Nondestructive testing method for uniformity of cement mixing pile reinforced roadbed

Abstract

The invention discloses a nondestructive testing method for the uniformity of a cement mixing pile reinforced roadbed, and relates to the field of cement mixing pile uniformity detection.The nondestructive testing method comprises the steps that a sounding pipe is pre-buried in a cement mixing pile, and the sound wave propagation time, the receiving amplitude and the main frequency value of the whole pile length of a pile body are collected and detected through an ultrasonic transmitting probe and an ultrasonic receiving probe; the slope value of a virtual connecting line between the sending probe and the receiving probe relative to the horizontal plane is detected in real time through the two probes in the descending and ascending stages, and the two probes are dynamically adjusted to be at the same horizontal height in the pipe according to the slope value; comparing and screening the ultrasonic characteristic data of the pile body collected at the same depth in the descending and ascending stages; and calculating three indexes including a sound velocity uniformity coefficient, a wave amplitude uniformity index and dominant frequency dispersion based on the effective data set, and forming a comprehensive uniformity index through weighted fusion. Through double-stroke detection, dynamic leveling and multi-index analysis, detection interference is effectively eliminated, and data reliability is improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of cement mixing pile uniformity detection, and relates to a nondestructive testing method for the uniformity of a cement mixing pile reinforced roadbed. BACKGROUND

[0002] With the increasing traffic load and the increasing demand for engineering construction under complex geological conditions, the use of cement mixing piles to reinforce soft ground has become a key technical means to improve the bearing capacity of roadbeds and control settlement deformation, and is widely used in the fields of highways, railways, municipal engineering, etc. The cement mixing pile forms a columnar reinforcement body by forcibly mixing cement with foundation soil, and the uniformity of the pile body material is a core index affecting the reinforcement effect, directly related to the overall quality and service life of the project.

[0003] Currently, there are technologies for detecting the uniformity of cement mixing pile reinforced roadbeds, such as the invention patent with publication number CN102409706B, which proposes a method for determining the uniformity of cement-soil mixing pile body. By combining the physical quality characteristics and mechanical strength characteristics of the pile body, it is converted into a single uniformity coefficient, and then four levels of uneven, basically uniform, uniform, and very uniform are clearly divided, providing a standardized and quantitative technical method for objective evaluation of the uniformity of cement-soil mixing pile body, avoiding the qualitative and subjective problems that may exist in traditional determination.

[0004] Although the above-mentioned existing scheme has achieved certain results in the uniformity detection of cement mixing pile reinforced roadbeds, it still has the following shortcomings: first, the existing technology takes multiple physical samples of the pile body, which is a destructive detection, not only damaging the integrity of the pile body structure, but also having obvious deficiencies in sample representativeness. The existing technology intercepts cement-soil core samples of a specific specification for testing, and only uses single-core samples as the detection object, which cannot realize repeated or continuous monitoring of the same pile, and is easy to make excessive denial of the pile body which is overall qualified but has only a small local deviation, thereby affecting the reliability of the detection result.

[0005] Secondly, the uniformity of the pile body not only depends on the solid particle content and the compressive strength, but also closely related to the internal structure continuity, material property stability and other multi-dimensional factors. The existing technology only uses the product of the quality coefficient and the strength coefficient as the basis for determination, and this single-dimensional parameter combination cannot fully reflect the essential characteristics of uniformity, limiting its systematic evaluation of the overall uniformity of the pile body. SUMMARY

[0006] In view of this, in order to solve the problems raised in the background art, the present application provides a nondestructive testing method for the uniformity of a cement mixing pile reinforced roadbed.

[0007] The purpose of the present application can be achieved by the following technical solutions: A uniformity nondestructive testing method for cement mixing pile reinforced roadbed, comprising: S1, two vertical acoustic measuring pipes are symmetrically pre-buried in the cement mixing piles on both sides of the roadbed relative to the center of the pile body, and the pipes are filled with clear water, and an ultrasonic transmitting probe and a receiving probe are respectively arranged at the pipe openings.

[0008] S2, the two probes are controlled to move downward from the pipe openings simultaneously, the slope value of the virtual connection line between the transmitting and receiving probes relative to the horizontal plane is detected in real time, the positions of the two probes in the pipe are dynamically adjusted to be at the same horizontal height according to the slope value, and the pile body ultrasonic characteristic data, including the sound wave propagation time, the received wave amplitude and the main frequency value, are collected.

[0009] S3, when the two probes reach the pipe bottom, they are controlled to rise to the pile top simultaneously, and the slope dynamic adjustment probe operation is repeated, and the pile body ultrasonic characteristic data at the same depth are collected.

[0010] S4, the pile body ultrasonic characteristic data collected at the same depth in the descending and ascending stages are compared, and the effective data set of the pile body ultrasonic characteristic data is screened.

[0011] S5, the sound velocity uniformity coefficient, the wave amplitude uniformity index and the main frequency dispersion are calculated based on the effective data set.

[0012] S6, a quality detection report of the uniformity of the cement mixing pile reinforced roadbed is generated according to the sound velocity uniformity coefficient, the wave amplitude uniformity index and the main frequency dispersion.

[0013] Compared with the prior art, the present application has the following advantages: (1) the present application adopts the method of pre-buried acoustic measuring pipe in the cement mixing pile, and collects and detects the sound wave propagation time, the received wave amplitude and the main frequency value of the whole pile length through the ultrasonic transmitting and receiving probes, without needing to cut the pile core sample, solving the problems of strong destructiveness, insufficient sample representativeness, pile body structure damage and one-sided detection results.

[0014] (2) the present application detects the slope value of the virtual connection line between the transmitting and receiving probes relative to the horizontal plane in real time through the two probes in the descending and ascending stages, dynamically adjusts the positions of the two probes in the pipe to be at the same horizontal height according to the slope value, avoids the data distortion caused by the mispositioning of the probes, and ensures that the detection data can truly reflect the uniformity state of the pile body at the corresponding depth.

[0015] (3) the present application can accurately distinguish between the local slight deviation caused by the positioning error of the probes and the overall uniformity state caused by the local defects of the pile body through the comparison and screening of the pile body ultrasonic characteristic data collected at the same depth in the descending and ascending stages, effectively solving the problem of over-denying the pile body with overall qualified and only local deviation, affecting the reliability of the detection.

[0016] (4) The application calculates three indexes of sound velocity uniformity coefficient, wave amplitude uniformity index and main frequency dispersion degree based on effective data groups, forms a comprehensive uniformity index through weighted fusion, and effectively solves the problems of single determination basis, inability to comprehensively reflect multi-dimensional characteristics of uniformity, and limitation of system evaluation of overall uniformity performance of the pile body. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions of the embodiments of the application, the drawings needed to be used in the following embodiment description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0018] Figure 1 The method embodiment of the application is shown in the flowchart.

[0019] Figure 2 The structure schematic diagram of the laser range finder and the probe of the application is shown.

[0020] Figure 3 The pile body ultrasonic feature data group optimization determination flowchart of the application is shown.

[0021] BRIEF DESCRIPTION OF DRAWINGS: 1-laser range finder, 2-ultrasonic emission probe, 3-acoustic measuring pipe, 4-cement mixing pile, 5-ultrasonic receiving probe. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the application will be described clearly and completely in the following with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only some embodiments of the application, but not all the embodiments. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the protection scope of the application.

[0023] Please refer to Figure 1 As shown in the drawings, the application provides a cement mixing pile reinforced roadbed uniformity nondestructive testing method, which comprises the following steps: S1, two vertical acoustic measuring pipes are symmetrically pre-buried in the cement mixing piles on both sides of the roadbed relative to the pile body center, and the pipes are filled with clear water, and an ultrasonic emission probe and a receiving probe are respectively arranged at the two pipe openings.

[0024] It should be noted that the two acoustic measuring pipes are symmetrically pre-buried relative to the pile body center, so that the sound wave propagation path between the ultrasonic probes can uniformly cover the key area of the pile body cross section, and the detection blind area caused by path deviation is avoided.

[0025] The filled clear water in the sounding pipe serves as a coupling medium between the ultrasonic probe and the pile body, which can avoid the attenuation of sound waves caused by direct contact between the probe and air. For example, air has strong absorption ability to ultrasonic waves, which can greatly reduce the detection signal strength. The uniformity and stability of clear water ensure the consistency of the sound wave propagation path in the pipe, reducing the detection error caused by uneven medium.

[0026] S2, control the two probes to move downward from the pipe openings of the sounding pipes simultaneously, detect the slope value of the virtual connection line between the detection sending and receiving probes relative to the horizontal plane in real time, dynamically adjust the positions of the two probes in the pipes to be at the same horizontal height according to the slope value, and collect pile ultrasonic characteristic data including sound wave propagation time, received wave amplitude and main frequency value.

[0027] Referring to Figure 2 A specific implementation step of the slope value of the virtual connection line between the detection sending and receiving probes relative to the horizontal plane is as follows: two laser range finders are fixedly installed above the two sounding pipes and the measurement beams thereof are vertically aligned with the probes in the respective pipe openings.

[0028] Specifically, the laser range finders are fixedly installed above the two sounding pipes through rigid supports and are precisely leveled to ensure that the laser emission axes thereof are parallel to the center lines of the sounding pipes and vertically downward. The sampling frequency of the laser range finders should be higher than the probe lowering speed and the data acquisition frequency to ensure real-time performance.

[0029] More specifically, a reflecting surface is arranged on the top of the ultrasonic probe, such as a rough sticker, for optimizing the diffuse reflection of the laser beam and ensuring that the range finder can obtain stable and accurate readings in any environment.

[0030] The two range finders are triggered to work synchronously during the lowering of the probes, and the distances from the range finders to the top of the transmitting probe and the top of the receiving probe are measured respectively.

[0031] The real-time absolute elevations of the transmitting probe and the receiving probe are calculated respectively based on the installation heights of the two range finders.

[0032] Specifically, since the installation base surfaces of the two range finders are on the same horizontal plane, the installation heights thereof are fixed known values. The absolute elevation values of the transmitting probe and the receiving probe are obtained by subtracting the installation heights from the real-time absolute elevations of the transmitting probe and the receiving probe respectively.

[0033] The real-time elevation difference between the two probes is obtained by subtracting the absolute elevation of the transmitting probe from the absolute elevation of the receiving probe.

[0034] It should be noted that the sign of the real-time elevation difference directly indicates which probe is in the leading position.

[0035] The real-time slope value of the virtual connection between the two probes relative to the horizontal plane is obtained by dividing the elevation difference by the center distance between the two acoustic pipes.

[0036] It should be noted that the center distance between the two acoustic pipes is a fixed value measured after the pipe is buried.

[0037] By completely non-contact measurement, the universality and sealing of the probe are maintained without changing the structure of the probe body. At the same time, the absolute elevation is directly measured to avoid cumulative error, and the measurement result is accurate and reliable.

[0038] The specific content of dynamically adjusting the position of the two probes in the pipe to the same horizontal height according to the slope value is as follows: the real-time slope value of the virtual connection between the probes in the horizontal direction is received, if the absolute value of the slope value is greater than zero, it is determined that there is an elevation difference between the two probes, and the adjustment process is entered, if the absolute value of the slope value is equal to zero, the current synchronous motion state is maintained.

[0039] It should be noted that the absolute value of the slope value is determined by the elevation difference between the two probes, and the two are in a positive proportional relationship, that is, when the center distance is fixed, the larger the elevation difference, the larger the absolute value of the slope. Only when the elevation difference between the two probes is equal to zero, the absolute value of the slope value is zero, and the two probes are at the same horizontal height. If the absolute value of the slope is greater than zero, there must be a height difference between the two probes.

[0040] If the slope value is greater than zero when entering the adjustment process, it indicates that the elevation of the transmitting probe is higher than that of the receiving probe, and the receiving probe lags behind, and vice versa.

[0041] According to the lag determination result, an acceleration adjustment instruction is output to the lifting mechanism corresponding to the lagging probe, while the current running speed of the lifting mechanism of the other probe is maintained.

[0042] It should be noted that if the elevation difference between the two probes is not accelerated to be leveled, the elevation difference between the two probes will continue to exist, resulting in that the ultrasonic propagation path is always an inclined straight line, the actual propagation distance is greater than the center distance, and further, the ultrasonic propagation time is overestimated, the calculated sound velocity value is smaller, and the data such as wave amplitude attenuation and main frequency change are affected by the increase of the propagation distance, which cannot correspond to the actual quality of the pile at the target depth, and finally introduces detection error.

[0043] Therefore, accelerating the lagging probe and maintaining the speed of the other probe can correct the position deviation, ensure that the ultrasonic detection meets the requirements of its physical principles, and provide reliable raw data for subsequent data screening and uniformity coefficient calculation.

[0044] The slope value is dynamically converged and stabilized at zero to control the same elevation motion of the two probes.

[0045] The dynamic adjustment of the probe to the same level according to the slope value is a core technical link for eliminating the deviation of the detection path, ensuring the authenticity of the original data, and supporting the subsequent uniformity evaluation, and directly determines the accuracy and effectiveness of the entire nondestructive testing method.

[0046] The output acceleration adjustment instruction of the lifting mechanism corresponding to the lagging probe has the following specific content: the pulse width of the acceleration adjustment instruction is in a positive correlation with the absolute value of the slope value.

[0047] It should be noted that the absolute value of the slope value is in a positive proportion to the height difference of the two probes, and the larger the absolute value of the slope, the more significant the height difference of the two probes, the greater the height difference, and the more serious the interference to the ultrasonic detection data, and stronger adjustment is needed to quickly eliminate the deviation.

[0048] When a large height difference is detected, i.e., the absolute value of the slope is large, strong acceleration through a long pulse width can make the slope value quickly converge to zero, ensuring that the probe recovers to the same level in a short time and reducing invalid data collection caused by lagging adjustment.

[0049] When the height difference is small, i.e., the absolute value of the slope is small, weak acceleration through a short pulse width can achieve fine adjustment, avoid repeated over-adjustment caused by adjustment exceeding the deviation, and ensure a smooth adjustment process.

[0050] When it is monitored that the absolute value of the slope value remains monotonically decreasing in a plurality of consecutive sampling periods, the pulse width of the current adjustment instruction is maintained.

[0051] It should be noted that when the absolute value of the slope monotonically decreases in a plurality of consecutive sampling periods, it indicates that the pulse width of the current output acceleration adjustment instruction has effectively pushed the lagging probe to catch up with the leading probe, and the height difference between the two probes is continuously decreasing, and the deviation correction direction is correct and the adjustment strength can meet the current needs.

[0052] When it is monitored that the absolute value of the slope value monotonically increases in two consecutive sampling periods, the pulse width of the adjustment instruction is increased by a preset proportion.

[0053] It should be noted that the absolute value of the slope value monotonically increases in two consecutive sampling periods, which indicates that the current adjustment strength is insufficient to overcome the deviation, and the adjustment strength of the adjustment instruction is increased by a preset proportion, i.e., a wider pulse width is immediately used to correct the deviation at a faster speed.

[0054] The determination principle of the preset proportion is: under the premise of ensuring that the system does not oscillate violently, sufficient adjustment strength is provided to quickly eliminate the deviation. Generally, before the device is shipped, different out-of-sync conditions can be simulated, such as artificially creating a height difference for multiple tests, observing the response curve of the system, and finally selecting an optimal proportion value that can make the system quickly and stably converge.

[0055] When the absolute value of the slope value after increasing the adjustment intensity is still greater than the absolute value of the slope value in the last sampling period, a mechanism state diagnosis program is immediately started and a pre-warning signal is sent out.

[0056] Specifically, after increasing the adjustment intensity, the controller immediately checks the effect in the next sampling period: if the absolute value of the new slope value is less than the value before the increase, it indicates that the adjustment is effective, and the system returns to the normal adjustment process.

[0057] If the absolute value of the new slope value is still greater than the value before the increase, it is determined that the system is abnormal, such as the probe being stuck by foreign matter, the motor being out of step, the pulley being slippery, etc. The controller will immediately start the mechanism state diagnosis program, for example, control the motor to move in reverse and then forward again to try to get out of trouble, check whether the motor current is overloaded, and send out a pre-warning signal through the sound and light alarm to prompt the operator to intervene and check, while suspending the detection process to prevent equipment damage and invalid data collection.

[0058] It should be noted that the acceleration adjustment instruction ensures that the collected ultrasonic feature data truly reflects the uniformity of the pile body by precisely controlling the horizontal position of the probe, thereby providing reliable raw data support for subsequent data screening, uniformity index calculation, and quality determination.

[0059] The acquisition step of the sound wave propagation time is as follows: the ultrasonic analog signal propagated through the pile body is collected by the receiving probe, the collected ultrasonic analog signal is preprocessed, and it is converted into a digital signal.

[0060] Specifically, when the control system determines that the two probes are at the same elevation, i.e., the slope value tends to zero, the master control unit sends a trigger instruction to the ultrasonic emitter to emit an electric pulse, and the master control unit simultaneously collects the analog voltage signal from the receiving probe at a high sampling rate. Since the received original analog signal is very weak and contains noise, it is input to a programmable gain amplifier, which automatically adjusts the amplification multiple according to the signal strength to make the signal amplitude reach the optimal measurement range. Subsequently, the signal passes through a band-pass filter to filter out high-frequency noise generated by the probe's inherent resonance and low-frequency interference on site.

[0061] The digital signal waveform after analysis and processing identifies the arrival time of the first arrival wave of the ultrasonic pulse and calculates the sound wave propagation time between emission and reception.

[0062] Specifically, first, a threshold voltage higher than the background noise is set, and the first point exceeding the threshold is recorded as the rough arrival point of the first arrival wave. Subsequently, the short-time average energy of the signal is calculated within a certain range before the point, and the point at which the energy first starts to increase continuously is determined as the more accurate sound time starting point. The time difference between this time and the emission trigger time is the sound time of the sound wave propagating in the pile body.

[0063] The propagation speed of acoustic wave in solid medium is high and uniform, indicating that the pile body is dense, high in strength and good in elasticity. A sudden decrease in acoustic speed or a large dispersion indicates that there may be holes, segregation, insufficient cement content and other defects that reduce density and strength at the location. The acoustic speed is a core indicator for evaluating the overall strength and uniformity of the pile body.

[0064] The acquisition step of the received amplitude is as follows: the maximum peak amplitude of the received signal waveform is extracted, and the ratio of the maximum peak amplitude to the initial transmitted amplitude is calculated to obtain the relative received amplitude value.

[0065] Specifically, after determining the acoustic time starting point, the processor searches for the maximum peak point on the complete received waveform, records the absolute value of the voltage at the point, and compares the amplitude value with the reference amplitude measured on the defect-free concrete calibration block to calculate the percentage of the absolute value of the voltage to the reference amplitude, which is recorded as the relative amplitude value. The relative amplitude value effectively eliminates the influence of the instrument and cable loss, and directly reflects the degree of energy attenuation of the ultrasonic wave in the pile body.

[0066] The received amplitude represents the strength of the energy carried by the ultrasonic wave, and a significant decrease in the amplitude, even if the acoustic speed does not change much, often means that there are local defects such as cracks, mud inclusions and honeycombs in the pile body, which seriously affect the integrity and durability of the pile body.

[0067] The acquisition step of the main frequency value is as follows: the received signal is subjected to frequency spectrum analysis, the frequency point with the maximum amplitude in the frequency spectrum graph is determined, and the frequency value corresponding to the frequency point is extracted as the main frequency value.

[0068] Specifically, the processor performs fast Fourier transform on the received entire waveform segment to convert the time domain signal to a frequency domain signal to obtain a frequency spectrum graph. The frequency point with the maximum amplitude on the frequency spectrum graph is found, and the frequency point is the main frequency value of the received signal.

[0069] The main frequency value can reflect the uniformity of the microstructure of the pile body, and a significant decrease in the main frequency reveals subtle material changes and poor mixing uniformity that cannot be discovered by the acoustic speed and amplitude.

[0070] S3. When the two probes reach the pipe bottom, control them to ascend to the pile top synchronously, and repeat the slope dynamic adjustment probe operation and collect the pile body ultrasonic characteristic data at the same depth.

[0071] The running resistance of the probe lifting mechanism and the motor response characteristics during the ascending process may be different from those in the descending phase, which can easily lead to a height difference between the two probes again. By monitoring the slope value in real time and dynamically adjusting the probes to the same level, it can be ensured that the ultrasonic wave propagation path is still a horizontal straight line during the ascending phase, avoiding problems such as overestimation of the propagation time, abnormal amplitude attenuation caused by the inclination of the path, and ensuring that the data in the ascending phase and the data in the descending phase have the same condition comparability.

[0072] S4, comparing the pile ultrasonic characteristic data collected at the same depth in the falling and rising stages to screen the effective data group of the pile ultrasonic characteristic data.

[0073] Referring to Figure 3 As shown, the specific content of screening the effective data group of the pile ultrasonic characteristic data is as follows: the pile ultrasonic characteristic data collected in the falling and rising stages are accurately matched according to the depth coordinates to form the falling stage data group and the rising stage data group at the same depth point.

[0074] The stage data group optimization rules are formulated, and the following priority determination levels are established based on the physical characteristics of sound wave propagation: a) if the sound wave propagation time of one data group is less than that of another data group, and the difference exceeds the sound wave propagation time measurement error range, the data group with smaller sound wave propagation time value is selected.

[0075] It should be noted that the sound wave propagation time measurement error range can be determined by repeating the measurement in a uniform medium for hundreds of times, and taking the multiple of the standard deviation of the measurement value.

[0076] b) if the difference of the sound wave propagation time of the two data groups is within the sound wave propagation time measurement error range, the stage data group with larger received wave amplitude value is selected.

[0077] c) if the difference of the received wave amplitude is within the received wave amplitude measurement error range, the stage data group with higher main frequency value is selected.

[0078] It should be noted that the received wave amplitude measurement error range can be determined by repeating the measurement in a uniform medium for hundreds of times, and taking the multiple of the standard deviation of the measurement value.

[0079] The smaller sound wave propagation time value indicates higher wave speed and reflects that the pile material is more compact, the larger received wave amplitude value indicates smaller sound wave energy attenuation and reflects that the pile integrity is better, and the larger main frequency value indicates that more high-frequency components are retained and reflects that the pile microstructure is more uniform.

[0080] Through the above hierarchical comparison principles, it is ensured that when multiple parameters may be contradictory, scientific selection is made according to the physical meaning and importance level of the acoustic parameters, and it is ensured that the finally selected data group can most accurately reflect the actual quality condition of the pile.

[0081] First, the sound wave propagation time of the falling and rising stages at the depth point is compared, and according to the comparison result, the stage data group meeting the conditions is directly selected, or the next level comparison is entered.

[0082] When the preferred data group cannot be determined after two levels of comparison, the data of the two stages are marked as equivalent data at the same time.

[0083] Need to explain, at this time two-stage data in reflecting the quality of the index of pile characteristics equivalent, no good or bad. Retain both rather than forced to avoid the introduction of subjective rules of human bias.

[0084] Record the data set selection results of each depth point to form a complete sequence of effective data sets.

[0085] The effective data set is screened out to eliminate distorted data caused by accidental interference, system error or detection condition fluctuation, and to retain ultrasonic feature data that can truly reflect the actual uniformity of the pile body, thereby providing reliable and accurate basis for subsequent uniformity index calculation and quality determination.

[0086] S5, based on the effective data set, the sound velocity uniformity coefficient, the wave amplitude uniformity index and the main frequency dispersion degree are calculated.

[0087] The sound velocity uniformity coefficient calculation step is as follows: based on the screened effective data set, the sound wave propagation time of each depth point is extracted, and the sound velocity value of each depth point is calculated according to the center distance of the sound measuring tube.

[0088] The sound velocity values of all depth points in the whole pile length range are counted, the average value and the standard deviation of the sound velocity values are calculated, the ratio of the standard deviation to the average value of the sound velocity values is taken as the sound velocity uniformity coefficient, and the coefficient is normalized.

[0089] Specifically, the normalization process is as follows: based on the detection data statistics of the same type of cement mixing pile, the minimum value of the sound velocity uniformity coefficient in the pile body with unqualified quality is determined as the industry limit value, the ratio of the sound velocity uniformity coefficient to the industry limit value is taken as the standardized value, if the standardized value is greater than the value 1, the sound velocity uniformity coefficient is taken as the value 1, and if the standardized value is less than the value 0, the sound velocity uniformity coefficient is taken as the value 0.

[0090] Need to explain, the sound velocity uniformity coefficient reflects the uniformity of the cement mixing pile, the sound velocity value of the cement mixing pile is positively correlated with its density, that is, the higher the density, the greater the material density of the pile body, and the faster the ultrasonic wave propagation speed.

[0091] If the pile uniformity is good and the density difference at each depth is small, the sound velocity value is concentrated around the average value, the standard deviation is small, and the sound velocity uniformity coefficient value is small.

[0092] If the pile has local loose, cavity or uneven cement content, the corresponding depth sound velocity value will be significantly low or high, resulting in an increase in the standard deviation and the sound velocity uniformity coefficient value.

[0093] The wave amplitude uniformity index calculation step is as follows: based on the screened effective data set, the received wave amplitude value of each depth point is extracted.

[0094] The average value of the received wave amplitudes of all depth points in the whole pile length range is calculated as a reference amplitude value.

[0095] The ratio of the received wave amplitude of each depth point to the reference amplitude value is calculated to obtain the relative value of the wave amplitude of each point.

[0096] The deviation of all wave amplitude relative values from the value 1 is calculated.

[0097] The arithmetic mean of all deviation values is defined as the wave amplitude uniformity index.

[0098] It should be noted that the received wave amplitude reflects the degree of energy attenuation of the ultrasonic wave in the pile body. When the pile body is dense and uniform, the sound wave energy attenuation is small, and the received wave amplitude is high. When the pile body has loose, hollow or uneven cement distribution, the sound wave scattering and attenuation are intensified, and the received wave amplitude is low.

[0099] The main frequency dispersion calculation step is as follows: based on the screened effective data set, the main frequency values of each depth point are extracted, and the maximum value and the minimum value of the main frequency values of all depth points in the whole pile length range are determined.

[0100] The difference between the maximum value and the minimum value of the main frequency is calculated to obtain the main frequency range.

[0101] The average value of the main frequency values of all depth points in the whole pile length range is calculated as a reference main frequency.

[0102] The ratio of the main frequency range to the reference main frequency is defined as the main frequency dispersion, and the main frequency dispersion is normalized.

[0103] Specifically, the normalization process has the following specific steps: based on the detection data statistics of the same type of cement mixing pile, the minimum value of the main frequency dispersion in the unqualified pile body is determined as the industry limit value, the ratio of the main frequency dispersion to the industry limit value is taken as the standardized main frequency dispersion value, if the standardized main frequency dispersion value is greater than the value 1, the main frequency dispersion value is taken as the value 1, and if the standardized main frequency dispersion value is less than the value 0, the main frequency dispersion value is taken as the value 0.

[0104] It should be noted that the main frequency reflects the frequency characteristics of the ultrasonic signal after propagating through the pile body. When the pile body material is uniform and the consistency is consistent, the frequency attenuation law of the sound wave in the propagation process is stable, the main frequency values of each depth are distributed around the reference main frequency, and the main frequency dispersion is small. When the pile body has local loose, cement block or hollow, the sound wave will be scattered and reflected, resulting in the attenuation of high frequency components, or the frequency shift caused by interface reflection, so that the local depth main frequency value is significantly reduced or increased, resulting in the increase of the main frequency range and the increase of the dispersion.

[0105] Through the collaborative analysis of the three indexes of sound velocity uniformity coefficient, wave amplitude uniformity index and main frequency dispersion, different types of uniformity defects can be captured comprehensively, the risk of missing judgment by a single index can be avoided, and the accuracy of evaluation can be ensured.

[0106] S6, generating a quality detection report of the cement mixing pile reinforced roadbed uniformity according to the sound velocity uniformity coefficient, the wave amplitude uniformity index and the main frequency dispersion.

[0107] The specific content of the quality detection report is as follows: receiving the three characteristic data of sound velocity uniformity coefficient, wave amplitude uniformity index and main frequency dispersion.

[0108] According to the numerical size of the three characteristic data, a comprehensive uniformity index is obtained by weighted fusion according to a preset weight proportion.

[0109] After normalization, the same scale is comparable, the fairness of weight distribution is ensured, and the comprehensive uniformity index can truly reflect the synergistic effect of the three dimensions.

[0110] Specifically, the comprehensive uniformity index , wherein, are the preset weights of the sound velocity uniformity coefficient, the wave amplitude uniformity index and the main frequency dispersion respectively, and , represents the sound velocity uniformity coefficient, represents the wave amplitude uniformity index, represents the main frequency dispersion.

[0111] The above formula is explained as follows: represents the conversion of the negative index into a positive index. Since are all negative indexes with smaller values being better, through the conversion of the difference between the numerical value 1 and the index value, it is consistent with the evaluation logic that the larger the comprehensive index is, the better it is, and the larger the weight is, the more significant the influence of the uniformity performance of the corresponding index on the final comprehensive result is. After normalization, the same scale is comparable, the fairness of weight distribution is ensured, and the comprehensive uniformity index can truly reflect the synergistic effect of the three dimensions.

[0112] The determination method of the preset weight proportion is as follows: collecting the detection data of the same type of cement mixing pile, including the sound velocity uniformity coefficient, the wave amplitude uniformity index and the main frequency dispersion of each pile body, and the corresponding pile body entity quality verification result.

[0113] Calculate the correlation coefficient of the sound velocity uniformity coefficient, the wave amplitude uniformity index and the main frequency dispersion with the pile body entity quality score: the larger the absolute value of the correlation coefficient is, the stronger the correlation between the index and the actual quality of the pile body is, and a higher weight should be given.

[0114] Using multiple linear regression analysis, taking the pile body entity quality score as the dependent variable and The three independent variables are taken as variables, the standardized regression coefficients of the three independent variables are calculated by a regression model, the coefficients are initial contribution degrees of the indexes, and the initial contribution degrees are normalized to obtain final weights.

[0115] The comprehensive uniformity index value is compared with preset multiple quality level threshold intervals.

[0116] If the index value is better than the first threshold value, the pile uniformity level is determined to be excellent, if the index value is between the first threshold value and the second threshold value, the pile uniformity level is determined to be qualified, and if the index value is lower than the second threshold value, the pile uniformity level is determined to be unqualified.

[0117] It should be noted that the comprehensive uniformity index combines the uniformity characteristics of the three dimensions of sound velocity, wave amplitude and main frequency, and the value size directly reflects the overall uniformity level of the pile material distribution, density and structural integrity. The larger the comprehensive uniformity index, the more uniform the stress of the pile, and the less likely to cause damage due to local stress concentration. The smaller the comprehensive uniformity index, the easier it is for local defects to become weak points, reducing the overall bearing performance.

[0118] The first threshold value and the second threshold value are selected for cement mixing pile samples under different construction conditions, ultrasonic detection and entity quality verification are performed on each pile, according to the entity quality verification result, the samples are divided into excellent, qualified and unqualified, the comprehensive uniformity index of the samples after labeling is statistically analyzed, the first threshold value is selected to have the highest identification accuracy of the excellent samples, and the second threshold value is selected to have the highest accuracy of distinguishing the qualified samples from the unqualified samples.

[0119] The threshold values preliminarily determined are applied to actual engineering detection, and the consistency of the determination results and the actual performance of the pile is tracked and verified: if a pile determined to be excellent but with actual settlement exceeding the standard is found, the first threshold value should be appropriately increased, and if a pile determined to be unqualified but with actual performance meeting the standard is found, the second threshold value should be appropriately reduced; in the present application, the first threshold value is set to 0.85, and the second threshold value is set to 0.7.

[0120] The parameters involved in the above formula are de-dimensioned to calculate their numerical values, the formula is obtained by software simulation of a large amount of data to reflect the most real situation, and the preset parameters in the formula are set by a person skilled in the art according to the actual situation.

[0121] The above embodiments can be realized wholly or partially by software, hardware, firmware or any other combination. When realized by software, the above embodiments can be realized in the form of a computer program product wholly or partially.

[0122] Those skilled in the art can understand that the modules and algorithm steps of each example described in combination with the embodiments disclosed herein can be realized in electronic hardware or a combination of computer software and electronic hardware. Whether the functions are realized in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to realize the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0123] In addition, each functional module in each embodiment of the present application can be integrated in one processing module, or each module can exist physically alone, or two or more modules can be integrated in one module.

[0124] The above is merely specific embodiments of the present application, but the protection scope of the present application is not limited thereto, any person skilled in the art can easily think of changes or replacements within the technical scope disclosed in the present application, which should be covered in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

[0125] Finally, the above is merely preferred embodiments of the present application, and is not used to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be covered in the protection scope of the present application.

Claims

1. A non-destructive testing method for the uniformity of cement-mixed pile-reinforced roadbed, characterized in that: The method comprises the following steps: S1, two vertical sounding pipes are symmetrically embedded in cement mixing piles on both sides of the roadbed, and the pipes are filled with clean water, and the ultrasonic transmitting probe and the receiving probe are respectively placed at the pipe openings; S2, the two probes are controlled to move downward from the pipe openings simultaneously, the slope value of the virtual connection line between the transmitting probe and the receiving probe relative to the horizontal plane is detected in real time, the positions of the two probes in the pipe are dynamically adjusted to the same height according to the slope value, and the pile ultrasonic characteristic data, including the sound wave propagation time, the received wave amplitude and the main frequency value, are collected; S3, when the two probes reach the pipe bottom, they are controlled to rise to the pile top simultaneously, and the slope dynamic adjustment probe operation is repeated, and the pile ultrasonic characteristic data at the same depth are collected; S4, the pile ultrasonic characteristic data collected at the same depth in the downward and upward stages are compared, and the effective data set of the pile ultrasonic characteristic data is screened; S5, the sound velocity uniformity coefficient, the amplitude uniformity index and the main frequency dispersion are calculated based on the effective data set; S6, the quality detection report of the cement mixing pile reinforced roadbed uniformity is generated according to the sound velocity uniformity coefficient, the amplitude uniformity index and the main frequency dispersion.

2. The method for nondestructive testing of the uniformity of a cement mixing pile reinforced roadbed according to claim 1, characterized in that: The specific steps of the slope value of the virtual connection line between the transmitting probe and the receiving probe relative to the horizontal plane are as follows: Two laser range finders are fixedly installed above the two sounding pipes, and the measuring beams of the two laser range finders are vertically aligned with the probes at the respective pipe openings; The two range finders are triggered to work synchronously during the downward movement of the probes, and the distances from the range finders to the top of the transmitting probe and the top of the receiving probe are respectively measured; The real-time absolute elevations of the transmitting probe and the receiving probe are respectively calculated based on the installation heights of the two range finders; The real-time elevation difference between the two probes is obtained by subtracting the absolute elevation of the transmitting probe from the absolute elevation of the receiving probe; The elevation difference is divided by the center distance between the two sounding pipes, and the quotient value is the real-time slope value of the virtual connection line between the two probes relative to the horizontal plane.

3. The method for nondestructive testing of the uniformity of a cement mixing pile reinforced roadbed according to claim 1, characterized in that: The specific content of dynamically adjusting the positions of the two probes in the pipe to the same height according to the slope value is as follows: The slope value of the virtual connection line between the real-time receiving probes in the horizontal direction, if the absolute value of the slope value is greater than zero, it is determined that there is an elevation difference between the two probes, and the adjustment process is entered, if the absolute value of the slope value is equal to zero, the current synchronous motion state is maintained; If the slope value is greater than zero when the adjustment process is entered, it indicates that the elevation of the transmitting probe is higher than that of the receiving probe, the receiving probe lags behind, and vice versa; According to the lag determination result, an acceleration adjustment instruction is output to the lifting mechanism corresponding to the lagging probe, and the current running speed of the lifting mechanism of the other probe is maintained; The slope value is dynamically converged and stabilized at zero to control the same elevation movement of the two probes.

4. The method for nondestructive testing of uniformity of cement mixing pile reinforced roadbed according to claim 3, characterized in that: The specific content of outputting the acceleration adjustment instruction to the lifting mechanism corresponding to the lagging probe is as follows: The pulse width of the acceleration adjustment instruction is positively correlated with the absolute value of the slope value; When it is monitored that the absolute value of the slope value remains monotonically decreasing in a plurality of consecutive sampling periods, the current adjustment instruction pulse width is maintained; When it is monitored that the absolute value of the slope value presents monotonically increasing in two consecutive sampling periods, the adjustment instruction pulse width is increased by a preset proportion. When the absolute value of the slope value is still greater than the absolute value of the slope value in the last sampling period after increasing the adjustment strength, the mechanism state diagnosis program is started immediately and a pre-warning signal is sent out.

5. The method for nondestructive testing of the uniformity of a cement mixing pile reinforced roadbed according to claim 1, characterized in that: The specific steps of collecting the pile body ultrasonic characteristic data are as follows: The ultrasonic analog signal propagated through the pile body is collected by the receiving probe, the collected ultrasonic analog signal is preprocessed, and the ultrasonic analog signal is converted into a digital signal; The analyzed and processed digital signal waveform is analyzed and processed, the arrival time of the first arrival wave of the ultrasonic pulse is identified, and the sound wave propagation time between the emission and the reception is calculated; The maximum peak amplitude of the received signal waveform is extracted, and the ratio of the maximum peak amplitude to the initial emission wave amplitude is calculated to obtain the relative received amplitude value; The received signal is subjected to frequency spectrum analysis, the frequency point with the maximum amplitude in the frequency spectrum diagram is determined, and the frequency value corresponding to the frequency point is extracted as the main frequency value.

6. The method for nondestructive testing of the uniformity of a cement mixing pile reinforced roadbed according to claim 1, characterized in that: The specific content of the effective data group of the pile body ultrasonic characteristic data is as follows: The pile body ultrasonic characteristic data collected in the descending stage and the ascending stage are accurately matched according to the depth coordinates to form the descending stage data group and the ascending stage data group of the same depth point; The stage data group optimization rules are formulated, and the following priority determination levels are established based on the physical characteristics of sound wave propagation: a) If the sound wave propagation time of one data group is less than that of another data group, and the difference exceeds the sound wave propagation time measurement error range, the data group with the smaller sound wave propagation time value is selected preferentially; b) If the sound wave propagation time difference of two data groups is within the sound wave propagation time measurement error range, the stage data group with the larger received amplitude value is selected preferentially; c) If the received amplitude difference is within the received amplitude measurement error range, the stage data group with the higher main frequency value is selected preferentially; Firstly, the sound wave propagation times of the descending stage and the ascending stage at the depth point are compared, and the stage data group meeting the conditions is directly selected according to the comparison result, or the next level comparison is entered; When the preferred data group cannot be determined after two levels of comparison, the data of the two stages are simultaneously retained as equivalent data. The data group selection results of each depth point are recorded to form a complete effective data group sequence.

7. The method for nondestructive testing of the uniformity of a cement mixing pile reinforced roadbed according to claim 1, characterized in that: The sound velocity uniformity coefficient calculation steps are as follows: Based on the selected effective data group, the sound wave propagation time of each depth point is extracted, and the sound velocity value of each depth point is calculated according to the sound probe center distance; The sound velocity values of all depth points in the whole pile length range are counted, the average value and the standard deviation of the sound velocity values are calculated, the ratio of the standard deviation to the average value of the sound velocity values is taken as the sound velocity uniformity coefficient, and the coefficient is normalized.

8. The method for nondestructive testing of the uniformity of a cement mixing pile reinforced roadbed according to claim 1, characterized in that: The wave amplitude uniformity index calculation steps are as follows: Based on the selected effective data group, the received amplitude values of each depth point are extracted; The average value of the received amplitudes of all depth points in the whole pile length range is calculated as the reference amplitude value; The ratio of the received amplitude of each depth point to the reference amplitude value is calculated to obtain the amplitude relative value of each point; The deviation amount of all amplitude relative values from the value 1 is calculated; The arithmetic mean value of all deviation amounts is defined as the wave amplitude uniformity index.

9. The method for nondestructive testing of the uniformity of a cement mixing pile reinforced roadbed according to claim 1, characterized in that: The main frequency dispersion calculation steps are as follows: Based on the selected effective data group, the main frequency values of each depth point are extracted, and the maximum value and the minimum value of the main frequency values of all depth points in the whole pile length range are determined; The difference between the maximum value and the minimum value of the main frequency is calculated to obtain a main frequency range; The average value of the main frequency values of all depth points in the whole pile length range is counted as a reference main frequency; The ratio of the main frequency range to the reference main frequency is defined as a main frequency dispersion, and the main frequency dispersion is normalized.

10. The method for nondestructive testing of the uniformity of a cement mixing pile reinforced roadbed according to claim 1, characterized in that: The specific content of the quality detection report is as follows: The three characteristic data of the sound velocity uniformity coefficient, the wave amplitude uniformity index and the main frequency dispersion are received; According to the numerical values of the three characteristic data, a comprehensive uniformity index is obtained by weighted fusion according to a preset weight proportion; The comprehensive uniformity index value is compared with a plurality of preset quality level threshold intervals; If the index value is better than the first-level threshold, it is determined that the pile body uniformity level is excellent, if the index value is between the first-level and the second-level threshold, it is determined that the pile body uniformity level is qualified, and if the index value is lower than the second-level threshold, it is determined that the pile body uniformity level is unqualified.

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