A method for calculating stability of structural soil subgrade under rainfall infiltration condition

Abstract

The application discloses a kind of structural soil subgrade stability calculation methods under rainfall infiltration condition.First, according to the change of the euler number of the microstructure characteristics of the structural soil filled in subgrade after rainfall infiltration, combined with the shear strength of surface subgrade structural soil, the evolution relationship of structural soil shear strength with infiltration time is established.Then, according to the influence of rainfall infiltration process on the strength of structural soil, the expression of structural soil shear strength changing with infiltration time and burial depth is established, and finally a refined finite element calculation model is established to analyze the stability of structural soil subgrade under rainfall infiltration condition.This method only needs to use consolidated undrained triaxial test and microstructure test to obtain the shear strength index and euler number of the surface structural soil of subgrade, and through simple calculation, the stability of rainfall infiltration structural soil subgrade can be calculated by inputting into finite element software.

Description

Technical Field

[0001] This invention relates to the field of transportation engineering, specifically to a method for calculating the stability of structural soil subgrade under rainfall infiltration conditions. Background Technology

[0002] To address the issue of uneven development, the focus of highway construction has gradually shifted from economically developed coastal plains to less developed mountainous and hilly areas. This process often encounters poorly structured soils. Naturally deposited clay develops a certain structural strength over its geological history, but some clays, such as Zhanjiang clay, possess strong structural integrity. This structural integrity provides added strength to natural clay, resulting in high compressive strength, allowing it to support overlying loads without further compaction while maintaining a high porosity. However, under the influence of rainfall infiltration, especially after heavy rainfall, the soil's structure is disrupted, and its strength significantly decreases. High and steep embankments constructed with this structural soil are prone to collapse and settlement.

[0003] When embankments constructed with structured soil are subjected to rainfall infiltration, the strength decay of deeper-buried structured soil lags behind that of shallower-buried soil. Furthermore, the magnitude of shear strength decay varies significantly across different burial depths. Many scholars and engineers have conducted valuable research on the strength decay patterns of structured soil during immersion and the stability of slopes affected by rainfall infiltration, utilizing theoretical analysis, numerical simulation, and experiments. However, existing theoretical analysis methods typically rely on theories of permeability and unsaturated soils to study the strength characteristics of embankment fill during rainfall, failing to adequately consider the influence of soil structure on strength. Numerical simulation methods require sophisticated model establishment and parameter selection, while experimental methods are resource-intensive. Furthermore, methods that comprehensively consider the influencing factors of rainfall infiltration time and burial depth are relatively few for analyzing the stability of structured soil subgrades.

[0004] Therefore, by studying the variation law of shear strength of embankment structural soil under rainfall infiltration conditions with the influence of infiltration time and burial depth, and combining it with finite element numerical calculation software to analyze the stability of embankment slope, this study provides a theoretical basis for the design, construction and management of structural soil subgrades, and has great theoretical and practical significance for highway and railway construction and ensuring the safety of people's lives and property. Summary of the Invention

[0005] To overcome the shortcomings of existing technical solutions, this invention provides a method for calculating the stability of structural soil subgrades under rainfall infiltration conditions, which can simply and quickly calculate the stability of structural soil subgrades under rainfall infiltration conditions.

[0006] To achieve the above objectives, the present invention employs the following technical solution:

[0007] A method for calculating the stability of structural soil subgrade under rainfall infiltration conditions, characterized by comprising the following steps:

[0008] S1: Determine the cohesion of surface non-permeable structural soil using indoor consolidated undrained shear tests. and internal friction angle According to Mohr-Coulomb's theory, the non-permeable structural soil under normal stress... The shear strength under the action is ;

[0009] S2: Take the rainfall infiltration times as T=0 and T= t T=2 t ... T= nt The surface structural soil was tested using microstructure experiments to determine the Euler number of the surface structural soil during rainfall infiltration. ,in , And it is an integer;

[0010] S3: The Euler number of the surface structural soil based on the different infiltration times determined in step S2. Calculate infiltration time T Rainfall impact coefficient and the infiltration time T Rainfall impact coefficient Perform a fitting operation to obtain its expression;

[0011] S4: Based on the infiltration time T Rainfall impact coefficient The expression determines the rainfall infiltration time. T Shear strength of surface structural soil at that time and the cohesion at this time and internal friction angle ;

[0012] S5: Based on rainfall infiltration time T Shear strength of surface structural soil at that time As a result, the vertical distance from the roadbed slope surface was calculated as the burial depth. h Structural soil infiltration T Shear strength over time and roadbed depth h Structural soil infiltration T The cohesive force of time and internal friction angle ;

[0013] S6: Establish a refined finite element calculation model to calculate the stability of the structural soil subgrade under rainfall infiltration conditions.

[0014] The infiltration time mentioned in step S3 T Rainfall impact coefficient The expression is obtained through the following sub-steps:

[0015] S31: Using the formula Calculate infiltration time T=0, T= t T=2 t ... T= nt Rainfall impact coefficient ,in,

[0016] Indicates the Euler number of non-permeable structural soil.

[0017] Indication of infiltration T Temporal structural earth Euler number;

[0018] S32: Adopted The model's influence coefficient on rainfall varies with infiltration time. T The variation pattern is fitted, where: T Indicates infiltration time. a and b These are the undetermined coefficients for fitting.

[0019] Rainfall infiltration time in step S4 T Shear strength of surface structural soil at that time Rainfall infiltration time T surface structural soil cohesion at that time and rainfall infiltration time T The internal friction angle of the surface structure soil at that time The calculation formula is:

[0020] ;

[0021] ;

[0022] .

[0023] In step S5, the vertical distance from the roadbed slope surface is the burial depth. h Structural soil infiltration T Shear strength over time It can be obtained through the following formula:

[0024] ,in,

[0025] ,

[0026] ;

[0027] The diffusion coefficient has a range of values ​​of 1000. ,

[0028] The hindrance factor has a range of values ​​of . .

[0029] In step S5, the burial depth h Structural soil, infiltration T The cohesive force of time It is obtained through the following calculation formula:

[0030] ,

[0031] The burial depth h Structural soil, infiltration T The internal friction angle over time is obtained using the following formula: .

[0032] In step S6, establishing a refined finite element calculation model includes the following sub-steps:

[0033] S61: Calculate the cohesion and internal friction angle of structural soils with different infiltration times and burial depths, and plot the variation curves;

[0034] S62: Calculate Rainfall Infiltration T When the cohesion or internal friction angle is an integer, the soil layers are divided parallel to the slope at this depth. When the thickness of the divided soil layers exceeds the roadbed fill height, the division of soil layers is stopped.

[0035] S63: Rainfall infiltration at the interface between this layer and the previous layer T The average value of cohesion or internal friction angle represents the shear strength index of the soil layer.

[0036] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0037] (1) This invention fully considers the strength attenuation of structural soil caused by the infiltration process of rainfall into the roadbed, and can obtain the strength of structural soil at different burial depths and infiltration times. The strength changes are fully considered in the finite element modeling process, and the roadbed stability is calculated more objectively.

[0038] (2) This invention only requires testing on the surface structural soil of the subgrade to obtain data such as strength index and Euler number. Through simple calculation, the stability of the subgrade can be analyzed. The calculation results are beneficial to optimizing design and improving construction quality. It is convenient for early targeted treatment and prevention. The calculation efficiency is high and the application prospects are broad. Attached Figure Description

[0039] Figure 1 The variation patterns of Euler number and rainfall influence coefficient;

[0040] Figure 2 This represents the evolution law of cohesion;

[0041] Figure 3 This describes the evolution of the internal friction angle. Detailed Implementation

[0042] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments.

[0043] This embodiment provides a method for calculating the stability of structural soil subgrade under rainfall infiltration conditions, which is implemented through the following steps:

[0044] Step S1: Determine the cohesion of the surface non-permeable structural soil using an indoor consolidated undrained shear test. and internal friction angle According to Mohr-Coulomb's theory, the non-permeable structural soil under normal stress... The shear strength under the action is ;

[0045] Step S2: Take the rainfall infiltration time as T=0, T= t T=2 t T=4 t ..., T=2 nt The surface structural soil was tested using microstructure experiments to determine the Euler number of the surface structural soil during rainfall infiltration. ,in , And it is an integer;

[0046] Step S3: Based on the Euler number of the stratigraphic structure soil at different infiltration times Calculate infiltration time T Rainfall impact coefficient and to To obtain its expression, we perform a fitting process, specifically:

[0047] S31: Using the formula Calculate infiltration time T=0, T= t T=2 t ... T= nt Rainfall impact coefficient ,in Indicates the Euler number of non-permeable structural soil. Indication of infiltration T Time-structured Earth Euler number.

[0048] S32: Adopted The model's influence coefficient on rainfall varies with infiltration time. T The variation pattern is fitted, where: T Indicates infiltration time. a and b These are the undetermined coefficients for fitting.

[0049] Step S4: From The expression determines the rainfall infiltration time. T Shear strength of surface structural soil at that time and the cohesion at this time and internal friction angle ;in , and The calculation formula is:

[0050] ;

[0051] ;

[0052] .

[0053] Step S5: According to As a result, the vertical distance from the roadbed slope surface was calculated as the burial depth. h Structural soil infiltration T Shear strength over time and roadbed depth h Structural soil infiltration T The cohesive force of time and internal friction angle Specifically:

[0054] ,in , ; The diffusion coefficient has a range of values ​​of 1000. , The hindrance factor has a range of values ​​of . .

[0055] ,

[0056] .

[0057] Step S6: Establish a refined finite element calculation model to calculate the stability of the structural soil subgrade under rainfall infiltration conditions. This includes the following sub-steps:

[0058] S61: Calculate the cohesion and internal friction angle of structural soils with different infiltration times and burial depths, and plot the variation curves;

[0059] S62: Calculate Rainfall Infiltration T When the cohesion or internal friction angle is an integer, the soil layers are divided parallel to the slope at this depth. When the thickness of the divided soil layers exceeds the roadbed fill height, the division of soil layers is stopped.

[0060] S63: Rainfall infiltration at the interface between this layer and the previous layer T The average value of cohesion or internal friction angle represents the shear strength index of the soil layer. Example

[0061] A highway in Guangdong Province uses structured clay as its roadbed. The road surface is 35.0m wide and the fill height is 8.0m. The region is hot and humid, with frequent heavy rainfall during the rainy season, which can easily lead to roadbed instability. On a certain day, the weather forecast predicts 10 hours of heavy rainfall. It is necessary to calculate the stability of this structured clay roadbed.

[0062] Shear strength parameters of surface non-infiltrating structural soil were determined by consolidated undrained (CU) laboratory tests. , .

[0063] Topsoil structural samples were collected at rainfall infiltration times of T=0, T=0.5h, T=1h, T=2h, and T=4h. The Euler number of the topsoil structural sample during the rainfall infiltration process was determined using a microstructure test method. ,Depend on The variation patterns of the Euler number and the rainfall influence coefficient are as follows: Figure 1 As shown.

[0064] according to The pattern of change, Figure 1 By fitting the variation pattern of the rainfall impact coefficient, we obtain... a =1.33, b =1.55. That is... The fitted curve is as follows Figure 1 As shown.

[0065] Thus, the shear strength of the structural soil under infiltration can be obtained.

[0066]

[0067] The shear strength index of the surface non-permeable structural soil , Substituting into the above equation, we obtain the shear strength of the structural soil during the infiltration process, which, after simplification, is expressed as:

[0068]

[0069] The simplified expressions for cohesion and internal friction angle during infiltration are:

[0070]

[0071]

[0072] according to As a result, take , ,have to

[0073] ,

[0074] in , ;

[0075] ,

[0076] .

[0077] Finally, 41 time points were taken at intervals of 0.25 hours within the infiltration time range of 0–10 hours, and 101 layers of structural soil were taken at intervals of 0.1 meters within the structural soil burial depth range of 0–10 meters. A program was developed using MATLAB software to calculate the shear strength index under 41 × 101 = 4141 working conditions. To facilitate the analysis of the evolution law of the shear strength index using a combination of numerical and graphical methods, the structural soil burial depth was used as the baseline. x Axis, infiltration time is y Shaft, shear strength index is z In a Cartesian rectangular coordinate system of the axes, the evolution surface of the shear strength index is plotted using Origin plotting software, such as... Figure 2 and Figure 3 As shown.

[0078] Calculate the burial depth when the cohesion value is an integer after 10 hours of rainfall infiltration. Divide the soil layers parallel to the slope at this burial depth. Stop dividing the soil layers when the thickness of the divided soil layers reaches 8m of the roadbed filling height.

[0079] The shear strength index of the soil layer is represented by the cohesion and internal friction angle when rainfall infiltrates for 10 hours at the centerline depth of each layer.

[0080] soil layer 0 1 2 3 4 5 6 7 8 Cohesion (kPa) 28.0 29.0 30.0 31.0 32.0 33.0 34.0 35.0 36.0 Burial depth (m) 0 0.49 0.99 1.52 2.09 2.75 3.54 4.68 7.54

[0081] After dividing the soil layers, a calculation model was established in the finite element software to analyze the stability of the structural soil subgrade. The calculation showed that the stability safety factor was 1.31, indicating that the subgrade slope would not become unstable.

Claims

1. A method for calculating the stability of structural soil subgrade under rainfall infiltration conditions, characterized in that, Includes the following steps: S1: Determine the cohesion of surface non-permeable structural soil using indoor consolidated undrained shear tests. and internal friction angle According to Mohr-Coulomb's theory, the non-permeable structural soil under normal stress... The shear strength under the action is ; S2: Surface structural soil samples were taken at rainfall infiltration times of T=0, T=t, T=2t, ..., T=nt. The Euler number of the surface structural soil during the rainfall infiltration process was determined using microstructure testing. ,in , And it is an integer; S3: The Euler number of the surface structural soil based on the different infiltration times determined in step S2. Calculate the rainfall influence coefficient at infiltration time T. And the rainfall influence coefficient at the infiltration time T. Perform a fitting operation to obtain its expression; S4: Rainfall influence coefficient at the infiltration time T The expression determines the shear strength of the surface structural soil at rainfall infiltration time T. and the cohesion at this time and internal friction angle ; S5: Shear strength of surface structural soil based on rainfall infiltration time T As a result, the shear strength of the structural soil at a depth h at a vertical distance from the roadbed slope surface was calculated at an infiltration time T. And the cohesion of the structural soil at a subgrade depth h during infiltration time T. and internal friction angle ; S6: Establish a refined finite element calculation model to calculate the stability of structural soil subgrade under rainfall infiltration conditions; The shear strength of the surface structural soil at rainfall infiltration time T in step S4 Cohesion of surface structural soil at rainfall infiltration time T and the internal friction angle of surface structural soil at rainfall infiltration time T The calculation formula is: ； ； ； In step S5, the shear strength of the structural soil at a depth h, which is a vertical distance from the roadbed slope surface, during the infiltration time T is calculated. It can be obtained through the following formula: ,in, ， ； The diffusion coefficient has a range of values ​​of 1000. , The hindrance factor has a range of values ​​of . ; In step S5, the cohesion of the structural soil at a burial depth h during infiltration time T is... It is obtained through the following calculation formula: ， The internal friction angle of the structural soil at a burial depth h at an infiltration time T is obtained using the following formula: .

2. The method for calculating the stability of structural soil subgrade under rainfall infiltration conditions according to claim 1, characterized in that, Rainfall influence coefficient at infiltration time T as described in step S3 The expression is obtained through the following sub-steps: S31: Using the formula Calculate the rainfall influence coefficient at infiltration times T=0, T=t, T=2t, ..., T=nt. ,in, Indicates the Euler number of non-permeable structural soil. Indicates the Euler number of the structural soil at infiltration time T; S32: Adopted The model fits the variation of the rainfall impact coefficient with infiltration time T, where T represents the infiltration time, and a and b are undetermined fitting coefficients.

3. The method for calculating the stability of structural soil subgrade under rainfall infiltration conditions according to claim 1, characterized in that, In step S6, establishing a refined finite element calculation model includes the following sub-steps: S61: Calculate the cohesion and internal friction angle of structural soils with different infiltration times and burial depths, and plot the variation curves; S62: When calculating rainfall infiltration T, the depth at which the cohesion or internal friction angle is an integer is used to divide the soil layers parallel to the slope at this depth. When the thickness of the divided soil layers exceeds the roadbed fill height, the division of soil layers is stopped. S63: The shear strength index of the soil layer is represented by the average cohesion or internal friction angle at the rainfall infiltration T at the interface of this layer and the interface of the previous layer.

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