Single pile foundation p-y curve construction method considering influence of three-dimensional sliding mechanism

Abstract

The invention provides a single pile foundation p-y curve construction method considering the influence of a three-dimensional sliding mechanism. The single pile foundation p-y curve construction method comprises the steps that all geometric dimension parameters of a single pile foundation are determined; measuring the distribution parameter of the undrained shear strength of the seabed foundation soil body along with the depth; measuring the roughness of the interface between the single pile foundation and the soil body; taking a foundation soil body to carry out a soil unit single shear test, and measuring the maximum shear stiffness and shear stress-strain curve of the soil body; fitting a stress-strain curve measured by the single shear test by adopting a high-order polynomial to obtain a fitting shape factor; calculating the maximum influence depth of the three-dimensional sliding mechanism; and based on the obtained fitting shape factor and the three-dimensional sliding mechanism influence coefficient, a single pile foundation p-y curve within the maximum depth range of the three-dimensional sliding mechanism influence is calculated. According to the method, the influence of a three-dimensional sliding mechanism caused by the free mud surface on the p-y curve is considered, the technical defects of a traditional method are overcome, and the method has important engineering practical value for design and engineering quantity optimization of a single-pile foundation.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of ocean engineering, and in particular to a method for constructing a p-y curve of a single pile foundation considering the influence of a three-dimensional sliding mechanism. BACKGROUND

[0002] Under the global energy transformation and carbon neutralization target, offshore wind power is becoming a strategic highland of renewable energy development. Compared with onshore wind power, offshore wind energy resources are more abundant and stable, and the single machine capacity is larger (the current mainstream model is up to 15MW+, and the model that has been put into operation is more than 20MW). In addition, it is close to the coastal power load center, effectively alleviating the pressure of power transmission. As the mainstream support structure of global offshore wind power (accounting for more than 80%), the single pile foundation becomes the preferred solution for offshore wind power projects due to its simple structure, low cost (cost advantage is significant when the water depth is less than 30 meters), short construction period and other characteristics. Its typical structure is a hollow steel pipe pile with a diameter of 6-10 meters, which penetrates the seabed sediment layer through hydraulic hammering to form a fixed support.

[0003] Horizontal bearing capacity is a core indicator of single pile foundation resistance to transverse loads such as wind and waves, and directly determines the wind turbine's ability to resist overturning and service safety. Currently, the calculation of single pile foundation horizontal bearing response mainly uses the p-y curve method, which replaces the linear elastic soil spring along the depth distribution in the elastic foundation reaction method with a nonlinear soil spring, enabling it to reflect the nonlinear characteristics of the soil around the pile under load. The mechanical properties of soil springs at different depths are described by nonlinear p-y curves, where p is the horizontal soil resistance of the single pile foundation (kN / m), and y is the horizontal displacement of the single pile foundation (m). Therefore, selecting the appropriate and accurate p-y curve is the key to single pile foundation design.

[0004] Currently, the p-y curve recommended by the API specification is widely used in engineering, but this p-y curve only considers the deep pile-soil interaction mechanism and does not consider the influence of the three-dimensional sliding mechanism caused by the free mud surface at the pile head. A large number of three-dimensional finite element analysis studies have shown that different pile-soil interaction mechanisms directly affect the p-y curve, and ignoring the influence of the three-dimensional sliding mechanism of pile-soil will significantly underestimate the stiffness and strength of the p-y curve, directly affecting the reliability and accuracy of the prediction of the bearing capacity of the single pile foundation. Currently, there is still a lack of p-y curve models and construction methods that consider the influence of the three-dimensional sliding mechanism of pile-soil, which poses a challenge to the fine design and calculation of the bearing capacity of single pile foundations. SUMMARY

[0005] The purpose of the present application is to fill the gap in the prior art and provide a method for constructing a p-y curve of a single pile foundation considering the influence of a three-dimensional sliding mechanism, which serves the optimization design of offshore wind power engineering foundation and provides more accurate p-y curve input for the bearing capacity design of large-diameter single pile foundations of offshore wind turbines.

[0006] The purpose of the present application is achieved by the following technical solutions:

[0007] A single pile foundation p-y curve construction method considering the influence of three-dimensional sliding mechanism, comprising the following steps:

[0008] S1, determine the geometric size parameters of the single pile foundation: single pile outer diameter D, single pile soil depth L;

[0009] S2, measure the undrained shear strength s of the seabed soil body u The distribution parameters with depth include the undrained shear strength s of the soil body at the mud surface um , the undrained shear strength growth gradient k with depth; at this time, the undrained shear strength distribution of the seabed soil body is represented as: s u =s um +kz, wherein z is the depth of the soil body;

[0010] S3, measure the interface roughness α of the single pile foundation and the soil body;

[0011] S4, take soil unit simple shear test of the soil body, measure the maximum shear stiffness G max of the soil body, and measure the shear stress-strain curve τ-ε curve at the same time; adopt high-order polynomial to fit the stress-strain curve τ-ε curve measured by the simple shear test, to obtain the fitting shape factor ζ;

[0012] S5, calculate the maximum depth Z max of the influence of three-dimensional sliding mechanism;

[0013] S6, calculate the three-dimensional sliding mechanism influence coefficient χ of the single pile foundation p-y curve;

[0014] S7, based on the obtained fitting shape factor ζ and the three-dimensional sliding mechanism influence coefficient χ, calculate the single pile foundation p-y curve within the maximum depth Z max of the influence of three-dimensional sliding mechanism;

[0015] Wherein, the steps S1, S2, S3, S4 are not in order.

[0016] While adopting the above technical solutions, the present application can also adopt or combine the following technical solutions:

[0017] As a preferred technical solution of the present application, the following high-order polynomial is adopted to fit the shear stress-strain curve τ-ε curve measured by the simple shear test, to obtain the fitting shape factor ζ:

[0018] f(τ)=τ 4 -2G max (ζ+ε)τ 3 +G max 2 (ζ+ε)2 τ 2 +4s u 2 G max ζτ-4s u 2 G max 2 ζε

[0019] In the formula, τ is a shear stress; ε is a shear strain; G max is the maximum shear stiffness of the soil body; s u is the undrained shear strength of the foundation soil body.

[0020] As a preferred technical solution of the present application, the maximum depth Z max is calculated according to the following formula:

[0021]

[0022] In the formula, D is the outer diameter of the single pile; L is the soil penetration depth of the single pile; α is the interface roughness between the single pile foundation and the soil body; k is the gradient of the undrained shear strength of the seabed foundation soil body with depth.

[0023] As a preferred technical solution of the present application, the three-dimensional sliding mechanism influence coefficient χ of the single pile foundation p-y curve is calculated according to the following formula:

[0024]

[0025] In the formula, z is the depth of the soil body; D is the outer diameter of the single pile.

[0026] As a preferred technical solution of the present application, based on the obtained fitting shape factor ζ and the three-dimensional sliding mechanism influence coefficient χ, the single pile foundation p-y curve within the maximum depth Z max of the three-dimensional sliding mechanism influence is calculated according to the following formula:

[0027]

[0028] In the formula, p is the horizontal soil resistance of the single pile foundation; y is the horizontal displacement of the single pile foundation; s u is the undrained shear strength of the seabed soil body; D is the outer diameter of the single pile; α is the interface roughness between the single pile foundation and the soil body; k is the gradient of the undrained shear strength of the seabed foundation soil body with depth; ζ is the stress-strain curve fitting shape factor; χ is the three-dimensional sliding mechanism influence coefficient of the single pile foundation p-y curve.

[0029] The present application has the following beneficial effects:

[0030] 1. The present application considers the influence of the three-dimensional sliding mechanism caused by the free mud surface on the p-y curve, which makes up for the technical defects of the traditional method of significantly underestimating the stiffness and strength of the p-y curve in the depth range of the three-dimensional sliding mechanism;

[0031] 2. The p-y curve construction method for single pile foundation considering the influence of three-dimensional sliding mechanism provided by the present application does not need to rely on complex numerical analysis means, but only uses limited basic measurement or structural parameters and formulas to calculate the results, which is efficient and fast, overcomes the defects of traditional numerical analysis such as complexity and long time consumption, and has important engineering practical value;

[0032] 3. The p-y curve for single pile foundation considering the influence of three-dimensional sliding mechanism obtained by the present application can provide more accurate p-y curve input for the bearing capacity design of offshore wind turbine single pile foundation, and improve the design precision and reliability of single pile foundation. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 It is a single pile foundation and seabed soil body undrained shear strength distribution schematic diagram of the present application;

[0034] Figure 2 It is a shear stress-strain curve τ-ε curve fitting effect diagram measured by the single shear test of the present application;

[0035] Figure 3 It is a three-dimensional sliding mechanism influence coefficient χ of the p-y curve of the single pile foundation of the present application with depth distribution graph.

[0036] Figure 4 It is a comparison diagram of the p-y curve calculated by the present application and the p-y curve calculated by three-dimensional finite element calculation and traditional method at a typical depth. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical scheme and advantages of the present application more clear and explicit, the present application is further described in detail below combined with examples and drawings, the schematic embodiment of the present application and its description are only used to explain the present application, and are not as a limitation on the present application.

[0038] Example: The diameter of the single pile foundation of a certain offshore wind power project is 10m, and the soil depth is 50m; the seabed soil body is soft clay, the undrained shear strength of the soil body at the mud surface is 5kPa, and the undrained shear strength increases by 1.5kPa / m with depth; the interface roughness of the single pile foundation and the soil body is 1. The p-y curve of the single pile foundation considering the influence of three-dimensional sliding mechanism is constructed.

[0039] Referring to the drawings, the p-y curve construction method for single pile foundation considering the influence of three-dimensional sliding mechanism provided by the present application has the following implementation steps:

[0040] S1, determine the geometric size parameters of the single pile foundation: single pile outer diameter D = 10 m, single pile soil depth L = 50 m, as shown in Figure 1 ;

[0041] S2, measure the undrained shear strength s u of the seabed soil body, the distribution parameters with depth, including the undrained shear strength s um of the soil body at the mud surface s u = 5 kPa, the undrained shear strength growth gradient k with depth k = 1.5 kPa / m; at this time, the undrained shear strength distribution of the seabed soil body is s um = s max +kz = 5 + 1.5z, where z is the depth of the soil body, as shown in Figure 1 ;

[0042] S3, measure the interface roughness a of the single pile foundation and the soil body a = 1;

[0043] S4, take the soil unit single shear test of the foundation soil body (in this example, take the soil body at z = 10 m depth), measure the maximum shear stiffness G 4 of the soil body G max = 10000 kPa, and measure the shear stress-strain curve τ-ε curve, as shown in Figure 2 ;

[0044] S5, use the following high-order polynomial to fit the shear stress-strain curve τ-ε curve measured by the single shear test to obtain the fitting shape factor ζ:

[0045] f(τ) = τ 3 - 2G max (ζ + ε)τ 2 + G 2 (ζ + ε) 2 τ u + 4s 2 G max ζτ - 4s u 2 G max 2 ζε

[0046] In the formula, τ is the shear stress; ε is the shear strain; G max is the maximum shear stiffness G max of the soil body; s u is the undrained shear strength of the foundation soil body; in this example, the depth of the soil body z = 10 m, G max = 10000 kPa, s u = s um +kz = 5 + 1.5z = 5 + 1.5*10 = 20 kPa;

[0047] According to the optimal fitting, the fitting shape factor ζ = 0.15 is obtained, and the fitting effect is as shown in Figure 2 ;

[0048] S6, the maximum depth Z of three-dimensional sliding mechanism is calculated according to the following formula max :

[0049]

[0050] In the formula, D is the outer diameter of the single pile; L is the soil penetration depth of the single pile; α is the interface roughness of the single pile foundation and the soil; k is the gradient of the undrained shear strength of the seabed foundation soil with depth.

[0051] The calculated Z max = 13.8m, that is, the p-y curve of the pile soil in the depth range of 0-13.8m will be affected by the three-dimensional sliding mechanism;

[0052] S7, the three-dimensional sliding mechanism influence coefficient χ of the p-y curve of the single pile foundation is calculated according to the following formula:

[0053]

[0054] In the formula, z is the depth of the soil; D is the outer diameter of the single pile.

[0055] The calculated three-dimensional sliding mechanism influence coefficient χ of the p-y curve of the single pile foundation in the depth range of Z max = 13.8m is as shown in Figure 3 ;

[0056] S8, based on the obtained fitting shape factor ζ and the three-dimensional sliding mechanism influence coefficient χ, the p-y curve of the single pile foundation in the maximum depth Z max range of the three-dimensional sliding mechanism is calculated according to the following formula:

[0057]

[0058]

[0059] In the formula, p is the horizontal soil resistance of the single pile foundation; y is the horizontal displacement of the single pile foundation; s u is the undrained shear strength of the seabed soil; D is the outer diameter of the single pile; α is the interface roughness of the single pile foundation and the soil; k is the gradient of the undrained shear strength of the seabed foundation soil with depth; ζ is the stress-strain curve fitting shape factor; χ is the three-dimensional sliding mechanism influence coefficient of the p-y curve of the single pile foundation.

[0060] The calculated p-y curve of the single pile foundation in the maximum depth Z max range of the three-dimensional sliding mechanism (i.e. in the range of 13.8m), Figure 4 shows the calculation results at a typical depth.

[0061] Figure 4 Also included are the p-y curves of single pile foundation considering the influence of three-dimensional sliding mechanism calculated by the three-dimensional finite element method and the p-y curves calculated by the traditional method (without considering the influence of three-dimensional sliding mechanism). It can be seen from the comparison that the p-y curves calculated based on the method provided by the application are in good agreement with the three-dimensional finite element calculation results, verifying the reliability and accuracy of the method provided by the application.

[0062] In addition, from Figure 4 It can also be seen that, compared with the calculation results of the application, the traditional method (without considering the influence of three-dimensional sliding mechanism) will significantly underestimate the stiffness and strength of the p-y curve, which is easy to cause the redundancy of the design of single pile foundation, increase the engineering quantity and construction cost, and is not conducive to the development of offshore wind power at a flat price. The method for constructing the p-y curve of single pile foundation considering the influence of three-dimensional sliding mechanism provided by the application can overcome the technical defects of the conventional method, provide more accurate p-y curve input for the bearing capacity design of offshore wind turbine single pile foundation, which has important engineering practical value for the design and engineering quantity optimization of single pile foundation.

[0063] The above is only an embodiment of the application and is not used to limit the application. The application can have various changes and variations for those skilled in the art. Any modification, equivalent replacement, improvement, etc. within the spirit and principle of the application shall be included in the scope of claims of the application.

Claims

1. A method for constructing the Py curve of a single pile foundation considering the influence of a three-dimensional sliding mechanism, characterized in that, The method includes the following steps: S1. Determine the geometric dimensions of the single pile foundation, including the outer diameter D of the single pile and the depth of the single pile into the soil L; S2, the measured undrained shear strength s of the seabed foundation soil. u Distribution parameters with depth, including the undrained shear strength s of the soil at the mud surface. um The gradient k of undrained shear strength with depth; the distribution of undrained shear strength of seabed soil is expressed as: s u =s um +kz, where z is the soil depth; S3. Measure the roughness α of the interface between the single pile foundation and the soil. S4. Conduct a single shear test on the foundation soil to measure the maximum shear stiffness G of the soil. max Simultaneously, the shear stress-strain curve τ-ε curve was measured; the stress-strain curve τ-ε curve measured by the single shear test was fitted with a higher-order polynomial to obtain the fitting shape factor ζ. S5. Calculate the maximum depth Z affected by the three-dimensional sliding mechanism. max ; S6. Calculate the influence coefficient χ of the three-dimensional sliding mechanism of the py curve of a single pile foundation; S7. Based on the obtained fitted shape factor ξ and the influence coefficient χ of the three-dimensional sliding mechanism, calculate the depth Z where the three-dimensional sliding mechanism has the maximum influence. max The py curve of a single pile foundation within the specified range; Steps S1, S2, S3, and S4 are not in any particular order.

2. The method for constructing the py curve of a single pile foundation considering the influence of a three-dimensional sliding mechanism according to claim 1, characterized in that, The 3D sliding mechanism has the greatest influence on the depth Z. max Calculate using the following formula: In the formula, D is the outer diameter of a single pile; L is the depth of a single pile into the soil; α is the roughness of the interface between the single pile foundation and the soil; and k is the gradient of the undrained shear strength of the seabed foundation soil with increasing depth.

3. The method for constructing the py curve of a single pile foundation considering the influence of a three-dimensional sliding mechanism according to claim 1, characterized in that, The influence coefficient χ of the three-dimensional sliding mechanism of the py curve of a single pile foundation is calculated by the following formula: In the formula, z is the soil depth; D is the outer diameter of a single pile.

4. The method for constructing the py curve of a single pile foundation considering the influence of a three-dimensional sliding mechanism according to claim 1, characterized in that, Based on the obtained shape factor ζ and the influence coefficient of the three-dimensional sliding mechanism χ, the maximum influence depth Z of the three-dimensional sliding mechanism is calculated using the following formula. max Py curve of single pile foundation within the range: In the formula, p is the horizontal soil resistance of a single pile foundation; y is the horizontal displacement of a single pile foundation; s u denoted as undrained shear strength of seabed soil; D is the outer diameter of a single pile; α is the roughness of the interface between the single pile foundation and the soil; k is the gradient of undrained shear strength of seabed foundation soil with depth; ζ is the shape factor for fitting the stress-strain curve. χ is the influence coefficient of the three-dimensional sliding mechanism of the py curve of a single pile foundation.

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