A multi-channel annular array imaging method for pile integrity detection

Abstract

The present invention provides a multi-channel annular array imaging method for pile integrity detection, comprising: a plurality of acceleration sensors are evenly distributed in a ring shape along the circumference and pasted on the side of the pile, and the acceleration sensors are connected to a multi-channel array receiving device based on FPGA; a reflected time domain signal is obtained by repeatedly striking the top of the pile foundation with a nylon hammer, and a time domain signal with high repeatability is collected; a multi-channel signal coupling algorithm is used to overlap the time domain information in the same phase to obtain a time domain enhancement signal, so as to realize one-dimensional damage location detection; a HHT sub-modal processing algorithm is used to perform HHT on the time domain signal with high repeatability to obtain a three-dimensional Hilbert spectrum of time-frequency-energy, and a ring array imaging algorithm is applied to obtain a three-dimensional imaging diagram of the pile, and the type and position of the pile body defects are quantitatively displayed through the three-dimensional imaging diagram. The present invention solves the technical problem that only one-dimensional time domain curves and frequency response curves can be obtained at present, resulting in low defect location accuracy.

Description

Technical Field

[0001] The invention relates to the field of material structure damage detection, and in particular to a multi-channel annular array imaging method for pile integrity detection. Background Art

[0002] With the advancement and development of civil engineering construction technology, pile foundations have been widely used in high-rise buildings, heavy factories, port terminals and other projects. At present, the commonly used non-destructive testing methods for pile foundations include static load method, high strain method and ultrasonic method. The static load method and high strain method are greatly limited in engineering testing due to their low efficiency, relatively large detection error and easy damage to the pile foundation. In contrast, the ultrasonic method and low strain method are widely used due to their advantages of convenient detection, high accuracy and relatively low cost.

[0003] Based on the one-dimensional wave theory of the plane section assumption, the theoretical basis of the old stress wave reflection method simplifies the pile into a one-dimensional rod, and only places a single acceleration sensor on the top of the pile to receive the sound wave signal generated by the knocking. Therefore, only a one-dimensional time domain curve and frequency response curve can be obtained. The accuracy is low when locating defects, and the ability to capture weak reflection waves generated by special defects is poor, and it is easily interfered by high-frequency clutter. At the same time, the obtained signal requires a high level of experience for the inspection personnel, and the imaging results are not intuitive, which can easily lead to misjudgment and omission of defects. Summary of the invention

[0004] In view of the shortcomings in the prior art, the present invention provides a multi-channel annular array imaging method for pile foundation integrity detection, which solves the technical problem that current commercial pile foundation detection instruments can only obtain one-dimensional time domain curves and frequency response curves, resulting in low defect positioning accuracy.

[0005] The present invention achieves the above technical objectives through the following technical means.

[0006] A multi-channel annular array imaging method for pile integrity detection, comprising:

[0007] S01: A plurality of acceleration sensors are evenly distributed in a ring along the circumferential direction and attached to the side of the foundation pile. The acceleration sensors are connected to a multi-channel array receiving device based on FPGA to form a multi-channel ring array imaging detection platform. The size of the ring changes according to the circumference of the foundation pile. The acceleration sensors are used to collect damage signals in the pile foundation structure.

[0008] S02: Use a nylon hammer to repeatedly strike the top of the pile foundation to obtain multi-channel reflection time domain signals and collect time domain signals with high repeatability;

[0009] S03: using a multi-channel signal coupling algorithm, the time domain information obtained by the multi-channel annular array imaging detection platform is superimposed in phase to obtain a time domain enhanced signal, thereby realizing one-dimensional damage location detection;

[0010] S04: Perform HHT on the highly repeatable time domain signal obtained in step S02 by using the HHT sub-modal processing algorithm inside the FPGA-based multi-channel array receiving device to obtain a three-dimensional Hilbert spectrum of time-frequency-energy. Apply the annular array imaging algorithm to obtain a three-dimensional imaging diagram of the foundation pile, and quantitatively display the type and location of the pile body defects through the three-dimensional imaging diagram.

[0011] Furthermore, the number of the acceleration sensors is eight.

[0012] Furthermore, the acceleration sensor is adhered to the side of the pile by butter.

[0013] Furthermore, the specific steps of performing HHT in step S04 are: decomposing the time domain signal with high repeatability obtained in step S02 into several IMF components by using the EMD method, and then performing Hilbert transform to derive a three-dimensional Hilbert time-frequency spectrum of time-frequency-energy.

[0014] Furthermore, in step S04, the circular array imaging algorithm is applied to obtain the three-dimensional imaging diagram of the pile foundation, which is specifically:

[0015] The frequency axis of the Hilbert spectrum is converted to a position where one of the acceleration sensors is located as a base point, and the other acceleration sensors are deflected around the piezoelectric piece, and the time axis is converted to the distance of wave propagation. The energy size is displayed by grayscale value, and a distance-circumference-amplitude multi-channel annular array deflection grayscale map is obtained;

[0016] By analyzing the one-dimensional damage location detection results in step S03, the pile bottom is identified, the pile length is calculated according to the existing wave velocity, and a cylindrical model with the same length as the pile body is established;

[0017] The grayscale image is coupled to the cylindrical model, the x-axis direction in the grayscale image is parallel to the length direction of the cylindrical model, and the three-dimensional imaging image of the pile foundation is obtained by capturing the highlighted part in the grayscale image and placing it in a concave and convex state of equal proportion.

[0018] Furthermore, for any of the IMF component functions c j (τ) to y j (t) is defined as:

[0019]

[0020] Where: τ is the integral variable of Hilbert transform, using c j (τ) and y j (t) The obtained analytical signal z j (t) is:

[0021]

[0022] Where: a j (t) is the instantaneous amplitude of the signal, θ j (t) is the signal phase;

[0023] or j (t) is expressed as:

[0024]

[0025] Where: A is the instantaneous amplitude of the signal, λ is the signal attenuation factor, f is the signal oscillation frequency, is the initial phase of the signal;

[0026] After each of the IMF components completes the Hilbert transform, the amplitude spectrum function X(t) is expressed as:

[0027]

[0028] Where: a i (t) and ω i (t) are the instantaneous amplitude and angular velocity of the i-th IMF component, respectively.

[0029] Beneficial effects of the present invention:

[0030] The multi-channel annular array imaging method provided by the present invention uses a coupling agent to bond a plurality of acceleration sensors arranged in an annular shape on the side surface of the pile body near the top of the foundation pile, and the size of the annular shape can be changed according to the circumference of the pile, thereby constructing a high-precision damage detection platform with one shot and multiple receptions, and enhancing the amplitude of the reflected signal by superimposing the multi-channel annular array, so that the reflected wave of the typical defect is more obvious; performing HHT analysis on the waveform, the waveform signal can be extracted by frequency division, which helps to eliminate the influence of non-steady-state signals, and the signal positioning after processing is more accurate, and the accuracy is higher than that of traditional commercial low-strain detection; using the HHT analysis signal to obtain a three-dimensional Hilbert spectrum of time-frequency-energy, constructing an annular array imaging algorithm, and quantitatively displaying the type and position of the pile body defects through three-dimensional imaging, the imaging is intuitive, easy to judge, and avoids interference from human subjective factors. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A schematic diagram of an acceleration sensor arrangement according to an embodiment of the present invention;

[0032] Figure 2 is a time domain diagram of a reflection signal according to an embodiment of the present invention;

[0033] Figure 3 It is a three-dimensional imaging diagram of the detection result according to an embodiment of the present invention.

[0034] Figure 4 It is a deflection grayscale image of a multi-channel annular array according to an embodiment of the present invention. DETAILED DESCRIPTION

[0035] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and should not be construed as limiting the present invention.

[0036] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "upper", "lower", "axial", "radial", "vertical", "horizontal", "inner", "outer" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limiting the present invention.

[0037] In the present invention, unless otherwise clearly specified and limited, the terms "installed", "connected", "connected", "fixed" and the like should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0038] The following first describes in detail a multi-channel annular array imaging method for pile integrity detection according to an embodiment of the present invention in conjunction with the accompanying drawings, including the following steps:

[0039] S01: A number of acceleration sensors are evenly distributed in a ring along the circumferential direction and attached to the side of the foundation pile. The acceleration sensors are connected to a multi-channel array receiving device based on FPGA through wires to form a multi-channel ring array imaging detection platform. The size of the ring varies according to the circumference of the foundation pile. The larger the pile diameter, the more sensors are needed. The acceleration sensors are used to collect damage signals in the pile foundation structure.

[0040] In this embodiment, there are eight acceleration sensors, which are attached to the side of the pile by coupling agent butter.

[0041] S02: The center position of the top of the foundation pile is used as the excitation point. The excitation point is hit multiple times with a nylon hammer. After receiving the excitation force, the excitation point generates a stress wave. The stress wave is mainly propagated in the pile body in the form of longitudinal waves. When the stress wave passes through the defect, a reflected wave will be generated due to the impedance change. Each reflected wave reaches each acceleration sensor in turn and generates a vibration effect, thereby obtaining a multi-channel reflection time domain signal. After multiple hammer strikes, a time domain signal with high repeatability is collected, such as Figure 2 The FPGA device shown in (a) arranges the time domain signals transmitted by each channel in parallel according to the channels to obtain a time domain curve;

[0042] S03: using a multi-channel signal coupling algorithm, the time domain information obtained by the multi-channel annular array imaging detection platform is superimposed in phase to obtain a time domain enhanced signal, thereby realizing one-dimensional damage location detection;

[0043] like Figure 2 (b) Analyze the superimposed time domain curve, and determine the first wave and the pile bottom reflection wave by the known wave velocity and pile length. If there is no obvious reflection peak between the first wave and the pile bottom reflection wave, the pile body is judged to be intact and the low strain detection is ended; if there is an obvious reflection wave between the first wave and the pile bottom reflection wave, it is judged that there is a defect, and the one-dimensional preliminary detection result is used as a reference for the three-dimensional array imaging detection, and the next step is entered;

[0044] S04: Perform HHT on the highly repeatable time domain signal obtained in step S02 by using the HHT sub-modal processing algorithm inside the FPGA-based multi-channel array receiving device to obtain a three-dimensional Hilbert spectrum of time-frequency-energy. Apply the annular array imaging algorithm to obtain a three-dimensional imaging diagram of the foundation pile, and quantitatively display the type and location of the pile body defects through the three-dimensional imaging diagram.

[0045] The specific steps of HHT are: decomposing the time domain signal with high repeatability obtained in step S02 into several IMF components by using the EMD method, such as Figure 3 The effective IMF components are derived as shown in FIG. 1 , and a three-dimensional Hilbert spectrum of time-frequency-energy can be obtained by performing Hilbert transform processing on the IMF component functions of each channel.

[0046] For any of the IMF component functions c j (τ) to y j (t) is defined as:

[0047]

[0048] Where: τ is the integral variable of Hilbert transform, using c j (τ) and y j (t) The obtained analytical signal z j (t) is:

[0049]

[0050] Where: a j (t) is the instantaneous amplitude of the signal, θ j (t) is the signal phase;

[0051] or j (t) is expressed as:

[0052]

[0053] Where: A is the instantaneous amplitude of the signal, λ is the signal attenuation factor, f is the signal oscillation frequency, is the initial phase of the signal;

[0054] After each of the IMF components completes the Hilbert transform, the amplitude spectrum function X(t) is obtained, which is expressed as:

[0055]

[0056] Where: a i (t) and ω i (t) are the instantaneous amplitude and angular velocity of the i-th IMF component, respectively.

[0057] Using the annular array imaging algorithm, the three-dimensional imaging diagram of the pile foundation is as follows:

[0058] Step A1: The frequency axis of the Hilbert spectrum is converted to the position of one of the acceleration sensors as the base point, and the other acceleration sensors are deflected around the piezoelectric piece. The time axis is converted to the distance of wave propagation, and the energy size is displayed by the grayscale value to obtain the distance-circumference-amplitude multi-channel annular array deflection grayscale map, such as Figure 4 As shown;

[0059] Step A2: by analyzing the one-dimensional damage location detection results in step S03, the pile bottom is identified, the pile length is calculated according to the existing wave velocity, and a cylindrical model with the same length as the pile body is established;

[0060] Step A3: coupling the grayscale image to the cylindrical model, wherein the x-axis direction in the grayscale image is parallel to the length direction of the cylindrical model, and obtaining a three-dimensional imaging image of the pile foundation by capturing the highlighted portion of the grayscale image and placing it in equal proportions of concave and convex conditions.

[0061] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0062] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A multi-channel annular array imaging method for pile integrity detection, characterized in that: include: S01: A plurality of acceleration sensors are evenly distributed in a ring along the circumferential direction and attached to the side of the foundation pile. The acceleration sensors are connected to a multi-channel array receiving device based on FPGA to form a multi-channel ring array imaging detection platform. The size of the ring changes according to the circumference of the foundation pile. The acceleration sensors are used to collect damage signals in the pile foundation structure. S02: Use a nylon hammer to hit the top of the pile foundation multiple times to obtain multi-channel reflection time domain signals and collect time domain signals with high repeatability; S03: using a multi-channel signal coupling algorithm, the time domain information obtained by the multi-channel annular array imaging detection platform is superimposed in phase to obtain a time domain enhanced signal, thereby realizing one-dimensional damage location detection; S04: Perform HHT on the highly repeatable time domain signal obtained in step S02 by using the HHT sub-modal processing algorithm inside the FPGA-based multi-channel array receiving device to obtain a three-dimensional Hilbert spectrum of time-frequency-energy. Apply the annular array imaging algorithm to obtain a three-dimensional imaging diagram of the foundation pile, and quantitatively display the type and location of the pile body defects through the three-dimensional imaging diagram.

2. The multi-channel annular array imaging method for pile integrity detection according to claim 1, characterized in that: The number of the acceleration sensors is eight.

3. The multi-channel annular array imaging method for pile integrity detection according to claim 1, characterized in that: The acceleration sensor is adhered to the side surface of the foundation pile by butter.

4. The multi-channel annular array imaging method for pile integrity detection according to claim 1, characterized in that: The specific steps of performing HHT in step S04 are: decomposing the time domain signal with high repeatability obtained in step S02 into a plurality of IMF components by using the EMD method, and then performing Hilbert transform to derive a three-dimensional Hilbert time-frequency spectrum of time-frequency-energy.

5. The multi-channel annular array imaging method for pile integrity detection according to claim 1, characterized in that: In step S04, the circular array imaging algorithm is applied to obtain the three-dimensional imaging diagram of the pile foundation: The frequency axis of the Hilbert spectrum is converted into a position where one of the acceleration sensors is located as a base point, and the other acceleration sensors are deflected around the acceleration sensor at the base point. The time axis is converted into the distance of wave propagation, and the energy size is displayed by grayscale value to obtain a distance-circumference-amplitude multi-channel annular array deflection grayscale map; By analyzing the one-dimensional damage location detection results in step S03, the pile bottom is identified, the pile length is calculated according to the existing wave velocity, and a cylindrical model with the same length as the pile body is established; The grayscale image is coupled to the cylindrical model, the x-axis direction in the grayscale image is parallel to the length direction of the cylindrical model, and the three-dimensional imaging image of the pile foundation is obtained by capturing the highlighted part in the grayscale image and placing it in a concave and convex state of equal proportion.

6. The multi-channel annular array imaging method for pile integrity detection according to claim 4, characterized in that: For any of the IMF component functions c j (τ) to y j (t) is defined as: Where: τ is the integral variable of Hilbert transform, using c j (τ) and y j (t) The obtained analytical signal z j (t) is: Where: a j (t) is the instantaneous amplitude of the signal, θ j (t) is the signal phase; or j (t) is expressed as: Where: A is the instantaneous amplitude of the signal, λ is the signal attenuation factor, f is the signal oscillation frequency, is the initial phase of the signal; after each of the IMF components completes the Hilbert transform, the amplitude spectrum function X(t) is expressed as: Where: a i (t) and ω i (t) are the instantaneous amplitude and angular velocity of the i-th IMF component, respectively.

Images