A self-excitation detection method for the reinforcement quality of vibro-stone pile composite foundation

Abstract

The present invention discloses a self-excited detection method for the reinforcement quality of a vibro-compacted gravel pile composite foundation. The pre-treated foundation is subjected to elastic wave velocity testing and test pile test velocity zoning, and at the same time, excess pore pressure monitoring is performed to obtain excess pore pressure; a detector and a collector are selected to establish a gravel pile construction excitation signal acquisition system, and a spatial array of detectors is arranged; elastic wave signals are collected in real time, filtered and processed, and signal identification is performed, the arrival time of the elastic wave signal is extracted, a travel time equation group is constructed, and the elastic wave velocity of the velocity partition is iteratively inverted; a corresponding relationship between the effective confining pressure, relative density, and elastic wave velocity of the soil is established, the relative density of the soil is input, and the reinforcement quality is judged by comparison. The present invention iteratively processes the travel time equation by velocity inversion and analysis to invert the elastic wave velocity and then interprets the velocity to determine the relative density of the soil, thereby realizing real-time detection of the reinforcement quality of the gravel pile composite foundation, and has the advantages of a large detection range, a wide detection time domain, and intelligent detection.

Description

Technical Field

[0001] The invention belongs to the technical field of monitoring and is a method for detecting the construction quality of foundation treatment, in particular to a self-excitation detection method for the reinforcement quality of a vibro-stone pile composite foundation. Technical Background

[0002] With the rapid economic and social development of my country, buildings and structures are becoming increasingly large. Because these large structures often carry heavy loads or are located in areas with high seismic intensity, natural foundations often struggle to meet requirements for bearing capacity and liquefaction resistance. Therefore, appropriate foundation treatment technologies are needed to improve the physical and mechanical properties of the natural foundation to meet engineering requirements.

[0003] Vibro-stone piles are a commonly used foundation treatment method. They generate horizontal vibrations that compress surrounding filler and soil, compacting the loose soil or combining the filler and foundation into a composite foundation. This improves foundation bearing capacity, reduces settlement, increases foundation stability, and enhances the foundation's resistance to earthquake liquefaction. They are widely used to reinforce weak foundations, such as those found in hydropower station dams, power station foundations, port and wharf foundations, petrochemical engineering foundations, and highway and railway foundations.

[0004] Because the construction quality of vibro-compacted gravel piles is affected by multiple factors, including the performance of the vibrator, the properties of the soil surrounding the pile, and the duration of the vibro-compacting, it is impossible to guarantee that the compaction effect of the soil surrounding the pile will reach the designed value. Consequently, it is difficult to guarantee the anti-liquefaction ability of the vibro-compacted gravel pile composite foundation, posing a significant safety hazard. Therefore, it is necessary to test the compaction degree of the soil surrounding the pile to ensure that the construction quality of the vibro-compacted gravel pile composite foundation meets the design requirements.

[0005] Elastic wave velocity testing is an important part of engineering exploration. Its magnitude can directly reflect the density and hardness of the soil and is an important parameter for construction quality inspection. Currently, for vibro-compacted gravel pile composite foundations, the construction quality inspection methods based on elastic wave velocity to characterize the relative density of the soil mainly include the single-hole method, the cross-hole method, and the surface wave method. Regardless of the method, the elastic wave velocity of a certain area is detected through artificial source excitation after the vibro-compacting construction. Due to the limitations of the detection range and time domain, and the fact that the obtained elastic wave velocity characterizes the relative density of the soil based on empirical relationships, it is not intuitive, making it difficult to reflect the vibration compaction effect during the construction process and unable to achieve a full-process evaluation of the construction quality. Therefore, it is necessary to develop a full-time-domain and full-range vibro-compacted gravel pile construction quality inspection method. Summary of the Invention

[0006] In order to realize the detection and analysis of the relative density of vibration during the entire construction process of vibro-compacted gravel piles and the entire range of the foundation, the present invention discloses a self-excitation detection method for the reinforcement quality of vibro-compacted gravel pile composite foundations. By testing the elastic wave velocity of the entire construction process of vibro-compacted gravel piles and the entire range of the foundation, the vibration compaction condition of the soil around the piles is inverted in real time, providing a basis for construction quality.

[0007] The present invention uses the exciting vibration during the operation of the vibrator as the excitation source, receives the elastic wave signal of the vibration source through a reasonably arranged detector array, constructs a travel time equation group using known parameters such as the wave arrival time and the detector position, and solves iteratively to determine the elastic wave velocity of the foundation. Finally, through the relative density calculation of the elastic wave velocity inversion, the real-time change of the relative density of the soil around the pile during the vibratory impact process can be detected.

[0008] The technical solutions adopted in the present invention are as follows:

[0009] S1. Conduct an elastic wave velocity test on the pretreated foundation to determine the vertical distribution of the elastic wave velocity of the foundation soil, and then vertically partition the elastic wave velocity of the pretreated foundation based on the vertical distribution of the elastic wave velocity; conduct a pile test to select an elastic wave as a typical elastic wave, and radially partition the elastic wave velocity of the pretreated foundation based on the radial distribution of the velocity of the typical elastic wave; monitor the excess pore pressure during the pile test, and obtain the excess pore pressure of all partitions of the pretreated foundation by fitting;

[0010] S2. Select a detector based on the waveform characteristic parameters of the elastic wave obtained in S1, and connect the detector with signal amplifiers, concentrators, signal collectors and other signal acquisition devices to form a gravel pile construction excitation signal acquisition system;

[0011] The gravel pile construction excitation signal acquisition system is used to pick up, collect and store elastic wave signals generated during the vibro-impact gravel pile construction process.

[0012] S3, arranging the spatial array of geophones based on the frequency response characteristics and working range of the geophones selected in S2, the spatial position of the gravel piles, and the plane range of the pre-treated foundation;

[0013] The spatial range of the detector covers the range of the foundation.

[0014] S4, using the spatial array of geophones designed in S3 to collect and store elastic wave signals generated during the construction of vibro-stone piles in real time, filtering and identifying the elastic wave signals based on the typical elastic waves obtained in S1, determining and storing effective elastic wave signals for elastic wave velocity inversion;

[0015] S5, reading the effective elastic wave signal described in S4, extracting the arrival time of the elastic wave signal, and using the elastic wave velocity after each velocity partition in S1 as the initial value, constructing a set of elastic wave spatial propagation travel time equations, and optimizing and solving the optimal value of the elastic wave velocity of each velocity partition through an iterative inversion algorithm;

[0016] S6, based on the density ρ of the pre-treated foundation soil, the lateral pressure coefficient K0, the maximum / minimum porosity ratio e max / e min The corresponding relationship between the effective confining pressure, relative density and elastic wave velocity of the soil is established based on the physical and mechanical parameters such as S5. The relative density of the soil after the excess pore pressure dissipates is obtained according to the optimal value of the elastic wave velocity of each velocity zone during the gravel pile construction obtained by S5 and the corresponding relationship between the excess pore pressure input obtained by S1. The relative density is then compared with the designed relative density of the vibro-compacted gravel pile composite foundation to detect the reinforcement quality of the vibro-compacted gravel pile composite foundation.

[0017] The method of the present invention measures elastic wave velocity and excess pore pressure by pre-treating the influence of vibration impact construction during foundation pile test, and then uses it to reinforce the foundation, evaluate the foundation reinforcement quality, and realize self-excitation detection.

[0018] The present invention uses the vibrator of the vibratory crushed stone pile construction machinery as the excitation source, and can detect the reinforcement quality of the vibratory crushed stone pile composite foundation during the vibratory crushed stone pile construction process, thereby realizing real-time and full-range composite foundation reinforcement quality detection and evaluation during the vibratory crushed stone pile composite foundation construction process.

[0019] The gravel pile of the present invention is a vibratory gravel pile. A trial pile test is carried out on the pretreated foundation (the purpose is to determine whether the gravel pile design parameters meet the engineering needs). The vibration of the vibrator will be used to squeeze the gravel filler into the pretreated foundation to form a gravel pile, and the vibration of the vibrator will be used as the excitation source.

[0020] In the step S1, specifically:

[0021] S11: Use the cross-hole method to conduct wave velocity testing to obtain the elastic wave velocity of the soil at different depths of the pre-treated foundation, and vertically partition the soil of the pre-treated foundation according to the differences in elastic wave velocity at different depths along the vertical direction to obtain various vertical partitions;

[0022] The pretreated foundation is the foundation before reinforcement.

[0023] S12: a test pile is laid out in the pretreated foundation by vibro-flotation construction, multiple wave velocity test holes are arranged in each vertical partition of the pretreated foundation along a radial direction of the test pile, a geophone is installed at the same depth in each wave velocity test hole, elastic waves are picked up by the geophones arranged in the multiple wave velocity test holes at the same depth, a propagation velocity and an attenuation coefficient of the elastic wave along the radial direction of the test pile are calculated, and then a current depth of the pretreated foundation soil is radially partitioned according to the propagation velocity and the attenuation coefficient to obtain various radial partitions;

[0024] S13: Based on the results of S11 and S12, the pre-treated foundation is divided into zones to obtain various wave velocity zones;

[0025] S14: In each vertical partition of the pretreated foundation, multiple excess pore pressure monitoring holes are arranged along a radial direction of the test pile. A piezometer is installed in each excess pore pressure monitoring hole. The radial excess pore pressure variation relationship at the current depth is determined based on the excess pore pressures collected by piezometers arranged at the same depth but at different radial distances. The excess pore pressures of each velocity partition at the current depth are further fitted. The excess pore pressures of all velocity partitions of the pretreated foundation are then obtained based on the excess pore pressures of each velocity partition at different depths.

[0026] The propagation path of elastic waves within the velocity partition satisfies the Fermat principle, and on the velocity partition interface, it satisfies the Snell principle, such as Figure 2 shown.

[0027] In step S2, the gravel pile construction excitation signal acquisition system includes a detector, a signal amplifier, a hub and a signal acquisition instrument. The detector is connected to the input end of the signal amplifier via the hub, and the output end of the signal amplifier is connected to the signal acquisition instrument.

[0028] The characteristics and functions of each component in the gravel pile construction excitation signal acquisition system are as follows:

[0029] The detector is used to pick up vibration signals generated by gravel pile construction or artificially excited, and its frequency response range is larger than the bandwidth of the vibration signals generated by gravel pile construction and artificially excited.

[0030] The signal amplifier is used to amplify the collected vibration signal, and the amplification factor is set comprehensively based on the signal amplitude and the foundation background noise level.

[0031] The hub is connected to the signal amplifier and the detector, and aggregates the vibration signals received by multiple detectors to form a multi-channel vibration signal.

[0032] The signal acquisition instrument is used to digitally sample multi-channel vibration signals, the sampling frequency is greater than twice the main frequency of the vibration signal, and the output bit number is not less than 24 bits.

[0033] In the step S3, specifically:

[0034] S31: Within the plane range of the pre-treated foundation, vibro-stone piles are evenly spaced to form a vibro-stone pile composite foundation;

[0035] S32: Dividing the plane range of the pre-treated foundation into a grid based on the preset pile spacing, with λ times the pile spacing as the grid spacing, with the corner points of the grid located in the soil between the gravel piles, and the corner points of the grid serving as the plane positions for the geophone deployment;

[0036] S33: At the plane position of each geophone arrangement described in S31, a plurality of geophones are arranged from top to bottom at intervals from the ground surface according to the vertical partitioning result of S1.

[0037] The multiple λ of the pile spacing is required to meet the following conditions:

[0038] The effective working radius R of the detector can be calculated based on the multiple λ of the pile spacing according to the following formula:

[0039]

[0040] Where R is the effective working radius of the detector, and d is the axial pile spacing of the gravel pile;

[0041] Then, a circle is established with each gravel pile as the center and the effective working radius R of the detector as the radius of the circle as the construction area of ​​the current gravel pile. The number of detectors in the current construction area of ​​each gravel pile minus the number of velocity partitions in the current gravel pile construction area should be no less than 3. Only in this way can the number of detectors in any construction area meet the requirements of subsequent velocity inversion of each velocity partition in the area.

[0042] In the step S4, specifically:

[0043] S41: Based on the elastic waves collected in the pile test in S1 as typical elastic waves, the maximum amplitude, duration, rise time, main frequency, spectrum distribution and other characteristics of the typical elastic waves are extracted as characteristic parameters to form a waveform characteristic parameter database. Then, a typical elastic wave probability distribution model of the waveform characteristic parameters is established through mathematical statistics;

[0044] S1 The sample capacity of elastic waves collected in the pile test shall not be less than 200.

[0045] S42: determining filtering parameters such as bandwidth and threshold based on characteristic parameters such as the main frequency and spectrum distribution in a typical elastic wave probability distribution model, and then filtering the elastic wave signal picked up by the spatial array of detectors arranged in S3 based on the filtering parameters;

[0046] S43: The maximum amplitude, duration, rise time, main frequency, and spectral distribution of the filtered elastic wave signal are used as characteristic parameters and compared with the characteristic parameters of a typical elastic wave. The Fisher linear discriminant method is used to determine whether the elastic wave signal picked up in real time by the spatial array of detectors is a valid elastic wave signal generated during the construction of vibro-compacted gravel piles. The valid elastic wave signal is then stored.

[0047] In step S5, the details are as follows:

[0048] S51: Read the effective elastic wave signal obtained in S4, and use the method to extract the arrival time of the effective elastic wave signal to obtain the arrival time t observed by each detector k , k is the serial number of the detector;

[0049] S52: Based on the elastic wave velocity results of the pre-treated foundation in S1, the initial slowness matrix [S] of the vibro-replacement gravel pile composite foundation is established. The expression is as follows:

[0050]

[0051]

[0052] in, represents the foundation slowness of the i-th vertical partition and the j-th radial partition; represents the foundation elastic wave velocity in the velocity zone of the i-th vertical zone and the j-th radial zone;

[0053] S53: Use the shortest path ray tracing method to determine the propagation path L of the elastic wave from the excitation source to each detector under the initial slowness matrix [S] k :

[0054]

[0055] Where, is the propagation distance within the velocity partition of the i-th vertical partition and the j-th radial partition, and k represents the ordinal number of the detector;

[0056] S54: Calculate the propagation path L of the elastic wave along the path determined in S53 k Travel time propagated to each detector

[0057]

[0058] Where t0 is the excitation moment picked up by the detector, are the calculated elastic wave travel times of different detectors in the initial slowness field, k = 1, 2, ... N, where N is the total number of detectors; represents the slowness of the foundation soil in the wave velocity zone of the i-th vertical zone and the j-th radial zone;

[0059] S55: The travel time t observed by each detector determined in combination with S51 k The travel time of each detector determined by S54 Calculate the difference Δt k :

[0060]

[0061] S56: The difference Δt determined according to S54 k Processing to obtain the slowness correction value of the wave velocity partition

[0062]

[0063] S57: Then use the slowness correction value Add to each slowness Make corrections on

[0064] S58: Repeat the above S53 to S57 to iteratively optimize each element in the wave velocity partition slowness field matrix [S] until the time difference function f meets the accuracy requirements. Then, the final wave velocity partition slowness matrix [S] is used as the optimal matrix, and the optimal value of the elastic wave velocity of each wave velocity partition during the gravel pile construction is obtained from each element in the total optimal matrix.

[0065] The time difference function f is expressed as follows:

[0066]

[0067] In the initial slowness matrix [S], the initial value of the elastic wave velocity of each velocity partition is obtained by dividing the result of the velocity test in S11 according to the partition results of each velocity partition in S13 in S1.

[0068] In step S6, the process of establishing the characterization relationship between the elastic wave velocity, effective confining pressure level, and relative density of each partitioned soil is as follows:

[0069] S61: First, according to the wave velocity zones determined in S1 and the geological survey of the pre-treated foundation, determine the density of the soil in each wave velocity zone thickness and lateral pressure coefficient Then the average effective confining pressure of the soil in each wave velocity zone is obtained by the following formula:

[0070]

[0071] Where q represents the traversal sequence number of the vertical partition soil parameters, and q starts from 0; represents the average effective confining pressure of the soil in the wave velocity zone of the i-th vertical zone and the j-th radial zone, and g is the local gravitational acceleration; represents the excess pore pressure of the soil in the wave velocity zone of the i-th vertical zone and the j-th radial zone;

[0072] S62: Then, the average effective confining pressure of the soil in each wave velocity zone is processed according to the characterization relationship between the elastic wave velocity and the porosity of the soil in each wave velocity zone in the following formula to obtain the porosity of the soil in each wave velocity zone:

[0073]

[0074] Where, is the porosity ratio of the soil in the wave velocity partition of the i-th vertical partition and the j-th radial partition; A t and b t are the first and second fitting parameters determined by the wave velocity test of the graded consolidation test, t=1,2,…,s, t represents the ordinal number of the soil, s represents the total number of soil types, P A is atmospheric pressure, V i j represents the optimal value of elastic wave velocity of the velocity partition of the i-th vertical partition and the j-th radial partition;

[0075] S63: Then determine the maximum void ratio of different soils in the pre-treated foundation through geological survey and minimum porosity ratio The porosity ratio of the soil in each velocity zone is processed according to the relationship between the relative density of the soil in each velocity zone and the elastic wave velocity in the following formula to obtain the relative density of the soil in each velocity zone:

[0076]

[0077] Where, It represents the relative density of soil in the wave velocity zone of the i-th vertical zone and the j-th radial zone; and They represent the maximum porosity and minimum porosity of the soil with ordinal number t, respectively;

[0078] S64: Finally, the reinforcement quality of the vibro-compacted gravel pile composite foundation is judged based on the relative density of the soil in each wave velocity zone.

[0079] The elastic wave velocity of the present invention is the shear wave velocity.

[0080] Specifically, the S64 is as follows: according to the relative density of the soil in each wave velocity zone, the soil in each wave velocity zone is divided into three density states: loose, medium dense and dense according to the relative density classification of soil in the national standard "Code for Investigation of Geotechnical Engineering" (50021-2001); at the same time, the relative density of each wave velocity zone is compared with the designed relative density, and the wave velocity zone with a relative density greater than the designed relative density is recorded as qualified, otherwise it is recorded as unqualified.

[0081] Finally, a quality evaluation report on the soil compaction status of each wave velocity zone and whether the reinforcement quality is qualified or not can be given.

[0082] The present invention first obtains the propagation law of elastic waves in the pre-treated foundation and the attenuation law of typical elastic waves generated by vibro-compacted gravel pile construction in the pre-treated foundation through wave velocity testing, and monitors the spatiotemporal distribution law of the super-static pore pressure field generated by vibro-compacted gravel pile construction, and accordingly divides the foundation elastic wave velocity into zones; determines instruments and equipment such as detectors and pore pressure gauges to form a gravel pile construction excitation signal acquisition system; determines the spatial array of pre-treated foundation detectors and pore pressure gauges; installs and debugs the gravel pile construction excitation signal acquisition system to collect, store and analyze the elastic waves and pore pressure signals generated during the vibro-compacted gravel pile construction; inverts to obtain the elastic wave velocity in different zones during the vibro-compacted gravel pile construction; conducts indoor tests to calibrate the relationship between the elastic wave velocity of the soil between piles and the effective confining pressure and density, converts the relative density of the soil between piles after the pore pressure dissipates based on the inverted elastic wave velocity and pore pressure test data in the zone, and detects and judges the reinforcement quality of the vibro-compacted gravel pile composite foundation.

[0083] Beneficial effects of the present invention:

[0084] 1. The present invention realizes the real-time detection of the relative density of the treated foundation soil during the vibro-flotation construction process. Compared with the current construction quality detection method of local sampling, the present invention has the advantages of large detection range, wide detection time domain, and intelligent detection.

[0085] 2. The present invention can realize three-dimensional visualization of the inversion results of the relative density of the foundation in the entire process and full range of vibro-flotation construction. At the same time, it has an automatic early warning mechanism for insufficient relative density control, thereby realizing dynamic adjustment of the entire construction process based on construction quality control and realizing intelligent construction.

[0086] 3. The equipment and system of the present invention can be used as a monitoring system for monitoring the long-term changes in the relative density of the foundation, thereby providing a basis for evaluating the long-term service performance of the treated foundation.

[0087] In summary, this invention is applicable to foundation treatment methods involving seismic excitation, such as vibro-replacement crushed stone piles, and can achieve real-time detection and evaluation of the relative density of treated foundations. By utilizing a proprietary velocity inversion and analysis method, this invention iteratively solves the travel-time equation to invert the wave velocity, and interprets the wave velocity to determine the relative density of the soil. Ultimately, this enables real-time monitoring of construction quality and provides a factual basis for dynamic adjustments during the construction process. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] Figure 1 It is a schematic diagram of horizontal division of elastic wave velocity in pile test;

[0089] Figure 2 is a schematic diagram of the elastic wave propagation path;

[0090] Figure 3 is the radial distribution diagram of the peak pore water pressure in the test pile test;

[0091] Figure 4 This is a schematic diagram of the monitoring hole array grid division style;

[0092] Figure 5 is a schematic diagram of the sensor array;

[0093] Figure 6 This is a schematic diagram of the composition of the self-excited quality detection system;

[0094] Figure 7 It is a schematic diagram of wave velocity partitions and sensor array positions;

[0095] Figure 8 It is a schematic diagram of relative density within the wave velocity zone;

[0096] Figure 9 It is a technology roadmap diagram. DETAILED DESCRIPTION

[0097] The present invention will be further described below in conjunction with the accompanying drawings and specific implementation examples. The following implementation examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope limited by the claims appended hereto.

[0098] like Figure 9 As shown, the embodiment of the present invention and its implementation process are as follows:

[0099] S1. Conduct an elastic wave velocity test on the pretreated foundation to determine the vertical distribution of the elastic wave velocity of the foundation soil, and based on this, vertically partition the elastic wave velocity of the pretreated foundation; conduct a pile test to select an elastic wave as a typical elastic wave, and radially partition the elastic wave velocity of the pretreated foundation based on the radial distribution of the typical elastic wave velocity in the soil between piles; monitor excess pore pressure during the pile test to identify the spatial distribution of the pore pressure around the pile with vertical depth and radial distance, and its dissipation pattern over time, and obtain the excess pore pressure of all partitions of the pretreated foundation by fitting;

[0100] S11: Use the cross-hole method to conduct wave velocity testing to obtain the elastic wave velocity of the soil at different depths of the pre-treated foundation, and vertically partition the soil of the pre-treated foundation according to the difference in elastic wave velocity at different depths along the vertical direction. The specific implementation of the elastic wave velocity vertical partition is shown in the schematic diagram. Figure 1 ;

[0101] Because natural foundations may contain multiple layers of soil, each of which is of different types and located at different depths, the corresponding elastic wave velocities are also different. Therefore, it is necessary to divide the vertical wave velocity into zones so that the elastic wave velocities in each zone are similar and can be regarded as constant.

[0102] S12: Conducting a test pile test process: one or two test piles are laid out in the pretreated foundation through vibro-flotation construction, multiple wave velocity test holes are arranged along a radial direction of the test piles in each vertical partition of the pretreated foundation, and the spacing between two adjacent wave velocity test holes gradually increases from the inside to the outside along the radial direction of the test piles, a detector is installed at the same depth in each wave velocity test hole, elastic waves are picked up by the detectors arranged in the multiple wave velocity test holes at the same depth, the propagation velocity and attenuation coefficient of the elastic wave along the radial direction of the test piles are calculated, and then the current depth of the pretreated foundation soil is radially partitioned according to the propagation velocity and attenuation coefficient;

[0103] During the pile test, the number of wave velocity test holes shall be no less than 4, and the distance between two adjacent wave velocity test holes shall gradually increase from the inside to the outside along the radial direction of the pile. The piezometer in the wave velocity test hole shall collect the excess pore pressure data generated by the vibroflotation construction, and analyze the variation pattern of the excess pore pressure along the radial distance and time, such as Figure 3 shown.

[0104] S13: Based on the results of S11 and S12, the pre-treated foundation is divided into zones, elastic wave velocity zones are completed, and various wave velocity zones are obtained;

[0105] In the pre-treated foundation after partitioning, the elastic wave velocity in each partition is recorded as Where i = 1, 2, …, m, j = 1, 2, …, n, m and n represent the total number of elastic wave velocity partitions from top to bottom vertically and from inside to outside radially, respectively; i and j represent the ordinal numbers of the elastic wave velocity partitions from top to bottom vertically and from inside to outside radially, respectively.

[0106] The results of the S11 velocity test are divided according to the partition results of each velocity partition to obtain the elastic wave velocity of each velocity partition in S5 under the initial conditions.

[0107] S14: Considering that the continuous vibration of the construction vibration source will generate excess pore pressure in the near-field soil, affecting the magnitude of the elastic wave velocity, the excess pore pressure generated by the vibro-compacted gravel pile construction is monitored.

[0108] In each vertical partition of the pretreated foundation, multiple excess pore pressure monitoring holes are arranged along a certain radial direction of the test pile, and the spacing between two adjacent excess pore pressure monitoring holes gradually increases from the inside to the outside along the radial direction of the test pile. A piezometer is installed in each excess pore pressure monitoring hole. The radial excess pore pressure variation relationship at the current depth is determined based on the excess pore pressures collected by piezometers arranged at the same depth but at different radial distances, and the excess pore pressures of each wave velocity partition at the current depth are further fitted. The excess pore pressures of all wave velocity partitions of the pretreated foundation are then fitted based on the excess pore pressures of each wave velocity partition at different depths, which is used as the basis for the subsequent calculation of the effective confining pressure of the soil between piles.

[0109] During the pile test, the number of excess pore pressure monitoring holes located at the same depth shall be no less than 3. The excess pore pressure monitoring holes may be the same as the wave velocity test holes, that is, the number and distribution of the excess pore pressure monitoring holes shall be the same as the number and distribution of the wave velocity test holes.

[0110] S2. Based on the waveform characteristic parameters of the elastic wave obtained in S1, a detector with a larger frequency response and measuring range is selected, and the detector is connected with a signal amplifier, a hub, a signal acquisition instrument and other signal acquisition devices to form a gravel pile construction excitation signal acquisition system;

[0111] In step S2, the gravel pile construction excitation signal acquisition system includes a detector, a signal amplifier, a hub and a signal acquisition instrument. The detector is connected to the input end of the signal amplifier via the hub, and the output end of the signal amplifier is connected to the signal acquisition instrument.

[0112] S3, arranging the spatial array of geophones based on the frequency response characteristics and working range of the geophones selected in S2, the spatial position of the gravel piles, and the plane range of the pre-treated foundation;

[0113] S31: Evenly spaced vibro-stone piles are arranged within the plane of the pre-treated foundation to form a reinforced vibro-stone pile composite foundation;

[0114] S32: Dividing the plane range of the pre-treated foundation into a grid according to the preset pile spacing with λ times the pile spacing as the grid spacing, with the corner points of the grid located in the soil between the gravel piles, and using the corner points of the grid as the plane positions for the geophone deployment;

[0115] In a specific implementation, the shape of the grid division is determined according to the design and arrangement of the gravel piles.

[0116] S33: At the plane position where each geophone is arranged in S31, multiple geophones are arranged at preset intervals from top to bottom on the ground surface according to the vertical partitioning result of S1.

[0117] In S33, the vertical spacing between two adjacent detectors is the same as the spacing of the vertical partitions in S1, and the layout depth of the lowest detector is greater than the depth of the pre-treated foundation.

[0118] The multiple of the pile spacing λ is required to meet the following conditions:

[0119] The effective working radius R of the detector can be calculated based on the multiple λ of the pile spacing according to the following formula:

[0120]

[0121] Where R is the effective working radius of the detector, and d is the axial pile spacing of the gravel pile;

[0122] Then, a circle is established with each gravel pile as the center and the effective working radius R of the detector as the radius of the circle as the construction area of ​​the current gravel pile. The number of detectors in the current construction area of ​​each gravel pile minus the number of velocity partitions in the current gravel pile construction area should be no less than 3. Only in this way can the number of detectors in any construction area meet the requirements of subsequent velocity inversion of each velocity partition in the area.

[0123] The vibration-impacting process will disturb the soil around the gravel pile, causing the soil around the pile to undergo different mechanical states such as liquefaction, plastic deformation, and elastic compression. With the gravel pile construction hole as the center, there are obvious differences in the elastic wave velocity in the radial area. The wave velocity is zoned along the radial direction, so that the elastic wave velocity difference within each radial zone of the vertically same layer of soil is relatively small.

[0124] In the specific implementation, the λ value is determined by rounding the ratio of the effective working radius of the detector to the spacing between the gravel piles, as follows: Figure 4 Then, geophones are arranged on the grid nodes from the surface downwards according to the vertical division of wave velocity. The depth of geophone arrangement should be greater than the depth of vibro-compacted gravel pile composite foundation. Figure 5 , to ensure that the number of detectors in any construction area meets the requirements of subsequent velocity inversion of each velocity partition in the area.

[0125] S4. Install a gravel pile excitation signal acquisition system according to the spatial array of geophones designed in S3. Use the spatial array of geophones designed in S3 to collect and store elastic wave signals generated during the construction of vibro-compacted gravel piles in real time. Perform filtering and signal recognition on the elastic wave signals based on the typical elastic waves obtained in S1 to determine and store effective elastic wave signals for elastic wave velocity inversion.

[0126] In step S4, specifically:

[0127] S41: Based on the elastic waves collected in the pile test in S1 as typical elastic waves, that is, the elastic waves picked up by the detector in the wave velocity test hole set in S12, the maximum amplitude, duration, rise time, main frequency, spectrum distribution, etc. of the elastic waves are extracted as characteristic parameters through Fourier transform or wavelet transform to form a waveform characteristic parameter database, and then a typical elastic wave probability distribution model of the waveform characteristic parameters is established through mathematical statistics;

[0128] S42: determining filtering parameters such as bandwidth and threshold based on characteristic parameters such as the main frequency and spectrum distribution in a typical elastic wave probability distribution model, and then filtering the elastic wave signal picked up by the spatial array of detectors arranged in S3 based on the filtering parameters;

[0129] S43: The maximum amplitude, duration, rise time, main frequency, and spectral distribution of the filtered elastic wave signal are used as characteristic parameters and compared with the characteristic parameters of a typical elastic wave. The Fisher linear discriminant method is used to determine whether the elastic wave signal picked up in real time by the spatial array of detectors is a valid elastic wave signal generated during the construction of vibro-compacted gravel piles. The valid elastic wave signal is then stored.

[0130] S5, read the effective elastic wave signal of S4, extract the arrival time of the elastic wave signal, and use the elastic wave velocity after each velocity partition in S1 as the initial value to construct the elastic wave spatial propagation travel time equations, and optimize and solve the optimal value of the elastic wave velocity of each velocity partition through an iterative inversion algorithm;

[0131] In step S5, the inversion process of the elastic wave velocity in each velocity partition is as follows:

[0132] S51: Read the effective elastic wave signal obtained in S4, and extract the arrival time of the effective elastic wave signal using the threshold method, long short time average method (LTA / STA), and pooling criterion method (AR-AIC) to obtain the arrival time t observed by each detector. k , k is the serial number of the detector;

[0133] S52: Based on the elastic wave velocity results of the pre-treated foundation in S1, the initial slowness matrix [S] of the vibro-replacement gravel pile composite foundation is established. The expression is as follows:

[0134]

[0135]

[0136] in, represents the slowness of the foundation in the i-th vertical partition and the j-th radial partition; represents the elastic wave velocity of the foundation in the i-th vertical partition and the j-th radial partition;

[0137] S53: Use the shortest path ray tracing method to determine the propagation path L of the elastic wave from the excitation source to each detector under the initial slowness matrix [S] k :

[0138]

[0139] Where, is the propagation distance within the velocity partition of the i-th vertical partition and the j-th radial partition, and k represents the ordinal number of the detector;

[0140] S54: Calculate the propagation path L of the elastic wave along the path determined in S53 k Travel time propagated to each detector

[0141]

[0142] Where t0 is the moment when the soil vibration is caused by the same excitation source picked up by the geophone, are the calculated elastic wave travel times of different detectors in the initial slowness field, k = 1, 2, ... N, where N is the total number of detectors; represents the slowness of the foundation soil in the wave velocity zone of the i-th vertical zone and the j-th radial zone;

[0143] S55: The travel time t observed by each detector determined in combination with S51 k The travel time of each detector determined by S54 Calculate the difference Δt k :

[0144]

[0145] S56: The difference Δt determined according to S54 k Combined with the propagation path L determined by S53 k Processing to obtain the slowness correction value of the wave velocity partition

[0146]

[0147] S57: Then use the slowness correction value Added to the slowness parameter in each wave velocity zone of the vibro-replacement gravel pile composite foundation The specific assignment is expressed as follows:

[0148]

[0149] S58: Repeat the above S53 to S57 to iteratively optimize each element in the wave velocity partition slowness field matrix [S] until the time difference function f meets the accuracy requirement. The velocity field mapped to the slowness field is the wave velocity inversion result. The final wave velocity partition slowness field matrix [S] is used as the optimal matrix. The optimal value of the elastic wave velocity of each wave velocity partition during gravel pile construction is obtained from each element in the total optimal matrix.

[0150] The time difference function f is expressed as follows:

[0151]

[0152] S6, based on the density ρ of the pre-treated foundation soil, the lateral pressure coefficient K0, the maximum / minimum porosity ratio e max / e min Based on the physical and mechanical parameters such as S5, an indoor graded consolidation elastic wave velocity test was carried out to establish the corresponding relationship between the effective confining pressure, relative density and elastic wave velocity of the soil. According to the optimal value of the elastic wave velocity of each velocity zone during the gravel pile construction obtained by S5 and the corresponding relationship between the excess pore pressure input obtained by S1, the relative density of the soil after the excess pore pressure dissipated was obtained, and compared with the designed relative density of the vibro-compacted gravel pile composite foundation to detect the reinforcement quality of the vibro-compacted gravel pile composite foundation.

[0153] In step S6, the process of establishing the characterization relationship between the elastic wave velocity, effective confining pressure level, and relative density of each partitioned soil is as follows:

[0154] S61: First, according to the wave velocity zones determined in S1 and the geological survey of the pre-treated foundation, determine the density of the soil in each wave velocity zone thickness and lateral pressure coefficient Then the average effective confining pressure of the soil in each wave velocity zone is obtained by the following formula:

[0155]

[0156] Where q represents the traversal sequence number of the vertical partition soil parameters, and q starts from 0; represents the average effective confining pressure of the soil in the wave velocity zone of the i-th vertical zone and the j-th radial zone, and g is the local gravitational acceleration; represents the excess pore pressure of the soil in the wave velocity zone of the i-th vertical zone and the j-th radial zone, which is obtained by S1;

[0157] S62: Then, the average effective confining pressure of the soil in each wave velocity zone is processed according to the characterization relationship between the elastic wave velocity and the porosity of the soil in each wave velocity zone in the following formula to obtain the porosity of the soil in each wave velocity zone:

[0158]

[0159] Where, is the porosity ratio of the soil in the wave velocity partition of the i-th vertical partition and the j-th radial partition; A t and b t are the first and second fitting parameters determined by the graded consolidation wave velocity test, t=1,2,…,s, t represents the ordinal number of the soil, s represents the total number of soil types, P A is atmospheric pressure, usually 100kPa, V i j represents the optimal value of elastic wave velocity of the velocity partition of the i-th vertical partition and the j-th radial partition obtained by S5;

[0160] The characterization relationship between the elastic wave velocity and porosity of the soil in each wave velocity zone is obtained by taking different types of pre-treated foundation soils and conducting graded consolidation wave velocity tests indoors, and drawing curves fitting the relationship between the elastic wave velocity and porosity of different types of soils under different consolidation confining pressures.

[0161] S63: Then determine the maximum void ratio of different soils in the pre-treated foundation through geological survey and minimum porosity ratio The porosity ratio of the soil in each velocity zone is processed according to the relationship between the relative density of the soil in each velocity zone and the elastic wave velocity in the following formula to obtain the relative density of the soil in each velocity zone:

[0162]

[0163] Where, It represents the relative density of the soil in the wave velocity zone of the i-th vertical zone and the j-th radial zone; and They represent the maximum porosity and minimum porosity of the soil with ordinal number t, respectively;

[0164] S64: Finally, the reinforcement quality of the vibro-compacted gravel pile composite foundation is judged based on the relative density of the soil in each wave velocity zone.

[0165] S64 is specifically as follows: according to the relative density of the soil in each wave velocity zone, the soil in each wave velocity zone is divided into three density states: loose, medium dense and dense according to the national standard "Code for Geotechnical Engineering Investigation" (50021-2001); at the same time, the relative density of each wave velocity zone is compared with the designed relative density, and the wave velocity zone with a relative density greater than the designed relative density is recorded as qualified, otherwise it is recorded as unqualified.

[0166] Finally, a quality evaluation report on the soil compaction status of each wave velocity zone and whether the reinforcement quality is qualified or not can be given.

[0167] The specific system is composed of a geophone, a piezometer, a signal amplifier, a concentrator, a signal acquisition instrument, a data storage unit, a signal processing unit, a wave velocity inversion unit, a wave velocity interpretation unit, a comparative analysis and data visualization unit, etc. The specific functions of each component are as follows:

[0168] The detector receives and records the vibration signal generated by any excitation within the effective detection range of each sensor in the form of an electrical signal.

[0169] The pore water pressure gauge records the analog signal of the saturated soil pore water pressure at each sensor location in the form of a frequency signal or an electrical signal.

[0170] The signal amplifier amplifies the collected vibration signal.

[0171] The hub connects the amplifier and detectors and aggregates the vibration signals received by multiple detectors.

[0172] The signal acquisition instrument synchronizes the signal acquisition time by setting parameters such as sampling frequency, signal duration, and detector trigger threshold, collects the electrical signal transmitted by the detector and amplified by the amplifier, forms a digital electrical signal, and stores it. The stored elastic wave digital signal is then uploaded to the signal processing unit by limited or wireless transmission.

[0173] The data storage unit stores the elastic wave signal transmitted by the signal acquisition instrument and the effective elastic wave signal determined by the signal processing unit in real time.

[0174] The signal processing unit reads the elastic wave signal transmitted by the signal acquisition instrument in the data storage unit, selects a suitable filtering method for filtering, performs waveform recognition on the filtered signal, determines the validity of the signal, stores the valid elastic wave signal, and selects a suitable time-picking method for time-picking the synchronously collected elastic wave.

[0175] The wave velocity inversion unit inputs the spatial coordinates of the detector, reads the effective elastic wave signal and the signal arrival time picking result determined by the signal processing unit in the data storage unit, substitutes the arrival time of the effective signal and the spatial coordinates of the corresponding detector into the travel time equation group, and uses the ray tracing method to invert the wave velocity of each partition.

[0176] The wave velocity interpretation unit substitutes the wave velocity of each zone and the pore pressure dissipation law into the characterization formula of relative density and wave velocity in S63 to calculate the relative density of the soil in each wave velocity zone.

[0177] The comparative analysis and data visualization unit compares the relative density of the soil in each wave velocity zone output by the wave velocity interpretation unit with the design value of the vibro-stone pile composite foundation, and outputs the comparison results in a three-dimensional visualization form to evaluate the quality of the vibro-stone pile composite foundation.

[0178] The signal acquisition instrument has a synchronous acquisition function, which can digitally acquire the elastic wave signals received by each detector at the same time, and record the initial acquisition time as zero time.

[0179] The signal processing unit in the system has the functions of filtering, signal recognition, and time-based picking.

[0180] The filtering process is to determine the filtering bandwidth based on the waveform characteristic parameters of the typical elastic waves generated during the construction process of the vibro-stone pile determined by S1, and perform filtering through the filter.

[0181] Signal recognition can extract the waveform characteristic parameters of the elastic wave signal, such as the maximum amplitude, duration, rise time, main frequency, and spectral distribution, through Fourier transform and wavelet transform. Based on the Fisher linear discriminant method, the waveform characteristic parameters are compared with those of typical elastic waves to determine whether the fluctuation signal is an elastic wave signal generated by vibro-compacted gravel pile construction.

[0182] The arrival time picking can automatically pick the first arrival time of the elastic wave signal received by the detector at the same time by setting the picking method and judgment threshold.

[0183] The data visualization module in the system can display the relative density of the foundation soil in real time in the form of a three-dimensional cloud map, and compare it with the design value or specification value of the vibro-stone pile composite foundation, highlighting the areas where the relative density of the foundation soil does not meet the design value or specification value, and evaluate the quality of the vibro-stone pile composite foundation in real time.

[0184] In a specific embodiment, a foundation needs to be treated with vibro-stone piles. The estimated depth of the treatment area is 26m. The soil in the treatment area includes two layers: a sandy gravel layer and a silty clay layer. The soil thicknesses are 12m and 18m respectively. The stone piles are arranged in a triangular pattern.

[0185] The first step is to obtain the vertical and radial distribution of elastic wave velocity of the natural foundation through the cross-hole method and foundation gravel pile test, and divide the foundation into 6 zones according to the wave velocity. The specific divisions are shown in Figure 6 ;

[0186] The second step is to analyze and extract the maximum amplitude, duration, rise time, main frequency and other parameters of typical signals collected from foundation gravel pile test, and build a typical vibration signal feature library;

[0187] The third step is to select a detector with a frequency response range of 15 to 1000 Hz based on the vibrator's speed parameter of 1450 rpm. Based on the noise conditions at the construction site, select an amplifier with a gain of 5 to 10 dB. Based on the typical vibration signal frequency of 24 Hz collected in the pile test, select a digital signal acquisition instrument with 6 channels and set the sampling frequency to 2000 Hz.

[0188] The fourth step is to install and debug the equipment. The installation and debugging of the system architecture specifically includes:

[0189] 1) According to the arrangement of gravel piles, determine the arrangement of sensor arrays, such as Figure 7 As shown in the figure, the sensors were deployed at depths of 4m, 8m, 12m, 16m, 18m, 20m, 24m, 27m, and 30m. The vertical depth was greater than the depth of the treated gravel piles. The horizontal distance between the sensor deployment points and the gravel piles was 25m.

[0190] 2) All detectors are connected to a signal acquisition instrument. The signal acquisition instrument first amplifies the electrical signal transmitted by the detector through a built-in signal amplifier, then synchronizes the time through a timer, and then uploads it to the signal processing unit at the same time.

[0191] 3) The signal processing unit is mainly composed of a filter and a computer system. First, the filter parameters are set according to the frequency spectrum of the typical elastic wave signal. The sampled signal is filtered through the filter. Then, Fourier transform or wavelet transform is performed to extract the characteristic parameters of the signal, such as the maximum amplitude, duration, rise time, and main frequency. The parameters are compared with the characteristic parameters of the typical elastic wave signal sampled in the pile test. The effective elastic wave signal is uploaded to the data storage unit for signal storage.

[0192] In the fifth step, the effective elastic wave signal after filtering is automatically identified by setting parameters such as threshold value and time window length, and the elastic wave first arrival time t is recorded. k , see Table 1 for details.

[0193] Table 1 Arrival time of the first arrival wave of the excitation sensor at a certain moment

[0194]

[0195] The sixth step is to calculate the first arrival time t of the typical elastic wave received by each detector. k Substitute into the travel time equations, select the iterative solution algorithm and set the solution accuracy to 10 -6 , solve the travel time equation and obtain 6 elastic wave velocities, see Table 2.

[0196] Table 2 Elastic wave velocities in the velocity zones obtained by inversion

[0197]

[0198] In the seventh step, the elastic wave velocity obtained by inversion is substituted into the velocity and relative density function of the effective confining pressure corrected by the excess pore pressure function to obtain the relative density in each velocity zone and display it in the form of a cross-sectional cloud diagram, as shown in the figure below: Figure 8 The functional relationship between elastic wave velocity and relative density is obtained by indoor step-by-step loading consolidation test and measuring the elastic wave velocity under different consolidation pressures.

[0199] In the eighth step, in the data visualization unit, the relative density of the soil in each wave velocity zone output by the wave velocity interpretation unit can be compared with the design value of the vibro-stone pile composite foundation, and the comparison results can be output in the form of three-dimensional visualization to evaluate the quality of the vibro-stone pile composite foundation, so as to guide the dynamic optimization and adjustment of the construction quality.

Claims

1. A self-excitation detection method for the reinforcement quality of vibro-stone pile composite foundation, characterized by: The method comprises the following steps: S1. Conduct an elastic wave velocity test on the pretreated foundation to determine the vertical distribution of the elastic wave velocity of the foundation soil, and then vertically partition the elastic wave velocity of the pretreated foundation based on the vertical distribution of the elastic wave velocity; conduct a pile test to select an elastic wave as a typical elastic wave, and radially partition the elastic wave velocity of the pretreated foundation based on the radial distribution of the velocity of the typical elastic wave; monitor the excess pore pressure during the pile test, and obtain the excess pore pressure of all partitions of the pretreated foundation by fitting; S2. Select a detector based on the waveform characteristic parameters of the elastic wave obtained in S1, and connect the detector with signal amplifiers, concentrators, signal collectors and other signal acquisition devices to form a gravel pile construction excitation signal acquisition system; S3, arranging the spatial array of geophones based on the frequency response characteristics and working range of the geophones selected in S2, the spatial position of the gravel piles, and the plane range of the pre-treated foundation; S4, using the spatial array of geophones designed in S3 to collect and store elastic wave signals generated during the construction of vibro-stone piles in real time, filtering and identifying the elastic wave signals based on the typical elastic waves obtained in S1, determining and storing effective elastic wave signals for elastic wave velocity inversion; S5, reading the effective elastic wave signal described in S4, extracting the arrival time of the elastic wave signal, and using the elastic wave velocity after each velocity partition in S1 as the initial value, constructing a set of elastic wave spatial propagation travel time equations, and optimizing and solving the optimal value of the elastic wave velocity of each velocity partition through an iterative inversion algorithm; S6, based on the density ρ of the pre-treated foundation soil, the lateral pressure coefficient K0, the maximum / minimum porosity ratio e max / e min The corresponding relationship between the effective confining pressure, relative density and elastic wave velocity of the soil is established based on the physical and mechanical parameters such as S5. The relative density of the soil after the excess pore pressure dissipates is obtained according to the optimal value of the elastic wave velocity of each velocity zone during the gravel pile construction obtained by S5 and the corresponding relationship between the excess pore pressure input obtained by S1. The relative density is then compared with the designed relative density of the vibro-compacted gravel pile composite foundation to detect the reinforcement quality of the vibro-compacted gravel pile composite foundation.

2. The self-excitation detection method for the reinforcement quality of vibro-stone pile composite foundation according to claim 1 is characterized by: In the S1, specifically: S11: Use the cross-hole method to conduct wave velocity testing to obtain the elastic wave velocity of the soil at different depths of the pre-treated foundation, and vertically partition the soil of the pre-treated foundation according to the differences in elastic wave velocity at different depths along the vertical direction; S12: a test pile is laid out in the pretreated foundation by vibro-flotation construction, multiple wave velocity test holes are arranged in each vertical partition of the pretreated foundation along the radial direction of the test pile, a geophone is installed at the same depth in each wave velocity test hole, elastic waves are picked up by the geophones arranged in the multiple wave velocity test holes at the same depth, a propagation velocity and an attenuation coefficient of the elastic wave along the radial direction of the test pile are calculated, and then the current depth of the pretreated foundation soil is radially partitioned according to the propagation velocity and the attenuation coefficient; S13: Based on the results of S11 and S12, the pre-treated foundation is divided into zones to obtain various wave velocity zones; S14: In each vertical partition of the pretreated foundation, multiple excess pore pressure monitoring holes are arranged along the radial direction of the test piles. A piezometer is installed in each excess pore pressure monitoring hole. The radial excess pore pressure variation relationship at the current depth is determined based on the excess pore pressures collected by piezometers arranged at the same depth but at different radial distances. The excess pore pressures of each velocity partition at the current depth are further fitted. The excess pore pressures of all velocity partitions of the pretreated foundation are then obtained based on the excess pore pressures of each velocity partition at different depths.

3. The self-excitation detection method for the reinforcement quality of vibro-stone pile composite foundation according to claim 1 is characterized by: In S2, the gravel pile construction excitation signal acquisition system includes a detector, a signal amplifier, a hub and a signal acquisition instrument. The detector is connected to the input end of the signal amplifier via the hub, and the output end of the signal amplifier is connected to the signal acquisition instrument.

4. The self-excitation detection method for the reinforcement quality of vibro-stone pile composite foundation according to claim 1 is characterized by: In the S3, specifically: S31: Within the plane range of the pre-treated foundation, vibro-stone piles are evenly spaced to form a vibro-stone pile composite foundation; S32: Dividing the plane range of the pre-treated foundation into a grid based on the preset pile spacing, with λ times the pile spacing as the grid spacing, with the corner points of the grid located in the soil between the gravel piles, and the corner points of the grid serving as the plane positions for the geophone deployment; S33: At the plane position where each geophone is arranged in S32, a plurality of geophones are arranged at intervals from top to bottom on the ground surface according to the vertical partitioning result of S1.

5. The self-excitation detection method for the reinforcement quality of vibro-stone pile composite foundation according to claim 4 is characterized by: The multiple λ of the pile spacing is required to meet the following conditions: The effective working radius R of the detector can be calculated based on the multiple λ of the pile spacing according to the following formula: Where R is the effective working radius of the detector, and d is the axial pile spacing of the gravel pile; Then, a circle is established with each gravel pile as the center and the effective working radius R of the detector as the radius of the circle as the construction area of ​​the gravel pile. The number of detectors in the construction area of ​​each gravel pile minus the number of wave velocity zones in the construction area of ​​the current gravel pile should be no less than 3.

6. The self-excitation detection method for the reinforcement quality of vibro-stone pile composite foundation according to claim 1 is characterized by: In the S4, specifically: S41: Based on the elastic waves collected in the pile test in S1 as typical elastic waves, the maximum amplitude, duration, rise time, main frequency, spectrum distribution and other characteristics of the typical elastic waves are extracted as characteristic parameters to form a waveform characteristic parameter database. Then, a typical elastic wave probability distribution model of the waveform characteristic parameters is established through mathematical statistics; S42: determining filtering parameters such as bandwidth and threshold based on characteristic parameters such as the main frequency and spectrum distribution in a typical elastic wave probability distribution model, and then filtering the elastic wave signal picked up by the spatial array of detectors arranged in S3 based on the filtering parameters; S43: The maximum amplitude, duration, rise time, main frequency, and spectral distribution of the filtered elastic wave signal are used as characteristic parameters and compared with the characteristic parameters of a typical elastic wave. The Fisher linear discriminant method is used to determine whether the elastic wave signal picked up in real time by the spatial array of detectors is a valid elastic wave signal generated during the construction of vibro-compacted gravel piles. The valid elastic wave signal is then stored.

7. The self-excitation detection method for the reinforcement quality of vibro-stone pile composite foundation according to claim 1 is characterized by: In said S5, the details are as follows: S51: Read the effective elastic wave signal obtained in S4, and use the method to extract the arrival time of the effective elastic wave signal to obtain the arrival time t observed by each detector k , k is the serial number of the detector; S52: Based on the elastic wave velocity results of the pre-treated foundation in S1, the initial slowness matrix [S] of the vibro-replacement gravel pile composite foundation is established. The expression is as follows: in, represents the foundation slowness of the i-th vertical partition and the j-th radial partition; represents the foundation elastic wave velocity in the velocity zone of the i-th vertical zone and the j-th radial zone; S53: Use the shortest path ray tracing method to determine the propagation path L of the elastic wave from the excitation source to each detector under the initial slowness matrix [S] k : Where, is the propagation distance within the velocity partition of the i-th vertical partition and the j-th radial partition, and k represents the ordinal number of the detector; S54: Calculate the propagation path L of the elastic wave along the path determined in S53 k Travel time propagated to each detector Where t0 is the excitation moment picked up by the detector, are the calculated elastic wave travel times of different detectors in the initial slowness field, k = 1, 2, ... N, where N is the total number of detectors; represents the slowness of the foundation soil in the wave velocity zone of the i-th vertical zone and the j-th radial zone; S55: The travel time t observed by each detector determined in combination with S51 k The travel time of each detector determined by S54 Calculate the difference Δt k : S56: The difference Δt determined according to S54 k Processing to obtain the slowness correction value of the wave velocity partition S57: Then use the slowness correction value Add to each slowness Make corrections on S58: Repeat the above S53 to S57 to iteratively optimize each element in the wave velocity partition slowness field matrix [S] until the time difference function f meets the accuracy requirements. Then, the final wave velocity partition slowness matrix [S] is used as the optimal matrix, and the optimal value of the elastic wave velocity of each wave velocity partition during the gravel pile construction is obtained from each element in the total optimal matrix.

8. The self-excitation detection method for the reinforcement quality of vibro-stone pile composite foundation according to claim 7, characterized in that: The time difference function f is expressed as follows:

9. The self-excitation detection method for the reinforcement quality of vibro-stone pile composite foundation according to claim 1, characterized in that: In S6, the process of establishing the characterization relationship between the elastic wave velocity, effective confining pressure level, and relative density of each sub-region soil is as follows: S61: First, according to the wave velocity zones determined in S1 and the geological survey of the pre-treated foundation, determine the density of the soil in each wave velocity zone thickness and lateral pressure coefficient Then the average effective confining pressure of the soil in each wave velocity zone is obtained by the following formula: Where q represents the traversal sequence number of the vertical partition soil parameters, and q starts from 0; represents the average effective confining pressure of the soil in the wave velocity zone of the i-th vertical zone and the j-th radial zone, and g is the local gravitational acceleration; represents the excess pore pressure of the soil in the wave velocity zone of the i-th vertical zone and the j-th radial zone; S62: Then, the average effective confining pressure of the soil in each wave velocity zone is processed according to the characterization relationship between the elastic wave velocity and the porosity of the soil in each wave velocity zone in the following formula to obtain the porosity of the soil in each wave velocity zone: Where, is the porosity ratio of the soil in the wave velocity partition of the i-th vertical partition and the j-th radial partition; A t and b t are the first and second fitting parameters determined by the wave velocity test of the graded consolidation test, t=1,2,…,s, t represents the ordinal number of the soil, s represents the total number of soil types, P A is atmospheric pressure, V i j represents the optimal value of elastic wave velocity of the velocity partition of the i-th vertical partition and the j-th radial partition; S63: Then determine the maximum void ratio of different soils in the pre-treated foundation through geological survey and minimum porosity ratio The porosity ratio of the soil in each velocity zone is processed according to the relationship between the relative density of the soil in each velocity zone and the elastic wave velocity in the following formula to obtain the relative density of the soil in each velocity zone: Where, It represents the relative density of soil in the wave velocity zone of the i-th vertical zone and the j-th radial zone; and They represent the maximum porosity and minimum porosity of the soil with ordinal number t, respectively; S64: Finally, the reinforcement quality of the vibro-compacted gravel pile composite foundation is judged based on the relative density of the soil in each wave velocity zone.

10. The self-excitation detection method for the reinforcement quality of vibro-stone pile composite foundation according to claim 9, characterized in that: Specifically, S64 comprises the following steps: classifying the soil in each velocity zone into three compaction states: loose, medium-dense, and dense, according to the relative density of the soil in each velocity zone; and comparing the relative density of each velocity zone with the designed relative density. The velocity zone with a relative density greater than the designed relative density is marked as qualified, and otherwise is marked as unqualified.

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