Method for evaluating roadway bolt-shotcrete support layer

Abstract

The application discloses a roadway anchor shot supporting layer evaluation method. The application regards a coal mine roadway supporting system as a multilayer elastic medium, extracts a wideband surface wave dispersion curve, inverses physical characteristics (dynamic elastic modulus) of each layer, further establishes a quantitative safety criterion with a multilayer stiffness coefficient as a key parameter, introduces a dynamic elastic modulus true value after a surface transient impact, and realizes the judgment and effective early warning of the interface stability of the supporting structure and the loosening expansion of each layer after the dynamic elastic modulus true value is brought into a transfer formula.

Description

Technical Field

[0001] This invention belongs to the field of non-destructive testing of mine roadways and safety evaluation of surrounding rock support. Specifically, it relates to an in-situ evaluation method and system for using multi-point dispersive Rayleigh surface waves to invert the dynamic elastic modulus of each layer of the sprayed layer-surrounding rock system, and to evaluate the interlayer cooperative bearing stability accordingly. Background Technology

[0002] Chinese invention patent application CN120251315A, published on July 4, 2025, discloses a method for evaluating the impact hazard of a working face based on transient induced impact of coal and rock structure. The method includes: acquiring geological data of the target working face and determining the area to be evaluated; determining the stress state of the area to be evaluated before and after the structural transient; calculating the impact stress of the working face under the transient excitation of the overburden space structure based on the stress state before and after the structural transient; establishing impact hazard evaluation indicators for the area to be evaluated based on the stress state before and during the structural transient; and classifying the area to be evaluated based on the impact hazard evaluation indicators.

[0003] Current methods for evaluating the quality of shotcrete roadway support in coal mines mainly rely on geological surveys or surface shotcrete strength testing, which has the following limitations for such complex, multi-layered structures: 1. Unable to obtain continuous mechanical gradient: It cannot reflect the stiffness variation law from the surface of the sprayed layer to the depth of the surrounding rock.

[0004] 2. The conversion relationship between wave velocity and intensity in geological exploration lacks true values: There are significant differences in nonlinear coupling in fractured surrounding rock and shotcrete anchoring layers, making it almost impossible to judge by reflected waves from the profile.

[0005] 3. Inability to quantify weak interfaces: It is difficult to capture the shear dilatation and delamination trends at the interface between the sprayed layer and the surrounding rock, and the support effect between multiple layers cannot be quantified, resulting in the inability to provide early warning of sudden support failure. Summary of the Invention

[0006] The core objective of this invention is to treat the coal mine roadway support system as a multi-layered elastic medium, extract the broadband surface wave dispersion curve, invert the physical characteristics (dynamic elastic modulus) of each layer, establish a quantitative safety criterion with the "multi-layer stiffness coefficient" as the key parameter, introduce the true value of the dynamic elastic modulus after the surface transient impact, and substitute it into the transfer formula to realize the judgment and effective early warning of the stability of the support structure interface and the loosening and expansion of each layer.

[0007] To solve the above-mentioned technical problems, the present invention provides a method for evaluating roadway anchor-sprayed support layers, comprising the following steps: Step 1. Arrange the connecting equipment: On the shotcrete layer of the arch / waist of the tunnel to be inspected, three accelerometers (receiving devices DP1, DP2, DP3) are evenly arranged in a straight line. Their sampling frequency is set to 100kHz. They are equipped with data acquisition detection equipment and industrial computer. The above-mentioned accelerometers, data acquisition detection equipment and industrial computer are connected in communication. The distance L between adjacent accelerometers is equal. Step 2. Transient Impact and Data Acquisition: With the three accelerometers (receiving devices DP1, DP2, and DP3) aligned on the extension of a straight line, a spherical impactor (impact device) is used to apply a transient impact to the shotcrete layer in the roadway to be inspected at a distance L from the end sensor (DP1 or DP3). The spherical impactor is equipped with an accelerometer. The three accelerometers (receiving devices DP1, DP2, and DP3) receive body wave signals from the vibration, which are then converted into digital signals by the data acquisition and detection equipment and transmitted to the industrial computer. Step 3. Calculate the multi-layer stiffness coefficient A of the roadway to be tested, and use this to determine the stiffness of the anchor-sprayed support layer of the roadway to be tested after the surface shotcrete layer: Bandpass filtering is performed in 500Hz intervals from 500 to 5000Hz, and then the cross-correlation function of adjacent channels is calculated one by one. : , The peak value of the cross-correlation function is taken as the propagation time delay. Finally, the delay difference between the DP1-DP2 and DP2-DP3 channels is calculated separately, and their average value is taken. ,

[0008] The tunnel support layer is abstracted into a three-layer medium model consisting of "surface shotcrete – transition interface – internal intact original rock". A dispersion curve objective function is established, and the medium wave velocity of the internal original rock is obtained by least squares inversion. V 内部原岩 and the medium wave velocity of the surface sprayed concrete layer V 表层喷射混凝土 According to the following formula, , The multi-layer stiffness coefficient A is calculated, which quantitatively describes the degree of stiffness matching when stress is transferred from the surrounding rock to the sprayed layer from the perspective of deformation coordination. If A≥1, it indicates that the deep part is stiffer and the shallow part is relatively flexible, which is conducive to coordinated bearing. If 1>A≥0.8, the staff should pay attention to strengthen the observation and monitoring of the arch of the roadway to be tested. If A<0.8, it means that there is a significant stiffness change between the interface between the shallow hard shell and the soft part or between the deep part, which is very easy to cause debonding or crushing. The staff should be notified to rebuild the arch support of the roadway to be tested as soon as possible.

[0009] This design shifts the focus from traditional single-location independent testing of "absolute strength" to comprehensive evaluation of "multi-layer relative stiffness." By utilizing the changing matching law of layered dynamic modulus to assess the long-term stability of the support system, it avoids the physical defects of the traditional "wave velocity-strength" empirical conversion formula failing in fractured rock zones.

[0010] As an optimization, L=100mm.

[0011] As an optimization, it also includes: Step 4. At the striking end, acquire the impact time t and impact acceleration curve p(t) during the impact, integrate the first half of the peak signal within the impact time t and divide by 2 to obtain the collision velocity v_impact. Based on the impact relationship between a sphere and a semi-infinite plane, and combined with Hertz's contact formula, the modulus E of the surface shotcrete can be calculated using the following formula. 表混 :

[0012] Where μ is the Poisson's ratio of the material (0.2 for concrete and 0.3 for steel ball), R is the radius of the steel ball, and m is the mass of the steel ball; this gives the modulus of the surface shotcrete.

[0013] Step 5. Similarly, according to the Hertz contact formula, the equivalent modulus of the surface concrete should not be lower than the design value of 18 GPa. Otherwise, it is determined that the surface stiffness is insufficient or the interface is weak, and the staff should be notified to reinforce the arch support of the tunnel to be tested as soon as possible. This design does not rely on any drilling or destructive excavation. It only performs multi-channel surface wave acquisition on the surface of the shotcrete layer, making full use of the Rayleigh surface wave's dispersion characteristics of shallow high frequency and deep low frequency, and realizing non-destructive quantitative evaluation of the layered structure of the shotcrete layer, cemented transition layer, and original loosened rock zone.

[0014] As an optimization, step 5 involves simultaneously inputting the inversion depth and equivalent dynamic elastic modulus of each layer from each measuring point into the imaging module to generate a three-layer dynamic elastic modulus tomography chromatogram of the tunnel support layer. The graph automatically identifies the thickness scale and different wave velocity color gradients, and marks multi-layer stiffness mismatch areas or shear dilatation anomalies in the transition layer, providing a direct basis for operational safety. This design, using Hertzian contact dynamics to obtain the true dynamic elastic modulus of the surface layer as a measured benchmark, eliminates the ambiguity of the inversion and achieves accurate quantitative early warning of weak delamination at concealed interfaces and weakening and propagation of deep surrounding rock.

[0015] This invention treats the coal mine roadway support system as a multi-layered elastic medium. By extracting the broadband surface wave dispersion curve, the physical characteristics (dynamic elastic modes) of each layer are obtained by inversion. Then, a quantitative safety criterion with "multi-layer stiffness coefficient" as the key parameter is established. The true value of the dynamic elastic mode after the transient impact of the surface layer is introduced and substituted into the transfer formula to realize the judgment and effective early warning of the stability of the support structure interface and the loosening and expansion of each layer. Attached Figure Description

[0016] The method for evaluating the roadway anchor-sprayed support layer of the present invention will be further explained below with reference to the accompanying drawings: Figure 1 This is a schematic diagram of the hardware deployment for step 1 of the roadway anchor spraying support layer evaluation method of the present invention; Figure 2 This is a schematic diagram of the signal acquisition waveform in step 2 of the roadway anchor spraying support layer evaluation method of the present invention; Figure 3 This is the three-layer dynamic modulus chromatography chromatogram of step 5 in the roadway anchor spraying support layer evaluation method of the present invention. Detailed Implementation

[0017] Implementation method one: such as Figure 1-3 As shown, the method for evaluating the roadway anchor-sprayed support layer of the present invention includes the following steps: Step 1. Arrange the connecting equipment: On the shotcrete layer of the arch / waist of the tunnel to be inspected, three accelerometers (receiving devices DP1, DP2, DP3) are evenly arranged in a straight line. Their sampling frequency is set to 100kHz. They are equipped with data acquisition detection equipment and industrial computer. The above-mentioned accelerometers, data acquisition detection equipment and industrial computer are connected in communication. The distance L between adjacent accelerometers is equal. Step 2. Transient Impact and Data Acquisition: With the three accelerometers (receiving devices DP1, DP2, and DP3) aligned on the extension of a straight line, a spherical impactor (impact device) is used to apply a transient impact to the shotcrete layer in the roadway to be inspected at a distance L from the end sensor (DP1 or DP3). The spherical impactor is equipped with an accelerometer. The three accelerometers (receiving devices DP1, DP2, and DP3) receive body wave signals from the vibration, which are then converted into digital signals by the data acquisition and detection equipment and transmitted to the industrial computer. Step 3. Calculate the multi-layer stiffness coefficient A of the roadway to be tested, and use this to determine the stiffness of the anchor-sprayed support layer of the roadway to be tested after the surface shotcrete layer: Bandpass filtering is performed in 500Hz intervals from 500 to 5000Hz, and then the cross-correlation function of adjacent channels is calculated one by one. : , The peak value of the cross-correlation function is taken as the propagation time delay. Finally, the delay difference between the DP1-DP2 and DP2-DP3 channels is calculated separately, and their average value is taken. ,

[0018] The tunnel support layer is abstracted into a three-layer medium model consisting of "surface shotcrete – transition interface – internal intact original rock". A dispersion curve objective function is established, and the medium wave velocity V of the internal original rock is obtained by least squares inversion. 内部原岩 The medium wave velocity V of the surface sprayed concrete layer 表层喷射混凝土 According to the following formula,

[0019] The multi-layer stiffness coefficient A was calculated, which quantitatively describes the degree of stiffness matching when stress is transferred from the surrounding rock to the shotcrete layer from the perspective of deformation coordination. If A ≥ 1, it indicates that the deeper layers are stiffer and the shallower layers are relatively flexible, which is conducive to coordinated load bearing. If 1 > A ≥ 0.8, staff should pay close attention to the observation and monitoring of the arch support of the roadway to be tested. If A < 0.8, it means that there is a significant stiffness abrupt change between the interface between the shallow hard shell and the weak layer or between the deep layers, which is very likely to cause debonding or crushing. Staff should be notified to quickly re-secure the arch support of the roadway to be tested. L = 100mm.

[0020] Step 4. At the striking end, acquire the impact time t and impact acceleration curve p(t) during the impact. Integrate the first half of the peak signal within the impact time t and divide by 2 to obtain the collision velocity vp. Based on the impact relationship between a sphere and a semi-infinite plane, and combined with Hertz's contact formula, the modulus E of the surface shotcrete can be calculated using the following formula. 表混 :

[0021] Where μ is the Poisson's ratio of the material (0.2 for concrete, 0.3 for steel spheres), R is the radius of the steel sphere, and m is the mass of the steel sphere; this gives the modulus of the surface shotcrete. Step 5. Similarly, the equivalent modulus of the surface concrete tested according to the Hertz contact formula should not be less than the design value of 18 GPa. Otherwise, it is determined that the surface stiffness is insufficient or the interface is weak. The staff should be notified to re-shotcrete and reinforce the arch support of the tunnel to be tested as soon as possible.

[0022] Simultaneously, the inversion depth of each measuring point and the equivalent dynamic elastic modulus of each layer are input into the imaging module to draw a three-layer dynamic elastic modulus tomography chromatogram of the roadway support layer. The thickness scale and different wave velocity color gradients are automatically marked on the graph, and the multi-layer stiffness mismatch area or the shear dilatation delamination anomaly point of the transition layer is marked, providing an intuitive basis for operation and maintenance safety.

[0023] Core technologies 1. Detection device Impact device SP: Includes a high-frequency spherical impactor and an acceleration sensor, which applies transient impact to the shotcrete layer through the end of the impactor and excites elastic wave signals.

[0024] Receiver RP: An array of receiving sensors is arranged along the anchor spray layer, with a spacing of L between the sensors. It is responsible for receiving bulk wave signals and recording time series data.

[0025] Data acquisition and testing equipment (DE): used to collect, filter and store sensor signals from various ends, and to evaluate support strength, material and delamination.

[0026] 2. Multi-frequency surface wave signal acquisition and dispersion curve extraction Receiver devices RP are arranged at fixed intervals L along the tunnel axis. A wideband Rayleigh glass is excited using a percussion device SP, ensuring a wavelength coverage range of at least 1 meter. Frequency-velocity transformation is performed on the array signal (using methods such as phase method, frequency domain-wavenumber method FK, or multichannel surface wave analysis MASW), extracting the dispersion curve of the surface wave phase velocity as a function of frequency. In this curve, the high-frequency velocity reflects the properties of the grout layer, while the low-frequency velocity reflects the properties of the deep surrounding rock.

[0027] 3. Layered wave velocity structure inversion Substitute the three-layer medium model of the support structure, namely "surface shotcrete - transition interface - internal intact original rock", and use the least squares method to fit the wave velocity of the dispersion curve to obtain the elastic wave velocity value and model layer thickness of each layer.

[0028] 4. Calculation of stiffness coefficient of multi-story buildings Based on the theory of elastic wave motion, the wave velocity of a medium is proportional to its elastic modulus and the structure's resistance to deformation. Therefore, a core evaluation index—the multilayer stiffness coefficient A—is introduced.

[0029] It quantitatively describes the degree of stiffness matching when stress is transferred from the surrounding rock to the sprayed layer from the perspective of deformation coordination. A ratio close to or greater than 1 indicates that the deeper part is stiffer and the shallow part is relatively flexible, which is conducive to synergistic load bearing; a ratio that is too low (the lower limit is 0.8) means that there is a significant stiffness abrupt change between the shallow hard shell and the weak interface or between the deep part, which is very easy to cause debonding or crushing.

[0030] 5. Surface judgment based on transient impact values At the starting point or representative location of the survey line, after a transient impact, the acceleration time history curve of the impact point is collected, and the surface dynamic elastic modulus is calculated according to Hertzian contact theory. Logically, the test value should not be less than 18 GPa of the surface design equivalent modulus.

[0031] 6. Evaluation Results Output Finally, a three-layer dynamic modulus chromatography chromatogram was generated from this test, with thickness scales and color gradients for different wave velocities marked. Based on criteria 4 and 5, abnormal areas were automatically identified, providing a clear basis for operational safety.

[0032] Beneficial effects 1. A fundamental shift in evaluation mechanism: from traditional single-location independent testing of "absolute strength" to comprehensive evaluation of "multi-layer relative stiffness". The long-term stability of the support system is assessed by utilizing the changing matching law of the layered dynamic modulus, avoiding the physical defects of the traditional "wave velocity-strength" empirical conversion formula in fractured rock zones.

[0033] 2. High-precision separation of dispersion depth: Without relying on any drilling or destructive excavation, multi-channel surface wave acquisition is performed on the surface of the shotcrete layer in a single blow, making full use of the dispersion characteristics of Rayleigh surface waves for shallow high frequencies and deep low frequencies, so as to realize the non-destructive quantitative evaluation of the layered structure of the shotcrete layer, cemented transition layer and original rock loosening zone.

[0034] 3. Refined early warning of support status: By obtaining the true dynamic elastic modulus of the surface through Hertzian contact dynamics as the measured true value scale, the multiple solutions of the inversion are eliminated, and accurate quantitative early warning of weak delamination at hidden interfaces and weakening and expansion of deep surrounding rock is realized.

Claims

1. A method for evaluating roadway anchor-sprayed support layers, comprising the following steps: Step 1. Arrange the connecting equipment: On the shotcrete layer of the arch / waist of the tunnel to be inspected, three accelerometers (DP1, DP2, DP3) are evenly arranged in a straight line. Their sampling frequency is set to 100kHz. Data acquisition and detection equipment and industrial computer are also provided. The above accelerometers, data acquisition and detection equipment and industrial computer are connected in communication. The distance L between adjacent accelerometers is equal. Step 2. Transient Impact and Data Acquisition: With the three accelerometers (DP1, DP2, DP3) aligned on the extension of a straight line, a spherical impactor is used to apply a transient impact to the shotcrete layer in the roadway to be inspected at a distance L from the end sensor (DP1 or DP3). The spherical impactor is equipped with an accelerometer. The three accelerometers (DP1, DP2, DP3) are subjected to body wave signals from vibration, which are converted into digital signals by the data acquisition and detection equipment and transmitted to the industrial computer. Step 3. Calculate the multi-layer stiffness coefficient A of the roadway to be tested, and use this to determine the stiffness of the anchor-sprayed support layer of the roadway to be tested after the surface shotcrete layer: Bandpass filtering is performed in 500Hz intervals from 500 to 5000Hz, and then the cross-correlation function of adjacent channels is calculated one by one. : ， The peak value of the cross-correlation function is taken as the propagation time delay. Finally, the delay difference between the DP1-DP2 and DP2-DP3 channels is calculated separately, and their average value is taken. , The tunnel support layer is abstracted into a three-layer medium model consisting of "surface shotcrete – transition interface – internal intact original rock". A dispersion curve objective function is established, and the medium wave velocity of the internal original rock is obtained by least squares inversion. V 内部原岩 and the medium wave velocity of the surface sprayed concrete layer V 表层喷射混凝土 According to the following formula, ， The multi-layer stiffness coefficient A is calculated. If A≥1, it indicates that the deeper part is stiffer and the shallow part is relatively flexible, which is conducive to joint bearing. If 1>A≥0.8, staff should pay attention to strengthen the observation and monitoring of the arch of the roadway to be tested. If A<0.8, it means that there is a significant stiffness change between the interface between the shallow hard shell and the soft interface or between the deep part, which is very easy to cause debonding or crushing. Staff should be notified to rebuild the arch support of the roadway to be tested as soon as possible.

2. The method for evaluating roadway anchor-sprayed support layer according to claim 1, characterized in that: The value of L is 100mm.

3. The method for evaluating roadway anchor-sprayed support layer according to claim 1, characterized in that: It also includes: Step 4. At the striking end, acquire the impact time t and impact acceleration curve p(t) during the impact. Integrate the first half of the peak signal within the impact time t and divide by 2 to obtain the collision velocity vp. Based on the impact relationship between a sphere and a semi-infinite plane, and combined with Hertz's contact formula, the modulus E of the surface shotcrete can be calculated using the following formula. 表混 : Where μ is the Poisson's ratio of the material, 0.2 for concrete and 0.3 for steel spheres; R is the radius of the steel sphere; m 钢球 - The mass of the steel ball; to obtain the modulus of the surface shotcrete. Step 5. Similarly, the equivalent modulus of the surface concrete tested according to the Hertz contact formula should not be less than the design value of 18 GPa. Otherwise, it is determined that the surface stiffness is insufficient or the interface is weak. The staff should be notified to reinforce the arch support of the tunnel to be tested as soon as possible.

4. The method for evaluating roadway anchor-sprayed support layer according to claim 3, characterized in that: Step 5. Simultaneously input the inversion depth of each measuring point and the equivalent dynamic elastic modulus of each layer into the imaging module to draw a three-layer dynamic elastic modulus tomography chromatogram of the roadway support layer. The thickness scale and different wave velocity color gradients are automatically marked on the graph, and the multi-layer stiffness mismatch area or the shear dilatation delamination anomaly point of the transition layer is marked, providing an intuitive basis for operation and maintenance safety.

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