A comprehensive non-destructive testing method for latent defects in the initial support of a water diversion tunnel

Abstract

The present invention discloses a comprehensive non-destructive detection method for hidden defects in the initial support of a water diversion tunnel, which includes the following steps: using a dual-channel ground penetrating radar to detect the shallow and deep parts of the initial support respectively to obtain electromagnetic wave data; performing forward modeling on the electromagnetic wave values and comparing the forward modeling results with the measured electromagnetic wave data to preliminarily determine the positions of various hidden defects in the depth direction; using the impact echo audio method to detect the change in medium density of hidden defects in the shallow layer to determine the types of shallow hidden defects; using the seismic reflection / refraction method to detect the change in medium density of hidden defects in the deep layer to determine the types of deep hidden defects; and using the engineering borehole coring method for verification. The present invention realizes the rapid and accurate diagnosis of the types and scopes of hidden defects in the initial support of the water diversion tunnel, ensuring the high-quality construction and long-term safe operation of the initial support project of the tunnel. Moreover, the detection cost is low and it is convenient for popularization and application.

Description

Technical Field

[0001] The invention belongs to the technical field of water conservancy and hydropower engineering, and particularly relates to a comprehensive non-destructive testing method for concealed defects in the initial support of a diversion tunnel. Background Art

[0002] (Long-distance) The initial support of a diversion tunnel refers to the support structure that is timely (or appropriately) constructed after the tunnel excavation to control the deformation of the surrounding rock and prevent collapse, including forms such as anchor bolts, shotcrete, combined support of shotcrete and wire mesh, combined support of shotcrete, anchor bolts and wire mesh, and combined support of the above support structures and steel frames.

[0003] Due to various factors during construction and use, different types and degrees of concealed defects will occur in the initial support of the tunnel, endangering the safety of the overall tunnel structure. At the same time, the construction progress of the tunnel is tight. Usually, after the initial support is completed, it is necessary to immediately master its engineering quality, and the testing work needs to be carried out in a timely manner and the test results need to be provided in real time. Therefore, it is urgent to master the causes of various concealed defects and preventive measures to correctly guide the construction unit to carry out corresponding construction operations for treatment, ensure the project quality, and ensure the high-quality construction and long-term safe operation of the tunnel lining and support project.

[0004] The types and formation causes of hidden defects in the initial support of tunnels can be roughly divided into the following six categories: (1) Cavities behind the initial support: The problem of cavities behind the initial support (behind the lining) is the most common disease in long-distance water diversion tunnels. As a result, phenomena such as uneven backfilling of the initial support, upward bulging of the arch crown, and cracking and spalling of the inner edge of the lining are common, which in turn affects the bonding degree between the lining, support and surrounding rock. In severe cases, it can lead to the instability and collapse of the overall structure. The main reasons for the formation of cavities behind the initial support are as follows: (a) Due to the shrinkage characteristics of concrete, the sprayed concrete cannot be closely attached to the rock surface, resulting in voids and forming cavities; (b) The overexcavation is serious and the thickness of the sprayed concrete is too large. Under the action of gravity, the concrete sinks as a whole, forming cavities; (c) Blasting causes the surrounding rock to be broken. When excavating the lower bench, the upper arch feet are displaced downward or even spalled under the action of blasting vibration and gravity. The cavities formed after spalling can be repaired by spraying concrete visually, but the cavities formed due to sliding are not easy to detect. Coupled with the low visibility of the working environment, there are potential quality and safety hazards; (2) Concrete voids: When spraying concrete during construction, it may be blocked by steel frames, anchor bolts or formwork, resulting in an overhead phenomenon and forming voids after shaping; (3) Incomplete consolidation grouting of the tunnel: After overexcavation of Class IIIb and IV surrounding rocks, the grouting positions of the entire cross-section of the tunnel may not reach the top or arch feet of the tunnel, resulting in local incomplete consolidation; (4) Distribution of internal steel frames and steel bars: Steel arch frames or advanced guide rods are distributed in the initial support where temporary support is required at the tunnel entrance or the front end of the heading face, making there are metal substances in the initial support structure, which interferes with traditional radar detection; (5) Thickness of support and lining: The number of construction passes of local sprayed concrete is insufficient, resulting in insufficient thickness of the initial support; (6) Karst: There may be karst, solution cavities, etc. behind Class IIIb, IV or V surrounding rocks, which are difficult to identify.

[0005] At present, the main detection methods for hidden defects in the initial support of tunnels mainly include: ground penetrating radar method, impact echo method, seismic reflection method, drilling method, etc.

[0006] Ground Penetrating Radar Method: The detection principle of ground penetrating radar is based on the fact that the waveform characteristics of electromagnetic waves change when propagating in different electrically conductive media, and then the distribution of the media is inferred. Ground penetrating radar uses the reflection of electromagnetic waves, such as the in-phase axis or the amplitude strength, to identify defects. It has high resolution, fast detection speed, and is non-destructive to the object being measured, and is widely used in the quality inspection of concrete. Although ground penetrating radar has achieved certain success in detecting concrete defects, due to the interference of metals such as metal bolts in the initial support structure on the electromagnetic waves transmitted or received by ground penetrating radar, there are multiple solutions for anomalies during image interpretation, making it difficult to accurately determine the support and hidden defects behind. Because there are a large number of advanced support bolts, advanced small ducts or steel arches (made of metal) in the initial support structure, it will bring strong interference to the detection and evaluation of the ground penetrating radar method based on the electromagnetic wave method, resulting in inaccurate detection or misjudgment. In addition, the traditional single-channel ground penetrating radar method can only detect 1 survey line within a certain depth range at a time, and there is a lack of joint interpretation with other methods. If direct drilling verification is carried out, the detection efficiency is low, and the damage rate to the structure is high, which is generally difficult to achieve in general construction, resulting in construction and management personnel being unable to accurately grasp the quality of the initial support, bringing potential hazards to the stability of the tunnel structure.

[0007] Impact Echo Method: The impact echo method uses the attenuation of elastic wave reflected acoustic waves to identify defects. It is not affected by metals, is non-destructive to the object being measured, and is widely used in the detection of structural delamination or voids. Although the impact echo method has achieved certain success in detecting concrete defects, due to the large scale of the initial support structure of the tunnel, the impact echo method is generally point measurement, and the detection efficiency is low. At the same time, the hammering excitation energy is small, and it is impossible to identify the reflected acoustic waves from a large cavity behind the support.

[0008] Seismic Reflection Method: The seismic reflection method uses the energy attenuation of elastic wave refraction or reflected waves to identify defects. It is not affected by metals, is non-destructive to the object being measured, and is widely used in the detection of large cavities in stratum structures or bad geological bodies. Although the seismic reflection method has achieved certain success in detecting concrete defects, because the thickness of the shotcrete in the initial support of the tunnel is generally within 0.5 meters, the excitation energy of seismic refraction or reflected waves is too large, making it difficult to identify the internal defects of the thin-layer concrete. At the same time, the diameter of the diversion tunnel is generally large, and the high-altitude operation difficulty of the seismic reflection method is large and the detection efficiency is low.

[0009] In view of the deficiencies of the above physical detection methods, such as single function, incomplete detection results (limitations or misjudgments), and inability to comprehensively grasp various hidden defects in the initial support of the tunnel, the present invention proposes a method for jointly diagnosing hidden defects in the initial support of a diversion tunnel by using a comprehensive non-destructive detection technology based on different physical methods, so as to achieve rapid and accurate detection of hidden defects. Summary of the Invention

[0010] In view of the problems existing in the above-mentioned prior art, the present invention provides a comprehensive non-destructive testing method for hidden defects in the initial support of a water diversion tunnel.

[0011] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0012] A comprehensive non-destructive testing method for hidden defects in the initial support of a water diversion tunnel, comprising the following steps:

[0013] S1. Adopt the geological radar method, use a dual-channel geological radar to detect the shallow and deep parts of the initial support respectively, and obtain the geological radar electromagnetic wave data of hidden defects at different depths of the initial support;

[0014] S2. Carry out forward modeling of the numerical values of the geological radar electromagnetic waves of typical hidden defects in the initial support, and compare the results of the forward modeling with the measured geological radar electromagnetic wave data. Initially judge the positions of various hidden defects in the depth direction through the similarity of the in-phase axis characteristics and chromatographic characteristics;

[0015] S3. Adopt the impact echo audio method to detect the change in the medium density of hidden defects in the shallow layer, and determine the type of shallow hidden defects through the defect inversion color plate of the audio echo;

[0016] S4. Adopt the seismic reflection / refraction method of the seismic imaging method to detect the change in the medium density of hidden defects in the deep layer, and determine the type of deep hidden defects through the distribution, size and positive and negative of the wave amplitude;

[0017] S5. Use the engineering drilling and coring method to verify the abnormal areas where hidden defects are detected by the geological radar method, the impact echo audio method and the seismic imaging method, and determine the types and ranges of hidden defects in the abnormal areas of the initial support of the tunnel.

[0018] Preferably, in step S1, the dual-channel geological radar uses two types of antennas, high-frequency and low-frequency, at one time, and two survey lines at the same position are detected at one time, and the shallow and deep parts of the initial support are detected simultaneously.

[0019] Preferably, the survey lines of the dual-channel geological radar are arranged at the left and right arch shoulders and the arch crown respectively.

[0020] Preferably, in step S2, it further includes: performing inversion processing on the typical hidden defect spectrum of the geological radar to improve the resolution of the geological radar method.

[0021] Preferably, the audio survey line using the impact echo method is arranged in the abnormal area at the arch shoulder or the arch crown, and the survey line using the seismic imaging method is arranged in the abnormal area at the arch shoulder or the arch crown.

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] (1) The comprehensive non-destructive testing method of the present invention is a comprehensive non-destructive testing method that can quickly and accurately detect hidden defects behind the initial support. It solves the technical problem that a single testing method (ground penetrating radar method) is easily interfered by metals inside the initial support structure, resulting in inaccurate or misjudged detection and discrimination.

[0024] (2) The comprehensive non-destructive testing method of the present invention can quickly and accurately detect hidden defects in the initial support, solving the technical problems of limited detection or misjudgment, poor real-time detection, low detection efficiency, and various restricted working areas of a single testing method (seismic reflection method, impact echo method).

[0025] (3) The present invention first applies methods such as ground penetrating radar method, seismic reflection method, and impact echo method to the joint interpretation of the depth (plane position) boundary and spatial distribution range of hidden defects in the initial support of diversion tunnels. That is, first, through the ground penetrating radar method, combined with the forward simulation recognition of typical electromagnetic wave defects and the inversion technology of typical ground penetrating radar maps, it is initially determined that there are differences in medium density of hidden defects at different depths. Then, the impact echo audio method is used to detect the change in medium density of hidden defects in the shallow layer, and combined with the defect inversion color plate of audio echo to determine the type of shallow hidden defects; then, the seismic reflection refraction / reflection method is used to detect the change in medium density of hidden defects in the deep layer, and the type of deep hidden defects is determined by the distribution, size, and positive and negative of the wave amplitude. Finally, the physical properties of hidden defects in the initial support of the tunnel are jointly interpreted and determined by comprehensively considering the change in dielectric properties of electromagnetic waves and the change in medium density of elastic waves, thereby realizing the rapid and accurate detection of the type and scope of hidden defects in the initial support of diversion tunnels. It provides technical support for the safety of the initial support structure of long-distance diversion tunnels, ensuring the high-quality construction and long-term safe operation of tunnel lining and support projects. Moreover, the detection method of the present invention has low detection cost and can be widely applied. Description of the Drawings

[0026] Figure 1 It is a schematic diagram of the working principle of the profile method and its radar image profile;

[0027] Figure 2 It is a radar numerical simulation result diagram when there is a steel mesh in the shotcrete of the initial support;

[0028] Figure 3 It is a radar numerical simulation result diagram when there is a cavity between the shotcrete of the initial support and the surrounding rock;

[0029] Figure 4 It is an inversion image of radar detection data of the steel mesh inside the typical tunnel initial support;

[0030] Figure 5It is the radar profile image of the interface between the initial support of the tunnel and the surrounding rock;

[0031] Figure 6 It is the radar profile image with a cavity existing between the initial support of the tunnel and the surrounding rock;

[0032] Figure 7 It is the schematic flow diagram of the impact echo audio method detection;

[0033] Figure 8 It is the cloud map of the shallow delamination defect (color plate - Ⅴ - A);

[0034] Figure 9 It is the measured example diagram of the shallow delamination defect part of the initial support (color plate - Ⅴ - A);

[0035] Figure 10 It is the detection cloud map of the middle - layer delamination defect (color plate - V - B);

[0036] Figure 11 It is the measured example diagram of the middle delamination defect part inside the initial support (color plate - V - B);

[0037] Figure 12 It is the cloud map of the deep - layer delamination defect (color plate - V - C);

[0038] Figure 13 It is the measured example diagram of the deep - layer delamination defect part behind the initial support (color plate - V - C);

[0039] Figure 14 It is the schematic flow diagram of the refraction wave detection of the seismic reflection method;

[0040] Figure 15 It is the schematic flow diagram of the reflection wave detection of the seismic reflection method;

[0041] Figure 16 It is the seismic reflection measured diagram of the karst defect behind the initial support;

[0042] Figure 17 It is the schematic diagram of the chromatographic value characteristics;

[0043] Figure 18 It is the schematic diagram of the event axis characteristics;

[0044] Figure 19 It is the schematic diagram of the deep - layer hidden defect detected by the 200 - MHz ground - penetrating radar antenna in the embodiment of the present invention;

[0045] Figure 20 It is the schematic diagram of the shallow - layer hidden defect detected by the 900 - MHz ground - penetrating radar antenna in the embodiment of the present invention;

[0046] Figure 21Schematic diagram of the detection result of the impact echo audio method in the embodiment of the present invention;

[0047] Figure 22 Schematic diagram of the detection result of the seismic reflection method in the embodiment of the present invention;

[0048] Figure 23 Borehole measurement and borehole camera image in the embodiment of the present invention. Detailed implementation manners

[0049] In the following description, specific details such as specific system structures and technologies are presented for the purpose of illustration rather than limitation, so as to thoroughly understand the embodiments of the present invention. However, those skilled in the art should understand that the present invention can also be implemented in other embodiments without these specific details.

[0050] The ground penetrating radar method is based on the fact that when electromagnetic waves propagate in different dielectric media, their waveform characteristics change, and then the distribution of the media is inferred. The electrical characteristics of the media refer to the dielectric constant, conductivity, and attenuation coefficient of the media. The common hidden defects in the initial support of the tunnel detected and discriminated by the ground penetrating radar method mainly include:

[0051] (a) Discrimination of the cavity between the initial support and the surrounding rock: There is a cavity between the initial support of the tunnel and the surrounding rock. The existence of the void layer increases the electromagnetic wave reflection coefficient at the void interface by several times. The intensity of the reflected wave from the void interface increases significantly, the amplitude is enhanced, the reflected wave group is disrupted, and there is a sharp contrast in the propagation of the radar wave in the void area and in the non-void medium, thus identifying the void area.

[0052] (b) Discrimination of concrete void: The existence of the void layer increases the interface reflection coefficient by several times. Therefore, when the void layer exists, the intensity of the reflected wave from the concrete interface increases significantly, and there is a sharp contrast in the propagation of the electromagnetic wave in the void part of the concrete and in the concrete, thus achieving the purpose of identifying the existence of the void.

[0053] (c) Discrimination of non-dense consolidation grouting in the tunnel: If the consolidation grouting in the tunnel is not dense, it will inevitably lead to different dielectric constants. The electromagnetic wave is reflected and scattered in the non-dense area. The amplitude of the radar reflection wave caused by the non-dense area in the radar profile image is generally large. The in-phase axis of the electromagnetic reflection wave in the non-dense area is discontinuous, disordered or curved, and its wavelength changes greatly compared with the uniform and dense area, and the wave amplitude changes significantly, and the wave group characteristics change significantly. If the slurry in the consolidation grouting area is not solidified, the propagation speed of the radar wave in the slurry is slow, the waveform becomes thick, the electromagnetic wave energy decays quickly, showing low-frequency and low-speed characteristics, which is in sharp contrast to the propagation in the surrounding rock.

[0054] (d) Discrimination of steel bar mesh: During the detection by radar, when the electromagnetic wave propagates to the interface of the steel bar mesh, the steel bar mesh has shielding effect on the radar wave. The radar wave undergoes total reflection at the steel bar interface, and the wave amplitude increases abnormally. On the radar profile image, it shows an abnormal amplitude hyperbolic reflection arc. The vertex of the reflection arc is the position and burial depth of the steel bar, and the distance between the vertices of the reflection arcs is the distance between the steel bars. The steel I-beam arch also shows a strong reflection arc curve on the radar profile image, and the vertex position is the position and burial depth of the steel arch.

[0055] (e) Measuring the thickness of shotcrete: Before the initial support detection, first calibrate the radar wave velocity of the shotcrete in different sections. Obtain the electromagnetic wave velocity of the shotcrete in different sections through the calibration method. The interface of the initial support of the shotcrete is obvious. Read the propagation time of the radar wave inside the initial support, and the lining thickness value can be calculated.

[0056] (f) Discrimination of karst: In the tunnel section with karst development, if the consolidated grouting is not full, when the electromagnetic wave propagates in the karst-developed rock mass, the reflection coefficient of the radar wave increases. The radar wave group generates strong reflection and scattering in the karst area, the waveform is disordered, and the amplitude is strong, which is in sharp contrast to the uniform propagation in the surrounding rock, so as to identify the karst in the rock mass behind the initial support.

[0057] The working principle of the comprehensive non-destructive detection of the above hidden defects existing in the initial support of the present invention is as follows:

[0058] (1) Ground penetrating radar detection technology

[0059] The ground penetrating radar technology is based on the dielectric difference between the detected target and the surrounding medium. Use the transmitting antenna to emit high-frequency pulsed electromagnetic waves to the detected medium. When the electromagnetic wave propagates in the underground medium, its amplitude, phase and frequency characteristics change with the dielectric property and geometric shape of the medium. When it encounters a dielectric interface, reflection occurs. The receiving antenna receives the electromagnetic waves and direct waves reflected from different dielectric interfaces in the detected medium. By analyzing this electromagnetic wave carrying the geoelectric information of the underground medium, determine the spatial distribution characteristics of the underground medium. Specifically, utilize the principle that the propagation path of the electromagnetic wave in the medium, the electromagnetic field intensity and the waveform change with the electromagnetic property and geometric shape of the medium passed through. By studying the round-trip travel time, amplitude, frequency and phase characteristics of the reflected wave relative to the direct wave, achieve a detection method for determining the hidden object in the detected medium.

[0060] The present invention adopts the measurement method of the profile method, such as Figure 1Shown is the schematic diagram of the working principle of the cross-section method and its radar image cross-section image. According to the electromagnetic field theory, when electromagnetic waves encounter different dielectric media during propagation, reflection and refraction phenomena will occur at their interfaces, thus changing the propagation direction of the electromagnetic waves. By synchronously moving the transmitting antenna and the receiving antenna along the cross-section, a radar cross-section (the geological radar time cross-section image) composed of reflection records can be obtained. The abscissa of the image records the position of the antenna on the ground surface, and the ordinate is the two-way travel time t of the reflected wave. t represents the time required for the radar pulse to travel from the transmitting antenna, be reflected by the underground interface, and return to the receiving antenna. The distribution of its in-phase axis has an intuitive corresponding relationship with the morphology of different dielectric targets, and this record can accurately reflect the morphology of each reflection interface at different depths.

[0061] Using the two-way travel time t of the reflected wave received by the geological radar, if the propagation speed v of the electromagnetic wave in the medium and the distance x between the transmitting and receiving antennas are known, the depth d of the reflection interface can be calculated by the following formula (1):

[0062]

[0063] In formula (1): wave velocity where c = 0.3 m / ns (speed of light in vacuum), ε r is the relative dielectric constant of the medium.

[0064] ① Forward numerical simulation of electromagnetic waves for typical hidden defects in tunnel linings:

[0065] Forward numerical simulation of electromagnetic waves is an effective method for analyzing tunnel detection problems and studying the propagation law of radar electromagnetic waves in media. By establishing a numerical model for the propagation of electromagnetic waves in tunnel linings, it provides good guidance for the inversion and interpretation of tunnel lining radar detection data. In this invention, the forward numerical simulation results of radar in two cases are exemplified as follows: Figure 2 As shown, it is the radar numerical simulation result diagram when electromagnetic waves propagate to the internal support steel mesh of the shotcrete for the initial support. The simulated detection antenna frequency is 900 MHz. Since there are double-layer anchor bolts in the initial support model, strong reflections occur when electromagnetic waves propagate to the steel mesh, showing a hyperbolic shape. The vertex of the hyperbola corresponds to the actual position of the steel bar, the distance between the vertices is the steel bar spacing, and the number of hyperbolas corresponds one-to-one with the number of steel bars in the lining. The numerical simulation results provide theoretical guidance and reference for the identification of steel bars in radar lining detection data; Figure 3 As shown, it is the radar numerical simulation result diagram of the existence of a cavity between the shotcrete for the initial support and the surrounding rock. Figure 3Among them, the red area in the upper left corner is the lining model, where the circles simulate the steel bars in the lining, the light green simulates the surrounding rock behind the lining, and the triangular blue area simulates the void between the lining and the surrounding rock. The simulation detection antenna frequency is 900 MHz. The results of the numerical simulation show that the steel bars in the lining are shown as a hyperbolic shape in the radar profile. The interface between the lining and the surrounding rock is clear, which is a uniform near-horizontal radar reflection wave in-phase axis. In the void area between the shotcrete of the primary support and the surrounding rock, the radar waves show obvious discontinuity, the amplitude becomes stronger, and there is an obvious difference from the radar reflection wave group without voids around. The results of the numerical simulation provide theoretical guidance for the inversion interpretation of radar data.

[0066] ② Inversion technology of typical GPR profiles:

[0067] In order to improve the resolution of radar detection, the inversion technology of typical GPR profiles is also adopted. In the GPR data acquisition, in order to retain as much information as possible, the all-pass recording method is usually used, so that the effective waves and interference waves are recorded simultaneously. In order to remove the interference signals in the data, digital filtering methods need to be adopted. If there is a relatively obvious boundary between the frequency spectra of the effective signals and the interference signals, then a reasonable filter can be designed according to the distribution of the specific interference signals to filter it out, and the result after filtering is obtained. According to the different frequency spectra of the interference signals, low-pass, high-pass or band-pass methods can be adopted to suppress the detected interference waves, and the interference waves can be effectively removed without damaging the effective waves, so as to improve the resolution of the radar detection profile.

[0068] Figure 4 It is the inversion image of the radar detection data of the steel mesh in the primary support of a typical tunnel, showing that the display feature of the steel mesh in the radar profile image is a hyperbolic shape, corresponding to the results of the numerical simulation in the above Figure 2 ; Figure 5 It is the radar profile image of the interface between the primary support and the surrounding rock of the tunnel. The radar reflection wave group at the layered interface is bright and clear. By reading the travel time of the radar wave reaching the layered interface, the thickness of the lining can be calculated; Figure 6 It is the radar profile image of the void between the primary support and the surrounding rock of the tunnel. This void is a typical pincer-shaped void. The radar profile image shows that the radar wave amplitude is strong at the void, the radar reflection coefficient becomes larger, which is significantly different from the surrounding, corresponding to the numerical simulation results in the above Figure 3 ;

[0069] (2) Impact echo audio method

[0070] The Impact Echo Acoustic Emission (IAE) method uses a microphone instead of a vibration sensor to pick up the vibration signal of the object under test. The longitudinal wave propagates into the structure and is reflected back by defects and the bottom surface of the component. These reflected waves are received by sensors installed near the impact point and sent to a portable instrument with built-in high-speed data acquisition and signal processing capabilities. After performing Fourier transform on the recorded time-domain signal, spectral analysis is carried out. The obvious peaks in the spectrogram are caused by the reflection of void defects inside the concrete structure. As Figure 7 shown in the schematic diagram of the detection process of the Impact Echo Acoustic Emission method.

[0071] Determine the travel time t of the reflected wave of the defect or the bottom surface of the structure from the recorded echo signal R = 1 / F T , according to the propagation speed V of the stress wave in concrete P , the thickness of the concrete or the depth T of the defect can be calculated by the following formula (2):

[0072] T = α s (V P t R ) / 2 (2)

[0073] In formula (2), T is the thickness of the concrete or the depth of the defect; α s is a coefficient related to the geometric shape of the component cross-section; V P is the propagation speed of the stress wave in concrete; t R is the travel time of the reflected wave.

[0074] Convert the recorded data signal to the frequency domain through Fast Fourier Transform (FFT) for analysis, obtain its amplitude, and then get the resonance frequency of the stress wave. Then use the following formula (3) to calculate and determine the thickness of the structural concrete and the depth of the defect:

[0075] T = α s V P / (2f) (3)

[0076] In formula (3), f is the resonance frequency of the stress wave.

[0077] ① Impact Echo Acoustic Emission method color plate inversion technology

[0078] Using the Impact Echo Acoustic Emission (IAE) method for joint diagnosis of voids behind the primary support is divided into: (table) shallow voids, middle voids, and deep voids. The inversion color plate images of typical shallow voids, middle voids, and deep voids, as well as the measured example diagrams of shallow, middle, and deep void defects behind the primary support are as Figure 8 - 13 shown.

[0079] (III) Seismic reflection method

[0080] The seismic image method is a commonly used shallow stratum exploration method developed based on the optimal offset technology in the reflection wave method. It can use various elastic waves such as reflection waves, refraction waves, and surface waves as effective waves for detection.

[0081] In actual work, if the refraction wave is selected as the effective wave, the first in-phase axis on the seismic image waveform diagram is the refraction wave. The change of the refraction wave in-phase axis reflects the change of the refraction interface depth and / or the velocity of the medium above the interface. When the interface is horizontal, the arrival time of the refraction wave reflects the depth of the interface under the excitation point, which is also the depth of each point on the interface. When the interface undulates, the arrival time of the refraction wave can only represent the average depth of the interface within the propagation path of the head wave. As Figure 14 shown, it is a schematic flow diagram of the refraction wave detection of the seismic image method.

[0082] When quantitatively interpreting according to the change characteristics of the in-phase axis, it is necessary to determine the interface dip angle, the interface velocity, and the velocity of the overlying medium, which can be calculated using the following formula (4).

[0083]

[0084] In the formula, T is the propagation time, z is the depth of the overlying layer, L is the horizontal distance, i is the interface dip angle, V1 is the interface velocity, and V2 is the velocity of the overlying medium.

[0085] In actual work, if the reflection wave is selected as the effective wave, the first in-phase axis on the seismic image waveform diagram is the reflection wave.

[0086] When the interface depth changes, the propagation time of the reflection wave will change, such as showing a sudden change on both sides of the fault; if it is an inclined interface, the position of the reflection point will deviate from the recording point and move towards the up-dip direction of the interface. Similarly, the undulation of the interface can be qualitatively inferred according to the change of the reflection wave in-phase axis. As Figure 15 shown, it is a schematic flow diagram of the reflection wave detection of the seismic image method.

[0087] The physical prerequisite for the seismic image method is that there must be obvious elastic (density, velocity, Poisson's ratio) differences between the detection target body and the surrounding medium, so that the seismic wave is reflected or undergoes wave decomposition and conversion on the detection target body, and thus the wave transmits the relevant information of the target body to the receiving device set on the surface of the primary support and is utilized.

[0088] Assume that there is a cavity behind the primary support. Due to the density difference, ρ 岩 ≤ρ 空 , ρ 空 takes the value of 0, and its reflection coefficient γ is as shown in the following formula (5):

[0089]

[0090] Equation (5) shows that when the incident wave encounters the air-filled roof interface of the hole, all the energy will be reflected back to the ground, and the corresponding observation point on the ground will receive a reflected wave with a 180° phase change. During the actual detection process, when the scale of the bad geological body is small, the reflection coefficient will decrease, and the energy of the top reflected wave will also weaken. As Figure 16 shown, it is the measured seismic image of the karst defect behind the initial support.

[0091] The present invention provides a comprehensive non-destructive detection method for hidden defects in the initial support of a long-distance water diversion tunnel, including the following steps;

[0092] S1. Using the geological radar method, a dual-channel geological radar is used to detect the shallow and deep parts of the initial support respectively, and the geological radar electromagnetic wave data of hidden defects at different depths of the initial support are obtained;

[0093] S2. Conduct a forward simulation of the numerical value of the geological radar electromagnetic wave of typical hidden defects in the initial support, and compare the forward simulation result with the measured geological radar electromagnetic wave data. The position of various hidden defects in the depth direction is initially judged through the similarity of the in-phase axis characteristics and chromatographic characteristics;

[0094] Specifically, comparing the forward simulation result with the measured geological radar electromagnetic wave data is by comparing the characteristics of the hidden defects. The characteristics of the hidden defects include chromatographic value characteristics and in-phase axis characteristics, etc.; among them, the chromatographic value characteristics: refer to the amplitude strength of the radar wave represented by a standard chromatogram. Red represents a strong positive wave amplitude, blue represents a strong negative wave amplitude, and yellow represents the standard amplitude. The amplitude strength of the radar wave corresponds one-to-one with the formation reflection coefficient; as Figure 17 shown is the schematic diagram of the chromatographic value characteristics. The in-phase axis characteristics: refer to the connection line of the extreme values (commonly known as wave peaks or wave valleys) with the same vibration phase in each channel of the geological radar electromagnetic wave record. Different in-phase axes are drawn according to the regularly appearing radar sub-waves with similar shapes on the radar record. They represent radar waves of different layers, reflecting the distribution characteristics of different formation structures and the same-layer media; as Figure 18 shown is the schematic diagram of the in-phase axis characteristics;

[0095] S3. Using the impact echo audio method to detect the change in the medium density of hidden defects in the shallow layer, and determining the category of shallow hidden defects through the defect inversion color plate of the audio echo;

[0096] S4. Using the seismic imaging refraction / reflection method to detect the change in the medium density of hidden defects in the deep layer, and determining the category of deep hidden defects through the distribution, size and positive and negative of the wave amplitude;

[0097] S5. For the abnormal areas of the concealed defects detected by the geological radar method, the impact echo audio method, and the seismic reflection method, the engineering drilling and coring method is used for verification to determine the types and scopes of the concealed defects in the abnormal areas of the initial support of the tunnel.

[0098] Preferably, in step S1, the dual-channel geological radar uses two types of antennas, high-frequency and low-frequency, at one time to detect two survey lines at the same position in one detection, and simultaneously detect the shallow and deep parts of the initial support.

[0099] Preferably, the survey lines of the dual-channel geological radar are respectively arranged at the left and right arch shoulders and the arch crown.

[0100] Preferably, in step S2, it further includes: performing inversion processing on the typical concealed defect spectrum of the geological radar to improve the detection resolution of the geological radar method.

[0101] Preferably, the audio survey line using the impact echo method is arranged in the abnormal area at the arch shoulder or the arch crown, and the survey line using the seismic reflection method is arranged in the abnormal area at the arch shoulder or the arch crown.

[0102] Preferably, the audio survey line using the impact echo method is arranged in the abnormal area at the arch shoulder or the arch crown, and the survey line using the seismic reflection method is arranged in the abnormal area at the arch shoulder or the arch crown.

[0103] Example 1

[0104] For a certain water diversion tunnel project with a length of 120 km, the TBM method is used for construction. The initial support uses C20 shotcrete with a shotcrete thickness of 30 cm, and the support method is mortar bolt support. At present, 92.3% of the initial support has been completed, and the detection of the concealed defects in the initial support is carried out to facilitate the backfill grouting construction.

[0105] (I) Survey line arrangement

[0106] (1) The survey lines of the dual-channel geological radar are respectively arranged at the left and right arch shoulders and the arch crown;

[0107] (2) The impact echo audio survey line and the seismic reflection survey line are arranged in the abnormal area at the same position of the arch shoulder or the arch crown.

[0108] (II) Detection steps:

[0109] S1. Use the dual-channel geological radar with two types of antennas, high-frequency and low-frequency, to respectively detect the shallow and deep parts of the initial support, and obtain the geological radar electromagnetic wave data of the concealed defects at different depths of the initial support; among them, the parameter settings of the dual-channel geological radar during the measurement of the concealed defects in the initial support are shown in Table 1:

[0110] Table 1

[0111]

[0112]

[0113] S2. Numerically simulate and forward model typical hidden defects of electromagnetic waves. The simulation and forward modeling process is as follows: establish a model (where the frequency of the simulated detection antenna is 900 MHz) and defect size → assign material parameters → divide the grid → calculate using the finite difference method → output the simulation and forward modeling results, compare the obtained simulation and forward modeling results with the measured ground penetrating radar electromagnetic wave data, and preliminarily determine the positions of various hidden defects in the depth direction through the similarity of the in-phase axis characteristics and chromatographic value characteristics; then perform inverse modeling of the typical hidden defect map of the ground penetrating radar. The inverse modeling process is as follows: initial estimation of the source wave → extraction of the source wave → calculation of the Green's function → source wave estimation → input of the initial dielectric constant and conductivity → input of the residual value and iteration step → full waveform inverse modeling → output of the inverse modeling results;

[0114] S3. Use the impact echo audio method to detect the change in the medium density in the shallow layer of hidden defects, and determine the category of hidden defects through the impact echo audio defect inverse color plate; among them, the parameter settings of the impact echo audio method are shown in Table 2:

[0115] Table 2

[0116] Record length 1024ms Sampling interval 5.0ms Trace interval 0.05m Shot interval 0.05m

[0117] S4. Use the reflection method of the seismic reflection method to detect the change in the medium density in the deep layer of hidden defects, and determine the category of deep hidden defects through the distribution, size, and positive and negative of the wave amplitude; among them, the parameter settings of the seismic reflection method are shown in Table 3;

[0118] Table 3

[0119]

[0120]

[0121] S5. Verify through drilling and downhole camera, and then determine the physical characteristics of the hidden defects behind the initial support of the tunnel, including category, nature, and scope, etc.

[0122] (3) Result analysis:

[0123] (1) Detection results of the dual-channel ground penetrating radar

[0124] As Figure 19 shown, it is a schematic diagram of deep hidden defects detected by a 200 MHz ground penetrating radar antenna; as Figure 20 shown, it is a schematic diagram of shallow hidden defects detected by a 900 MHz ground penetrating radar antenna; from Figure 19and 20 The preliminary exploration results of the dual-channel geological radar show that the initial support of the GD-DKXX2+232-244 arch was suspected to be hollow and the thickness of the shotcrete was insufficient.

[0125] (2) Results of joint interpretation of impact echo and acoustic frequency

[0126] like Figure 21 As shown in the figure, it is a schematic diagram of the detection results of the impact echo acoustic method. Figure 21 The test results show that the initial support of the GD-DKXX2+232-244 arch is not thick enough and has gaps.

[0127] (3) Results of joint interpretation of seismic images

[0128] like Figure 22 As shown in the figure, it is a schematic diagram of the detection results of the seismic imaging method. Figure 21 The test results show that there are gaps in the initial support of the GD-DKXX2+232-244 arch.

[0129] (4) Drilling (coring) and in-hole video verification

[0130] like Figure 23 The following are the drilling measurements and in-hole photography. Figure 23 The results show that the drilling verification results at the initial support of the GD-DKXX2+232-244 arch show that the designed thickness is 30cm, but the actual measured thickness is 25cm; there is a 5cm cavity behind it.

[0131] Through the above-mentioned comprehensive non-destructive testing technology and drilling and in-hole video verification, it was found that there was a cavity behind the initial support at the initial support of the GD-DKXX2+232-244 arch, and its physical properties and geometric dimensions were given to provide basic data for subsequent backfill grouting.

[0132] The present invention identifies the internal quality and hidden defects of the initial support through non-destructive testing of the initial support of the tunnel, and determines the specific locations of the abnormal parts of the hidden defects, including the pile number, elevation and lateral distribution position, and comprehensively analyzes and gives accurate quality information, so as to correctly guide the construction unit to carry out the construction work of the void treatment project behind the initial support, ensure the quality of the project, improve production efficiency, and prevent the occurrence of voids behind the initial support. At the same time, reasonable disposal measures and suggestions for defects such as voids behind the initial support are proposed, which provides technical support for the safety of the initial support structure of long-distance water diversion tunnels and ensures the high-quality construction and long-term safe operation of tunnel lining and support projects.

[0133] As described above, it is only the preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its improved concept, makes equivalent substitutions or changes, and should be covered by the protection scope of the present invention.

Claims

1. A comprehensive non-destructive testing method for hidden defects in the initial support of a water diversion tunnel, characterized in that, It includes the following steps: S1. Adopt the ground penetrating radar method, and use a dual-channel ground penetrating radar to detect the shallow and deep parts of the primary support respectively, so as to obtain the ground penetrating radar electromagnetic wave data of the hidden defects at different depths of the primary support; S2. Conduct forward modeling on the ground penetrating radar electromagnetic wave values of typical hidden defects in the primary support, and compare the forward modeling results with the measured ground penetrating radar electromagnetic wave data, and preliminarily determine the positions of various hidden defects in the depth direction through the similarity of the characteristics of the event axis and the chromatographic characteristics; S3. Adopt the impact echo audio method to detect the change of the medium density of the hidden defects in the shallow layer, and determine the types of the shallow hidden defects through the defect inversion color plate of the audio echo; S4. Adopt the seismic reflection / refraction method of the seismic imaging method to detect the change of the medium density of the hidden defects in the deep layer, and determine the types of the deep hidden defects through the distribution, size and positive and negative of the wave amplitude; S5. Use the engineering drilling and coring method to verify the abnormal areas where the hidden defects detected by the ground penetrating radar method, the impact echo audio method and the seismic imaging method exist, and determine the types and scopes of the hidden defects in the abnormal areas of the primary support of the tunnel.

2. The comprehensive non-destructive testing method according to claim 1, characterized in that In the step S1, the dual-channel ground penetrating radar uses two types of antennas, high-frequency and low-frequency, at one time, and two survey lines at the same position are detected at one time, and the shallow and deep parts of the primary support are detected simultaneously.

3. The comprehensive non-destructive testing method according to claim 1, characterized in that The survey lines of the dual-channel ground penetrating radar are arranged at the left and right arch shoulders and the crown respectively.

4. The comprehensive non-destructive testing method according to claim 1, characterized in that, In the step S2, it also includes: performing inversion processing on the ground penetrating radar typical hidden defect map.

5. The comprehensive non-destructive testing method according to claim 1, characterized in that The audio survey line using the impact echo method is arranged in the abnormal area at the arch shoulder or the crown, and the survey line using the seismic imaging method is arranged in the abnormal area at the arch shoulder or the crown.

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