory roller. During the construction of the riprap reinforcement area on the Lianghekou Dam crest, a total of 94 gradations and porosity were tested, including 49 in the upstream area and 45 in the downstream area. The gradation test results are shown below. Figure 32 .

[0154] 82. Evaluation Method for Gradation of Rockfill Material

[0155] First, convert the mass percentage P5 of particles smaller than 5mm in each test gradation to the maximum experimental particle size (d). max The equivalent P5 (=400mm) is determined based on the three-factor diagram of the relative density test of the riprap. [16,28] Find the maximum porosity n of this gradation. max =33.2% and minimum porosity n min =13.3%, and the relative density compaction standard Dr=0.71 corresponding to the detected porosity is calculated according to formula (1), which can be used to evaluate whether each test gradation of the rockfill meets the compaction requirements.

[0156] Figure 33 , 34 The statistical characteristics of the porosity and relative density of the fill gradation in the modulated rockfill area are shown respectively. The average relative density of the fill is 0.74, of which 5 groups do not meet the requirements of the dual control standard, and the compaction guarantee rate is 94.7%.

[0157] Comparison of Examples:

[0158] To demonstrate the role of the rockfill enhancement zone on the dam crest, two sets of dam design structures were adopted: Scheme I – the original dam design structure; Scheme II – the rockfill above the dam crest elevation of 2814m was designated as the enhancement zone (average relative density increased to 0.76), while the remaining structures remained consistent with the original design. A unified generalized plastic model of soil and rock and the indoor triaxial test parameters in Table 1-2 were used to perform three-dimensional viscoelastic-plastic static consolidation finite element analysis of the dam body. The two different dam crest rockfill zoning schemes are as follows: Figures 6-7 As shown.

[0159] The study compares the impact of the two schemes on dam deformation and stress, focusing on the impact of dam crest design structure on dam operation safety from aspects such as dam crest cracking, core wall arch effect and hydraulic splitting, and demonstrates the feasibility of the dam crest modulus zone scheme.

[0160] Calculation parameters

[0161] Based on the results of the triaxial test of the dam material in the laboratory, the parameters are summarized in Table 1.

[0162] Table 1 Parameters of the Unified Generalized Plastic Model for Dam Materials River and Sea

[0163] Dam material name Ce Ct m <![CDATA[M f ]]> <![CDATA[n f ]]> Mc α β d Stoned Area I 0.0055 0.0019 0.61 2.76 0.89 1.79 1.30 0.2 1.26 Stoned Zone III 0.0055 0.0020 0.61 2.76 0.88 1.79 1.30 0.2 1.26 Modular rockfill area 0.0023 0.0007 0.75 2.98 0.87 1.77 1.20 0.1 1.07 transition material 0.0054 0.0017 0.58 2.86 0.89 1.84 0.97 0.28 1.09 Reverse Filter I 0.0047 0.0016 0.60 2.92 0.85 1.75 1.49 0.1 1.06 Reverse Filter II 0.0045 0.0015 0.68 2.08 0.95 1.72 1.24 0.1 1.029 Heart Wall Material 0.0046 0.0015 0.71 0.85 0.94 0.75 0.38 0.03 1.01

[0164] Based on the results of the single-line wetting test of the riprap at Lianghekou, the calculation parameters are summarized in Table 2.

[0165] Table 2 Parameters of the Wetting Model Test for Rockfill

[0166] Based on on-site testing data, the permeability coefficient of the crushed stone core wall is taken as the average value of 3.6 × 10⁻⁶. -7 cm / s.

[0167] (a) Distribution of dam settlement during the completion period.

[0168] Depend on Figures 9-10 visible:

[0169] The two schemes showed the same dam deformation distribution pattern, with very small differences in the calculated extreme values. For example, the maximum settlement of the core wall at the completion period was 313.3 cm and 312.9 cm, respectively, and the maximum settlement of the rockfill area was 315.3 cm and 315.5 cm, respectively.

[0170] Distribution of dam settlement difference calculated under completed and full-storage conditions

[0171] The modified rockfill area on the dam crest has little impact on the overall deformation of the dam, but it significantly improves the deformation of the dam crest. For example, at the completion date, the extreme reductions in settlement between the upstream and downstream rockfill areas were 8.7 cm and 7.5 cm, respectively, at an elevation of 2845 m; while after the reservoir was fully filled, the extreme reductions in settlement between the upstream and downstream rockfill areas were 10.9 cm and 6.5 cm, respectively. The differential settlement between the upstream and downstream rockfill areas on the dam crest caused by reservoir impoundment and wetting was reduced, and this scheme improved the deformation incoordination problem between the dam crest core wall and the dam shell material.

[0172] (ii) The horizontal distribution of shear stress in the dam body during the full storage period calculated by the two schemes is the same.

[0173] After the addition of a reinforced rockfill zone on the dam crest, the stress state within the zone improved. The maximum shear stress level decreased from 0.59 to 0.52. However, under water pressure, the shear stress level in the upstream rockfill zone of Scheme II increased, with its maximum value increasing from 0.82 to 0.83. This demonstrates that the reinforced rockfill zone on the dam crest provides some constraint on different sections of the dam, but this constraint is weak, and the dam body elements will not experience shear failure.

[0174] (iii) The minimum principal stress at the dam crest decreases when the dam is fully filled.

[0175] Selecting the upstream water-facing element of the core wall at section 0+310, we analyze the relationship between the minor principal stress and the external water pressure during rapid water impoundment. Figure 15 It is evident that when using Scheme II, which involves adding a rockfill area to the dam crest during full storage, the minimum principal stress at the dam crest is slightly reduced, but the minimum principal stress value is still basically greater than the external water pressure value, and will not endanger the hydraulic fracturing safety of the dam body.

[0176] (iv) The core wall arch effect will not lead to hydraulic fracturing that endangers the safety of the dam body.

[0177] The arching effect caused by the difference in deformation modulus between the core wall and the dam shell materials on both sides can be expressed by the core wall arching effect coefficient.

[21] That is, the vertical stress of the element With the weight of the soil strip above The ratio of the strength to the strength is used to characterize the degree of strength.

[0178] Figures 16-17 The figure shows the distribution of the arching effect coefficient of the core wall during the full storage period. As can be seen from the figure, the distribution patterns are consistent. Due to the higher pore water pressure at the bottom of the core wall, the effective stress of the soil decreases, resulting in the smallest arching effect coefficient and the most pronounced arching effect. With increasing elevation, the arching effect coefficient gradually increases, while the degree of arching effect decreases. In Scheme II, due to the constraint of the dam crest modulus zone, the arching effect coefficient is slightly reduced; for example, the calculated maximum value decreases from 0.70 in Scheme I to 0.69. Considering that hydraulic fracturing generally occurs near the dam crest, and the arching effect coefficient of the core wall top area element is around 0.6, the core wall arching effect will not lead to hydraulic fracturing that endangers the safety of the dam.

[0179] Due to differences in the properties of the fill materials and filling standards in different zones, uneven settlement generally occurs at the dam crest. When the difference in uneven settlement reaches a certain limit, cracks will form on the dam crest surface, leading to a series of safety accidents such as landslides. Using the deformation inclination method proposed by Li Junchun et al., a critical inclination of 1% is used as the qualitative judgment criterion for dam crest cracking problems.

[0180] (v) Distribution of the slope of the dam crest area along the river direction

[0181] Compare the transverse and longitudinal deformation inclinations and settlement values ​​of the dam crest during the full storage period calculated using Scheme I and Scheme II with the modulated rockfill area, selecting nodes within an 8m depth range of the dam crest:

[0182] Depend on Figures 2-5A comparison of the transverse and longitudinal deformation and settlement values ​​of the dam crest under the two schemes during full storage shows that the transverse dip of both bank sections and the riverbed section is significantly reduced after the adoption of the modulus-enhancing zone. This is mainly due to the reduced settlement of the rockfill area on the dam crest after the adoption of the modulus-enhancing zone. The settlement reduction is greater in the upstream area of ​​the dam crest and smaller in the downstream area. Overall, the difference in settlement between the upstream and downstream sections of the dam crest is reduced, and the problem of deformation incoordination between the dam shell material and the core wall is improved. Under Scheme I, the transverse deformation dip of the dam crest is relatively larger, with a maximum value of 1.2%. This is located at the junction of the downstream side core wall and the filter wall on the dam crest at the 0+310 section of the riverbed, where longitudinal (dam axis) cracks may occur. Under Scheme II, the transverse deformation dip of the dam crest is significantly reduced, with a maximum value of 0.9%. The modulus-enhancing rockfill area on the dam crest significantly suppresses the dam crest settlement, and the degree of settlement at the top of the upstream rockfill area is greater than that in the downstream rockfill area. The problem of deformation incoordination between the dam shell material and the core wall can be improved, and cracking of the dam crest can be suppressed.

[0183] (vi) Analysis of the impact of seismic performance of the dam

[0184] According to the 2017 "Research Report on Site-Related Design Response Spectrum of Lianghekou Hydropower Station Dam Site in Sichuan Province", the design peak ground acceleration of the bedrock at the dam site is 287.8 gal, with a 2% exceedance probability in the 100-year reference period. The input seismic acceleration time history is shown in [reference missing]. Figures 19-21 .

[0185] ① The maximum subsidence of the dam has decreased significantly.

[0186] Table 3 shows the extreme values ​​of the seismic response of the dam calculated using the three-dimensional elastoplastic dynamic finite element method. Figures 22-23 , Figures 24-25 The figures show the extreme values ​​of absolute acceleration along the river and the distribution of seismic subsidence in the dam body. It can be seen that the amplification factor of the acceleration response ranges from 1.95 to 2.59, with the whiplash effect being more pronounced in the seismic response of the 300m-class ultra-high dam, and the maximum values ​​all located in the dam crest region. The seismic acceleration response value of Scheme II is higher than that of Scheme I, but the difference is not significant; for example, the extreme value of horizontal acceleration along the river decreases from 587.3 gal to 564.5 gal, a difference of only 4%. The subsidence of Scheme II is significantly smaller than that of Scheme I, with maximum values ​​of 49.2 cm and 61.7 cm respectively. The dam crest enhancement zone reduces the maximum subsidence of the dam by 25%, a significant effect.

[0187] Table 3. Extreme values ​​of three-dimensional elastoplastic dynamic response of the dam under design seismic conditions.

[0188] ② Suppress the seismic response of the dam

[0189] according to Figures 26-27The following data shows the seismic acceleration response amplification factor and subsidence distribution along the elevation of the dam in the river direction. The acceleration response amplification factor increases from 1.31 times at the 2815m elevation to 2.04 times at the dam crest. The subsidence also increases significantly from approximately the 2815m elevation to the dam crest, indicating a significantly enhanced seismic response amplification effect. This suggests that the location of the modulated rockfill zone in Scheme II is reasonable for suppressing the seismic response of the dam.

[0190] ③ Effectively reduce the volume of potential landslide blocks and lower the risk of earthquake-induced landslides.

[0191] Figures 28-31 The images show the location of the most potentially dangerous slip arc on the dam during the earthquake and the slip volume calculated using the Newmark method. It can be seen that the most potentially dangerous slip arc caused by the earthquake is basically located near the dam crest, with its escape point elevation around 2830m. During the earthquake, the locations of the most potentially dangerous slip arcs on the upstream dam slope were basically the same for both schemes, but the slip volume in Scheme II was significantly lower than in Scheme I, with maximum values ​​of 47.6cm and 55.6cm respectively. The modulus enhancement zone reduced the slip volume by 16%, and the escape elevation of the slip arc was raised, effectively reducing the volume of the potential sliding block and thus lowering the risk of earthquake-induced landslides.

Claims

1. A method for controlling water storage cracking and whiplash effect in a core-wall rockfill dam by setting a dam crest enhancement zone, characterized in that, Includes the following steps: S1. Set up a rockfill zone at a position 1 / 3 to 1 / 5 of the dam height below the dam crest; S2. Determine the filling gradation: the maximum particle size is ≤600mm and ≤2 / 3 of the thickness of the compacted layer, and the mass percentage of particles with a particle size <5mm is between 10% and 30%. S3. Determine the filling standard: Select the minimum porosity standard n of the rockfill material according to the "Design Specification for Rolled Earth-Rock Dams NB / T 10872_2021". d And calculate the minimum porosity standard n of the riprap. d Corresponding relative density compaction standard : （1）； Where, n max To satisfy the condition that porosity equals n d The maximum porosity of the gradation; n min For porosity equal to n d The minimum porosity of the graded distribution; S4. Based on the relative density compaction standard Dr in step S3, conduct indoor triaxial tests on scaled gradation samples to determine the constitutive model parameters of the dam material. S5. A unified generalized plastic model of soil and rock is adopted as the constitutive model for the dam finite element calculation including the design scheme of the modulus-enhanced rockfill area. Three-dimensional finite element static and dynamic calculations of the dam including the modulus-enhanced rockfill area are performed. The formula for calculating the loading modulus of the unified generalized plastic model of soil and rock is: （2）； In the formula, Indicates the plastic modulus at the time of loading. Indicates the reference stress. Indicates the average normal stress. The modulus factor reflects the influence of stress path. ,in, These are the compression parameters for the isotropic compression curve; The springback parameters are from the isotropic compression test. m is a material parameter for coarse-grained soil, reflecting the degree of influence of confining pressure; d represents the material parameters of the soil and rock; This represents the ratio of shear dilatation stress of coarse-grained material under various confining pressures. , and These are material parameters, obtained through fitting via indoor experiments; This represents the peak stress ratio of coarse-grained soil under various confining pressures. , and These are material parameters, obtained through fitting via indoor experiments; Indicates the stress ratio; S6. Verify the compatibility of zonal deformation, which includes the following sub-steps: S61. Hydraulic fracturing conditions of the core wall: The deformation compatibility requirement is not met. Core wall arch effect coefficient: The deformation compatibility requirement is not met. In the formula, This refers to the splitting pressure, which is the hydrostatic pressure that causes hydraulic splitting. The minimum total principal stress of the soil; It is the tensile strength of the soil. This refers to the vertical stress of the soil. This refers to the dry density of the soil. The height of the soil column at the calculation point; S62. Repeat steps S1 to S5 until the deformation compatibility requirements are met. S7. During construction, the minimum porosity standard for riprap shall be followed. d The relative density compaction standard Dr dual-control standard compacted the rockfill area on the dam crest.

2. The method for controlling water storage cracking and the whiplash effect of seismic response in a core-wall rockfill dam by setting up a dam crest enhancement zone according to claim 1, characterized in that, The elevation of the modulated rockfill area is set at more than 79% of the total dam height, and the relative density Dr≥0.

71.

3. The method for controlling water storage cracking and the whiplash effect of seismic response in a core-wall rockfill dam by setting up a dam crest enhancement zone according to claim 1, characterized in that, In step S3, the maximum and minimum dry densities of different gradations within the envelope are determined through on-site density barrel tests. The gradation with the worst filling relationship within the envelope or the lower envelope is selected as the minimum porosity standard n for the rockfill. d The required gradation.

4. The method for controlling water storage cracking and the whiplash effect of seismic response in a core-wall rockfill dam by setting up a dam crest enhancement zone according to claim 1, characterized in that, Step S4 specifically includes the following sub-steps: S41. Based on the gradation of the modulated rockfill area determined in step S1, scale down the rockfill area according to the scaling-down method in GB / T 50123-2019 Standard for Geotechnical Testing Methods. S42. Use the relative density compaction standard determined in step S3. As a standard for preparing triaxial test specimens for indoor scaled gradation; S43. Conduct indoor triaxial tests on the dam material in the reinforced rockfill area according to the procedure of GBT 50123-2019 Standard for Geotechnical Testing Methods to determine the constitutive model parameters of the dam material.

5. The method for controlling water storage cracking and the whiplash effect of seismic response in a core-wall rockfill dam by setting up a dam crest enhancement zone according to claim 1, characterized in that, Step S5 also includes a verification step for subsequent safety measures. Specifically, the verification method involves extracting the following key results under full-storage conditions during the water storage period: A. Spatial distribution of minimum total principal stress in the core wall, used for verification of water splitting resistance of clay core wall; B. The ratio of vertical stress in the core wall section to the self-weight of the overlying soil strip is used to calculate the arch effect coefficient of the core wall. C. The cumulative settlement at each measuring point along the dam crest monitoring line is used for deformation and inclination calculation; D. Permanent settlement and relative displacement of dam slope under seismic action are used for earthquake damage verification.

6. The method for controlling water storage cracking and the whiplash effect of seismic response in a core-wall rockfill dam by setting up a dam crest enhancement zone according to claim 1, characterized in that, In step S5, the Rayleigh damping matrix is ​​used for the three-dimensional finite element static and dynamic calculation of the dam body: （5）； in, The structural mass matrix, Here is the instantaneous tangent stiffness matrix. Let a, b, be the initial stiffness matrix. The proportionality coefficient and b and They cannot occur simultaneously, so b0=0 is used in the calculation; the damping ratio of the dam material is taken as 5%.

7. The method for controlling water storage cracking and the whiplash effect of seismic response in a core-wall rockfill dam by setting up a dam crest enhancement zone according to claim 1, characterized in that, Between steps S6 and S7, the deformation inclination method is used to verify the cracking of the dam crest, and the formula is as follows: （4）； In the formula: The inclination of the deformation is dimensionless. This indicates the angle between the line connecting the settlement points and the horizontal plane. These represent the cumulative settlement measured on a specific date. express , The horizontal distance between two points.

8. The method for controlling water storage cracking and the whiplash effect of seismic response in a core-wall rockfill dam by setting up a dam crest enhancement zone according to claim 1, characterized in that, In step S7 of construction quality control, the compaction guarantee rate is ≥94.7%, and the content of particles with a diameter <5mm in the gradation test is controlled between 10% and 30%.

9. The method for controlling water storage cracking and the whiplash effect of seismic response in a core-wall rockfill dam by setting up a dam crest enhancement zone according to claim 1, characterized in that, The modulated rockfill area is compacted by a vibratory roller for no less than 10 passes, with a loose thickness of no more than 1m and a water content of no less than 5%.

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