Multifunctional permeation grouting low-field nuclear magnetic resonance testing device and method

Abstract

The invention provides a multifunctional permeation grouting low-field nuclear magnetic resonance testing device and method, and relates to the technical field of permeation grouting, the device specifically comprises a permeation grouting control unit, a permeation grouting unit and a low-field nuclear magnetic resonance unit; the permeation grouting control unit is connected with the permeation grouting unit through a pipeline; according to different test working conditions, a sample bin of the permeation grouting unit is detached and put into the low-field nuclear magnetic resonance unit for low-field nuclear magnetic resonance superposition sampling and imaging. According to the technical scheme, the problems that in the prior art, the influence of the sand layer percolation effect on slurry diffusion cannot be microscopically observed, and the percolation grouting and diffusion rule cannot be microscopically analyzed are solved.

Description

Technical Field

[0001] The invention relates to the technical field of penetration grouting, and in particular to a multifunctional penetration grouting low-field nuclear magnetic resonance testing device and method. Background Art

[0002] Loose sand bodies and loose sand layers are common sources of geological disasters in underground engineering construction. Due to the loose sand layer structure's particle size, uneven distribution, low sand layer strength, poor injectability, uncontrollable slurry diffusion, diverse changes in slurry properties, and poor intuitiveness of grouting effects, there is a lack of research on grouting reinforcement and slurry diffusion mechanisms in loose sand layers, making it difficult to guide their application in engineering practice.

[0003] The prior art has the following problems:

[0004] In the prior art, the research on infiltration grouting considering the infiltration effect is mostly based on numerical simulation, and the model is established to carry out experiments. It is mostly aimed at one-dimensional suspension flow, and mostly considers macroscopic phenomena such as sand layer structure, seepage concentration, and changes in grouting inlet and outlet pressure. At present, in order to study the infiltration effect, many scholars have carried out a large number of theoretical formulas and model derivations, numerical simulations and indoor grouting tests (large-scale macro grouting tests). Most of the infiltration experiments are observed by the naked eye or a camera (e.g. CN201910064556.X). The test precision and accuracy need to be improved, and new technologies such as nuclear magnetic resonance have not been fully utilized, and less attention has been paid to the microscopic changes inside the medium. There is a lack of research on pore changes, slurry migration, and deep infiltration grouting at the microscopic level.

[0005] Therefore, there is a need for a multifunctional low-field nuclear magnetic resonance testing device and method for infiltration grouting that can microscopically observe the influence of the sand layer percolation effect on the diffusion of the slurry and realize the microscopic analysis of the infiltration grouting and diffusion law. Summary of the invention

[0006] The main purpose of the present invention is to provide a multifunctional low-field nuclear magnetic resonance testing device and method for infiltration grouting, so as to solve the problems in the prior art that the influence of sand layer infiltration effect on the diffusion of slurry cannot be microscopically observed and the infiltration grouting and diffusion law cannot be microscopically analyzed.

[0007] To achieve the above-mentioned purpose, the present invention provides a multifunctional infiltration grouting low-field nuclear magnetic resonance testing device, which specifically comprises: an infiltration grouting control unit, an infiltration grouting unit and a low-field nuclear magnetic resonance unit; the infiltration grouting control unit and the infiltration grouting unit are connected by a pipeline; according to different test conditions, the sample bin of the infiltration grouting unit is removed and placed in the low-field nuclear magnetic resonance unit for low-field nuclear magnetic resonance superposition sampling and imaging.

[0008] Furthermore, the infiltration grouting control unit includes: a water source, an infiltration grouting power control end, a slurry storage tank and a sample bin connected in sequence through pipelines, and the infiltration grouting power control end is also connected to the infiltration grouting data acquisition end; the infiltration grouting control unit also includes: a leachate collection dish; the leachate collection dish is located directly below the sample bin to collect the leachate in the sample bin.

[0009] Furthermore, the low-field nuclear magnetic resonance unit comprises: a low-field nuclear magnetic resonance instrument, a low-field nuclear magnetic resonance control and data acquisition terminal and a cold tank which are connected in sequence.

[0010] Furthermore, the sample bin includes: a removable leak-proof plug, a bin body and a grouting port base. The bottom of the bin body is provided with a removable leak-proof plug, the end of the bin body away from the removable leak-proof plug is the grouting port base, and the pipeline is connected to the slurry channel inside the grouting port base.

[0011] Furthermore, the inner diameter of the sample chamber body is 40 mm, the height of the sample chamber is 80 mm, the sample chamber is columnar and is made of PEEK material.

[0012] The present invention also provides a multifunctional infiltration grouting low-field nuclear magnetic resonance testing method, which specifically comprises the following steps:

[0013] S1, collect sand samples in the field, measure and configure test samples.

[0014] S2, debug the low-field nuclear magnetic resonance unit to prepare for grouting tests.

[0015] S3, after each grouting period, the sample chamber is unloaded and NMR test is carried out. The results of multiple NMR tests are superimposed and sampled to measure the porosity and invert the T2 spectrum.

[0016] S4, during the NMR test, the test sample is continuously imaged by the low-field NMR unit and the pseudo-color image parameters are adjusted.

[0017] Furthermore, step S1 specifically includes the following steps:

[0018] S1.1. Take sand samples on site and determine basic parameters, including: use the national standard ring knife to obtain the particle size distribution curve of the actual sample; use the measuring cylinder method and vibration compaction method to measure the minimum dry density and maximum dry density of the sand sample respectively, and calculate the relative density of the sand sample; use the constant rate mercury injection method to obtain the porosity of the sand sample.

[0019] S1.2, configure the test samples in the indoor test room according to the actual sand sample parameters measured on site.

[0020] Furthermore, step S2 specifically includes the following steps:

[0021] S2.1. Place a layer of mesh at the bottom of the sample chamber and place the configured test sample into the sample chamber.

[0022] S2.2, adjust the low-field NMR parameters, and perform NMR test on the test sample. When the test result is correct, invert to obtain the T2 spectrum, and export the data of the test sample before and after the NMR test.

[0023] Furthermore, step S3 specifically includes the following steps:

[0024] S3.1, pour the test sample obtained in step S1 into the slurry storage tank, and use a turbidity meter to measure the suspended particle concentration of the test sample; after selecting a determined grouting rate value, start the grouting test. During the grouting process, open the leak-stop plug at regular intervals to observe and take the leachate, and use a turbidity meter to measure the leachate particle concentration and record it as Z.

[0025] S3.2, select the sample bin as the unit body, set the length to L, and the cross-sectional area to a. Then the porosity n of the test sample at any time is:

[0026]

[0027] Substituting the concentration distribution in the pores into formula (1) yields:

[0028]

[0029] Among them, n i is the initial porosity, V d is the volume of particles deposited in the sample chamber, V s is the volume of suspended particles in the sample chamber, m is the concentration of deposited particles, C is the concentration of suspended particles in the sample chamber, ρ s is the density of suspended particles in slurry;

[0030] S3.3, according to the Kozeny-Carman equation, the permeability K of the loose sand layer is:

[0031]

[0032] Where c is the Kozeny-Carman constant, q is the specific surface area of ​​the solid phase;

[0033] Substituting formula (2) into formula (3), the permeability K of loose sand layer is obtained as:

[0034]

[0035] S3.4, according to the principle of nuclear magnetic resonance:

[0036]

[0037] in, is the surface relaxation time, is the diffusion relaxation time, is the free relaxation time;

[0038] Relaxation time of fluid in pores It is expressed as:

[0039]

[0040] Where, ρ2 is the surface relaxation rate, V is the pore volume, and S is the pore surface area;

[0041] S3.5, use the CPMG sequence test to obtain the magnetization intensity M(t) of the sand sample at time t, and then invert the transverse relaxation time T2:

[0042]

[0043] Among them, M 0n (0) is the magnetization vector of the nth relaxation component at the initial moment, M0 is the initial magnetization intensity, ρ(T2) is the distribution density of T2, T 2i is the transverse relaxation time corresponding to each pore, and exp is an exponential function.

[0044] S3.6, convert the NMR signal of the test sand sample into porosity by calibrating the standard porosity sample:

[0045]

[0046] in, is the total porosity of the sample, in %; P is the cumulative NMR signal per unit volume of the sample, and A and B are constants.

[0047] Further, step S4 is specifically as follows:

[0048] The sample bin and sand sample are placed in the detection sample tube of the low-field nuclear magnetic resonance unit, and the obtained water signal quantity analysis image is imported into the nuclear magnetic resonance image processing software, and the image is partially enlarged and rotated, and the required image research range is circled, and pseudo-coloring is performed, and the high hydrogen nuclear density range is colored red and the low hydrogen nuclear density range is colored blue. The low-field nuclear magnetic resonance image tone, brightness and contrast are adjusted to obtain the low-field nuclear magnetic resonance pseudo-color image of the sand sample at different grouting times

[0049] The present invention has the following beneficial effects:

[0050] (1) The present invention takes into account the influence of the percolation effect on the infiltration grouting and slurry diffusion process, and designs a set of equipment specifically used for nuclear magnetic resonance testing of the infiltration grouting and slurry diffusion process. The equipment does not contain paramagnetic substances and can meet the nuclear magnetic resonance test requirements within a temperature of 50°C and a pressure of 7MPa. The equipment is accurate and reliable in tests such as nuclear magnetic resonance spectroscopy and nuclear magnetic resonance imaging.

[0051] (2) A nuclear magnetic resonance testing method for studying the slurry filtration effect is proposed, which includes sampling selection, instrument assembly, equipment self-test, parameter setting, online grouting and sampling throughout the entire process. It can realize real-time monitoring of the reaction process and realize the use of nuclear magnetic resonance technology in the study of filtration effect.

[0052] (3) The data processing methods are given, and the T2 spectrum curve and pseudo-color map are obtained through inversion, imaging and other further processing. Through the data processing, the significant characteristics of the slurry affected by the infiltration effect can be observed from a microscopic perspective, thus providing more accurate and sufficient data for studying the diffusion law. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the specific implementation of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the specific implementation or the prior art description. Obviously, the drawings described below are some implementations of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work. In the drawings:

[0054] Figure 1 A diagram of a multifunctional infiltration grouting low-field nuclear magnetic resonance testing device of the present invention is shown.

[0055] Figure 2 Shows Figure 1 The sample chamber structure diagram.

[0056] Figure 3 A schematic diagram of the sample T2 spectrum curve obtained through step S3 is shown.

[0057] Figure 4 A columnar schematic diagram showing the change in peak area of ​​different pore sizes in the T2 spectrum before and after grouting of the sand sample.

[0058] Figure 5 The NMR images of sand samples at different grouting times are shown.

[0059] The reference numerals in the above drawings are:

[0060] 1. Infiltration grouting data acquisition terminal; 2. Water source; 3. Infiltration grouting power control terminal; 4. Slurry storage tank; 5. Sample bin; 50. Pipeline; 51. Removable leak-stopping plug; 52. Bin body; 53. Grouting port base; 6. Leachate collection dish; 7. Low-field nuclear magnetic resonance instrument; 8. Low-field nuclear magnetic resonance control and data acquisition terminal; 9. Cold tank. DETAILED DESCRIPTION

[0061] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0062] like Figure 1 A multifunctional infiltration grouting low-field nuclear magnetic resonance testing device is shown, which specifically includes: an infiltration grouting control unit, an infiltration grouting unit and a low-field nuclear magnetic resonance unit; the infiltration grouting control unit and the infiltration grouting unit are connected by a pipeline; after each grouting period, the sample chamber of the infiltration grouting unit is removed and placed in the low-field nuclear magnetic resonance unit for low-field nuclear magnetic resonance superposition sampling.

[0063] The low-field nuclear magnetic resonance unit includes: a low-field nuclear magnetic resonance instrument 7, a low-field nuclear magnetic resonance control and data acquisition terminal 8 and a cold tank 9 connected in sequence. The low-field nuclear magnetic resonance control and data acquisition terminal collects data from the low-field nuclear magnetic resonance instrument. The magnet in the low-field nuclear magnetic resonance instrument must maintain a constant temperature during the entire test process. The cold tank is used to dissipate heat and cool the magnet. The temperature setting range of the constant temperature cold tank is 20-25°C, and the temperature of the cold tank can be appropriately adjusted according to room temperature. Based on the characteristics of atomic nuclei absorbing and emitting electromagnetic waves in an external magnetic field and the resonance characteristics of biomagnetic nuclei (such as hydrogen nuclei) in a magnetic field, the T2 spectrum and nuclear magnetic resonance imaging of the sand layer in the penetration grouting test are obtained.

[0064] Specifically, the infiltration grouting control unit includes: a water source 2, an infiltration grouting power control terminal 3, a slurry storage tank 4 and a sample bin 5 which are sequentially connected through pipelines. The infiltration grouting power control terminal is also connected to the infiltration grouting data acquisition terminal 1.

[0065] The infiltration grouting control unit also includes: a leachate collection dish 6; the leachate collection dish 6 is located directly below the sample bin and collects the leachate in the sample bin. The water source provides pressure for the infiltration grouting power control end, and the infiltration grouting data collection end collects data from the infiltration grouting power control end.

[0066] Specifically, Figure 2As shown, the sample bin 5 includes: a removable leak-stop plug 51, a bin body 52 and a grouting port base 53. The removable leak-stop plug 51 is provided at the bottom of the bin body 52, and the end of the bin body away from the removable leak-stop plug 51 is the grouting port base 53. The pipeline is connected to the slurry channel inside the grouting port base.

[0067] The sample bin is a columnar PEEK bin with an inner diameter of 40mm and a height of 80mm. The base of the grouting port is a conical cavity, which can ensure that the slurry is slowly and evenly injected into the sand layer. The mesh is placed at the bottom of the sample bin, so that the slurry can be smoothly injected into the sand layer while preventing the upper sand body from falling due to gravity and blocking the grouting hole. The sample bin is made of polyetheretherketone (PEEK) material, which has the advantages of corrosion resistance, aging resistance, self-lubrication, high strength, and easy processing. After testing, PEEK material is a special engineering plastic without paramagnetic substances, and can withstand normal test grouting pressure, which meets the needs of studying the diffusion and percolation effect of sand layers on slurry. The removable stopper can be used as needed. Opening the removable stopper can observe and collect the percolation liquid that percolates through the sample in real time. The grouting port is located at the connection point between the base and the pipeline. The grouting port adopts a threaded structure and can be connected to the grouting pipeline. It can be disassembled quickly, which is convenient for rapid sampling for nuclear magnetic resonance testing. It has a variety of specifications and can be flexibly applied to a variety of grouting pump interfaces, which can reduce the cost of use. It can meet the requirements of indoor test operations, such as convenient operation, rapid disassembly, low cost, temperature within 50°C, and pressure within 7MPa. Nuclear magnetic resonance testing and grouting testing requirements can be accurately and reliably used in low-field nuclear magnetic resonance spectroscopy, nuclear magnetic resonance imaging and other tests.

[0068] A multifunctional infiltration grouting low-field nuclear magnetic resonance testing method specifically comprises the following steps:

[0069] S1, collect sand samples in the field, measure and configure test samples.

[0070] S2, debug the low-field nuclear magnetic resonance unit to prepare for the grouting test. The sand samples for the test are usually of the same type. The first sand sample is debugged, and the subsequent sand samples can use the same parameters without debugging again.

[0071] S3, after each grouting period, the sample chamber is unloaded and NMR test is carried out. The results of multiple NMR tests are superimposed and sampled to measure the porosity and invert the T2 spectrum.

[0072] Connect the infiltration grouting data acquisition end, the infiltration grouting power control end and the slurry storage tank in sequence. After the grouting pipeline is connected, tighten the pipeline to the grouting port of the sample bin to complete the connection of the slurry channel. Configure the corresponding slurry according to the test design, pour the slurry evenly into the slurry storage tank, and use a turbidity meter to measure its suspended particle concentration; open the grouting pipe valve, select a certain grouting rate value and start the grouting test. During the grouting process, the removable stopper can be opened regularly to observe and take the leachate. The leachate particle concentration is measured by a turbidity meter and recorded as Z. After each grouting time, the sample bin is quickly removed, low-field nuclear magnetic resonance superposition sampling is performed, and the T2 data is exported and saved.

[0073] S4, during the NMR test, the test sample is continuously imaged by the low-field NMR unit and the pseudo-color image parameters are adjusted.

[0074] Specifically, step S1 includes the following steps:

[0075] S1.1. Take sand samples on site and determine basic parameters, including: use the national standard ring knife to obtain the particle size distribution curve of the actual sample; use the measuring cylinder method and vibration compaction method to measure the minimum dry density and maximum dry density of the sand sample respectively, and calculate the relative density of the sand sample; use the constant rate mercury injection method to obtain the porosity of the sand sample.

[0076] S1.2, according to the actual sand layer sample parameters measured on site, configure the test samples in the indoor test room. The on-site sand layer samples usually contain certain paramagnetic substances. The present invention uses high-purity quartz sand of different particle sizes to configure the indoor samples through the measured on-site sand layer sample parameters, and adjusts the particle size ratio, porosity, and density parameters to ensure that the basic physical properties of the test sand samples are consistent with the on-site sand layer samples. The configured high-purity quartz sand sample has pure composition and uniform properties, avoiding the interference and influence of paramagnetic substances on the test, and ensuring the accuracy and reliability of the test.

[0077] Specifically, step S2 includes the following steps:

[0078] S2.1, lay a layer of mesh at the bottom of the sample bin and put the prepared test sample into the sample bin to prevent sand from leaking out from the bottom when the removable stopper is opened to take the percolation slurry.

[0079] S2.2, adjust the low-field NMR parameters, and perform NMR test on the test sample. When the test result is correct, invert to obtain the T2 spectrum, and derive the data of the test sample before and after the NMR test. If the equilibrium stable area of ​​the measured curve accounts for more than one-third of the whole, the test result is judged to be correct.

[0080] Combined with the testing principle of low-field nuclear magnetic resonance system, the nuclear magnetic parameters are determined according to the hydrogen content in the tested sample, and the relaxation spectrum is obtained by testing.

[0081] S2.2.1, first of all, the center frequency correction is performed. Select the Fid sequence and run a single sampling. Observe the real part, imaginary part and modulus curves of the data. The "real part" is the yellow signal line, the "imaginary part" is the green signal line and the "modulus" is the blue signal line. If the front end of the blue signal line is relatively straight, it is judged as over-gain and the preamplifier gear needs to be reduced. Perform a single sampling again. After completion, click Stop. Click the center frequency. When the three curves are separated, the center frequency correction is completed.

[0082] S2.2.2, before finding the pulse width, you need to determine the waiting time. If the maximum value of the model before and after a single sampling changes by more than 1%, you need to increase the waiting time. If it is less than 1%, the waiting time is appropriate. Perform 90° pulse width correction in sequence to form a peak and a trough, which means the correction is accurate, and determine the 90° pulse width and 180° pulse width. Roughly understand the strength of the H signal in the sample to be tested, that is, the H+ (hydrogen ion) signal, and continue to use the Fid sequence to determine the modification of the pre-shift position, the waiting time of the sample to be tested, the sampling frequency, the RF delay, the analog gain, and the digital gain according to the nuclear magnetic sampling of the sample to be tested.

[0083] S2.2.3. After finding the parameters, switch to CPMG sequence, input the measured sampling frequency, RF delay, analog gain, digital gain, preamplifier gear, and waiting time, and modify the accumulation times according to the signal strength of the sample to be tested. If the signal is strong, reduce the accumulation times, and if the signal is weak, increase the accumulation times.

[0084] S2.2.4, adjust the echo time and the number of echoes. First, set the echo time to 0.2 and the number of echoes to 8000. Click on cumulative sampling. If a pop-up box pops up to increase the RF delay, increase the sampling frequency. If the stable length of the acquisition curve accounts for 1 / 3, the parameters are appropriate. The time on the horizontal axis is the product of the echo time and the number of echoes. At this point, the parameters are adjusted. Click on cumulative sampling to perform the NMR test of the sample to be tested. When the test results are correct, you can perform inversion and export the sample data before and after the test.

[0085] Specifically, step S3 includes the following steps:

[0086] S3.1, pour the test sample obtained in step S1 into the slurry storage tank, and use a turbidity meter to measure the suspended particle concentration of the test sample; after selecting a determined grouting rate value, start the grouting test. During the grouting process, open the leak-stop plug at regular intervals to observe and take the leachate, and use a turbidity meter to measure the leachate particle concentration and record it as Z.

[0087] S3.2, as the cement slurry continues to migrate in the pores of the loose sand layer, cement particles are deposited under the action of hydrodynamics, gravity, etc., causing the pore channels to narrow continuously until they are blocked, and the permeability to change continuously. The present invention proposes a method for calculating the permeability K of a sample at any time during a relatively short grouting process, which is used to analyze the influence of the sand layer percolation effect on the permeation grouting and slurry diffusion.

[0088] The sample bin is selected as a unit body, the length is set to L, and the cross-sectional area is A. The porosity n of the test sample at any time is:

[0089]

[0090] Substituting the concentration distribution in the pores into formula (1) yields:

[0091]

[0092] Among them, n i is the initial porosity, V d is the volume of particles deposited in the sample chamber, V s is the volume of suspended particles in the sample chamber, m is the concentration of deposited particles, C is the concentration of suspended particles in the sample chamber, ρ s is the density of suspended particles in slurry.

[0093] S3.3, according to the Kozeny-Carman equation, the permeability K of the loose sand layer is:

[0094]

[0095] Where c is the Kozeny-Carman constant, q is the specific surface area of ​​the solid phase;

[0096] Substituting formula (2) into formula (3), the permeability K of loose sand layer is obtained as:

[0097]

[0098] Under the condition of short grouting time, it is considered that the concentration of suspended particles in the loose sand layer is the same as the initial slurry suspended particle concentration, and slurry particle deposition has not yet occurred. That is, it is approximately considered that the difference between the slurry suspended particle concentration and the suspended particle concentration in the unit body is the deposited particle concentration. When the initial injection slurry concentration is known to be M, only one unknown number, S, of the deposited particle concentration, needs to be measured experimentally to obtain the change in the permeability of the loose sand layer medium after the slurry particle deposition. In the experiment, the initial porosity n was obtained by nuclear magnetic resonance. i, the turbidity meter was used to measure the leachate particle concentration Z at different times. The slurry was self-prepared and the suspended particle concentration was known. According to the relationship between the three, S = MZ; where M is the slurry concentration. The test slurry was self-prepared and the concentration was known. Bringing back equation (4), the permeability change of loose sand layer grouting diffusion affected by the percolation effect can be obtained.

[0099] S3.4, the present invention uses nuclear magnetic resonance technology to invert the T2 spectrum to process data, obtain the sample pore size distribution and slurry diffusion, and study the diffusion behavior of slurry in loose sand layers and the influence of filtration effect on it from a microscopic perspective. According to the principle of nuclear magnetic resonance, it can be known that:

[0100]

[0101] in, is the surface relaxation time, is the diffusion relaxation time, is the free relaxation time;

[0102] The three different relaxation mechanisms of the fluid in the sand layer pores have different effects on the total T2. Free relaxation and diffusion relaxation are much smaller than surface relaxation. Therefore, the relaxation time of the fluid in the pores can be approximately expressed as:

[0103]

[0104] Where ρ2 is the surface relaxation rate, V is the pore volume; S p is the pore surface area.

[0105] Assuming that the pores inside the sand layer are simple in shape, the pore radius r = ρ2FsT2 is calculated. For slit-type, cylindrical and spherical pores, Fs is 1, 2 and 3 respectively. Let D = ρ2Fs, where D is the conversion coefficient. For the same type of sand layer, ρ2 is a fixed value, Fs is a constant, and therefore D is also a constant. r is proportional to T2. The longer T2 is, the larger r is. The higher the amplitude of T2 is, the larger the pore volume corresponding to the pore size is.

[0106] By using a CPMG pulse sequence with a shorter echo time, the transverse relaxation time T2 of the fluid in the rock pores can be measured and inverted to obtain the distribution state of the fluid in the rock pores. Porous media such as rocks can be considered as a combination of media containing continuously distributed single pores of different sizes, each of which has its own pore surface area S i and pore volume V i , the transverse relaxation time corresponding to each pore is T 2i .

[0107] S3.5, use the CPMG sequence test to obtain the magnetization intensity M(t) of the sand sample at time t, and then invert the transverse relaxation time T2:

[0108]

[0109] Among them, M 0n (0) is the magnetization vector of the nth relaxation component at the initial moment, M0 is the initial magnetization intensity, ρ(T2) is the distribution density of T2, T 2i is the transverse relaxation time corresponding to each pore, and exp is an exponential function.

[0110] The step-by-step iterative optimization algorithm is used to set the number of iterations to control the accuracy of the transverse relaxation time of magnetization intensity inversion.

[0111] S3.6, there is a linear correlation between the sample porosity and the nuclear magnetic signal. By calibrating the standard porosity sample, the nuclear magnetic signal of the test sand sample is converted into porosity:

[0112]

[0113] in, is the total porosity of the sample, in %; P is the cumulative NMR signal per unit volume of the sample, and A and B are constants.

[0114] The image processing method adopted by the present invention is to draw the image with T 2i As the horizontal coordinate, the magnetization intensity is the vertical coordinate, and the logarithm of the horizontal coordinate with base 10 is taken to obtain the T2 spectrum curve, such as Figure 3 As shown in the figure, the pore structure type in the sand sample is determined based on the T2 spectrum of the measured sample. The pores are divided into types with corresponding numbers according to the number of relaxation peaks, and then the relaxation time corresponding to different types of pores is roughly corresponded according to the distribution range of each relaxation peak. The test results of the sand layer contain 3 relaxation peaks, and the pores are divided into three types: small pores, medium pores, and large pores. According to the outflow of slurry from the outlet of the multi-purpose sample bin during the grouting process, the grouting time section is designed and determined, and the nuclear magnetic resonance test is carried out according to the designed grouting time. According to the changes in the T2 spectrum during the grouting time designed by the experiment, the connectivity of the sand layer pores and the pore size type transformation during the slurry diffusion process are studied; when the slurry penetrates the sand layer and the water-cement ratio of the leachate does not change or the slurry completely blocks the slurry flow channel, it is determined as the end point of grouting. The area closed by the relaxation peaks under different pore types and the percentage of each part are calculated, the changes in the relative content of different pores in the sand sample are analyzed, and the transformation of the pore type in the sand layer under the influence of slurry diffusion and percolation effect is judged.

[0115] The pore structure characteristics in the sand sample are determined based on the T2 spectrum of the sample. The T2 spectrum of the test sample shows a three-peak structure, revealing that its pore size can be divided into three categories, namely large pores, medium pores, and small pores. According to the test results and the relaxation time distribution corresponding to the relaxation peaks, from left to right are the first peak, whose relaxation time is 0.1~10ms, and the corresponding pore size is 0.001~0.1μm, which is used to represent the small pores of the sample; the relaxation time of the second peak is 10~500ms, and the corresponding pore size is 0.1~5μm, which is used to represent the medium pores of the sample; the relaxation time of the third peak is 500~10000ms, and the corresponding pore size is 5~100μm, which is used to represent the large pores of the sample. Draw the area closed by the relaxation peaks of large pores, medium pores, and small pores, as well as the percentage of each part (such as Figure 4 As shown in the figure, by analyzing the numerical changes of the peak areas of different pore sizes during the grouting process, the flow, fracturing and connectivity of the slurry in the pores are analyzed to analyze the influence of the filtration effect on the sand layer.

[0116] Specifically, in the previous analysis, it was believed that the concentration of suspended particles in the loose sand layer was the same as the concentration of suspended particles in the initial slurry, and no deposition occurred in a short period of time. In reality, the deposited particles should include the deposition of some suspended particles in the loose medium. In order to further intuitively observe the changes in particle deposition in the loose medium, the present invention performs pseudo-color processing on the nuclear magnetic resonance image.

[0117] Step S4 is specifically as follows:

[0118] The sample chamber and sand sample are placed in the detection sample tube of the low-field nuclear magnetic resonance unit (specifically, the nuclear magnetic resonance imaging analyzer MesoMR12-060H-I), and the changes in the water content and distribution of the slurry material are studied by utilizing the relaxation characteristics of protons in water molecules. The principle is to observe the state of water in the sand sample and analyze the pore distribution in the sample through the H+ in the sample. After pre-scanning, positioning, and imaging steps, the analysis image of the sample on the water signal quantity is obtained.

[0119] The obtained water signal analysis image was imported into the nuclear magnetic resonance image processing software, and the image was partially enlarged and rotated, the required image research range was circled, and pseudo-coloring was performed, with high hydrogen nuclear density range colored in red and low hydrogen nuclear density range colored in blue. The low-field nuclear magnetic resonance image hue, brightness and contrast were adjusted to obtain low-field nuclear magnetic resonance pseudo-color images of sand samples with different grouting times. Figure 5The image shows the sample imaged by a low-field nuclear magnetic resonance imaging analyzer. It directly shows the distribution of pores in the sand sample to analyze the filtration effect of the sand layer on the slurry. The color scale shows that the range of signal intensity gradually transitions from high red values ​​(high hydrogen nucleus density) to low blue values ​​(low hydrogen nucleus density). The brighter the area, the larger the pore radius; the darker the area, the less water and the smaller the pore radius. The diffusion process of the slurry and the particle deposition can be directly observed.

[0120] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A multifunctional low-field nuclear magnetic resonance testing device for infiltration grouting, characterized in that: Specifically include: Infiltration grouting control unit, infiltration grouting unit and low-field nuclear magnetic resonance unit; the infiltration grouting control unit and the infiltration grouting unit are connected through pipelines; according to different test conditions, the sample chamber of the infiltration grouting unit is removed and placed in the low-field nuclear magnetic resonance unit for low-field nuclear magnetic resonance superposition sampling and imaging.

2. A multifunctional low-field nuclear magnetic resonance testing device for infiltration grouting according to claim 1, characterized in that: The infiltration grouting control unit includes: a water source, an infiltration grouting power control end, a slurry storage tank and a sample bin connected in sequence through pipelines. The infiltration grouting power control end is also connected to the infiltration grouting data acquisition end; the infiltration grouting control unit also includes: a leachate collection dish; the leachate collection dish is located directly below the sample bin to collect the leachate in the sample bin.

3. A multifunctional low-field nuclear magnetic resonance testing device for infiltration grouting according to claim 1, characterized in that: The low-field nuclear magnetic resonance unit comprises: a low-field nuclear magnetic resonance instrument, a low-field nuclear magnetic resonance control and data acquisition terminal and a cold tank which are connected in sequence.

4. A multifunctional low-field nuclear magnetic resonance testing device for infiltration grouting according to claim 1, characterized in that: The sample bin includes: a detachable leak-proof plug, a bin body and a grouting port base. The bottom of the bin body is provided with a detachable leak-proof plug, the end of the bin body away from the detachable leak-proof plug is the grouting port base, and the pipeline is connected with the slurry channel inside the grouting port base.

5. A multifunctional low-field nuclear magnetic resonance testing device for infiltration grouting according to claim 4, characterized in that: The inner diameter of the sample chamber body is 40 mm, the height of the sample chamber is 80 mm, the sample chamber is columnar and is made of PEEK material.

6. A multifunctional low-field nuclear magnetic resonance testing method for infiltration grouting, using the device described in any one of claims 1 to 5, characterized in that: The specific steps include: S1, collect sand samples in the field, measure and configure test samples; S2, commissioning the low-field NMR unit to prepare for grouting tests; S3, after each grouting period, the sample bin is unloaded, and nuclear magnetic resonance testing is performed. Multiple nuclear magnetic resonance test results are superimposed and sampled to measure porosity and invert the T2 spectrum; S4, during the NMR test, the test sample is continuously imaged by the low-field NMR unit and the pseudo-color image parameters are adjusted.

7. A multifunctional infiltration grouting low-field nuclear magnetic resonance testing method according to claim 6, characterized in that: Step S1 specifically includes the following steps: S1.1, take sand samples on site and determine basic parameters, including: use national standard ring cutter to obtain the particle size distribution curve of the actual sample; use measuring cylinder method and vibration compaction method to measure the minimum dry density and maximum dry density of the sand sample respectively, and calculate the relative density of the sand sample; use constant rate mercury injection method to obtain the porosity of the sand sample; S1.2, configure the test samples in the indoor test room according to the actual sand sample parameters measured on site.

8. A multifunctional infiltration grouting low-field nuclear magnetic resonance testing method according to claim 6, characterized in that: Step S2 specifically includes the following steps: S2.1, lay a layer of mesh at the bottom of the sample chamber and load the configured test sample into the sample chamber; S2.2, adjust the low-field NMR parameters, and perform NMR test on the test sample. When the test result is correct, invert to obtain the T2 spectrum, and export the data of the test sample before and after the NMR test.

9. A multifunctional infiltration grouting low-field nuclear magnetic resonance testing method according to claim 6, characterized in that: Step S3 specifically includes the following steps: S3.1, pour the test sample obtained in step S1 into a slurry storage tank, and use a turbidity meter to measure the suspended particle concentration of the test sample; after selecting a determined grouting rate value, start the grouting test, during the grouting process, open the stop plug regularly to observe and take the leachate, and use a turbidity meter to measure the leachate particle concentration and record it as Z; S3.2, select the sample bin as the unit body, set the length to L, and the cross-sectional area to A. Then the porosity n of the test sample at any time is: Substituting the concentration distribution in the pores into formula (1) yields: Among them, n i is the initial porosity, V d is the volume of particles deposited in the sample chamber, V s is the volume of suspended particles in the sample chamber, m is the concentration of deposited particles, C is the concentration of suspended particles in the sample chamber, ρ s is the density of suspended particles in slurry; S3.3, according to the Kozeny-Carman equation, the permeability K of the loose sand layer is: Where c is the Kozeny-Carman constant, q is the specific surface area of ​​the solid phase; Substituting formula (2) into formula (3), the permeability K of loose sand layer is obtained as: S3.4, according to the principle of nuclear magnetic resonance: in, is the surface relaxation time, is the diffusion relaxation time, is the free relaxation time; Relaxation time of fluid in pores It is expressed as: Where, ρ2 is the surface relaxation rate, V is the pore volume, S is the pore surface area; S3.5, use the CPMG sequence test to obtain the magnetization intensity M(t) of the sand sample at time t, and then invert the transverse relaxation time T2: Among them, M 0n (0) is the magnetization vector of the nth relaxation component at the initial moment, M0 is the initial magnetization intensity, ρ(T2) is the distribution density of T2, T 2i is the transverse relaxation time corresponding to each pore, and exp is an exponential function; S3.6, convert the NMR signal of the test sand sample into porosity by calibrating the standard porosity sample: in, is the total porosity of the sample, in %; P is the cumulative NMR signal per unit volume of the sample, and A and B are constants.

10. A multifunctional infiltration grouting low-field nuclear magnetic resonance testing method according to claim 6, characterized in that: Step S4 is specifically as follows: The sample bin and sand sample are placed in the detection sample tube of the low-field nuclear magnetic resonance unit, and the obtained water signal quantity analysis image is imported into the nuclear magnetic resonance image processing software, and the image is locally enlarged and rotated, and the required image research range is circled, and pseudo-coloring is performed, with high hydrogen nuclear density range colored in red and low hydrogen nuclear density range colored in blue. The hue, brightness and contrast of the low-field nuclear magnetic resonance image are adjusted to obtain low-field nuclear magnetic resonance pseudo-color images of sand samples with different grouting times.

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