A tunnel advanced geological prediction method and system based on three-level synchronization of wireless data transmission

Abstract

The present application relates to a kind of tunnel advanced geological prediction method and system based on three-level synchronization of wireless data transmission, and in the present application, acquisition host computer and acquisition node instrument establish wireless data transmission network;Acquisition host computer broadcasts synchronous clock command, and acquisition node instrument carries out clock frequency synchronization accordingly;Acquisition host computer and acquisition node instrument carry out bidirectional time difference measurement, and acquisition node instrument carries out local clock phase synchronization according to the result of bidirectional time difference measurement;After seismic source triggers, acquisition node instrument collects seismic wave data and returns, and acquisition terminal generates residual offset correction amount according to cross-correlation result and feeds back to acquisition node instrument to modify its local clock again;Repeat cross-correlation correction process, until the time synchronization error of all acquisition node instruments converges to within preset range.The present application realizes high-precision time synchronization in the environment without GPS through the three-level progressive mechanism of frequency synchronization, phase synchronization and mutual close-loop recalibration based on physical signal.

Description

Technical Field

[0001] This invention relates to the field of geophysical exploration technology, specifically to a method and system for advanced geological prediction of tunnels based on three-level synchronization of wireless data transmission. Background Technology

[0002] With the rapid development of tunnel engineering construction in my country, safety issues during tunnel construction have become increasingly important. Many tunnels in my country have complex geological environments, and geological disasters such as mudslides and water inrushes occur frequently. Therefore, it is necessary to use advanced geological prediction technology to detect adverse geological conditions ahead of the tunnel face in advance, ensuring construction progress and the safety of construction personnel. It is particularly important to use scientific and accurate prediction methods to determine the nature, scale, and location of adverse geological bodies within the tunnel's passage, especially in areas with complex geological conditions and when using modern construction techniques such as shield tunneling. Advanced geological prediction provides an important basis for selecting tunnel construction methods and changing support forms, significantly reducing the uncertainty of construction.

[0003] Currently, geophysical exploration methods for advanced geological prediction in shield tunnel construction mainly include elastic wave reflection, electromagnetic wave reflection, and high-resolution direct current methods. Among these, elastic wave reflection is the most widely used, employed to delineate stratigraphic boundaries ahead of the tunnel face, detect concealed faults and fracture zones, detect underground caverns, and determine aquifer distribution. An elastic wave reflection-based advanced geological prediction system mainly comprises a vibration device, a detection device, a data acquisition device, and data processing and interpretation software.

[0004] In the data acquisition stage, the existing tunnel advanced geological prediction system has the following main shortcomings.

[0005] First, traditional data acquisition systems rely on wired networking, with sensors and the acquisition host connected by cables. Laying cables in narrow tunnel environments is complex and time-consuming. Furthermore, environmental factors such as humidity and vibration in tunnels affect the reliability of wired connections, thus limiting the system's deployment flexibility and environmental adaptability.

[0006] Second, the accuracy of existing wireless synchronization technologies is insufficient. NTP and other wireless synchronization technologies typically achieve millisecond-level synchronization accuracy over wireless channels, while the elastic wave reflection method, which uses seismic wave wavefield separation and polarization analysis for geological imaging, requires microsecond-level time synchronization errors between acquisition nodes. Assuming a P-wave velocity of 3000 to 6000 m / s in tunnel surrounding rock, a 1-millisecond time error corresponds to a 3-6 meter spatial positioning deviation, sufficient to lead to missed or misjudged faults and fracture zones. Millisecond-level synchronization accuracy cannot meet the time reference requirements for wavefield separation and polarization analysis in advanced geological prediction using the elastic wave reflection method.

[0007] Third, GPS or BeiDou satellite signals cannot be received inside the tunnel, rendering the multi-node clock synchronization scheme based on satellite timing ineffective in the tunnel environment. If each acquisition node relies on its own independent free-running clock for acquisition, the clock frequency deviation and phase shift between multiple nodes accumulate over time, resulting in a non-negligible time misalignment between the seismic wave waveforms recorded by each channel, which seriously affects the consistency and reliability of the data.

[0008] Fourth, existing synchronization methods based on protocol layer timestamps suffer from insufficient accuracy. Wireless synchronization protocols using bidirectional timestamp ranging calculate transmission delay and clock skew by exchanging timestamps at the protocol layer. Their synchronization accuracy is limited by the resolution of the protocol timestamps and the random jitter of WiFi channel access delay. Under wireless channel conditions, the measurement accuracy of protocol layer timestamps typically only reaches the sub-microsecond level, making it difficult to further break through to the 0.1 microsecond level.

[0009] In summary, existing tunnel advanced geological prediction systems face multiple constraints in the data acquisition stage, such as complex wired network deployment, insufficient wireless synchronization accuracy, unavailability of GPS signals, and insufficient synchronization accuracy of pure protocol layer. There is an urgent need for a multi-node wireless synchronization acquisition solution that does not rely on GPS signals or wired connections and achieves synchronization accuracy at the microsecond level. Summary of the Invention

[0010] The main objective of this invention is to provide a method and system for advanced geological prediction of tunnels based on three-level synchronization of wireless data transmission, so as to solve the technical problem of how to reduce the time synchronization error of multi-node data in wireless transmission under the existing technology in the tunnel construction environment.

[0011] To achieve the above objectives, this invention provides a tunnel advanced geological prediction method based on three-level synchronization of wireless data transmission, applied to a tunnel advanced geological prediction system including a data acquisition host, multiple data acquisition nodes, and data acquisition terminals, comprising the following steps: S1. The data acquisition host establishes a wireless data transmission network with multiple data acquisition nodes; S2. The acquisition host broadcasts a synchronization clock command to each of the acquisition nodes, and each of the acquisition nodes synchronizes its clock frequency according to the received synchronization clock command. S3. The acquisition host and each acquisition node perform bidirectional time difference measurement to obtain the measurement result, and each acquisition node performs local clock phase synchronization based on the measurement result; S4. After the earthquake source is triggered, each of the acquisition nodes acquires seismic wave data and transmits it back to the acquisition terminal through the wireless data transmission network. The acquisition terminal determines the cross-correlation result between the seismic wave data based on the seismic wave data of different acquisition nodes, generates a residual offset correction amount based on the cross-correlation result, and feeds back the residual offset correction amount to the corresponding acquisition node to correct its local clock again. S5. Repeat step S4 until the time synchronization error of all acquisition nodes converges to the preset range.

[0012] Furthermore, step S2 specifically includes the following steps: The acquisition host broadcasts the synchronization clock command every integer second; Obtain the reception time of the synchronization clock command recorded by each of the acquisition nodes, and obtain the deviation between the time interval of two adjacent receptions of the synchronization clock command and 1 second; When the deviation exceeds the preset deviation threshold, each of the acquisition nodes adjusts the control voltage of its own voltage-controlled crystal oscillator to correct its own clock frequency; The clock frequency synchronization is continuously and periodically executed during the operation of the tunnel advanced geological prediction system.

[0013] Furthermore, step S3 specifically includes the following steps: The data acquisition host sends a time difference measurement command and records the sending time. The sending time Send to the data acquisition node; The data acquisition node receives the time difference measurement command and records the receiving time. ; The data acquisition node sends a time difference measurement command to the data acquisition host and records the sending time. ; The data acquisition host receives a time difference measurement command from the data acquisition node and records the receiving time. The receiving time Send to the data acquisition node; The data acquisition node calculates the clock offset O and adjusts its local clock accordingly; the calculation formula is as follows: ; Repeat the above bidirectional time difference measurement until the clock offset O converges to ≤1μs.

[0014] Further, in step S4, the acquisition terminal determines the cross-correlation results between the seismic wave data based on the seismic wave data from different acquisition nodes, and generates residual migration corrections based on the cross-correlation results, specifically including the following steps: The wireless link quality index between each of the acquisition nodes and the acquisition host is obtained, and the acquisition terminal selects the acquisition node with the highest wireless link quality index as the reference node. The acquisition terminal controls the reference node to perform bidirectional time difference measurement with the acquisition host to obtain the residual clock offset of the reference node relative to the acquisition host. ; For each non-reference acquisition node, the acquisition terminal selects the first arrival segment of the direct P-wave of the non-reference acquisition node and the reference node as the cross-correlation analysis window. Within the cross-correlation analysis window, the normalized cross-correlation function of the non-reference acquisition node signal and the reference node signal is calculated. The delay time corresponding to the peak value of the cross-correlation function is extracted by cubic spline interpolation. , which is the residual clock offset of the non-reference acquisition node relative to the reference node; The acquisition terminal calculates the residual offset correction amount of the non-reference acquisition node. The data is transmitted to the non-reference acquisition node via the wireless data transmission network. After receiving the data, the non-reference acquisition node fine-tunes its local clock according to the residual offset correction amount. The calculation formula is as follows: .

[0015] Furthermore, step S5 specifically includes the following steps: When the absolute value of the residual offset correction of all non-reference acquisition nodes is no greater than 0.1μs, the iteration is terminated and the current clock state is locked. When the number of consecutive iterations reaches the preset maximum number of iterations, and there is still a residual offset correction value of non-reference acquisition nodes that is greater than 0.1 μs, the iteration stops, and data acquisition continues with a reduced accuracy. The accuracy level identifier is written into the acquired seismic wave data file.

[0016] Furthermore, the following steps are included after step S5: Each of the acquisition nodes periodically measures the wireless link quality indicators between itself and the acquisition host, and reports the wireless link quality indicators to the acquisition host; wherein, the wireless link quality indicators include received signal strength indication and packet loss rate; The system determines whether the wireless link quality indicators meet the preset communication conditions. When the received signal strength of a certain acquisition node is lower than the first preset threshold or the packet loss rate is higher than the second preset threshold, it is determined that the preset communication conditions are not met, and the acquisition host marks the acquisition node as a relay candidate node. When the received signal strength of a certain acquisition node is greater than or equal to the first preset threshold and the packet loss rate is less than or equal to the second preset threshold, it is determined that the preset communication conditions are met. The data acquisition host selects the data acquisition node closest to the candidate relay node from among the other data acquisition nodes whose wireless link quality indicators meet the preset communication conditions as the relay node; The acquisition host sends configuration commands to the relay node and the relay candidate node respectively, so that the relay candidate node can communicate with the acquisition host through the relay node.

[0017] More preferably, after the relay candidate node communicates with the acquisition host via the relay node, relay forwarding delay compensation is performed, specifically including the following steps: When forwarding the time difference measurement command, the relay node measures the forwarding processing delay. and reverse forwarding processing latency and the forwarding processing delay and the reverse forwarding processing delay Attached to the forwarded command frame; When calculating the clock offset O, the relay candidate node uses a correction formula: ; When there are multiple levels of relays, the forward forwarding processing delay and the reverse forwarding processing delay of each level of relay node are accumulated and deducted respectively.

[0018] Furthermore, prior to step S4, the following steps are also included: During the static installation phase, the three-component accelerometer in each of the acquisition nodes operates in the first response mode to measure the static component of the gravity vector. Based on the static component of the gravity vector, the pitch angle, roll angle, and azimuth angle of each of the acquisition nodes are calculated and reported to the acquisition terminal. The acquisition terminal sends a mode switching command to each of the acquisition nodes, so that each of the acquisition nodes switches the three-component accelerometer to the second response mode to acquire seismic wave data. The acquisition terminal constructs a rotation matrix based on the pitch, roll, and azimuth angles of each acquisition node to convert the acquired seismic wave data into a unified geodetic coordinate system.

[0019] More preferably, after step S4, the following step is further included: The acquisition terminal uses the long-short time window energy ratio method to pick the first arrival time of the direct P-wave of the same source event from the seismic wave data after it has been converted to a unified geodetic coordinate system. By combining the installation coordinates of each acquisition node and the P-wave velocity of the rock mass, a set of time difference equations is constructed and the three-dimensional coordinates of the seismic source are inverted; The three-dimensional coordinates of the earthquake source are compared with the coordinates of the designed impact point. When the deviation between the two exceeds the preset tolerance, a quality control anomaly warning is issued.

[0020] The present invention also provides a tunnel advanced geological prediction system based on three-level synchronization of wireless data transmission, which executes the tunnel advanced geological prediction method based on three-level synchronization of wireless data transmission as described above, including a data acquisition host, multiple data acquisition nodes and a data acquisition terminal; The acquisition host establishes a wireless data transmission network with the multiple acquisition nodes, broadcasts a synchronization clock command to each acquisition node, performs bidirectional time difference measurement with each acquisition node and obtains the measurement results, and receives the seismic source trigger signal. The data acquisition node is configured to synchronize its clock frequency according to the received synchronization clock command, synchronize its local clock phase according to the measurement results of the bidirectional time difference measurement, acquire seismic wave data after the earthquake source is triggered and transmit it back to the acquisition terminal through the wireless data transmission network, and receive the residual offset correction amount fed back by the acquisition terminal and correct the local clock accordingly. The data acquisition node has a built-in magnetic control switch, a three-axis accelerometer and a wireless communication module. The bottom of the data acquisition node is provided with expansion screw mounting holes, and the data acquisition node is fixedly installed on the tunnel face by expansion screws. Acquisition terminal: Determines the cross-correlation results between seismic wave data based on the seismic wave data from different acquisition nodes, generates the residual migration correction amount based on the cross-correlation results, and feeds back the residual migration correction amount to the corresponding acquisition node; In this process, after each earthquake source is triggered and the seismic wave data acquisition and residual offset correction feedback are completed, the acquisition terminal controls each acquisition node to repeatedly perform seismic wave data acquisition and local clock correction until the time synchronization error of all acquisition nodes converges to a preset range.

[0021] Compared with the prior art, the present invention has the following beneficial effects: This invention addresses the challenges of tunnel construction environments lacking 4G / 5G and GPS signals. It establishes a wireless data transmission network between a host acquisition unit and multiple acquisition nodes, replacing traditional wired connections. This eliminates the constraints of cable length and routing on node deployment, significantly reducing deployment time in narrow tunnel face conditions. Master-slave clock frequency synchronization is achieved through broadcast synchronization commands, while master-slave clock phase synchronization is accomplished through bidirectional time difference measurement. This ensures microsecond-level time consistency across all acquisition nodes on a purely wireless channel, providing a fundamental time reference for precise alignment of subsequent seismic wave waveforms. This overcomes the limitations of unavailable satellite time synchronization and insufficient accuracy of common network time protocols like NTP in tunnel environments. Based on this, after the acquisition terminal acquires the seismic wave data synchronously acquired by each acquisition node, it performs cross-correlation calculations on the seismic wave data of different acquisition nodes, extracts the small clock deviations remaining between the acquisition nodes after the first two stages of synchronization, generates residual offset corrections, and feeds them back to the corresponding acquisition nodes to correct their local clocks again. The closed-loop process of acquisition, cross-correlation calculation, and feedback correction is repeated, using the physical signal of the seismic wave excited by the earthquake source as a synchronization reference. This breaks through the accuracy limit of pure protocol layer timestamp synchronization, and ultimately brings the time synchronization error between the acquisition nodes from the microsecond level to the sub-microsecond level. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0023] Figure 1 This is a flowchart illustrating a tunnel advanced geological prediction method based on three-level synchronization of wireless data transmission, according to an embodiment of the present invention. Figure 2 This is a topology diagram of a tunnel advanced geological prediction system based on three-level synchronization of wireless data transmission according to an embodiment of the present invention. Figure 3 for Figure 2 A simplified schematic diagram of the structure of the data acquisition node instrument; Figure 4 This is a timing diagram of bidirectional time difference measurement interaction in one embodiment of the present invention. In the diagram, the host is the acquisition host and the slave is the acquisition node instrument.

[0024] In the picture: 1. Data acquisition terminal; 2. Data acquisition host; 3. Data acquisition node; 4. Magnetic control switch; 5. Expansion screw mounting hole.

[0025] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0026] It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0028] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0029] Furthermore, the use of terms such as "first" and "second" in this invention is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this invention.

[0030] Please see Figures 1 to 4 This embodiment provides a tunnel advanced geological prediction method based on three-level synchronization of wireless data transmission, applied to a tunnel advanced geological prediction system. The tunnel advanced geological prediction system includes a data acquisition host, multiple data acquisition nodes, and a data acquisition terminal. In this embodiment, the data acquisition host integrates a dual-band WiFi module supporting 2.4GHz and 5GHz frequency bands, a timing module, a triggering module, and a battery module; the number of data acquisition nodes is eight, each integrating a WiFi module, a wireless synchronization module, a three-component accelerometer sensor, a data acquisition circuit, and a built-in battery; the data acquisition terminal is a tablet or laptop computer with WiFi networking capabilities.

[0031] Each data acquisition node has a built-in battery with a battery life of no less than 12 hours. During the equipment deployment phase, each data acquisition node is powered on using a magnetic switch with a trigger distance of no less than 5cm. Each data acquisition node has expansion bolt mounting holes located at its bottom. Operators secure the data acquisition node to the rock mass by driving expansion bolts into drill holes in the tunnel face or tunnel wall and using these mounting holes. To prevent accidental power-on / off activation using magnetic tools during installation, the physical distance between the expansion bolt mounting holes and the magnetic switch is greater than 5cm.

[0032] The acquisition host is equipped with a waterproof aviation plug. When the trigger signal line of an external vibration source is inserted into and contacts the waterproof aviation plug, the acquisition host can be automatically woken up and powered on.

[0033] Specifically, the following steps are included: S1. The data acquisition host establishes a wireless data transmission network with multiple data acquisition nodes; Specifically, after the data acquisition host is powered on, it activates the WiFi hotspot function. Upon powering on, each data acquisition node and terminal automatically searches for and connects to the WiFi hotspot of the data acquisition host, thereby establishing a wireless data transmission network between the data acquisition host, each data acquisition node, and the data acquisition terminal. Each data acquisition node reports its device status information to the data acquisition terminal via this wireless data transmission network.

[0034] This embodiment also includes an automatic attitude compensation process, as detailed below: Before the seismic wave data acquisition officially begins, and while each data acquisition node is installed and stationary, the three-component accelerometer within the node operates in low-frequency response mode (first response mode). The node continuously measures the static components of the Earth's gravity vector along the sensor's three axes within a 1-5 second time window, and averages the acquired data to filter out weak high-frequency vibration interference from the tunnel environment. Based on the averaged static components of the gravity vector, the node calculates its own coordinate system's pitch, roll, and azimuth angles relative to the standard geodetic coordinate system, and reports these angles to the acquisition terminal via the wireless data transmission network. The noise density of the three-component accelerometer is no greater than 1. This ensures that the accuracy of attitude angle measurement is no greater than 0.1°.

[0035] After receiving the attitude angle information from all acquisition nodes, the acquisition terminal sends a mode switching command to each acquisition node via a wireless data transmission network. Upon receiving the command, each acquisition node switches its three-component accelerometer from low-frequency response mode to high-frequency response mode (second response mode) to remove the gravity DC component and adjust the gain, preparing for subsequent seismic wave data acquisition. This mode switching is a unidirectional and irreversible operation; once in high-frequency response mode, it will not respond to commands to switch back to low-frequency response mode unless the device is restarted.

[0036] The acquisition terminal then constructs a three-dimensional coordinate rotation matrix for each acquisition node based on the received pitch, roll, and azimuth angles. After acquiring the seismic wave data from each acquisition node in subsequent steps, the acquisition terminal uses the corresponding rotation matrix to transform the seismic wave data from the local coordinate system of each acquisition node to a unified geodetic coordinate system.

[0037] S2. The acquisition host broadcasts a synchronization clock command to each of the acquisition nodes, and each of the acquisition nodes synchronizes its clock frequency according to the received synchronization clock command. Specifically, to eliminate temperature drift and aging errors of the crystal oscillator inside the acquisition node, the acquisition host broadcasts a synchronization clock command to each acquisition node once every integer second via a wireless data transmission network.

[0038] Upon receiving the synchronization clock command, each data acquisition node records its local reception time. Each node compares the time interval between two consecutive received synchronization clock commands with the deviation from a standard 1 second. When the deviation exceeds a preset deviation threshold, the wireless synchronization module inside the data acquisition node outputs a control signal to adjust the control voltage of its voltage-controlled crystal oscillator, thereby changing the clock oscillation frequency to correct its own clock frequency and align the clock speed of the data acquisition node with that of the main data acquisition unit. This clock frequency synchronization is continuously and periodically performed during the operation of the tunnel advanced geological prediction system.

[0039] S3. The acquisition host and each acquisition node perform bidirectional time difference measurement to obtain the measurement result, and each acquisition node performs local clock phase synchronization based on the measurement result; Specifically, based on the alignment of travel rates, errors in the absolute time phase are further eliminated. The acquisition host and each acquisition node perform bidirectional time difference measurement.

[0040] The specific data flow is as follows: First, the acquisition host sends a time difference measurement command and records the sending time. The acquisition host encodes the transmission time T1 into the payload of the time difference measurement command and sends it to each acquisition node.

[0041] The data acquisition node receives the time difference measurement command and records the reception time. Subsequently, the data acquisition node immediately sends a time difference measurement command to the data acquisition host and records the sending time. .

[0042] After receiving the time difference measurement command from the acquisition node, the acquisition host records the reception time. The acquisition host then generates a response frame, specifying the received time. The data is encoded and sent to the corresponding data acquisition node.

[0043] The data acquisition node has collected all the data. , , and After four timestamps, according to the formula: clock offset It calculates its own clock offset O relative to the acquisition host.

[0044] The acquisition node adjusts the count value of its local clock register based on the calculated clock offset O. Each acquisition node repeats the above bidirectional time difference measurement and adjustment process until the clock offset O converges to no more than 1 μs.

[0045] S4. After the earthquake source is triggered, each of the acquisition nodes acquires seismic wave data and transmits it back to the acquisition terminal through the wireless data transmission network. The acquisition terminal determines the cross-correlation result between the seismic wave data based on the seismic wave data of different acquisition nodes, generates a residual offset correction amount based on the cross-correlation result, and feeds back the residual offset correction amount to the corresponding acquisition node to correct its local clock again. Specifically, after completing the time synchronization of the first two protocol layers, the system enters the closed-loop recalibration phase based on physical signals: The earthquake source generates seismic waves, and a trigger signal is simultaneously sent to the trigger module of the acquisition host. Upon receiving the acquisition start command broadcast by the acquisition host, which includes the trigger time, each acquisition node synchronously activates its three-component accelerometer to acquire data, with a sampling rate set to no less than 10kHz. Each acquisition node transmits the acquired raw seismic wave data back to the acquisition terminal in real time via a wireless data transmission network, with the wireless transmission delay controlled to be less than 50ms.

[0046] Before the mutual loop closure process, the acquisition node periodically measures the wireless link quality indicators between itself and the acquisition host, and reports the wireless link quality indicators to the acquisition terminal. The wireless link quality indicators include Received Signal Strength Indicator (RSSI) and Packet Loss Rate (PLR).

[0047] The acquisition terminal selects the acquisition node with the highest RSSI as the reference node based on the received wireless link quality index. The acquisition terminal controls the reference node to perform a bidirectional time difference measurement with the acquisition host to obtain the reference residual clock offset of the reference node relative to the acquisition host at the current moment. .

[0048] Subsequently, the acquisition terminal performs cross-correlation calculations on the remaining non-reference acquisition nodes, excluding the reference node. For each non-reference acquisition node, the acquisition terminal selects the same component (e.g., the Z component) between the seismic wave data transmitted from that non-reference node and the seismic wave data transmitted from the reference node, and extracts a segment containing the first arrival waveform of the direct P-wave as the cross-correlation analysis window. The length of the cross-correlation analysis window is set to 256 to 1024 sampling points. Within the cross-correlation analysis window, the acquisition terminal calculates the normalized cross-correlation function of the two signals, and improves the temporal resolution of the cross-correlation function using a cubic spline interpolation algorithm, extracting the delay time corresponding to the peak value of the cross-correlation function. .

[0049] The acquisition terminal calculates the residual offset correction amount of the non-reference acquisition node. The data is transmitted to the non-reference acquisition node via the wireless data transmission network. After receiving the data, the non-reference acquisition node fine-tunes its own voltage-controlled crystal oscillator control voltage or adjusts its local clock register based on the residual offset correction amount. The calculation formula is as follows: .

[0050] S5. Repeat step S4 until the time synchronization error of all acquisition nodes converges to the preset range.

[0051] Specifically in this embodiment, the acquisition terminal determines the residual offset correction amount of each non-reference acquisition node. Does it meet the convergence condition? If an absolute value exists | For nodes with a duration greater than 0.1 μs, step S4 is repeated upon the next earthquake source trigger, forming a closed-loop iteration.

[0052] When the absolute value of the residual offset correction of all non-reference acquisition nodes | When the clock speed is no greater than 0.1 μs, the acquisition terminal determines that the system has synchronously converged, terminates the iteration process, and sends a command to each acquisition node to lock the current clock state. Subsequent acquisitions are based on this locked state.

[0053] To prevent cross-correlation calculations from diverging and entering an infinite loop due to severe environmental noise, the acquisition terminal is set to a maximum of 10 iterations. When the preset maximum number of iterations is reached, and there are still non-reference acquisition nodes... When the accuracy exceeds 0.1 μs, the acquisition terminal stops iterating and continues to perform conventional seismic wave data acquisition with a reduced accuracy (i.e., relying on the accuracy of no more than 1 μs achieved in step S3). At this time, the acquisition terminal writes an accuracy level identifier in the header of the generated seismic wave data file to prompt the data processing personnel later.

[0054] In this embodiment, under tunnel construction conditions lacking 4G / 5G and GPS signals, a wireless data transmission network is established between the acquisition host and multiple acquisition nodes, replacing traditional wired cable connections. This removes the constraints of cable length and routing for node deployment, significantly reducing deployment time on narrow tunnel faces. Master-slave clock frequency synchronization is achieved through broadcast synchronization clock commands, while master-slave clock phase synchronization is completed through bidirectional time difference measurement. This ensures microsecond-level time consistency across all acquisition nodes on a purely wireless channel, providing a fundamental time reference for precise alignment of subsequent seismic wave waveforms. This overcomes the limitations of unavailable satellite time synchronization and insufficient accuracy of common network time protocols like NTP in tunnel environments. Based on this, after the acquisition terminal acquires the seismic wave data synchronously acquired by each acquisition node, it performs cross-correlation calculations on the seismic wave data of different acquisition nodes, extracts the small clock deviations remaining between the acquisition nodes after the first two stages of synchronization, generates residual offset corrections, and feeds them back to the corresponding acquisition nodes to correct their local clocks again. The closed-loop process of acquisition, cross-correlation calculation, and feedback correction is repeated, using the physical signal of the seismic wave excited by the earthquake source as a synchronization reference. This breaks through the accuracy limit of pure protocol layer timestamp synchronization, and ultimately brings the time synchronization error between the acquisition nodes from the microsecond level to the sub-microsecond level.

[0055] In one embodiment, the following steps are included after step S5: Each of the acquisition nodes periodically measures the wireless link quality indicators between itself and the acquisition host, and reports the wireless link quality indicators to the acquisition host; wherein, the wireless link quality indicators include received signal strength indication and packet loss rate; The wireless link quality indicators are determined to meet the preset communication conditions. When the received signal strength of a certain acquisition node is lower than the first preset threshold or the packet loss rate is higher than the second preset threshold, the preset communication conditions are not met, and the acquisition host marks the acquisition node as a relay candidate node. When the received signal strength of a certain acquisition node is greater than or equal to the first preset threshold and the packet loss rate is less than or equal to the second preset threshold, the preset communication conditions are met. The data acquisition host selects the data acquisition node closest to the candidate relay node from among the other data acquisition nodes whose wireless link quality indicators meet the preset communication conditions as the relay node; The acquisition host sends configuration commands to the relay node and the relay candidate node respectively, so that the relay candidate node can communicate with the acquisition host through the relay node.

[0056] More preferably, after the relay candidate node communicates with the acquisition host via the relay node, relay forwarding delay compensation is performed, specifically including the following steps: When forwarding the time difference measurement command, the relay node measures the forwarding processing delay. and reverse forwarding processing latency and the forward forwarding processing delay and the reverse forwarding processing delay Attached to the forwarded command frame; When calculating the clock offset O, the relay candidate node uses a correction formula: ; When there are multiple levels of relays, the forward forwarding processing delay and the reverse forwarding processing delay of each level of relay node are accumulated and deducted respectively.

[0057] Specifically, in this embodiment, the unevenness caused by tunnel face excavation may result in a data acquisition node being obstructed by rocks, affecting wireless communication. During system operation, each data acquisition node measures and reports its own RSSI and PLR every 500ms.

[0058] When the RSSI of a certain acquisition node is lower than a first preset threshold or its PLR is higher than a second preset threshold, the acquisition terminal or the acquisition host marks the acquisition node as a relay candidate node. In this embodiment, the first and second preset thresholds are configurable, with typical values ​​for the first preset threshold being -75dBm and 5%.

[0059] Subsequently, from the remaining acquisition nodes that meet the preset communication conditions (i.e., RSSI≥-75dBm and PLR≤5%), the acquisition node closest to the candidate relay node in terms of spatial Euclidean distance is selected as the relay node by comparing the installation coordinates of each acquisition node.

[0060] The data acquisition host sends network configuration commands to both the relay node and the candidate relay node to establish a new wireless routing table, enabling data and synchronization commands from the candidate relay node to be forwarded to the data acquisition host via the relay node. This embodiment supports a maximum of two levels of relays to limit the maximum communication latency.

[0061] Once the relay link is established, the time difference measurement data packets will experience processing delays when passing through the relay node. The microcontroller inside the relay node uses a local high-frequency counter to accurately measure the forwarding processing delay between receiving and forwarding the time difference measurement command. And the reverse forwarding processing delay during the reverse forwarding process. The forwarding delay measurement accuracy is no greater than 100 ns. The relay node will measure the... and The values ​​are written into the reserved additional fields of the forwarding command frame.

[0062] When the relay candidate node receives the time difference measurement command passing through the relay node and is preparing to calculate the clock offset O, it reads the bidirectional forwarding processing delay attached to the command frame and uses the following correction formula: ; When there are two levels of relays, the forwarding processing delay in the above formula is the sum of the delays generated by each level of relay node and then subtracted, thereby eliminating the asymmetric delay error caused by the wireless relay forwarding link and ensuring that the acquisition node in the blind zone can still obtain sufficient synchronization accuracy.

[0063] In one embodiment, after step S4, the following step is further included for source quality control: The acquisition terminal uses the long-short time window energy ratio method to pick the first arrival time of the direct P-wave of the same source event from the seismic wave data after it has been converted to a unified geodetic coordinate system. By combining the installation coordinates of each acquisition node and the P-wave velocity of the rock mass, a set of time difference equations is constructed and the three-dimensional coordinates of the seismic source are inverted; The three-dimensional coordinates of the earthquake source are compared with the coordinates of the designed impact point. When the deviation between the two exceeds the preset tolerance, a quality control anomaly warning is issued.

[0064] Specifically, after each seismic wave data acquisition is completed, and the seismic wave data from each acquisition node is transformed to a unified geodetic coordinate system via a rotation matrix constructed by the acquisition terminal, the acquisition terminal performs source localization to verify the location and quality of the actual impact point.

[0065] The acquisition terminal uses the STA / LTA (long-short window energy ratio) method to automatically pick up the first arrival time of the direct P wave of the same source event from the seismic wave data of each acquisition node instrument.

[0066] The acquisition terminal uses the known three-dimensional installation coordinates of each acquisition node and the measured or estimated rock mass P-wave velocity as known quantities, and the earthquake source occurrence time and the three-dimensional spatial coordinates of the earthquake source as unknown quantities, to construct a nonlinear time difference equation system.

[0067] The acquisition terminal uses the damped least squares method to solve for the three-dimensional coordinates of the earthquake source.

[0068] The acquisition terminal compares the spatial Euclidean distance between the inverted three-dimensional coordinates of the seismic source and the pre-input design impact point coordinates. When the distance deviation exceeds a preset tolerance, the acquisition terminal issues a quality control anomaly warning via a screen pop-up or audible and visual alarm, indicating to the on-site operators that the actual impact location may deviate from the design requirements or that the surrounding rock wave velocity has changed drastically. In this embodiment, the preset tolerance is set to 0.5m.

[0069] The present invention also provides a tunnel advanced geological prediction system based on three-level synchronization of wireless data transmission, which executes the tunnel advanced geological prediction method based on three-level synchronization of wireless data transmission as described above, including a data acquisition host, multiple data acquisition nodes and a data acquisition terminal; The acquisition host establishes a wireless data transmission network with the multiple acquisition nodes, broadcasts a synchronization clock command to each acquisition node, performs bidirectional time difference measurement with each acquisition node and obtains the measurement results, and receives the seismic source trigger signal. The data acquisition node is configured to synchronize its clock frequency according to the received synchronization clock command, synchronize its local clock phase according to the measurement results of the bidirectional time difference measurement, acquire seismic wave data after the earthquake source is triggered and transmit it back to the acquisition terminal through the wireless data transmission network, and receive the residual offset correction amount fed back by the acquisition terminal and correct the local clock accordingly. The data acquisition node has a built-in magnetic control switch, a three-axis accelerometer and a wireless communication module. The bottom of the data acquisition node is provided with expansion screw mounting holes, and the data acquisition node is fixedly installed on the tunnel face by expansion screws. Acquisition terminal: Determines the cross-correlation results between seismic wave data based on the seismic wave data from different acquisition nodes, generates the residual migration correction amount based on the cross-correlation results, and feeds back the residual migration correction amount to the corresponding acquisition node; In this process, after each earthquake source is triggered and the seismic wave data acquisition and residual offset correction feedback are completed, the acquisition terminal controls each acquisition node to repeatedly perform seismic wave data acquisition and local clock correction until the time synchronization error of all acquisition nodes converges to a preset range.

[0070] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.

Claims

1. A tunnel advanced geological prediction method based on three-level synchronization of wireless data transmission, applied to a tunnel advanced geological prediction system including a data acquisition host, multiple data acquisition nodes, and data acquisition terminals, characterized in that, Includes the following steps: S1. The data acquisition host establishes a wireless data transmission network with multiple data acquisition nodes; S2. The acquisition host broadcasts a synchronization clock command to each of the acquisition nodes, and each of the acquisition nodes synchronizes its clock frequency according to the received synchronization clock command. S3. The acquisition host and each acquisition node perform bidirectional time difference measurement to obtain the measurement result, and each acquisition node performs local clock phase synchronization based on the measurement result; S4. After the earthquake source is triggered, each of the acquisition nodes acquires seismic wave data and transmits it back to the acquisition terminal through the wireless data transmission network. The acquisition terminal determines the cross-correlation result between the seismic wave data based on the seismic wave data of different acquisition nodes, generates a residual offset correction amount based on the cross-correlation result, and feeds back the residual offset correction amount to the corresponding acquisition node to correct its local clock again. S5. Repeat step S4 until the time synchronization error of all acquisition nodes converges to the preset range.

2. The tunnel advanced geological prediction method based on three-level synchronization of wireless data transmission according to claim 1, characterized in that, Step S2 specifically includes the following steps: The acquisition host broadcasts the synchronization clock command every integer second; Obtain the reception time of the synchronization clock command recorded by each of the acquisition nodes, and obtain the deviation between the time interval of two adjacent receptions of the synchronization clock command and 1 second; When the deviation exceeds the preset deviation threshold, each of the acquisition nodes adjusts the control voltage of its own voltage-controlled crystal oscillator to correct its own clock frequency; The clock frequency synchronization is continuously and periodically executed during the operation of the tunnel advanced geological prediction system.

3. The tunnel advanced geological prediction method based on three-level synchronization of wireless data transmission according to claim 1, characterized in that, Step S3 specifically includes the following steps: The data acquisition host sends a time difference measurement command and records the sending time. The sending time Send to the data acquisition node; The data acquisition node receives the time difference measurement command and records the receiving time. ; The data acquisition node sends a time difference measurement command to the data acquisition host and records the sending time. ; The data acquisition host receives a time difference measurement command from the data acquisition node and records the receiving time. The receiving time Send to the data acquisition node; The data acquisition node calculates the clock offset O and adjusts its local clock accordingly; the calculation formula is as follows: ; Repeat the above bidirectional time difference measurement until the clock offset O converges to ≤1μs.

4. The tunnel advanced geological prediction method based on three-level synchronization of wireless data transmission according to claim 1, characterized in that, In step S4, the acquisition terminal determines the cross-correlation results between the seismic wave data based on the seismic wave data from different acquisition nodes, and generates residual migration corrections based on the cross-correlation results. This specifically includes the following steps: The wireless link quality index between each of the acquisition nodes and the acquisition host is obtained, and the acquisition terminal selects the acquisition node with the highest wireless link quality index as the reference node. The acquisition terminal controls the reference node to perform bidirectional time difference measurement with the acquisition host to obtain the residual clock offset of the reference node relative to the acquisition host. ; For each non-reference acquisition node, the acquisition terminal selects the first arrival segment of the direct P-wave of the non-reference acquisition node and the reference node as the cross-correlation analysis window. Within the cross-correlation analysis window, the normalized cross-correlation function of the non-reference acquisition node signal and the reference node signal is calculated. The delay time corresponding to the peak value of the cross-correlation function is extracted by cubic spline interpolation. , which is the residual clock offset of the non-reference acquisition node relative to the reference node; The acquisition terminal calculates the residual offset correction amount of the non-reference acquisition node. The data is transmitted to the non-reference acquisition node via the wireless data transmission network. After receiving the data, the non-reference acquisition node fine-tunes its local clock according to the residual offset correction amount. The calculation formula is as follows: .

5. The tunnel advanced geological prediction method based on three-level synchronization of wireless data transmission according to claim 1, characterized in that, Step S5 specifically includes the following steps: When the absolute value of the residual offset correction of all non-reference acquisition nodes is no greater than 0.1μs, the iteration is terminated and the current clock state is locked. When the number of consecutive iterations reaches the preset maximum number of iterations, and there is still a residual offset correction value of non-reference acquisition nodes that is greater than 0.1 μs, the iteration stops, and data acquisition continues with a reduced accuracy. The accuracy level identifier is written into the acquired seismic wave data file.

6. The tunnel advanced geological prediction method based on three-level synchronization of wireless data transmission according to claim 1, characterized in that, Step S5 is followed by the following steps: Each of the acquisition nodes periodically measures the wireless link quality indicators between itself and the acquisition host, and reports the wireless link quality indicators to the acquisition host; wherein, the wireless link quality indicators include received signal strength indication and packet loss rate; The wireless link quality indicators are determined to meet the preset communication conditions. When the received signal strength of a certain acquisition node is lower than the first preset threshold or the packet loss rate is higher than the second preset threshold, the preset communication conditions are not met, and the acquisition host marks the acquisition node as a relay candidate node. When the received signal strength of a certain acquisition node is greater than or equal to the first preset threshold and the packet loss rate is less than or equal to the second preset threshold, the preset communication conditions are met. The data acquisition host selects the data acquisition node closest to the candidate relay node from among the other data acquisition nodes whose wireless link quality indicators meet the preset communication conditions as the relay node; The acquisition host sends configuration commands to the relay node and the relay candidate node respectively, so that the relay candidate node can communicate with the acquisition host through the relay node.

7. The tunnel advanced geological prediction method based on three-level synchronization of wireless data transmission according to claim 6, characterized in that, After the relay candidate node communicates with the acquisition host via the relay node, relay forwarding delay compensation is performed, specifically including the following steps: When forwarding the time difference measurement command, the relay node measures the forwarding processing delay. and reverse forwarding processing latency and the forwarding processing delay and the reverse forwarding processing delay Attached to the forwarded command frame; When calculating the clock offset O, the relay candidate node uses a correction formula: ； When there are multiple levels of relays, the forward forwarding processing delay and the reverse forwarding processing delay of each level of relay node are accumulated and deducted respectively.

8. The tunnel advanced geological prediction method based on three-level synchronization of wireless data transmission according to claim 1, characterized in that, Before step S4, the following steps are also included: During the static installation phase, the three-component accelerometer in each of the acquisition nodes operates in the first response mode to measure the static component of the gravity vector. Based on the static component of the gravity vector, the pitch angle, roll angle, and azimuth angle of each of the acquisition nodes are calculated and reported to the acquisition terminal. The acquisition terminal sends a mode switching command to each of the acquisition nodes, so that each of the acquisition nodes switches the three-component accelerometer to the second response mode to acquire seismic wave data. The acquisition terminal constructs a rotation matrix based on the pitch, roll, and azimuth angles of each acquisition node to convert the acquired seismic wave data into a unified geodetic coordinate system.

9. The tunnel advanced geological prediction method based on three-level synchronization of wireless data transmission according to claim 8, characterized in that, Following step S4, the following steps are also included: The acquisition terminal uses the long-short time window energy ratio method to pick the first arrival time of the direct P-wave of the same source event from the seismic wave data after it has been converted to a unified geodetic coordinate system. By combining the installation coordinates of each acquisition node and the P-wave velocity of the rock mass, a set of time difference equations is constructed and the three-dimensional coordinates of the seismic source are inverted; The three-dimensional coordinates of the earthquake source are compared with the coordinates of the designed impact point. When the deviation between the two exceeds the preset tolerance, a quality control anomaly warning is issued.

10. A tunnel advanced geological prediction system based on three-level synchronization of wireless data transmission, executing the tunnel advanced geological prediction method based on three-level synchronization of wireless data transmission as described in any one of claims 1-9, characterized in that, Includes a main data acquisition unit, multiple data acquisition nodes, and data acquisition terminals; The acquisition host establishes a wireless data transmission network with the multiple acquisition nodes, broadcasts a synchronization clock command to each acquisition node, performs bidirectional time difference measurement with each acquisition node and obtains the measurement results, and receives the seismic source trigger signal. The data acquisition node is configured to synchronize its clock frequency according to the received synchronization clock command, synchronize its local clock phase according to the measurement results of the bidirectional time difference measurement, acquire seismic wave data after the earthquake source is triggered and transmit it back to the acquisition terminal through the wireless data transmission network, and receive the residual offset correction amount fed back by the acquisition terminal and correct the local clock accordingly. The data acquisition node has a built-in magnetic control switch, a three-axis accelerometer and a wireless communication module. The bottom of the data acquisition node is provided with expansion screw mounting holes, and the data acquisition node is fixedly installed on the tunnel face by expansion screws. Acquisition terminal: Determines the cross-correlation results between seismic wave data based on the seismic wave data from different acquisition nodes, generates the residual migration correction amount based on the cross-correlation results, and feeds back the residual migration correction amount to the corresponding acquisition node; In this process, after each earthquake source is triggered and the seismic wave data acquisition and residual offset correction feedback are completed, the acquisition terminal controls each acquisition node to repeatedly perform seismic wave data acquisition and local clock correction until the time synchronization error of all acquisition nodes converges to a preset range.

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