Rock-soil stress analysis method for corner piles in seabed mixed type foundation

Abstract

The invention relates to the technical field of ocean energy development, in particular to a rock-soil stress analysis method for corner piles in a seabed mixed type foundation. The method comprises the following steps: collecting seabed geological data and design parameters of a pile foundation, analyzing lateral pile-soil interaction of a steel corner pile in the seabed mixed pile foundation in a complex layered sea soil environment by adopting a finite difference method, and setting reasonable boundary conditions and initial conditions according to actual engineering conditions, and the model can accurately reflect actual conditions. According to the method, a corner pile analysis algorithm is provided, the corner pile analysis algorithm can quickly and effectively complete lateral deformation and stress estimation of a corner pile of a mixed pile foundation in sea soil, the limitation of a conventional estimation calculation method is broken through, a finite difference method is used for carrying out difference on a complex flexural differential equation, a foundation is laid for subsequent programming design, and the calculation efficiency is improved. Therefore, the problem of time consumption of traditional manual calculation is solved, and the application range is expanded.

Description

Technical Field

[0001] The invention relates to the technical field of marine energy development, and in particular to a rock and soil stress analysis method for angle piles in a submarine hybrid foundation. Background Art

[0002] As a new type of foundation for underwater systems, hybrid foundations are widely used in the field of offshore oil and gas development, and are used as fixed ends of marine risers or submarine pipelines, etc., and have important theoretical significance and application value. Layered soil is a relatively complex situation in seabed soil. There are many studies on the lateral bearing of piles in homogeneous sea soil, but there are fewer studies on the lateral bearing of piles in complex layered sea soil, mainly including: For piles in cohesive or non-cohesive soils, scholars have proposed design methods (reference [1]: Chiou JS, Chien HY. Analytical interaction diagram for lateral responses of a rigid pile in homogeneous overconsolidated clay [J]. Journal of Geotechnical and Geoenvironmental Engineering, 2021, 147 (9): 05021008.). There are also some design specifications in the industry. For example, the American Petroleum Institute standard (API) adopts the common bearing calculation model for cohesive soft clay and sand, which is one of the most widely used algorithms in the lateral bearing calculation of pile foundations. On this basis, scholars have established complex finite element models for simulation research on cohesive soil covered with non-cohesive soil, non-cohesive soil covered with cohesive soil, and complex layered soil (Reference [2]: Bildik S, Tanriover H. Numerical Investigation of the pile-soil interaction problem under dynamic loads [J]. Applied Sciences, 2023, 13 (21): 11653; Reference [3]: Li XY, Wan JH, Zhao HP, Liu SW. Three-dimensional analysis of nonlinear pile-soil interaction responses using 3D pile element model [J]. International Journal of Geomechanics, 2021, 21 (8): 04021129), which improves the estimation accuracy of the lateral bearing of suction piles in layered soil. However, this finite element simulation method is more suitable for the detailed design stage due to its long time consumption and high computational cost. Layered soil is a more complex condition in seabed soil. There are many studies on the lateral bearing of piles in homogeneous sea soil, but there are fewer studies on the lateral bearing of piles in complex layered sea soil. Therefore, a geotechnical force analysis method for angle piles in submarine hybrid foundation is designed. Summary of the invention

[0003] The purpose of the present invention is to provide a geotechnical force analysis method for angle piles in a submarine hybrid foundation, so as to solve the problems that the finite element simulation method proposed in the above background technology is time-consuming, has high calculation cost and has little research on the lateral bearing of piles in complex layered marine soil.

[0004] To achieve the above object, the present invention provides a method for analyzing the geotechnical stress of angle piles in a submarine hybrid foundation, comprising the following steps:

[0005] S1. Collect seabed geological data and pile foundation design parameters. The seabed geological data at least includes soil type, soil stratification information, and physical and mechanical parameters of each layer of soil. The pile foundation design parameters at least include pile diameter, pile length, and pile material properties;

[0006] S2. The lateral pile-soil interaction of steel angle piles in submarine hybrid pile foundations in complex layered sea-soil environment was analyzed using the finite difference method. Based on the collected data, a mathematical model was established using the finite difference method to simulate the pile-soil interaction under different conditions.

[0007] S3. Set reasonable boundary conditions and initial conditions according to the actual engineering situation to ensure that the model can accurately reflect the actual situation;

[0008] S4. Use computer software to perform numerical calculations of the above model to obtain the stress state and deformation of the corner piles under different working conditions. Then, analyze the calculation results in detail, evaluate the safety, stability and economy of the pile foundation, and put forward optimization suggestions.

[0009] As a further improvement of the technical solution, the finite difference method is used in S2 to analyze the lateral pile-soil interaction of the steel angle piles in the submarine hybrid pile foundation in the complex layered sea soil environment. The specific steps are as follows:

[0010] S21. Establish the differential equation of the angular pile deflection based on the mechanical relationship;

[0011] S22. According to the design characteristics of the angle piles of submarine hybrid foundations in engineering practice, the flexural differential equation is further refined;

[0012] S23, using the finite difference method to differentiate the refined corner pile deflection differential equation;

[0013] S24, using the Glesser algorithm to process the differential equations, and obtain the expression of the lateral deformation of the segmented pile length;

[0014] S25, make an initial assumption about the secant modulus of the foundation reaction at each depth, substitute it into the expression and solve it, and obtain a set of lateral deformations of the corner piles;

[0015] S26, calculating the py curve corresponding to each node depth of the corner pile according to the property parameters of each layer of sea soil, and substituting the obtained lateral deformation into the py curve to obtain a new foundation reaction secant modulus;

[0016] S27, obtaining the secant modulus within the allowable accuracy range through iterative calculation;

[0017] S28. Calculate and obtain the lateral deformation of the corner pile at each depth and the lateral force acting on the rock and soil.

[0018] As a further improvement of the technical solution, the S21 is specifically as follows:

[0019]

[0020] Wherein, E is the elastic modulus of the corner pile material; I is the moment of inertia of the corner pile section; z is the depth below the seabed mud surface where the corner pile microelement is located; y is the deflection at the corner pile microelement; N is the axial force at the corner pile microelement; p is the foundation reaction force per unit area at the corner pile microelement; and D is the outer diameter of the corner pile at the corner pile microelement.

[0021] As a further improvement of the technical solution, the refined flexural differential equation in S22 is as follows:

[0022]

[0023] Where I(z) is the moment of inertia of the section taking into account the depth variation; N(z) is the axial force on the corner pile at position z; and p(z,y) is the foundation reaction per unit area that depends on the depth z and the deflection y of the corner pile at that position.

[0024] As a further improvement of the technical solution, the refined flexural differential equation in S22 is:

[0025]

[0026] Wherein, t1 is the wall thickness of the corner pile in the interval z≤z1; t2 is the wall thickness of the corner pile in the interval z1≤z≤z2; z1 is the first depth; z2 is the second depth;

[0027]

[0028] Among them, N t is the initial axial force at the top of the corner pile; W(z) is the weight per unit length of the corner pile; F skin (z) is the friction between the corner pile and the surrounding soil; m for a specific depth;

[0029]

[0030] Wherein, W1 is the pile weight per unit length of the upper wall thickness t1 portion of the corner pile; W2 is the pile weight per unit length of the lower wall thickness t2 portion of the corner pile;

[0031]

[0032] Among them, α z is the friction angle coefficient between soil and corner pile; c uz is the undrained shear strength of the soil; A z is the surface area of ​​the corner pile in contact with the soil at depth z; l z is the contact length of the corner pile at depth z.

[0033] As a further improvement of the technical solution, the S23 uses the finite difference method to differentiate the refined corner pile deflection differential equation, as follows:

[0034] A i y i+2 +B i y i+1 +C i y i +D i y i-1 +E i y i-2 =0;

[0035] Among them, y i+2 is the lateral deflection of the i+2th microelement segment; y i+1 is the lateral deflection of the i+1th microelement segment; y i-1 is the lateral deflection of the i-1th microelement segment; y i-2 is the lateral deflection of the i-2th microelement segment;

[0036] A i =E·I i+1 ;

[0037] B i =-2E·I i+1 -2E·I i +N i ·(Δl) 2 ;

[0038] C i =E·I i+1 +4E·I i +E·I i-1 -2N i ·(Δl) 2 +D i ·(E s ) i ·(Δl) 4;

[0039] D i =-2E·I i -2E·I i-1 +2N i ·(Δl) 2 ;

[0040] E i =E·I i-1 ;

[0041] Among them, I i+1 is the section inertia moment of the i+1th infinitesimal segment; I i is the section inertia moment of the i-th microelement segment; I i-1 is the section inertia moment of the i-1th infinitesimal segment; N i is the axial force of the ith microelement segment; Δl is;

[0042] D i is the secant modulus of foundation reaction; (E s ) i is the secant modulus of the foundation reaction of the i-th microelement segment;

[0043] Boundary conditions at the free end of the pile bottom:

[0044] Q n =0;

[0045] M n =0;

[0046] Boundary conditions at the fixed end of the pile top:

[0047] Q0=H0;

[0048] M0=0;

[0049] Among them, Q n is the shear force; M n is the bending moment; H0 is a constant, representing the lateral shear force.

[0050] As a further improvement of the technical solution, the differential equation group is processed in S24 to obtain an expression for the lateral deformation of the segmented pile length, which is as follows:

[0051] Divide the pile into n micro-element segments, and the length of each micro-element segment is Δz. Then the discretized difference equation is:

[0052]

[0053] Among them, y i is the lateral deformation of the ith microelement segment; z i is the depth of the ith microelement segment; p(z i ,y i) is the ultimate lateral bearing capacity.

[0054] As a further improvement of the technical solution, the S25 makes an initial assumption on the foundation reaction secant modulus at each depth, specifically as follows:

[0055] Assume that the initial foundation reaction secant modulus k s,i is a constant:

[0056]

[0057] Among them, k s,i is the secant modulus of the initial foundation reaction force; c is the cohesion of the soil; γ is the density of the soil; J is the lateral pressure coefficient of the soil;

[0058] y c =2.5∈ C ·D;

[0059] Among them, y C is the critical lateral deformation; ∈ C is the critical strain, indicating that under this strain, the foundation reaction reaches the limit value;

[0060] The initial assumption k S Substitute this into the difference equation and solve for y i .

[0061] As a further improvement of the technical solution, the S26 is specifically as follows:

[0062]

[0063] Among them, z R is the critical depth;

[0064]

[0065] Update the secant modulus of foundation reaction:

[0066]

[0067] Among them, k s,I ′ is the updated secant modulus of foundation reaction.

[0068] As a further improvement of the present technical solution, the iterative solution in S27 is based on repeating the steps of S25 and S26 until the lateral deformation y of all micro-element segments is i Convergence means that the deformation change between two adjacent iterations is less than a preset minimum value ∈.

[0069] Compared with the prior art, the present invention has the following beneficial effects:

[0070] In this method of geotechnical stress analysis of corner piles in a submarine hybrid foundation, a simple and fast estimation algorithm for corner pile analysis is proposed, which meets the requirements of international design specifications. The corner pile analysis algorithm can quickly and effectively complete the lateral deformation and stress estimation of the corner piles of the hybrid pile foundation in the sea soil, breaking the limitations of conventional estimation calculation methods, and using the finite difference method to differentiate complex flexural differential equations, laying the foundation for subsequent programming design, thereby solving the time-consuming problem of traditional manual calculations and expanding its application scope. BRIEF DESCRIPTION OF THE DRAWINGS

[0071] Figure 1 The figure is a flow chart of the overall method of the present invention. DETAILED DESCRIPTION

[0072] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0073] Example

[0074] See also Figure 1 As shown, a method for analyzing the geotechnical stress of angle piles in a submarine hybrid foundation is provided, comprising the following steps:

[0075] S1. Collect seabed geological data and pile foundation design parameters. The seabed geological data at least includes soil type, soil stratification information, and physical and mechanical parameters of each layer of soil (such as density, elastic modulus, internal friction angle, etc.). The pile foundation design parameters at least include pile diameter, pile length and pile material properties;

[0076] S2. The lateral pile-soil interaction of steel angle piles in submarine hybrid pile foundations in complex layered sea-soil environment was analyzed using the finite difference method. Based on the collected data, a mathematical model was established using the finite difference method to simulate the pile-soil interaction under different conditions.

[0077] S3. Set reasonable boundary conditions and initial conditions according to the actual engineering situation to ensure that the model can accurately reflect the actual situation;

[0078] S4. Use computer software to perform numerical calculations of the above model to obtain the stress state and deformation of the corner piles under different working conditions. Then, analyze the calculation results in detail, evaluate the safety, stability and economy of the pile foundation, and put forward optimization suggestions.

[0079] In S2, the finite difference method is used to analyze the lateral pile-soil interaction of steel angle piles in the submarine hybrid pile foundation in a complex layered sea-soil environment. The specific steps are as follows:

[0080] S21. Establish the differential equation of the angular pile deflection based on the mechanical relationship;

[0081] S22. According to the design characteristics of the angle piles of submarine hybrid foundations in engineering practice, the flexural differential equation is further refined;

[0082] S23, using the finite difference method to differentiate the refined corner pile deflection differential equation;

[0083] S24, using the Glesser algorithm to process the differential equations, and obtain the expression of the lateral deformation of the segmented pile length;

[0084] S25, make an initial assumption about the secant modulus of the foundation reaction at each depth, substitute it into the expression and solve it, and obtain a set of lateral deformations of the corner piles;

[0085] S26, calculating the py curve corresponding to each node depth of the corner pile according to the property parameters of each layer of sea soil, and substituting the obtained lateral deformation into the py curve to obtain a new foundation reaction secant modulus;

[0086] S27, obtaining the secant modulus within the allowable accuracy range through iterative calculation;

[0087] S28. Calculate and obtain the lateral deformation of the corner pile at each depth and the lateral force acting on the rock and soil.

[0088] S21 is as follows:

[0089]

[0090] Among them, E is the elastic modulus of the corner pile material; I is the moment of inertia of the corner pile section; z is the depth below the seabed mud surface where the corner pile microelement is located; y is the deflection at the corner pile microelement; N is the axial force at the corner pile microelement; p is the foundation reaction force per unit area at the corner pile microelement; D is the outer diameter of the corner pile at the corner pile microelement. The refined flexural differential equation in S22 is as follows:

[0091]

[0092] Where I(z) is the moment of inertia of the section taking into account the depth variation; N(z) is the axial force on the corner pile at position z; p(z,y) is the foundation reaction per unit area that depends on the depth z and the deflection y of the corner pile at that position, because the foundation reaction to the corner pile depends not only on the depth but also on the displacement of the corner pile;

[0093] represents the curvature of the corner pile at z, that is, the second-order derivative of the deflection y with respect to the depth z; It describes the bending moment of the corner pile at z, and the response to the external force is the second derivative of this bending moment with respect to z; is the slope of the corner pile at z, i.e. the first derivative of the deflection y with respect to the depth z; This expression represents the effect of the axial force N(z) on the change of the slope of the corner pile, or the change of the shear force caused by the axial force; p(z,y)·D represents the force of the foundation on the corner pile, which changes with the change of the diameter of the corner pile, reflecting the support force of the foundation on the corner piles of different sizes;

[0094] This equation describes the equilibrium state of the corner pile in the soil, that is, the equilibrium relationship between the change in bending moment generated inside the corner pile, the change in shear force caused by the axial force and the support force provided by the foundation. The sum of the terms on the left side of the equation is equal to zero, which means that at any given point z, the total effects of these forces cancel each other out, making the corner pile in a static equilibrium state.

[0095] In the refined flexural differential equation in S22, in the design and construction of submarine hybrid foundations, the outer diameter of the corner piles used is usually consistent with the material (i.e., D and E in equations (1) and (2) are constants), but it is common for the corner piles to contain upper and lower sections with different wall thicknesses. Therefore, considering the change in the cross section of the corner pile and its moment of inertia I with depth, the formula is as follows:

[0096]

[0097] Wherein, t1 is the wall thickness of the corner pile in the interval z≤z1; t2 is the wall thickness of the corner pile in the interval z1≤z≤z2. The wall thickness refers to the distance from the outer surface to the inner surface of the corner pile, reflecting the thickness of the corner pile; z1 is the first depth; z2 is the second depth, which is used to distinguish the wall thickness changes of the corner pile in different depth ranges;

[0098] The I(z) formula shows that the moment of inertia of the corner piles at different depths is different, which is mainly caused by the change in the wall thickness of the corner piles. This design may be to adapt to the changes in soil conditions at different depths and optimize the structural performance of the corner piles. For example, at shallow depths, thicker walls may be required to enhance the stiffness and bearing capacity of the corner piles; at deeper locations, the soil has a stronger supporting effect, so the wall thickness can be appropriately reduced to save materials.

[0099] During the installation of the submarine hybrid foundation, a small length is usually reserved on the upper part of the corner pile after it is driven into the sea soil to facilitate the assembly of the corner pile top and the lock structure. Therefore, the difference between the axial force N on the corner pile above the sea soil and below the sea soil (the axial friction provided by the sea soil) should be considered, and the sea soil stratification and its specific property parameters as well as the difference in wall thickness between the upper and lower sections of the corner pile should be considered. The formula is:

[0100]

[0101] Among them, N t is the initial axial force at the top of the corner pile, that is, the axial force applied at z = 0, which is usually the force transmitted from the superstructure; W(z) is the weight per unit length of the corner pile, which varies with the depth z; F skin (z) is the friction between the corner pile and the surrounding soil, also known as “skin friction”. This force varies with depth z and reflects the resistance of the soil to the corner pile; m is a specific depth marking the point where the axial force calculation method changes;

[0102]

[0103] Where W1 is the pile weight per unit length of the upper wall thickness t1 part of the corner pile; W2 is the pile weight per unit length of the lower wall thickness t2 part of the corner pile; W1 and W2 are constants, representing the weight coefficient per unit length in different depth intervals;

[0104] Assume that the sea soil is layered into clays of different properties:

[0105]

[0106] Among them, α z is the friction angle coefficient between soil and corner pile, which reflects the friction characteristics between soil and corner pile surface. This coefficient is usually determined by experiments or empirical data; c uz The undrained shear strength of soil indicates the ability of soil to resist shear failure under undrained conditions. This parameter reflects the cohesion of soil and is usually obtained through field tests or laboratory tests. z is the surface area of ​​the corner pile in contact with the soil at depth z; l z is the contact length of the corner pile at depth z, which can usually be considered as a small length of the corner pile at that depth.

[0107] S23 uses the finite difference method to differentiate the refined corner pile deflection differential equation as follows:

[0108] A i y i+2 +B i y i+1 +C i y i +D i y i-1 +E i y i-2 =0;

[0109] Among them, y i+2is the lateral deflection of the i+2th microelement segment; y i+1 is the lateral deflection of the i+1th microelement segment; y i-1 is the lateral deflection of the i-1th microelement segment; y i-2 is the lateral deflection of the i-2th microelement segment;

[0110] A i =E·I i+1 ;

[0111] B i =-2E·I i+1 -2E·I i +N i ·(Δl) 2 ;

[0112] C i =E·I i+1 +4E·I i +E·I i-1 -2N i ·(Δl) 2 +D i ·(E s ) i ·(Δl) 4 ;

[0113] D i =-2E·I i -2E·I i-1 +2N i ·(Δl) 2 ;

[0114] E i =E·I i-1 ;

[0115] Among them, I i+1 is the section inertia moment of the i+1th infinitesimal segment; I i is the section inertia moment of the i-th microelement segment; I i-1 is the section inertia moment of the i-1th infinitesimal segment; N i is the axial force of the ith microelement segment; Δl is;

[0116] D i is the secant modulus of foundation reaction; (E s ) i is the secant modulus of the foundation reaction of the i-th microelement segment;

[0117] Boundary conditions at the free end of the pile bottom:

[0118] Q n =0;

[0119] There is no shear force at the bottom of the pile, which means that there is no lateral shear force at the bottom of the pile;

[0120] M n =0;

[0121] There is no bending moment at the bottom of the pile, which means that there is no bending moment at the bottom of the pile;

[0122] Boundary conditions at the fixed end of the pile top:

[0123] Q0=H0;

[0124] The shear force at the top of the pile is H0, which means there is a known transverse shear force H0 at the top of the pile.

[0125] M0=0;

[0126] There is no bending moment at the pile top, which means that there is no bending moment at the pile top;

[0127] Among them, Q n is the shear force; M n is the bending moment; H0 is a constant, representing the lateral shear force.

[0128] In S24, the differential equations are processed to obtain the expression of the lateral deformation of the segmented pile length, which is as follows:

[0129] Divide the pile into n micro-element segments, and the length of each micro-element segment is Δz. Then the discretized difference equation is:

[0130]

[0131] Among them, y i is the lateral deformation of the ith microelement segment; z i is the depth of the ith microelement segment; p(z i ,y i ) is the ultimate lateral bearing capacity, that is, the reaction force of the foundation under the maximum bearing capacity.

[0132] S25 makes initial assumptions about the secant modulus of the foundation reaction at each depth, as follows:

[0133] Assume that the initial foundation reaction secant modulus k s,i is a constant:

[0134]

[0135] Among them, k s,i is the secant modulus of the initial foundation reaction force; c is the cohesion of the soil, which indicates the ability of the soil to resist shear failure under tension-free conditions. This is an important parameter for soft clay; γ is the weight of the soil, that is, the weight of the soil per unit volume. It reflects the density and water content of the soil; J is the lateral pressure coefficient of the soil, which describes the relationship between the lateral pressure and the vertical pressure of the soil;

[0136] yc =2.5∈ c ·D;

[0137] Among them, y c is the critical lateral deformation, indicating that under this deformation degree, the foundation reaction force reaches the limit value; ∈ c is the critical strain, indicating that under this strain, the foundation reaction reaches the limit value.

[0138] For soft clay, ε c =0.005, for static load conditions:

[0139]

[0140] Where P is the actual foundation reaction, that is, the foundation reaction under the actual deformation y; P ult It is the ultimate foundation reaction, that is, the reaction of the foundation under the maximum bearing capacity.

[0141] The initial assumption k s Substitute this into the difference equation and solve for y i .

[0142] S26 is as follows:

[0143] The foundation reaction p of each microelement of p(z,y) is related to the specific property parameters of the sea soil at the depth z and the lateral deformation degree y of the microelement of the corner pile. In clay soil, API 2A adopts the Matlock Soft Clay model, and the calculation of the ultimate lateral load follows the py curve:

[0144]

[0145] Among them, z R is the critical depth, indicating that the foundation reaction is calculated differently above and below this depth;

[0146]

[0147] Update the secant modulus of foundation reaction:

[0148]

[0149] Among them, k s,i ′ is the updated secant modulus of foundation reaction.

[0150] The iterative solution in S27 is based on repeating the steps of S25 and S26 until the lateral deformation y of all micro-element segments is i Convergence means that the deformation change between two adjacent iterations is less than a preset minimum value ∈. Usually, ∈ can be set to 10-6 or less; specifically:

[0151] ①Set the number of iterations to i * ; Assume a set of initial values ​​of the secant modulus of the foundation reaction (E s ) iter＝0 , there is no foundation reaction force on the corner pile wall above the mud line E s =0, and use the formula to solve a set of y i Estimated value;

[0152] ②Use a set of y i Estimated value, substitute into the py curve, and get a set of p i ;

[0153] ③Use a group of p i Estimated value, by E s = p / y to obtain a new set of (E s ) iter＝1 ;

[0154] ④The new (E s ) iter＝1 Assign the value to the assumed value and repeat the iterative calculation steps ①-③ until ABS((E s ) iter＝nn -(E s ) iter＝nn-1 )<ε, where ε is the allowable accuracy condition.

[0155] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments, and the above embodiments and descriptions are only preferred examples of the present invention, and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A method for analyzing the geotechnical forces of angle piles in a submarine hybrid foundation, characterized by: The steps include: S1. Collect seabed geological data and pile foundation design parameters. The seabed geological data at least includes soil type, soil stratification information, and physical and mechanical parameters of each layer of soil. The pile foundation design parameters at least include pile diameter, pile length, and pile material properties; S2. The lateral pile-soil interaction of steel angle piles in submarine hybrid pile foundations in complex layered sea-soil environment was analyzed using the finite difference method. Based on the collected data, a mathematical model was established using the finite difference method to simulate the pile-soil interaction under different conditions. S3. Set reasonable boundary conditions and initial conditions according to the actual engineering situation to ensure that the model can accurately reflect the actual situation; S4. Use computer software to perform numerical calculations of the above model to obtain the stress state and deformation of the corner piles under different working conditions. Then, analyze the calculation results in detail, evaluate the safety, stability and economy of the pile foundation, and put forward optimization suggestions.

2. The method for analyzing the geotechnical stress of angle piles in a submarine hybrid foundation according to claim 1 is characterized by: In S2, the finite difference method is used to analyze the lateral pile-soil interaction of the steel angle piles in the submarine hybrid pile foundation in the complex layered sea soil environment. The specific steps are as follows: S21. Establish the differential equation of the angular pile deflection based on the mechanical relationship; S22. Based on the design characteristics of the angle piles of the submarine hybrid foundation in engineering practice, the flexural differential equation is further refined; S23, using the finite difference method to differentiate the refined corner pile deflection differential equation; S24, using the Glesser algorithm to process the differential equations, and obtain the expression of the lateral deformation of the segmented pile length; S25, make an initial assumption about the secant modulus of the foundation reaction at each depth, substitute it into the expression and solve it, and obtain a set of lateral deformations of the corner piles; S26, calculating the py curve corresponding to each node depth of the corner pile according to the property parameters of each layer of sea soil, and substituting the obtained lateral deformation into the py curve to obtain a new foundation reaction secant modulus; S27, obtaining the secant modulus within the allowable accuracy range through iterative calculation; S28. Calculate and obtain the lateral deformation of the corner pile at each depth and the lateral force acting on the rock and soil.

3. The method for analyzing the geotechnical stress of angle piles in a submarine hybrid foundation according to claim 2 is characterized by: The S21 is specifically as follows: Wherein, E is the elastic modulus of the corner pile material; I is the moment of inertia of the corner pile section; z is the depth below the seabed mud surface where the corner pile microelement is located; y is the deflection at the corner pile microelement; N is the axial force at the corner pile microelement; p is the foundation reaction force per unit area at the corner pile microelement; and D is the outer diameter of the corner pile at the corner pile microelement.

4. The method for analyzing rock and soil stress of angle piles in a submarine hybrid foundation according to claim 3 is characterized by: The refined flexural differential equation in S22 is as follows: Where I(z) is the moment of inertia of the section taking into account the depth variation; N(z) is the axial force on the corner pile at position z; and p(z,y) is the foundation reaction per unit area that depends on the depth z and the deflection y of the corner pile at that position.

5. The method for analyzing the geotechnical stress of angle piles in a submarine hybrid foundation according to claim 4, characterized in that: The refined flexural differential equation in S22 is: Wherein, t1 is the wall thickness of the corner pile in the interval z≤z1; t2 is the wall thickness of the corner pile in the interval z1≤z≤z2; z1 is the first depth; z2 is the second depth; Among them, N t is the initial axial force at the top of the corner pile; W(z) is the weight per unit length of the corner pile; F skin (z) is the friction between the corner pile and the surrounding soil; m for a specific depth; Wherein, W1 is the pile weight per unit length of the upper wall thickness t1 portion of the corner pile; W2 is the pile weight per unit length of the lower wall thickness t2 portion of the corner pile; Among them, α z is the friction angle coefficient between soil and corner pile; c uz is the undrained shear strength of the soil; A z is the surface area of ​​the corner pile in contact with the soil at depth z; l z is the contact length of the corner pile at depth z.

6. The method for analyzing the geotechnical stress of angle piles in a submarine hybrid foundation according to claim 5, characterized in that: The S23 uses the finite difference method to differentiate the refined corner pile deflection differential equation, which is as follows: TO i and i+2 +B i and i+1 +C i and i +D i and i-1 +E i and i-2 =0; Among them, y i+2 is the lateral deflection of the i+2th microelement segment; y i+1 is the lateral deflection of the i+1th microelement segment; y i-1 is the lateral deflection of the i-1th microelement segment; y i-2 is the lateral deflection of the i-2th microelement segment; TO i =E·I i+1 ; B i =-2E·I i+1 -2E·I i +N i ·(Δl) 2 ; C i =E·I i+1 +4E I i +E·I i-1 -2N i ·(Δl) 2 +D i ·(E s ) i ·(Δl) 4 ; D i =−2E·I i -2E·I i-1 +2N i ·(Δl) 2 ; E i =E·I i-1 ; Among them, I i+1 is the section inertia moment of the i+1th infinitesimal segment; I i is the section inertia moment of the i-th microelement segment; I i-1 is the section inertia moment of the i-1th infinitesimal segment; N i is the axial force of the ith microelement segment; Δl is; D i is the secant modulus of foundation reaction; (E s ) i is the secant modulus of the foundation reaction of the i-th microelement segment; Boundary conditions at the free end of the pile bottom: Q n ＝0； M n ＝0； Boundary conditions at the fixed end of the pile top: Q0=H0; M0＝0； Among them, Q n is the shear force; M n is the bending moment; H0 is a constant, representing the lateral shear force.

7. The method for analyzing the geotechnical stress of angle piles in a submarine hybrid foundation according to claim 6, characterized in that: In S24, the differential equation group is processed to obtain an expression for the lateral deformation of the segmented pile length, which is as follows: Divide the pile into n micro-element segments, and the length of each micro-element segment is Δz. Then the discretized difference equation is: Among them, y i is the lateral deformation of the ith microelement segment; z i is the depth of the ith microelement segment; p(z i ,y i ) is the ultimate lateral bearing capacity.

8. The method for analyzing the geotechnical stress of angle piles in a submarine hybrid foundation according to claim 7, characterized in that: The S25 makes an initial assumption on the foundation reaction secant modulus at each depth, as follows: Assume that the initial foundation reaction secant modulus k s,i is a constant: Among them, k s,i is the secant modulus of the initial foundation reaction force; c is the cohesion of the soil; γ is the density of the soil; J is the lateral pressure coefficient of the soil; y c =2.5∈ c ·D; Among them, y c is the critical lateral deformation; ∈ c is the critical strain, indicating that under this strain, the foundation reaction reaches the limit value; The initial assumption k s Substitute this into the difference equation and solve for y i .

9. The method for analyzing rock and soil stress of angle piles in a submarine hybrid foundation according to claim 8, characterized in that: The S26 is specifically as follows: Among them, z R is the critical depth; Update the secant modulus of foundation reaction: Among them, k s,i ′ is the updated secant modulus of foundation reaction.

10. The method for analyzing the geotechnical stress of angle piles in a submarine hybrid foundation according to claim 9, characterized in that: The iterative solution in S27 is based on repeating the steps of S25 and S26 until the lateral deformation y of all micro-element segments is i Convergence means that the deformation change between two adjacent iterations is less than a preset minimum value ∈.

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