A geological tube wave detection signal processing method for vertical string-shaped karst cave in karst landform

Abstract

The application discloses a kind of geological tube wave detection signal processing methods for vertical string-shaped karst cave in karst topography, applicable to geological exploration field, this method is mainly by first carrying out wavelet threshold denoising method processing to vertical string-shaped karst cave in karst topography geological tube wave detection signal to remove noise, mean filtering is carried out to obtain direct tube wave waveform and reflected tube wave waveform, two-dimensional filtering and fourier transform are carried out to reflected tube wave waveform to obtain uplink reflected tube wave waveform and downlink reflected tube wave waveform, finally waveform is analyzed to obtain time-depth curve, barycentric frequency-depth curve and reflection coefficient-depth curve to be used for the quantitative interpretation of tube wave detection result.The tube wave signal processing method proposed in the application has the advantages of strong anti-interference, small error, etc., compared with the traditional tube wave signal processing method, and has better applicability under the geological conditions of vertical string-shaped karst cave in karst topography.

Description

Technical Field

[0001] The present invention relates to a tube wave detection signal processing method, and in particular to a tube wave detection signal processing method for karst landform vertical string cave geology. Background Art

[0002] The word "karst" originates from a Yugoslavian place name. Karst landforms primarily refer to various landforms formed by the dissolution of limestone by groundwater and the accompanying mechanical action. Under the influence of water, these areas often contain caves of varying sizes, vividly referred to as "string caves." During construction projects in karst areas, the presence of caves can pose risks such as foundation instability, building subsidence, or collapse. Therefore, it is essential to identify and address these underground caves, such as through grouting reinforcement.

[0003] Currently, the core drilling method is often used to detect caves in karst areas. While this method is intuitive and effective, it is also costly and has a limited detection range. Tube wave detection, a new and increasingly popular detection method, involves transmitting a low-frequency, high-energy pulse signal from a transmitter probe into a liquid-filled borehole. The transmitter vibrates and interacts with the pore fluid, generating tube waves between the fluid and the borehole wall. After propagating for a certain distance, the tube waves generate reflection waves as the geological conditions change. These reflections are received by a receiver probe located synchronously near the transmitter probe and output as a tube wave detection time profile via an electronic recorder. Analysis of these tube wave detection time profiles reveals the distribution of caves near the borehole. However, current analysis of tube wave detection results often relies on amplitude changes along the measured line of the tube wave detection time profile. This approach has significant drawbacks, being susceptible to interference and resulting in large errors. Furthermore, the complex and variable nature of caves in karst regions makes this analysis method unsuitable for field applications. Therefore, it is necessary to develop a method for processing geological tube wave detection signals for vertical string caves in karst landforms to minimize the interference of uncertain factors and present the essential characteristics of the signals, so as to facilitate accurate interpretation and analysis of the signals and ensure the smooth progress of subsequent projects. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for processing geological tube wave detection signals for vertical string caves in karst landforms, which has the advantages of strong anti-interference and small error compared with traditional signal processing methods.

[0005] The purpose of the present invention can be achieved by adopting the following technical solutions:

[0006] S101, perform tube wave detection on the vertical string cave geological drilling holes in the karst landform to obtain the tube wave detection time profile results;

[0007] S102, using a wavelet threshold denoising method to reduce the noise of the tube wave detection time profile result to obtain a noise-reduced tube wave detection time profile;

[0008] S103, processing the denoised tube wave detection time profile using a mean filter method to obtain a direct tube wave waveform, and subtracting the direct tube wave waveform from the denoised tube wave detection time profile to obtain a reflected tube wave waveform;

[0009] S104, applying frequency-wavenumber threshold two-dimensional filtering and Fourier transform to the reflected tube wave waveform to obtain an uplink reflected tube wave waveform and a downlink reflected tube wave waveform;

[0010] S105, calculating the centroid frequency of each survey line of the tube wave detection time profile after noise reduction, and obtaining a centroid frequency-depth map based on the calculation results;

[0011] S106, performing first wave positioning on the direct tube wave waveform, obtaining the arrival time of each tube wave, and drawing a time-depth graph;

[0012] S107, calculating the reflection coefficient of each survey line, and drawing a reflection coefficient-depth curve based on the calculation results;

[0013] S108, quantitatively interpreting the tube wave detection results based on the obtained center of gravity frequency-depth curve, time-depth curve, and reflection coefficient-depth curve.

[0014] Furthermore, in the above S102, the threshold of the wavelet threshold denoising method is selected as rigsure, the threshold function is selected as the soft threshold function, and the calculation formula is shown in formula (1):

[0015]

[0016] Where, ω j,k is the wavelet coefficient; is the quantized wavelet coefficient; sign is the sign function; λ is the threshold. The selection method is rigsure.

[0017] Furthermore, in the above S103, the mean filtering method takes a certain depth as the center, reads the N most adjacent survey line data, takes the amplitude mean as the amplitude value of the depth, constructs the amplitude-time curve as the filtering result of the point, changes the depth point and repeats it. After all depth points are completed, the direct tube wave waveform can be obtained, where N is the mean filtering parameter value range of 10 to 20.

[0018] Furthermore, in the above S105, the calculation formula of the center of gravity frequency is formula (2),

[0019]

[0020] Where FC is the center of gravity frequency and P(f) is the power spectrum of the signal.

[0021] Furthermore, in the above S107, the calculation formula of the reflection coefficient is shown in formula (3),

[0022]

[0023] Where k is the reflection coefficient, A(ω) is the direct tube amplitude spectrum, and B(ω) is the upward reflection tube amplitude spectrum. The beneficial effects of the present invention are:

[0024] Compared with the prior art, the present invention is a method for processing geological tube wave detection signals for vertical string caves in karst landforms. Compared with traditional signal processing methods, the present invention has the advantages of strong anti-interference and small error. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 : This is a flow chart of a method for processing geological tube wave detection signals for vertical string caves in karst landforms according to the present invention. DETAILED DESCRIPTION

[0026] In order to have a clearer understanding of the technical features, purposes and effects of the present invention, specific embodiments of the present invention are described with reference to the accompanying drawings.

[0027] like Figure 1 As shown in FIG, the present invention proposes a flow chart of a method for processing geological tube wave detection signals for vertical string caves in karst landforms, and the flow chart includes the following contents.

[0028] S101, perform tube wave detection on the vertical string cave geological drilling holes in the karst landform to obtain the tube wave detection time profile results;

[0029] S102, using a wavelet threshold denoising method to reduce the noise of the tube wave detection time profile result to obtain a noise-reduced tube wave detection time profile;

[0030] Specifically, in the above S102, the threshold of the wavelet threshold denoising method is selected as rigsure, the threshold function is selected as the soft threshold function, and the calculation formula is shown in formula (1):

[0031]

[0032] Where, ω j,k is the wavelet coefficient; is the quantized wavelet coefficient; sign is the sign function; λ is the threshold. The selection method is rigsure.

[0033] S103, processing the denoised tube wave detection time profile using a mean filter method to obtain a direct tube wave waveform, and subtracting the direct tube wave waveform from the denoised tube wave detection time profile to obtain a reflected tube wave waveform;

[0034] Specifically, in the above S103, the mean filtering method takes a certain depth as the center, reads the N most adjacent survey line data, takes the amplitude mean as the amplitude value of the depth, constructs the amplitude-time curve as the filtering result of the point, changes the depth point and repeats it. After all depth points are completed, the direct tube wave waveform can be obtained, where N is the mean filtering parameter value range of 10 to 20.

[0035] S104, applying frequency-wavenumber threshold two-dimensional filtering and Fourier transform to the reflected tube wave waveform to obtain an uplink reflected tube wave waveform and a downlink reflected tube wave waveform;

[0036] S105, calculating the centroid frequency of each survey line of the tube wave detection time profile after noise reduction, and obtaining a centroid frequency-depth map based on the calculation results;

[0037] Specifically, in the above S105, the calculation formula of the center of gravity frequency is formula (2),

[0038]

[0039] Where FC is the center of gravity frequency and P(f) is the power spectrum of the signal.

[0040] S106, performing first wave positioning on the direct tube wave waveform, obtaining the arrival time of each tube wave, and drawing a time-depth graph;

[0041] S107, calculating the reflection coefficient of each survey line, and drawing a reflection coefficient-depth curve based on the calculation results;

[0042] Specifically, in the above S107, the calculation formula of the reflection coefficient is shown in formula (3),

[0043]

[0044] Where k is the reflection coefficient, A(ω) is the amplitude spectrum of the direct tube, and B(ω) is the amplitude spectrum of the uplink reflection tube.

[0045] S108, quantitatively interpreting the tube wave detection results based on the obtained center of gravity frequency-depth curve, time-depth curve, and reflection coefficient-depth curve.

[0046] In the above embodiment, the present invention discloses a method for processing geological tube wave detection signals for vertical string-like karst caves. The method mainly performs wavelet threshold denoising on the geological tube wave detection signals for vertical string-like karst caves to remove noise, then performs mean filtering to obtain direct tube wave waveforms and reflected tube wave waveforms, performs two-dimensional filtering and Fourier transform on the reflected tube wave waveforms to obtain uplink reflected tube wave waveforms and downlink reflected tube wave waveforms, and finally analyzes the waveforms to obtain time-depth curves, centroid frequency-depth curves, and reflection coefficient-depth curves for quantitative interpretation of the tube wave detection results. Compared with traditional tube wave signal processing methods, the tube wave signal processing method proposed in the present invention has the advantages of strong anti-interference and small error, and at the same time has better applicability under the geological conditions of vertical string-like karst caves in karst landforms.

[0047] The above description is an illustrative embodiment of the present invention and is not intended to limit the scope of the present invention. Any equivalent changes and modifications made by those skilled in the art without departing from the concept and principle of the present invention should fall within the scope of protection of the present invention.

Claims

1. A method for processing geological tube wave detection signals for vertical string caves in karst landforms, characterized in that: The method comprises the following steps: 1) Conduct tube wave detection on the vertical string-like karst cave geological drilling holes to obtain the tube wave detection time profile results; 2) Using the wavelet threshold denoising method to reduce the noise of the tube wave detection time profile results to obtain the tube wave detection time profile after noise reduction; 3) The denoised tube wave detection time profile is processed using the mean filter method to obtain the direct tube wave waveform. The reflected tube wave waveform is obtained by subtracting the direct tube wave waveform from the denoised tube wave detection time profile. 4) Applying frequency-wavenumber threshold two-dimensional filtering and Fourier transform to the reflected tube wave waveform to obtain the uplink reflected tube wave waveform and the downlink reflected tube wave waveform; 5) Calculate the centroid frequency of each measurement line of the noise-reduced tube wave detection time profile, and obtain a centroid frequency-depth map based on the calculation results; 6) Locate the first wave of the direct tube wave waveform, obtain the arrival time of each tube wave, and draw a time-depth diagram; 7) Calculate the reflection coefficient of each survey line and draw a reflection coefficient-depth curve based on the calculation results; 8) Quantitatively interpret the tube wave detection results based on the obtained center of gravity frequency-depth curve, time-depth curve and reflection coefficient-depth curve.

2. The method for processing geological tube wave detection signals for vertical string caves in karst landforms according to claim 1, characterized in that: In the wavelet threshold denoising method 2), the threshold is selected as rigsure, the threshold function is selected as the soft threshold function, and the calculation formula is shown in formula (1): Where, ω j,k is the wavelet coefficient; is the quantized wavelet coefficient; sign is the sign function; λ is the threshold; the selection method is rigsure.

3. The method for processing geological tube wave detection signals for vertical string caves in karst landforms according to claim 1, characterized in that: In the above 3), the mean filtering method takes a certain depth as the center, reads the data of N most adjacent survey lines, takes the amplitude mean as the amplitude value of the depth, constructs the amplitude-time curve as the filtering result of the point, changes the depth point and repeats it. After all depth points are completed, the direct tube wave waveform can be obtained, where N is the mean filtering parameter value range of 10 to 20.

4. The method for processing geological tube wave detection signals for vertical string caves in karst landforms according to claim 1, characterized in that: The calculation formula of the center of gravity frequency in 5) is formula (2), Where FC is the center of gravity frequency and P(f) is the power spectrum of the signal.

5. The method for processing geological tube wave detection signals for vertical string caves in karst landforms according to claim 1, characterized in that: The calculation formula of the reflection coefficient in 7) is shown in formula (3), Where k is the reflection coefficient, A(ω) is the amplitude spectrum of the direct tube, and B(ω) is the amplitude spectrum of the uplink reflection tube.

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