A method for acoustic emission monitoring of underground jet grouting effects during construction

Abstract

The application discloses a kind of acoustic emission monitoring methods for underground rotary jet grouting effect in construction process.In the monitoring area of underground rotary jet grouting pile target pile diameter, waveguide pipe is respectively buried inside and outside, acoustic emission sensor is coupled at the end of waveguide pipe exposed to surface, real-time pickup acoustic emission signal generated by rotary jet grouting medium cutting soil in construction process, acoustic emission characteristic information of rotary jet grouting pile at different rotary jet grouting depth and different radial position of pile body is counted;With the acoustic emission characteristic information counted at near-surface and from center axis, actual rotary jet grouting times at fixed rotary jet grouting elevation in construction process as reference value, acoustic emission characteristic information counted at different positions is homogenized, defined as soil cutting coefficient, soil cutting coefficient is compared and analyzed, rotary jet grouting effect is classified, grouting condition and pile quality are real-time feedback;It can real-time, continuously and quantitatively monitor rotary jet grouting effect of underground rotary jet grouting pile, realize visual construction of underground concealed engineering, ensure construction quality and reduce construction cost.

Description

Technical Field

[0001] This invention relates to the field of jet grouting pile construction quality testing technology in the field of foundation treatment, specifically to an acoustic emission monitoring method for the underground jet grouting effect during construction. Background Technology

[0002] Acoustic emission (AE) technology, as a non-destructive testing method, can continuously capture elastic waves released by stress concentration within materials under load in real time. It is currently widely used in quasi-continuous media materials, such as metals, rocks, and concrete. When a material is subjected to external loads, the microscale degradation process within the material is often accompanied by the release of strain energy. Most of this strain energy is released in the form of elastic waves, which can be detected and recorded as acoustic emission signals by acoustic emission sensors.

[0003] Jet grouting is a new technology used for foundation reinforcement and water-stop curtains. It has advantages such as wide applicability, convenient construction, high efficiency, and simple operation. It is suitable for foundation anti-settlement, anti-seepage, and foundation reinforcement. The principle of this technology is to use a drilling rig to drill the jet grouting pipe and nozzle to the designed depth at the bottom of the pile. The pre-prepared grout is injected with high-pressure energy by a high-pressure generator and then ejected at high speed from the nozzle on the side of the grouting pipe, forming a highly concentrated liquid flow that directly damages the soil. During the injection process, the drill rod rotates and is lifted, so that the grout and soil are fully mixed and formed into a columnar solidified body of a certain diameter in the soil, thereby reinforcing the foundation.

[0004] Jet grouting pile construction is a concealed underground project, inherently invisible. Currently, conventional detection methods include core drilling, high and low strain gauge analysis, ground-penetrating radar, and high-density electrical resistivity tomography (EDS). However, most of these methods are for post-construction pile quality inspection, providing guidance for remedial work, but failing to detect problems during construction and allow for timely adjustments and improvements. Therefore, to promptly and accurately identify quality issues in underground high-pressure jet grouting construction, a dynamic detection method is urgently needed to continuously acquire real-time data on the pile formation process.

[0005] Chinese Patent CN 202010034562.3 discloses an acoustic emission evaluation method for the thermal stability of surrounding rock under high-temperature conditions in underground engineering. This method relates to the field of surrounding rock thermal damage technology, utilizing the mechanical parameters of rock damaged by heat for inversion, and combining this with acoustic emission signals generated by thermal fracturing to evaluate the degree and location of surrounding rock damage. The method includes: A. In-situ laboratory testing of the mechanical parameters and acoustic emission characteristics of unaffected surrounding rock under temperature and pressure conditions, followed by in-situ loading tests on surrounding rock samples affected by high-temperature conditions in the engineering evaluation area; obtaining stress and acoustic emission information, and inverting the temperature range experienced by the surrounding rock; B. Arranging joint surface and underground drilling, installing acoustic emission sensors, and analyzing the temporal variation characteristics of acoustic emission to obtain the dynamic evolution process of temperature-induced fracturing of the surrounding rock; C. Determining the degree and location of surrounding rock damage based on multi-point acoustic emission information. This method solves the problem of judging the thermal stability of surrounding rock under high-temperature conditions and has advantages such as simple operation and accurate spatiotemporal positioning. Chinese Patent CN 201610034383.3 discloses a multi-channel acoustic emission monitoring system and positioning method for underground engineering construction. The system includes: several three-dimensional acoustic emission sensors connected to a multi-channel acoustic emission synchronous data acquisition device; the multi-channel acoustic emission synchronous data acquisition device is connected to a fiber optic network switch via a first photoelectric converter; and the fiber optic network switch is connected to a host computer via a second photoelectric converter. This system can perform real-time monitoring, waveform display, real-time positioning, signal strength measurement, and data recording of acoustic emission signals. It achieves real-time monitoring of the surrounding rock mass in underground engineering, reflects the rock mass's damage status, and helps to promptly detect precursory information of water inrush, providing technical support for the prevention of water inrush disasters. Chinese patent CN201210302216.4 discloses a method for accurately mapping the downhole condition of an oilfield using acoustic emission positioning monitoring. The method involves setting at least three signal receivers at intervals and in any direction on the ground around the injection well to collect and process dynamic signals of formation fractures. Fluid is injected into the injection well using fracturing and water injection equipment. The injected fluid causes the formation to crack or close, and the fluid flow generates low-frequency sound. This low-frequency sound signal is received and processed using a low-frequency sound signal receiving and processing device. Based on this signal, the sound source signal is located, and a rectangular coordinate diagram of the distribution of each sound source signal point is drawn with the injection well as the origin. This method can accurately determine the downhole condition of the injection well and effectively utilizes the changing low-frequency sound generated after the injection of fluid into the oil reservoir to quickly and accurately map the downhole condition of the injection well, significantly improving the economic benefits of the oilfield. However, considering the complexity of the acoustic emission signal positioning algorithm and the significant impact of the positioning accuracy on the propagation performance of the medium, the existing technology is somewhat insufficient for widespread application.

[0006] Chinese Patent CN 202011282092.9 discloses a rock fracture early warning method based on statistical analysis of acoustic emission signals, belonging to the fields of rock mechanics and geotechnical engineering. First, real-time acoustic emission monitoring of the rock deformation and failure process is performed, recording and acquiring ring counts. Second, characteristic statistics of the ring counts, including variance and autocorrelation coefficient, are calculated using formulas, and the rate of change of the variance and autocorrelation coefficient of the ring counts are calculated. Finally, early warning signals are determined based on the rate of change of the variance and autocorrelation coefficient of the ring counts. When the rate of change exceeds a threshold, the system automatically alarms, indicating that the rock is about to fracture. If the threshold is not exceeded, monitoring and determination continue. In this early warning method, the early warning signal points are easily identifiable and the calculation is stable, ensuring the objectivity and accuracy of the method. The calculation process is simple and easy to operate; it can track and warn in real time, and can be widely used in rock failure early warning in engineering fields such as water conservancy and hydropower, transportation, mineral resource extraction, and underground space development. Chinese patent CN 202110514578.9 discloses a method for testing and evaluating the heterogeneity of rock mechanics based on acoustic emission. First, a complete stratum to be tested is selected. Second, a core column is obtained by drilling the stratum. Third, the core column is processed to obtain a rock sample. Fourth, acoustic emission sensors are arranged on both sides of the rock sample. Fifth, during a splitting experiment, the data measured by the acoustic emission sensors is recorded. Based on the recorded data, the number of acoustic emission signal events is counted, and the total number of acoustic emission events, the fracture component ratio coefficient of the rock sample, and the heterogeneity coefficient of the rock are calculated. The heterogeneity coefficient is used to evaluate the mechanical heterogeneity of the rock, and the mechanical response heterogeneity characteristics of the rock are obtained based on the heterogeneity coefficient. This method is convenient for preparing rock samples, simple to calculate, and highly practical, helping to quantitatively evaluate the internal heterogeneity of rocks and promoting the evaluation and classification of surrounding rock quality in underground engineering. However, considering that both technologies rely on acoustic emission ring counting as the basis for judgment, and that acoustic emission ring counting is greatly affected by noise, threshold values, and sensor placement, which may have a certain impact on the accuracy of the results, the existing technologies are somewhat inadequate. Summary of the Invention

[0007] Technical problem solved: In view of the problems in the existing technology of jet grouting piles that cannot detect problems during construction and make timely adjustments and improvements, the present invention provides an acoustic emission monitoring method for underground jet grouting effect during construction. By calibrating the pile diameter during the construction of jet grouting piles, the method continuously monitors in real time whether the cement grout injection range meets the specifications, thereby avoiding potential safety hazards of pile foundation caused by insufficient cement grout injection.

[0008] Technical solution:

[0009] An acoustic emission monitoring method for underground jet grouting effects during construction, the method specifically includes the following steps:

[0010] S1. Waveguides are installed both inside and outside the monitoring area for the target pile diameter of underground jet grouting piles;

[0011] S2. Couple an acoustic emission sensor to one end of the waveguide that is exposed on the ground surface, and connect the acoustic emission sensor to a preamplifier, a data acquisition system and a data processing software system to build an acoustic emission monitoring system;

[0012] S3. Collect the acoustic emission signals generated by the jet grouting medium cutting the soil during construction, and use the data processing software system to statistically analyze the acoustic emission characteristics of the jet grouting pile at different jet grouting depths and different radial positions of the pile.

[0013] S4. Using the actual number of jet grouting passes at a fixed depth during construction, and the acoustic emission characteristics statistically obtained near the ground surface and from the central axis as reference values, the acoustic emission characteristics statistically obtained at different jet grouting depths and different radial positions of the pile body are homogenized and defined as the soil cutting coefficient; by comparing and analyzing the values ​​of the soil cutting coefficient, the jet grouting effect is classified, and the grouting status and pile quality are fed back in real time.

[0014] Step S1 specifically involves:

[0015] S11. According to the required diameter of the jet grouting pile, a pilot hole is drilled along the central axis of the jet grouting pile, which is defined as hole A, and a mud pipe is installed in hole A.

[0016] S12. Drilling operations are carried out within and outside the diameter range of the central axis of the jet grouting pile, respectively defined as hole B, hole C, hole D..., and waveguides are buried in the holes B, hole C, hole D... The waveguides are installed to the designed depth of the bottom of the jet grouting pile, the waveguides are vertical and the ends protrude 0.5 to 1m above the ground surface, and a sleeve is provided at the end of the waveguides that protrudes above the ground surface;

[0017] Step S3 specifically involves:

[0018] S31. Start the rotary jet engine, use the established acoustic emission monitoring system to test the background noise of the construction environment, and filter the environmental noise in the data processing software system;

[0019] S32. Jet grouting pile construction operation and acoustic emission monitoring process: Start the jet grouting device, rotate the mud pipe clockwise at a fixed jet grouting depth, and spray the jet grouting medium from the mud pipe at a pressure of 20-50MPa to cut the soil 5-7 times; when the jet grouting medium cuts the soil, the cut soil will generate local strain or stress concentration, generating elastic waves; the elastic waves propagate through the surrounding medium to the waveguide, and the waveguide rapidly transmits the elastic waves from underground to the acoustic emission sensor, where they are detected and recorded as acoustic emission signals; the acoustic emission monitoring device is used to monitor the jet grouting pile at different jet grouting depths and different radial positions of the pile in real time during the construction process, and can pick up the acoustic emission signals of the jet grouting pile at different locations;

[0020] S33. Based on the acquired acoustic emission signals, use a data processing software system to statistically analyze the acoustic emission characteristics of jet grouting piles at different jet grouting depths and different radial positions of the pile body;

[0021] Step S4 specifically involves:

[0022] S41. Record the actual number of jet grouting strokes N0 at a fixed jet grouting depth during construction;

[0023] S42. Using data processing software, statistically analyze the acoustic emission characteristics E at the near-ground surface and distance from the central axis. 00 ;

[0024] S43. Using data processing software, statistically analyze acoustic emission characteristics at different jet grouting depths and radial positions of the pile. ij N ij ;

[0025] S44. Using N0, E obtained in steps S41 and S42 00 As a reference value, the E obtained in step S43 is used... ij N ij After normalization, it is defined as the soil cutting coefficient R. ij and n ij ;

[0026] S45. By comparing and analyzing the soil cutting coefficients at different jet grouting depths and radial positions of the pile, the jet grouting effect is classified into grades, enabling real-time feedback on grouting status and pile quality.

[0027] As a preferred technical solution of the present invention: one end of the mud pipe extending into hole A is provided with a rotary jet drill bit, and one or a group of nozzles are provided at the drill bit.

[0028] As a preferred technical solution of the present invention: step S2 is to install the acoustic emission sensor on the surface of the end of the waveguide exposed on the ground surface using strong adhesive, and connect it to a preamplifier, a data acquisition system and a data processing software system; a set of acoustic emission sensors are installed at the end of the waveguide exposed on the ground surface to monitor the acoustic emission signal generated by the jet grouting medium cutting the soil during the construction process, and to perform comparative verification analysis.

[0029] As a preferred embodiment of the present invention: the statistical acoustic emission characteristic information includes acoustic emission energy rate and the number of energy rate peaks. The acoustic emission energy rate refers to the area under the detector envelope of the acoustic emission signal within one unit time (1 second), reflecting the relative energy rate or intensity change of the acoustic emission signal. The area under the detector envelope of the acoustic emission signal refers to the time t taken from the start to the end of the jet grouting process, the sampling frequency of the acoustic emission device Δt, and the positive voltage amplitude of the signal measured at time t denoted as V. + (t), the negative voltage amplitude is V-(t), then the area E under the cumulative envelope of the acoustic emission signal detection from time t1 to time t2 is... MARSE The specific calculation formula is as follows:

[0030]

[0031] The number of energy rate peaks refers to the number of times the energy rate periodically reaches its maximum value.

[0032] As a preferred embodiment of the present invention: the waveguide is a solid metal dielectric material with an elastic wave conduction velocity of 5000 m / s or higher; the sleeve is a soft rubber dielectric material with an elastic wave conduction velocity of less than 100 m / s.

[0033] As a preferred technical solution of the present invention: the jet spraying medium is a solid-liquid mixture including bentonite and cement slurry, the amount of bentonite is 5 to 15% of the cement slurry, and the water-cement ratio of the cement slurry is between 0.8 and 1.5.

[0034] As a preferred technical solution of the present invention: the location near the ground surface of the jet grouting pile and from the central axis refers to a location 1.0 to 2.0m below the ground surface and 0.5 to 0.8m from the central axis.

[0035] As a preferred embodiment of the present invention: the normalization processing of the acoustic emission characteristic information statistically obtained at different locations in step S4 refers to calculating the ratio between the acoustic emission characteristic information statistically obtained at other locations and the reference value, which is defined as the soil cutting coefficient R. ij and n ij This allows for quantitative analysis of the spraying quality at different jet grouting depths and radial positions of the pile body.

[0036] As a preferred technical solution of the present invention: the soil cutting coefficient R ij and n ij The specific calculation formula is as follows;

[0037]

[0038]

[0039] As a preferred technical solution of the present invention: when 0.7 < soil cutting coefficient R ij ≤1, and 0.7 < soil cutting coefficient n ij When the value is ≤1, the jet grouting effect during construction is good, the pile quality is good, and the cutting grade is classified as Grade A.

[0040] When the soil cutting coefficient R is less than 0.4 ij ≤0.7, and 0.4 < soil cutting coefficient n ij When the value is ≤0.7, the jet grouting effect during construction is moderate, the pile quality is moderate, and the cutting grade is classified as Grade B.

[0041] When 0 < soil cutting coefficient R ij ≤0.4, and 0 < soil cutting coefficient n ij When the value is ≤0.4, the jet grouting effect during construction is poor, the pile quality is poor, and the cutting grade is classified as Grade C.

[0042] Beneficial effects:

[0043] Compared with the prior art, this application has the following advantages:

[0044] (1) The acoustic emission monitoring system can monitor the jet grouting effect of underground jet grouting piles in real time, continuously and quantitatively, and filter environmental noise. The monitoring results are simple and intuitive. The resolution based on acoustic emission characteristic information (acoustic emission energy rate, number of energy rate peaks) is high. The parameter calculation is simple and is less affected by threshold, noise, etc.

[0045] (2) By using acoustic emission monitoring, the construction of deep hidden projects can be visualized, which overcomes the shortcomings of existing technologies and achieves the purpose of real-time, continuous, quantitative analysis and dynamic control. The optimal construction parameters that meet the design requirements can be selected, which can not only ensure the quality of construction, but also reduce the cost of construction.

[0046] (3) Acoustic emission monitoring instruments are lightweight, easy to carry, simple to operate, quick, low-cost and non-destructive, making them suitable for widespread application. Attached Figure Description

[0047] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, wherein:

[0048] Figure 1This is a schematic diagram of an acoustic emission (AE) monitoring method for underground jet grouting effect during construction, according to the present invention.

[0049] Figure 2 This is a schematic diagram illustrating the specific monitoring method steps in an embodiment of the present invention;

[0050] Figure 3 This is a graph showing the soil cutting coefficient-time relationship in the Class A cutting zone calculated in this embodiment of the invention.

[0051] Figure 4 This is a graph showing the soil cutting coefficient-time relationship in the Class B cutting zone calculated in this embodiment of the invention.

[0052] Figure 5 This is a graph showing the soil cutting coefficient-time relationship in the Class C cutting zone calculated in this embodiment of the invention.

[0053] Explanation of reference numerals in the attached drawings: 1-Jet jet pile; 2-Mushroom pipe; 3-Nozzle; 4-Waveguide; 5-Sleeve; 6-Acoustic emission sensor. Detailed Implementation

[0054] To more clearly illustrate the technical problems, technical solutions, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0055] This invention is based on the principle that periodic elastic waves are generated by the jet grouting medium cutting the soil during construction, and these elastic waves propagate periodically through the waveguide 4 to the acoustic emission sensor 6. Figure 1 As shown, the evaluation method of the present invention is proposed.

[0056] To better illustrate the present invention, a construction site was selected for testing. The test site was a clay soil site. The jet grouting effect of the jet grouting pile 1 at a depth of 70m underground was monitored in real time. The acoustic emission sensor 6 was used to monitor three sets of acoustic emission signals picked up at different radial positions at a fixed jet grouting depth in real time. The correspondence between the pile quality and the acoustic emission characteristic information parameters was analyzed.

[0057] like Figure 2 As shown, an acoustic emission monitoring method for underground jet grouting effects during construction includes the following steps:

[0058] S1. Waveguides 4 are buried inside and outside the target pile diameter monitoring area of ​​underground jet grouting pile 1 respectively; the waveguide 4 refers to a solid metal medium material with an elastic wave transmission rate of 5000m / s or above, so as to ensure that the elastic waves generated by the jet grouting medium cutting the soil during construction are transmitted to the acoustic emission sensor 6 coupled to one end of the waveguide 4 exposed on the ground surface.

[0059] S2. Couple acoustic emission sensor 6 to one end of waveguide 4 that is exposed on the ground surface, and connect acoustic emission sensor 6 to preamplifier, data acquisition system and data processing software system to build acoustic emission monitoring system;

[0060] S3. Collect the acoustic emission signals generated by the jet grouting medium cutting the soil during construction, and use the data processing software system to statistically analyze the acoustic emission characteristics of the jet grouting pile 1 at different jet grouting depths and different radial positions of the pile body.

[0061] S4. Using the actual number of jet grouting operations at a fixed depth during construction, and the acoustic emission characteristics collected near the ground surface and from the central axis as reference values, the acoustic emission characteristics collected at different jet grouting depths and different radial positions of the pile are uniformized and defined as the soil cutting coefficient. The soil cutting coefficient values ​​are compared and analyzed to classify the jet grouting effect and provide real-time feedback on grouting status and pile quality. The location near the ground surface and from the central axis of the jet grouting pile 1 refers to a position 1.0 to 2.0 m below the ground surface and 0.5 to 0.8 m from the central axis. This is because the jet grouting effect is good and the pile quality is high at this location, and the picked-up acoustic emission signal has large energy and complete periodicity.

[0062] The specific process is as follows:

[0063] Step S1 is as follows:

[0064] S11. According to the required diameter of the jet grouting pile 1, a pilot hole is drilled along the central axis of the jet grouting pile 1, defined as hole A. A mud pipe 2 is embedded in hole A, and a jet grouting drill bit is provided at one end of the mud pipe 2 extending into hole A. One or a set of nozzles 3 are provided at the drill bit. S12. Pilot holes are drilled both within and outside the diameter range of the central axis of the jet grouting pile 1, defined as holes B, C, D, etc. Waveguides 4 are embedded in holes B, C, D, etc. The waveguides 4 are installed to the designed depth of the bottom of the jet grouting pile 1. The waveguides 4 are vertical and the end protrudes 0.5 to 1m above the ground surface. A sleeve 5 is provided at the end of the waveguides 4 protruding above the ground surface. The sleeve 5 is made of a soft rubber medium material with an elastic wave conduction velocity of less than 100m / s to isolate the background noise generated by surface frost heave and environmental vibration during construction from signal interference of the elastic waves generated by the jet medium cutting the soil.

[0065] Step S2 is as follows:

[0066] S21. The acoustic emission sensor 6 is mounted on the surface of the waveguide 4 at one end exposed to the ground using strong adhesive, and connected to the preamplifier, data acquisition system and data processing software system;

[0067] S22. Environmental noise test: Start the rotary jet engine, use the established acoustic emission monitoring system to test the background noise of the construction environment, and filter the environmental noise in the data processing software system;

[0068] Step S3 specifically involves:

[0069] S31. Start the jet grouting device, rotate the mud pipe 2 clockwise at the fixed jet grouting depth, and spray the jet grouting medium from the mud pipe 2 at a pressure of 20-50MPa to cut the soil 5-7 times; record the actual number of jet grouting times N0 at the fixed jet grouting depth during the construction process; the jet grouting medium is a solid-liquid mixture including bentonite and cement slurry, the amount of bentonite is 5-15% of the cement slurry, and the water-cement ratio of the cement slurry is between 0.8 and 1.5. When the jet grouting medium cuts the soil, the cut soil will generate local strain or stress concentration, generating elastic waves;

[0070] S32. The elastic wave propagates through the surrounding medium to the waveguide 4, and is rapidly transmitted from underground to the acoustic emission sensor 6 via the waveguide 4, where it is detected and recorded as an acoustic emission signal S. An acoustic emission monitoring device is used to monitor different jet grouting depths and radial positions of the piles during construction in real time, capturing the acoustic emission signals S of the jet grouting pile 1 at different locations. ij , where i takes the values ​​1, 2, 3, ..., n respectively, marking different jet grouting depth positions; j takes the values ​​1, 2, 3, ..., n respectively, marking different radial positions of the pile body;

[0071] Step S4 specifically involves:

[0072] S41. Based on the acquired acoustic emission signals, using a data processing software system, statistically analyze the acoustic emission energy rate at locations 1.0–2.0 m below the ground surface and 0.5–0.8 m from the central axis, and quantify it as E. 00 ;

[0073] S42. Using the data processing software system, statistically analyze the energy rate and number of energy rate peaks of acoustic emission at different jet grouting depths and different radial positions of the pile, and distribute them as E. ij and N ij ;

[0074] S43. Normalization process: Using N0 and E obtained in S31 and step S41 00 As a reference value, the E values ​​statistically analyzed for S42 ij N ij Normalization is performed, and the soil cutting coefficient R is defined. ij and n ij This allows for the quantitative analysis of the spraying quality at different jet grouting depths and radial positions within the pile body. The specific calculation formula is as follows;

[0075]

[0076]

[0077] S44. Comparative analysis of soil cutting coefficient R calculated for jet grouting pile 1 at different jet grouting depths and different radial positions of the pile body. ij and n ij The size of the nozzle can be used to distinguish the intensity and frequency of the jet grout cutting the soil, thereby providing feedback on the grouting situation and pile formation effect.

[0078] The soil cutting coefficient R ij and n ij The soil cutting coefficient R is between 0 and 1. ij and n ij The larger the value, the better the jet grouting effect is evaluated; the soil cutting coefficient R ij and n ij The smaller the value, the worse the spray effect is rated, such as... Figures 3-5 As shown.

[0079] Example 1

[0080] The method of the present invention is applied to real-time monitoring of the pile formation effect of underground jet grouting piles during construction, and includes the following steps:

[0081] A1: Select the evaluation area. According to the required diameter of the jet grouting pile 1, perform pilot hole operation along the center of the jet grouting pile 1, which is defined as hole A, and bury mud pipe 2 in hole A; perform pilot hole operation within and outside the diameter range of the central axis of the jet grouting pile 1, corresponding to hole B, hole C, hole D... respectively, and bury waveguide 4 in the holes B, hole C, hole D... and install the waveguide 4 to the designed depth of the jet grouting pile 1;

[0082] A2: Mount the acoustic emission sensor 6 on the surface of the waveguide 4 with strong adhesive, and connect it to the preamplifier, data acquisition system and data processing software system; start the rotary jet engine, use the constructed acoustic emission monitoring system to test the background noise of the construction environment, and filter the environmental noise in the data processing software system.

[0083] A3: Start the jet grouting device, rotate the mud pipe 2 clockwise at the fixed jet grouting depth, and spray the jet grouting medium from the nozzle with a rotating drill bit at one end of the mud pipe into hole A at a pressure of 40MPa, cutting the soil N0 5 times; the jet grouting medium is a solid-liquid mixture including bentonite and cement slurry, wherein the amount of bentonite is 10% of the cement slurry, and the water-cement ratio of the cement slurry is 1:1. When the jet grouting medium cuts the soil, the cut soil will generate local strain or stress concentration, generating elastic waves; the elastic waves propagate through the surrounding medium to the waveguide 4, and the waveguide 4 transmits the elastic waves from underground to the acoustic emission sensor 6, where they are detected and recorded as acoustic emission signals; the acoustic emission monitoring device is used to monitor the different jet grouting depths and different radial positions of the piles in real time during the construction process, and can pick up the acoustic emission signals of the jet grouting pile 1 at different positions; A4: Based on the picked-up acoustic emission signals, the data processing software system is used to statistically analyze the distance 2.0m below the ground surface. Specifically, the acoustic emission energy rate and the number of energy rate peaks at a depth of 2.0m underground and 0.5m from the central axis were calculated and categorized as reference value E. 00 and N 00 Using data processing software, the acoustic emission energy rate and energy rate peak count at radial positions of 0.8m, 1.0m, and 1.2m were statistically analyzed for a jet grouting depth of 70.0m underground. The distribution was then statistically analyzed as E... 11 N 11 and E 12 N 12 and E 13 N 13

[0084] A5: Normalize the acoustic emission energy rate and energy rate peak number obtained in the above steps, and calculate the soil cutting coefficient. The acoustic emission energy rate normalization process refers to calculating the statistical acoustic emission energy rate E at different locations. 11 E 12 , and E 13 Comparing with the energy rate reference value E respectively 00 The ratio between them; the normalization of the number of acoustic emission energy rate peaks refers to calculating the number N of acoustic emission energy rate peaks at different locations. 11 N 12 , and N 13 The ratios between the soil cut by the jet jet medium and the soil N0, respectively;

[0085] A6: By comparing and analyzing the soil cutting coefficient values ​​calculated at different jet grouting depths and radial positions of the pile 1, the strength distribution and number of cuts of the jet grouting medium cutting the soil can be identified, thereby providing feedback on the grouting situation and pile formation effect; A7: Based on the acoustic emission characteristic information obtained in the above steps and the calculated soil cutting coefficient, the level of soil cutting by the jet grouting medium is divided into Grade A, Grade B and Grade C, corresponding to three situations: good jet grouting effect, medium jet grouting effect and poor jet grouting effect, respectively;

[0086] Furthermore, when the soil cutting coefficient R is less than 0.7, ij ≤1, and 0.7 < soil cutting coefficient n ij When the value is ≤1, the jet grouting effect during the construction process is good, the pile quality is good, and the cutting grade is classified as Grade A.

[0087] When the soil cutting coefficient R is less than 0.4 ij ≤0.7, and 0.4 < the soil cutting coefficient n ij When the value is ≤0.7, the jet grouting effect during the construction process is moderate, the pile quality is moderate, and the cutting grade is classified as Grade B.

[0088] When 0 < soil cutting coefficient R ij ≤0.4, and 0 < soil cutting coefficient n ij If the value is ≤0.4, the jet grouting effect during the construction process is poor, the pile quality is poor, and the cutting grade is classified as Grade C.

[0089] Figures 3-5 The method provided in this application presents acoustic emission monitoring results of the jet grouting effect obtained at a depth of 70m underground and radial positions of 0.8m, 1.0m, and 1.2m. These results are applied according to the soil cutting coefficient R. ij and n ij It can be seen that Figure 3 The soil cutting coefficient R mentioned in the text ij All are greater than 0.7, and n ij =1, therefore it is determined that the soil around the waveguide is subjected to a large degree of cutting by the jet grouting medium, the grouting effect is good, and the soil cutting level is Class A; Figure 4 The soil cutting coefficient R mentioned in the text ij The values ​​are 0.50, 0.58, and 0.72 respectively, and n ij =0.6, therefore it can be inferred that the soil around the waveguide is generally subjected to the cutting effect of the jet grouting medium, the jet grouting effect is generally average, and the soil cutting level is Class B. Figure 5 The soil cutting coefficient R mentioned in the text ij All are less than 0.14, and n ij =0, therefore it can be inferred that the soil around the waveguide is not cut by the jet grouting medium, the quality of the jet grouting pile is poor, the cutting level is Class C, and it does not meet the design requirements.

[0090] This invention is an acoustic emission monitoring method for underground jet grouting during construction. It enables visualized construction of deep, concealed projects through acoustic emission technology. The test process was smooth, and the monitored waveform data was displayed in real time. By extracting acoustic emission energy rate information, the jet grouting effect of underground jet grouting piles can be monitored in real time, continuously, and quantitatively. This provides important guidance for optimizing construction parameters during jet grouting, ensuring construction quality, and reducing construction costs. The sample testing method is simple and convenient, and the test results are accurate, fully demonstrating the reliability of the method and making it suitable for widespread application.

[0091] The above embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the implementation of the present invention. For those skilled in the art, other variations or modifications can be made based on the above description, and it is impossible to exhaustively list all embodiments here. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for monitoring the acoustic emission effect of underground jet grouting during construction, characterized in that, Specifically, the following steps are included: S1. Waveguides (4) are installed inside and outside the target pile diameter monitoring area of ​​underground jet grouting pile (1); S2. Couple an acoustic emission sensor (6) to the end of the waveguide (4) exposed on the ground surface, and connect the acoustic emission sensor (6) to a preamplifier, a data acquisition system and a data processing software system to build an acoustic emission monitoring system; S3. Collect the acoustic emission signals generated by the jet grouting medium cutting the soil during construction, and use the data processing software system to statistically analyze the acoustic emission characteristics of the jet grouting pile (1) at different jet grouting depths and different radial positions of the pile body; S4. Using the actual number of jet grouting operations at a fixed depth during construction, and the acoustic emission characteristics at the near-ground surface and distance from the central axis as reference values, the acoustic emission characteristics at different jet grouting depths and different radial positions of the pile are uniformized and defined as the soil cutting coefficient; the soil cutting coefficient values ​​are compared and analyzed to achieve the classification of jet grouting effect levels, and to provide real-time feedback on grouting status and pile quality; at the near-ground surface and distance from the central axis of the jet grouting pile (1), it refers to a distance of 1.0~2.0m below the ground surface and 0.5~0.8m from the central axis; Step S1 specifically involves: S11. According to the pile diameter requirements of the jet grouting pile (1), the pilot hole operation is carried out along the central axis of the jet grouting pile (1), which is defined as hole A, and a mud pipe (2) is buried in hole A. S12. Drilling operations are carried out within and outside the diameter range of the central axis of the jet grouting pile (1), respectively defined as hole B, hole C, hole D..., and waveguides (4) are buried in the holes B, hole C, hole D... The waveguides (4) are installed to the designed depth of the bottom of the jet grouting pile (1), the waveguides (4) are vertical and the end protrudes 0.5~1m above the ground surface, and the end of the waveguides (4) protruding above the ground surface is provided with a sleeve (5). Step S2 is as follows: S21. Install the acoustic emission sensor (6) on the surface of the waveguide (4) exposed at the ground surface using strong adhesive, and connect it to the preamplifier, data acquisition system and data processing software system; S22. Environmental noise test: Start the rotary jet engine, use the established acoustic emission monitoring system to test the background noise of the construction environment, and filter the environmental noise in the data processing software system; Step S3 specifically involves: S31. Start the jet grouting device, rotate the mud pipe (2) clockwise at the fixed jet grouting depth, and spray the jet grouting medium from the mud pipe (2) at a pressure of 20-50 MPa to cut the soil 5-7 times; record the actual number of jet grouting times at the fixed jet grouting depth during the construction process. N 0; The jet grouting medium is a solid-liquid mixture including bentonite and cement slurry. The amount of bentonite is 5-15% of the cement slurry, and the water-cement ratio of the cement slurry is between 0.8 and 1.

5. When the jet grouting medium cuts the soil, the cut soil will generate local strain or stress concentration, and generate elastic waves. S32. The elastic wave propagates through the surrounding medium to the waveguide (4), and is rapidly transmitted from underground to the acoustic emission sensor (6) via the waveguide (4), where it is detected and recorded as an acoustic emission signal. S Acoustic emission monitoring devices are used to monitor the jet grouting at different depths and radial positions of the piles during construction in real time, and can pick up the acoustic emission signals of the jet grouting pile 1 at different locations. S ij where i takes the values ​​1, 2, 3, ... n The positions are marked with different jet depths; j takes values ​​of 1, 2, 3, ... n Mark the radial position of different pile bodies; Step S4 specifically involves: S41. Based on the acquired acoustic emission signals, using a data processing software system, statistically analyze the acoustic emission energy rate at locations 1.0–2.0 m below the ground surface and 0.5–0.8 m from the central axis, and then statistically analyze it as follows: E 00 ; S42. Using the data processing software system, statistically analyze the energy rate and number of energy rate peaks of acoustic emission at different jet grouting depths and different radial positions of the pile, and distribute them as follows: E ij and N ij ; S43. Normalization process: Based on the results obtained in S31 and step S41 N 0 , E 00 As a reference value, the statistics for S42 E ij ,N ij Normalization is performed, and the soil cutting coefficient is defined. R ij and n ij The soil cutting coefficient R ij and n ij The specific calculation formula is as follows: , ; S44. Comparative analysis of soil cutting coefficient values ​​calculated for jet grouting pile 1 at different jet grouting depths and different radial positions of the pile body. R ij and n ij The size of the nozzle can be used to distinguish the intensity and frequency of the jet grout cutting the soil, thereby providing feedback on the grouting situation and pile formation effect.

2. The acoustic emission monitoring method for underground jet grouting effect during construction according to claim 1, characterized in that, The mud pipe (2) extends into hole A and is equipped with a rotary jet drill bit at one end, and a set of nozzles (3) are provided at the drill bit.

3. The acoustic emission monitoring method for underground jet grouting effect during construction according to claim 1, characterized in that, A set of acoustic emission sensors (6) are installed on the exposed end of the waveguide (4) to monitor the acoustic emission signals generated by the jet grouting medium cutting the soil during the construction process, and to conduct comparative verification analysis.

4. The acoustic emission monitoring method for underground jet grouting effect during construction according to claim 1, characterized in that: The statistical acoustic emission characteristic information includes acoustic emission energy rate and the number of energy rate peaks. The acoustic emission energy rate refers to the area under the detector envelope of the acoustic emission signal within one unit of time (1 second), reflecting the relative energy rate or intensity change of the acoustic emission signal. The area under the detector envelope of the acoustic emission signal is defined as follows: t represents the time elapsed from the start to the end of the jet grouting process; Δt represents the sampling frequency of the acoustic emission device; and V represents the positive voltage amplitude of the signal measured at time t. + (t), the negative voltage amplitude is V - (t), then the area under the cumulative envelope of the acoustic emission signal detection from time t1 to time t2. E MARSE The specific calculation formula is as follows: The energy rate peak count refers to the number of times the energy rate periodically reaches its maximum value.

5. The acoustic emission monitoring method for underground jet grouting effect during construction according to claim 1, characterized in that: The waveguide (4) refers to a solid metal medium material with an elastic wave conduction velocity of 5000 m / s or higher, and the sleeve (5) is a soft rubber medium material with an elastic wave conduction velocity of less than 100 m / s.

6. The acoustic emission monitoring method for underground jet grouting effect during construction according to claim 1, characterized in that: When the soil cutting coefficient is less than 0.7 R ij ≤1, and 0.7 < soil cutting coefficient n ij When the value is ≤1, the jet grouting effect during construction is good, the pile quality is good, and the cutting grade is classified as Grade A. When the soil cutting coefficient is less than 0.4 R ij ≤0.7, and 0.4 < soil cutting coefficient n ij When the value is ≤0.7, the jet grouting effect during construction is moderate, the pile quality is moderate, and the cutting grade is classified as Grade B. When 0 < soil cutting coefficient R ij ≤0.4, and 0 < soil cutting coefficient n ij When the value is ≤0.4, the jet grouting effect during construction is poor, the pile quality is poor, and the cutting grade is classified as Grade C.

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