A method for applying a modified p-y curve to the design of offshore large-diameter monopile foundations

Abstract

The application belongs to the field of ocean engineering design, and discloses a design method for applying a modified p-y curve to offshore large-diameter single-pile foundation, which opens up the use path of the modified p-y curve theory in actual design work. The scheme comprises the following steps: using SACS to establish a large-diameter single-pile mud surface line upper structure model input file sacinp.1 and an environmental working condition input file seainp.1; inputting the physical and mechanical parameters of each rock-soil layer, the structure size and material properties of the large-diameter single-pile structure under the mud surface line, and establishing a pile-soil interaction input file psiinp.1; based on the sacinp.1 file, the seainp.1 file and the psiinp.1 file, performing static analysis on the pile-soil interaction by using SACS to obtain the pile-soil interaction curve of each rock-soil layer; using the modified p-y curve model to modify the p-y curve of each rock-soil layer; inputting the modified p-y curve, the t-z curve and the q-z curve of each rock-soil layer, and establishing a pile-soil interaction input file psiinp.2; using the sacinp.1 file, the seainp.1 file and the psiinp.2 file to perform static analysis on the pile-soil interaction by using SACS, thereby optimizing the design of the large-diameter single-pile foundation structure.

Description

Technical Field

[0001] This invention belongs to the field of marine engineering design, specifically relating to a method for applying a modified py curve to the design of large-diameter monopile foundations at sea. Background Technology

[0002] In recent years, with the continuous increase in the single-unit capacity of offshore wind turbines, in order to adapt to complex marine hydrogeological and natural conditions, and at the same time meet the strict requirements of the upper wind turbine equipment for foundation deformation during normal operation, the pile diameter of monopile foundations has been continuously increasing (up to 10m). More and more engineering practices have shown that the hyperbolic tangent model (API specification) derived from field tests of small-diameter piles (pile diameter not exceeding 1.2m) has poor applicability to large-diameter piles.

[0003] To further improve the applicability of the py curve method, scholars both domestically and internationally have conducted extensive research:

[0004] Georgiadis [1] Kim [2] and Klinkvort [3] The hyperbolic tangent model was corrected through centrifugal model tests, and the hyperbolic model is recommended for calculating the py curve of sand. (Sorensen) [4] With Kallehave [5] The initial stiffness K of the sandy soil foundation py curve was determined through indoor tests. i Discussions were held, and revised calculation formulas were given respectively. (Broms) [6] Barton [7] Zhu Bin [8] Guo [9] and Kim

[10] Based on indoor model test results, the ultimate resistance p of sandy soil foundation py curve u Research was conducted, and respective suggested formulas were provided. (Hu Zhongbo)

[11] The initial stiffness K of medium-coarse sand strata was discussed based on field measurement data. i and ultimate resistance p u The variation law with depth is presented, and correction formulas considering the effects of pile diameter and burial depth are given respectively. These theoretical studies have all modified the API specification's py curve model to varying degrees, resulting in a modified py curve theoretical model that is more suitable for large-diameter monopile foundations at sea under certain conditions.

[0005] However, current research is still focused on proposing modified Py curve theoretical models, which are difficult to apply directly to the structural design of actual engineering projects. There is a lack of a design method that can combine the numerous proposed modified Py curve theoretical models with the widely used offshore wind turbine foundation structure design software (finite element analysis software SACS), thereby opening up the application path of modified Py curve theory in actual design work.

[0006] [1] Georgiadis M, Anagnostopoulos C, Saflekou S. Centrifugal testing of laterally loaded piles in sand[J]. Canadian Geotechnical Journal, 1992, 29(2):208-216.

[0007] [2]Kim BT,Kim NK,Lee WJ,et al.Experimental load-transfer curves of laterally loaded piles in Nak-Dong river sand[J].Journal of Geotechnical&Geoenvironmental Engineering,2004,130(4):416-425.

[0008] [3]Klinkvort RT,Hededal O.Effect of load eccentricity and stresslevel on monopile support for offshore wind turbines[J].Canadian GeotechnicalJournal,2014,51(9):966-974.

[0009] [4]Sorensen SPH,Ibsen LB,Augustesen A H.Effects of diameter oninitial stiffness of py curves for large-diameter piles in sand[C].TheEuropean Conference on Numerical Methods in Geotechnical Engineering.Norway,2010:907-912.

[0010] [5]Kallehave D, Thilsted CLB, Liingaard M A. Modification of the APIp-y formulation of initial stiffness of sand[C]. 7th International Conference: Offshore Site Investigation and Geotechnics: Integrated Technologies-Present and Future. London, 2012: 465-472.

[0011] [6]Broms B.The lateral resistance of piles in cohesionless soils[J].Journal of Soil Mechanics and Foundation Division,1964,90(3):123-156.

[0012] [7]Barton Y O. Laterally loaded model piles in sand: Centrifuge tests and finite element analysis[D]. University of Cambridge,1982.

[0013] [8] Zhu Bin, Zhu Ruiyan, Luo Jun, et al. Experimental study on the horizontal displacement behavior of marine high pile foundations [J]. Chinese Journal of Geotechnical Engineering, 2010, 32(4): 521-530.

[0014] [9]Guo WD, Zhu B T. Laterally loaded fixed-headed piles in sand[C]. 9thAustralia New Zealand Conference on Geomechanics,Auckland,New Zealand,2004:88-94.

[0015]

[10] Kim D,Choo YW,Kwak K.Comparison of lateral behavior of rock-socketed large-diameter offshore monopiles in sands with different relativedensities[J].International Journal of Offshore and Polar Engineering,2015,25(2):156-160.

[0016]

[11] Hu Zhongbo, Zhai Endi, Luo Lunbo, et al. Study on py curve of offshore wind power steel pipe pile in sand based on static load test [J]. Acta Energiae Solaris Sinica, 2019, 40(12):3571-3577. Summary of the Invention

[0017] The technical problem to be solved by this invention is to propose a design method for applying the modified Py curve to large-diameter offshore monopile foundations, thereby opening up the application path of the modified Py curve theory in actual design work, solving the problem that the calculation formula of the traditional API specification is not applicable to the structural design of large-diameter offshore wind power monopile foundations, and thus ensuring the safety and applicability of the structural design of large-diameter monopile foundations.

[0018] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0019] A method for applying modified Py curves to the design of large-diameter monopile foundations at sea includes the following steps:

[0020] S1. Use SACS software to create input files for the superstructure model of a large-diameter single pile mudline and environmental conditions.

[0021] S2. Input the physical and mechanical parameters of each soil and rock layer, the structural dimensions of the large-diameter single pile below the mudline and its material properties, and create the first pile-soil interaction input file.

[0022] S3. Based on the structural model input file, environmental condition input file, and first pile-soil interaction input file, static analysis of pile-soil interaction of large-diameter single pile structure is performed using SACS software.

[0023] S4 and SACS software calculate the pile-soil interaction curves for each soil layer according to API specifications, including the py curve in the transverse support direction, the tz curve in the axial friction direction, and the qz curve in the pile end support direction.

[0024] S5. The modified py curve model is used to modify the py curves of each soil and rock layer calculated by SACS software according to API specifications to obtain modified py curves of each soil and rock layer applicable to the current pile diameter.

[0025] S6. Input the corrected pile-soil interaction curves for each soil layer, as well as the structural dimensions and material properties of the large-diameter single pile below the mudline, and create a second pile-soil interaction input file.

[0026] S7. Based on the structural model input file, environmental condition input file, and second pile-soil interaction input file, static analysis of pile-soil interaction of large-diameter single pile structure is performed using SACS software, thereby optimizing the design of large-diameter single pile foundation structure.

[0027] Furthermore, step S1 also includes integrating the structural model input file and the environmental condition input file into one file to form an integrated input file.

[0028] Furthermore, in step S3, the input file based on the structural model, the input file based on the environmental conditions, and the input file based on the first pile-soil interaction are based on the integrated input file and the first pile-soil interaction input file; in step S7, the input file based on the structural model, the input file based on the environmental conditions, and the input file based on the second pile-soil interaction are based on the integrated input file and the second pile-soil interaction input file.

[0029] Furthermore, in step S4, the mathematical expression for calculating the py curve in the lateral support direction according to the API specification is as follows:

[0030]

[0031] Where p is the soil resistance; A is the correction factor; p u y represents the ultimate soil resistance in the horizontal direction; Ki represents the initial stiffness of the py curve; and y represents the horizontal displacement.

[0032]

[0033] Where γ is the effective unit weight of the soil; z is the depth below the mud surface; D is the pile diameter; and C1, C2, and C3 are parameters related to the internal friction angle in the API specification.

[0034] Furthermore, in step S5, the modified py curve model includes a modified py hyperbola model proposed based on the results of centrifugation model experiments, with the following expression:

[0035]

[0036] Where p is the soil resistance; p uy represents the ultimate soil resistance in the horizontal direction; Ki represents the initial stiffness of the py curve; and y represents the horizontal displacement.

[0037] Furthermore, in step S5, the modified py curve model includes the initial stiffness Ki and the horizontal ultimate resistance p of the py curve model for sandy soil foundation based on indoor test results. u The py curve model obtained by performing correction calculations.

[0038] Furthermore, in step S6, the input modified pile-soil interaction curves for each soil layer include the tz curve in the axial friction direction calculated according to API specifications, the qz curve in the pile end support direction, and the modified py curve.

[0039] Furthermore, in step S6, the input of the corrected pile-soil interaction curves for each soil and rock layer refers to inputting a series of coordinate data points on the curves respectively.

[0040] The beneficial effects of this invention are:

[0041] Based on the above-mentioned solution of the present invention, the numerous proposed modified py curve theoretical models can be effectively combined with the industry-wide offshore wind turbine foundation structure design software (finite element analysis software SACS), opening up the application path of modified py curve theory in actual design work; and by applying the modified py curve model to the structural design of offshore wind turbine foundations, the problem that the calculation formulas of the traditional API specification are not applicable to the structural design of large-diameter monopile foundations for offshore wind power can be effectively solved, further ensuring the safety and applicability of the structural design of large-diameter monopile foundations. Attached Figure Description

[0042] Figure 1 This is a flowchart illustrating the design method of applying the modified py curve to a large-diameter monopile foundation in marine applications, as described in this invention. Detailed Implementation

[0043] This invention aims to propose a design method for large-diameter monopile foundations at sea by applying the modified Py curve, thereby opening up the application path of the modified Py curve theory in practical design work, solving the problem that the calculation formulas of the traditional API specification are not applicable to the structural design of large-diameter monopile foundations for offshore wind power, and thus ensuring the safety and applicability of the structural design of large-diameter monopile foundations.

[0044] The scheme first uses SACS software to create input files for the upper structure model and environmental conditions of a large-diameter monopile above the mudline. Then, it inputs the physical and mechanical parameters of each soil layer, the dimensions of the large-diameter monopile below the mudline, and its material properties to create the first pile-soil interaction input file. Next, based on the structural model input file, environmental condition input file, and the first pile-soil interaction input file, it performs a static analysis of the pile-soil interaction of the large-diameter monopile structure using SACS software. Finally, SACS software calculates the pile-soil interaction curves for each soil layer according to API specifications, including the py curve in the transverse support direction, the tz curve in the axial friction direction, and the pile end support curve. The process begins by generating the qz curve in the support direction. Next, a modified py curve model is used to correct the py curves of each soil layer calculated by the SACS software according to API specifications, obtaining modified py curves suitable for the current pile diameter. Then, the corrected pile-soil interaction curves for each soil layer, along with the structural dimensions and material properties of the large-diameter single pile below the mudline, are input to create a second pile-soil interaction input file. Finally, based on the structural model input file, environmental condition input file, and the second pile-soil interaction input file, static pile-soil interaction analysis is performed on the large-diameter single pile structure using SACS software, thereby optimizing the design of the large-diameter single pile foundation structure.

[0045] Example:

[0046] The method for applying the modified py curve to the design of large-diameter monopile foundations at sea, as provided in this embodiment, requires the use of SACS, a widely used finite element analysis software for offshore wind turbine foundation design. The implementation process is as follows: Figure 1 As shown, the processing steps include the following:

[0047] S1. Use SACS software to create the input file sacinp.1 for the superstructure model of the large-diameter single pile mud surface and the input file seainp.1 for environmental conditions;

[0048] Optionally, the environmental condition input file seainp.1 in this step can be combined with the structural model input file sacinp.1 to form a single input file sacinp.1; of course, the file names sacinp and seainp can also be replaced with other names, this embodiment is just an example of sacinp.1 and seainp.1.

[0049] S2. Input the physical and mechanical parameters of each soil and rock layer, the structural dimensions of the large-diameter single pile below the mudline and its material properties, and create the pile-soil interaction input file psiinp.1;

[0050] In one feasible implementation, the input parameters for the clay layer are effective unit weight and undrained shear strength, and the input parameters for the sand layer are effective unit weight, internal friction angle of sand, support coefficient of sand, and ultimate bearing capacity of pile tip. The pile size input includes the outer diameter, wall thickness, pile length into the ground, and effective area of ​​pile tip. The pile material properties input includes elastic modulus, shear modulus, density, and yield strength.

[0051] Optionally, the psiinp file name in this step can be replaced with other names; this embodiment simply uses psiinp.1 as an example.

[0052] S3. Using the sacinp.1, seainp.1, and psiinp.1 files, perform static pile-soil interaction analysis on a large-diameter monopile structure using SACS software.

[0053] In this step, if the seainp.1 and sacinp.1 files were integrated in step S1, then the integrated file should be entered here.

[0054] S4 and SACS software calculate the pile-soil interaction curves for each soil layer according to API specifications, namely the py curve in the transverse support direction, the tz curve in the axial friction direction, and the qz curve in the pile end support direction.

[0055] Alternatively, the API specification provides the following mathematical expression for calculating the py curve: (1)

[0056]

[0057] Where p is the soil resistance, in kN / m; A is the correction factor, expressed as in equation (2); p u The ultimate horizontal soil resistance is expressed in kN / m, and its expression is given by equation (3); Ki is the initial stiffness of the py curve, in kN / m. 2 ; y represents the horizontal displacement, in meters.

[0058]

[0059] P u =γzmin(C1z+C2D,C3D) (3)

[0060] Where γ is the effective unit weight of the soil, in kN / m³. 3 z is the depth below the mud surface, in meters; D is the pile diameter, in meters; C1, C2, and C3 are parameters related to the internal friction angle, and their values ​​are specified in the API specification.

[0061] S5. Use the modified py curve model to modify the py curves of each soil and rock layer calculated by SACS software according to API specifications, so as to obtain modified py curves of each soil and rock layer that are more suitable for the current pile diameter.

[0062] As an optional approach, the modified py curve model in this step includes a modified py hyperbola model proposed based on the results of centrifugation model experiments, expressed as follows (4):

[0063]

[0064] The meanings of the symbols are the same as before.

[0065] As an alternative approach, the modified py curve model in this step includes the initial stiffness Ki and the horizontal ultimate resistance p of the py curve model for sandy soil foundation based on indoor test results. u The py curve model obtained by performing correction calculations.

[0066] Since the tz and qz curves have little impact on the horizontal bearing characteristics of large-diameter single piles, the tz and qz curves calculated by SACS software according to API specifications can be used directly in the following calculation inputs.

[0067] As those skilled in the art will know, the tz and qz curves can also be corrected using a method similar to that used for the py curve correction, and the corrected tz and qz curves can be input into the calculation input of the subsequent S6 step.

[0068] S6. Input the corrected py curve, tz curve and qz curve for each soil and rock layer, as well as the structural dimensions and material properties of the large-diameter single pile below the mudline, and establish the pile-soil interaction input file psiinp.2;

[0069] Optionally, the psiinp file name in this step can be replaced with other names; the input for correcting the py curve, tz curve, and qz curve is done by inputting a series of coordinate data points on each curve.

[0070] S7. Using the sacinp.1, seainp.1, and psiinp.2 files, static analysis of pile-soil interaction is performed on the large-diameter monopile structure through SACS software, thereby optimizing the design of the large-diameter monopile foundation structure.

[0071] In this step, if the seainp.1 and sacinp.1 files were integrated in step S1, then the integrated file should be entered here.

[0072] Although the present invention has been described herein with reference to embodiments thereof, the above embodiments are merely preferred embodiments of the present invention, and the implementation of the present invention is not limited to the above embodiments. It should be understood that those skilled in the art can design many other modifications and implementations, which will fall within the scope and spirit of the principles disclosed in this application.

Claims

1. A method of applying a revised p-y curve to the design of offshore large diameter monopile foundations, characterized in that, The method comprises the following steps: S1, using SACS software to establish a large-diameter single pile mud line upper structure model input file and an environmental condition input file; S2, inputting the physical and mechanical parameters of each rock-soil layer, the size and material properties of the large-diameter single pile structure under the mud line, and establishing a first pile-soil interaction input file; S3, based on the structure model input file, the environmental condition input file and the first pile-soil interaction input file, the SACS software is used to perform a static force analysis on the pile-soil interaction of the large-diameter single pile structure; S4, the SACS software calculates the pile-soil interaction curves of each rock-soil layer according to the API specification, including the p-y curve in the lateral support direction, the t-z curve in the axial friction direction, and the q-z curve in the pile end support direction; S5, using a modified p-y curve model to modify the p-y curve of each rock-soil layer calculated by the SACS software according to the API specification, to obtain a modified p-y curve of each rock-soil layer suitable for the current pile diameter; The modified p-y curve model includes a modified p-y hyperbolic curve model based on the results of centrifugal model tests, and the expression is: ； where p is the soil resistance; p u is the horizontal ultimate soil resistance; K1is the initial stiffness of the p-y curve; y is the horizontal displacement; Alternatively, the modified p-y curve model includes initial stiffness Ki and horizontal ultimate resistance p of the p-y curve model of the sand ground based on the results of the indoor test u the p-y curve model obtained by the modification calculation; S6, inputting the modified pile-soil interaction curves of each rock-soil layer, and the size and material properties of the large-diameter single pile structure under the mud line, and establishing a second pile-soil interaction input file; the input modified pile-soil interaction curves of each rock-soil layer include the t-z curve in the axial friction direction, the q-z curve in the pile end support direction, and the modified p-y curve calculated according to the API specification; S7, based on the structure model input file, the environmental condition input file and the second pile-soil interaction input file, the SACS software is used to perform a static force analysis on the pile-soil interaction of the large-diameter single pile structure, thereby optimizing the design of the large-diameter single pile foundation structure.

2. The method of claim 1, wherein the modified p-y curve is applied to the design of the offshore large-diameter single pile foundation, and the method further comprises the following steps: In step S1, the structure model input file and the environmental condition input file are integrated into one file to form an integrated input file.

3. The method of claim 2, wherein the method further comprises the following steps: In step S3, the structure model input file, the environmental condition input file and the first pile-soil interaction input file are based on the integrated input file and the first pile-soil interaction input file; in step S7, the structure model input file, the environmental condition input file and the second pile-soil interaction input file are based on the integrated input file and the second pile-soil interaction input file.

4. The method of claim 1, wherein the method further comprises the following steps: In step S4, the mathematical expression for calculating the p-y curve in the lateral support direction according to the API specification is: ； where p is the soil resistance; A is the correction factor; p u is the horizontal ultimate soil resistance; Ki is the initial stiffness of the p-y curve; y is the horizontal displacement; ； ； wherein γ is the effective unit weight of the soil; z is the depth below the mud line; D is the pile diameter; C1, C2 and C3 are parameters related to the internal friction angle in the API specification.

5. The method for applying the revised p-y curve to the design of offshore large-diameter single pile foundation according to any one of claims 1-4, characterized in that, In step S6, the input of the revised pile-soil interaction curve of each rock-soil layer refers to the input of a series of coordinate data points on the curve respectively.

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