CN109765303B

CN109765303B - Detection method for void degree behind lining structure

Info

Publication number: CN109765303B
Application number: CN201910108424.2A
Authority: CN
Inventors: 龙士国; 唐海翔
Original assignee: Xiangtan University
Current assignee: Xiangtan University
Priority date: 2019-01-18
Filing date: 2019-01-18
Publication date: 2021-06-15
Anticipated expiration: 2039-01-18
Also published as: CN109765303A

Abstract

The invention discloses a method for detecting the degree of rear void of a lining structure, which comprises the steps of carrying out sound wave detection outside a lining to be detected, carrying out data processing on a received pulse echo signal, extracting a characteristic parameter based on a frequency domain signal from a sound wave signal frequency domain diagram, and calculating a frequency energy density ratio alpha of the extracted characteristic parameter so as to judge the degree of rear void of the lining structure. The method for detecting the void degree behind the lining structure provided by the invention is used for carrying out sound wave detection on the lining in the tunnel; carrying out data processing on the received sound wave signals; extracting a characteristic parameter based on a frequency domain signal from a frequency domain graph; and defining the parameter as a frequency energy density ratio alpha so as to judge whether the lining is hollow and the hollow degree. The method has simple process and obvious advantages.

Description

Detection method for void degree behind lining structure

Technical Field

The invention provides a detection method, relates to the technical field of engineering structure defect detection, and particularly relates to a detection method for the void degree behind a tunnel lining.

Background

In recent decades, the construction of railways and highways in China has been in the high-speed development period. However, due to the wide regions and the complicated and variable geological conditions, the difficulty of construction in many mountain regions is greatly increased. The tunnel is used as a main structural form in underground engineering, and the engineering problem is well solved. The application of the tunnel not only shortens the driving distance and improves the driving efficiency, but also plays a certain role in protecting the natural environment.

However, tunnel engineering is mostly underground, and has concealment, complexity and uncertainty in the construction process, and once quality problems occur, serious engineering accidents are often caused. The lining of the tunnel body is a supporting structure built by reinforced concrete along the periphery of the tunnel body and is used for bearing the pressure of surrounding rocks and preventing the surrounding rocks from deforming, and the common tunnel quality problem is that the lining is hollow behind the back. Fig. 1 is a schematic view of a tunnel structure without a void, and fig. 2 is a schematic view of a tunnel structure with a void. Due to the limitation of the prior art, due to the concealment of the lining grouting process, insufficient grouting pressure or shielding effect of the steel bars can cause the phenomenon that the lining and the surrounding rock are separated, as shown in fig. 2. When the lining structure has the cavity, the bearing capacity of the lining structure can be reduced, and the lining structure can be failed seriously, so that the quality detection of the lining structure is particularly important, and if the cavity can not be detected in time, huge engineering problems can be caused and huge loss is brought.

The acoustic wave detection is an effective nondestructive detection method and is widely applied to the detection of internal defects of the structure. The acoustic wave method has the advantages of easy excitation, simple detection process, convenient operation and the like. And sound waves with different frequencies can be selected for detection according to different detection objects. Research shows that much information capable of describing the internal defects of the structure is hidden in echo signals received by an acoustic wave instrument, and some domestic researchers develop related detection research aiming at tunnel nondestructive detection by an acoustic wave method. For example, the Chinese patent application discloses a method for detecting the void of tunnel lining concrete, which comprises the steps of firstly manufacturing a tunnel lining concrete standard module according to the construction process of the tunnel lining concrete, then measuring the sound wave reflection parameter of the standard module, and taking the sound wave reflection parameter as the standard parameter; then arranging a group of measuring points on the surface of the lining concrete to be measured, arranging a sound wave frequency transmitting and receiving vibration pickup at each measuring point, wherein the sound wave frequency transmitting and receiving vibration pickup is connected with a sound wave frequency transmitting and receiving instrument; and measuring the sound wave reflection parameters of each measuring point of the lining concrete to be measured by a sound wave frequency transmitting and receiving instrument, comparing the sound wave reflection parameters of each measuring point with the standard parameters, and obtaining the void condition of the lining concrete at each measuring point according to the comparison result. The test block needs to be manufactured, and the test block has a large difference from the actual engineering condition, so that the size degree of the void cannot be judged.

However, few studies on the aspect of how to quantitatively detect the properties of the cavity are needed, and accurate detection of the size of the internal defect of the structure is a research focus in the field of acoustic wave detection, and is one of the problems which are urgently needed to be solved in the technical field of engineering structure defect detection.

Disclosure of Invention

Aiming at the technical problems in the prior art, the invention provides a method for detecting the void degree behind a lining structure, which extracts characteristic parameters (such as sound wave signals) in frequency spectrum data to perform data processing, so that the precise detection of the void degree behind the lining structure is realized.

In order to solve the technical problems, the technical scheme provided by the invention is as follows:

the method for detecting the void degree behind the lining structure comprises the following steps:

step a) exciting a pulse wave at a lining part to be detected, and receiving a pulse echo signal reflected inside a lining structure to be detected;

step b) carrying out data processing on the pulse echo signals obtained in the step a), and calculating frequency and mass density E corresponding to adjacent peaks of a frequency domain graph of the sound wave signals_f；

Step c) the frequency density E obtained in step b)_fAnd comparing and judging the back void degree of the measured lining part.

Preferably, the frequency density E is calculated by the formula (1)_f：

Wherein the frequency energy density E_fIs the average energy of the sound wave signal in a certain frequency band, A (f) is the variation curve of the frequency domain graph of the sound wave signal, f₁Is the starting frequency, f, of the first peak of the frequency domain plot of the acoustic signal₂Is the cut-off frequency of the first peak of the frequency domain plot of the acoustic signal.

It should be noted that E is due to_fThe frequency density varies irregularly according to different test environments, and the void can be judged only by the numerical value of the frequency density (the larger the frequency density is, the higher the void degree is), so that the void height behind the lining structure is difficult to be judged directly by the single frequency density, and therefore, the frequency density E is obtained by the inventor_fFurther data processing is performed to obtain formula (2), i.e. a characteristic parameter frequency energy density ratio alpha is defined, therebyJudging the void degree behind the lining structure, wherein the formula (2) is as follows:

wherein, the frequency energy density ratio alpha is the average energy ratio of the acoustic wave signals in two frequency bands, A (f) is the variation curve of the frequency domain diagram of the acoustic wave signals, f_1’Is the starting frequency, f, of the first peak of the frequency domain plot of the acoustic signal_2’Is the cut-off frequency, f, of the first peak of the frequency domain plot of the acoustic signal_3’Is the starting frequency, f, of the second peak of the frequency domain plot of the acoustic signal_4’Is the cut-off frequency of the second peak of the frequency domain plot of the acoustic signal.

Preferably, the method for detecting the void degree behind the lining structure comprises the following steps:

step a') exciting pulse waves at a lining part to be detected, and receiving pulse echo signals reflected inside a lining structure to be detected;

step b ') carrying out data processing on the pulse echo signals obtained in the step a') to obtain a sound wave signal frequency domain diagram;

and c ') selecting frequencies corresponding to adjacent peaks of the sound wave signal frequency domain diagram obtained in the step b'), calculating a frequency-energy density ratio alpha through a formula (2), and judging the back void degree of the measured lining part.

And the pulse echo is subjected to data processing by adopting a fast Fourier transform method.

The variation curve A (f) of the sound wave signal frequency domain graph is obtained by a fast Fourier transform method.

It is worth mentioning that when the lining structure is detected by the sound wave, the inventor finds that two obvious frequency peaks exist when a cavity exists and only one obvious frequency peak exists when no cavity exists from comparison analysis on a sound wave signal frequency domain diagram, and conjectures that the second frequency peak possibly has relationship with the existence of the cavity, thereby obtaining the frequency quantity density formula (1) of the frequency section where the peak exists

The test result shows that the frequency energy density of the peak frequency band shows a linear increasing trend along with the increase of the size of the hollow hole. In order to eliminate the influence of different operators and operation methods, the frequency energy density of the frequency band with the second frequency peak value and the frequency energy density of the frequency band with the first frequency peak value are subjected to ratio to obtain a frequency energy density ratio alpha calculation formula (2), the frequency energy density ratio alpha also shows a linear increasing trend along with the increase of the radius of the cavity, and meanwhile, because the same operator and the same operation method are adopted, the frequency energy density ratio alpha can be regarded as a dimensionless parameter defined for avoiding errors, so that the test result is more accurate.

Compared with the prior art, the method for detecting the void degree behind the lining structure provided by the invention has the advantages that the acoustic wave detection is carried out on the lining in the tunnel; carrying out data processing on the received sound wave signals; extracting a characteristic parameter based on a frequency domain signal from a frequency domain graph; and defining the parameter as a frequency energy density ratio alpha so as to judge whether the lining is hollow and the hollow degree. The method has simple process and obvious advantages:

1. the invention can judge whether the cavity appears by measuring the frequency density, overcomes the defects that the position of the cavity can only be roughly determined in the prior art and the degree of the cavity is difficult to judge, and can roughly describe the property of the cavity by calculating alpha by the method;

2. the invention determines the void degree of the lining by the value of the frequency energy density ratio alpha and the ratio of different frequency segments of the frequency domain signal is defined as the frequency energy density ratio alpha, and the determination result is visual and accurate.

3. The invention adopts a method for comparing the energy densities of two different frequency bands, can effectively eliminate external interference such as manual error or uneven contact surface in the detection process, has accurate detection result and reduces the accident occurrence probability.

Drawings

FIG. 1 is a schematic view of a tunnel structure without voids;

FIG. 2 is a schematic diagram of a tunnel structure with voids;

FIG. 3 is a schematic view of a finite element model in the presence of voids in the lining;

FIG. 4 is a schematic view of a finite element model with no void present in the lining;

FIG. 5a is a schematic diagram showing the propagation of impulse waves with a lining of 10cm, 12cm, 14cm, 16cm, 18cm and 20 cm;

FIG. 5b is a schematic diagram showing the propagation of pulse waves with no void in the lining and 2cm, 4cm, 6cm and 8cm respectively;

FIG. 6a is a frequency domain diagram of acoustic signals of lining with 10cm, 12cm, 14cm, 16cm, 18cm and 20cm of pulse wave fast Fourier transform;

FIG. 6b is a frequency domain diagram of acoustic signals of the liner without a cavity and with 2cm, 4cm, 6cm and 8cm of pulse wave fast Fourier transform;

FIG. 7 is a graph of the frequency energy density ratio for different cavity heights;

FIG. 8 is a schematic diagram of an experimental model;

FIG. 9 is a contour plot of experimental model test results.

Detailed Description

The following detailed description of embodiments of the invention refers to the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating the present invention, are given by way of illustration and explanation only, not limitation.

Example 1 mathematical model testing

(1) Selecting a material model, setting the elastic modulus (E), the density (rho) and the Poisson ratio (v) of related materials according to the actual conditions (shown in figures 1 and 2) in tunnel construction engineering, respectively establishing finite element models of partial tunnel structures (namely tunnel structures with the cavity heights of 0, 2cm, 4cm, 6cm, 8cm, 10cm, 12cm, 14cm, 16cm, 18cm and 20 cm) with cavities of different sizes and without cavities in COMSOL multiprophy, and using the material parameters as shown in Table 1:

TABLE 1

	E(GPa)	ρ(kg/m³)	v
				Concrete and its production method	33	2600	0.2
Rock	30	2160	0.3
				Water-proof layer	3.5	1350	0.315

(2) As shown in fig. 3 and 4, fig. 3 is a schematic view of a finite element model when a lining has a void, fig. 4 is a schematic view of a finite element model when a lining does not have a void, a stress wave of 5K is excited at a position a in the model, and a stress wave reflection signal, i.e., a time domain vibration signal, is received at a point B (0.05 m in fig. 3 is a distance between two corresponding points A, B, i.e., a distance between an excitation point and a receiving point, i.e., a distance between two acoustic wave transducers) at a position B5 cm on the right side of the position a;

(3) filtering the time domain vibration signals (waveform signals) received by each finite element model obtained in the step (2), wherein the low cut-off frequency is set to be 100Hz, the high cut-off frequency is set to be 10KHz, and the obtained pulse wave propagation situation schematic diagrams are shown in FIG. 5a and FIG. 5 b;

(4) performing fast Fourier transform on the time domain waveform obtained by filtering in the step (3) to obtain a frequency domain signal, wherein a frequency domain diagram of the obtained sound wave signal is shown in FIGS. 6a and 6 b;

(5) judging two adjacent energy peaks in the graph by observing the sound wave signal frequency domain graph obtained in the step (4), substituting the frequency corresponding to the frequency domain signal peak obtained in the step (4) into a formula (2) to calculate the frequency-energy density ratio alpha:

In this example, the frequency energy density ratio α was calculated for each of the void heights of 0, 2cm, 4cm, 6cm, 8cm, 10cm, 12cm, 14cm, 16cm, 18cm and 20cm, and as is clear from FIGS. 5a and 5b, f was calculated_1’Set to 0kHz, f_2’Set to 5kHz, f_3’Set to 5kHz, f_4’The frequency energy density ratio α and the void height were obtained as shown in table 2, using 10kHz as the calculation result.

TABLE 2

Height of cavity	α
			0	0.17937
0.02	0.25173
		0.04	0.27253
0.06	0.4679
		0.08	0.79981
0.1	0.83063
		0.12	1.11669
0.14	1.44065
		0.16	1.79569
0.18	1.91164
		0.2	1.92411

(6) The data in table 2 are subjected to data fitting, the linear relationship between the frequency energy density ratio α and the void height after fitting is shown in fig. 7, and the corresponding linear relationship formula (3) is as follows:

H＝0.09912α+0.000962

wherein H is the cavity height in m.

As can be seen from fig. 7, when there is no cavity, the frequency energy density ratio α is 0.25, and the frequency energy density ratio tends to increase linearly as the cavity height increases.

Because a plurality of factors interfering the detection result exist in the actual measurement, although the result obtained by the detection method provided by the invention cannot accurately measure the void height behind the lining structure, when the tunnel structure to be detected in the engineering is measured, the error of the judgment result of the void degree behind the lining structure can be controlled within 5cm, and the requirement of the engineering on the tunnel quality is completely met. Therefore, a measurement result alpha obtained by performing sound wave detection on the lining structure to be detected can be used for judging the size of the void behind the lining structure, and the specific judgment method comprises the following steps: substituting alpha into formula (3), or correspondingly matching the point value of alpha according to fig. 7, so as to roughly judge the size of the hole; if alpha is 0-0.5, the height of the cavity is 0-5 cm; when alpha is 0.5-1, the height of the cavity is 5-10 cm; when alpha is 1-1.5, the height of the cavity is 10-15 cm; when alpha is 1.5-2, the height of the cavity is 15-20 cm; when α is greater than 2, the height of the cavity is greater than 20 cm. The above-described determination of the void height is summarized in table 3.

TABLE 3

α	Height of cavity (cm)
		0～0.5	0～5
0.5～1	5～10
		1～1.5	10～15
1.5～2	15～20
		>2	>20

Example 2 Experimental model validation

(1) Pouring a solid two-layer concrete model, and arranging a semi-conical cavity (the size of the cavity can be directly measured) in the two-layer concrete model, as shown in figure 8;

(2) using a TH402 sound wave tester of the subject group to acquire data, exciting stress waves through a TH-CCJ rare earth super-magnetic transducer of a super-magnetic transducer, and receiving the stress waves through a TH piezoelectric transducer;

(3) 305 measuring points are divided on a test surface of a concrete layer model containing a cavity (in order to verify the accuracy of the detection method provided by the invention, the invention divides the measuring points on the test surface as many as possible, the number of the measuring points is determined by the size of the test surface, the number of the measuring points is the number of the measuring points uniformly distributed on the test surface), the measuring point interval selected in the embodiment is 5cm, the selection of the measuring point interval is determined according to the actual condition and the actual requirement (the void degree of a certain point can be obtained by testing once), and the test is respectively carried out on each measuring point to obtain a time domain vibration signal;

(4) [ 5 ] the same as in example 1, wherein the α value at each measurement point obtained in step (5) is shown in Table 4.

TABLE 4

(6) The results were plotted as contour plots, see FIG. 9. The contour map adopted in this embodiment is only for making the result look more intuitive, and a conclusion can be reached by any data display method in the prior art, which is not described herein again.

As can be seen from fig. 9, the dark regions are regions without voids, the white regions are regions with voids, the lighter the color is, the larger the size of the voids is, that is, the size of the voids can be roughly determined by the α value, the larger the α value is, the larger the size of the voids is, and as can be seen from the legend beside the white regions, the white regions have the largest α, the gray regions have the lowest order, and the black is the smallest, and the degree of void in each place of the sample can be seen. When the void height corresponding to the measurement result needs to be estimated, the measured alpha value can be substituted into the table 3, and the range of the void height value at the back of the lining structure can be obtained, and compared with the preset void height value, the error is within a reasonable range, and the result is shown in the table 5. The height range greater than 20cm is not described in detail in this embodiment, and since the correctness of the detection method provided by the present invention is not affected, a person skilled in the art can continue to measure according to the detection method provided by the present invention as needed, and details are not described herein.

TABLE 5

Example 2 measurement of alpha	Calculating void height value Range (cm)	Preset cavity height value (cm)
			2.12335	>20	21
1.87408	15～20	19
			1.32883	10～15	13
0.66349	5～10	9

The foregoing is considered as illustrative of the preferred embodiments of the invention and is not to be construed as limiting the invention in any way. Although the present invention has been described with reference to the preferred embodiments, it is not intended to be limited thereto. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical spirit of the present invention should fall within the protection scope of the technical scheme of the present invention, unless the technical spirit of the present invention departs from the content of the technical scheme of the present invention.

Claims

1. The method for detecting the rear void degree of the lining structure is characterized in that sound wave detection is carried out outside a lining to be detected, received pulse echo signals are subjected to data processing, characteristic parameters based on frequency domain signals are extracted from a sound wave signal frequency domain diagram, and the extracted characteristic parameters are substituted into a formula (2) to calculate a frequency energy density ratio alpha, so that the rear void degree of the lining structure is judged;

wherein, the frequency energy density ratio alpha is the average energy ratio of the acoustic wave signals in two frequency bands, A (f) is the variation curve of the frequency domain diagram of the acoustic wave signals, f_1’Is the starting frequency, f, of the first peak of the frequency domain plot of the acoustic signal_2’Is the cut-off frequency, f, of the first peak of the frequency domain plot of the acoustic signal_3’Is the frequency domain of acoustic signalsStarting frequency, f, of the second peak of the graph_4’Is the cut-off frequency of the second peak of the frequency domain plot of the acoustic signal.

2. The method for detecting the void degree behind the lining structure is characterized by comprising the following steps of:

Step c) the frequency density E obtained in step b)_fComparing and judging the back void degree of the measured lining part;

wherein the frequency density E_fIs the average energy of the sound wave signal in a certain frequency band.

3. The method for detecting the degree of void behind a lining structure according to claim 1, comprising the steps of:

4. The method for detecting the void degree behind the lining structure according to claim 1 or 2, wherein the pulse echo is subjected to data processing by using a fast Fourier transform method.

5. The method for detecting the degree of void behind a lining structure according to claim 1, wherein the curve A (f) of the frequency domain graph of the acoustic signal is obtained by a fast Fourier transform method.

6. Method for detecting the degree of void behind a lining structure according to claim 2, wherein the frequency density E is calculated by formula (1)_f：

Wherein the frequency density E_fIs the average energy of the sound wave signal in a certain frequency band, A (f) is the variation curve of the frequency domain graph of the sound wave signal, f₁Is the starting frequency, f, of the first peak of the frequency domain plot of the acoustic signal₂Is the cut-off frequency of the first peak of the frequency domain plot of the acoustic signal.