Simplified analysis method for pile-soil interaction of large-diameter single pile foundation

Abstract

The invention discloses a simplified analysis method for pile-soil interaction of a large-diameter single-pile foundation, which belongs to the technical field of offshore wind power and comprises the following steps: S1, acquiring soil mechanics of a seabed foundation in a target area and pile body parameters of the large-diameter single-pile foundation; s2, calculating a soil stress-strain curve at the reference depth; s3, the rigidity type of the large-diameter single-pile foundation is judged according to the pile-soil relative rigidity; s4, for the rigid or semi-rigid single pile foundation, determining the position of a base rotation point and the corresponding effective action length of the base; s5, on the basis of the stress-strain curve and the soil body strength parameters at the rotating points, calculating the ultimate resistance bending moment at the rotating points; s6, performing scaling processing on the stress-strain curve, and constructing a substrate rotation nonlinear spring model at a rotation point; and S7, coupling the base rotation nonlinear spring model with the pile side soil counter-force model to realize the prediction of the horizontal bearing capacity of the large-diameter single pile foundation. The prediction precision of the horizontal bearing capacity of the single pile can be improved.

Description

A Simplified Analysis Method for Pile-Soil Interaction in Large-Diameter Single-Pile Foundations Technical Field

[0001] This invention relates to the field of offshore wind power technology, and in particular to a simplified analysis method for pile-soil interaction in large-diameter monopile foundations. Background Technology

[0002] In the field of marine engineering, large-diameter monopile foundations have become the mainstream foundation type for structures such as nearshore wind turbines and offshore photovoltaic supports in water depths of up to 40 meters due to their significant advantages, including simple structural form, reduced steel consumption, and convenient construction and installation. With the acceleration of the global energy transition and the continuous increase in wind turbine power, wind turbine structures are showing a trend towards larger and taller structures. This has significantly increased the horizontal overturning force and overturning moment borne by monopile foundations, and the diameter of monopile foundations has gradually increased from the early 4 meters to 10 meters or even larger. Against this backdrop, accurately predicting the horizontal bearing capacity of large-diameter monopile foundations has become a core technical requirement for ensuring the in-situ stability of structures under complex marine environmental loads.

[0003] Currently, the Py-curve method recommended by the API standard is widely used in the engineering field for calculating the horizontal bearing capacity of single piles. This method establishes a nonlinear relationship between the horizontal reaction force of the soil along the pile and the horizontal displacement of the pile, and combines Winkler's foundation beam theory to solve for the stress and deformation of the pile. However, in sandy soil foundations, the traditional Py-curve method has significant drawbacks: on the one hand, it cannot accurately characterize the initial foundation reaction modulus and the horizontal ultimate soil reaction force corresponding to large-diameter single piles, resulting in generally higher calculation results; on the other hand, this method ignores the contribution of the rotational resistance generated by the soil when the foundation of a large-diameter single pile rotates to the horizontal bearing capacity. This omission is particularly evident in rigid piles and semi-rigid piles with large diameters and small length-to-diameter ratios, further reducing the accuracy of horizontal bearing capacity prediction.

[0004] Although many studies have modified the standard Py curve method, the accuracy of the calculation results still has room for improvement because the contribution of the rotational resistance of large-diameter single pile foundation to the horizontal bearing capacity is ignored. Summary of the Invention

[0005] To address the issue of overestimating the calculated results using the traditional API specification Py curve method, this invention provides a simplified analysis method for pile-soil interaction in large-diameter monopile foundations. By combining this method with an advanced modified Py curve, the accuracy of predicting the horizontal bearing capacity of monopile foundations can be further improved.

[0006] The technical solution adopted in this invention, a simplified analysis method for pile-soil interaction in large-diameter single-pile foundations, is as follows:

[0007] A simplified analysis method for pile-soil interaction in large-diameter monopile foundations includes the following steps.

[0008] S1. Obtain the soil mechanics parameters of the seabed foundation in the target area and the pile parameters of the large-diameter single pile foundation;

[0009] S2. Calculate the soil stress-strain curve at the reference depth based on soil mechanical parameters;

[0010] S3. Determine the rigidity type of a large-diameter single pile foundation based on the pile-soil relative stiffness;

[0011] S4. For rigid or semi-rigid single pile foundations, determine the location of the base rotation point and the corresponding effective length of the base.

[0012] S5. Based on the stress-strain curve and the soil strength parameters at the rotation point, calculate the ultimate resistance bending moment at the rotation point;

[0013] S6. By scaling the stress-strain curve, a nonlinear spring model of the base rotation at the rotation point is constructed.

[0014] S7. Couple the base rotational nonlinear spring model with the pile side soil reaction model to realize the prediction of the horizontal bearing capacity of large-diameter single pile foundation.

[0015] A further improvement to the technical solution of this invention lies in that: the soil mechanical parameters include the internal friction angle φ of the sand and the relative density. void ratio e, effective unit weight of soil Soil elastic modulus linear rate of change with depth With the maximum shear modulus of the soil The relevant model parameters A, m, and n are related to the maximum shear stress of the soil. The relevant model parameters are B, u, and v.

[0016] A further improvement to the technical solution of this invention lies in that: the pile parameters include the single pile outer diameter D, wall thickness t, and steel elastic modulus. The depth of the pile into the mud (L), the length-to-diameter ratio of a single pile (L / D), and the bending stiffness of the pile section. .

[0017] A further improvement to the technical solution of the present invention lies in: the reference depth in step S2. The soil stress-strain curve is calculated based on 2 / 3 of the pile penetration depth L, including:

[0018]

[0019]

[0020]

[0021]

[0022] Where τ is the soil shear stress; γ is the soil strain; Secant shear modulus of sand; This is the maximum shear modulus of the soil. for The corresponding shear strain threshold; This represents the maximum shear stress in the soil. The average effective stress; For reference stress, ; For reference depth, take ; The effective unit weight of sandy soil; The horizontal earth pressure coefficient is calculated using the following expression: φ is the internal friction angle of the sand.

[0023] A further improvement to the technical solution of the present invention lies in: the relative stiffness of the pile-soil relationship in step S3. The calculation is based on the ratio of the pile's bending stiffness to the soil stiffness. The criterion for determining the rigidity type is:

[0024]

[0025] when When it is a rigid pile, At that time, it was a semi-rigid pile. For flexible piles, the nonlinear spring model of base rotation is only applicable to semi-rigid piles and rigid piles.

[0026] A further improvement to the technical solution of the present invention is that the calculation expression for the effective working length of the substrate in step S4 is:

[0027]

[0028] Where L is the depth of the pile into the mud, D is the outer diameter of a single pile, and the distance from the rotation point to the bottom of the pile is equal to the effective working length H of the foundation.

[0029] A further improvement to the technical solution of the present invention lies in: the ultimate resistance bending moment at the rotation point in step S5. The expression is:

[0030]

[0031] in, This represents the maximum shear stress at the point of rotation; due to the maximum shear stress in the soil... It increases approximately linearly with increasing depth, therefore k is The rate of change is approximately linear with depth.

[0032] A further improvement of the technical solution of the present invention is that: the scaling process in step S6 adopts a rotation angle scaling factor. and moment scaling factor , The value range is 0.05-0.06. The value range is 1.3-1.4, and the expression for the base rotational nonlinear spring model is:

[0033]

[0034] in, The base rotational bending moment; The base rotation angle.

[0035] A further improvement of the technical solution of the present invention is that: in step S7, the soil reaction model on the pile side is a modified py curve model, the base rotational nonlinear spring model and the modified py curve model are coupled through the Winkel foundation beam model, the Winkel foundation beam model applies the soil reaction on the pile side to the pile element in the form of a distributed spring by discretizing the pile element, and applies the base rotational nonlinear spring to the rotation point.

[0036] The technological advancements achieved by this invention due to the adoption of the above technical solutions are as follows:

[0037] This invention integrates the complex pile-soil interaction at the bottom of a large-diameter monopile foundation into a single nonlinear spring model at the rotation point. This model can be directly integrated into the classic nonlinear Winkler foundation beam model without the need to construct a complex three-dimensional finite element model. Compared to traditional finite element analysis methods, this simplifies the modeling process, reduces computational load, and improves computational efficiency.

[0038] This invention obtains the base rotational spring M by scaling the soil stress-strain relationship curve. R -θ R The stress-strain curve can fully utilize the soil strength parameters measured by geotechnical tests to directly improve the accuracy of pile-soil nonlinear stiffness prediction. Furthermore, the soil stress-strain curve can comprehensively reflect its material characteristics, significantly improving the applicability of this calculation method in sandy soils with different properties.

[0039] The invention provides the rotation point of a large-diameter single pile. This spring, unlike traditional Py springs, reflects different soil constraints, thus eliminating constraint conflicts and offering greater flexibility. For large-diameter rigid and semi-rigid piles, the nonlinear spring arrangement shown in Figure 2 can be used... The spring is used in combination with any advanced modified PY spring to further improve the accuracy of predicting the horizontal bearing capacity of a single pile. Attached Figure Description

[0040] Figure 1 is a schematic diagram of the geometric dimensions and soil strength distribution of the large-diameter single pile provided by the present invention;

[0041] Figure 2 shows the invention utilizing... Calculation principle diagram of the prediction accuracy of horizontal bearing capacity of large-diameter single pile using spring lifting;

[0042] Figure 3 shows the stress-strain curve calculated by this invention and the rotation point of the semi-rigid pile. curve. Detailed Implementation

[0043] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings. In the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily obscuring the concept of this invention.

[0044] A nearshore large-diameter monopile wind turbine foundation has a diameter of D=9 m and a wall thickness of t=96.35 mm. The elastic modulus of the selected steel is... The pile foundation has a penetration depth of L=45m. The foundation soil is normally consolidated sand with an internal friction angle of [missing information]. relative density Void ratio e=0.737, effective unit weight of soil Soil elastic modulus linear rate of change with depth With the maximum shear modulus of the soil The relevant model parameters are A=48.95 MPa, m=0.3, n=2.5, and are related to the maximum shear stress of the soil. The relevant model parameters are B=0.24 MPa, u=0.5, and v=1.76.

[0045] This embodiment provides a simplified analysis method for pile-soil interaction in large-diameter monopile foundations. The specific implementation steps are as follows:

[0046] (1) Determine the physical and mechanical parameters of the sand, including the internal friction angle. relative density Void ratio e=0.737, effective unit weight of soil Soil elastic modulus linear rate of change with depth With the maximum shear modulus of the soil The relevant model parameters are A=48.95 MPa, m=0.3, n=2.5, and are related to the maximum shear stress of the soil. The relevant model parameters are B=0.24 MPa, u=0.5, and v=1.76.

[0047] (2) Determine the geometric dimensions and material parameters of the large-diameter monopile. The outer diameter of the monopile is D=9 m, the wall thickness is t=96.35 mm, and the elastic modulus of the steel is... The pile penetration depth is L = 45 m; therefore, the length-to-diameter ratio of a single pile is determined to be L / D = 5. .

[0048] (3) Calculate the reference depth Stress-strain curve of the soil at the location, , , , , , The stress-strain curve of the sand at the reference point determined thus is shown in Figure 3, and its corresponding functional expression is:

[0049] .

[0050] (4) Determine the rigidity of large-diameter single piles. Based on the calculation, the pile-soil relative stiffness is... ,because Therefore, it is a semi-rigid pile.

[0051] (5) Calculate the length of the single pile foundation. The length of the semi-rigid pile foundation is H=13m, and the rotation point is 13m from the pile bottom.

[0052] (6) Through

[0053]

[0054] Calculate the ultimate resistance bending moment at the rotation point ,in, This represents the maximum shear stress at the rotation point; as shown in Figure 1, due to the maximum shear stress of the soil... It increases approximately linearly with increasing depth, therefore k is Approximately linear rate of change with depth. Maximum shear strain of soil at the depth of the rotation point. =550.8 kPa, The linear rate of change with depth, k = 17 kPa / m, determines the ultimate bending moment resistance at the rotation point. .

[0055] (7) Determine the base rotation spring curve at the rotation point ,in , Therefore, The curve is shown in Figure 3, and its corresponding expression is:

[0056] .

[0057] In the above embodiments, a simplified analysis method for pile-soil interaction in large-diameter monopile foundations is provided. This invention integrates the complex pile-soil interaction at the bottom of the large-diameter monopile foundation into a single nonlinear spring model at the rotation point. This model can be directly integrated into the classic nonlinear Winkler foundation beam model without the need to construct a complex three-dimensional finite element model. Compared with traditional finite element analysis methods, this simplifies the modeling process, reduces the amount of computation, and improves computational efficiency. This invention obtains the base rotation spring by scaling the soil stress-strain relationship curve. The stress-strain curve can fully utilize soil strength parameters measured by geotechnical tests to directly improve the accuracy of pile-soil nonlinear stiffness prediction. Furthermore, the soil stress-strain curve comprehensively reflects its material characteristics, significantly improving the applicability of this calculation method in sandy soils with different properties. The invention provides the following information regarding the rotation point of a large-diameter single pile. This spring, unlike traditional Py springs, reflects different soil constraints, thus eliminating constraint conflicts and offering greater flexibility. For large-diameter rigid and semi-rigid piles, the nonlinear spring arrangement shown in Figure 2 can be used... The spring is used in combination with any advanced modified PY spring to further improve the accuracy of predicting the horizontal bearing capacity of a single pile.

[0058] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the concept and scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the inventive concept should fall within the protection scope of the present invention. All technical contents for which protection is sought in this invention are fully described in the claims.

Claims

1. A simplified analysis method for pile-soil interaction in large-diameter single-pile foundations, characterized in that: The process includes the following steps: S1, obtaining the soil mechanics parameters of the seabed foundation in the target area and the pile parameters of the large-diameter monopile foundation; S2, calculating the soil stress-strain curve at the reference depth based on the soil mechanics parameters; S3, determining the rigidity type of the large-diameter monopile foundation based on the pile-soil relative stiffness. S4. For rigid or semi-rigid monopile foundations, determine the location of the base rotation point and the corresponding effective length of the base; S5. Based on the stress-strain curve and the soil strength parameters at the rotation point, calculate the ultimate resisting bending moment at the rotation point; S6. By scaling the stress-strain curve, construct a nonlinear rotational spring model of the base at the rotation point; S7. Couple the nonlinear rotational spring model of the base with the pile side soil reaction model to achieve prediction of the horizontal bearing capacity of large-diameter monopile foundations.

2. The simplified analysis method for pile-soil interaction in a large-diameter single-pile foundation according to claim 1, characterized in that: The soil mechanical parameters include the internal friction angle φ of the sand and the relative density. void ratio e, effective unit weight of soil Soil elastic modulus linear rate of change with depth With the maximum shear modulus of the soil The relevant model parameters A, m, and n are related to the maximum shear stress of the soil. The relevant model parameters are B, u, and v.

3. The simplified analysis method for pile-soil interaction in large-diameter single-pile foundations according to claim 1, characterized in that: The pile parameters include the outer diameter D of a single pile, the wall thickness t, and the elastic modulus of the steel. The depth of the pile into the mud (L), the length-to-diameter ratio of a single pile (L / D), and the bending stiffness of the pile section. 。 4. The simplified analysis method for pile-soil interaction in a large-diameter single-pile foundation according to claim 1, characterized in that, The reference depth in step S2 The soil stress-strain curve is calculated based on 2 / 3 of the pile penetration depth L. include: ； ； ； Where τ is the soil shear stress and γ is the soil strain; Secant shear modulus of sand; This is the maximum shear modulus of the soil. for The corresponding shear strain threshold; This represents the maximum shear stress in the soil. The average effective stress; For reference stress, ； For reference depth, take ； The effective unit weight of sandy soil; The horizontal earth pressure coefficient is calculated using the following expression: φ is the internal friction angle of the sand.

5. The simplified analysis method for pile-soil interaction in a large-diameter single-pile foundation according to claim 1, characterized in that, In step S3, the pile-soil relative stiffness The calculation is based on the ratio of the pile's bending stiffness to the soil stiffness. The criterion for determining the rigidity type is: ;when When it is a rigid pile, At that time, it was a semi-rigid pile. For flexible piles, the nonlinear spring model of base rotation is only applicable to semi-rigid piles and rigid piles.

6. The simplified analysis method for pile-soil interaction in a large-diameter single-pile foundation according to claim 1, characterized in that, The expression for calculating the effective action length of the substrate in step S4 is as follows: Where L is the depth of the pile into the mud, D is the outer diameter of a single pile, and the distance from the rotation point to the bottom of the pile is equal to the effective working length H of the foundation.

7. The simplified analysis method for pile-soil interaction in a large-diameter single-pile foundation according to claim 1, characterized in that, The ultimate resistance bending moment at the rotation point in step S5 The expression is: ;in, This represents the maximum shear stress at the point of rotation; due to the maximum shear stress in the soil... It increases approximately linearly with increasing depth, therefore k is The rate of change is approximately linear with depth.

8. The simplified analysis method for pile-soil interaction in a large-diameter single-pile foundation according to claim 1, characterized in that, The scaling process in step S6 uses a rotation angle scaling factor ξ. R1 and moment scaling factor ， The value range is 0.05-0.

06. The value range is 1.3-1.4, and the expression for the base rotational nonlinear spring model is: ;in, The base rotational bending moment; The base rotation angle.

9. The simplified analysis method for pile-soil interaction in a large-diameter single-pile foundation according to claim 1, characterized in that: In step S7, the soil reaction model along the pile is a modified py curve model. The base rotational nonlinear spring model is coupled with the modified py curve model through the Winkel foundation beam model. The Winkel foundation beam model applies the soil reaction along the pile as a distributed spring to the pile element by discretizing the pile element, and applies the base rotational nonlinear spring at the rotation point.

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