A calculation method for thermal-mechanical coupling response of variable-stiffness energy pile groups

Abstract

The present invention relates to the technical field of thermal coupling response calculation, specifically disclosing a method for calculating the thermal coupling response of a variable-stiffness energy pile group. The method is implemented by the following technical steps: first, selecting a load transfer model that simulates pile-soil nonlinear interaction and determining an equal-stiffness energy pile group algorithm; second, determining the type of the variable-stiffness energy pile group (variable pile diameter, variable pile length), calculating the pile-side and pile-end soil elastic displacement interaction factors considering pile-pile interaction, and determining the pile-soil interaction model of the variable-stiffness energy pile group; then, determining the pile-side and pile-end soil interaction model parameters; and finally, substituting the pile-side and pile-end soil interaction models of the variable-stiffness energy pile group into the equal-stiffness energy pile group algorithm to calculate the thermal coupling response of the variable-stiffness energy pile group. The present invention has a simple principle, is easy to use, and can provide a method and theoretical basis for improving and enriching the thermal coupling calculation method of energy piles.

Description

Technical Field

[0001] The present invention relates to the technical field of thermal-mechanical coupling response calculation, and in particular to a method for calculating the thermal-mechanical coupling response of a variable-rigidity energy pile group. Background Art

[0002] Pile foundations are a cost-effective deep foundation method capable of controlling both overall and differential settlement. Currently, conventional pile foundation designs often employ a uniform stiffness design, where individual piles within a pile group have identical lengths, diameters, and material properties. While this design is convenient and easy to implement, it fails to accurately reflect the actual load conditions of the pile group, resulting in significant differential settlement and a serious threat to the service life of the foundation and superstructure.

[0003] To address the problems associated with the design of pile groups with equal stiffness, the Technical Specifications for Building Pile Foundations proposes a variable stiffness leveling design concept. By using pile foundations with varying stiffness, the overall stiffness of the pile group is increased to offset the uneven stiffness distribution caused by the pile group effect, thereby effectively controlling differential settlement of the pile group. For example, in deep soft or compressible soil layers, the raft's contribution to the long-term stiffness of the foundation gradually decreases, necessitating increased pile stiffness to improve the stress characteristics of the foundation and superstructure. Furthermore, for flexible rafts and rafts subjected to uneven loads, increasing the diameter or length of the piles in the pile group to increase stiffness is a necessary measure for controlling differential settlement of the pile group.

[0004] In recent years, energy piles, a derivative of traditional building pile foundations, have become an important green geotechnical engineering technology in the context of the dual-carbon era. They combine heat exchange tubes with pile foundations, providing both load-bearing and heat-exchange functions. Since the application of energy piles requires that the load-bearing properties of the pile foundation not be compromised, their pile group layout inevitably resembles that of traditional building pile foundations. Variable-stiffness energy pile group layouts are particularly applicable for conditions requiring strict control of differential settlement. In the thermal-mechanical coupling design of energy piles, the load transfer method, with its simple concept and ease of use, effectively simulates the nonlinear load transfer mechanism of pile-soil interaction and has been widely used. However, existing research has focused on the thermal-mechanical coupling characteristics of energy pile groups with constant stiffness. Calculation methods for the thermal-mechanical coupling response of variable-stiffness energy pile groups remain lacking, creating a gap in the field of energy pile technology.

[0005] Furthermore, compared to traditional variable-stiffness pile groups, the response mechanism of variable-stiffness energy pile groups is more complex. Specifically, the response of variable-stiffness energy pile groups must account for the effects of thermal loads on the interaction between the energy piles and soil within the pile group. Furthermore, the deformation and stress response characteristics of the energy piles and the surrounding soil under thermal-mechanical coupling must be considered, as well as the complex coupling effects between piles and soil, and between piles, rafts, and soil. Therefore, traditional calculation methods for the response of variable-stiffness energy pile groups are unable to assess the interaction and thermal-mechanical coupling responses of variable-stiffness energy pile groups, necessitating the development of new calculation methods to address this gap. Summary of the Invention

[0006] To solve the problems existing in the prior art, the present invention provides a method for calculating the thermal-mechanical coupling response of variable-stiffness energy pile groups by analyzing the interactions between piles-soil, piles-raft-soil, and piles-piles in variable-stiffness energy pile groups. This method can quickly evaluate the thermal-mechanical coupling performance and solve the problems mentioned in the above background technology.

[0007] To achieve the above object, the present invention provides the following technical solution: a method for calculating the thermal-mechanical coupling response of a variable-stiffness energy pile group, comprising the following steps:

[0008] S1. Select a load transfer model to simulate the pile-soil nonlinear interaction and determine the algorithm for equal stiffness energy pile groups;

[0009] S2. Determine the type of the variable stiffness energy pile group, calculate the pile side-soil elastic displacement interaction factor considering the pile-pile interaction, and determine the pile side-soil interaction model of the variable stiffness energy pile group;

[0010] S3. Determine the type of the variable stiffness energy pile group, calculate the pile tip-soil elastic displacement interaction factor considering the pile-pile interaction, and determine the pile tip-soil interaction model of the variable stiffness energy pile group;

[0011] S4. Determine the pile side- and pile tip-soil interaction model parameters;

[0012] S5. Substitute the pile side- and pile tip-soil interaction models of the variable stiffness energy pile group into the equal stiffness energy pile group algorithm to calculate the thermal-mechanical coupling response of the variable stiffness energy pile group.

[0013] Preferably, in step S1, the pile-soil relative displacement consists of two parts: nonlinear displacement and elastic displacement; the nonlinear displacement is calculated by a load transfer model, and the elastic displacement is obtained by the relevant principles of the shear displacement method.

[0014] Preferably, the load transfer model is an exponential model, a hyperbola model, a double-broken-line model, a triple-broken-line model or an ideal elastic-plastic model.

[0015] Preferably, in step S2, the following steps are specifically included:

[0016] S21. If the variable stiffness energy pile group is of variable diameter type, the pile side-soil elastic displacement interaction factor only considers the replacement of the pile diameter, thus obtaining the pile side-soil interaction model of the variable stiffness energy pile group.

[0017] S22. If the variable stiffness energy pile group type is a variable pile length type energy pile group, then the pile side-soil elastic displacement interaction factor of any long pile in the pile group should take into account the following six factors: 1) axial displacement caused by the load on itself; 2) displacement increment caused by other long piles in the pile group that are within the influence range of the shear radius; 3) displacement reduction caused by the "reinforcement-curtain" effect of other long piles in the pile group that are within the influence range of the shear radius; 4) displacement increment caused by other short piles in the pile group that are within the influence range of the shear radius; 5) displacement reduction caused by the "reinforcement-curtain" effect of other short piles in the pile group that are within the influence range of the shear radius; 6) displacement increment caused by the pile ends of other short piles in the pile group that are within the influence range of the shear radius; thus, the pile side-soil interaction model of the variable stiffness energy pile group is obtained;

[0018] S23. If the variable stiffness energy pile group type is a variable pile length type energy pile group, the pile side-soil elastic displacement interaction factor of any short pile in the pile group should consider the following five factors: 1) the axial displacement caused by the load on itself; 2) the displacement increment caused by other short piles in the pile group that are within the influence of the shear radius; 3) the displacement reduction caused by the "reinforcement-curtain" effect of other short piles in the pile group that are within the influence of the shear radius; 4) the displacement increment caused by other long piles in the pile group that are within the influence of the shear radius; 5) the displacement reduction caused by the "reinforcement-curtain" effect of other long piles in the pile group that are within the influence of the shear radius; that is, the pile side-soil interaction model of the variable stiffness energy pile group is obtained.

[0019] Preferably, in step S3, the following steps are specifically included:

[0020] S31. If the variable stiffness energy pile group is a variable diameter type energy pile group, then the pile tip-soil elastic displacement interaction factor only considers the replacement of the pile diameter, thus obtaining the pile tip-soil interaction model of the variable stiffness energy pile group;

[0021] S32. If the variable stiffness energy pile group is a variable length type energy pile group, then the pile tip-soil elastic displacement interaction factor of any length pile in the pile group only considers the axial displacement caused by the load on the pile itself, thus obtaining the pile tip-soil interaction model of the variable stiffness energy pile group;

[0022] S33. If the variable stiffness energy pile group type is a variable pile length type energy pile group, then the pile tip-soil elastic displacement interaction factor of any short pile in the pile group should consider the following two factors: 1) the pile tip displacement caused by the load it bears itself; 2) the reduction in pile tip displacement of other long piles in the pile group that are within the influence range of the shear radius due to the "reinforcement-curtain" effect; that is, the pile tip-soil interaction model of the variable stiffness energy pile group is obtained.

[0023] Preferably, in step S4, the model parameters include 1) pile-soil interface shear strength; 2) pile side-soil initial shear stiffness; 3) pile tip ultimate strength; 4) pile tip-soil interaction initial stiffness; 5) pile-raft contact stiffness.

[0024] Preferably, in step S5, the algorithm for equal stiffness energy pile groups is similar in structure to the general energy pile load transfer algorithm, except that the elastic displacement interaction factor between equal stiffness energy piles is taken into account. The algorithm for equal stiffness energy pile groups specifically includes the following steps:

[0025] S51. Select the load transfer model and pile top contact stiffness to simulate the pile-soil nonlinear interaction.

[0026] S52. Calculate the pile side- and pile tip-soil elastic displacement interaction factors considering pile-pile interaction;

[0027] S53. Determine the pile-side and pile-tip-soil interaction models for equal stiffness energy pile groups;

[0028] S54, determining pile side- and pile tip-soil interaction model parameters;

[0029] S55. Substitute the pile side- and pile tip-soil interaction models of the equal-stiffness energy pile group into the energy pile single-pile thermal-mechanical coupling algorithm to obtain the equal-stiffness energy pile group thermal-mechanical coupling response.

[0030] The present invention has the following beneficial effects: The method for calculating the thermal-mechanical coupling response of variable-stiffness energy pile groups can calculate the magnitude and distribution of coupled stress, strain, and displacement in variable-stiffness energy pile groups with different pile diameters and lengths. It also considers the "reinforcement-shading" effect between variable-stiffness energy piles within the group, as well as the pile group effect. The method is simple in principle and easy to use, providing a methodology and theoretical basis for improving and enriching thermal-mechanical coupling calculation methods for energy piles. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Flowchart of the method for calculating the thermal-mechanical coupling response of variable-stiffness energy pile groups in an embodiment of the present invention;

[0032] Figure 2 This is a flow chart of the algorithm for medium-rigidity energy pile groups in an embodiment of the present invention;

[0033] Figure 3 This is a schematic diagram of a variable stiffness energy pile group case in an embodiment of the present invention;

[0034] Figure 4 1. It is a schematic diagram of finite element simulation parameters in a verification case of a variable stiffness energy pile group according to an embodiment of the present invention;

[0035] Figure 5 1. Parameter diagram of the calculation method of the present invention in a verification case of a variable stiffness energy pile group in an embodiment of the present invention;

[0036] Figure 6 1 is a comparison diagram of the calculation and simulation results of the variable stiffness energy pile group in the embodiment of the present invention, (a) is the comparison of the axial thermal stress of the long piles in the pile group; (b) is the comparison of the axial thermal stress of the short piles; (c) is the comparison of the axial thermal stress of the energy piles with larger diameters; and (d) is the comparison of the axial thermal stress of the energy piles with smaller diameters. DETAILED DESCRIPTION

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. 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 making creative efforts are within the scope of protection of the present invention.

[0038] In the method for calculating the thermal-mechanical coupling response of variable-rigidity energy pile groups of the present invention, the following basic assumptions are made: 1) the load transfer model parameters, the thermal physical and mechanical properties of the pile body material and the surrounding soil do not change with temperature. Existing studies have shown that within the temperature variation range of 15 to 20°C during the operation of the energy pile, the properties of the pile body concrete and the soil hardly change; 2) Existing studies have shown that the radial deformation of the pile and the pile side normal stress under the action of thermal-mechanical coupling have little effect on the change in the mechanical properties of the pile body. Therefore, the study mainly considers the influence of the axial deformation of the pile; 3) the stress and strain of the pile body are compressive and positive, the upward frictional resistance is positive, and the upward displacement of the pile body is positive; 4) the cross-sectional geometry, physical and mechanical properties and temperature changes of the pile body are uniformly distributed along the pile body.

[0039] See also Figure 1 The present invention provides a technical solution: a method for calculating the thermal-mechanical coupling response of variable-stiffness energy pile groups. Based on the above basic assumptions, the specific implementation steps are as follows:

[0040] (1) Select a load transfer model to simulate the nonlinear interaction between piles and soil and determine the algorithm for equal stiffness energy pile groups;

[0041] (2) Determine the type of variable stiffness energy pile group (variable pile diameter, variable pile length), calculate the pile side-soil elastic displacement interaction factor considering the pile-pile interaction, and determine the pile side-soil interaction model of the variable stiffness energy pile group;

[0042] (3) Determine the type of variable stiffness energy pile group (variable pile diameter, variable pile length), calculate the pile tip-soil elastic displacement interaction factor considering the pile-pile interaction, and determine the pile tip-soil interaction model of the variable stiffness energy pile group;

[0043] (4) Determine the pile side- and pile tip-soil interaction model parameters;

[0044] (5) The pile side- and pile end-soil interaction models of the variable stiffness energy pile group are substituted into the equal stiffness energy pile group algorithm to calculate the thermal-mechanical coupling response of the variable stiffness energy pile group.

[0045] In the step (1), the relative displacement between pile and soil consists of two parts: nonlinear displacement and elastic displacement. The specific calculation method is as follows: nonlinear displacement can be calculated by load transfer model, including but not limited to exponential model, hyperbola model, bilinear model, trilinear model, ideal elastic-plastic model, etc.; elastic displacement can be obtained by the relevant principles of shear displacement method; the algorithm of equal stiffness energy pile group is similar to the general energy pile load transfer algorithm in structure, the difference is that the elastic displacement interaction factor between equal stiffness energy piles is considered. The steps of the equal stiffness energy pile group algorithm are as follows: Figure 2 As shown, specifically:

[0046] 1) Select the load transfer model and pile top contact stiffness to simulate the pile-soil nonlinear interaction.

[0047] 2) Calculate the pile side- and pile tip-soil elastic displacement interaction factors considering pile-pile interaction, as shown in Equations (1) and (2), respectively:

[0048]

[0049] Where: G is the shear modulus of the soil around the pile; r0 is the pile diameter; r m is the shear influence radius; r ij G is the axial distance between the piles and adjacent piles in the pile group; b is the shear modulus of soil at the pile tip; ν b is the Poisson's ratio of the soil at the pile tip.

[0050] 3) Determine the pile-side and pile-tip-soil interaction models for the equal-stiffness energy pile group. Preferably, taking the exponential model as an example, the pile-side and pile-tip-soil interaction models are respectively expressed as Equations (3) and (4).

[0051]

[0052]

[0053] Where: u s is the sum of the nonlinear displacement and elastic displacement of the soil at the pile side; u s0 and τ s0 are the total displacement and shear stress of the pile side at the unloading point or reloading point respectively; η is the loading and unloading state judgment factor; τ su is the shear strength of the soil at the pile side; G s,max is the initial shear stiffness of the pile side-soil; τ si is the pile side shear stress; u p is the sum of the nonlinear displacement and elastic displacement of the pile end; u p0 and τ b0 are the total displacement and shear stress of the pile tip at the unloading point or reloading point, respectively; G b,max Initial stiffness of pile tip-soil interaction; κ is the loading and unloading state judgment factor; τ bu is the ultimate end resistance; τ bi Pile tip resistance.

[0054] 4) Determine the parameters of the pile-side and pile-tip-soil interaction model. These key parameters include the pile-soil interface shear strength, pile-side-soil initial shear stiffness, pile-tip ultimate strength, pile-tip-soil initial stiffness, and pile-raft contact stiffness. These parameters can be determined using field test results, unit test results, and corresponding empirical formulas.

[0055] 5) The pile side- and pile end-soil interaction models of equal stiffness energy pile groups are substituted into the thermal-mechanical coupling algorithm of energy piles to obtain the thermal-mechanical coupling response of equal stiffness energy pile groups.

[0056] The specific implementation method of step (2) is as follows: if it is a type of energy pile group with variable pile diameter, then its elastic displacement interaction factor is similar to the expression of the energy pile group with equal stiffness, and only the corresponding pile diameter needs to be replaced; if it is a type of energy pile group with variable pile length, then the pile side-soil elastic displacement interaction factor of any long pile in the pile group needs to consider six factors: 1) the axial displacement caused by the load on itself; 2) the displacement increment caused by other long piles in the pile group that are within the influence range of the shear radius; 3) the displacement reduction caused by the "reinforcement-curtain" effect of other long piles in the pile group that are within the influence range of the shear radius; 4) the displacement increment caused by other short piles in the pile group that are within the influence range of the shear radius; 5) the displacement reduction caused by the "reinforcement-curtain" effect of other short piles in the pile group that are within the influence range of the shear radius; 6) the displacement increment caused by the pile ends of other short piles in the pile group that are within the influence range of the shear radius.

[0057] like Figure 3As shown in the figure, taking a 1×4 variable stiffness energy pile group as an example, the axial displacement caused by any long pile in the pile group under its own load is:

[0058]

[0059] 2) displacement increment caused by other long piles in the pile group that are within the influence range of the shear radius;

[0060]

[0061] The displacement reduction of other long piles in the pile group within the influence range of the shear radius due to the “reinforcement-curtain” effect is:

[0062]

[0063] The displacement increment caused by other short piles in the pile group within the influence range of the shear radius is:

[0064]

[0065] The displacement reduction of other short piles in the pile group within the influence range of the shear radius due to the “reinforcement-curtain” effect is:

[0066]

[0067] The displacement increment caused by the pile tips of other short piles in the pile group within the influence range of the shear radius is:

[0068]

[0069] Then the pile side-soil elastic displacement interaction factor of any long pile in the pile group is:

[0070]

[0071] The pile-soil elastic displacement interaction factor of any short pile in a pile group needs to consider five factors: 1) the axial displacement caused by the load on the pile itself; 2) the displacement increment caused by other short piles in the pile group that are within the influence of the shear radius; 3) the displacement reduction caused by the "reinforcement-curtain" effect of other short piles in the pile group that are within the influence of the shear radius; 4) the displacement increment caused by other long piles in the pile group that are within the influence of the shear radius; 5) the displacement reduction caused by the "reinforcement-curtain" effect of other long piles in the pile group that are within the influence of the shear radius.

[0072] like Figure 3 As shown in the figure, taking a 1×4 variable stiffness energy pile group as an example, the axial displacement caused by any short pile in the pile group under its own load is:

[0073]

[0074] The displacement increment caused by other short piles in the pile group that are within the influence range of the shear radius is:

[0075]

[0076] The displacement reduction of other short piles in the pile group within the influence range of the shear radius due to the “reinforcement-curtain” effect is:

[0077]

[0078] The displacement increment caused by other long piles in the pile group within the influence range of the shear radius is:

[0079]

[0080] The displacement reduction of other long piles in the pile group within the influence range of the shear radius due to the “reinforcement-curtain” effect is:

[0081]

[0082] Then the pile side-soil elastic displacement interaction factor of any short pile in the pile group is:

[0083]

[0084] Combined with the exponential model, the pile-soil interaction model of variable stiffness energy pile groups is:

[0085]

[0086] According to the type of variable stiffness pile group, it is necessary to replace ψ with ψ siL or ψ siS .

[0087] The specific implementation method of step (3) is as follows: if the energy pile group is of variable pile diameter type, then its elastic displacement interaction factor is similar to the expression of the equal stiffness energy pile group, and only the corresponding pile diameter needs to be replaced; if the energy pile group is of variable pile length type, then the pile tip-soil elastic displacement interaction factor of any long pile in the pile group needs to take into account the axial displacement caused by the load on the pile itself;

[0088] The pile tip-soil elastic displacement interaction factor of any short pile in a pile group needs to consider two factors: 1) the pile tip displacement caused by the pile's own load; and 2) the reduction in pile tip displacement caused by the "reinforcement-curtain" effect of other long piles in the pile group that are within the influence range of the shear radius.

[0089] like Figure 3As shown in the figure, taking a 1×4 variable stiffness energy pile group as an example, the axial displacement caused by any short pile in the pile group under its own load is:

[0090]

[0091] The reduction in pile tip displacement of other long piles in the pile group within the shear radius due to the “reinforcement-curtain” effect is:

[0092]

[0093] Then the pile tip-soil elastic displacement interaction factor of any short pile in the pile group is:

[0094]

[0095] The pile tip-soil interaction model of variable stiffness energy pile groups is:

[0096]

[0097] According to the type of variable stiffness pile group, λ in the formula needs to be replaced accordingly.

[0098] The parameter determination method in step (4) is similar to that of the equal-stiffness energy pile group. Taking the exponential model as an example, the main parameters include the shear strength of the pile-soil interface, the initial shear stiffness of the pile side-soil, the ultimate strength of the pile end, the initial stiffness of the pile end-soil interaction, and the pile-raft contact stiffness, which can be determined through field test results, unit test results and corresponding empirical formulas.

[0099] The present invention verifies the reliability and effectiveness of the proposed method in analyzing the thermal-mechanical coupling response of variable-stiffness energy pile groups through finite element simulation cases, and the cases include two working conditions. In working condition one, the pile group consists of two 20m-long energy piles and two 30m-long energy piles, both with a pile diameter of 0.6m and a pile spacing of 1.8m; in working condition two, the pile group consists of two energy piles with a pile diameter of 0.6m and two energy piles with a pile diameter of 0.8m, both with a pile length of 20m and a pile spacing of 1.8m. Under both working conditions, it is assumed that there is no mechanical load on the pile top, the pile-raft contact stiffness is zero, and the temperature load is 10 and 30°C. The calculation parameters of the finite element simulation and the method proposed in the present invention are as follows, respectively. Figure 4 and 5 shown.

[0100] described Figure 6 Comparison between the calculation results of the method proposed in this invention and the finite element simulation results. Figure 6 In the figure, (a) is the comparison of axial thermal stress of long piles in pile group; (b) is the comparison of axial thermal stress of short piles; (c) is the comparison of axial thermal stress of energy piles with larger diameter; (d) is the comparison of axial thermal stress of energy piles with smaller diameter. Figure 6It can be found that under different thermal loads, the calculation results and simulation results maintain good consistency, which proves the effectiveness and reliability of the invented method in calculating the thermal-mechanical coupling response of variable stiffness energy pile groups.

[0101] In the embodiments provided by the embodiments of the present invention, the method embodiments described above are merely illustrative. For example, the flowcharts and block diagrams in the accompanying drawings show the possible architectures, functions, and operations of the methods and computer program products according to multiple embodiments of the present invention. In this regard, each box in the flowchart or block diagram can represent a module, a program segment, or a portion of code, and the module, program segment, or a portion of code contains one or more executable instructions for implementing the specified logical functions. It should also be noted that in some alternative implementations, the functions marked in the box can also occur in an order different from that marked in the accompanying drawings. For example, two consecutive boxes can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram and / or flowchart, and the combination of boxes in the block diagram and / or flowchart, can be implemented using a dedicated hardware-based system that performs the specified function or action, or can be implemented using a combination of dedicated hardware and computer instructions.

[0102] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The singular forms "a", "an", "the" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms unless the context clearly indicates otherwise.

[0103] It should be understood that the term "and / or" as used herein is merely a description of the relationship between associated objects, indicating that three possible relationships exist. For example, "A and / or B" can represent: A exists alone, A and B exist simultaneously, or B exists alone. Furthermore, the character " / " in this document generally indicates that the associated objects are in an "or" relationship.

[0104] The word "if," as used herein, may be interpreted as "at the time of" or "when" or "in response to determining" or "in response to detecting," depending on the context. Similarly, the phrases "if it is determined" or "if (stated condition or event) is detected" may be interpreted as "when it is determined" or "in response to the determination" or "when detecting (stated condition or event)" or "in response to detecting (stated condition or event)," depending on the context.

[0105] The references to "first" and "second" in the embodiments merely distinguish similar objects and do not represent a specific ordering of the objects. It is understood that the specific order or precedence of "first" and "second" can be interchanged where appropriate. It should be understood that the objects distinguished by "first" and "second" can be interchanged where appropriate, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein.

[0106] Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for calculating the thermal-mechanical coupling response of variable stiffness energy pile groups, characterized in that: The steps include: S1. Select a load transfer model to simulate the pile-soil nonlinear interaction and determine the algorithm for equal stiffness energy pile groups; S2. Determine the type of the variable stiffness energy pile group, calculate the pile side-soil elastic displacement interaction factor considering the pile-pile interaction, and determine the pile side-soil interaction model of the variable stiffness energy pile group; specifically, the steps include: S21. If the variable stiffness energy pile group is of variable diameter type, the pile side-soil elastic displacement interaction factor only considers the replacement of the pile diameter, thus obtaining the pile side-soil interaction model of the variable stiffness energy pile group. S22. If the variable stiffness energy pile group type is a variable pile length type energy pile group, then the pile side-soil elastic displacement interaction factor of any long pile in the pile group shall take into account the following six factors: 1) the axial displacement caused by the load on the pile itself; 2) the displacement increment caused by other long piles in the pile group that are within the influence range of the shear radius; 3) the displacement reduction caused by the "reinforcement-curtain" effect of other long piles in the pile group that are within the influence range of the shear radius; 4) the displacement increment caused by other short piles in the pile group that are within the influence range of the shear radius; 5) the displacement reduction caused by the "reinforcement-curtain" effect of other short piles in the pile group that are within the influence range of the shear radius; 6) the displacement increment caused by the pile tips of other short piles in the pile group that are within the influence range of the shear radius; thus, the pile side-soil interaction model of the variable stiffness energy pile group is obtained; S23. If the variable stiffness energy pile group type is a variable pile length type energy pile group, then the pile side-soil elastic displacement interaction factor of any short pile in the pile group shall take into account the following five factors: 1) the axial displacement caused by the load on the pile itself; 2) the displacement increment caused by other short piles in the pile group that are within the influence range of the shear radius; 3) the displacement reduction caused by the "reinforcement-curtain" effect of other short piles in the pile group that are within the influence range of the shear radius; 4) the displacement increment caused by other long piles in the pile group that are within the influence range of the shear radius; 5) the displacement reduction caused by the "reinforcement-curtain" effect of other long piles in the pile group that are within the influence range of the shear radius; thus, the pile side-soil interaction model of the variable stiffness energy pile group is obtained; S3. Determine the type of the variable stiffness energy pile group, calculate the pile tip-soil elastic displacement interaction factor considering the pile-pile interaction, and determine the pile tip-soil interaction model of the variable stiffness energy pile group; S4. Determine the pile side- and pile tip-soil interaction model parameters; S5. Substituting the pile side- and pile tip-soil interaction models of the variable stiffness energy pile group into the equal stiffness energy pile group algorithm to calculate the thermal-mechanical coupling response of the variable stiffness energy pile group; The specific steps of the equal stiffness energy pile group algorithm include: S51. Select the load transfer model and pile top contact stiffness to simulate the pile-soil nonlinear interaction. S52. Calculate the pile side- and pile tip-soil elastic displacement interaction factors considering pile-pile interaction; S53. Determine the pile-side and pile-tip-soil interaction models for equal stiffness energy pile groups; S54, determining pile side- and pile tip-soil interaction model parameters; S55. Substitute the pile side- and pile tip-soil interaction models of the equal-stiffness energy pile group into the energy pile single-pile thermal-mechanical coupling algorithm to obtain the equal-stiffness energy pile group thermal-mechanical coupling response.

2. The method for calculating the thermal-mechanical coupling response of variable-rigidity energy pile groups according to claim 1 is characterized by: In step S1, the pile-soil relative displacement consists of two parts: nonlinear displacement and elastic displacement; the nonlinear displacement is calculated by the load transfer model, and the elastic displacement is obtained by the relevant principles of the shear displacement method.

3. The method for calculating the thermal-mechanical coupling response of variable-rigidity energy pile groups according to claim 2 is characterized by: The load transfer model is an exponential model, a hyperbola model, a double-broken-line model, a three-broken-line model or an ideal elastic-plastic model.

4. The method for calculating the thermal-mechanical coupling response of variable-stiffness energy pile groups according to claim 1 is characterized by: In step S3, the following steps are specifically included: S31. If the variable stiffness energy pile group is a variable diameter type energy pile group, then the pile tip-soil elastic displacement interaction factor only considers the replacement of the pile diameter, thus obtaining the pile tip-soil interaction model of the variable stiffness energy pile group; S32. If the variable stiffness energy pile group is a variable length type energy pile group, then the pile tip-soil elastic displacement interaction factor of any length pile in the pile group only considers the axial displacement caused by the load on the pile itself, thus obtaining the pile tip-soil interaction model of the variable stiffness energy pile group; S33. If the variable stiffness energy pile group type is a variable pile length type energy pile group, then the pile tip-soil elastic displacement interaction factor of any short pile in the pile group should consider the following two factors: 1) the pile tip displacement caused by the load it bears; 2) the reduction in pile tip displacement caused by the "reinforcement-curtain" effect of other long piles in the pile group that are within the influence range of the shear radius; that is, the pile tip-soil interaction model of the variable stiffness energy pile group is obtained.

5. The method for calculating the thermal-mechanical coupling response of variable-stiffness energy pile groups according to claim 1 is characterized by: In step S4, the model parameters include 1) pile-soil interface shear strength; 2) pile side-soil initial shear stiffness; 3) pile tip ultimate strength; 4) pile tip-soil interaction initial stiffness; 5) pile-raft contact stiffness.

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