An improved evaluation method for cementation effect of sandy soil based on microstructure characteristics

Abstract

The application discloses an improved sand soil cementation effect evaluation method based on microstructure characteristics, carries out indoor tests on cemented samples and plain soil samples, obtains the mechanical strength improvement rate and the water physical strength improvement rate of the cemented soil body sample, carries out three-dimensional surface measurement on the damaged section caused by the indoor test, collects SEM images of the damaged section, obtains the micro-mechanical characteristics of the cemented soil body sample, calculates the mechanical friction coefficient of the damaged section of the cemented soil body sample, carries out CT test on the cemented soil body sample, obtains the micro-pore characteristics of the cemented soil body sample, calculates the cementation coefficient of the cemented soil body sample, and quantitatively evaluates the cementation effect of the soil body. The application combines macro and micro levels to evaluate the improvement effect of the cemented soil body, quantitatively evaluates the advantages and disadvantages of the cementation effect of the soil body by expressing the cementation coefficient. The application can quantitatively express the microstructure information transmitted by the SEM image, and guide the determination of the optimal dosage of the polymer.

Description

Technical Field

[0001] This invention relates to the field of engineering geology, specifically to an evaluation method for the cementation effect of improved sand based on microstructural characteristics. Background Technology

[0002] Natural soil is widely used as a natural foundation filler in engineering, but its poor engineering properties often lead to uneven ground settlement, ground fissures, and other disasters, necessitating necessary reinforcement measures. Currently, polymers such as bio-adhesives are commonly used to improve soil. The cementing effect of polymers can fill soil pores, bridge and encapsulate soil particles, and bind loose soil particles together, thus achieving a good improvement effect. CT, NMR, and SEM techniques can intuitively obtain the microstructural characteristics of cemented soil. However, current research on the microstructure of cemented soil mainly focuses on its influence on the mechanical and hydraulic properties of cemented soil, neglecting the study of the microstructure itself. There is a lack of research on the cementing effect of modified soil based on microstructure, and a quantitative method for evaluating the quality of soil cementing effects is lacking. Therefore, this invention proposes a method for evaluating the cementing effect of modified sand based on microstructural characteristics. Summary of the Invention

[0003] The purpose of this invention is to provide an improved method for evaluating the cementation effect of sand based on microstructural characteristics. This method can quantitatively evaluate the quality of the cementation effect of the soil.

[0004] To achieve the above functions, this invention designs an improved method for evaluating the cementation effect of sandy soil based on microstructural characteristics. For the target soil, the following steps S1-S5 are performed to complete the quantitative evaluation of the quality of the soil cementation effect:

[0005] Step S1: Collect cemented soil samples and plain soil samples from the target soil body. Conduct laboratory tests on the mechanical characteristics of the cemented soil samples and plain soil samples respectively, including unconfined compressive strength test, direct shear test and tensile test, and obtain the mechanical strength improvement rate of the cemented soil samples, including the improvement rate of compressive strength, shear strength and tensile strength.

[0006] Step S2: Perform three-dimensional surface measurement on the failure section of the cemented soil sample caused by the indoor test, acquire SEM image of the failure section, simulate the indoor test results of mechanical characteristics, obtain the micromechanical characteristics of the cemented soil sample, including the undulation, roughness, cementation rate and particle cohesion of the failure section, and further calculate the mechanical friction coefficient of the failure section of the cemented soil sample.

[0007] Step S3: Conduct indoor tests on the hydraulic characteristics of cemented soil samples and plain soil samples, including evaporation cracking test, scour test and disintegration test, to obtain the hydraulic strength improvement rate of cemented soil samples, including erosion reduction rate and crack area reduction rate.

[0008] Step S4: Perform CT tests on cemented soil samples to obtain the microscopic hydrophysical characteristics of cemented soil samples, including porosity, interconnected porosity, isolated porosity and pore coordination number, and further calculate the pore characteristic coefficients of cemented soil samples.

[0009] Step S5: Based on the mechanical strength improvement rate of the cemented soil sample and the mechanical friction coefficient of the failure section of the cemented soil sample; based on the hydraulic strength improvement rate of the cemented soil sample and the porosity characteristic coefficient of the cemented soil sample, calculate the cementation coefficient of the cemented soil sample to quantitatively evaluate the cementation effect of the soil.

[0010] Beneficial effects: Compared with the prior art, the advantages of the present invention include:

[0011] 1. This invention can evaluate the effectiveness of different polymers in improving soil by combining the microstructural characteristics of soils cemented by different polymers with the results of laboratory tests;

[0012] 2. This invention performs digital analysis on SEM image information, quantitatively expresses the microstructure information transmitted by the SEM image, and uses the microstructure information to guide the determination of the optimal doping amount of polymer. Attached Figure Description

[0013] Figure 1 This is a flowchart of an improved sand cementation effect evaluation method based on microstructural characteristics provided by an embodiment of the present invention;

[0014] Figure 2 These are stained SEM images of the fracture cross section of a cemented soil sample provided in an embodiment of the present invention;

[0015] Figure 3 This is a pore coordination number distribution diagram provided according to an embodiment of the present invention. Detailed Implementation

[0016] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0017] This invention provides a method for evaluating the cementation effect of improved sandy soil based on microstructural characteristics. For the target soil, referencing... Figure 1 Perform the following steps S1-S5 to complete the quantitative evaluation of the soil cementation effect:

[0018] Step S1: Collect cemented soil samples and plain soil samples from the target soil body. Conduct laboratory tests on the mechanical characteristics of the cemented soil samples and plain soil samples, including unconfined compressive strength test, direct shear test and tensile test, and obtain the mechanical strength improvement rate of the cemented soil samples, including the improvement rate of compressive strength, shear strength and tensile strength, in order to evaluate the improvement effect of polymer on the mechanical properties of soil.

[0019] The increase rate Δq of the compressive strength of the cemented soil sample in step S1 is as follows:

[0020]

[0021] The rate of increase in shear strength Δu of cemented soil specimens is as follows:

[0022]

[0023] The increase rate Δv in the tensile strength of cemented soil samples is as follows:

[0024]

[0025] In the formula, q1, u1 and v1 are the compressive strength, shear strength and tensile strength of the cemented soil sample, respectively, and q0, u0 and v0 are the compressive strength, shear strength and tensile strength of the plain soil sample, respectively.

[0026] Step S2: Perform three-dimensional surface measurement on the failure section of the cemented soil sample caused by the indoor test, acquire SEM image of the failure section, simulate the indoor test results of mechanical characteristics, obtain the micromechanical characteristics of the cemented soil sample, including the undulation, roughness, cementation rate and particle cohesion of the failure section, and further calculate the mechanical friction coefficient of the failure section of the cemented soil sample.

[0027] The calculation steps for the undulation and roughness of the failure section of the cemented soil sample in step S2 are as follows:

[0028] Step S21: Measure the elevation of the damaged section using a white light interferometer, and set the plane containing the lowest point of the damaged section as the zero elevation plane, where the maximum elevation is d. max The undulation of the failure section is defined as d. q =d max ;

[0029] Step S22: Divide the failure section into m equal regions. The value of m should be such that the undulation d of the failure section in each region is such that... q Not greater than 0.05 mm;

[0030] Step S23: Select four points in each region, and take the average height of the four points as the average height d of that region. nWhere 1≤n≤m, n represents the nth region, and the roughness S of the damaged section. u Defined as follows:

[0031]

[0032] in,

[0033] The calculation steps for the cementation rate and particle cohesion of the cemented soil sample in step S2 are as follows:

[0034] Step S24: Establish a particle flow simulation model through sample preparation, preloading, cementing, unloading, loading plate, and loading process; the total number of particles in the particle flow simulation model should not be less than 6000, the soil particles are set as parallel bonded models, and the soil particles and loading plate are set as linear models.

[0035] Step S25: Use the trial and error method to calibrate the parameters of the particle flow simulation model. When the particle flow simulation results meet the requirements that the simulation curve and the actual curve have the same trend, the peak strength error is less than 10%, the peak strain error is less than 10%, and the elastic modulus error is less than 10%, the particle flow simulation results are considered to be effective and the parameter calibration is reliable. Obtain the contact model parameters at this time.

[0036] Step S26: Process the SEM image of the failure section of the cemented soil sample, referring to... Figure 2 The soil particles and colloidal particles were stained separately, and the total area S of the soil particles was identified using image processing software. t The total area S of the adhesive particles j The bonding ratio p of the failure section is as follows:

[0037]

[0038] Step S27: The particle cohesion of the failure section is defined as N = αS1 + βS2, ​​where S1 is the ratio of the area of ​​direct contact between soil particles to the area of ​​the failure section, S2 is the ratio of the contact area of ​​soil particles under cementation to the area of ​​the failure section, α is the effective modulus of the linear model in the particle flow software, and β is the effective modulus of the parallel bonded model in the particle flow software.

[0039] The mechanical friction coefficient f of the failure section of the cemented soil sample in step S2 is as follows:

[0040]

[0041] in, The interlocking coefficient of the damaged section; E represents the cementing force at the breaking section, and E is the elastic modulus of the cemented soil sample.

[0042] Step S3: Conduct laboratory tests on the hydraulic characteristics of cemented soil samples and plain soil samples, including evaporation cracking test, scour test and disintegration test, to obtain the improvement rate of hydraulic strength of cemented soil samples, including erosion reduction rate and crack area reduction rate, in order to evaluate the improvement effect of polymer on the hydraulic properties of soil.

[0043] In step S3, the erosion reduction rate of the cemented soil sample is Δb = b1 - b0, and the crack area reduction rate of the cemented soil sample is... Where b1 and p1 are the erosion rate and crack area of ​​the cemented soil sample, and b0 and p0 are the erosion rate and crack area of ​​the plain soil sample.

[0044] Step S4: Perform CT tests on cemented soil samples to obtain the microscopic hydrophysical characteristics of cemented soil samples, including porosity, interconnected porosity, isolated porosity and pore coordination number, and further calculate the pore characteristic coefficients of cemented soil samples.

[0045] In step S4, the porosity of the cemented soil sample is defined as follows:

[0046]

[0047] Among them, V V and V T These represent pore volume and total soil volume, respectively.

[0048] The interconnected porosity and isolated porosity of cemented soil samples are defined as follows: Among them, V l V g These represent the volumes of connected pores and isolated pores, respectively.

[0049] Reference Figure 3 The porosity coordination number of a cemented soil sample is defined as... Where, N B N represents the number of branch pores connected to a given node. E N represents the number of end-point pores. J Let C be the number of nodes, and let C be the coordination number corresponding to the maximum percentage of coordination numbers. max .

[0050] The porosity characteristic coefficient Q of the cemented soil sample in step S4 is as follows:

[0051]

[0052] Step S5: Based on the mechanical strength improvement rate of the cemented soil sample and the mechanical friction coefficient of the failure section of the cemented soil sample; based on the hydraulic strength improvement rate of the cemented soil sample and the porosity characteristic coefficient of the cemented soil sample, calculate the cementation coefficient of the cemented soil sample to quantitatively evaluate the cementation effect of the soil.

[0053] The cementation coefficient L of the cemented soil sample in step S5 is as follows:

[0054]

[0055] In the formula, Δu is the rate of increase in shear strength, Δq is the rate of increase in compressive strength, Δv is the rate of increase in tensile strength, f is the coefficient of mechanical friction of the failure section of the cemented soil sample, and Q is the porosity characteristic coefficient of the cemented soil sample.

[0056] In one application embodiment, the dry density of the soil sample was set to 1.62 g / cm³. 3 The soil sample had a moisture content of 23%, a curing agent content of 0.5%, and a curing period of 24 hours. A certain mass of curing agent, soil, and water was thoroughly mixed to prepare a cemented soil sample. Indoor tests were conducted, yielding Δq = 19.44%, Δu = 12.36%, Δv = 28.83%, Δb = 41.68%, and Δp = 61.97%. A CT scan of the sample was performed to obtain the n... l =27.66%, n g =2.67% and C max =10, Q=2.14. A white light interferometer was used to measure the failure section of the cemented soil sample after the test, obtaining the failure section d. q =d max =1.04mm, S u =0.44, f y =0.98; SEM images of the fractured cross sections of cemented soil samples were acquired, the SEM images were preprocessed, and numerical experiments were conducted based on the indoor test results, yielding p = 1.8%, S1 = 0.04%, S2 = 0.11%, and α = 10. 8 β = 3.65 × 10 7 E = 2.14 × 10 6 N = 8.02 × 10 4 f j =0.15, f=0.33, L=0.82. The cementation effect in the improved soil is quantitatively evaluated based on the value of L.

[0057] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. A method for evaluating the cementation effect of improved sandy soil based on microstructural characteristics, characterized in that, For the target soil, perform the following steps S1-S5 to complete a quantitative evaluation of the soil's cementation effect: Step S1: Collect cemented soil samples and plain soil samples from the target soil body. Conduct laboratory tests on the mechanical characteristics of the cemented soil samples and plain soil samples respectively, including unconfined compressive strength test, direct shear test and tensile test, and obtain the mechanical strength improvement rate of the cemented soil samples, including the improvement rate of compressive strength, shear strength and tensile strength. Step S2: Perform three-dimensional surface measurement on the failure section of the cemented soil sample caused by the indoor test, acquire SEM image of the failure section, simulate the indoor test results of mechanical characteristics, obtain the micromechanical characteristics of the cemented soil sample, including the undulation, roughness, cementation rate and particle cohesion of the failure section, and further calculate the mechanical friction coefficient of the failure section of the cemented soil sample. Step S3: Conduct indoor tests on the hydraulic characteristics of cemented soil samples and plain soil samples, including evaporation cracking test, scour test and disintegration test, to obtain the hydraulic strength improvement rate of cemented soil samples, including erosion reduction rate and crack area reduction rate. Step S4: Perform CT tests on cemented soil samples to obtain the microscopic hydrophysical characteristics of cemented soil samples, including porosity, interconnected porosity, isolated porosity and pore coordination number, and further calculate the pore characteristic coefficients of cemented soil samples. Step S5: Calculate the cementation coefficient of the cemented soil sample based on the mechanical strength enhancement rate, mechanical friction coefficient of the failure section, hydraulic strength enhancement rate, and pore characteristic coefficient, so as to quantitatively evaluate the cementation effect of the soil.

2. The method for evaluating the cementation effect of improved sandy soil based on microstructural characteristics according to claim 1, characterized in that, The increase in compressive strength Δ of the cemented soil sample in step S1 q As shown in the following formula: D q = ×100% The rate of increase in shear strength Δ of cemented soil specimens u As shown in the following formula: D u = ×100% The rate of increase in tensile strength Δ of cemented soil specimens v As shown in the following formula: D v = ×100% In the formula, q 1. u 1 and v 1 represents the compressive strength, shear strength, and tensile strength of the cemented soil sample, respectively. q 0、 u 0 and v 0 represents the compressive strength, shear strength, and tensile strength of the soil sample, respectively.

3. The method for evaluating the cementation effect of improved sandy soil based on microstructural characteristics according to claim 1, characterized in that, The calculation steps for the undulation and roughness of the failure section of the cemented soil sample in step S2 are as follows: Step S21: Measure the elevation of the damaged section using a white light interferometer, and set the plane containing the lowest point of the damaged section as the zero elevation plane, where the maximum elevation is... The undulation of the failure section is defined as ; Step S22: Divide the failure section into equal parts m Each region m The value of should be chosen such that the undulation of the failure section in each region is commensurate with respect to . d q Not greater than 0.05 mm; Step S23: Select four points in each region and take the average height of the four points as the average height of the region. d n , where 1≤ n ≤ m , n Indicates the first n In each region, the roughness of the damaged cross section is affected. Defined as follows: in, .

4. The method for evaluating the cementation effect of improved sandy soil based on microstructural characteristics according to claim 3, characterized in that, The calculation steps for the cementation rate and particle cohesion of the cemented soil sample in step S2 are as follows: Step S24: Establish a particle flow simulation model through sample preparation, pre-compression, bonding, unloading, loading plate, and loading process; Step S25: Use the trial and error method to calibrate the parameters of the particle flow simulation model. When the particle flow simulation results meet the requirements that the simulation curve and the actual curve have the same trend, the peak strength error is less than 10%, the peak strain error is less than 10%, and the elastic modulus error is less than 10%, the particle flow simulation results are considered to be effective and the parameter calibration is reliable. Obtain the contact model parameters at this time. Step S26: Process the SEM image of the failure section of the cemented soil sample, coloring the soil particles and cement particles separately, and identify the total area of ​​the soil particles using image processing software. S t The total area of ​​the adhesive particles S j Cementation rate of the damaged section p As shown in the following formula: Step S27: The particle cohesion at the failure section is defined as... ,in S 1 represents the ratio of the area of ​​direct contact between soil particles to the area of ​​the failure cross section. S 2 represents the ratio of the contact area of ​​soil particles under cementation to the area of ​​the failure cross section. The effective modulus of the linear model in granular flow software. This is the effective modulus in the parallel bonding model of the granular flow software.

5. The method for evaluating the cementation effect of improved sandy soil based on microstructural characteristics according to claim 4, characterized in that, The mechanical friction coefficient of the failure section of the cemented soil sample in step S2 f As shown in the following formula: in, = The interlocking coefficient of the damaged section; = To break the bonding force of the cross section, E This represents the elastic modulus of the cemented soil sample.

6. The method for evaluating the cementation effect of improved sandy soil based on microstructural characteristics according to claim 1, characterized in that, The erosion reduction rate Δ of the cemented soil sample in step S3 b = b 1- b 0, Crack area reduction rate Δ of cemented soil sample p = ×100%, of which b 1, p 1 represents the erosion rate and crack area of ​​the cemented soil sample, respectively. b 0, p 0 represents the erosion rate and crack area of ​​the plain soil sample, respectively.

7. The method for evaluating the cementation effect of improved sandy soil based on microstructural characteristics according to claim 1, characterized in that, In step S4, the porosity of the cemented soil sample is defined as follows: in, and These represent pore volume and total soil volume, respectively. The interconnected porosity and isolated porosity of cemented soil samples are defined as follows: , ,in, , These represent the volumes of connected pores and isolated pores, respectively. The porosity coordination number of a cemented soil sample is defined as follows: ,in, The number of branch pores connected to a given node. The number of endpoint pores. Let be the number of nodes, and denote the coordination number corresponding to the maximum percentage of coordination numbers as . .

8. The method for evaluating the cementation effect of improved sandy soil based on microstructural characteristics according to claim 7, characterized in that, Pore ​​characteristic coefficient of cemented soil sample in step S4 Q As shown in the following formula:

9. The method for evaluating the cementation effect of improved sandy soil based on microstructural characteristics according to claim 1, characterized in that, The cementation coefficient of the cemented soil sample in step S5 L As shown in the following formula: In the formula, Δ u Δ represents the rate of increase in shear strength. q Δ represents the rate of increase in compressive strength. v denoted as the tensile strength enhancement rate, f is the mechanical friction coefficient of the failure section of the cemented soil sample, and Q is the porosity characteristic coefficient of the cemented soil sample. Δ b Δ represents the erosion reduction rate of the cemented soil sample. p This represents the reduction rate of crack area in cemented soil samples.

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