Calculation method for shear strength of root-soil composite considering soil moisture content

Abstract

This invention provides a method for calculating the shear strength of root-soil composites considering soil moisture content, and a method for determining the shear strength of root-soil composites based on soil moisture content and the total root area within a region. By measuring the soil moisture content and the total root area within the region, and combining this with an improved Wu model that considers a moisture content correction coefficient, a method for calculating the shear strength of root-soil composites considering moisture content is obtained, which is used to determine the shear strength values ​​of root-soil composites under different moisture contents. This solves the problem of difficulty in calculating the shear strength values ​​of root-soil composites under different moisture contents, and has important theoretical and practical significance for the stability analysis and monitoring and early warning of landslides in vegetated areas under rainfall.

Description

Technical Field

[0001] This invention belongs to the field of geotechnical and geological engineering technology, specifically a method for calculating the shear strength of root-soil composites considering soil moisture content. Background Technology

[0002] In recent years, extreme rainfall has become increasingly frequent worldwide, triggering geological disasters such as shallow landslides and debris flows. For example, the hilly and mountainous areas along the southeastern coast of China are frequently hit by typhoons. The heavy rainfall brought by typhoons adversely affects slope stability, making these areas prone to landslides. A noteworthy characteristic of these landslides is their high vegetation cover. With the continuous updating of soil and water conservation concepts, the important role of plant roots in slope stability and erosion control has been recognized. Plant roots can reinforce soil by maintaining or reducing soil moisture content and enhancing soil shear strength. Based on the mechanical size effect of roots, the most widely accepted theories are the anchoring effect of coarse roots and the reinforcing effect of fine roots.

[0003] For vegetated slopes, the combination of strong plant roots and weaker soil forms a root-soil complex. Through their mutual physical and mechanical interactions, this complex enhances the soil's shear strength and resistance to deformation. Due to the complexity of root systems, accurately calculating the shear strength of the root-soil complex has always been a challenge, especially for calculating shear strength values ​​under different moisture contents. A method for calculating the shear strength of the root-soil complex considering moisture content can provide important data for analyzing landslide stability in vegetated areas under rainfall. Summary of the Invention

[0004] To address the shortcomings and deficiencies of existing technologies, the present invention aims to provide a method for calculating the shear strength of root-soil composites considering soil moisture content, and a method for determining the shear strength of root-soil composites based on soil moisture content and the total root area within the region. This is achieved by measuring the soil moisture content and the total root area within the region, combined with a moisture content correction factor k. sθ With k rθ An improved Wu model was developed, resulting in a method for calculating the shear strength of the root-soil composite considering moisture content. This method is used to determine the shear strength values ​​of the root-soil composite under different moisture contents. It solves the problem of difficulty in calculating the shear strength values ​​of the root-soil composite under different moisture contents, and has important theoretical and practical significance for the stability analysis and monitoring and early warning of landslides in vegetated areas under rainfall.

[0005] It measures the soil moisture content and the total root area within the region, combined with a correction factor k′ and a soil cohesion correction factor k that takes into account the moisture content. sθ Correction factor k for additional root cohesion rθAn improved Wu model was developed to calculate the shear strength of the root-soil composite considering moisture content, which was then used to determine the shear strength values ​​of the root-soil composite under different moisture contents. This solves the problem of difficulty in calculating the shear strength values ​​of the root-soil composite under different moisture contents, and has important theoretical and practical significance for the stability analysis and monitoring and early warning of vegetated slopes under rainfall.

[0006] The specific technical solution adopted by this invention to solve its technical problem is as follows:

[0007] A method for calculating the shear strength of a root-soil composite considering soil moisture content, characterized by: measuring the soil moisture content and the total root area within the region, combined with a moisture content correction factor k. sθ With k rθ The improved Wu model was used to calculate the shear strength of the root-soil composite considering the water content.

[0008] Furthermore, the specific steps include:

[0009] Step S1: The traditional Wu model does not consider the effect of moisture on the strength of the root-soil composite, and therefore cannot calculate the strength of the root-soil composite at different moisture contents. Therefore, based on the Wu model, this step considers the influence of moisture content on the soil's inherent cohesion and the additional cohesion of the roots, and introduces a correction coefficient k related to the soil moisture content. sθ With k rθ Calculate the shear strength of the root-soil composite considering soil moisture content:

[0010]

[0011] In the formula: s * θ The shear strength of the root-soil composite considering moisture content (kPa); σ is the normal stress on the shear plane (kPa); c is the soil cohesion (kPa); The internal friction angle of the soil (°); s r Additional cohesion (kPa) provided to the root system. ρ d The dry density of soil (g.cm) 3 );ρ w Pore ​​water density (g·cm³) 3 );θ w Volumetric moisture content (%); h shear plane depth (cm); k′ is a correction factor, which is the ratio of the measured value to the model value of the additional root cohesion; k sθ The soil cohesion correction factor considering moisture content; k rθ The root cohesion correction factor considering moisture content; T r A is the average tensile strength of the root system (kPa); A is the area of ​​the shear zone (cm²). 2 A s The total area of ​​the root within the region (cm²)2 ).

[0012] Among them, the soil cohesion correction factor k considering water content sθ The expression is:

[0013] k sθ =c+dθ w (2)

[0014] In the formula: c and d are soil properties;

[0015] Root cohesion correction factor k considering moisture content rθ The expression is:

[0016] k rθ =aθ w b (3)

[0017] In the formula: a and b are soil properties;

[0018] Step S2: Measure the soil cohesion (c) and internal friction angle at different moisture contents using indoor geotechnical experiments. By fitting the soil cohesion at different moisture contents, a soil cohesion correction coefficient k considering moisture content is obtained. sθ Soil properties c, d;

[0019] Step S3: Obtain the total root area A within the root-soil complex area through field surveys and tests. s And the additional cohesion of the root system in the root-soil composite under natural moisture content. r The correction coefficient k′ is obtained by comparing the calculated value with that of the Wu model.

[0020] Step S4: Obtain the total root area A within the root-soil complex area through field surveys and tests. s The additional cohesion of the root system in the root-soil composite under different moisture contents was compared with the calculated value of the Wu model after correction factor k′ to obtain the additional cohesion k of the root-soil composite considering moisture content. rθ Additional cohesion k of root-soil composites under different moisture contents rθ By performing fitting, soil parameters a and b are obtained;

[0021] Step S5: Obtain the required average tensile strength T of the root system through indoor single-root tensile tests. r ;

[0022] Step S6: Based on the soil cohesion correction factor k obtained in step S2, considering the water content... sθSoil parameters c and d; correction factor k′ in step S3; additional root cohesion k of the root-soil composite considering moisture content measured in step S4. rθ And in conjunction with step S5, the required average tensile strength T of the root system is obtained. r Substituting into equation (1), we get the calculation model for the shear strength of the root-soil composite considering the water content; for the root-soil composite under different water contents, the volumetric water content θ is used as the formula. w The total area A within the region s Substituting the shear surface depth h, the shear strength of the root-soil composite is calculated.

[0023] Furthermore, in step S1, the specific process for obtaining the formula for the shear strength of the root-soil composite considering soil moisture content is as follows:

[0024] 1a) Within the scope of the prior art, based on the Wu model, there is a simple model that can estimate the shear strength of the root-soil composite.

[0025]

[0026] In the formula: s * σ is the shear strength of the root-soil composite (kPa); σ is the normal stress on the shear surface (kPa); c is the soil cohesion (kPa); The internal friction angle of the soil is (°).

[0027] in:

[0028] s r =1.2T r (A s / A) (5)

[0029] In the formula: T r Let A be the average tensile strength of the root system and A be the area of ​​the shear zone (cm²). 2 A s The total area of ​​the root within the region (cm²) 2 ).

[0030] 1b) Considering the in-situ direct shear test, for the shear surface of the root-soil composite, the normal stress is:

[0031] σ=ρVg / A=(ρ d +ρ d w)Vg / A=(ρ d +ρ d w)hg (6)

[0032] ρ d ρ is the dry density of the soil. w ρ is the pore water density; w is the mass water content;

[0033] 1c) Considering the collected moisture content as volumetric moisture content, the conversion relationship between volumetric moisture content and mass moisture content is as follows:

[0034] θ w =V W / V=wρ d / ρ w (7)

[0035] In the formula: θ w V represents the volumetric water content. W V is the pore water volume; V is the total volume of the soil sample.

[0036] 1d) By combining equations (6) and (7), the relationship between the normal stress on the shear surface of the root-soil composite and the volumetric water content of the soil is obtained:

[0037] σ=(ρ d +θ w ρ w Vg / A=(ρ d +θ w ρ w )gh (8)

[0038] 1e) Considering the additional cohesion provided by the root system, the calculation results of the Wu model are too high. Therefore, a correction factor is introduced into the model to correct the Wu model, and equation (5) is rewritten as:

[0039] s r =k′1.2T r (A s / A) (9)

[0040] In the formula: k′ is the correction coefficient, which is the ratio of the measured value of the additional cohesion of the root system to the model value;

[0041] 1f) The modified Wu model corresponding to equation (9) is used to calculate the additional root cohesion of different RARs, which is taken as the additional root cohesion of the root system under normal moisture content. It is compared with the measured additional root cohesion under different moisture contents. The ratio of the additional root cohesion under the influence of moisture to the additional root cohesion of the root system calculated by the modified Wu model under natural moisture content is defined as the correction coefficient of the additional root cohesion considering moisture content. The correction coefficient k rθ The expression for the change with moisture content is:

[0042] k rθ =aθ w b (10)

[0043] In the formula: a and b are soil properties;

[0044] 1g) Due to the internal friction angle of colluvial cohesive soil Since the change in moisture content is limited, the internal friction angle at the natural moisture content or the corresponding moisture content is used in the calculation. For soil cohesion, because it decreases significantly with increasing moisture content, a soil cohesion correction factor k that considers moisture content is adopted. sθ :

[0045] k sθ =c+dθ w (11)

[0046] In the formula: c and d are soil properties;

[0047] 1h) From equations (4), (9) and the correction coefficient, we obtain the expression of equation (1).

[0048] Furthermore, the soil cohesion correction factor k, considering the moisture content, was measured. sθ The soil parameters c and d in the expression for changes with water content are specifically obtained by dividing the measured cohesion of the soil at different water contents by the cohesion at the natural water content, thus obtaining the cohesion correction coefficient k for different water contents. sθ The value is based on the soil cohesion correction factor k. sθ - Moisture content data, with moisture content on the x-axis and soil cohesion correction factor k. sθ Using the vertical axis as the ordinate, plot a scatter plot, perform linear fitting, and obtain the soil parameters c and d.

[0049] The specific method for measuring the correction coefficient k′ is as follows: divide the measured value of the additional cohesion of the root system by the value calculated by the Wu model, and the resulting ratio is k′.

[0050] The measured soil cohesion correction factor k considering moisture content sθ The soil parameters c and d in the expression for the change with water content are specifically calculated as follows: The modified Wu model corresponding to equation (9) is used to calculate the additional cohesion of the root system for different RARs, which is taken as the additional cohesion of the root system under normal water content. This is compared with the measured additional cohesion of the root system under different water contents. The ratio of the additional cohesion of the root system under the influence of water to the additional cohesion of the root system under natural water content calculated by the modified Wu model is defined as k. rθ Based on the root system additional cohesion correction factor k considering moisture content rθ - Moisture content data, plotted on the x-axis, with root cohesion correction factor k. rθ Using the vertical axis as the ordinate, a scatter plot is drawn and a nonlinear fit is performed to obtain the soil parameters a and b.

[0051] Compared to existing technologies, this invention and its preferred embodiment utilize soil moisture content and total root area within a region, combined with an improved Wu model, to calculate the shear strength of the root-soil composite considering moisture content. This allows for the determination of the shear strength values ​​of the root-soil composite at different moisture contents, solving the problem of difficulty in calculating the shear strength values ​​of the root-soil composite at different moisture contents. For vegetated slopes, the combination of high-strength plant roots and low-strength soil forms the root-soil composite, which enhances the shear strength and deformation resistance of the soil through mutual physical and mechanical interactions. Therefore, calculating the shear strength of the root-soil composite at different moisture contents using soil moisture content and total root area within a region, combined with the improved Wu model, has significant theoretical and practical implications for the stability analysis and monitoring and early warning of vegetation landslides under rainfall. Attached Figure Description

[0052] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments:

[0053] Figure 1 The soil cohesion correction factor k in the embodiments of the present invention sθ - Moisture content curve fitting diagram;

[0054] Figure 2 The root system additional cohesion correction coefficient k in the embodiments of the present invention rθ - Moisture content curve fitting diagram. Detailed Implementation

[0055] To make the features and advantages of this patent more apparent and understandable, specific embodiments are provided below for detailed explanation:

[0056] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used in this specification have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0057] like Figure 1 , Figure 2 As shown, this embodiment of the invention provides a method for calculating the shear strength of a root-soil composite considering soil moisture content, comprising the following steps:

[0058] To achieve the above objectives, the present invention provides a method for calculating the shear strength of a root-soil composite considering moisture content, comprising the following steps:

[0059] 1) The traditional Wu model does not consider the influence of moisture on the strength of the root-soil composite, and therefore cannot calculate the strength of the root-soil composite at different moisture contents. Therefore, this invention, based on the Wu model, considers the influence of moisture content on the soil's inherent cohesion and the additional cohesion of the roots, and introduces a correction coefficient k related to the soil moisture content. sθ With k rθA method for calculating the shear strength of the root-soil composite considering soil moisture content is proposed:

[0060]

[0061] In the formula: s * θ The shear strength of the root-soil composite considering moisture content (kPa); σ is the normal stress on the shear plane (kPa); c is the soil cohesion (kPa); The internal friction angle of the soil (°); s r Additional cohesion (kPa) provided to the root system. ρ d The dry density of soil (g.cm) 3 );ρ w Pore ​​water density (g·cm³) 3 );θ w Volumetric moisture content (%); h shear plane depth (cm); k′ is a correction factor, which is the ratio of the measured value to the model value of the additional root cohesion; k sθ The soil cohesion correction factor considering moisture content; k rθ The root cohesion correction factor considering moisture content; T r A is the average tensile strength of the root system (kPa); A is the area of ​​the shear zone (cm²). 2 A s The total area of ​​the root within the region (cm²) 2 ).

[0062] Among them, the soil cohesion correction factor k considering water content sθ The expression is:

[0063] k sθ =c+dθ w (2)

[0064] In the formula: c and d are soil properties.

[0065] Root cohesion correction factor k considering moisture content rθ The expression is:

[0066] k rθ =aθ w b (3)

[0067] In the formula: a and b are soil properties.

[0068] Based on the Wu model, considering the influence of moisture content on the cohesion of the soil itself and the additional cohesion of the root system, a method for calculating the shear strength of the root-soil composite considering soil moisture content is proposed. The specific process is as follows:

[0069] 1a) Based on the relevant theories of soil mechanics and materials mechanics, Wu et al. established a simple model that can estimate the shear strength of the root-soil composite.

[0070]

[0071] In the formula: s * σ is the shear strength of the root-soil composite (kPa); σ is the normal stress on the shear surface (kPa); c is the soil cohesion (kPa); The internal friction angle of the soil is (°).

[0072] in:

[0073] s r =1.2T r (A s / A) (5)

[0074] In the formula: T r Let A be the average tensile strength of the root system and A be the area of ​​the shear zone (cm²). 2 A s The total area of ​​the root within the region (cm²) 2 ).

[0075] 1b) In the in-situ direct shear test, the normal stress on the shear surface of the root-soil composite is:

[0076] σ=ρVg / A=(ρ d +ρ d w)Vg / A=(ρ d +ρ d w)hg (6)

[0077] In the formula: ρ d ρ is the dry density of the soil. w ρ is the pore water density; w is the mass water content.

[0078] 1c) Since many soil moisture sensors used in landslide monitoring employ the TDR principle, the collected moisture content is volumetric moisture content. The conversion relationship between volumetric moisture content and mass moisture content is as follows:

[0079] θ w =V W / V=wρ d / ρ w (7)

[0080] In the formula: θ w V represents the volumetric water content. W V represents the pore water volume; V represents the total volume of the soil sample.

[0081] 1d) By combining equations (6) and (7), the relationship between the normal stress on the shear surface of the root-soil composite and the volumetric water content of the soil can be obtained.

[0082] σ=(ρ d +θ w ρ w Vg / A=(ρ d +θ w ρ w )gh (8)

[0083] 1e) Regarding the additional cohesion provided by the root system, many scholars have found that the calculation results of the Wu model are too high. Therefore, many scholars have introduced a correction factor into the model to correct the Wu model. Equation (5) can be rewritten as:

[0084] s r =k′1.2T r (A s / A) (9)

[0085] In the formula: k′ is the correction coefficient, which is the ratio of the measured value of the additional cohesion of the root system to the model value.

[0086] 1f) The modified Wu model (Equation 9) is used to calculate the additional root cohesion of different RARs, which is taken as the additional root cohesion of the root system under normal moisture content. The result is compared with the measured additional root cohesion under different moisture contents. The ratio of the additional root cohesion under the influence of moisture to the additional root cohesion calculated by the modified Wu model under natural moisture content is defined as the correction coefficient of the additional root cohesion considering moisture content. The correction coefficient k rθ The expression for the change with moisture content is:

[0087] k rθ =aθ w b (10)

[0088] In the formula: a and b are soil properties.

[0089] 1g) Due to the internal friction angle of colluvial cohesive soil Since the change in moisture content is limited, the internal friction angle at the natural moisture content or the corresponding moisture content can be used in the calculation. For soil cohesion, because it decreases significantly with increasing moisture content, a soil cohesion correction factor k that considers moisture content is used. sθ

[0090] k sθ =c+dθ w (11)

[0091] In the formula: c and d are soil properties.

[0092] 1h) From equations (4) and (9) and subsequent correction coefficients, the formula for calculating the shear strength of the root-soil composite considering the change in soil moisture content can be obtained:

[0093]

[0094] In the formula: s * The shear strength of the root-soil composite considering moisture content (kPa); σ is the normal stress on the shear plane (kPa); c is the soil cohesion (kPa); The internal friction angle of the soil (°); s r Additional cohesion (kPa) provided to the root system. ρ d ρ is the dry density of the soil. w θ is the density of pore water; w Volumetric water content; h is the shear plane depth; k′ is a correction factor, which is the ratio of the measured value to the model value of the additional root cohesion; k sθ The soil cohesion correction factor considering moisture content; k rθ Root cohesion correction factor k considering moisture content rθ ;T r A is the average tensile strength of the root system (kPa); A is the area of ​​the shear zone (cm²). 2 A s The total area of ​​the root within the region (cm²) 2 ).

[0095] 2) The soil cohesion c and internal friction angle at different moisture contents were measured by indoor geotechnical experiments. By fitting the soil cohesion at different moisture contents, a soil cohesion correction coefficient k considering moisture content is obtained. sθ The soil properties c and d.

[0096] 3) Obtain the total root area A within the root-soil complex area through field surveys and tests. s And the additional cohesion of the root system in the root-soil composite under natural moisture content. r By comparing the calculated value with that of the traditional Wu model, the correction coefficient k′ is obtained.

[0097] 4) Obtain the total root area A within the root-soil complex area through field surveys and tests. s The additional cohesion of the root system in the root-soil composite under different moisture contents was compared with the calculated value of the Wu model after correction factor k′ to obtain the additional cohesion k of the root-soil composite considering moisture content. rθ Additional cohesion k of the root system in root-soil composites under different moisture contents. rθ By fitting the data, soil parameters a and b are obtained.

[0098] 5) Obtain the average tensile strength T of the required root system through indoor single-root tensile tests. r

[0099] 6) Based on the soil cohesion correction factor k obtained in step 2) considering the water content. sθ Soil parameters c and d; Step 3) Correction coefficient k′; Step 4) Measured root-soil composite root cohesion k considering moisture content. rθ And in conjunction with step 5), obtain the required average tensile strength T of the root system. r Substituting into equation (1), we get the calculation model for the shear strength of the root-soil composite considering the water content. For root-soil composites with different water contents, we only need to consider the volumetric water content θ. w The total area A within the region s Substituting the shear surface depth h, the shear strength of the root-soil composite can be calculated.

[0100] The invention will be further described below with reference to specific examples:

[0101] The example used in this embodiment is a root-soil composite consisting of the root system of *Pinus massoniana* and colluvial residual clay in Wuping area, Longyan, Fujian. First, colluvial residual clay consistent with the root-soil composite was collected on-site. Indoor direct shear tests were conducted on remolded soil with volumetric water contents of 25%, 30%, 35%, 40%, and 45% to obtain the changes in cohesion of the colluvial residual clay at different water contents. The results were then fitted according to equation (11), and the fitted curve is shown below. Figure 1 As shown. The soil parameters obtained are c = 2.09, d = -0.04, and the soil cohesion correction factor k considering water content is... sθ The expression is: k sθ =2.09-0.04θ. Then, the total root area A within the root-soil composite area of ​​*Pinus massoniana* was obtained through on-site root-soil composite shear strength tests. s And the additional cohesion of the root system in the root-soil composite under natural moisture content. r Comparing the calculated values ​​with those of the traditional WU model, a correction coefficient k′ = 0.16 was obtained. The total root area A within the root-soil composite region was obtained through field tests on the shear strength of root-soil composites at different moisture contents. s The additional cohesion of the root system in the root-soil composite under different moisture contents was compared with the calculated value of the WU model after correction coefficient k′, and fitted according to equation (10). The fitted curve is shown in the figure. Figure 2 As shown. The additional cohesion k of the root system in the root-soil composite considering moisture content is obtained. rθ The soil parameters are a = 10.67 and b = -0.74. The correction factor k for the additional cohesion of the root system in the root-soil composite, considering moisture content, is... rθ The expression is: k rθ =10.67θ w -0.74 The average tensile strength T of the Masson pine root system was obtained through indoor single-root tensile tests. r=15470kPa. Substituting the data into equation (1), for the Masson pine root-soil composite under different moisture contents, it is only necessary to change the volumetric water content θ. w The total area A within the region s Substituting the shear surface depth h, the shear strength of the root-soil composite can be calculated. Field direct shear tests were conducted on two Masson pine trees to verify the model. The measured values ​​were compared with the calculated values, and the error range was reasonable and relatively accurate, as shown in Table 1.

[0102] Table 1 Calculation results of the modified WU model

[0103]

[0104] Existing root-soil composite calculation models cannot calculate the shear strength of root-soil composites under different moisture contents. This invention utilizes a moisture content sensor to measure soil moisture content, and employs an excavation method and electronic calipers to measure the total root area within the region. Combined with an improved Wu model, it calculates the shear strength of the root-soil composite considering moisture content, thereby determining the shear strength value of the root-soil composite under different moisture contents. This solves the problem of difficulty in calculating the shear strength value of the root-soil composite under different moisture contents. For vegetated slopes, calculating the shear strength of the root-soil composite considering moisture content has significant theoretical and practical implications for the stability analysis and monitoring and early warning of vegetation landslides under rainfall.

[0105] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any other way. Any person skilled in the art may make changes or modifications to the above-disclosed technical content to create equivalent embodiments. However, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the protection scope of the present invention.

[0106] This patent is not limited to the above-described preferred embodiments. Anyone can derive other methods for calculating the shear strength of root-soil composites that take into account soil moisture content under the guidance of this patent. All equivalent changes and modifications made within the scope of this patent application shall fall within the scope of this patent.

Claims

1. A method for calculating the shear strength of a root-soil composite considering soil moisture content, characterized in that: By measuring the soil moisture content and the total root area within the region, and taking into account the moisture content correction factor... and The improved Wu model was used to calculate the shear strength of the root-soil composite considering the water content. Specifically, the following steps are included: Step S1: Based on the Wu model, considering the influence of moisture content on the soil's inherent cohesion and the additional cohesion of the roots, a correction coefficient related to the soil moisture content is introduced. and Calculate the shear strength of the root-soil composite considering soil moisture content: （1） In the formula: Shear strength of root-soil composite considering moisture content; For shear plane normal stress; It is the soil cohesion; The internal friction angle of the soil; Additional cohesive force provided to the root system; The dry density of the soil; The density of pore water; Volumetric moisture content; Shear depth; The correction factor is the ratio of the measured value to the model value of the additional cohesion of the root system. The soil cohesion correction factor is taken into account the moisture content; An additional cohesion correction factor for the root system, taking into account moisture content; This represents the average tensile strength of the root system. The area of ​​the shear region; The total area of ​​the root within the region; Among them, the soil cohesion correction factor considering water content The expression is: （2） In the formula: c and d are soil properties; Root cohesion correction factor considering moisture content The expression is: （3） In the formula: a and b are soil properties; Step S2: Measure the soil cohesion at different moisture contents using indoor geotechnical experiments. Angle of friction with soil By fitting the soil cohesion under different moisture contents, a soil cohesion correction coefficient considering moisture content is obtained. Soil properties c, d; Step S3: Obtain the total root area within the root-soil complex area through field surveys and tests. And the additional cohesion of the root system in the root-soil composite under natural moisture content. The correction coefficients are obtained by comparing them with the calculated values ​​from the Wu model. ; Step S4: Obtain the total root area within the root-soil complex area through field surveys and tests. And the additional cohesion of the root system in the root-soil composite under different moisture contents, and the modified coefficient. The root cohesion correction factor considering moisture content was obtained by comparing the calculated values ​​of the modified Wu model. ; Added root cohesion correction factor for different moisture contents By performing fitting, soil parameters a and b are obtained; Step S5: Obtain the required average tensile strength of the root system through indoor single-root tensile tests. ; Step S6: Based on the soil cohesion correction factor considering moisture content obtained in step S2. Soil parameters c, d; correction factor in step S3 The root cohesion correction factor considering moisture content, measured in step S4. And in conjunction with step S5, the required average tensile strength of the root system is obtained. Substituting into equation (1), we get the calculation model for the shear strength of the root-soil composite considering the water content; for root-soil composites with different water contents, the volumetric water content is... Total root area within the region Shear depth Substitute the values ​​to calculate the shear strength of the root-soil composite.

2. The method for calculating the shear strength of the root-soil composite considering soil moisture content according to claim 1, characterized in that: In step S1, the specific process for obtaining the formula for the shear strength of the root-soil composite considering soil moisture content is as follows: 1a) Based on the Wu model, there is a simple model that can estimate the shear strength of the root-soil composite; （4） In the formula: For the shear strength of the root-soil composite; For shear plane normal stress; It is the soil cohesion; The internal friction angle of the soil; in: （5） In the formula: The average tensile strength of the root system. The area of ​​the shear region; The total area of ​​the root within the region; 1b) Considering the in-situ direct shear test, for the shear surface of the root-soil composite, the normal stress is: （6） The dry density of the soil; The density of pore water; Moisture content (by weight); 1c) Considering the collected moisture content as volumetric moisture content, the conversion relationship between volumetric moisture content and mass moisture content is as follows: （7） In the formula: This refers to the volumetric water content. The volume of pore water; This represents the total volume of the soil sample. 1d) By combining equations (6) and (7), the relationship between the normal stress on the shear surface of the root-soil composite and the volumetric water content of the soil is obtained: （8） 1e) Considering the additional cohesion provided by the root system, the calculation results of the Wu model are too high. Therefore, a correction factor is introduced into the model to correct the Wu model, and equation (5) is rewritten as: （9） In the formula: The correction factor is the ratio of the measured value to the model value of the additional root cohesion. 1f) The modified Wu model corresponding to equation (9) is used to calculate the additional root cohesion of different RARs, which is taken as the additional root cohesion of the root system under normal moisture content. It is compared with the measured additional root cohesion under different moisture contents. The ratio of the additional root cohesion under the influence of moisture to the additional root cohesion of the root system calculated by the modified Wu model under natural moisture content is defined as the correction coefficient of the additional root cohesion considering moisture content. The expression for the change with moisture content is: （10） In the formula: a and b are soil properties; 1g) Due to the internal friction angle of colluvial cohesive soil Since the change in moisture content is limited, the internal friction angle at the natural moisture content or the corresponding moisture content is used in the calculation. For soil cohesion, because it decreases significantly with increasing moisture content, a soil cohesion correction factor considering moisture content is adopted. : （11） In the formula: c and d are soil properties; 1h) From equations (4), (9) and the correction coefficient, we obtain the expression of equation (1).

3. The method for calculating the shear strength of the root-soil composite considering soil moisture content according to claim 1, characterized in that: Measured soil cohesion correction factor considering moisture content The soil parameters c and d in the expression for changes with water content are specifically obtained by dividing the measured cohesion of the soil at different water contents by the cohesion at the natural water content to obtain the cohesion correction coefficients at different water contents. Value, based on soil cohesion correction factor - Moisture content data, with moisture content on the x-axis and soil cohesion correction factor. Using the vertical axis as the scatter plot, perform linear fitting to obtain the soil parameters c and d; Measured correction coefficient The specific method is as follows: Divide the measured value of the additional cohesion of the root system by the value calculated by the Wu model, and the resulting ratio is... ; Measured soil cohesion correction factor considering moisture content The soil parameters c and d in the expression for the change with water content are specifically calculated as follows: The modified Wu model corresponding to equation (9) is used to calculate the additional cohesion of the root system for different RARs, which is taken as the additional cohesion of the root system under normal water content. This is compared with the measured additional cohesion of the root system under different water contents. The ratio of the additional cohesion of the root system under the influence of water to the additional cohesion of the root system under natural water content calculated by the modified Wu model is defined as: Based on the root system additional cohesion correction factor considering moisture content - Moisture content data, with moisture content on the x-axis and root cohesion correction factor. Using the vertical axis as the ordinate, a scatter plot is drawn and a nonlinear fit is performed to obtain the soil parameters a and b.

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