A tower foundation stability analysis method considering soil strength attenuation during rainfall

Abstract

The present invention provides a method for analyzing the stability of an iron tower foundation under soil strength attenuation during rainfall. By constructing a dynamic coupling model of soil mechanical parameters under rainfall infiltration conditions, the present invention breaks through the limitations of traditional static soil parameter evaluation, accurately simulates the impact mechanism of soil saturation changes on foundation stability, and develops a multi-scale stability analysis method based on the spatiotemporal evolution of hydraulic characteristics, providing a more accurate theoretical basis and technical support for the stability evaluation of iron tower foundations under unsaturated soil conditions.

Description

Technical Field

[0001] The invention belongs to the technical field of geotechnical engineering, and in particular relates to a tower foundation stability analysis method taking soil strength attenuation into consideration during rainfall. Background Art

[0002] In the Loess Plateau region, rainfall significantly impacts the soil, especially under heavy rainfall. This can cause the soil's hydraulic gradient to drop, shifting from an unsaturated to a saturated state. This significantly reduces soil strength, which can easily lead to engineering problems such as reduced bearing capacity and settlement deformation in tower foundations. Traditional tower foundation stability analysis methods often fail to fully consider the impact of rainfall on soil strength, making it difficult to accurately assess foundation safety in real-world projects.

[0003] Traditional tower foundation stability analysis methods rely primarily on static, averaged soil parameters, failing to dynamically and accurately capture the local attenuation characteristics and spatial heterogeneity of soil strength during rainfall. These methods typically employ simplified continuum models, treating the soil as a homogeneous continuum and ignoring the significant variations in strength parameters at different depths and spatial locations. Particularly in complex geological conditions such as collapsible loess, soil heterogeneity can lead to localized instability in the foundation's load-bearing mechanism. Traditional analysis methods struggle to identify and quantify these potential instability risks. Summary of the Invention

[0004] Aiming at the stability assessment of iron tower foundations in loess regions, the present invention provides a foundation stability analysis method that takes into account the attenuation of soil strength during rainfall. Based on the Mohr-Coulomb model for unsaturated soil, the nonlinear relationship between the soil's cohesion, internal friction angle, density, Poisson's ratio, and saturation is taken into account, and a tower foundation seepage-stress coupling analysis model that couples rainfall infiltration and stress fields is established. This method can effectively characterize the mechanism by which soil heterogeneity and changes in mechanical parameters affect foundation stability. Compared with traditional analysis methods, the model established by the present invention can dynamically simulate the spatiotemporal changes in soil mechanical parameters during rainfall, providing a more accurate and reliable basis for the safety assessment of iron tower foundations in loess regions.

[0005] The technical solution adopted by the present invention is:

[0006] A tower foundation stability analysis method for soil strength attenuation during rainfall includes the following steps:

[0007] Step 1: Determine the tower foundation type and soil parameters:

[0008] The parameters of the tower foundation and soil include: material parameters of the tower foundation, size of the tower foundation, load of the tower foundation, physical and mechanical parameters of the soil, and unsaturated seepage parameters;

[0009] Step 2: The cohesion and internal friction angle of unsaturated soil at different degrees of saturation are obtained through indoor consolidation-drained triaxial tests. An appropriate fitting function is selected. Based on the soil constitutive theory, combined with the experimental data and theoretical constraints, a model for the evolution of density, Poisson's ratio, and elastic modulus of soil at different degrees of saturation is derived and constructed.

[0010] Step 3: Use geotechnical engineering simulation software to draw the three-dimensional geometric model of the tower foundation and soil;

[0011] Step 4: Using the finite element seepage numerical calculation method, the rainfall infiltration process is simulated. The soil saturation distribution at different spatial locations is extracted through a subroutine. Based on the saturation-mechanical parameter relationship established in indoor experiments, the spatial dynamic conversion of soil mechanical parameters is achieved. The seepage-stress coupling calculation framework includes the key steps of ground stress balance analysis, load application, seepage calculation and dynamic parameter reconstruction, and calculation result output. The nonlinear evolution process of soil mechanical parameters is realized in the seepage calculation analysis stage.

[0012] Step 5: Based on the seepage-parameter coupling theory, stability analysis is carried out from two dimensions: the spatiotemporal evolution of hydraulic characteristics and the interaction between foundation and soil.

[0013] In step 1, the tower foundation type and soil parameters are as follows:

[0014] The tower foundation is a 220kV transmission line tower foundation in a collapsible loess area. The foundation type is a stepped foundation and the foundation material is C80 concrete with a density of 2g / m 3 , Poisson's ratio is 0.3, and the elastic modulus is 3×10 4 MPa, the soil is silt, and the dry density is 1.3g / m 3 , Poisson's ratio is 0.3, elastic modulus is 20 MPa, and permeability coefficient is 2.4×10 -4 m / s.

[0015] In step 2, the fitting formulas for cohesion and internal friction angle at different saturations obtained through indoor consolidation and drainage triaxial tests are as follows:

[0016]

[0017] Where: c is the cohesion of soil, kPa; is the internal friction angle, °; S r is the soil saturation, %;

[0018] The calculation formula for soil density based on saturation is:

[0019]

[0020] ρ=ρd (1+ω)

[0021] Where: S r is the soil saturation, %; d s is the relative density of soil particles; e is the porosity of soil; ω is the real-time water content, %; ρ is the real-time density, g / m 3 ρ d is the dry density of soil, g / m 3 ;

[0022] Conversion formulas for Poisson's ratio and elastic modulus of soil at different degrees of saturation:

[0023]

[0024] E i v i =Ev=const

[0025] Where: β is the empirical coefficient used to establish the friction angle and the relationship between Poisson's ratio v, E and E i are the elastic modulus of soil before and after reduction, MPa; v and v i is the Poisson's ratio of soil before and after reduction.

[0026] In step 3, based on the tower foundation and soil type, a three-dimensional finite element simulation model of the tower foundation and soil is drawn using geotechnical engineering simulation software. In order to simplify the calculation, the soil is regarded as a homogeneous soil without stone particles and plant roots to eliminate heterogeneous factors.

[0027] In step 4, a finite element seepage numerical calculation method is used to extract the soil saturation distribution at different spatial positions through a subroutine, and the saturation-mechanical parameter correlation model established by indoor experiments is combined to achieve spatiotemporal dynamic conversion of soil mechanical parameters;

[0028] Based on the seepage-parameter coupling theory, we deeply analyze the spatiotemporal evolution of soil hydraulic characteristics and the interaction mechanism between foundation and soil interface during rainfall infiltration, construct a multi-scale stability assessment theoretical framework, and quantitatively evaluate the mechanical response and critical instability state of the tower foundation under unsaturated soil conditions.

[0029] This invention breaks through the limitations of traditional static soil parameter evaluation by constructing a dynamic coupling model of soil mechanical parameters under rainfall infiltration conditions, accurately simulates the impact mechanism of soil saturation changes on foundation stability, and develops a multi-scale stability analysis method based on the spatiotemporal evolution of hydraulic characteristics, providing a more accurate theoretical basis and technical support for the stability evaluation of tower foundations under unsaturated soil conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a flow chart of the technical method for analyzing the stability of the tower foundation during rainfall according to the present invention.

[0031] Figure 2 This is the geometric dimension drawing of the tower foundation.

[0032] Figure 3 is the fitting curve of soil cohesion changing with saturation.

[0033] Figure 4 is the fitting curve of the soil internal friction angle changing with saturation.

[0034] Figure 5 is the fitting curve of soil Poisson's ratio changing with saturation.

[0035] Figure 6 is the fitting curve of soil elastic modulus changing with saturation.

[0036] Figure 7 is the fitting curve of soil density changing with saturation.

[0037] Figure 8 It is a three-dimensional simulation model of the tower foundation and soil.

[0038] Figure 9 This is the calculation flow chart of the seepage-stress coupling model.

[0039] Figure 10 This is the spatiotemporal distribution of soil saturation during rainfall.

[0040] Figure 11 This is a cloud diagram of vertical stress changes during rainfall infiltration.

[0041] Figure 12 The displacement-time curves of the tower foundation under the same rainfall intensity and different rainfall patterns.

[0042] Figure 13 The tower foundation settlement-time curve under the same rainfall pattern and different rainfall intensities.

[0043] Figure 14 The lateral friction force distribution curve based on . DETAILED DESCRIPTION

[0044] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation methods. It should be noted that, under the premise of no conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0045] A tower foundation stability analysis method for soil strength attenuation during rainfall includes the following steps:

[0046] Step 1: Determine the tower foundation type and soil parameters:

[0047] The tower foundation type is a stepped foundation, and the foundation material is C80 concrete with a density of 2g / m 3 , Poisson's ratio is 0.3, and the elastic modulus is 3×10 4 MPa, the soil is silt, and the dry density is 1.3g / m 3 , Poisson's ratio is 0.3, elastic modulus is 20 MPa, and permeability coefficient is 2.4×10 -4 m / s.

[0048] Step 2: The cohesion and internal friction angle of unsaturated soil at different degrees of saturation are obtained through indoor consolidation-drained triaxial tests. An appropriate fitting function is selected. Based on the soil constitutive theory, combined with the experimental data and theoretical constraints, a model for the evolution of density, Poisson's ratio, and elastic modulus of soil at different degrees of saturation is derived and constructed.

[0049] The fitting formulas for cohesion and internal friction angle at different saturations obtained through indoor consolidation and drainage triaxial tests are as follows:

[0050]

[0051] Where:

[0052] c is the cohesion of soil, kPa; is the internal friction angle, °; S r is the soil saturation, %.

[0053] Conversion formulas for Poisson's ratio and elastic modulus of soil at different degrees of saturation:

[0054]

[0055] E i v i =Ev=const

[0056] Where:

[0057] β is an empirical coefficient used to establish the friction angle and the relationship between Poisson's ratio v, E and E i are the elastic modulus of soil before and after reduction, MPa; v and v i is the Poisson's ratio of soil before and after reduction.

[0058] The calculation formula for soil density based on saturation is:

[0059]

[0060] ρ=ρ d (1+ω)

[0061] Where:

[0062] S r is the soil saturation, %; d s is the relative density of soil particles; e is the porosity of soil; ω is the real-time water content, %; ρ is the real-time density, g / m 3 ρ d is the dry density of soil, g / m 3 .

[0063] Step 3: Based on the tower foundation and soil type, use geotechnical engineering simulation software to draw a three-dimensional finite element simulation model of the tower foundation and soil. Figure 8 This is a three-dimensional simulation model of the tower foundation and soil. To simplify the calculation, the soil is considered to be homogeneous without stone particles and plant roots, eliminating heterogeneity factors.

[0064] Step 4: Using the finite element seepage numerical calculation method, a subroutine was used to extract the soil saturation distribution at different spatial locations. Combined with the saturation-mechanical parameter correlation model established through laboratory experiments, this method achieved the spatiotemporal dynamic conversion of soil mechanical parameters. The seepage-stress coupling calculation framework includes key steps such as ground stress balance analysis, load application, seepage calculation and dynamic parameter reconstruction, and calculation result output. The nonlinear evolution of soil mechanical parameters is implemented during the seepage calculation and analysis phase.

[0065] Step 5: Based on the seepage-parameter coupling theory, a multi-scale numerical simulation method is used to deeply reveal the spatiotemporal evolution mechanism of soil hydraulic characteristics and the dynamic response characteristics of the foundation-soil interface during rainfall infiltration. A nonlinear coupling stability assessment and analysis framework is constructed to accurately quantify the mechanical behavior and hydraulic characteristics changes of the tower foundation in an unsaturated soil environment.

[0066] Example:

[0067] The present invention provides a tower foundation stability analysis method considering the attenuation of soil strength during rainfall. The basic flow chart is as follows: Figure 1 shown.

[0068] Step 1: Determine the tower foundation type and soil parameters:

[0069] In order to establish a more accurate tower foundation stability analysis model during rainfall, the present invention selects a 220kV transmission line tower foundation in a collapsible loess area, and the foundation type is a stepped foundation. Figure 2 This is the geometric dimension diagram of the tower foundation. The foundation material is C80 concrete with a density of 2g / m 3 , Poisson's ratio is 0.3, and the elastic modulus is 3×10 4 MPa, the soil is silt, and the dry density is 1.3g / m 3, Poisson's ratio is 0.3, elastic modulus is 20 MPa, and permeability coefficient is 2.4×10 -4 m / s.

[0070] Step 2: Establish the relationship between soil strength parameters and saturation:

[0071] The cohesion and internal friction angle of unsaturated soil at different degrees of saturation were obtained through indoor consolidation and drainage triaxial tests. An appropriate fitting function was selected and, based on the soil constitutive theory, combined with the experimental data and theoretical constraints, an evolution model of the density, Poisson's ratio, and elastic modulus of soil at different degrees of saturation was derived and constructed.

[0072] Figure 3 is the fitting curve of soil cohesion changing with saturation, Figure 4 is the fitting curve of the internal friction angle of soil with saturation. The fitting formulas for cohesion and internal friction angle at different saturations obtained through indoor consolidation and drainage triaxial tests are as follows:

[0073]

[0074] Where:

[0075] c is the cohesion of soil, kPa; is the internal friction angle, °; S r is the soil saturation, %.

[0076] Conversion formulas for Poisson's ratio and elastic modulus of soil at different degrees of saturation:

[0077]

[0078] E i v i =Ev=const

[0079] Where:

[0080] β is an empirical coefficient used to establish the friction angle and the relationship between Poisson's ratio v, E and E i are the elastic modulus of soil before and after reduction, MPa; v and v i is the Poisson's ratio of soil before and after reduction. Figure 5 is the fitting curve of soil Poisson’s ratio changing with saturation, Figure 6 is the fitting curve of soil elastic modulus changing with saturation.

[0081] The calculation formula for soil density based on saturation is:

[0082]

[0083] ρ=ρ d (1+ω)

[0084] Where:

[0085] S r is the soil saturation, %; d s is the relative density of soil particles; e is the porosity of soil; ω is the real-time water content, %; ρ is the real-time density, g / m 3 ρ d is the dry density of soil, g / m 3 . Figure 7 is the fitting curve of soil density changing with saturation.

[0086] Step 3: Use geotechnical engineering simulation software to draw the three-dimensional geometric model of the tower foundation and soil:

[0087] Based on the tower foundation and soil type, a three-dimensional finite element simulation model of the tower foundation and soil was drawn using geotechnical engineering simulation software. In order to simplify the calculation, the soil was regarded as a homogeneous soil without stone particles and plant roots to eliminate heterogeneous factors.

[0088] At the same time, in order to minimize the influence of boundary effects, the soil boundary of the pile side in the pile-soil model is set at more than 12 times the pile diameter, and the soil depth boundary of the pile end is set at twice the pile burial depth. This can fully utilize the soil bearing capacity and meet the calculation accuracy requirements. A three-dimensional soil model with project dimensions of length × width × height of 20m × 20m × 22m is established. The groundwater level layer is below 20m. The overall simulation model includes two parts: the tower foundation and the soil. Figure 8 A three-dimensional simulation model of the tower foundation-soil was established.

[0089] In addition, to ensure that the soil saturation distribution at the initial moment is consistent with the actual situation, it is necessary to measure the moisture content of the soil at different depths. Then, the saturation of the soil at different depths is calculated using the following formula. The calculated results are used as the initial seepage conditions for rainfall infiltration analysis. Table 1 shows the conversion results of soil saturation at different depths.

[0090]

[0091] Where:

[0092] S r is the soil saturation, %; d s is the relative density of soil particles; e is the porosity of soil; ω is the real-time water content, %.

[0093] Table 1 Conversion results of soil saturation at different depths

[0094]

[0095] Step 4: Using the finite element seepage numerical calculation method, the soil saturation distribution at different spatial locations is extracted through subroutines, and the saturation-mechanical parameter correlation model established by indoor experiments is combined to realize the spatiotemporal dynamic conversion of soil mechanical parameters; the seepage-stress coupling calculation framework includes key steps such as ground stress balance analysis, load loading, seepage calculation and dynamic parameter reconstruction, and calculation result output. Figure 9 The calculation flow chart of the seepage-stress coupling model is shown in Figure 2, in which the nonlinear evolution process of soil mechanical parameters is realized in the seepage calculation and analysis stage.

[0096] Step 5: Analysis of finite element simulation results:

[0097] The results are analyzed from two aspects: the spatiotemporal evolution mechanism of soil hydraulic characteristics during rainfall infiltration and the dynamic response characteristics of the foundation-soil interface. Figure 10 This is the spatiotemporal distribution diagram of soil saturation during rainfall. The spatiotemporal distribution diagram of soil saturation shows that rainwater infiltration only affects the hydraulic parameters of the surface soil, and the saturation distribution of the soil in the non-infiltration area is relatively stable. Figure 11 This is a cloud diagram of vertical stress changes during rainfall infiltration. The vertical stress in the soil around the foundation gradually increases with depth and shows a slight decreasing trend as the rainfall duration increases. This stress reduction phenomenon is mainly due to the increase in pore water pressure in the soil caused by rainwater infiltration, which partially offsets the vertical load.

[0098] Figure 12 The displacement-time curve of the tower foundation under the same rainfall intensity and different rainfall patterns is shown in Figure 2. Figure 13 Figure 2 shows the tower foundation settlement-time curves under the same rainfall pattern and different rainfall intensities. The results show that both rainfall pattern and rainfall intensity affect the stability of the tower foundation. The early accumulated settlement of the foundation is greater under the moderate-peak and uniform rainfall patterns. This difference is primarily due to the high rainfall intensity in the initial stages of moderate-peak and uniform rainfall patterns, which allows the surface soil to absorb water quickly, leading to a rapid attenuation of matrix suction and a reduction in soil shear strength, resulting in greater early settlement. Furthermore, rainfall intensity and foundation settlement responses exhibit a significant positive correlation. Figure 14 The side friction force distribution curve of the foundation shows that the distribution of side friction resistance along the foundation burial depth shows obvious zoning characteristics, which is manifested as the side friction resistance distribution first increases and then decreases, and then gradually increases after reaching the neutral point. Above the neutral point is negative friction resistance, below the neutral point, the negative friction resistance disappears, and the positive friction resistance begins to take effect.

[0099] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A tower foundation stability analysis method for soil strength attenuation during rainfall, characterized by: The following steps are involved: Step 1: Determine the tower foundation type and soil parameters: The parameters of the tower foundation and soil include: material parameters of the tower foundation, size of the tower foundation, load of the tower foundation, physical and mechanical parameters of the soil, and unsaturated seepage parameters; Step 2: The cohesion and internal friction angle of unsaturated soil at different degrees of saturation are obtained through indoor consolidation-drained triaxial tests. An appropriate fitting function is selected. Based on the soil constitutive theory, combined with the experimental data and theoretical constraints, a model for the evolution of density, Poisson's ratio, and elastic modulus of soil at different degrees of saturation is derived and constructed. Step 3: Use geotechnical engineering simulation software to draw the three-dimensional geometric model of the tower foundation and soil; Step 4: Using the finite element seepage numerical calculation method, the rainfall infiltration process is simulated. The soil saturation distribution at different spatial locations is extracted through a subroutine. Based on the saturation-mechanical parameter relationship established in indoor experiments, the spatial dynamic conversion of soil mechanical parameters is achieved. The seepage-stress coupling calculation framework includes the key steps of ground stress balance analysis, load application, seepage calculation and dynamic parameter reconstruction, and calculation result output. The nonlinear evolution process of soil mechanical parameters is realized in the seepage calculation analysis stage. Step 5: Based on the seepage-parameter coupling theory, stability analysis is carried out from two dimensions: the spatiotemporal evolution of hydraulic characteristics and the interaction between foundation and soil.

2. The tower foundation stability analysis method for soil strength attenuation during rainfall according to claim 1, characterized in that: In step 1, the tower foundation type and soil parameters are as follows: The tower foundation is a 220kV transmission line tower foundation in a collapsible loess area. The foundation type is a stepped foundation and the foundation material is C80 concrete with a density of 2g / m 3 , Poisson's ratio is 0.3, and the elastic modulus is 3×10 4 MPa, the soil is silt, and the dry density is 1.3g / m 3 , Poisson's ratio is 0.3, elastic modulus is 20 MPa, and permeability coefficient is 2.4×10 -4 m / s.

3. The tower foundation stability analysis method for soil strength attenuation during rainfall according to claim 1 is characterized by: In step 2, the fitting formulas for cohesion and internal friction angle at different saturations obtained through indoor consolidation and drainage triaxial tests are as follows: Where: c is the cohesion of soil, kPa; is the internal friction angle, °; S r is the soil saturation, %; The calculation formula for soil density based on saturation is: p=p d (1+ω) Where: S r is the soil saturation, %; d s is the relative density of soil particles; e is the porosity of soil; ω is the real-time water content, %; ρ is the real-time density, g / m 3 ρ d is the dry density of soil, g / m 3 ; Conversion formulas for Poisson's ratio and elastic modulus of soil at different degrees of saturation: E i v i =Ev=const Where: β is the empirical coefficient used to establish the friction angle and the relationship between Poisson's ratio v, E and E i are the elastic modulus of soil before and after reduction, MPa; v and v i is the Poisson's ratio of soil before and after reduction.

4. The tower foundation stability analysis method for soil strength attenuation during rainfall according to claim 1, characterized in that: In step 3, based on the tower foundation and soil type, a three-dimensional finite element simulation model of the tower foundation and soil is drawn using geotechnical engineering simulation software. In order to simplify the calculation, the soil is regarded as a homogeneous soil without stone particles and plant roots to eliminate heterogeneous factors.

5. The tower foundation stability analysis method for soil strength attenuation during rainfall according to claim 1 is characterized by: Based on the seepage-parameter coupling theory, we deeply analyze the spatiotemporal evolution of soil hydraulic characteristics and the interaction mechanism between foundation and soil interface during rainfall infiltration, construct a multi-scale stability assessment theoretical framework, and quantitatively evaluate the mechanical response and critical instability state of the tower foundation under unsaturated soil conditions.

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