Guided wave detection method for quality of cast-in-situ bored pile

Abstract

According to the guided wave detection method for the quality of the cast-in-situ bored pile, the ultrasonic transducer is placed on the outer side of the steel casing, and the pouring quality of concrete in the steel casing is detected through vertical propagation of guided waves along the wall of the steel casing, so that the use of a sounding pipe is avoided, the influence of bending and blocking of the sounding pipe is avoided, and the method is more reliable. Meanwhile, by means of the detection method, it can be avoided that a hollow sounding pipe is implanted into the pile foundation, the compactness of the pile foundation can be further improved, and the bearing capacity of the pile foundation is improved. The dispersion effect of the guided waves, namely different propagation speeds of the guided waves with different frequencies, is utilized, and the guided waves with different frequencies are incident to detect dispersion change caused by non-compact concrete pouring. And the overall characterization of the pile is realized.

Description

Technical Field

[0001] The present invention relates to the field of infrastructure construction, and in particular to a guided wave detection method for the quality of bored cast-in-place piles. Background Art

[0002] Bored piles are a common foundation form and are widely used in infrastructure such as super high-rise buildings and cross-sea bridges. Bored piles are usually composed of steel casing, steel cage and filled concrete, such as Figure 1 As shown. In order to detect the pouring quality of the concrete filled in the steel casing, an ultrasonic detection tube is usually tied to the steel cage. After the concrete pouring is completed, clean water is injected into the ultrasonic detection tube, and two sets of ultrasonic transducers are placed vertically. The ultrasonic waves are transmitted and received one by one, passing through the concrete to detect the density and pouring quality of the concrete filled inside the steel casing. However, since the ultrasonic detection tube may bend or clog during construction, it is impossible to insert the ultrasonic transducer. Therefore, the existing bored pile quality inspection method based on the ultrasonic detection tube has shortcomings, especially for the inspection of ultra-long pile foundations. The probability of the acoustic detection tube being bent or clogged increases, making the acoustic detection tube inspection impossible to implement.

[0003] The differences from the prior art are as follows: Technical comparison with patent CN114235971A "A method for identifying damage shape of woven composite materials based on ultrasonic guided waves" 1. Patent CN114235971A obtains guided wave propagation characteristics through semi-analytical finite element analysis, combines a surface-deployed sensor network to collect multipath guided wave signals, and uses elliptical weighted imaging and boundary point recognition algorithms to reconstruct the damage location and shape.

[0004] This patent places guided wave transducers on the outside of the steel casing to excite guided waves of different frequencies, collect their propagation signals and inversely calculate the dispersion curve, which is then compared with the theoretical dispersion curve to evaluate the quality of concrete pouring without the need for embedded sensors and complex signal networks.

[0005] There are essential differences between the two in terms of their technical implementation solutions.

[0006] 2. Patent CN114235971A is suitable for local damage monitoring of planar structures such as composite panels, focusing on high-precision imaging and damage shape recognition. It is often used in laboratories or environments where the structure surface is completely accessible.

[0007] This patent emphasizes resistance to construction interference and does not require embedded sensors. It is suitable for non-contact overall quality detection of underground or underwater pile foundation structures and is applicable to complex engineering sites.

[0008] There are essential differences between the two in their application scenarios.

[0009] Technical comparison with patent CN108760881A "A Kelly detection method based on ultrasonic guided waves" Patent CN108760881A uses a transmission coefficient comparison method. Transducers are placed at both ends of the kelly to excite a specific mode of guided wave, measure the signal amplitude, and calculate the transmission coefficient. This coefficient is then compared with the transmission coefficient of a nondestructive standard component to determine whether the structure is defective. This method relies on the energy attenuation characteristics of guided waves in the defect area and is an amplitude comparison-based nondestructive assessment method.

[0010] This patented method, based on the principle of frequency dispersion of guided waves, excites multi-frequency guided waves outside the steel casing. By analyzing the deviation between the measured and theoretical dispersion curves, it reflects the density and uniformity of the concrete pour. This method emphasizes the inversion of dispersion characteristics and the fitting of theoretical curves, enabling quantitative evaluation without the need for reference components.

[0011] There are essential differences between the two in detection methods and technical principles.

[0012] 2. Patent CN108760881A is mainly used to detect the structural integrity of metal drill pipes in scenarios such as oil drilling or coal mining, and is suitable for mechanical components in industrial manufacturing or service stages.

[0013] This patent is applied to pile foundation engineering, especially for problems such as easy pipe blockage and deep burial during concrete pouring, and emphasizes the assessment of the in-service quality of underground structures.

[0014] There are essential differences between the two in their application scenarios. Summary of the Invention

[0015] In order to solve the above technical problems, the present invention proposes a guided wave detection method for the quality of bored cast-in-place piles. An ultrasonic transducer is placed on the outside of the steel casing, and the quality of concrete pouring in the steel casing is detected by vertical propagation of guided waves along the wall of the steel casing, thereby avoiding the use of an acoustic detection tube, being unaffected by the bending or blockage of the acoustic detection tube, and being more reliable.

[0016] To achieve the above object, the technical solution adopted by the present invention is: A guided wave detection method for bored pile quality, characterized by comprising the following steps: Step S1: Calculate the theoretical dispersion curve of the guided wave When guided waves propagate in a steel pipe, they exhibit three modes: longitudinal expansion, torsion, and bending. The radial, circumferential, and longitudinal displacement fields of the steel pipe are expressed as follows: (1) (2) (3) Where z is the depth of the pile, , and are the radial, circumferential and longitudinal amplitudes, respectively, The longitudinal and torsional modes are axisymmetric, while the bending mode is non-axisymmetric. For axisymmetric modes, n = 0, and for bending modes, n = 1, 2, 3, ..., Therefore, the longitudinal mode is denoted by L(0, m), the torsional mode is denoted by T(0, m), and the bending mode is denoted by F(n, m), where n = 1, 2, 3, ..., and m = 1, 2, 3, ...; Step S2: Inversely calculate the dispersion curve using the measured signal The ultrasonic transducer is placed outside the steel casing or along the thickness direction to obtain the time-displacement signal of the ultrasonic guided wave. The ultrasonic transducer can transmit or receive ultrasonic waves and includes at least one exciter and at least one receiver. When there is more than one exciter, the exciters are evenly distributed. When there is more than one receiver, the receivers are evenly distributed. The signals of each receiver are averaged. The excitation signal is a swept frequency signal, and the frequency changes linearly from f1 to f2 within time T. Step S3: judge the concrete pouring quality of the entire pile foundation by the difference between the measured dispersion curve and the theoretical dispersion curve Perform short-time Fourier transform on the received signal of the receiver to obtain the measured dispersion curve spectrum. Calibrate the maximum value of each mode spectrum. At one frequency, one mode selects a maximum value to form the measured dispersion curve. Compare the measured dispersion curve with the theoretical dispersion curve and calculate the difference index var: (4) Where m is the modal order, l is the total number of observed modes, f is the frequency of the received signal, which varies linearly from the excitation frequency f1 to f2, real represents the measured dispersion curve, theory represents the theoretical dispersion curve, and the subscript fm represents the wave velocity of the m mode at the frequency f. The difference index threshold value (threshold) for the unqualified state is determined based on engineering experience or experiments. When var is less than the threshold, it indicates that the concrete pouring quality of the entire pile foundation is qualified. When var is greater than the threshold, it indicates that there are quality problems with the concrete pouring of the entire pile foundation.

[0017] As a preferred technical solution of the present invention: in step S1, the steel casing is set to be cylindrical, and a coordinate system of the steel casing is established with the center of the upper and lower end surfaces of the steel casing as the central axis.

[0018] As a preferred technical scheme of the present application: in step S2, When the ultrasonic transducer is placed outside the steel casing, the ultrasonic transducer is fixed on the outer wall of the steel casing and is uniformly placed along the circumferential direction of the steel casing; when the ultrasonic transducer is arranged along the thickness direction of the steel casing, the ultrasonic transducer is fixed on one end surface of the steel casing and is uniformly placed along the circumferential direction of the steel casing on the end surface.

[0019] Compared with the prior art, the present application has the following advantages: The present application places the ultrasonic transducer outside the steel casing, detects the concrete pouring quality inside the steel casing through the vertical propagation of the guided wave along the wall of the steel casing, thereby avoiding the use of the sounding pipe and the influence of the bending and blocking of the sounding pipe, and being more reliable. At the same time, using the detection method can avoid implanting the hollow sounding pipe inside the pile foundation, and can further improve the compactness of the pile foundation and the bearing capacity of the pile foundation. The dispersion effect of the guided wave is utilized, that is, the propagation speed of the guided wave of different frequencies is different, the guided wave of different frequencies is injected, and the dispersion change caused by the non-compactness of the concrete pouring is detected. The overall characterization of the pile is realized. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a typical cast-in-place pile structure in the prior art; Figure 2 is a flowchart of the present application; Figure 3 is a coordinate system diagram of the steel casing; Figure 4 is a theoretical dispersion curve diagram; Figure 5 is an ultrasonic transducer installation diagram Figure I ; Figure 6 is an ultrasonic transducer installation diagram Figure II ; Figure 7 is a waveform diagram of the excitation signal; Figure 8 is a measured dispersion curve diagram.

[0021] LIST OF REFERENCE NUMERALS 1, steel casing; 2, reinforcement cage; 3, sounding pipe; 4, ultrasonic transducer. DETAILED DESCRIPTION

[0022] The present application will be further described in detail below in combination with the drawings and specific embodiments: Bored piles are a common foundation method, widely used in infrastructure such as super-high-rise buildings and cross-sea bridges. To inspect the pouring quality of concrete within a steel casing, an ultrasonic detection tube 3 is typically tied to a steel cage 2. An ultrasonic transducer 4 is placed inside the tube, transmitting and receiving ultrasonic waves through the concrete to detect the density and pouring quality of the concrete inside the steel casing. However, the ultrasonic detection tube 3 can bend or become blocked during construction, making it impossible to insert the ultrasonic transducer.

[0023] In order to solve the above technical problems, Figure 2 As shown, the present invention proposes a guided wave detection method for bored pile quality, comprising the following steps: Step S1: Calculate the theoretical dispersion curve of the guided wave like Figure 3 As shown in the figure, when the guided wave propagates in the steel pipe, it exhibits three modes: longitudinal expansion, torsion, and bending. The radial, circumferential, and longitudinal displacement fields of the steel pipe are expressed as follows: (1) (2) (3) Where z is the depth of the pile, , and are the radial, circumferential and longitudinal (depth) amplitudes, The longitudinal and torsional modes are axisymmetric, while the bending mode is non-axisymmetric. For axisymmetric modes, n = 0, and for bending modes, n = 1, 2, 3, ..., Therefore, the longitudinal mode is represented by L(0, m), which is an axisymmetric mode, the torsional mode is represented by T(0, m), which is an axisymmetric mode, and the bending mode is represented by F(n, m), which is a non-axisymmetric mode, where n = 1, 2, 3..., and m = 1, 2, 3..., the longitudinal wave propagating along the depth direction of the steel casing 1, the dispersion curve is as follows Figure 4 As shown; Step S2: Inversely calculate the dispersion curve using the measured signal like Figure 5-6 As shown, the ultrasonic transducer 4 is placed outside the steel casing 1, or placed along the thickness direction, to obtain the time-displacement signal of the ultrasonic guided wave. The ultrasonic transducer 4 can transmit or receive ultrasonic waves, and includes at least one exciter and at least one receiver. When there is more than one exciter, the exciters are evenly distributed. When there is more than one receiver, the receivers are evenly distributed. The signals of each receiver are averaged. The excitation signal is a sweep frequency signal. The frequency changes linearly from f1 to f2 within T time. The waveform is as follows Figure 7 As shown; Step S3: judge the concrete pouring quality of the entire pile foundation by the difference between the measured dispersion curve and the theoretical dispersion curve Perform short-time Fourier transform on the received signal of the receiver to obtain the measured dispersion curve spectrum. Calibrate the maximum value of each mode spectrum. At one frequency, one mode selects a maximum value to form the measured dispersion curve, such as Figure 8 As shown, Compare the measured dispersion curve with the theoretical dispersion curve and calculate the difference index var: (4) Where m is the modal order, l is the total number of observed modes, f is the frequency of the received signal, which varies linearly from the excitation frequency f1 to f2, real represents the measured dispersion curve, theory represents the theoretical dispersion curve, and the subscript fm represents the wave velocity of the m mode at the frequency f. The difference index threshold value (threshold) for the unqualified state is determined based on engineering experience or experiments. When var is less than the threshold, it indicates that the concrete pouring quality of the entire pile foundation is qualified. When var is greater than the threshold, it indicates that there are quality problems with the concrete pouring of the entire pile foundation.

[0024] In step S1 , the steel casing 1 is configured to be cylindrical, and a coordinate system of the steel casing 1 is established with the centers of the upper and lower end surfaces of the steel casing 1 as central axes.

[0025] In step S2, When the ultrasonic transducer 4 is placed on the outside of the steel casing 1, the ultrasonic transducer 4 is fixed on the outer wall of the steel casing 1 and is evenly placed along its circumferential direction. When the ultrasonic transducer 4 is arranged along the thickness direction of the steel casing 1, the ultrasonic transducer 4 is fixed on one end face of the steel casing 1 and is evenly placed along the circumferential direction of the steel casing 1 on the end face.

[0026] Because guided waves have a dispersion effect, i.e., guided waves of different frequencies have different propagation velocities, the dynamic response of the steel casing 1 at different frequencies can be detected by injecting guided waves of different frequencies. Weak concrete pouring may cause changes in the guided wave dispersion pattern.

[0027] At the same time, pile foundation defects such as mud inclusion, broken piles, and segregation may cause reflection of guided waves within the steel casing 1.

[0028] Therefore, the application firstly calculates a theoretical dispersion curve of the guided wave, then inversely calculates the dispersion curve through the measured signal, and finally judges the concrete pouring quality of the whole pile foundation through the difference between the measured dispersion curve and the theoretical dispersion curve.

[0029] The application places the ultrasonic transducer 4 outside the steel casing 1, detects the concrete pouring quality in the steel casing 1 through the vertical propagation of the guided wave along the wall of the steel casing 1, thereby avoiding the use of the sounding pipe 3 and being not affected by the bending and blockage of the sounding pipe 3, and being more reliable. Meanwhile, the use of the detection method can avoid the implantation of the hollow sounding pipe 3 in the pile foundation, and can further improve the compactness of the pile foundation and the bearing capacity of the pile foundation. The dispersion effect of the guided wave is utilized, that is, the propagation speed of the guided wave of different frequencies is different, the guided wave of different frequencies is injected, and the dispersion change caused by the non-compactness of the concrete pouring is detected. The overall characterization of the pile is realized.

[0030] The application can be extended to the whole process monitoring of one pile from pouring, setting, deterioration and damage, the overall performance change of the pile is reflected through the var, and the corresponding relationship between the var and the mechanical parameters such as the ultimate bearing capacity and the overall elastic modulus of the pile can be established, thereby realizing the characterization of various physical states of the pile foundation based on dispersion.

[0031] The above is only a preferred embodiment of the application, and does not limit the application in any other form, and any modification or equivalent change made according to the technical essence of the application still falls within the scope of the application.

Claims

1. A guided wave detection method for bored pile quality, characterized in that: The steps include: Step S1: Calculate the theoretical dispersion curve of the guided wave When guided waves propagate in a steel pipe, they exhibit three modes: longitudinal expansion, torsion, and bending. The radial, circumferential, and longitudinal displacement fields of the steel pipe are expressed as follows: （1） （2） （3） Where z is the depth of the pile, , and are the radial, circumferential and longitudinal amplitudes, respectively, The longitudinal and torsional modes are axisymmetric, while the bending mode is non-axisymmetric. For axisymmetric modes, n = 0, and for bending modes, n = 1, 2, 3, ..., Therefore, the longitudinal mode is denoted by L(0, m), the torsional mode is denoted by T(0, m), and the bending mode is denoted by F(n, m), where n = 1, 2, 3, ..., and m = 1, 2, 3, ...; Step S2: Inversely calculate the dispersion curve using the measured signal An ultrasonic transducer (4) is placed outside the steel casing (1) or along the thickness direction to obtain a time-displacement signal of an ultrasonic guided wave. The ultrasonic transducer (4) can transmit or receive ultrasonic waves and includes at least one exciter and at least one receiver. When there is more than one exciter, the exciters are evenly distributed. When there is more than one receiver, the receivers are evenly distributed. The signals of each receiver are averaged. The excitation signal is a swept frequency signal, and the frequency changes linearly from f1 to f2 within time T. Step S3: judge the concrete pouring quality of the entire pile foundation by the difference between the measured dispersion curve and the theoretical dispersion curve Perform short-time Fourier transform on the received signal of the receiver to obtain the measured dispersion curve spectrum. Calibrate the maximum value of each mode spectrum. At one frequency, one mode selects a maximum value to form the measured dispersion curve. Compare the measured dispersion curve with the theoretical dispersion curve and calculate the difference index var: （4） Where m is the modal order, l is the total number of observed modes, f is the frequency of the received signal, which varies linearly from the excitation frequency f1 to f2, real represents the measured dispersion curve, theory represents the theoretical dispersion curve, and the subscript fm represents the wave velocity of the m mode at the frequency f. The difference index threshold value (threshold) for the unqualified state is determined based on engineering experience or experiments. When var is less than the threshold, it indicates that the concrete pouring quality of the entire pile foundation is qualified. When var is greater than the threshold, it indicates that there are quality problems with the concrete pouring of the entire pile foundation.

2. The method for detecting the quality of bored piles according to claim 1, wherein: In step S1, the steel casing (1) is configured to be cylindrical, and a coordinate system of the steel casing (1) is established with the centers of the upper and lower end surfaces of the steel casing (1) as central axes.

3. The guided wave detection method for bored pile quality according to claim 1, characterized in that: In step S2, When the ultrasonic transducer (4) is placed outside the steel casing (1), the ultrasonic transducer (4) is fixed on the outer wall of the steel casing (1) and is evenly placed along its circumferential direction. When the ultrasonic transducer (4) is arranged along the thickness direction of the steel casing (1), the ultrasonic transducer (4) is fixed on one end face of the steel casing (1) and is evenly placed on the end face along the circumferential direction of the steel casing (1).

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