A non-saturated soil energy pile heat-water-force multi-field coupling response calculation method

Abstract

The application provides a non-saturated soil energy pile heat-water-force multi-field coupling response calculation method, comprising the following steps: S1, determining a saturated soil energy pile load transmission algorithm; S2, determining a soil water characteristic curve model considering temperature effect; S3, calculating energy pile-non-saturated soil interface shear strength considering matrix suction contribution; S4, calculating pile end ultimate resistance considering temperature load and non-saturated condition coupling effect; S5, calculating pile surrounding soil shear modulus considering temperature load and non-saturated condition coupling effect; S6, calculating energy pile-raft contact stiffness; and S7, calculating non-saturated soil energy pile heat-water-force multi-physical field coupling response. The application aims to reveal the energy pile bearing mechanism under the comprehensive action of temperature load and non-saturated soil condition, and provide theoretical and method support for non-saturated soil energy pile analysis and design.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of geothermal energy, the technical field of energy pile in unsaturated soil, and particularly relates to a method for calculating the thermal-water-mechanical multi-field coupling response of an energy pile in unsaturated soil. BACKGROUND

[0002] Pile foundation can transfer the load of the upper building to the deep soil, and can also effectively control the uneven settlement of the upper building, and is widely used in geotechnical engineering practice. Reasonably and accurately calculating the bearing response of the pile foundation is the key to the geotechnical engineering design of the pile foundation. At present, the most widely used method for calculating the bearing response in the field of pile foundation research is mainly for the saturated soil condition, which assumes that the soil around the pile is in a dry or saturated state, and only considers the interaction between the pile and the dry / saturated soil in the analysis process. With the gradual deepening of people's understanding of unsaturated soil, the bearing response of the pile foundation in unsaturated soil has also attracted more and more attention. For example, Georgiadis et al. (2003) studied the influence of unsaturated soil conditions on the bearing response of pile foundation through finite element analysis. Liu and Vanapalli (2019) analyzed the load-displacement response of single pile foundation in unsaturated expansive soil based on the load transfer method. Vanapalli and Taylan (2012) extended the bearing capacity method of pile foundation in saturated soil to unsaturated soil under drained and undrained conditions. The above studies show that due to the different pore fluid states and mechanical mechanisms of the soil around the pile, the bearing response of the pile foundation is significantly different in unsaturated soil and saturated soil.

[0003] With the innovation of shallow geothermal energy development technology, the traditional pile foundation gradually develops from a single bearing structure to a dual function of bearing and heat exchange, giving birth to the energy pile technology with both heat transfer and bearing functions (Brandl, 2006; Laloui et al., 2006). The energy pile technology combines heat exchange pipes with building pile foundation, which can not only bear the load of the upper building, but also efficiently develop and utilize shallow geothermal energy, and has become an important green geotechnical engineering technology. As a derivative form of traditional building pile foundation, the bearing response design of energy pile usually follows the dry and saturated soil assumption and related theory of traditional building pile foundation, ignoring its applicability in unsaturated soil conditions (for example, the natural unsaturated state caused by the low groundwater level below the pile end in semi-arid areas). In addition, the temperature change range of the energy pile during service is between 5-45℃. Studies have shown that the change of pore water viscosity-density caused by the heat exchange process of the energy pile in this temperature range will drive the soil around the pile to transform from saturated to unsaturated state, indicating that even under saturated conditions, due to the action of temperature load and the long-term heat exchange of the pile body, the saturated soil around the energy pile may also be transformed into unsaturated soil, thereby affecting the bearing response of the energy pile. In this case, if the dry / saturated soil assumption and related theory are continued to be used, it may cause significant errors in the design results of the bearing response of the energy pile.

[0004] In recent years, researchers have gradually paid attention to the bearing response of energy piles in unsaturated soils (Wang et al., 2012; Goode and McCartney, 2015). For example, in order to reasonably estimate the bearing response of energy piles in unsaturated soils, Thota et al. (2021) comprehensively considered the thermodynamic properties of unsaturated soils and pile-soil interfaces, proposed an analysis framework for estimating the change of ultimate bearing capacity of energy piles in unsaturated fine-grained soils, and verified the effectiveness of the framework by using the test data of the ultimate bearing capacity of energy piles in unsaturated Bonny silt. Based on the theory of thermodynamics, Pham and Sutman (2023) established a non-isothermal soil water characteristic curve (SWCC) model considering temperature change, and further combined the model with the bearing capacity theory to propose a simplified analysis method for the bearing capacity of energy piles in unsaturated soils. Although the above methods provide effective means for calculating the bearing response of energy piles in unsaturated soils, there are still some limitations in related research: (1) the change of pile-soil interface shear strength under the coupling action of temperature load and unsaturated state of soil around the pile is not considered, which leads to errors in the estimation of pile side friction; (2) the contribution and influence of matric suction of unsaturated soil around the pile on the bearing response of the pile are not considered; (3) only the ultimate bearing capacity of energy piles in unsaturated soils can be estimated, and the key response characteristics such as axial strain, stress, side friction and displacement of energy piles and their distribution along the pile cannot be calculated. The above limitations make the research on energy piles in unsaturated soils still face the challenges of unclear pile-unsaturated soil interface interaction mechanism and lack of bearing response calculation method. SUMMARY

[0005] The present application provides a kind of unsaturated soil energy pile heat-water-force multi-field coupling response calculation method, to reveal the bearing mechanism of energy pile under the comprehensive action of temperature load and unsaturated soil condition, provide theory and method support for the analysis and design of unsaturated soil energy pile.

[0006] To achieve the above object, the technical scheme adopted by the present application is as follows:

[0007] An unsaturated soil energy pile heat-water-force multi-field coupling response calculation method comprises:

[0008] S1. Select pile side-soil, pile end-soil load transfer model, simulate the nonlinear interaction of pile-soil, determine the load transfer algorithm of saturated soil energy pile;

[0009] S2. Select soil water characteristic curve model considering temperature effect, simulate the relationship between matric suction and saturation under different temperature loads;

[0010] S3. Calculate the horizontal stress of the unsaturated soil on the side of the pile under the action of temperature load, and combine the soil water characteristic curve model considering the temperature effect, the matrix suction, the saturation, and the effective friction angle and the cohesive force of the pile-soil interface to calculate the pile-soil interface shear strength of the energy pile considering the contribution of the matrix suction;

[0011] S4. Based on the formula for calculating the ultimate resistance of the pile end of the energy pile in the saturated soil, a contribution term of the matrix suction is introduced to calculate the ultimate resistance of the pile end considering the coupling effect of the temperature load and the unsaturated condition;

[0012] S5. Calculate the shear modulus of the soil around the pile considering the coupling effect of the temperature load and the unsaturated condition, which is used for calculating the parameters of the load transfer model of the energy pile;

[0013] S6. According to the size of the raft, the Young's modulus and the Poisson's ratio of the soil under the raft, the contact stiffness of the energy pile-raft is calculated to simulate the interaction between the energy pile and the upper building;

[0014] S7. The pile-soil interface shear strength of the energy pile considering the contribution of the matrix suction, the ultimate resistance of the pile end considering the coupling effect of the temperature load and the unsaturated condition, the shear modulus of the soil around the pile considering the coupling effect of the temperature load and the unsaturated condition, and the contact stiffness of the energy pile-raft are substituted into the load transfer algorithm of the energy pile in the saturated soil to calculate the thermal-hydraulic-mechanical multi-physical field coupling response of the energy pile in the unsaturated soil.

[0015] In the specification, the relative displacement of the energy pile-soil in the nonlinear interaction of the pile-soil in S1 is composed of the nonlinear displacement of the pile-soil shear disturbed zone and the elastic displacement of the soil in the non-disturbed zone around the pile, wherein:

[0016] The nonlinear displacement of the pile-soil shear disturbed zone is calculated by a complete elastic-plastic model, an exponential model, a hyperbolic model, a double-line model, a triple-line model, or a generalized softening model;

[0017] The elastic displacement of the soil in the non-disturbed zone around the pile is solved by the elastic theory.

[0018] In the specification, the load transfer algorithm of the energy pile in the saturated soil in S1 is specifically:

[0019] The load transfer model simulating the nonlinear interaction of the pile-soil, the contact stiffness of the pile top are selected;

[0020] The pile-side-and-pile-end-soil interaction model in the saturated or dry soil is determined, and the pile-side-and-pile-end-soil interaction model is formula (1) and (2) respectively;

[0021] (1);

[0022] (2);

[0023] In the formula, is the ultimate shear strength; is the pile side soil shear modulus; is the pile radius; is the shear influence radius; is the pile tip soil shear modulus; is the pile tip soil Poisson's ratio; is the sum of the nonlinear displacement and the elastic displacement of the pile side soil; and are the total displacement of the pile side and the shear stress of the pile side at the unloading point or the reloading point, respectively; is the unloading and loading state judgment factor; is the pile side soil shear strength; is the initial shear stiffness of the pile side-soil; is the pile side shear stress; is the sum of the nonlinear displacement and the elastic displacement of the pile tip; and are the total displacement of the pile tip and the shear stress of the pile tip at the unloading point or the reloading point, respectively; is the initial stiffness of the pile tip-soil interaction; is the unloading and loading state judgment factor; is the ultimate tip resistance; is the tip resistance;

[0024] determining the pile side-soil and the pile tip-soil interaction model parameters, including the pile-soil interface shear strength, the initial shear stiffness of the pile side-soil, the ultimate strength of the pile tip, the initial stiffness of the pile tip-soil interaction, and the pile-raft contact stiffness;

[0025] substituting the pile side-soil and the pile tip-soil interaction model of the energy pile in the saturated or dry soil into the energy pile single pile load transfer algorithm to obtain the thermal-mechanical coupling response of the energy pile in the saturated or dry soil.

[0026] In the specification, the temperature correction parameter is introduced into the model of the soil water characteristic curve in S2 without considering the temperature effect, so as to obtain the soil water characteristic curve model considering the temperature effect; the model of the soil water characteristic curve without considering the temperature effect includes two types of empirical models and theoretical models, the theoretical models include thermodynamic models and pore network models, and the empirical models include van Genuchten model, Fredlund-Xing model, Brooks-Corey model, and Gardner model.

[0027] In the specification, the van Genuchten model is used in S2, the soil water characteristic curve model considering the temperature effect and the temperature correction parameter The corresponding formulas are formula (3) and formula (4), respectively;

[0028] (3);

[0029] (4);

[0030] wherein: is the degree of saturation; is the matrix suction; and are model parameters; is the temperature; and are model coefficients.

[0031] In the present description, in the calculation process of the horizontal stress of the unsaturated soil on the side of the pile under the action of the temperature load, the energy pile is considered as a perfect elastic body, and then the volume change of the energy pile under the action of the temperature load is equations (5) and (6);

[0032] (5);

[0033] (6);

[0034] wherein: is the volume of the energy pile under the action of the temperature; is the initial volume of the energy pile; is the thermal expansion coefficient of the pile; is the temperature change; is the length of the pile; is the radius of the pile under the action of the temperature, and according to equations (5) and (6), the change of the radius of the pile under the action of the temperature load is calculated

[0035] (7);

[0036] then the horizontal stress of the energy pile-unsaturated soil interface caused by the temperature load is

[0037] (8);

[0038] is the Young's modulus of the soil;

[0039] The total horizontal stress of the energy pile-unsaturated soil interface is the sum of the effective horizontal stress of the soil on the side of the pile and the horizontal stress of the pile-soil interface caused by the temperature load as shown in equation (9);

[0040] (9);

[0041] is the effective internal friction angle of the soil; is the effective unit weight of the soil; and z is the depth. ​​

[0042] The energy pile-unsaturated soil interface shear strength The soil cohesion contribution item, the horizontal stress contribution item, and the matrix suction contribution item, as shown in equation (10):

[0043] (10);

[0044] In the formula: is the Poisson's ratio of the soil; is the effective internal friction angle of the pile-soil interface; is the effective cohesion of the pile-soil interface; is the residual saturation; is the current saturation.

[0045] In this specification, the pile tip ultimate resistance considering the coupling of temperature load and unsaturated conditions in S4 is calculated according to equation (11): The calculation formula is:

[0046] (11);

[0047] In the formula: is the effective internal friction angle of the pile tip soil; is the effective vertical stress of the pile tip soil; is the effective cohesion of the pile tip soil; is a model coefficient, calculated according to equation (12) and equation (13);

[0048] (12);

[0049] (13);

[0050] In the formula: is an adjustment coefficient; is the effective cohesion of the pile tip soil; and exp is the exponential function.

[0051] is the limit tip resistance measurement data, and the adjustment coefficient is calculated through the empirical formula (14);

[0052] (14);

[0053] In the formula: and are 1 and -0.006, respectively.

[0054] In this specification, the pile tip soil shear modulus considering the coupling of temperature load and unsaturated conditions in S5 is calculated according to equation (15) and equation (16);

[0055] (15);

[0056] (16);

[0057] where k is a model parameter; and are the Young's modulus of the soil in dry and saturated states, respectively; is the measured Young's modulus of the soil in a state between dry and saturated; is the measured saturated soil.

[0058] In the specification, the energy pile-raft contact stiffness in S6 is calculated according to formula (17):

[0059] (17);

[0060] where: and are the raft width and length, respectively; is a calculation coefficient; for layered soil, the Young's modulus and Poisson's ratio are weighted average values are calculated according to formulas (18) and (19), respectively;

[0061] (18);

[0062] (19);

[0063] where: is the thickness of the soil layer; is the Young's modulus of each layer of soil; is the Poisson's ratio of each layer of soil.

[0064] In the specification, the relationship between the Young's modulus E and the shear modulus is shown in formula (20):

[0065] (20).

[0066] In summary, the present application has at least the following beneficial effects:

[0067] The present application considers the changes in the shear strength of the pile-soil interface under the coupling of temperature load and unsaturated state of the soil around the pile, as well as the contribution and influence of the matric suction of the unsaturated soil around the pile on the bearing response (load transfer) of the pile body, and can calculate the numerical value and distribution law of the thermal-hydraulic-mechanical multi-physical field coupling axial strain, stress, friction resistance, end resistance and displacement of the energy pile under the coupling of temperature load and unsaturated conditions. The method is simple in principle, simple and easy to use, and can provide theoretical support and calculation means for the analysis and design of unsaturated soil energy piles. BRIEF DESCRIPTION OF DRAWINGS

[0068] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed in the embodiment description. Obviously, the drawings in the following description are only some embodiments of the present application, and for those skilled in the art, other drawings can also be obtained from these drawings without creative labor.

[0069] Figure 1 It is a schematic diagram of the energy pile heat-water-force multi-field coupling response calculation method of the unsaturated soil involved in the present application.

[0070] Figure 2 It is a flowchart of the energy pile coupling response algorithm of the dry or saturated soil involved in the present application.

[0071] Figure 3 It is a schematic diagram of the calculation parameters involved in the verification case involved in the present application.

[0072] Figure 4 It is a schematic diagram of the soil-water characteristic curve at different temperatures involved in the present application.

[0073] Figure 5 It is a schematic diagram of the comparison of the simulated value and the test value of the pile bearing capacity involved in the present application.

[0074] Figure 6 It is a schematic diagram of the soil-water characteristic curve at different temperatures involved in the present application.

[0075] Figure 7 It is a schematic diagram of the comparison of the simulated value and the test value of the pile bearing capacity involved in the present application. DETAILED DESCRIPTION

[0076] In the following, only some exemplary embodiments are simply described. As those skilled in the art can recognize, the described embodiments can be modified in various different ways without departing from the spirit or scope of the embodiments of the present application. Therefore, the drawings and the description are considered to be exemplary in nature rather than limiting.

[0077] The following disclosure provides many different embodiments or examples for implementing different structures of the embodiments of the present application. In order to simplify the disclosure of the embodiments of the present application, the components and settings of specific examples are described in the following. Of course, they are only examples, and the purpose is not to limit the embodiments of the present application. In addition, the embodiments of the present application can repeatedly refer to numerals and / or reference letters in different examples, and such repetition is for the purpose of simplification and clarity, which itself does not indicate the relationship between the various embodiments and / or settings discussed.

[0078] The embodiments of the present application will be described in detail below with reference to the drawings.

[0079] As Figure 1 shown, the embodiment provides a non-saturated soil energy pile heat-water-force multi-field coupling response calculation method, comprising:

[0080] S1. Selecting a pile side-soil and pile end-soil load transfer model, simulating the nonlinear interaction between the pile and the soil, and determining the saturated soil energy pile load transfer algorithm;

[0081] S2. Selecting a soil water characteristic curve model considering temperature effect, simulating the relationship between matric suction and saturation under different temperature loads;

[0082] S3. Calculating the horizontal stress of the non-saturated soil at the pile side under the temperature load, and combining the soil water characteristic curve model considering temperature effect, the matric suction, the saturation, and the effective friction angle and the cohesive force of the pile-soil interface, to calculate the shear strength of the energy pile-non-saturated soil interface considering the contribution of the matric suction;

[0083] S4. Based on the pile end ultimate resistance calculation formula of the saturated soil energy pile, introducing a matric suction contribution term, to calculate the pile end ultimate resistance considering the coupling effect of the temperature load and the non-saturated condition;

[0084] S5. Calculating the shear modulus of the soil around the pile considering the coupling effect of the temperature load and the non-saturated condition, for the parameter calculation of the energy pile load transfer model;

[0085] S6. According to the size of the raft, the Young's modulus and the Poisson's ratio of the soil under the raft, calculating the energy pile-raft contact stiffness, to simulate the interaction between the energy pile and the upper building;

[0086] S7. Substituting the shear strength of the energy pile-non-saturated soil interface contributed by the matric suction, the pile end ultimate resistance considering the coupling effect of the temperature load and the non-saturated condition, the shear modulus of the soil around the pile considering the coupling effect of the temperature load and the non-saturated condition, and the energy pile-raft contact stiffness into the saturated soil energy pile load transfer algorithm, to calculate the heat-water-force multi-physical field coupling response of the non-saturated soil energy pile.

[0087] The present application is based on the following basic assumptions:

[0088] (1) Existing research shows that the radial deformation of the vertical load energy pile and the pile side normal stress have little effect on the change of the pile mechanical properties, so the influence of the axial deformation of the pile is mainly considered in the research;

[0089] (2) The stress and strain of the pile are positive under compression, the frictional force is positive upward, and the displacement of the pile is positive upward;

[0090] (3) The cross-sectional geometry, physical and mechanical properties, and temperature changes of the pile are uniformly distributed along the pile.

[0091] In some embodiments, in S1, the energy pile-soil relative displacement is composed of the nonlinear displacement of the pile-soil shear disturbed zone and the elastic displacement of the soil in the non-disturbed zone around the pile, and the specific calculation method is as follows: the nonlinear displacement of the pile-soil shear disturbed zone can be calculated by using a commonly used load transfer model, including but not limited to a complete elastic-plastic model, an exponential model, a hyperbolic model, a double-line model, a triple-line model, a generalized softening model, etc.; the elastic displacement of the soil in the non-disturbed zone around the pile can be solved by using an elastic theory related method; the thermal-hydraulic-mechanical coupling response algorithm of the unsaturated energy pile is similar to the load transfer algorithm of the energy pile in saturated or dry soil, and the difference lies in that the load transfer model of the pile side-soil and the pile end-soil considering the coupling of the temperature load and the unsaturated condition is used; the steps of the load transfer algorithm of the energy pile in saturated or dry soil are as shown in Figure 2 , and specifically are as follows:

[0092] 1) Selecting a load transfer model for simulating the nonlinear interaction between the pile and the soil, and a contact stiffness of the pile top.

[0093] 2) Determining a pile side-soil and a pile end-soil interaction model in saturated or dry soil. Preferably, taking the exponential model as an example, the pile side-soil and the pile end-soil interaction models are respectively formula (1) and (2).

[0094] (1);

[0095] (2);

[0096] In the formula, is the shear modulus of the soil around the pile side; is the pile diameter; is the shear influence radius; is the shear modulus of the soil at the pile end; is the Poisson's ratio of the soil at the pile end; is the sum of the nonlinear displacement and the elastic displacement of the soil at the pile side; and are respectively the total displacement of the pile side and the shear stress of the pile side at the unloading point or the reloading point; is a loading and unloading state judgment factor; is the shear strength of the soil at the pile side; is the initial shear stiffness of the pile side-soil; is the shear stress of the pile side; is the sum of the nonlinear displacement and the elastic displacement of the soil at the pile end; and are respectively the total displacement of the pile end and the shear stress of the pile end at the unloading point or the reloading point; is the initial stiffness of the pile end-soil interaction; is a loading and unloading state judgment factor; is the ultimate end resistance; is the pile end resistance.

[0097] 3) Determine the pile side-soil and pile tip-soil interaction model parameters. The main parameters include the pile-soil interface shear strength, the initial pile side-soil shear stiffness, the pile tip ultimate strength, the initial pile tip-soil interaction stiffness, and the pile-raft contact stiffness, which can be determined by field test results, element test results, and corresponding empirical formulas.

[0098] 4) Substitute the energy pile side-soil and pile tip-soil interaction model in saturated or dry soil into the energy pile single pile load transfer algorithm to obtain the energy pile thermal-mechanical coupling response in saturated or dry soil. The energy pile single pile load transfer (bearing response) algorithm can be realized by the finite element method, the finite difference method, the matrix displacement method, and the like.

[0099] In some embodiments, S2 is specifically implemented as follows: the SWCC model without considering temperature effects includes two types of empirical models and theoretical models, wherein the commonly used empirical models are van Genuchten model, Fredlund-Xing model, Brooks-Corey model, Gardner model, and the like; the commonly used theoretical models include thermodynamic models and pore network models. For coarse-grained soil, it is recommended to use the Brooks-Corey model; for fine-grained soil, it is recommended to use the van Genuchten model and the Fredlund-Xing model; the temperature correction parameter is introduced into the model without considering temperature effects, so as to obtain the SWCC model considering temperature effects, and the specific expression form of the temperature correction coefficient can be reasonably selected according to specific conditions.

[0100] Preferably, taking the van Genuchten model as an example, the SWCC model considering temperature effects and the temperature correction coefficient are formula (3) and formula (4), respectively.

[0101] (3);

[0102] (4);

[0103] In the formula: is the saturation degree; is the matric suction; and are model parameters; is the temperature; and are model coefficients.

[0104] In some embodiments, S3 is specifically implemented as follows: the horizontal stress of the unsaturated soil on the pile side under temperature load can be calculated by treating the pile as a perfectly elastic body; the shear strength of the energy pile-unsaturated soil interface consists of three parts: soil cohesion contribution, horizontal stress contribution, and matrix suction contribution. The soil cohesion contribution is related to the magnitude of the unsaturated soil cohesion, the horizontal stress contribution is related to the horizontal stress of the unsaturated soil on the pile side under temperature load and the effective friction angle of the pile-soil interface, and the matrix suction contribution is related to the SWCC model considering temperature effects, matrix suction, saturation, and the effective friction angle of the pile-soil interface.

[0105] In the calculation of horizontal stress of unsaturated soil on the pile side under temperature load, the energy pile is regarded as a completely elastic body. Then the volume change of the energy pile under temperature load is given by equations (5) and (6).

[0106] (5);

[0107] (6);

[0108] In the formula: It is the coefficient of thermal expansion of the pile body; It is the radius of the pile body; It is the change in temperature; It is the length of the pile; This is the pile radius under temperature load. According to equations (5) and (6), the change in pile radius under temperature load can be calculated as follows:

[0109] (7);

[0110] The horizontal stress at the energy pile-unsaturated soil interface caused by temperature load is:

[0111] (8);

[0112] The total horizontal stress at the energy pile-unsaturated soil interface is the sum of the effective horizontal stress of the soil on the pile side and the horizontal stress at the pile-soil interface caused by the temperature load, as shown in equation (9).

[0113] (9);

[0114] The shear strength of the energy pile-unsaturated soil interface consists of three parts: soil cohesion contribution, horizontal stress contribution, and matrix suction contribution, as shown in equation (10):

[0115] (10);

[0116] In the formula: It is the Poisson's ratio of the soil. is the effective internal friction angle of the pile-soil interface; is the effective cohesion of the pile-soil interface; is the residual saturation; is the current saturation.

[0117] In some embodiments, S4, the formula for calculating the ultimate end resistance of the pile considering the coupling of temperature load and unsaturated conditions is similar to the formula for calculating the ultimate end resistance of the energy pile in saturated soil, with the difference being that the contribution of the matrix suction needs to be considered.

[0118] The formula for calculating the ultimate end resistance of the pile considering the coupling of temperature load and unsaturated conditions is:

[0119] (11);

[0120] In the formula: is the effective internal friction angle of the pile end soil; is the effective vertical stress of the pile end soil; is the effective cohesion of the pile end soil; is a model coefficient, which can be calculated according to formulas (12) and (13).

[0121] (12);

[0122] (13);

[0123] In the formula: is an adjustment coefficient; is the measured data of the ultimate end resistance. According to a large amount of measured data statistics, the adjustment coefficient can be calculated by the empirical formula (14).

[0124] (14);

[0125] In the formula: and are 1 and -0.006, respectively.

[0126] In some embodiments, S5, the shear modulus of the soil around the pile considering the coupling of temperature load and unsaturated conditions is related to the shear modulus in dry and wet states, the specific surface area of soil particles, etc. The obtained shear modulus can be used for parameter calculation of the load transfer model of the energy pile.

[0127] The shear modulus of the soil around the pile considering the coupling of temperature load and unsaturated conditions can be calculated according to formulas (15) and (16).

[0128] (15);

[0129] (16);

[0130] wherein: and are the Young's modulus of the soil in dry and saturated states, respectively; is the measured Young's modulus of the soil in a state between dry and saturated; is the measured saturated soil.

[0131] In some embodiments, S6 the energy pile-raft contact stiffness is related to the raft size, the Young's modulus of the soil under the raft, the Poisson's ratio, etc. For layered soil, the weighted average of the Young's modulus and Poisson's ratio of the unsaturated soil in the energy pile depth range can be used.

[0132] The energy pile-raft contact stiffness can be calculated according to equation (17):

[0133] (17);

[0134] wherein: and are the raft width and length, respectively; is a calculation coefficient. For layered soil, the weighted average of the Young's modulus and Poisson's ratio is calculated according to equations (18) and (19), respectively.

[0135] (18);

[0136] (19);

[0137] wherein: is the thickness of the soil layer; is the Young's modulus of each layer of soil; is the Poisson's ratio of each layer of soil.

[0138] The relationship between the Young's modulus and the shear modulus is shown in equation (20):

[0139] (20);

[0140] The reliability and effectiveness of the proposed method in analyzing the thermal-hydraulic-mechanical multi-field coupling response of the energy pile in unsaturated soil are verified by two test cases, wherein case one is a centrifuge model test, and case two is a scaled model test. The calculation parameters involved in the verification cases are taken from the test work, as shown in Figure 3 The SWCC curve of case one is shown in Figure 4 , and the SWCC curve of case two is shown in Figure 6 . Figure 5 and 7The simulation values and test values of the pile body bearing capacity in cases 1 and 2 are shown in the table, and it can be found that the simulation results and test results are in good consistency under different temperatures and different soil saturation conditions, proving the effectiveness and reliability of the method in calculating the thermal-water-force multi-field coupling response of the non-saturated soil energy pile.

[0141] The above-described embodiments are used to illustrate the present application, and are not intended to limit the present application, so the numerical changes or equivalent element replacements of the examples should still belong to the scope of the present application.

[0142] From the above detailed description, it can be seen by those skilled in the art that the present application can achieve the above-mentioned purposes, and has met the requirements of the Patent Law.

[0143] Although the preferred embodiments of the present application have been described, those skilled in the art can make further changes and modifications to the embodiments once they know the basic inventive concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications falling within the scope of the present application. The above description is only the preferred embodiments of the present application and is not intended to limit the present application. It should be noted that any modification, equivalent replacement and improvement made within the spirit and principle of the present application should be included in the protection scope of the present application.

[0144] It should be noted that the above description of the flow is only for example and illustration, and does not limit the scope of the present application. Those skilled in the art can make various modifications and changes to the flow under the guidance of the present application. However, these modifications and changes are still within the scope of the present application.

[0145] The above has described the basic concept, and it is obvious that the above-mentioned invention disclosure is only as an example and does not constitute a limitation on the present application for those skilled in the art after reading this application. Although it is not explicitly stated here, those skilled in the art can make various modifications, improvements and modifications to the present application. Such modifications, improvements and modifications are suggested in the present application, so such modifications, improvements and modifications still belong to the spirit and scope of the exemplary embodiments of the present application.

[0146] Meanwhile, specific words are used in the present application to describe the embodiments of the present application. For example, "one embodiment", "an embodiment", and / or "some embodiments" means a certain feature, structure or characteristic related to at least one embodiment of the present application. Therefore, it should be emphasized and noted that the "an embodiment" or "one embodiment" or "an alternative embodiment" mentioned in different positions in the specification does not necessarily refer to the same embodiment. In addition, certain features, structures or characteristics in one or more embodiments of the present application can be properly combined.

[0147] Moreover, as will be appreciated by persons skilled in the art, the present application is capable of being embodied with several different types of categories or circumstances of patentable subject matter including any new and useful process, machine, manufacture, or composition of matter, or any new and useful improvement thereof. Accordingly, the various aspects of the present application can be embodied in hardware alone, in software alone, or in a combination of hardware and software. The above described hardware and software can be referred to as a "unit", "module" or "system". Furthermore, the various aspects of the present application can take the form of a computer program product embodied in one or more computer readable medium(s) having computer readable program code embodied thereon.

[0148] Computer program code for carrying out operations of the present application can be written in any combination of one or more programming languages, including an object oriented programming language such as Java, Scala, Smalltalk, Eiffel, JADE, Emerald, C++, C#, VB.NET, Python, conventional procedural programming languages, such as the C programming language, Visual Basic, Fortran 2103, Perl, COBOL 2102, PHP, ABAP, dynamic programming languages, such as Python, Ruby and Groovy, or another programming language. The program code can execute entirely on the user's computer, or it can be executed as a stand-alone software package, or it can execute partly on the user's computer and partly on a remote computer or entirely on the remote computer or server. In the latter scenario, the remote computer can be connected to the user's computer through any network, such as a local area network (LAN) or a wide area network (WAN), or the connection can be made to an external computer (for example, through the Internet) or within a cloud computing environment, or as a service, such as Software as a Service (SaaS).

[0149] Moreover, the order of execution or sequence of processing elements and sequences, unless otherwise specifically denoted, can not be limited to the description as set forth herein, nor specifically exemplified in the examples thereof, and the use of numbering or letters in the examples is not intended to limit the scope of the application. Although the above disclosure discusses several exemplary embodiments of the application, it should be apparent that various changes and modifications can be made by persons skilled in the art. For example, while the implementation of various components described above can be embodied in hardware, it can also be implemented as a software solution, for example, as an installation on an existing server or mobile device.

[0150] For similar reasons, it is to be appreciated that the teachings of the present application provided herein can be applied to any embodiment of the present application, and that actual claims applied for or patent granted can be broader than any single, featured embodiment. Accordingly, a patent applicant has constructed and filed examples to particularly point out and distinctly claim those aspects which are regarded as novel and those aspects specifically shown.

Claims

1. A method for calculating the multi-field coupled response of unsaturated soil energy piles based on thermal-hydraulic-mechanical fields, characterized in that, include: S1. Compare and select pile-side soil and pile-end soil load transfer models, simulate nonlinear pile-soil interaction, and determine the load transfer algorithm for saturated soil energy piles. S2. Compare and select soil-water characteristic curve models that take temperature effects into account, and simulate the relationship between matrix suction and saturation under different temperature loads. S3. Calculate the horizontal stress of the unsaturated soil on the pile side under temperature load. Combine the soil-water characteristic curve model considering the temperature effect, matrix suction, saturation, effective friction angle and cohesion of the pile-soil interface, and calculate the shear strength of the energy pile-unsaturated soil interface considering the contribution of matrix suction. S4. Based on the calculation formula of the ultimate resistance of the pile tip of the saturated soil energy pile, the matrix suction contribution term is introduced to calculate the ultimate resistance of the pile tip considering the coupling effect of temperature load and unsaturated conditions. S5. Calculate the shear modulus of the soil around the pile considering the coupling effect of temperature load and unsaturated conditions, for use in the calculation of load transfer model parameters of energy pile; S6. Based on the raft foundation dimensions, Young's modulus of the soil beneath the raft foundation, and Poisson's ratio, calculate the contact stiffness between the energy pile and the raft foundation, and simulate the interaction between the energy pile and the superstructure. S7. Substitute the shear strength of the energy pile-unsaturated soil interface contributed by the matrix suction, the ultimate resistance of the pile end considering the coupling effect of temperature load and unsaturated conditions, the shear modulus of the soil around the pile considering the coupling effect of temperature load and unsaturated conditions, and the contact stiffness of the energy pile-raft slab into the load transfer algorithm for saturated soil energy piles to calculate the thermal-hydraulic-mechanical multiphysics coupling response of unsaturated soil energy piles. In the calculation of horizontal stress in the unsaturated soil along the pile under temperature load, the energy pile is considered as a perfectly elastic body. Therefore, the volume change of the energy pile under temperature load is... For equations (5) and (6); (5)； (6)； In the formula: The volume of the energy pile when the temperature changes; The initial volume of the energy pile It is the coefficient of thermal expansion of the pile body; It is the change in temperature; It is the length of the pile; The radius of the pile under temperature load is calculated according to equations (5) and (6). for: (7)； The horizontal stress at the energy pile-unsaturated soil interface caused by temperature load for: (8)； Young's modulus of soil; The total horizontal stress at the energy pile-unsaturated soil interface is the sum of the effective horizontal stress of the soil along the pile and the horizontal stress at the pile-soil interface caused by temperature load. As shown in equation (9); (9)； The effective internal friction angle of the soil; Z represents the effective unit weight of the soil; z represents the depth. The shear strength of the energy pile-unsaturated soil interface It consists of three parts: soil cohesion contribution, horizontal stress contribution, and matrix suction contribution, as shown in equation (10): (10)； In the formula: It is the Poisson's ratio of the soil. It is the effective internal friction angle of the pile-soil interface; It is the effective cohesion at the pile-soil interface; It is residual saturation; This is the current saturation level.

2. The method for calculating the multi-field coupled response of unsaturated soil energy piles according to claim 1, characterized in that, In S1, the energy pile-soil relative displacement in the nonlinear pile-soil interaction consists of the nonlinear displacement of the pile-soil shear disturbance zone and the elastic displacement of the soil in the undisturbed zone around the pile, wherein: The nonlinear displacement of the pile-soil shear disturbance zone is calculated using a fully elastic-plastic model, an exponential model, a hyperbolic model, a bilinear model, a trilinear model, or a generalized softening model. The elastic displacement of the soil in the undisturbed zone around the pile is solved using elastic theory.

3. The method for calculating the multi-field coupled response of unsaturated soil energy piles according to claim 1, characterized in that, The specific algorithm for load transfer of saturated soil energy piles in S1 is as follows: Select the load transfer model and pile top contact stiffness to simulate the nonlinear interaction between pile and soil. Determine the pile side- and pile tip-soil interaction models in saturated or dry soil. The pile side- and pile tip-soil interaction models are Equations (1) and (2), respectively. (1)； (2)； In the formula: It is the ultimate shear strength; It is the shear modulus of the soil along the pile; The radius of the pile body; Radius affected by shear; Shear modulus of the soil at the pile tip; It is the Poisson's ratio of the soil at the pile tip; It is the sum of the nonlinear displacement and elastic displacement of the soil along the pile; and These are the total pile displacement and pile shear stress at the unloading point or reloading point, respectively. This serves as a factor for determining the loading / unloading status. Shear strength of the soil along the pile; The initial shear stiffness of the pile side-soil; This refers to the shear stress on the pile side; It is the sum of the nonlinear displacement and elastic displacement at the pile end; and These are the total displacement and shear stress at the pile end at the unloading point or reloading point, respectively. Initial stiffness of pile tip-soil interaction; This serves as a factor for determining the loading / unloading status. This is the resistance at the extreme end; Pile end resistance; Determine the parameters of the pile-side and pile-end soil interaction models, including 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 contact stiffness of the pile-raft slab. Substituting the side- and pile-end-soil interaction models of energy piles in saturated or dry soil into the single-pile load transfer algorithm of energy piles, the thermal coupling response of energy piles in saturated or dry soil is obtained.

4. The method for calculating the multi-field coupled response of unsaturated soil energy piles according to claim 1, characterized in that, In S2, by introducing a temperature correction parameter into the model of the soil-water characteristic curve that does not consider the temperature effect, a soil-water characteristic curve model that considers the temperature effect can be obtained. The soil-water characteristic curve model that does not consider the temperature effect includes two types: empirical models and theoretical models. Theoretical models include thermodynamic models and pore network models, while empirical models include the van Genuchten model, the Fredlund-Xing model, the Brooks-Corey model, and the Gardner model.

5. The method for calculating the multi-field coupled response of unsaturated soil energy piles according to claim 4, characterized in that, S2 uses the van Genuchten model, which considers the soil-water characteristic curve model and temperature correction parameters based on temperature effects. The corresponding formulas are (3) and (4), respectively. (3)； (4)； In the formula: It's saturation; It is matrix suction; and These are model parameters; It's temperature; and These are the model coefficients.

6. The method for calculating the multi-field coupled response of unsaturated soil energy piles according to claim 1, characterized in that, Ultimate pile end resistance considering the coupling effect of temperature load and unsaturated conditions in S4 The calculation formula is: (11)； In the formula: It is the effective internal friction angle of the soil at the pile tip; It is the effective vertical stress of the soil at the pile tip; It is the effective cohesion of the soil at the pile tip; These are the model coefficients, calculated according to equations (12) and (13); (12)； (13)； In the formula: It is an adjustment factor; The effective cohesion of the soil at the pile tip; exp is an exponential function; The adjustment coefficient is calculated using empirical formula (14) for the extreme end resistance measurement data; (14)； In the formula: and The values ​​are 1 and -0.006, respectively.

7. The method for calculating the multi-field coupled response of unsaturated soil energy piles according to claim 1, characterized in that, In S5, the shear modulus of the soil around the pile considering the coupling effect of temperature load and unsaturated conditions is calculated according to equations (15) and (16); (15)； (16)； In the formula: k is the model parameter; and These are the Young's modulus of soil under dry and saturated conditions, respectively. It is the Young's modulus, which measures soil conditions between dry and saturated. It measures saturated soil.

8. The method for calculating the multi-field coupled response of unsaturated soil energy piles according to claim 1, characterized in that, S6 Energy Pile-Raft Slab Contact Stiffness Calculate according to equation (17): (17)； In the formula: The Young's modulus of soil. Poisson's ratio of soil and These are the width and length of the raft board, respectively. These are calculation coefficients; for layered soils, the weighted average of Young's modulus is used. Poisson's weighted average Calculate according to equations (18) and (19) respectively; (18)； (19)； In the formula: It refers to the thickness of the soil layer; It is the Young's modulus of each soil layer; It is the Poisson's ratio of each soil layer.

9. The method for calculating the multi-field coupled response of unsaturated soil energy piles according to claim 1, characterized in that, Young's modulus E and shear modulus The relationship between them is shown in equation (20): (20)。

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