Method for judging collapsibility of silty-fine sand

Abstract

The invention discloses a method for judging collapsibility of silty-fine sand. The method specifically comprises the following steps: step 1, carrying out a standard penetration test on site and obtaining a target soil layer depth and a hammering number; 2, taking a soil sample from the standard penetration test, carrying out an indoor moisture content test to obtain a moisture content value, and carrying out a relative density test to obtain the maximum dry density and the minimum dry density; 3, establishing a relational expression among the hammering number N of the target soil layer, the relative compactness and the dry density according to an on-site standard penetration test, and substituting the hammering number, the water content, the depth of the target soil layer, the maximum dry density and the minimum dry density value into the relational expression to obtain the dry density of the target soil layer; 4, carrying out an indoor remolded soil collapsibility characteristic test, establishing a multiple linear regression prediction formula, substituting the moisture content value and the dry density, obtaining a collapsibility coefficient delta s of the silty-fine sand soil layer, and determining the collapsibility grade of the silty-fine sand; according to the method, the collapsibility of the silty-fine sand can be accurately judged on site.

Description

Technical Field

[0001] The invention belongs to the technical field of geotechnical engineering collapsibility determination methods, and in particular relates to a silt and fine sand collapsibility determination method. Background Art

[0002] In recent years, with the continuous exploration and development of various resources in the Maowusu Desert, engineering and technical personnel have encountered more and more unprecedented technical difficulties in engineering construction in the fine sand area. One of the most prominent problems is that when the building is on the fine sand foundation during the construction, if the fine sand foundation is deformed due to wetting, it will threaten the safety and stability of the basic engineering buildings in the construction area, leading to uneven settlement of the foundation of the engineering building, causing damage to traffic lines, loss of personnel and property, etc.

[0003] The collapse of fine sand is a complex physical and chemical process. The main influencing factors are water content, overburden pressure and relative density, and it is related to its mineral composition and structural structure. Under the action of additional load, the structure of some fine sand is destroyed after water injection, and the soil particles are displaced, resulting in deformation. In view of the huge harm caused by collapsible fine sand, it is of great significance to timely and accurately determine the collapse level of fine sand.

[0004] At present, there is no clear method for judging the collapsibility of fine sand. It is mainly based on the Code for Geotechnical Engineering Investigation (GB 50021-2001) (2009 edition). When the ratio of the amount of collapsibility to the width of the load plate ΔFs / b ≥ 0.023, it is judged as collapsible soil. The collapsible soil is divided into four grades: I, II, III, and IV. The evaluation of the collapsibility of fine sand is generally carried out through indoor compression tests or in-situ immersion load tests. According to the specifications, the collapsibility coefficient can be obtained, and the results have a certain degree of reliability. However, the immersion load test of fine sand is usually time-consuming, and it is difficult to obtain soil from the original ring-shaped fine sand, the cost is high, and it is easy to disturb.

[0005] Therefore, there is an urgent need for a method that is simple to operate, fast, accurate, cost-effective, and can be used to determine the collapsibility of fine sand on site. Summary of the invention

[0006] The invention aims to provide a method for determining the collapsibility of fine sand, which has the characteristic of being able to accurately determine the collapsibility of fine sand on site.

[0007] The technical solution of the present invention is a method for determining the collapsibility of fine sand, which is specifically implemented according to the following steps:

[0008] Step 1: Conduct a standard penetration test on site and obtain the target soil layer depth h and hammer number N;

[0009] Step 2: Take soil samples from the standard penetration test and conduct indoor moisture content test to obtain the moisture content value ω, and conduct relative density test to obtain the maximum dry density ρ dmax and minimum dry density ρ dmin ;

[0010] Step 3: Establish the target soil layer hammer number N and relative density D according to the on-site standard penetration test r , dry density ρ d The relationship between the hammer number N, water content ω, target soil depth h, and maximum dry density ρ dmax and the minimum dry density ρ dmin Substitute into the dry density of the target soil layer to obtain d ;

[0011] Step 4: Conduct indoor collapsible soil test, establish a multivariate linear regression prediction formula, and substitute the moisture content ω and dry density ρ d , the collapsibility coefficient δ of the fine sand layer is obtained s And determine the collapsibility grade of fine sand.

[0012] The present invention is also characterized in that step 2 is specifically implemented according to the following steps:

[0013] Step 2.1, after the standard penetration test is carried out on the target soil layer, soil samples are taken from the penetrometer for indoor moisture content test;

[0014] Step 2.2: According to the moisture content test calculation, the moisture content value ω is

[0015]

[0016] Among them, ω is the moisture content of the soil sample, m is the total mass of the soil sample, and m s is the total mass of solid particles in the soil sample;

[0017] Step 2.3: Take the soil sample from the penetrometer and conduct a relative density test to obtain the maximum dry density ρ dmax and the minimum dry density ρ dmin .

[0018] Step 3 is implemented as follows:

[0019] Step 3.1: Perform square shifting to obtain the mathematical transformation formula (σ+70)·D r 2 =210 2 N, where N is the number of blows;

[0020] Step 3.2: From the above, we know that σ=γh, γ=ρg, ρ=ρ d·(1+ω), and substituting it into the mathematical transformation formula in step 3.1, we get

[0021] [ρ d ·(1+ω)·g·h+70]·D r 2 =210 2 ·N (2)

[0022] Step 3.3: Substituting into formula (2), we can get the hammer number N and relative density D r and dry density ρ d The relationship is

[0023]

[0024] Among them, ρ d is the dry density of the soil layer, N is the number of standard penetration test hammer blows, ω is the moisture content of the soil layer, g is the gravity acceleration, h is the depth of the soil layer, ρ dmax is the maximum dry density of the soil layer, ρ dmin is the minimum dry density of the soil layer;

[0025] Step 3.4: Substitute the hammer blow number N, water content ω, target soil depth h, and maximum dry density ρ dmax and the minimum dry density ρ dmin Substituting into equation (3), we can obtain ρ d Dry density of the target soil layer.

[0026] Step 4 is implemented according to the following steps:

[0027] Step 4.1: Conduct indoor collapsible properties test of remolded soil.

[0028] Step 4.2, determine the fitting coefficients a1, a2 of different physical quantities in the multivariate linear regression formula, and the formula constant a3;

[0029] Step 4.3: Determine the moisture content ω and dry density ρ based on the fitting coefficients a1, a2 and the formula constant a3. d and the collapsibility coefficient δ s The multivariate linear regression prediction formula is:

[0030] δ s =a1·ω+a2·ρ d +a3 (4)

[0031] Among them, δ s is the collapsibility coefficient of fine sand, ω is the water content, ρ d is the dry density, a1 and a2 are the fitting coefficients of different physical quantities in the multiple linear regression formula, and a3 is the formula constant;

[0032] Step 4.4: Water content value ω and dry density ρ d Substituting into formula (4), the collapsibility coefficient δ of the fine sand layer is calculated as s ;

[0033] Step 4.5: According to the collapsibility coefficient δ of the fine sand layer s , determine the collapsible grade of collapsible silt sand.

[0034] Step 4.2 is implemented as follows:

[0035] Step 4.2.1, obtain soil samples from the target fine sand layer;

[0036] Step 4.2.2, pass the ground soil sample through a sieve with a pore size of 2 mm or 5 mm, mix thoroughly and measure the air-dried moisture content, store it in a moisturizing cylinder or plastic bag to obtain air-dried soil;

[0037] Step 4.2.3: Calculate the mass of air-dried soil required for sample preparation based on the cutter ring volume and the required dry density:

[0038] Step 4.2.4, calculate the amount of water required to prepare the sample according to the required moisture content of the sample;

[0039] Step 4.2.5: Dry the soil sample in step 4.2.3, and use a measuring cylinder to measure the amount of water required in step 4.2.4, spray it evenly on the air-dried soil, mix thoroughly, put it into a soil container, cover it tightly, and moisten it for a day and a night to obtain a reshaped soil sample;

[0040] Step 4.2.6, determine the moisture content at different positions of the wetted soil sample;

[0041] Step 4.2.7, subjecting the reshaped soil samples to a confined compression test to obtain the collapsibility coefficient of each reshaped sample;

[0042] Step 4.2.8: Use SPSS software to perform multiple linear regression fitting analysis to obtain the fitting relationship between the four basic physical parameters and the wetting coefficient. a1 and a2 are the fitting coefficients of different physical quantities in the multiple linear regression formula, and a3 is the formula constant.

[0043] Step 4.2.3 The calculation formula is:

[0044] m0=(1+0.01ω0)·ρ d ·V (5)

[0045] Where m0 is the mass of the soil sample at the air-dried moisture content required for preparing the sample, ω0 is the air-dried moisture content, and ρ d is the required dry density of the sample, V is the sample volume (cm 3 ).

[0046] Step 4.2.4 The calculation formula is:

[0047]

[0048] Among them, m ω is the amount of water needed to prepare the sample, ω1 is the required moisture content of the sample, and ω0 is the air-dried moisture content.

[0049] The beneficial effects of the present invention are:

[0050] 1. The present invention indirectly determines the collapsibility of fine sand through some easily measured indicators, which saves time and cost and has good economic effect and engineering technical value;

[0051] 2. In order to make the discrimination method more accurate, the present invention first finds out the index with good correlation with the collapsibility coefficient, uses mathematical means to perform correlation analysis on each index, and then re-establishes independent indexes that can be used to characterize the collapsibility of fine sand, and establishes a mathematical function equation of multiple linear regression, thereby realizing the evaluation of the collapsibility of fine sand;

[0052] 3. The method for determining the collapsibility of fine sand of the present invention is easy to operate, cost-effective, rapid and accurate, and is suitable for use in engineering construction on the southern edge of the Maowusu Desert. It can accurately determine the collapsibility of fine sand on site. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 It is a flow chart of the method for determining the collapsibility of fine sand of the present invention;

[0054] Figure 2 It is a comparison chart of the measured and predicted collapsible coefficient of fine sand of the present invention;

[0055] Figure 3 It is a comparison chart between the measured value and the predicted value of the collapsibility coefficient in the embodiment of the present invention. DETAILED DESCRIPTION

[0056] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0057] like Figure 1 As shown, the present invention provides a method for determining the collapsibility of fine sand, which is specifically implemented according to the following steps:

[0058] Step 1: Conduct a standard penetration test on the target soil layer on site in accordance with the Code for Geotechnical Engineering Investigation (GB50021-2001) (2009 edition) and obtain the target soil layer depth h and hammer number N; Based on the preliminary investigation, obtain the site target soil layer depth h, and obtain the hammer number N according to the standard penetration test;

[0059] Step 2: Take soil samples from the standard penetration test and conduct indoor moisture content test according to the "Standard for Geotechnical Test Methods" (GB / TS0123-2019), calculate the moisture content value ω, and conduct relative density test to obtain the maximum dry density ρ dmax and minimum dry density ρ dmin ;

[0060] Step 2.1, after the standard penetration test is carried out on the target soil layer, soil samples are taken from the penetrometer for indoor moisture content test;

[0061] Step 2.2: According to the moisture content test calculation, the moisture content value ω is

[0062]

[0063] Among them, ω is the moisture content of the soil sample, m is the total mass of the soil sample, and m s is the total mass of solid particles in the soil sample;

[0064] Step 2.3: Take the soil sample from the penetrometer and conduct a relative density test according to the Geotechnical Test Method Standard (GB / T50123-2019) to obtain the maximum dry density ρ dmax and the minimum dry density ρ dmin .

[0065] Step 3: Establish the target soil layer hammer number N and relative density D according to the on-site standard penetration test r , dry density ρ d The relationship between the hammer number N, water content ω, target soil depth h, and maximum dry density ρ dmax and the minimum dry density ρ dmin Substitute into the dry density of the target soil layer to obtain d ;

[0066] Step 3.1: Perform square shifting to obtain the mathematical transformation formula (σ+70)·D r 2 =210 2 -N, where N is the number of hammer blows;

[0067] Step 3.2: From soil mechanics, we know that σ=γh, γ=ρg, ρ=ρ d ·(1+ω), and substituting it into the mathematical transformation formula in step 3.1, we get

[0068] [ρ d ·(1+ω)·g·h+70]·D r 2 =210 2 ·N (2)

[0069] Step 3.3: Substituting into formula (2), we can get the hammer number N and relative density D r and dry density ρ d The relationship is

[0070]

[0071] Among them, ρ d is the dry density of the soil layer, N is the number of standard penetration test hammer blows, ω is the moisture content of the soil layer, g is the gravity acceleration, h is the depth of the soil layer, ρ dmax is the maximum dry density of the soil layer, ρ dmin is the minimum dry density of the soil layer;

[0072] Step 3.4: Substitute the hammer blow number N, water content ω, target soil depth h, and maximum dry density ρ dmax and the minimum dry density ρ dmin Substituting into equation (3), we can obtain ρ d Dry density of the target soil layer.

[0073] Step 4: Conduct indoor collapsible soil test, establish a multivariate linear regression prediction formula, and substitute the moisture content ω and dry density ρ d , the collapsibility coefficient δ of the fine sand layer is obtained s And determine the collapsibility grade of fine sand.

[0074] Step 4.1: Conduct indoor collapsible properties test of remolded soil.

[0075] Step 4.2, determine the fitting coefficients a1, a2 of different physical quantities in the multivariate linear regression formula, and the formula constant a3;

[0076] Step 4.2.1, obtain soil samples from the target fine sand layer;

[0077] Step 4.2.2, pass the ground soil sample through a sieve with a pore size of 2 mm or 5 mm, mix thoroughly and measure the air-dried moisture content, store it in a moisturizing cylinder or plastic bag to obtain air-dried soil;

[0078] Step 4.2.3: Calculate the mass of air-dried soil required for sample preparation based on the cutter ring volume and the required dry density:

[0079] The calculation formula is

[0080] m0=(1+0.01ω0)·ρ d ·V (5)

[0081] Where m0 is the mass of the soil sample at the air-dried moisture content required for preparing the sample, ω0 is the air-dried moisture content, and ρ d is the required dry density of the sample, V is the sample volume (cm 3 ).

[0082] Step 4.2.4, calculate the amount of water required to prepare the sample according to the required moisture content of the sample;

[0083] The calculation formula is

[0084]

[0085] Among them, m ω is the amount of water needed to prepare the sample, ω1 is the required moisture content of the sample, and ω0 is the air-dried moisture content.

[0086] Step 4.2.5: Dry the soil sample in step 4.2.3, and use a measuring cylinder to measure the amount of water required in step 4.2.4, spray it evenly on the air-dried soil, mix thoroughly, put it into a soil container, cover it tightly, and moisten it for a day and a night to obtain a reshaped soil sample;

[0087] Step 4.2.6, determine the moisture content at different positions of the wetted soil sample;

[0088] Step 4.2.7, subject the reshaped soil samples to a confined compression test according to the Geotechnical Test Method Standard (GB / T50123-2019) to obtain the collapsibility coefficient of each reshaped sample;

[0089] Step 4.2.8: Use SPSS software to perform multiple linear regression fitting analysis to obtain the fitting relationship between the four basic physical parameters and the wetting coefficient. a1 and a2 are the fitting coefficients of different physical quantities in the multiple linear regression formula, and a3 is the formula constant.

[0090] Step 4.3: Determine the moisture content ω and dry density ρ based on the fitting coefficients a1, a2 and the formula constant a3. d and the collapsibility coefficient δ s The multivariate linear regression prediction formula is:

[0091] δ s =a1·ω+a2·ρ d +a3 (4)

[0092] Among them, δ s is the collapsibility coefficient of fine sand, ω is the water content, ρ d is the dry density, a1 and a2 are the fitting coefficients of different physical quantities in the multiple linear regression formula, and a3 is the formula constant;

[0093] Step 4.4: Water content value ω and dry density ρ d Substituting into formula (4), the collapsibility coefficient δ of the fine sand layer is calculated as s ;

[0094] Step 4.5: According to the collapsibility coefficient δ of the fine sand layers , determine the collapsible grade of collapsible silt sand.

[0095] The invention can measure the shrinkage of sand soil without conducting an on-site shrinkage test when macroscopic parameters such as the number of hammer blows, water content, dry density and the like in a standard penetration test of sand soil are known.

[0096] like Figure 2 As shown, in order to make the discrimination method more accurate, the present invention first finds out the indicators with good correlation with the collapsibility coefficient, uses mathematical means to perform correlation analysis on the indicators, and then re-establishes independent indicators that can be used to characterize the collapsibility of fine sand, and establishes a mathematical function equation of multiple linear regression, thereby realizing the evaluation of the collapsibility of fine sand.

[0097] Example 1

[0098] This implementation is specifically implemented in the following steps: Step 1, conduct a standard penetration test on site in accordance with the "Geotechnical Engineering Investigation Code" (GB50021-2001) (2009 edition) and obtain the target soil layer depth h and hammer number N;

[0099] According to the preliminary investigation, the soil layer with a depth of 1.5m was selected as the target soil layer, that is, h = 1.5m; then a standard penetration test was carried out and N = 7 was obtained.

[0100] Step 2: Take soil samples from the standard penetration test and conduct indoor moisture content test to obtain the moisture content value ω. After calculation, the moisture content value of the target soil layer is 3.4%, and a relative density test is performed to obtain the maximum dry density ρ dmax and minimum dry density ρ dmin , the maximum dry density ρ of the target soil layer can be obtained by calculation dmax and minimum dry density ρ dmin 1.73 g / cm 3 , 1.43g / cm 3 .

[0101] Step 3: Establish the target soil layer hammer number N and relative density D according to the on-site standard penetration test r , dry density ρ d The relationship between the hammer number N, water content ω, target soil depth h, and maximum dry density ρ dmax and the minimum dry density ρ dmin Substitute into the dry density of the target soil layer to obtain d , the dry density ρ of the target soil layer can be obtained by calculation d 1.51 g / cm 3 ;

[0102] Step 4: Conduct indoor remolded soil collapsibility test and establish a multiple linear regression prediction formula, where a1 = -0.017024, a2 = -0.0047090, a3 = 0.107138, and substitute the moisture content ω and dry density ρ d , the collapsibility coefficient δ of the fine sand layer is obtained s The collapsibility level of the fine sand is determined. The predicted value of the collapsibility coefficient of the target fine sand layer is calculated to be 0.04214. The predicted value is compared with the measured value. If the error is less than 5%, the prediction is considered accurate. According to the Code for Geotechnical Engineering Investigation (GB50021-2001) (2009 edition), the collapsibility level of the target fine sand layer is determined based on the predicted value of the collapsibility coefficient calculated. The collapsibility level of the target fine sand layer is slight.

[0103] Example 2

[0104] This implementation is specifically implemented in the following steps: Step 1, conduct a standard penetration test on site in accordance with the "Geotechnical Engineering Investigation Code" (GB50021-2001) (2009 edition) and obtain the target soil layer depth h and hammer number N;

[0105] According to the preliminary investigation, the soil layer with a depth of 2.0m was selected as the target soil layer, that is, h = 2.0m; then a standard penetration test was carried out and N = 11 was obtained.

[0106] Step 2: Take soil samples from the standard penetration test and conduct indoor moisture content test to obtain the moisture content value ω. After calculation, the moisture content value of the target soil layer is 4.4%, and a relative density test is performed to obtain the maximum dry density ρ dmax and minimum dry density ρ dmin , the maximum dry density ρ of the target soil layer can be obtained by calculation dmax and minimum dry density ρ dmin 1.81 g / cm 3 , 1.39g / cm 3 .

[0107] Step 3: Establish the target soil layer hammer number N and relative density D according to the on-site standard penetration test r , dry density ρ d The relationship between the hammer number N, water content ω, target soil depth h, and maximum dry density ρ dmax and the minimum dry density ρ dmin Substitute into the dry density of the target soil layer to obtain d , the dry density ρ of the target soil layer can be obtained by calculation d 1.58g / cm 3 ;

[0108] Step 4: Conduct indoor remolded soil collapsibility test and establish a multiple linear regression prediction formula, where a1 = -0.017024, a2 = -0.0047090, a3 = 0.107138, and substitute the moisture content ω and dry density ρ d , the collapsibility coefficient δ of the fine sand layer is obtained s The collapsibility level of the fine sand is determined. The predicted value of the collapsibility coefficient of the target fine sand layer is calculated to be 0.02479. The predicted value is compared with the measured value. If the error is less than 5%, the prediction is considered accurate. According to the Code for Geotechnical Engineering Investigation (GB50021-2001) (2009 edition), the collapsibility level of the target fine sand layer is determined based on the predicted value of the collapsibility coefficient calculated. The collapsibility level of the target fine sand layer is slight.

[0109] Example 3

[0110] This implementation is specifically implemented in the following steps: Step 1, conduct a standard penetration test on site in accordance with the "Geotechnical Engineering Investigation Code" (GB50021-2001) (2009 edition) and obtain the target soil layer depth h and hammer number N;

[0111] According to the preliminary investigation, the soil layer with a depth of 1.0m was selected as the target soil layer, that is, h = 1.0m; then a standard penetration test was carried out and N = 8 was obtained.

[0112] Step 2: Take soil samples from the standard penetration test and conduct indoor moisture content test to obtain the moisture content value ω. After calculation, the moisture content value of the target soil layer is 3.4%, and a relative density test is performed to obtain the maximum dry density ρ dmax and minimum dry density ρ dmin , the maximum dry density ρ of the target soil layer can be obtained by calculation dmax and minimum dry density ρ dmin 1.74 g / cm 3 , 1.39g / cm 3 .

[0113] Step 3: Establish the target soil layer hammer number N and relative density D according to the on-site standard penetration test r , dry density ρ d The relationship between the hammer number N, water content ω, target soil depth h, and maximum dry density ρ dmax and the minimum dry density ρ dmin Substitute into the dry density of the target soil layer to obtain d , the dry density ρ of the target soil layer can be obtained by calculation d 1.57 g / cm 3 ;

[0114] Step 4: Conduct indoor remolded soil collapsibility test and establish a multiple linear regression prediction formula, where a1 = -0.017024, a2 = -0.0047090, a3 = 0.107138, and substitute the moisture content ω and dry density ρ d , the collapsibility coefficient δ of the fine sand layer is obtained s The collapsibility grade of silt sand is determined, and the predicted value of the collapsibility coefficient of the target silt sand layer can be calculated to be 0.04186. According to the Code for Geotechnical Engineering Investigation (GB50021-2001) (2009 edition), the collapsibility grade of the target silt sand layer is determined based on the predicted value of the collapsibility coefficient calculated, and the collapsibility grade of the target silt sand layer is slight collapsibility.

[0115] Example 4

[0116] This implementation is specifically implemented in the following steps: Step 1, conduct a standard penetration test on site in accordance with the "Geotechnical Engineering Investigation Code" (GB50021-2001) (2009 edition) and obtain the target soil layer depth h and hammer number N;

[0117] According to the preliminary investigation, the soil layer with a depth of 2.5m was selected as the target soil layer, that is, h = 2.5m; then a standard penetration test was carried out and N = 14 was obtained.

[0118] Step 2: Take soil samples from the standard penetration test and conduct indoor moisture content test to obtain the moisture content value ω. After calculation, the moisture content value of the target soil layer is 5.1%, and a relative density test is performed to obtain the maximum dry density ρ dmax and minimum dry density ρ dmin , the maximum dry density ρ of the target soil layer can be obtained by calculation dmax and minimum dry density ρ dmin 1.74 g / cm 3 , 1.39g / cm 3 .

[0119] Step 3: Establish the target soil layer hammer number N and relative density D according to the on-site standard penetration test r , dry density ρ d The relationship between the hammer number N, water content ω, target soil depth h, and maximum dry density ρ dmax and the minimum dry density ρ dmin Substitute into the dry density of the target soil layer to obtain d , the dry density ρ of the target soil layer can be obtained by calculation d 1.59 g / cm 3 ;

[0120] Step 4: Conduct indoor remolded soil collapsibility test and establish a multiple linear regression prediction formula, where a1 = -0.017024, a2 = -0.0047090, a3 = 0.107138, and substitute the moisture content ω and dry density ρ d , the collapsibility coefficient δ of the fine sand layer is obtained s And determine the collapsibility grade of silt and fine sand. The predicted value of the collapsibility coefficient of the target silt and fine sand layer is calculated to be 0.01283. According to the Code for Geotechnical Engineering Investigation (GB50021-2001) (2009 edition), the collapsibility grade of the target silt and fine sand layer is determined based on the predicted value of the collapsibility coefficient calculated. It can be obtained that the collapsibility grade of the target silt and fine sand layer is slight collapsibility.

[0121] Through the above four embodiments, the predicted results are compared with the measured results, as shown in Table 1 and Figure 3 As shown, the prediction effect of this application is good and the difference with the measured value is small.

[0122] Table 1

[0123]

[0124]

Claims

1. A method for determining the collapsibility of fine sand, characterized in that: Follow the steps below to implement it: Step 1: Conduct a standard penetration test on site and obtain the target soil layer depth h and hammer number N; Step 2: Take soil samples from the standard penetration test and conduct indoor moisture content test to obtain the moisture content value ω, and conduct relative density test to obtain the maximum dry density ρ dmax and minimum dry density ρ dmin ; Step 3: Establish the target soil layer hammer number N and relative density D according to the on-site standard penetration test r , dry density ρ d The relationship between the hammer number N, moisture content ω, target soil depth h, and maximum dry density ρ dmax and the minimum dry density ρ dmin Substitute into the dry density of the target soil layer to obtain d ; Step 4: Conduct indoor collapsible soil test, establish a multivariate linear regression prediction formula, and substitute the moisture content value ω and dry density ρ d , the collapsibility coefficient δ of the fine sand layer is obtained s And determine the collapsibility grade of fine sand.

2. The method for determining collapsibility of fine sand according to claim 1, characterized in that: The step 2 is specifically implemented according to the following steps: Step 2.1, after the standard penetration test is carried out on the target soil layer, soil samples are taken from the penetrometer for indoor moisture content test; Step 2.2: According to the moisture content test calculation, the moisture content value ω is obtained as Among them, ω is the moisture content of the soil sample, m is the total mass of the soil sample, and m s is the total mass of solid particles in the soil sample; Step 2.3: Take the soil sample from the penetrometer and conduct a relative density test to obtain the maximum dry density ρ dmax and the minimum dry density ρ dmin .

3. The method for determining collapsibility of fine sand according to claim 1, characterized in that: The step 3 is specifically implemented according to the following steps: Step 3.1: Perform square shifting to obtain the mathematical transformation formula (σ+70)·D r 2 =210 2 N, where N is the number of blows; Step 3.2: According to σ=γh, γ=ρg, ρ=ρ d ·(1+ω), and substituting it into the mathematical transformation formula in step 3.1, we get [r d ·(1+ω)·g·h+70]·D r 2 =210 2 ·N (2) Step 3.3: Substituting into formula (2), we can get the hammer number N and relative density D r and dry density ρ d The relationship is Among them, ρ d is the dry density of the soil layer, N is the number of standard penetration test hammer blows, ω is the moisture content of the soil layer, g is the gravity acceleration, h is the depth of the soil layer, ρ dmax is the maximum dry density of the soil layer, ρ dmin is the minimum dry density of the soil layer; Step 3.4: The hammer blow number N, water content ω, target soil layer depth h, maximum dry density ρ dmax and the minimum dry density ρ dmin Substituting into equation (3), we can obtain ρ d Dry density of the target soil layer.

4. The method for determining collapsibility of fine sand according to claim 1, characterized in that: The step 4 is specifically implemented according to the following steps: Step 4.1: Conduct indoor collapsible properties test of remolded soil. Step 4.2, determine the fitting coefficients a1, a2 of different physical quantities in the multivariate linear regression formula, and the formula constant a3; Step 4.3: Determine the moisture content ω and dry density ρ according to the fitting coefficients a1, a2 and the formula constant a3. d and the collapsibility coefficient δ s The multivariate linear regression prediction formula is: d s =a1·ω+a2·ρ d +a3 (4) Among them, δ s is the collapsibility coefficient of fine sand, ω is the water content, ρ d is the dry density, a1 and a2 are the fitting coefficients of different physical quantities in the multiple linear regression formula, and a3 is the formula constant; Step 4.4: The moisture content value ω and the dry density ρ d Substituting into formula (4), the collapsibility coefficient δ of the fine sand layer is calculated as s ; Step 4.5: According to the collapsibility coefficient δ of the fine sand layer s , determine the collapsible grade of collapsible silt sand.

5. The method for determining collapsibility of fine sand according to claim 4, characterized in that: The step 4.2 is specifically implemented according to the following steps: Step 4.2.1, obtain soil samples from the target fine sand layer; Step 4.2.2, pass the ground soil sample through a sieve with a pore size of 2 mm or 5 mm, mix thoroughly and measure the air-dried moisture content, store it in a moisturizing cylinder or plastic bag to obtain air-dried soil; Step 4.2.3: Calculate the mass of air-dried soil required for sample preparation based on the cutter ring volume and the required dry density: Step 4.2.4, calculate the amount of water required to prepare the sample according to the required moisture content of the sample; Step 4.2.5: Dry the soil sample in step 4.2.3, and use a measuring cylinder to measure the amount of water required in step 4.2.4, spray it evenly on the air-dried soil, mix thoroughly, put it into a soil container, cover it tightly, and moisten it for a day and a night to obtain a reshaped soil sample; Step 4.2.6, determine the moisture content at different positions of the wetted soil sample; Step 4.2.7, subjecting the reshaped soil samples to a confined compression test to obtain the collapsibility coefficient of each reshaped sample; Step 4.2.8: Use SPSS software to perform multiple linear regression fitting analysis to obtain the fitting relationship between the four basic physical parameters and the wetting coefficient. a1 and a2 are the fitting coefficients of different physical quantities in the multiple linear regression formula, and a3 is the formula constant.

6. The method for determining collapsibility of fine sand according to claim 5, characterized in that: The calculation formula in step 4.2.3 is: m0=(1+0.01ω0)·ρ d ·V (5) Where m0 is the mass of the soil sample at the air-dried moisture content required for preparing the sample, ω0 is the air-dried moisture content, and ρ d is the required dry density of the sample, V is the sample volume (cm 3 ).

7. The method for determining collapsibility of fine sand according to claim 5, characterized in that: The calculation formula in step 4.2.4 is: Among them, m ω is the amount of water needed to prepare the sample, ω1 is the required moisture content of the sample, and ω0 is the air-dried moisture content.

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