Deep-sea large-diameter pile group foundation underwater vibration table test model design method

Abstract

The invention discloses a deep-sea large-diameter pile group foundation underwater vibration table test model design method, and relates to the technical field of civil engineering, and the method comprises the steps: determining a test scale ratio and a similarity ratio according to a prototype pile group foundation pile foundation and a test environment; obtaining an ideal material model after scale reduction according to the test scale reduction ratio and the similarity ratio; equivalently replacing the pile foundation and the bearing platform of the test model according to the ideal material model; mounting holes are reserved in the pile foundation and the bearing platform of the test model, the hydrodynamic pressure gauges are embedded into the reserved mounting holes, and the hydrodynamic pressure gauges are led out from the interior of the pile foundation of the test model or the reserved holes of the bearing platform to the top of the test model through wires and then connected into an acquisition system for data acquisition. According to the method, the underwater vibration table model suitable for the deepwater large-diameter pile group foundation is constructed through similar skills, the method is suitable for a pile group structure, the detection data quality is improved by embedding the hydrodynamic pressure gauges into the reserved holes, the deepwater large-diameter pile group foundation test model is constructed, an earthquake simulation underwater vibration table test is carried out, and a good effect is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of civil engineering, and more specifically, to a design method for an underwater shaking table test model of a large-diameter group pile foundation in deep sea. Background Art

[0002] The underwater shaking table test needs to simultaneously satisfy the solid similarity criterion and the fluid similarity condition. Since the density of water cannot be changed, according to the geometric scale ratio, the hydrodynamic pressure and the structural inertial force cannot satisfy the similarity ratio. To solve this problem, there are mainly two solutions: (1) Develop simulation similar materials with equal density and low elastic modulus. This can be achieved when simulating relatively shallow water depths, but when the simulated water depth increases to more than 50m, it has been relatively difficult to develop simulation similar materials that meet the requirements based on the existing domestic underwater shaking table test conditions; (2) Change the width of the water-facing surface of the model structure, such as additionally installing hanging plates to increase the hydrodynamic pressure, so that the similarity ratio between the structural hydrodynamic pressure and the structural inertial force remains consistent. This method is feasible for single-pile or single-pier structures, but is not applicable to group pile structures.

[0003] In the prior art, a coordinated similarity design method for an underwater shaking table test model with the publication number CN115618514A uses the material of the prototype structure to make the test model, and makes the similarity ratio between the structural hydrodynamic pressure and the wave force and the external force received by the structure consistent by changing the width of the water-facing surface of the model structure and the wave height. This method provides an idea for solving the problem that the density of water cannot be changed in the underwater shaking table test, but there are also many deficiencies: (1) For the model determined according to the scale ratio, it is necessary to increase the water-facing surface of the model structure, and the determination of the water-facing surface is calculated using the radiation wave theory and the diffraction wave theory. The radiation wave theory and the diffraction wave theory require a large amount of simplification of the flow field and the structure, and the derivation process is relatively complex, and its calculation accuracy remains to be verified; (2) The radiation wave theory and the diffraction wave theory cannot consider the influence of the group pile effect, and currently cannot be applied to the calculation of group pile structures; (3) There is a group pile effect in the large-diameter group pile foundation. After the water-facing surface of the group pile increases, the group pile effect will change significantly, that is, it cannot truly reflect the influence of the group pile effect on the hydrodynamic pressure, resulting in the problem that the hydrodynamic force is difficult to determine. Therefore, this method is not applicable to the model design of group pile foundations; (4) Since the simulation of the unidirectional hydrodynamic pressure is achieved by increasing the water-facing surface area, it is difficult to take into account the hydrodynamic pressure in the vertical direction. This method is only applicable to the underwater shaking table model design of water-structure interaction under unidirectional seismic action, and is not applicable to the two-way shaking table test; (5) This patent application does not involve the description of the arrangement of the hydrodynamic pressure gauges. On this basis, it is an irresistible trend for cross-sea bridges to move from shallow water to deep water, and in the deep water environment above 50m, it is an irresistible trend for pile foundations to develop towards large diameters. Currently, the effective water depth of the underwater shaking table test is basically about 1m, and it is relatively difficult to design a scale model that meets the similarity criterion, and it is even more difficult to achieve the model design of the deep water large-diameter group pile foundation.

[0004] Therefore, how to propose a design method for the underwater shaking table test model of the deep-sea large-diameter pile group foundation and construct an underwater shaking table model suitable for the deep-water large-diameter pile group foundation through similarity techniques is an urgent problem to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention provides a design method for the underwater shaking table test model of the deep-sea large-diameter pile group foundation, and constructs an underwater shaking table model suitable for the deep-water large-diameter pile group foundation through similarity techniques. To achieve the above object, the present invention adopts the following technical solutions:

[0006] A design method for the underwater shaking table test model of the deep-sea large-diameter pile group foundation includes:

[0007] Determine the test scale ratio and similarity ratio according to the prototype pile group foundation piles and the test environment;

[0008] Obtain the scaled ideal material model according to the test scale ratio and similarity ratio;

[0009] Perform equivalent substitution of the test model pile foundation and the pile cap according to the ideal material model;

[0010] Reserve installation holes on the test model pile foundation and the pile cap, embed the hydrodynamic pressure gauges into the reserved installation holes, and lead them out from inside the test model pile foundation or the reserved holes of the pile cap to the top of the test model through wires and then connect them to the acquisition system for data acquisition.

[0011] Optionally, the determination of the test scale ratio includes: determining the geometric scale ratio according to the actual water depth h0 and the test water depth h1

[0012] Optionally, the steps for determining the similarity ratio are as follows:

[0013] The water body used in the test is the same as the water body of the prototype structure. The prototype structure and the model structure are in the same gravitational field, and the similarity ratio S g of the gravitational acceleration = 1, and the similarity ratio S a of the acceleration = 1;

[0014] Assume that there is an ideal material whose density is the same as the density of the prototype structure concrete, and the similarity ratio S ρ of the density = 1, and the similarity ratio of the elastic modulus Then it satisfies the similarity criterion of the underwater shaking table test:

[0015] Solid similarity criterion:

[0016] Fruder similarity criterion:

[0017] Euler similarity criterion:

[0018] Among them, S P is the hydrodynamic pressure similarity ratio, and S v is the velocity similarity ratio.

[0019] Optionally, the scaled ideal material model obtained according to the test scale ratio and similarity ratio includes:

[0020] According to the similarity relationship, the dimensions of the scaled ideal material model are: the outer diameter of the pile foundation inner diameter length of the pile foundation material density ρ1 = ρ0, elastic modulus Among them, R0, r0, L0, ρ0, and E0 are respectively the outer diameter, inner diameter, length, density, and elastic modulus of the pile foundation of the prototype structure.

[0021] Optionally, the equivalent substitution of the test model pile foundation and the cap according to the ideal material model includes:

[0022] S1: According to the similarity relationship, determine the ideal material model, and keep the outer diameter and layout form of the model pile foundation unchanged, that is, the outer diameter of the test model pile foundation

[0023] S2: Determine the material of the test model pile foundation, and obtain its elastic modulus E2 and density ρ2. By adjusting the wall thickness of the pile foundation, make the flexural rigidity of the test model pile foundation E2.I2 = E1.I1, where I1 and I2 are the section moments of inertia of the ideal material model and the test model pile foundation respectively, and E1 and E2 are the elastic moduli of the ideal material and the test model material;

[0024] S3: Based on the equivalence of the flexural rigidity of the model pile foundation, calculate the inner diameter of the test model pile foundation

[0025] S4: According to the outer diameter R2 and inner diameter r2 of the test model pile foundation, calculate the mass of a single test model pile foundation

[0026] S5: The mass of a single pile foundation of the ideal material model The difference m between the two 1-2 = m1 - m2.

[0027] Optionally, the material of the test model pile foundation is plexiglass material.

[0028] Optionally, it further includes: making up for the mass difference between the two models by evenly weighting the test model pile foundation from bottom to top to obtain m 1-2= m1 - m2. The counterweight is evenly divided into x parts according to the height of the test model pile foundation, and the mass of each part of the counterweight is

[0029] Optionally, the equivalent replacement of the bearing platform includes:

[0030] The bearing platform is a rigid body. The size and shape of the bearing platform are determined with reference to the ideal material model, and the mass is adjusted by uniformly reserved holes on the bearing platform;

[0031] Through the equivalent replacement of the pile foundation stiffness and the equivalent replacement of the masses of the pile foundation and the bearing platform, the test model and the ideal material model have the same acceleration, displacement, and strain.

[0032] Optionally, the small gaps between the hydrodynamic pressure gauges and the pile foundation wall or the bearing platform are sealed with sealant.

[0033] Optionally, the test model includes: a shaking table, a test model pile foundation, an adapter plate, and a bearing platform; the bottom of the test model pile foundation is fixedly connected to the adapter plate, the adapter plate is anchored to the shaking table surface by six anchor bolts, and the top of the test model pile foundation is fixedly connected to the bearing platform.

[0034] Through the above technical solutions, compared with the prior art, the present invention discloses a design method for an underwater shaking table test model of a deep-sea large-diameter pile group foundation, which has the following beneficial effects:

[0035] The present invention proposes a design method for an underwater shaking table test model of a deep-sea large-diameter pile group foundation, including: determining the test scale ratio and similarity ratio according to the pile foundation of the prototype pile group foundation and the test environment; obtaining the scaled ideal material model according to the test scale ratio and similarity ratio; performing equivalent replacement of the test model pile foundation and the bearing platform according to the ideal material model; reserving installation holes on the test model pile foundation and the bearing platform, embedding the hydrodynamic pressure gauges into the reserved installation holes, and leading them out from inside the test model pile foundation or the reserved holes of the bearing platform to the top of the test model through wires and then connecting them to the acquisition system for data acquisition. The present invention constructs an underwater shaking table model applicable to deep-water large-diameter pile group foundations through similarity techniques, which is applicable to pile group structures. By embedding the hydrodynamic pressure gauges into the reserved holes, the quality of the detected data is improved, an experimental model of a deep-sea large-diameter pile group foundation is constructed, and a simulated earthquake underwater shaking table test is carried out, achieving good results. Description of the Drawings

[0036] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained according to the provided drawings without creative efforts.

[0037] Figure 1 Schematic diagram of the underwater shaking table test model structure of a large-diameter group pile foundation in deep sea provided by the present invention.

[0038] Figure 2 Structural diagram of the counterweight block provided by the present invention.

[0039] Figure 3 Structural diagram of the connection between the pile foundation and the shaking table provided by the present invention.

[0040] Figure 4 Structural diagram of the connection between the pile cap and the pile foundation provided by the present invention. Specific implementation mode

[0041] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0042] The embodiments of the present invention disclose a design method for an underwater shaking table test model of a large-diameter group pile foundation in deep sea, including:

[0043] Determine the test scale ratio and similarity ratio according to the pile foundation of the prototype group pile foundation and the test environment;

[0044] Obtain the scaled ideal material model according to the test scale ratio and similarity ratio;

[0045] Perform equivalent substitution of the test model pile foundation and pile cap according to the ideal material model;

[0046] Reserve installation holes on the test model pile foundation and pile cap, embed the hydrodynamic pressure gauge into the reserved installation holes, and lead it out from inside the test model pile foundation or the reserved hole of the pile cap to the top of the test model through a wire and then connect it to the acquisition system for data acquisition.

[0047] Further, the determination of the test scale ratio includes: determining the geometric scale ratio according to the actual water depth h0 and the test water depth h1

[0048] Further, the determination steps of the similarity ratio are:

[0049] The water body used in the test is the same as the water body of the prototype structure. The prototype structure and the model structure are in the same gravitational field, and the similarity ratio of gravitational acceleration S g = 1, and the similarity ratio of acceleration S a = 1;

[0050] Assume that there is an ideal material with the same density as the prototype structural concrete, and the density similarity ratio S ρ = 1, and the elastic modulus similarity ratio Then it satisfies the similarity criteria for the underwater shaking table test:

[0051] Solid similarity criterion:

[0052] Fruder similarity criterion:

[0053] Euler similarity criterion:

[0054] Among them, S P is the hydrodynamic pressure similarity ratio, and S v is the velocity similarity ratio.

[0055] Furthermore, the scaled ideal material model obtained according to the test scale ratio and similarity ratio includes:

[0056] According to the similarity relationship, the dimensions of the scaled ideal material model are: the outer diameter of the pile foundation Inner diameter Length of the pile foundation The material density ρ1 = ρ0, and the elastic modulus Among them, R0, r0, L0, ρ0, and E0 are the outer diameter, inner diameter, length, density, and elastic modulus of the prototype structural pile foundation, respectively.

[0057] Furthermore, the equivalent substitution of the test model pile foundation and the pile cap according to the ideal material model includes:

[0058] S1: According to the similarity relationship, determine the ideal material model, and keep the outer diameter and layout form of the model pile foundation unchanged, that is, the outer diameter of the test model pile foundation

[0059] S2: Determine the material of the test model pile foundation, and obtain its elastic modulus E2 and density ρ2. By adjusting the pile wall thickness, make the flexural stiffness of the test model pile foundation E2.I2 = E1.I1, where I1 and I2 are the cross-sectional moments of inertia of the ideal material model and the test model pile foundation, respectively, and E1 and E2 are the elastic moduli of the ideal material and the test model material;

[0060] S3: Based on the equivalence of the flexural stiffness of the model pile foundation, calculate the inner diameter of the test model pile foundation

[0061] S4: According to the outer diameter R2 and inner diameter r2 of the test model pile foundation, calculate the mass of a single test model pile foundation

[0062] S5: Quality of a single pile foundation of the ideal material model The difference m between the two 1-2 = m1 - m2.

[0063] Furthermore, the material of the test model pile foundation is plexiglass material.

[0064] Furthermore, it also includes: compensating for the mass difference between the two models by evenly adding weights to the test model pile foundation from bottom to top to obtain m 1-2 = m1 - m2, dividing the added weights into x equal parts according to the height of the test model pile foundation, and the mass of each part of the added weight is

[0065] Furthermore, the equivalent substitution of the bearing platform includes:

[0066] The bearing platform is a rigid body. The size and shape of the bearing platform are determined with reference to the ideal material model, and the mass is adjusted by evenly reserving holes on the bearing platform;

[0067] Through the equivalent substitution of the pile foundation stiffness and the equivalent substitution of the masses of the pile foundation and the bearing platform, the test model and the ideal material model have the same acceleration, displacement, and strain.

[0068] Furthermore, the small gaps between the hydrodynamic pressure gauges and the pile foundation wall or the bearing platform are sealed with sealant.

[0069] Furthermore, the test model includes: a shaking table, a test model pile foundation, an adapter plate, and a bearing platform; the bottom of the test model pile foundation is fixedly connected to the adapter plate, the adapter plate is anchored to the shaking table surface through six anchor bolts, and the top of the test model pile foundation is fixedly connected to the bearing platform.

[0070] In the specific implementation manner, a design method for an underwater shaking table test model of a large-diameter group pile foundation in deep sea specifically includes the following steps:

[0071] The underwater shaking table test needs to satisfy both the solid similarity criterion and the fluid similarity criterion. In the test, the density of the water body cannot be changed. To ensure that the inertial force generated by the self-movement of the large-diameter group pile foundation model structure under the action of the shaking table and the hydrodynamic force of the fluid satisfy the similarity criterion, the design of the group pile foundation model is carried out:

[0072] Assume that the outer diameter of the pile foundation of the prototype group pile foundation is R0, the inner diameter is r0, the length of the pile foundation is L0, and the density of the concrete is ρ0; the contour dimensions of the bearing platform are a0×b0.

[0073] (1) Determination of the test scale ratio: According to the actual water depth h0 and the test water depth h1, the geometric scale ratio can be determined

[0074] (2) Determination of the similarity ratio: The water body used in the test is the same as that of the actual prototype structure; at the same time, the prototype structure and the model structure are in the same gravitational field, so there are: the similarity ratio of gravitational acceleration S g = 1, and the similarity ratio of acceleration S a = 1.

[0075] Assume that there is an ideal material whose density is the same as that of the prototype concrete (i.e., the similarity ratio of density S ρ = 1), and it satisfies the similarity ratio of elastic modulus Then the similarity criteria for the underwater shaking table test all meet the requirements. That is:

[0076] ① Solid similarity criterion:

[0077]

[0078] ② Fruder similarity criterion:

[0079]

[0080] ③ Euler similarity criterion:

[0081]

[0082] Among them: S P is the similarity ratio of hydrodynamic pressure; S v is the similarity ratio of velocity.

[0083] According to the similarity relationship, the dimensions of the ideal material model after scaling: the outer diameter of the pile foundation inner diameter the length of the pile foundation The material density ρ1 = ρ0, and the elastic modulus

[0084] For the case where the water depth exceeds 50m, according to the current underwater vibration test conditions, it is very difficult to develop an ideal material that simultaneously satisfies the similarity ratio of elastic modulus and the similarity ratio of density S and S ρ = 1. Therefore, certain similarity techniques and design methods are required to equivalently replace the ideal material model.

[0085] (3) Equivalent substitution and design of the model pile foundation: Due to the good mechanical properties, easy processing, high bonding strength, etc. of plexiglass, it can be selected as the replacement material. The elastic modulus of plexiglass is generally 1 / 12 - 1 / 8 of the elastic modulus of concrete, and the density is about 1 / 2 of that of concrete. Assume its elastic modulus is E2 and the density is ρ2.

[0086] For large-diameter pile group foundations, the hydrodynamic pressure will be affected by the pile group effect. In order to ensure that the hydrodynamic pressure satisfies the similarity relationship, it is not advisable to change the layout form of the pile foundation and the external dimensions of the pile cap. Therefore, in order to ensure that the inertia force and hydrodynamic similarity ratio of the model structure are consistent, it is necessary to ensure that the flexural stiffness and mass distribution of the test model structure remain unchanged. Therefore, the model pile foundation and pile cap are designed separately.

[0087] Specifically, the design steps of the model pile foundation include:

[0088] 1): According to the similarity relationship, the ideal material model can be determined. Keep the outer diameter and layout form of the model pile foundation unchanged, that is, the outer diameter of the plexiglass model (test model) pile foundation By adjusting the wall thickness of the plexiglass, make its flexural stiffness E2.I2 = E1.I1, where I1 and I2 are the section moments of inertia of the ideal material model pile foundation and the plexiglass model pile foundation respectively. Based on this, the inner diameter of the test model pile foundation is calculated

[0089] 2): According to the outer diameter R2 and inner diameter r2 of the test model pile foundation, the mass of a single plexiglass pile foundation can be calculated The mass of a single pile foundation of the ideal material model The difference m between the two 1-2 = m1 - m2.

[0090] To make up for the mass difference between the two models, it is solved by the method of evenly weighing from bottom to top inside the plexiglass tube. Divide the weighing into x parts according to the height of the model pile foundation, and the mass of each part of the weighing is

[0091] The weighing can be composed of steel blocks + steel sand, and the height of a single steel block should not exceed 10 cm. According to the weighing mass Δm 1-2 size, the steel block can be designed as a hollow or solid cylinder, such as Figure 2 shown. The weighing block is placed in the middle, and there should be a gap between the outer diameter of the cylinder and the inner diameter of the plexiglass tube. It is recommended that the gap be 0.4 - 1.0 cm, which mainly depends on the size of the hydrodynamic pressure gauge used. By adjusting the outer diameter d8 and inner diameter d9, to meet the required total weighing mass requirement; the steel sand is used as part of the weighing and is also used to fill the gap between the weighing block and the plexiglass tube tightly.

[0092] (4) Design of the model pile cap: Since the pile cap is a large-sized solid concrete structure with large stiffness, it can be regarded as a rigid body with deformation much smaller than displacement. Therefore, the model pile cap mainly ensures its shape and mass. Therefore, a steel pile cap that is easy to process can be used. At this time, the steel pile cap can still be regarded as a rigid body.

[0093] The size and shape of the test model pile cap are determined with reference to the ideal material model, and the quality is mainly adjusted and ensured by uniformly reserving holes.

[0094] Through the equivalent substitution of the pile foundation stiffness and the equivalent substitution of the masses of the pile foundation and the pile cap, the test model has the same acceleration, displacement, and strain as the ideal material model, and can replace the ideal material model for underwater shaking table tests.

[0095] (5) Installation of hydrodynamic pressure gauges: A large number of hydrodynamic pressure gauges need to be installed on the model pile foundation and pile cap for the measurement of hydrodynamic pressure in the group pile foundation model. Currently, relatively few underwater shaking table tests on group pile foundations have been carried out. In previous tests, the hydrodynamic pressure gauges were usually installed on the surface of the model structure, which would expose a large number of hydrodynamic pressure gauges, installation fixtures, and wires on the surface of the test model structure and in the flow field. This will not only bring large measurement errors but also greatly expand the influence of hydrodynamic pressure.

[0096] To reduce the interference of the hydrodynamic pressure gauges and wires on the flow field around the components of the group pile foundation model, small installation holes (with a diameter of about 1 cm) are reserved in advance during the fabrication of the pile foundation and the pile cap. The hydrodynamic pressure gauges are embedded in the reserved holes, and the wires are led out from inside the pile foundation and the reserved holes in the pile cap, emerging from the water surface at the top of the test model components, and connected to the suspension cables or auxiliary devices suspended in the air. Then, they are led to the shore of the test pool and connected to the acquisition system, as Figure 1 shown.

[0097] The small gaps between the hydrodynamic pressure gauges and the pipe wall or the pile cap are fixed and waterproofed with sealant. This installation method does not require additional fixtures, and the hydrodynamic pressure gauges and a large number of wires basically do not have an adverse impact on the flow field.

[0098] (6) Effective connection of the shaking table, pile foundation, and pile cap:

[0099] ① Fabricate a steel plate with a thickness of d3 as a transition plate. The bottom of the test model is connected to the transition plate, and the transition plate is anchored to the shaking table surface through six anchor bolts.

[0100] ② The bottom of the pile foundation can uniformly extend into the steel transition plate to a depth of d4, as Figure 3 shown. The remaining steel plate thickness (d3 - d4) is mainly used to bear the weight of the internal counterweight of the pile foundation and prevent the outflow of steel sand, etc. The small gap between the outer side of the bottom of the pile foundation and the transition plate is d5. The contact surface between the bottom surface of the pile foundation and the transition plate, and the small gaps between the side surface of the bottom of the pile foundation and the transition plate are all firmly pasted with epoxy resin glue.

[0101] ③ To ensure the quality of the pile cap and facilitate the rigid connection between the bottom of the pile cap and the top of the plexiglass tube, uniformly hollow out the corresponding positions above the steel pile cap and the pile foundation, so that the tops of all pile foundations can extend into the pile cap by a certain length L3, as Figure 4As shown in the figure. The diameter of the opening within the upper height L4 of the bearing platform is d6, and the diameter d6 should be less than the inner diameter of the pile foundation (2r2) so that the bearing platform can naturally rest on the top of the pile foundation. Among them, the heights L3, L4, and d6 can be adjusted as needed to meet the quality control requirements of the bearing platform.

[0102] Since too large a gap reserved between the opening of the bearing platform and the pile foundation is not conducive to firm connection, and too small a reserved gap will cause difficulties in assembling between the pile foundation and the bearing platform, a gap d7 should be left between the outer side of the top of the pile foundation and the reserved hole of the bearing platform. The tiny gaps between the contact surface of the top of the pile foundation and the bearing platform, and between the side surface of the top of the pile foundation and the bearing platform are firmly bonded with structural adhesive. The connection between the group piles and the bearing platform can be regarded as a fixed boundary condition. Among them, according to the production experience of the group pile model, L3≥3cm, d3≈0.4cm, d6≈0.4cm are set.

[0103] In the specific implementation manner, an application example of a design method for an underwater shaking table test model of a large-diameter group pile foundation in deep sea. The water depth at the location of the main tower foundation of the Jihoumen Road-Rail Bridge is 60m. For the first time at home and abroad, 18 super-large-diameter bored piles with a diameter of 6.3m are used. After completion, this group pile foundation will become the largest-diameter deep-water bridge bored pile foundation in the world. The bearing platform adopts a round-ended bearing platform with contour dimensions of 68m×46.4m×10m. The height from the seabed surface of the pile foundation to the bottom of the bearing platform is 54m, and the water depth of the bearing platform at normal water level is 6.0m. According to the actual water depth of 60m and the test water depth of 1m, the test geometric scale ratio is 1:60.

[0104] (1) Group pile design

[0105] The dynamic elastic modulus of the plexiglass used to make the pile foundation components in this embodiment is 4.01Gpa, and the density is 1198.96kg / m 3 . According to the geometric scale ratio of 1 / 60, the elastic modulus of the ideal material is 558.3MPa, and the density is 2550kg / m 3 , and the outer diameter of the pile foundation is 105mm. Under the condition of keeping the overall layout form of 18 pile foundations, the outer diameter of a single pile foundation, and the overall stiffness of the group piles unchanged, the ideal material solid pile foundation is equivalently replaced. It is determined that 18 pile foundations all adopt hollow plexiglass tubes: outer diameter 105mm, inner diameter 101mm, wall thickness 2mm. The stiffness difference between the two model pile foundations is about 2.3%, which is basically within a reasonable range, indicating that it is more appropriate to use the above-mentioned hollow plexiglass single pile to replace the ideal material single pile.

[0106] The ideal material for the pile foundation has an effective height range with a mass of 19.9 kg, and the acrylic pile foundation has a mass of 0.7 kg. To satisfy the similarity relationship of the material mass density, weights are evenly added from bottom to top inside each acrylic tube to make up for the mass density difference. To avoid the influence of the weighting material on the pile foundation stiffness and reduce the impact of shaking on the test results, and at the same time facilitate the passing of the wires of 20 hydrodynamic pressure gauges and others through the inside of the pile group - cap model components, 9 hollow cylindrical steel blocks with a diameter of 7 cm and a height of 10 cm are placed in the center of each pile foundation for weighting. The space between the steel blocks and the pile foundation wall is filled with prepared steel sand particles for compaction. The filling weight inside each acrylic tube is 19.2 kg, and the total weight of the 18 pile foundations is approximately 345.6 kg. Through internal mass weighting, the replaced acrylic hollow single pile and the ideal material single pile have the same equivalent mass.

[0107] (2) Design of the round - ended cap

[0108] Since the cap is a large - sized reinforced concrete structure, it can be regarded as a rigid body with deformation much smaller than displacement. Therefore, the simulation of the cap mainly ensures its external dimensions and mass. The contour dimensions of the round - ended cap are 113.3×77.3×16.7 cm. A steel cap that is easy to process is used, and the steel cap can still be regarded as a rigid body. To ensure the mass of the cap and facilitate the rigid connection between the bottom of the cap and the tops of the 18 acrylic tubes, 18 uniform cut - outs are made above the corresponding positions of the steel cap and the 18 pile foundations, so that the tops of the 18 pile foundations can all extend into the inside of the cap by a certain length. Since too large a gap reserved between the cap openings and the pile foundations is not conducive to firm connection, and too small a reserved gap will cause difficulties in assembling the 18 pile foundations and the cap. Before the formal assembly, a trial assembly of the complex pile group - cap foundation model was carried out to clarify the appropriate structural adhesive and the reasonable reserved gap. Finally, it was determined that the upper reserved hole diameter at the corresponding position of the round - ended cap is 8 cm and the height is 10.67 cm, and the lower reserved hole diameter is 11.3 cm and the height is 6 cm, so that the tops of the 18 acrylic tubes can uniformly extend into the upper cap by 6 cm. The tiny gaps between the contact surface of the pile foundation top and the cap and between the side surface of the pile foundation top and the cap are firmly pasted with structural adhesive. The connection between the 18 pile groups and the cap can be regarded as a fixed boundary condition.

[0109] The connection method of the 18-pile group with the lower steel adapter plate is similar to the fixed connection between the top of the pile group and the bearing platform. The diameters of the 18 reserved holes on the adapter plate are all 11.3 cm, slightly larger than the outer diameter of the pile foundation, which is 10.5 cm, and the height is 3.6 cm. The small gap between the outer side of the bottom of the pile foundation and the adapter plate is about 0.4 cm. The bottoms of the 18 pile foundations can uniformly extend into the steel adapter plate by 3.6 cm, and the remaining 0.4 cm steel plate thickness is mainly used to bear the internal counterweight of the pile foundation and prevent the outflow of steel sand, etc. The contact surface between the bottom surface of the pile foundation and the adapter plate, and the small gaps between the side surface of the bottom of the pile foundation and the adapter plate are all firmly connected with structural adhesive. The steel adapter plate is anchored to the shaking table with 6 high-strength bolts. The connections between the pile foundation, the adapter plate and the shaking table can also be regarded as fixed boundary conditions.

[0110] (3) After the underwater shaking table test, the connection conditions between the 18 pile foundations and the upper bearing platform and the lower adapter plate were checked again. All connections were firm and there was no loosening phenomenon, which proved that the connections between the shaking table, the pile foundation and the bearing platform were reliable.

[0111] (4) According to the numerical simulation calculation, the theoretical first-order frequency and second-order frequency of the prototype large-diameter pile group foundation are 1.0082 Hz and 1.0242 Hz respectively. According to the similarity relationship of the underwater shaking table test, the frequency of the test model and the frequency of the prototype structure should satisfy the similarity ratio where is the test scale ratio. Therefore, the target values of the theoretical first-order frequency and second-order frequency of the model are 7.8136 Hz and 7.9376 Hz respectively.

[0112] If the above design method is not adopted and the model is designed according to the traditional method, the test model uses the same concrete material as the prototype structure. After scaling, the theoretical calculated values of the first-order frequency and second-order frequency of the test model are 52.568 Hz and 53.041 Hz respectively. Comparing with the target values of the first-order frequency and second-order frequency, the deviations reach 572.8% and 568.2%, and the test error is significantly larger.

[0113] Using the above design method, the first-order frequency and second-order frequency of the test model were identified by white noise sweep frequency, which are 8.7112 Hz and 8.9960 Hz respectively. Comparing with the target values of the first-order frequency and second-order frequency, 7.8136 Hz and 7.9376 Hz, the deviations are 11.5% and 13.3% respectively. Considering the complexity of the large-diameter pile group foundation, the model error is basically within the acceptable range and is significantly better than the traditional model designed by the traditional method.

[0114] The various embodiments in this specification are described in a progressive manner. Each embodiment focuses on the differences from other embodiments. For the same and similar parts between the various embodiments, reference can be made to each other. For the device disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and reference can be made to the description in the method part for related parts.

[0115] The foregoing description of the disclosed embodiments enables those skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for designing a model for underwater shaking table test of deep-sea large-diameter pile group foundation, characterized in that: include: Determine the test scale ratio and similarity ratio based on the prototype pile group foundation and the test environment; The ideal material model after scaling is obtained according to the test scaling ratio and similarity ratio; Equivalent replacement of the pile foundation and cap of the test model according to the ideal material model; Installation holes are reserved on the pile foundation and the pedestal of the test model, and the dynamic water pressure gauge is embedded in the reserved installation holes. The gauge is led out from the inside of the pile foundation of the test model or the reserved hole of the pedestal to the top of the test model through a wire and then connected to the acquisition system for data collection.

2. The method for designing a model of an underwater shaking table test of a deep-sea large-diameter pile group foundation according to claim 1 is characterized in that: The method of determining the test scale ratio includes: determining the geometric scale ratio according to the actual water depth h0 and the test water depth h1.

3. The method for designing a model of an underwater shaking table test of a deep-sea large-diameter pile group foundation according to claim 1 is characterized in that: The steps for determining the similarity ratio are: The water used in the test is the same as that of the prototype structure. The prototype structure and the model structure are in the same gravity field, and the gravitational acceleration similarity ratio S g =1, acceleration similarity ratio S a =1; Assume that there is an ideal material whose density is the same as that of the prototype structural concrete, and the density similarity ratio S ρ =1, elastic modulus similarity ratio Then the similarity criterion of underwater shaking table test is met: Solid similarity criteria: Fruder similarity criterion: Euler similarity criterion: Among them, S P is the hydrodynamic pressure similarity ratio, S v is the speed similarity ratio.

4. The method for designing a model of an underwater shaking table test of a deep-sea large-diameter pile group foundation according to claim 1 is characterized in that: The ideal material model after scaling obtained according to the test scaling ratio and similarity ratio includes: According to the similarity relationship, the size of the ideal material model after scaling is: the outer diameter of the pile foundation inner diameter Pile length Material density ρ1=ρ0, elastic modulus Among them, R0, r0, L0, ρ0, and E0 are the outer diameter, inner diameter, length, density, and elastic modulus of the prototype structure pile foundation, respectively.

5. The method for designing a model of an underwater shaking table test of a deep-sea large-diameter pile group foundation according to claim 1 is characterized in that: The equivalent replacement of the test model pile foundation and the cap according to the ideal material model includes: S1: According to the similarity relationship, determine the ideal material model, keep the outer diameter and layout of the model pile foundation unchanged, that is, the outer diameter of the test model pile foundation S2: Determine the material of the test model pile foundation, and obtain its elastic modulus as E2 and density as ρ2. By adjusting the pile foundation wall thickness, the bending stiffness of the test model pile foundation is made E2.I2=E1.I1, where I1 and I2 are the moments of inertia of the pile foundation sections of the ideal material model and the test model, respectively, and E1 and E2 are the elastic moduli of the ideal material and the test model material, respectively; S3: Based on the equivalent bending stiffness of the model pile foundation, calculate the inner diameter of the test model pile foundation S4: Calculate the mass of a single test model pile according to the outer diameter R2 and inner diameter r2 of the test model pile foundation S5: Single pile foundation quality of ideal material model The difference between the two 1-2 =m1-m2.

6. The method for designing a model for underwater shaking table test of deep-sea large-diameter pile group foundation according to claim 5 is characterized in that: The test model pile foundation material is organic glass material.

7. The method for designing a model for underwater shaking table test of deep-sea large-diameter pile group foundation according to claim 5 is characterized in that: Also includes: The mass difference between the two models is compensated by evenly balancing the pile foundation of the test model from bottom to top to obtain m 1-2 =m1-m2, divide the weight into x parts according to the height of the test model pile foundation, and the mass of each weight is 8. The method for designing a model of an underwater shaking table test of a deep-sea large-diameter pile group foundation according to claim 1 is characterized in that: Equivalent alternatives to the cap include: The cap can be regarded as a rigid body, the size and shape of the cap are determined with reference to the ideal material model, and the mass is adjusted by evenly reserving holes on the cap; Through equivalent substitution of pile foundation stiffness and equivalent substitution of pile foundation and cap mass, the test model and the ideal material model have the same acceleration, displacement and strain.

9. The method for designing a model of an underwater shaking table test of a deep-sea large-diameter pile group foundation according to claim 1, characterized in that: The tiny gap between the hydrodynamic pressure gauge and the pile foundation wall or the cap is sealed by using sealant.

10. The method for designing a model of an underwater shaking table test of a deep-sea large-diameter pile group foundation according to claim 1, characterized in that: The test model comprises: a vibration table, a test model pile foundation, an adapter plate and a cap; the bottom of the test model pile foundation is fixedly connected to the adapter plate, the adapter plate is anchored on the vibration table surface by six anchor bolts, and the top of the test model pile foundation is fixedly connected to the cap.

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