A face dam model structure for dam-break test and a design method thereof

Abstract

The application discloses a kind of panel dam model structures and design methods for dam-break test, the upstream slope of the rockfill area is paved with the transition layer of uniform thickness, the transition layer is paved with continuous graded sand, and the maximum particle size of the continuous graded sand is less than the minimum particle size of the rockfill material;The slope of the transition layer is paved with the cushion layer of uniform thickness, the cushion layer is paved with fine material with smaller particle size and continuous grading than the sand of the transition layer, and the slope of the cushion layer is paved with the panel layer of uniform thickness, the panel layer is spliced by multiple bamboo-rib panels, there are vertical expansion joints from the dam top to the dam bottom between adjacent bamboo-rib panels, the main material of the bamboo-rib panel is gypsum, and the bamboo-rib panel is internally provided with a bamboo-rib framework.The panel dam model structure disclosed by the application has regular fracture shape in the centrifugal test for simulating dam-break, can be used for technical analysis, and can improve the success rate and accuracy of the panel dam dam-break model test.

Description

Technical Field

[0001] This invention relates to the field of indoor simulation testing technology for hydraulic engineering, and in particular to a panel dam model structure and design method for dam break tests. Background Technology

[0002] As an important geotechnical test for obtaining information on the morphological changes of rockfill, the evolution of dam break flow, the collapse morphology and extent of breach slope, the fracture status of the face panel, and shape changes, the panel dam breach model test provides a research method for studying the development of the breach and the evolution of the breach flood flow process in panel dams.

[0003] For example, application number 202110173000.1, invention titled "A Centrifugal Model Test Device and Method for Simulating the Collapse of a Panel Dam," involves laying gypsum board as a panel on the rockfill upstream of the collapse model. Figure 1 As shown, this method can perform dam-break tests on gypsum board dams, demonstrating the scouring and damage process of the dam-break water flow on the rockfill, and inferring the scouring path and extent, which is of great significance for the study of dam-break mechanisms. However, gypsum board is a brittle material, and its fracture occurs very rapidly with irregular crack patterns, making it difficult to use for analysis and affecting the accuracy of the test results. Moreover, actual gypsum board dams are made of reinforced concrete, which does not undergo sudden brittle fracture like gypsum board during a dam break. Therefore, the test results of this method do not quite match the actual scenario.

[0004] Therefore, there is an urgent need for a panel dam model to solve the problem of irregular panel fracture shape in dam break model tests, so that the model test results can be used for actual dam break theory research. Summary of the Invention

[0005] The purpose of this invention is to solve the problem that in existing panel dam models, the panels will suddenly fracture brittlely during dam break tests, resulting in cracks that do not match the actual dam break situation. The invention proposes a panel dam model structure that incorporates bamboo reinforcement into the panel structure, giving the gypsum panel a certain degree of toughness, and enabling it to more realistically simulate and reflect the actual dam break situation.

[0006] The technical solution of the present invention is as follows:

[0007] A panel dam model structure for dam break testing includes a rockfill zone. The upstream slope of the rockfill zone is covered with a uniformly thick transition layer, which is constructed of continuously graded sand with high shear strength, low compressibility, and good drainage. The maximum particle size of the continuously graded sand is smaller than the minimum particle size of the rockfill. A uniformly thick cushion layer is laid on the slope of the transition layer, using fine material with a smaller particle size and better gradation than the transition layer sand. A uniformly thick panel layer is laid on the slope of the cushion layer, composed of multiple bamboo-reinforced panels spliced ​​together. Vertical expansion joints from the dam crest to the dam base are present between adjacent bamboo-reinforced panels. A bamboo-reinforced skeleton is installed inside each bamboo-reinforced panel, and the main material of the bamboo-reinforced panels is gypsum.

[0008] The transition layer is located below the cushion layer and serves to protect it. The cushion layer is made of fine material with small particle size and good gradation. The fine material is rolled flat by rollers and has a certain degree of compaction to assist in seepage prevention. The cushion layer is located below the bamboo-reinforced panel and serves to flatten the bamboo-reinforced panel and avoid stress concentration. The bamboo-reinforced panel laid on the slope of the cushion layer has a certain tensile strength. In the overtopping dam failure test, the bamboo-reinforced panel will not break suddenly, and the fracture shape is regular, which can be used for technical analysis.

[0009] Preferably, epoxy asphalt is injected into the gap between two adjacent bamboo reinforcement panels, and acidic glass glue is used to bond the periphery of the bamboo reinforcement panels to the test tank.

[0010] Preferably, the bamboo reinforcement frame is formed by overlapping vertical and horizontal bamboo reinforcements arranged at equal intervals, and the bamboo reinforcement frame is located in the middle of the thickness direction of the bamboo reinforcement panel.

[0011] A design method for a panel dam model includes:

[0012] Step 1: Based on the similarity criteria, calculate the density, elastic modulus, ultimate tensile strength, and ultimate breaking moment of the bamboo-reinforced panel in the model dam according to the density, elastic modulus, ultimate tensile strength, and ultimate breaking moment of the reinforced concrete panel in the prototype dam.

[0013] Step 2: Calculate the thickness of the bamboo-reinforced panel;

[0014] Step 3: Calculate the total bending moment borne by the bamboo-reinforced panel under the combined action of self-weight load and water load, and compare it with the ultimate bending moment of the bamboo-reinforced panel. If the total bending moment is less than the ultimate bending moment of the bamboo-reinforced panel, increase the elevation of the reservoir water level during the test until the total bending moment borne by the bamboo-reinforced panel is greater than the ultimate bending moment.

[0015] Step four: Bamboo ribs are made from bamboo yellow material and a single-layer, two-way reinforcement method is adopted. The reinforcement ratio of the model panel is 0.3-0.5%. The bamboo rib skeleton is designed according to the ultimate tensile strength and ultimate breaking moment of the bamboo rib panel. The prepared gypsum slurry is poured into the bamboo rib skeleton.

[0016] Preferably, the mass ratio of water to solid components in the gypsum slurry is 1:0.85, wherein the solid components and their mass percentages are as follows: gypsum 45%, heavy calcium carbonate 35%, white cement 15%, hydroxypropyl methylcellulose ether 2%, ferrous sulfate 0.5%, polyacrylamide 0.5%, and adhesive powder 2%.

[0017] The beneficial effects of this invention are:

[0018] The panel dam model structure disclosed in this invention exhibits a regular fracture shape in centrifugal tests simulating dam failure, which can more realistically simulate and reflect the actual dam failure situation of panel dams, thereby improving the success rate and accuracy of panel dam failure tests.

[0019] The design method disclosed in this invention provides a model dam for dam failure testing designed based on the parameters of the prototype panel dam to be studied in the experiment. The resulting panel dam model is more consistent with the failure conditions of the prototype panel dam. Attached Figure Description

[0020] Figure 1 This is a structural schematic diagram of a panel dam model in the prior art;

[0021] Figure 2 This is a schematic diagram of a panel dam model provided by the present invention;

[0022] Figure 3 yes Figure 2 Exploded structural diagram;

[0023] Figure 4 This is a structural diagram of a bamboo-reinforced panel;

[0024] Figure 5 This is a diagram of the bamboo rib skeleton structure;

[0025] Figure 6 This is a schematic diagram of the structure of a single bamboo rib;

[0026] Figure 7 yes Figure 6 Enlarged view of a portion of point A in the middle;

[0027] Figure 8 It is the fracture shape of a pure gypsum board panel;

[0028] Figure 9 This is the structure of the bamboo-reinforced panel in Example 3;

[0029] Figure 10 This is the structure of the bamboo-reinforced panel after the model dam collapses in Example 3;

[0030] Figure 11 This is a comparison chart of the duration of dam break flow rates;

[0031] Figure 12It is a photo of the breached dam behind the ditch.

[0032] Among them, 1. bamboo reinforcement panel, 2. padding layer, 3. transition layer, 4. riprap area, 1-1. expansion joint, 1-2. vertical bamboo reinforcement, 1-3. horizontal bamboo reinforcement. Detailed Implementation

[0033] The present invention will be further described below with reference to the accompanying drawings and embodiments. Example 1

[0034] like Figure 2 , 3 As shown, the present invention discloses a panel dam model structure for dam break testing, comprising a rockfill zone 4. Viewed from both ends along the length of the panel dam, the end faces of the rockfill zone are triangular. A uniformly thick transition layer 3 is laid on the upstream slope of the rockfill zone. This transition layer is constructed using continuously graded sand with high shear strength, low compressibility, and good drainage. The maximum particle size of the continuously graded sand is smaller than the minimum particle size of the rockfill. A uniformly thick cushion layer 2 is laid on the slope of the transition layer. This cushion layer is constructed using fine material with a smaller particle size and better gradation than the sand in the transition layer. A uniformly thick panel layer 1 is laid on the slope of the cushion layer. This panel layer is composed of multiple bamboo-reinforced panels spliced ​​together. The joints of the bamboo-reinforced panels are vertical joints from the top to the bottom of the dam. The main material of the bamboo-reinforced panels is gypsum. The interior of the bamboo-reinforced panels contains a framework formed by connecting bamboo reinforcements. Figure 6 , 7 As shown, bamboo fiber is a unidirectional fiber composite material with a certain tensile strength.

[0035] The design thickness of transition layer 3 and cushion layer 2 is determined according to the "Design Code for Concrete-faced Rockfill Dams" NB / T 10871-2021, the prototype dam design drawings, and the scale of geometric dimensions.

[0036] The rockfill area is constructed using a layered filling method. Specifically, the area is marked on the bottom plate of the model test chamber, and the slope and layer heights are marked on the side plate. The first layer is filled with rockfill material that has high shear strength, low compressibility, and good permeability, and then compacted. The surface of the first layer is roughened, and then the next layer is filled until the height of the rockfill area is reached. The slope of the rockfill area is controlled while filling each layer. After the rockfill area is completed, the upstream slope of the rockfill area is roughened. Continuously graded sand with high shear strength, low compressibility, and good permeability is laid on the upstream slope of the rockfill area. The maximum particle size of the sand does not exceed 300mm, and the content of particles smaller than 0.075mm is less than 5%. The sand is then rolled, leveled, and compacted to the designed thickness of the transition layer. After the transition layer is laid, the surface of the transition layer slope is roughened. Then, a fine material with a continuous gradation and smaller particle size than the transition layer sand is laid on the slope. The maximum particle size is 80-100mm, the content of particles smaller than 5mm is 35%-55%, and the content of particles smaller than 0.075mm is 4%-8%. This is then leveled and compacted to the designed thickness of the subbase, forming the subbase. After the subbase is laid, the slope is roughened again, and then the bamboo-reinforced panels are laid. Example 2

[0037] This embodiment illustrates the design method of this panel dam model. The prototype dam in this embodiment is a gravel dam. The density of the reinforced concrete panel is 2.4 g / cm³, the elastic modulus of the reinforced concrete panel is 30 GPa, and the ultimate tensile strength of the reinforced concrete panel is 3 MPa. Taking this gravel dam as an example, the panel dam model is designed according to the following method:

[0038] Step 1: Based on the similarity criteria, calculate the density, elastic modulus, ultimate tensile strength, and ultimate breaking moment of the panel layer in the model dam according to the density, elastic modulus, ultimate tensile strength, and ultimate breaking moment of the reinforced concrete panel in the prototype dam.

[0039] The geometric dimensions of the prototype dam are scaled down proportionally, and the ratio of the geometric dimensions of the prototype dam to those of this model dam is defined as the length scale. λ l :

[0040]

[0041] In the formula: λ l Length scale; l m This refers to the length of a certain part of the model dam; l p This refers to the length of the corresponding part of the prototype dam.

[0042] Other additives, such as weighting agents and reinforcing agents, are added to the gypsum powder in a certain proportion to adjust the density of the panels and ensure that the panels have similar gravity. Based on the requirement of force similarity, the gravity scale of the bamboo-reinforced panels in this model dam is the same as that of the riprap. The gravity scale of the riprap is: λ G :

[0043]

[0044] In the formula: The unit weight of the rockfill material in the model dam, The bulk density of the rockfill material in the prototype dam. Let V be the volume of the rockfill material in the model dam. This refers to the volume of the rockfill material in the prototype dam. g This is the acceleration due to gravity.

[0045] Based on the requirement of force similarity, the gravitational scale of the panel should also be [value missing]. λ G The panel and the gravel have the same density ratio:

[0046]

[0047] In the formula, The density of the rockfill material in the prototype dam. The density of the rockfill material in the model dam;

[0048] The force that causes elastic deformation in bamboo fiber panels is elastic strain. ε Elastic modulus E and cross-sectional area A The product of the two, the elastic force of the panel is equal to that of the scale. λ F :

[0049]

[0050] In the formula: For the stress on the dam panel of the model, Let be the cross-sectional area of ​​the model dam. The elastic strain of the model dam panel. The elastic modulus of the model dam panel; The stress of the prototype dam face. This refers to the cross-sectional area of ​​the prototype dam. This refers to the elastic strain of the prototype dam face. The elastic modulus of the model dam panel;

[0051] Based on the similarity of forces, the elastic force is greater than the scale force. λ F Equal to the weight ratio of the piled-up stones λG Therefore, we can conclude that:

[0052]

[0053] Use cohesion C With cross-sectional area A The product of and represents the force exerted on the panel at its ultimate tensile strength; the cohesive force at break is equal to the strength of the scale. λ C for:

[0054]

[0055] According to the similarity criterion of forces, the cohesive force of the panel when it breaks is proportional to the scale. λ C Equal to the weight ratio of the piled-up stones λ G :

[0056]

[0057] In the formula, λ C The scale represents the cohesive force when the panel breaks. λ G The gravimetric scale of the piled stone. λ l For the length scale of the panel dam, C m This refers to the cohesive force at which the panel of the model dam breaks. C p The cohesive force of the reinforced concrete panel in the prototype dam when it breaks.

[0058] Based on the gradation curve of the riprap, the density ratio of the model is obtained. λρ It is 0.9. λ l Taking 1 / 100, and based on the similarity criterion, the density of bamboo fiber panel is 2.16 g / cm³. 3 The elastic modulus is 0.27 GPa, and the ultimate tensile strength is 27 kPa. The ultimate breaking moment of the prototype dam's reinforced concrete panel is 33.6 kN·m. Based on the force similarity criterion, the theoretical ultimate breaking moment of the bamboo-reinforced panel in this model dam is... M f 0 . 336 kN·m.

[0059] Step two: Calculate the thickness of the bamboo-reinforced panel. Assuming the deformation of the prototype dam panel soil under study is a plane strain problem, then the panel deflection displacement... V It can be represented as:

[0060]

[0061] In the formula: M(x) The distance from the fixed end (bottom end of the panel) is x Bending moment at any cross section; C 1 、C 2 The integral constant is determined based on the continuity condition and the boundary condition; EI For the bending stiffness of the panel; E The elastic modulus of the panel; I Let be the moment of inertia of the panel cross section.

[0062] Since the external loads and boundary conditions borne by the prototype dam panel and the bamboo-reinforced panel in this model are exactly the same, in order to achieve deformation equivalence, the bending stiffness of the prototype dam panel and the bamboo-reinforced panel in this model remains equal, that is:

[0063]

[0064] in:

[0065]

[0066] The thickness of the bamboo fiber panel can be obtained. d m The formula:

[0067]

[0068] In the formula: E p The elastic modulus of the prototype dam face; E m The elastic modulus of the model dam panel; I p The moment of inertia of the prototype dam face; I m Let be the moment of inertia of the model dam panel; d p The thickness of the prototype dam panel; d m This refers to the thickness of the dam panel in the model.

[0069] Step 3: Calculate the total bending moment borne by the bamboo-reinforced panel under the combined action of its own weight and water load:

[0070]

[0071] In the formula: ρ m1 The density of the model dam panel; The thickness of the dam panel in the model; L d This is the length of the broken bamboo strip panel; ρw H is the density of water; H is the elevation of the reservoir water level. Z f The elevation of the top of the bamboo-reinforced panel; .

[0072] Conditions for panel breakage:

[0073]

[0074] In the formula: M f The ultimate bending moment of the model dam panel (bamboo-reinforced panel) is calculated as follows: Value less than M f This can be achieved by raising the reservoir water level, thereby increasing the total bending moment.

[0075] Step four, according to Chezy's formula, the water flow velocity can be expressed as:

[0076]

[0077] In the formula, f The roughness coefficient is... R For hydraulic radius, J Because of the hydraulic gradient, the water flow velocity of this model dam and the prototype dam are equal.

[0078] Step 5: The bamboo reinforcement in the bamboo reinforcement panel is made of bamboo yellow with low tensile strength (about 60MPa), and a single-layer bidirectional reinforcement method is adopted. The reinforcement ratio of the model panel is 0.3-0.5%.

[0079] In this embodiment, based on the width of the panel layer, the panel layer is composed of five bamboo-reinforced panels spliced ​​together, with the gap between two adjacent bamboo-reinforced panels forming an expansion joint 1-1. Each bamboo-reinforced panel contains a skeleton formed by the same number of bamboo rebars. Based on the width and strength of each individual bamboo-reinforced panel, bamboo rebars are arranged at equal vertical and horizontal intervals. The horizontal and vertical bamboo rebars are then bound together with thin thread at the overlaps to form the bamboo-reinforced skeleton. Figure 4 As shown.

[0080] After the subgrade is prepared, first drive several anchor screws at intervals into the roughened slope surface of the subgrade. Hang the bamboo frame on the anchor screws, and secure the bamboo frame at its four nodes (the nodes are the anchor points). Figure 5 Fix the plaster block at the position of the black dot (center). The plaster block will raise the bamboo frame, ensuring that after the bamboo frame panel is formed, the bamboo frame is located in the middle of the thickness direction of the bamboo frame panel. Figure 5As shown. Then, the prepared gypsum grout is poured, and after hydration, multiple bamboo-reinforced panels are formed on the surface of the subbase. Expansion joints are formed between adjacent bamboo-reinforced panels, and epoxy asphalt (epoxy asphalt is a flexible waterproof composite material with high strength and strong adhesion) is injected between the expansion joints. The perimeter seams of the bamboo-reinforced panels are bonded to the acrylic plate of the test tank with acidic glass glue. Acidic glass glue has strong adhesion and short curing time. The surface of the bamboo-reinforced panels is uniformly coated with petroleum jelly. Example 3

[0081] This embodiment follows the structure of Embodiment 1 and the method of Embodiment 2, simulating a 268m high panel rockfill dam using a 1 / 400 scale model. The panel thickness of this panel rockfill dam is 30cm. The solid component mass ratio in the gypsum slurry is 1:0.85, as shown in Table 1. The bamboo reinforcement is made of bamboo pulp with a diameter of 1mm and a tensile strength of 60MPa. Figure 9 As shown, in this embodiment, the bamboo frame is formed by 6 vertical bamboo ribs and 28 horizontal bamboo ribs arranged at equal intervals.

[0082] Table 1. Solid components and mass percentage in gypsum slurry

[0083]

[0084] The particle size distribution of the riprap in the rockfill area is shown in Table 2. The riprap is filled in layers, with the thickness of the foundation layer being 1.3 times the thickness of the face panel. The foundation layer uses basalt sand and gravel with a particle size of 2–1 mm. The thickness of the transition layer is 1.5 times the thickness of the face panel. The foundation layer uses basalt sand and gravel with a particle size of less than 1 mm. The final result is a model dam with a height of 67 cm, a width of 30 cm, and a bamboo-reinforced face panel thickness of 1.2 cm. Figure 10 As shown.

[0085] Table 2 Particle size distribution of rockfill

[0086]

[0087] like Figure 8 As shown, the fracture surface of a simple gypsum board panel exhibits a highly irregular shape. Therefore, the structure and materials used to construct the panels of the model dam are crucial. It is necessary to increase the strength of the gypsum board panel, but concrete panels cannot be used directly because they are strong and not easily broken. Therefore, existing panel dam models lack suitable materials for panel construction. This embodiment incorporates bamboo reinforcement, which enhances the tensile strength of the panel, such as… Figure 10 As shown, the fracture surface of the bamboo-reinforced panel has a more regular shape, which is beneficial for analysis, such as... Figure 11 As shown, the breach flow rate of bamboo-reinforced panels is smaller, resulting in a longer breach formation time for the same total reservoir volume. Compared to... Figure 8 and Figure 10, Figure 10 The fracture shape of the bamboo-ribbed panel is more regular and closer to that of... Figure 12 The fracture shape of a real concrete panel dam is shown.

[0088] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A panel dam model structure for dam-break testing, characterized in that, The dam includes a rockfill area. The upstream slope of the rockfill area is covered with a uniformly thick transition layer, which is constructed using continuously graded sand. The maximum particle size of the continuously graded sand is smaller than the minimum particle size of the rockfill. A uniformly thick cushion layer is laid on the slope of the transition layer. This cushion layer is constructed using continuously graded fine material with a particle size smaller than that of the transition layer sand. A uniformly thick panel layer is laid on the slope of the cushion layer. The panel layer is composed of multiple bamboo-reinforced panels spliced ​​together. Vertical expansion joints run from the top to the bottom of the dam between adjacent bamboo-reinforced panels. A bamboo-reinforced skeleton is installed inside each bamboo-reinforced panel. The main material of the bamboo-reinforced panels is gypsum. The bamboo-reinforced skeleton is formed by overlapping vertical and horizontal bamboo reinforcements arranged at equal intervals, and is located in the middle of the thickness direction of the bamboo-reinforced panels.

2. The panel dam model structure for dam break testing according to claim 1, characterized in that, Epoxy asphalt was injected into the vertical expansion joints.

3. A design method for a panel dam model structure for dam-break testing according to any one of claims 1-2, characterized in that, include: Step 1: Based on the similarity criteria, calculate the density, elastic modulus, ultimate tensile strength, and ultimate breaking moment of the bamboo-reinforced panel in the model dam according to the density, elastic modulus, ultimate tensile strength, and ultimate breaking moment of the reinforced concrete panel in the prototype dam. Step 2: Calculate the thickness of the bamboo-reinforced panel; Step 3: Calculate the total bending moment borne by the bamboo-reinforced panel under the combined action of self-weight load and water load, and compare it with the ultimate bending moment of the bamboo-reinforced panel. If the total bending moment is less than the ultimate bending moment of the bamboo-reinforced panel, increase the elevation of the reservoir water level during the test until the total bending moment borne by the bamboo-reinforced panel is greater than the ultimate bending moment. Step four: Select bamboo yellow to make bamboo reinforcement, and adopt a single-layer bidirectional reinforcement method. The reinforcement ratio of the model panel is 0.3-0.5%. Design the bamboo reinforcement skeleton according to the ultimate tensile strength and ultimate breaking moment of the bamboo reinforcement panel, and pour the prepared gypsum slurry into the bamboo reinforcement skeleton.

4. The design method for a panel dam model structure for dam-break testing according to claim 3, characterized in that, The mass ratio of water to solid components in the gypsum slurry is 1:0.

85. The solid components and their mass percentages are as follows: gypsum 45%, heavy calcium carbonate 35%, white cement 15%, hydroxypropyl methylcellulose ether 2%, ferrous sulfate 0.5%, polyacrylamide 0.5%, and adhesive powder 2%.

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