Iron tower foundation stability analysis method for soil strength attenuation in rainfall process

Abstract

According to the iron tower foundation stability analysis method for soil body strength attenuation in the rainfall process, the limitation of traditional static soil body parameter evaluation is broken through by constructing a soil body mechanical parameter dynamic coupling model under the rainfall infiltration condition, the influence mechanism of soil body saturation change on the foundation stability is accurately simulated, and the foundation stability is improved. A multi-scale stability analysis method based on hydraulic characteristic spatio-temporal evolution is developed, and a more accurate theoretical basis and technical support are provided for iron tower foundation stability evaluation under the unsaturated soil body condition.

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 into account soil strength attenuation during rainfall. Background Art

[0002] In the loess region, rainfall has a significant impact on the soil, especially under heavy rainfall conditions, the hydraulic gradient of the soil decreases, causing the soil to change from an unsaturated state to a saturated state, and the soil strength is significantly reduced, which can easily lead to engineering problems such as the attenuation of the bearing capacity of the tower foundation and settlement deformation. Traditional tower foundation stability analysis methods often fail to fully consider the impact of rainfall on soil strength, resulting in the inability to accurately assess the safety of the foundation in actual engineering.

[0003] Traditional tower foundation stability analysis methods mainly rely on static and averaged soil parameters, and fail to dynamically and accurately capture the local attenuation characteristics and spatial heterogeneity of soil strength during rainfall. These methods usually use a simplified continuous medium model, treating the soil as a homogeneous continuum, and ignoring the significant differences in strength parameters of the soil at different depths and spatial locations. Especially under complex geological conditions such as collapsible loess, the inhomogeneity of the soil can lead to local instability of the foundation force mechanism, and traditional analysis methods are difficult 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 of unsaturated soil, the nonlinear relationship between the cohesion, internal friction angle, density, Poisson's ratio and saturation of the soil is taken into account, and a seepage-stress coupling analysis model of the iron tower foundation coupled with rainfall infiltration and stress field is established. This method can effectively characterize the influence mechanism of soil heterogeneity and mechanical parameter changes on foundation stability. Compared with traditional analysis methods, the model established by the present invention can dynamically simulate the spatiotemporal changes of 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, comprising 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 saturation levels are obtained through indoor consolidation and drainage triaxial tests. A suitable fitting function is selected. Based on the soil constitutive relationship theory, combined with the test data and theoretical constraints, the evolution model of density, Poisson's ratio and elastic modulus of soil at different saturation levels is derived and constructed.

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

[0011] Step 4: The rainfall infiltration process is simulated by the finite element seepage numerical calculation method, the soil saturation distribution at different spatial positions is extracted through the subroutine, and the spatial dynamic conversion of soil mechanical parameters is realized based on the saturation-mechanical parameter relationship established by the indoor test;

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

[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 with a dry density of 1.3 g·m -3 , Poisson's ratio is 0.3, elastic modulus is 20MPa, and permeability is 2.4×10 -4 m·s -1 .

[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 calculating soil density based on saturation is:

[0019]

[0020] ρ=ρ d (1+ω)

[0021] Where: S ris 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 soil dry density, g·m -3 ;

[0022] Conversion formula of Poisson's ratio and elastic modulus of soil at different saturation levels:

[0023]

[0024] E i v i =Ev=const

[0025] Where: β is the empirical coefficient used to establish the friction angle and Poisson's ratio v, E and E i are the elastic modulus of the 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-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, the 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 association model established by indoor experiments is combined to realize the spatiotemporal dynamic conversion of soil mechanical parameters; the seepage-stress coupling calculation framework includes the key steps of ground stress balance analysis, load loading, seepage calculation and parameter dynamic reconstruction, and calculation result output. The nonlinear evolution process of soil mechanical parameters is realized in the seepage calculation and analysis stage.

[0028] Based on the seepage-parameter coupling model, we deeply analyze the spatiotemporal evolution of soil hydraulic characteristics and the interaction mechanism of foundation-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] The present 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 The present invention is a flow chart of the technical method for analyzing the stability of the iron tower foundation during rainfall.

[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 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 degree.

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

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

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

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

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

[0042] Fig.13 This is the tower foundation settlement-time curve under the same rainfall pattern and different rainfall intensities.

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

[0044] The present invention is 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 a new embodiment.

[0045] A tower foundation stability analysis method for soil strength attenuation during rainfall, comprising 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 with a dry density of 1.3 g·m -3 , Poisson's ratio is 0.3, elastic modulus is 20MPa, and permeability is 2.4×10 -4 m·s -1 .

[0048] Step 2: The cohesion and internal friction angle of unsaturated soil at different saturation levels are obtained through indoor consolidation and drainage triaxial tests. A suitable fitting function is selected. Based on the soil constitutive relationship theory, combined with the test data and theoretical constraints, the evolution model of density, Poisson's ratio and elastic modulus of soil at different saturation levels 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 formula of Poisson's ratio and elastic modulus of soil at different saturation levels:

[0054]

[0055] E i v i =Ev=const

[0056] Where:

[0057] β is an empirical coefficient used to establish the friction angle and Poisson's ratio v, E and E i are the elastic modulus of the 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 calculating 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 soil dry density, 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-soil. Figure 8 This is a three-dimensional simulation model of the tower foundation-soil. In order to simplify the calculation, the soil is regarded as a homogeneous soil without stone particles and plant roots to eliminate heterogeneity factors.

[0064] Step 4: Using the finite element seepage numerical calculation method, the soil saturation distribution at different spatial positions is extracted through subroutines, and the saturation-mechanical parameter correlation model established by indoor tests 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 reconstruction of parameters, and output of calculation results. The nonlinear evolution process of soil mechanical parameters is realized in the seepage calculation and analysis stage.

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

[0066] Example:

[0067] The present invention provides a tower foundation stability analysis method taking into account 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 tower foundation is selected from 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 4MPa, the soil is silt with a dry density of 1.3 g·m -3 , Poisson's ratio is 0.3, elastic modulus is 20MPa, and permeability is 2.4×10 -4 m·s -1 .

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

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

[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 the change of saturation. The fitting formulas of cohesion and internal friction angle at different saturations obtained by indoor consolidation and drainage triaxial test 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 formula of Poisson's ratio and elastic modulus of soil at different saturation levels:

[0077]

[0078] E i v i =Ev=const

[0079] Where:

[0080] β is an empirical coefficient used to establish the friction angle and Poisson's ratio v, E and E i are the elastic modulus of the 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 calculating 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 soil dry density, g·m -3 . Figure 7 is the fitting curve of soil density changing with saturation degree.

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

[0087] Based on the tower foundation and soil type, a three-dimensional finite element simulation model of the tower foundation-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 eliminate the influence of boundary effects as much as possible, the soil boundary of the pile side in the pile-soil model is taken as more than 12 times the pile diameter, and the soil depth boundary of the pile end is taken as twice the pile burial depth. At this time, the bearing capacity of the soil can be fully utilized and the calculation accuracy requirements can be met. A three-dimensional soil model with the engineering dimensions of length × width × height of 20m × 20m × 22m is established, and 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, in order 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, and then calculate the saturation of the soil at different depths using the formula below. The calculation 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: Use the finite element seepage numerical calculation method to extract the soil saturation distribution at different spatial positions through subroutines, and combine the saturation-mechanical parameter correlation model established by indoor experiments 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 reconstruction of parameters, and output of calculation results. Fig. 9 This is the calculation flow chart of the seepage-stress coupling model, 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. Fig.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. Fig.11 This is a cloud diagram of vertical stress changes during rainfall infiltration. The vertical stress of the soil around the foundation gradually increases with depth, and with the increase in rainfall duration, the vertical stress of the soil shows a slight decreasing trend. This stress reduction phenomenon is mainly due to the increase in soil pore water pressure caused by rainwater infiltration, which partially offsets the load effect in the vertical direction.

[0098] Fig.12 The displacement-time curve of the tower foundation under the same rainfall intensity and different rainfall patterns. Fig.13 The following are the settlement-time curves of the tower foundation under the same rainfall pattern and different rainfall intensities. The results show that both rainfall pattern and rainfall intensity will affect the stability of the tower foundation. Under the medium-peak and uniform rainfall patterns, the early accumulated settlement of the foundation is relatively large. This difference is mainly because the medium-peak and uniform rainfall patterns have a large rainfall intensity in the initial stage, which allows the surface soil to absorb water quickly, resulting in rapid attenuation of matrix suction and reduced soil shear strength, which in turn produces a large early settlement. At the same time, the rainfall intensity and the settlement response of the foundation show a significant positive correlation. Fig.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 increases first and then decreases, and then gradually increases after reaching the neutral point. There is negative friction resistance above the neutral point, and the negative friction resistance disappears below the neutral point, and the positive friction resistance begins to take effect.

[0099] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary 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 saturation levels are obtained through indoor consolidation and drainage triaxial tests. A suitable fitting function is selected. Based on the soil constitutive relationship theory, combined with the test data and theoretical constraints, the evolution model of density, Poisson's ratio and elastic modulus of soil at different saturation levels is derived and constructed. Step 3: Use geotechnical engineering simulation software to draw the three-dimensional geometric model of the tower foundation-soil; Step 4: The rainfall infiltration process is simulated by the finite element seepage numerical calculation method, the soil saturation distribution at different spatial positions is extracted through the subroutine, and the spatial dynamic conversion of soil mechanical parameters is realized based on the saturation-mechanical parameter relationship established by the indoor test; Step 5: Based on the aforementioned seepage-parameter coupling model, stability analysis is carried out from two dimensions: spatiotemporal evolution of hydraulic characteristics and foundation-soil interaction.

2. According to the method for analyzing the stability of a tower foundation with soil strength attenuation during rainfall in claim 1, it is characterized by: 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 with a dry density of 1.3 g·m -3 , The Poisson's ratio is 0.3, the elastic modulus is 20 MPa, and the permeability coefficient is 2.4×10 -4 m·s -1 .

3. According to the method for analyzing the stability of a tower foundation with soil strength attenuation during rainfall in claim 1, it 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 calculating 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 soil dry density, g·m -3 ; Conversion formula of Poisson's ratio and elastic modulus of soil at different saturation levels: E i v i =Ev=const Where: β is the empirical coefficient used to establish the friction angle and Poisson's ratio v, E and E i are the elastic modulus of the 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 of soil strength attenuation during rainfall according to claim 1 is characterized by: In step 3, based on the tower foundation and soil type, a three-dimensional finite element simulation model of the tower foundation-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 of soil strength attenuation during rainfall according to claim 1 is characterized by: In step 4, a finite element seepage numerical calculation method is used to extract soil saturation distribution at different spatial positions through a subroutine, and a saturation-mechanical parameter correlation model established by indoor tests is combined to achieve spatiotemporal dynamic conversion of soil mechanical parameters; The seepage-stress coupling calculation framework includes the key steps of ground stress balance analysis, load loading, seepage calculation and dynamic parameter reconstruction, and calculation result output. The nonlinear evolution process of soil mechanical parameters is realized in the seepage calculation and analysis stage.

6. 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 model, we deeply analyze the spatiotemporal evolution of soil hydraulic characteristics and the interaction mechanism of foundation-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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