A method for evaluating collapsibility of silty fine sand based on resistivity

Abstract

The application discloses a kind of based on resistivity silt sand soil collapsibility evaluation method, belong to geotechnical engineering investigation and collapsibility evaluation technical field, the method specifically is: to silt sand soil ground base soil field collection disturbance sample and determine natural moisture content, soil particle specific gravity;Prepare different moisture content and dry density sample, test resistivity using two-phase electrode method, build the correlation model of moisture content, dry density, saturation and resistivity;Through natural moisture content, resistivity, dry density and saturation under natural state are calculated inversely, calculate collapsibility coefficient by substituting calculated porosity and saturation into collapsibility coefficient empirical calculation formula, and determine collapsibility grade.The application uses the above-mentioned one based on resistivity silt sand soil collapsibility evaluation method, only requires to collect disturbed soil sample, can quickly and simply evaluate its collapsibility, and collapsibility evaluation can be carried out to silt sand soil ground base soil body of any depth, has significant technical advantages.

Description

Technical Field

[0001] This invention relates to the field of geotechnical engineering investigation and collapsibility evaluation technology, and in particular to a method for evaluating the collapsibility of silty fine sand based on resistivity. Background Technology

[0002] Collapsible soils are widely distributed in my country. In addition to the common collapsible loess, collapsible gravelly soils and collapsible sandy soils, which are not loess types, are widely developed in the alluvial and colluvial fans (skirts) of arid and semi-arid regions of China. In recent years, deserts, Gobi and loess transition zones in the arid and semi-arid regions of Northwest China have become the core areas for wind power generation projects. At the same time, large-scale national energy development has led to an increasing number of oil and gas field projects (stations, underground pipelines, roads, etc.) that pass through or are built in these areas.

[0003] The silty fine sand soil in this area possesses certain structural strength under natural low moisture content (3%-6%) conditions. However, under immersion conditions (due to pipeline leakage, changes in hydrogeological conditions caused by rainfall), the soil structure deteriorates, resulting in significant additional settlement. This leads to foundation deformation and even instability, causing engineering defects such as bending, suspension, and breakage of oil and gas pipelines, and uneven settlement of wind turbine towers and oil and gas storage tank foundations, seriously threatening the safety of these structures. Therefore, accurate and efficient assessment of the collapsibility of silty fine sand soil foundations is of significant engineering importance.

[0004] Currently, the "Code for Geotechnical Investigation" (GB 50021-2001) (2009 edition) stipulates the evaluation criteria for non-loess collapsible soils: for silty fine sand where undisturbed samples can be obtained, the "Standard for Building Construction in Collapsible Loess Areas" (GB 50025-2018) can be referenced, with a collapsibility coefficient ≥0.015 obtained from indoor immersion collapsibility tests as the criterion for collapsibility determination. However, silty fine sand has a loose structure and weak cementation, making it extremely difficult to obtain undisturbed samples. Disturbance is very likely to occur during sampling, making it impossible to maintain the natural pore structure, leading to inaccurate indoor test results.

[0005] For silty fine sand where undisturbed samples cannot be obtained, the standard stipulates that in-situ immersion load tests should be used to determine its collapsibility, with the ratio of additional collapsibility under 200 kPa pressure to the width of the bearing plate being ≥0.023 as the criterion. However, in-situ immersion load tests have significant drawbacks: the testing cycle at a single point is as long as 7-10 days, requiring the excavation of test pits and the construction of complex loading devices; each test can only test the collapsibility of a soil layer at one depth, and the influence of immersion in adjacent tests must be avoided; the testing cost is high, making it difficult to meet the batch testing needs of large-area engineering surveys.

[0006] Therefore, given the difficulty in obtaining undisturbed samples of silty fine sand, there is an urgent need to develop a method for evaluating the collapsibility of silty fine sand that is simple to sample, has low testing costs, a short testing cycle, and can evaluate soil layers at any depth. Summary of the Invention

[0007] The purpose of this invention is to provide a method for evaluating the collapsibility of silty fine sand based on resistivity. This method can solve the problems of difficulty in obtaining undisturbed samples of silty fine sand and high cost and long cycle of field tests in the prior art. It can quickly and cost-effectively evaluate the collapsibility of silty fine sand foundations at any depth, and can also be cross-validated with the results of laboratory tests.

[0008] To achieve the above objectives, this invention provides a method for evaluating the collapsibility of silty fine sand based on resistivity, comprising the following steps: S1. Obtain disturbance samples of fine sandy soil foundation on site, conduct basic physical property tests on the soil samples, determine the natural moisture content and soil particle specific gravity, and the measured soil particle specific gravity is numerically equal to the soil particle density. S2. Based on the obtained moisture content of fine sand, prepare fine sand with different moisture content gradients, design different dry density gradients for each moisture content, and prepare fine sand samples with different moisture content gradients and dry densities using an insulating cylinder. S3. Conduct indoor two-phase electrode resistivity tests on the prepared fine sand samples. Based on the resistivity test results, construct the water content-resistivity function relationship and the dry density-resistivity function relationship respectively. Based on the soil particle density, construct the saturation-resistivity function relationship. S4. Substitute the natural moisture content into the moisture content-resistivity function to obtain the resistivity of silty fine sand under natural moisture conditions; substitute the resistivity under natural moisture conditions into the dry density-resistivity function and the saturation-resistivity function respectively to obtain the dry density and saturation of silty fine sand. S5. Substitute the particle density of the fine sand and the dry density under natural water content obtained from S1 and S4 into the porosity calculation formula to obtain the porosity of the fine sand. S6. Based on the calculation formulas for collapsibility coefficient, porosity, and saturation, substitute the saturation obtained in S4 and the porosity obtained in S5 to calculate the collapsibility coefficient of silty fine sand and determine its collapsibility level.

[0009] Preferably, S1 specifically includes the following steps: S11. Take on-site samples of fine sand to obtain soil samples that meet the test requirements; S12. Conduct an indoor moisture content test on the disturbed silty sand samples and calculate their moisture content; S13. For the disturbed silty sand sample, conduct a specific gravity bottle test and calculate the specific gravity of the soil particles, which is numerically equal to the particle density of the soil.

[0010] Preferably, in S2, specifically: based on the moisture content of the fine sand obtained in S1, firstly, fine sand samples with different gradient moisture contents are prepared, then sealed with plastic wrap and left to stand to retain moisture, so that the moisture is evenly distributed in the soil sample, and then the prepared fine sand samples are pressed into the insulating cylinder by static compaction method.

[0011] Preferably, step S3 specifically includes the following steps: S31. The resistivity of the fine sand sample prepared in S2 is tested using a low-frequency AC two-phase electrode. The measuring instrument is an LCR digital bridge. The measuring frequency is adjusted to the common 50Hz. A layer of graphene powder is coated on the upper and lower surfaces of the sample, and a copper sheet is used as an electrode to cover the upper and lower surfaces of the sample. The electrode is connected to the LCR digital bridge through a wire. The resistivity value is measured at least twice, the maximum value is read, and the actual resistivity value is calculated. S32. Based on the resistivity test data of fine sand under different moisture contents and dry densities, the power function is used to describe the nonlinear variation law of resistivity of fine sand with moisture content and dry density, and the functional relationship between moisture content and resistivity and dry density and resistivity is obtained. S33. Introduce the saturation parameter, establish a resistivity model that considers the combined effects of moisture content and dry density of silty fine sand, and establish a functional relationship between saturation and resistivity based on experimental data analysis.

[0012] Preferably, the formula for calculating the actual resistivity value is: ; In the formula, This is the actual resistivity; R For measuring resistance; S Electrode area; L The height of the sample; The formula for calculating the relationship between moisture content and resistivity is: ; The formula for calculating the dry density-resistivity function relationship is: ; In the formula, , , , These are the fitting parameters, w The moisture content of the soil sample. This represents the dry density of the soil sample. The formula for calculating the saturation parameter is: ; The formula for calculating the saturation-resistivity function relationship is: ; In the formula, For saturation parameters, The density of water, This represents the particle density of the soil sample. a , b These are the fitting coefficients.

[0013] Preferably, in S4, specifically: the natural moisture content obtained in S1 is substituted into the moisture content-resistivity function relationship in S3 to obtain the resistivity of silty fine sand under natural moisture conditions; the resistivity under natural moisture conditions is substituted into the dry density-resistivity function relationship and the saturation-resistivity function relationship respectively to obtain the dry density and saturation of silty fine sand.

[0014] Preferably, in S5, the formula for calculating the porosity of silty fine sand is: ; In the formula, n The porosity is the porosity of fine sand.

[0015] Preferably, step S6 specifically includes the following steps: S61. Based on the definition of the collapsibility coefficient, the empirical calculation formula for the collapsibility coefficient is derived. S62. By conducting collapsibility tests on silty sand in silty sandy areas, collapsibility correction parameters are obtained. The actual soil saturation and porosity values ​​obtained from S4 and S5, along with the collapsibility correction parameters, are substituted into the empirical formula for calculating the collapsibility coefficient to obtain the collapsibility coefficient of silty sandy soil. Finally, the collapsibility grade of silty sandy soil is determined.

[0016] Preferably, the empirical formula for calculating the collapsibility coefficient is: ; In the formula, This is the collapsibility coefficient. k This refers to the parameters for wet collapse.

[0017] Therefore, the beneficial effects of the above-mentioned method for evaluating the collapsibility of silty fine sand based on resistivity are as follows: (1) Low sampling requirements: Only disturbed soil samples are needed to complete the evaluation, which completely solves the technical problem of difficulty in obtaining undisturbed samples of fine sand and greatly reduces the difficulty and cost of on-site sampling.

[0018] (2) High testing efficiency: Indoor resistivity testing of a single sample only takes a few minutes, and the testing cycle of batch samples is much shorter than that of on-site immersion load testing, which can meet the batch testing needs of large-area engineering surveys.

[0019] (3) Wide evaluation scope: It can evaluate the collapsibility of silty sandy soil foundations at any depth without the need to conduct field tests for different depths, which significantly improves the efficiency of exploration.

[0020] (4) Reliable results: By constructing a multi-parameter resistivity model and calibrating the regional sinkhole correction coefficient, the accuracy of the evaluation results is guaranteed; at the same time, it can be cross-validated with the results of indoor immersion test and field load test, further improving the reliability of the evaluation.

[0021] (5) Strong applicability: It is especially suitable for evaluating the collapsibility of silty sandy soil foundations for wind power, oil and gas fields, transportation and other projects in arid and semi-arid areas such as deserts and Gobi, and has broad engineering application prospects.

[0022] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0023] Figure 1 This is a flowchart of a method for evaluating the collapsibility of silty fine sand based on resistivity according to the present invention. Figure 2 It is a graph showing the functional relationship between the resistivity and moisture content of silty sand. Figure 3 It is a graph showing the functional relationship between the resistivity and dry density of silty sand. Figure 4 It is a graph showing the functional relationship between the resistivity and saturation of silty sand. Figure 5 This is a comparison chart of the predicted and measured values ​​of the collapsibility coefficient of silty fine sand. Detailed Implementation

[0024] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0025] Unless otherwise defined, the technical or scientific terms used in this invention shall have the ordinary meaning understood by one of ordinary skill in the art to which this invention pertains. The terms "first," "second," and similar terms used in this invention do not indicate any order, quantity, or importance, but are merely used to distinguish different components. Terms such as "comprising" or "including" mean that the element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. Terms such as "connected" or "linked" are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. Terms such as "upper," "lower," "left," and "right" are used only to indicate relative positional relationships; when the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0026] Example 1: like Figure 1 As shown, this invention provides a method for evaluating the collapsibility of silty fine sand based on resistivity, comprising the following steps: S1. Take disturbed samples of silty fine sand foundation on site according to the "Code for Geotechnical Investigation" (GB 50021-2001) (2009 edition), and conduct basic physical property tests on the samples according to the "Standard for Geotechnical Testing Methods" (GBT 50123-2019), determining the natural moisture content and soil particle specific gravity. The determined soil particle specific gravity is numerically equal to the soil particle density. The specific steps include: S11. Take on-site samples of fine sand in accordance with the Code for Geotechnical Investigation (GB 50021-2001) (2009 edition) to obtain soil samples that meet the test requirements; S12. For the disturbed silty sand soil sample, conduct an indoor moisture content test according to the "Standard for Geotechnical Testing Methods" (GBT 50123-2019), and calculate its moisture content according to formula (1). w ; (1) in, w This represents the soil moisture content. The mass of water in the soil under natural conditions; The mass of solid soil particles in their natural state; S13. For the disturbed silty sand soil sample, conduct the specific gravity bottle test according to the "Standard for Geotechnical Testing Methods" (GBT 50123-2019), and calculate the specific gravity of the soil particles according to formula (2). It is numerically equal to the particle density of the soil. ; (2) in, The total mass of the specific gravity bottle and the water. For dry soil quality, The total mass of the specific gravity bottle, water, and dry soil; for The specific gravity of pure water is accurate to 0.001.

[0027] S2. Based on the moisture content of the fine sand obtained in step S1, prepare fine sand with different moisture content gradients according to the "Standard for Geotechnical Testing Methods" (GBT 50123-2019). Design different gradient dry densities for each moisture content, and prepare fine sand samples with different gradient moisture content and dry densities using an insulating cylinder.

[0028] S3. According to the "Standard for Geotechnical Testing Methods" (GBT 50123-2019), conduct indoor two-phase electrode resistivity tests on the silty fine sand samples prepared in step S2. Based on the resistivity test results, construct the functional relationships describing the water content-resistivity and dry density-resistivity. Based on the soil particle density obtained in step S1, construct the saturation-resistivity functional relationship. Specifically, this includes the following steps: S31. Use a low-frequency AC two-phase electrode to test the resistivity of the sample prepared in step S2. The measuring instrument is an LCR digital bridge. The measuring frequency is adjusted to the common 50Hz. Apply a layer of graphene powder to the upper and lower surfaces of the sample, and cover the upper and lower surfaces of the sample with a 60mm diameter circular copper sheet as an electrode. Connect the electrode sheet to the LCR digital bridge through a wire. Measure the resistivity value multiple times, read the maximum value, and calculate the actual resistivity value using formula (3). (3) in, This is the actual resistivity; R For measuring resistance; S Electrode area; L The height of the sample; S32. Based on the resistivity test data of fine sand under different moisture content and dry density conditions obtained in step S31, the power function is used to describe the nonlinear variation law of resistivity of fine sand with moisture content and dry density. The power function relationship is introduced to obtain the moisture content-resistivity function relationship (4) and the dry density-resistivity function relationship (5). (4) (5) In the formula, , , , These are the fitting parameters, w The moisture content of the soil sample. This represents the dry density of the soil sample. S33. Based on the data obtained in step S32, considering the combined influence of moisture content and dry density on the resistivity of the soil, the saturation parameter (formula (6)) is introduced to establish a resistivity model that considers the moisture content and dry density of fine sand. Based on the analysis of experimental data, the saturation-resistivity function relationship (7) is established. (6) (7) In the formula, For saturation parameters, The density of water, This represents the particle density of the soil sample.

[0029] S4. Substitute the natural moisture content obtained in step S1 into the moisture content-resistivity function relationship in step S3 to obtain the resistivity of silty fine sand under natural moisture conditions; substitute the resistivity under natural moisture conditions into the dry density, saturation and resistivity function relationship to obtain the dry density and saturation of silty fine sand.

[0030] Specifically, the natural moisture content obtained in step S1 is substituted into the moisture content-resistivity function relationship (4) obtained in step S3 to obtain the resistivity of fine sand under natural moisture conditions; the resistivity under natural moisture conditions is substituted into the dry density-resistivity function relationship (5) and the saturation-resistivity function relationship (7) respectively to obtain the dry density and saturation of fine sand.

[0031] S5. Substitute the soil particle density and actual dry density values ​​obtained in steps S1 and S4 into the porosity calculation formula to calculate the porosity of the silty fine sand, specifically: Substitute the particle density of fine sand obtained in steps S1 and S4 and the dry density under natural water content into the porosity calculation formula (8) to calculate the porosity of fine sand. (8) in, n The porosity is the porosity of fine sand.

[0032] S6. Based on the calculation formulas for the collapsibility coefficient, porosity, and saturation, substitute the saturation obtained in step S4 and the porosity obtained in step S5 to calculate the collapsibility coefficient of the silty fine sand. Determine its collapsibility level according to the "Building Standard for Collapsible Loess Areas" (GB50025-2018), which specifically includes the following steps: S61. Based on the definition formula (9) of the collapsibility coefficient, the empirical calculation formula (10) of the collapsibility coefficient is derived. (9) in, The height (mm) of the sample after it has settled and stabilized when a certain pressure is applied to maintain its natural humidity and structure. For the sample after pressure settling and stabilization, the height (mm) after settling and stabilization is added under saturated water immersion conditions; The original height of the sample (mm); (10) The derivation process is as follows, assuming the total volume of the silty fine sand sample is... V From the three-phase volume relationship of soil, we know that: (in For soil particle volume, (This refers to the pore volume of the soil). The pore volume is filled with water and gas, and is expressed as... (in, The volume of water in the pores. Porosity is defined as the volume of gas in the pores. ( Saturation is defined as ( Therefore, there is ( As water replaces the gas in the soil pores, soil particles fill the pores and settle, resulting in a theoretical volume change. In actual engineering, due to the cohesion between soil particles and the presence of closed pores, not all pores will completely collapse. Therefore, a collapsibility correction parameter is introduced. k This is corrected, specifically expressed as the actual volume change. For a cylindrical specimen (with a constant cross-section A), the actual volume change is expressed as the amount of collapsible settlement multiplied by the cross-sectional area, i.e. The total volume of the soil sample is Therefore By eliminating A Then there is According to the definition of the collapsibility coefficient in formula (9), formula (10) can be obtained. S62. By conducting a collapsibility test on the silty sand in the silty sand area, the collapsibility correction parameter is obtained. The actual saturation value of the soil, the porosity value of the soil, and the collapsibility correction parameter obtained in steps S4 and S5 are substituted into formula (10) to calculate the collapsibility coefficient of the silty sand. Then, the collapsibility grade of the silty sand is determined according to the evaluation standard of the "Code for Building Construction in Collapsible Loess Areas" (GB50025-2018).

[0033] Based on the above method, this embodiment has been put into practice, as follows: S1. Take samples of fine sand in the field according to the Code for Geotechnical Investigation (GB 50021-2001) (2009 edition) to obtain soil samples that meet the test requirements; conduct indoor moisture content tests on the disturbed fine sand samples according to the Standard for Geotechnical Testing Methods (GBT 50123-2019) and calculate the moisture content according to formula (1). w The specific gravity was 6.78%. The disturbed silty sand samples were tested using the specific gravity bottle method according to the "Standard for Geotechnical Testing Methods" (GBT 50123-2019), and the specific gravity of the soil particles was calculated according to formula (2). It is 2.63, which is numerically equal to the particle density of the soil. This is expressed as 2.63 g / cm³. 3 .

[0034] S2. Based on the moisture content of the fine sand obtained in step S1, prepare four fine sand samples with different moisture contents according to the "Standard for Geotechnical Testing Methods" (GBT 50123-2019). Then, seal them with plastic wrap and let them stand for 24 hours to keep them moist, so that the moisture is evenly distributed in the soil sample. Then, use static compaction method to press the prepared fine sand sample into an insulating cylinder with an inner diameter of 61.8 mm and a height of 80 mm.

[0035] S3. The resistivity of the sample prepared in step S2 is tested using a low-frequency AC two-phase electrode. The measuring instrument is an LCR digital bridge. The measuring frequency is adjusted to the common 50Hz. A layer of graphene powder is applied to the upper and lower surfaces of the sample. A 60mm diameter circular copper sheet is used as an electrode to cover the upper and lower surfaces of the sample. The electrode is connected to the LCR digital bridge through a wire. The resistivity value is measured multiple times, the maximum value is read, and the actual resistivity value is calculated using formula (3) as shown in Table 1. Table 1. Corresponding actual resistivity of silty fine sand at different moisture contents and dry densities.

[0036] Based on the resistivity test data of silty fine sand under different moisture contents and dry densities, a power function was used to describe the nonlinear variation of resistivity with moisture content and dry density. A power function relationship was introduced to fit the moisture content, dry density, and resistivity, and the fitted curves are shown below. Figure 2 , Figure 3 As shown; Considering the combined influence of moisture content and dry density on soil resistivity, a saturation parameter (formula (6)) is introduced to calculate the saturation of each group of samples. The results are shown in Table 2. Based on the saturation and the corresponding resistivity data, a power function is used for fitting, and the fitting curve is shown in Table 2. Figure 4 As shown.

[0037] Table 2. Degree of saturation of silty fine sand at different moisture contents and dry densities.

[0038] S4. Substituting the natural moisture content obtained in step S1 into the moisture content-resistivity function relationship (4) obtained in step S3, the resistivity of the silty fine sand under natural moisture conditions is 182.875Ω. Substituting the resistivity under natural moisture conditions into the dry density-resistivity function relationship (5) and the saturation-resistivity function relationship (7), the dry density of the silty fine sand is 1.75g / cm³. 3 With a saturation of 38.69%.

[0039] S5. The density of the fine sand particles obtained in steps S1 and S4 is 2.63 g / cm³. 3The dry density under natural moisture content is 1.75 g / cm³. 3 Substituting into the porosity calculation formula (8), the porosity of the fine sand is calculated to be 0.3346.

[0040] S6. In this embodiment, 12 sets of field immersion load tests were conducted on the silty fine sand soil of the site to calibrate the collapsibility correction parameters of the silty fine sand soil in this area. k =0.1132, therefore the empirical formula for calculating the collapsibility coefficient applicable to this region is: Substitute the actual soil saturation value of 38.69% and the soil porosity value of 0.3346 obtained in steps S4 and S5 into the formula. The collapsibility coefficient of the silty fine sand was calculated to be 0.0232. Subsequently, according to the evaluation criteria of the "Code for Building Construction in Collapsible Loess Areas" (GB50025-2018), the collapsibility level of the silty fine sand was determined to be slightly collapsible.

[0041] To verify the accuracy of the method of this invention, the predicted value of the collapsibility coefficient calculated by this method was compared with the measured value obtained from the field immersion load test. The results are as follows: Figure 5 As shown in the figure. The comparison results show that the Pearson correlation coefficient between the predicted and measured values ​​is... r =0.970, coefficient of determination R 2 =0.941, indicating that the evaluation results of the method of the present invention have extremely high accuracy and reliability.

[0042] Therefore, the present invention adopts the above-mentioned method for evaluating the collapsibility of silty fine sand based on resistivity, which can quickly and cost-effectively evaluate the collapsibility of silty fine sand foundations at any depth. It can also be cross-validated with the results of indoor tests, and is especially suitable for foundation investigation of wind power, oil and gas fields and other projects in arid and semi-arid regions such as deserts and Gobi.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for evaluating the collapsibility of silty fine sand based on resistivity, characterized in that, Includes the following steps: S1. Obtain disturbance samples of fine sandy soil foundation on site, conduct basic physical property tests on the soil samples, determine the natural moisture content and soil particle specific gravity, and the measured soil particle specific gravity is numerically equal to the soil particle density. S2. Based on the obtained moisture content of fine sand, prepare fine sand with different moisture content gradients, design different dry density gradients for each moisture content, and prepare fine sand samples with different moisture content gradients and dry densities using an insulating cylinder. S3. Conduct indoor two-phase electrode resistivity tests on the prepared fine sand samples. Based on the resistivity test results, construct the water content-resistivity function relationship and the dry density-resistivity function relationship respectively. Based on the soil particle density, construct the saturation-resistivity function relationship. S4. Substitute the natural moisture content into the moisture content-resistivity function to obtain the resistivity of silty fine sand under natural moisture conditions; substitute the resistivity under natural moisture conditions into the dry density-resistivity function and the saturation-resistivity function respectively to obtain the dry density and saturation of silty fine sand. S5. Substitute the particle density of the fine sand and the dry density under natural water content obtained from S1 and S4 into the porosity calculation formula to obtain the porosity of the fine sand. S6. Based on the calculation formulas for collapsibility coefficient, porosity, and saturation, substitute the saturation obtained in S4 and the porosity obtained in S5 to calculate the collapsibility coefficient of silty fine sand and determine its collapsibility level.

2. The method for evaluating the collapsibility of silty fine sand based on resistivity according to claim 1, characterized in that: S1 specifically includes the following steps: S11. Take on-site samples of fine sand to obtain soil samples that meet the test requirements; S12. Conduct an indoor moisture content test on the disturbed silty sand samples and calculate their moisture content; S13. For the disturbed silty sand sample, conduct a specific gravity bottle test and calculate the specific gravity of the soil particles, which is numerically equal to the particle density of the soil.

3. The method for evaluating the collapsibility of silty fine sand based on resistivity according to claim 1, characterized in that: In S2, specifically: based on the moisture content of the fine sand obtained in S1, firstly, fine sand samples with different gradient moisture contents are prepared, then sealed with plastic wrap and left to stand to retain moisture, so that the moisture is evenly distributed in the soil sample, and then the prepared fine sand samples are pressed into the insulating cylinder by static compaction method.

4. The method for evaluating the collapsibility of silty fine sand based on resistivity according to claim 1, characterized in that: S3 specifically includes the following steps: S31. The resistivity of the fine sand sample prepared in S2 is tested using a low-frequency AC two-phase electrode. The measuring instrument is an LCR digital bridge. The measuring frequency is adjusted to the common 50Hz. A layer of graphene powder is coated on the upper and lower surfaces of the sample, and a copper sheet is used as an electrode to cover the upper and lower surfaces of the sample. The electrode is connected to the LCR digital bridge through a wire. The resistivity value is measured at least twice, the maximum value is read, and the actual resistivity value is calculated. S32. Based on the resistivity test data of fine sand under different moisture contents and dry densities, the power function is used to describe the nonlinear variation law of resistivity of fine sand with moisture content and dry density, and the functional relationship between moisture content and resistivity and dry density and resistivity is obtained. S33. Introduce the saturation parameter, establish a resistivity model that considers the combined effects of moisture content and dry density of silty fine sand, and establish a functional relationship between saturation and resistivity based on experimental data analysis.

5. The method for evaluating the collapsibility of silty fine sand based on resistivity according to claim 4, characterized in that: The formula for calculating the actual resistivity is: ； In the formula, This is the actual resistivity; R For measuring resistance; S Electrode area; L The height of the sample; The formula for calculating the relationship between moisture content and resistivity is: ； The formula for calculating the dry density-resistivity function relationship is: ； In the formula, , , , These are the fitting parameters, w The moisture content of the soil sample. This represents the dry density of the soil sample. The formula for calculating the saturation parameter is: ； The formula for calculating the saturation-resistivity function relationship is: ； In the formula, For saturation parameters, The density of water, This represents the particle density of the soil sample. a , b These are the fitting coefficients.

6. The method for evaluating the collapsibility of silty fine sand based on resistivity according to claim 5, characterized in that: In S4, specifically: the natural moisture content obtained from S1 is substituted into the moisture content-resistivity function relationship in S3 to obtain the resistivity of silty fine sand under natural moisture conditions; the resistivity under natural moisture conditions is substituted into the dry density-resistivity function relationship and the saturation-resistivity function relationship respectively to obtain the dry density and saturation of silty fine sand.

7. The method for evaluating the collapsibility of silty fine sand based on resistivity according to claim 5, characterized in that: In S5, the formula for calculating the porosity of silty fine sand is: ； In the formula, n The porosity is the porosity of fine sand.

8. The method for evaluating the collapsibility of silty fine sand based on resistivity according to claim 7, characterized in that: S6 specifically includes the following steps: S61. Based on the definition of the collapsibility coefficient, the empirical calculation formula for the collapsibility coefficient is derived. S62. By conducting collapsibility tests on silty sand in silty sandy areas, collapsibility correction parameters are obtained. The actual soil saturation and porosity values ​​obtained from S4 and S5, along with the collapsibility correction parameters, are substituted into the empirical formula for calculating the collapsibility coefficient to obtain the collapsibility coefficient of silty sandy soil. Finally, the collapsibility grade of silty sandy soil is determined.

9. The method for evaluating the collapsibility of silty fine sand based on resistivity according to claim 8, characterized in that: The empirical formula for calculating the collapsibility coefficient is as follows: ； In the formula, This is the collapsibility coefficient. k This refers to the parameters for wet collapse.

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