An urban road underground cavity identification, positioning and early warning system

Abstract

This invention discloses a system for identifying, locating, and warning of underground cavities in urban roads, belonging to the field of urban road safety monitoring technology. The system includes sensing optical cables deployed along the road, a DAS demodulator, data processing equipment, and early warning equipment. It employs a single-line, single-sided or single-line, double-sided U-shaped optical fiber deployment method. The dual-fiber loop structure provides a physical carrier for signal cross-verification, significantly improving detection reliability and ultimately achieving accurate cavity location and risk warning. This invention solves the problems of traditional methods, such as inability to continuously monitor in real time, susceptibility to interference, and high false alarm rates. It has the advantages of wide coverage, high accuracy, high reliability, and low-cost deployment.

Description

Technical Field

[0001] This invention relates to the field of safety monitoring of urban road infrastructure, specifically to a system for identifying, locating, and providing early warning of underground cavities in urban roads. Background Technology

[0002] With the acceleration of urbanization, the traffic load on urban roads is increasing daily. However, due to various factors such as underground pipeline leakage, soil erosion, and improper construction, underground cavities are easily formed under roads. If these cavities are not detected and addressed in time, they may lead to roadbed settlement, road surface collapse, vehicle damage, and even serious casualties and property losses. Therefore, routine and effective monitoring of underground cavities in urban roads has become an urgent task for urban safety management.

[0003] Traditional methods for detecting cavities, such as drilling, ground-penetrating radar, and artificial seismic stations, generally have significant limitations in practical applications. First, these methods are mostly point-based or sampling-based, failing to achieve continuous, seamless coverage of an entire road segment, resulting in widespread monitoring blind spots. Second, their real-time performance is severely lacking; detection cycles are typically long, making it difficult to respond promptly and issue early warnings for sudden cavities. Furthermore, the complex urban environment, with its traffic loads and environmental noise, easily interferes with detection results, leading to misjudgments or missed detections. Finally, these traditional methods are often costly and difficult to implement, especially in existing urban road networks, where large-scale deployment faces significant challenges.

[0004] While distributed fiber acoustic sensing (DAS) technology offers advantages such as wide-area, continuous, and real-time monitoring, a mature and reliable solution remains lacking for its effective application in the accurate identification of underground cavities in urban roads and in suppressing interference in complex, high-noise urban environments. The key to this invention lies in addressing the fundamental nature of this problem—how to accurately extract cavity signals and reliably locate them spatially from massive amounts of noisy DAS data in low signal-to-noise ratio environments. This requires a systematic data calibration, signal enhancement, and decision-making mechanism. Therefore, this invention proposes a series of innovative technical solutions aimed at systematically addressing the aforementioned problems. Summary of the Invention

[0005] Based on the above problems, this invention proposes a system for identifying, locating and warning of underground cavities in urban roads.

[0006] A system for identifying, locating, and providing early warning of underground cavities in urban roads, comprising: The sensing optical cable is laid along the road to be measured and connected to the DAS demodulator. A distributed fiber acoustic sensor (DAS) demodulator is used to acquire scattered signals along the optical fiber and convert the signals into time-series response data. A data processing and storage device, communicatively connected to the DAS demodulator, is used to receive and process the timing response data; The early warning and display device is communicatively connected to the data processing and storage device. The sensing optical cable is deployed in one of the following two structures: Structure 1: Single-line, single-sided structure, wherein the sensing optical cable is a single optical fiber, laid in a straight line along one side of the road; the DAS demodulator collects vibration signals under the road on one side through the single optical fiber; Structure 2: U-shaped loop structure. The sensing optical cable consists of optical fiber A segment and optical fiber B segment laid in parallel along both sides of the road. The optical fiber A segment and optical fiber B segment are physically connected at one end of the road through optical fiber fusion splice or connector to form a U-shaped loop, and are connected to the same DAS demodulator, so that the DAS demodulator can synchronously collect vibration signals below both sides of the road. Preferably, for the single-line single-sided structure: the single optical fiber is divided into multiple continuous sensing channels, and any two of the sensing channels constitute a monitoring unit.

[0007] Preferably, for the U-shaped loop structure: the sensing channels on optical fiber A segment and optical fiber B segment that correspond to each other form a monitoring channel pair for cross-verification, realizing multi-scale spatial detection.

[0008] Preferably, in the U-shaped loop structure, a specific sensing channel on the B segment of the optical fiber and a series of continuous sensing channels on the A segment of the optical fiber together form a fan-shaped monitoring channel group, realizing planar spatial detection and multiple superimposed positioning of the area between the two optical fibers.

[0009] Preferred data processing and storage devices include: The data processing module receives the raw electrical signal from the DAS demodulator at its input end and outputs a filtered and de-trending digital signal at its output end. The cavity identification and positioning module generates a cavity positioning command based on the digital signal and sends the command to the early warning and display device. When the sensing optical cable is laid out as a single line on one side, the cavity identification and positioning unit processes the signal from a single optical fiber path; when it is laid out in a U-shaped loop, the cavity identification and positioning unit simultaneously processes and merges the signals from optical fiber segments A and B.

[0010] Preferably, the early warning and display device is communicatively connected to the data processing and storage device to receive and display the void space location, range, and risk level information output by the device; the early warning and display device includes a local photoelectric alarm device, a local monitoring and display device, and a mobile device for receiving early warning information.

[0011] Compared with the prior art, the present invention has the following significant advantages: (1) Large-scale, continuous, and real-time monitoring: It realizes all-weather, uninterrupted monitoring of underground cavities in urban roads, filling the gap of traditional methods.

[0012] (2) Low false alarm rate and high accuracy: Through dynamic threshold and multi-level fusion judgment mechanism, the high accuracy of judgment is ensured and the waste of resources caused by false alarm is effectively avoided.

[0013] (3) High reliability and adaptability: The system can adapt to changes in the environment and remain stable and reliable even in complex urban environments.

[0014] (4) Low cost and easy to promote: The invented U-shaped fiber optic deployment method reduces construction difficulty and cost, and has fault tolerance characteristics, making it easy to promote and apply on a large scale in cities. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly described below.

[0016] Figure 1 This is a schematic diagram of single-line single-sided optical fiber deployment and channel pair selection according to an embodiment of the present invention; Figure 2 This is a schematic diagram of single-line double-sided fiber optic deployment and channel pair selection according to an embodiment of the present invention; Figure 3 This is a flowchart framework of the core data processing and judgment logic in one embodiment of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the following detailed description, in conjunction with the accompanying drawings and embodiments, further illustrates the invention. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of the invention.

[0018] Example 1

[0019] This embodiment discloses a system for identifying, locating, and issuing early warnings for underground cavities in urban roads, consisting of both hardware and software components. The hardware system mainly includes the following components: Sensing optical cable: Deployed along the road, serving as the core of the distributed sensing array. This optical cable can utilize existing communication optical cables or be a specially added sensing optical fiber, providing significant flexibility and cost-effectiveness for system deployment. In this embodiment, efficient monitoring of underground cavities in urban roads is achieved through single-line single-sided fiber deployment and single-line double-sided fiber deployment. The single-line single-sided deployment scheme is suitable for general survey scenarios, while the single-line double-sided fiber deployment enhances one-dimensional linear sensing capabilities to planar detection capabilities. Channel pair selection strategies in single-line single-sided deployment include: 1) selecting adjacent channels to form channel pairs, and 2) selecting non-adjacent channels to form channel pairs. Single-line double-sided fiber deployment connects parallel optical fibers along both sides of the road at one end of the road. Channel pair selection strategies include: 1) similar to single-line double-sided fiber deployment, using a single-sided fiber to monitor cavities in the geological body beneath the fiber; and 2) using one channel from fiber segment B and multiple channels from fiber segment A to form a "ray-like" channel pair, achieving comprehensive detection of the area between the two optical fibers.

[0020] DAS demodulator: responsible for acquiring the scattered signal along the optical fiber and converting it into timing response data that can be processed by the software system.

[0021] Data processing and storage equipment: Responsible for processing, analyzing, and storing raw data. It includes a data storage module, a data processing module, and a hole identification and location module. Data storage module stores the raw DAS signals.

[0022] The data processing module performs filtering and detrending operations on the raw signals acquired by the DAS demodulator to remove high-frequency noise and low-frequency interference from the environment, laying the foundation for subsequent data processing. Then, for each channel pair, the system employs a cross-correlation and time-stretching algorithm to accurately calculate the rate of change of the acoustic wave velocity, dv / v. This algorithm can quantify the change in the elastic modulus of the formation medium under the influence of underground cavities, thus providing basic data for subsequent anomaly detection.

[0023] The cavity identification and localization module compares the dv / v value with a preset threshold and identifies and locates underground cavities based on a multi-level fusion judgment mechanism. Specifically, Single-sided analysis (including single-line single-sided scheme and single-sided fiber segment analysis in single-line double-sided scheme): Independent dv / v calculations are performed on segments A and B respectively; Double-sided analysis: A specific channel of fiber segment B is selected and sequentially paired with a series of channels within a specified range on fiber segment A to form multiple channel pairs, creating a fan-shaped detection path; By analyzing the continuity, amplitude, and spatial distribution of dv / v anomaly signals of multiple channel pairs, multiple superimposed positioning and consistency verification are performed. If a real and significant geological change (such as cavity formation) occurs in a certain area, then the dv / v of segments A and B at that location should simultaneously show anomaly signals with the same trend and exceeding the threshold. When the dv / v value exceeds the dynamic threshold, the system enters the multi-level fusion judgment stage. In this embodiment, by introducing consistency constraints, the confidence of the judgment is fundamentally improved.

[0024] Early warning and display equipment: This equipment presents the monitoring results to the user in an intuitive way. It includes local photoelectric alarm devices, local monitoring display devices, and mobile devices (such as mobile phones or tablets).

[0025] The software system primarily runs on data processing and storage devices, and its functional modules and logical flow are as follows: Data processing module: responsible for filtering and detrending the raw signal acquired by the DAS demodulator to remove high-frequency noise and low-frequency interference in the environment, and using cross-correlation and time stretching algorithms to estimate the rate of change of sound wave velocity dv / v.

[0026] The cavity identification and location module compares the DV / V value with a preset dynamic threshold and performs multi-level verification using a multi-channel / multi-fiber fusion judgment mechanism. Furthermore, this module precisely maps the identified DV / V anomaly signals to corresponding road sections by projecting the fiber optic channel onto the ground surface, thereby achieving spatial location of underground cavities. In addition, the system integrates continuous anomaly intervals to accurately determine the true extent of the cavity.

[0027] Early warning and display equipment: The system outputs the spatial location, extent, and risk level of the cavity to the early warning module. This module supports multi-party early warning mechanisms to ensure that information is delivered to relevant parties in a timely and effective manner. Specifically, it supports local photoelectric alarm device prompts and monitor display of cavity information, issuing audible and visual alarms on-site to warn passing vehicles and pedestrians. It also pushes early warning information to mobile devices (such as mobile phones and tablets used by maintenance personnel) in real time, facilitating remote monitoring by managers and enabling rapid response and on-site investigation.

[0028] In this embodiment, the single-line single-sided fiber optic deployment and the single-line double-sided fiber optic deployment are designed for different engineering needs, demonstrating the flexibility and scalability of this invention in commercial applications.

[0029] (1) Single-line single-sided fiber optic deployment scheme ① Physical deployment method like Figure 1 As shown, an optical fiber is laid in a straight line along one side of the road and connected to a DAS demodulator. The advantage of this deployment method is that it is extremely easy to construct and inexpensive, making it suitable for wide-area surveys or scenarios requiring rapid monitoring of long-distance lines.

[0030] ②Channel Pair Selection Strategy Channel: An optical fiber is divided into several channels, and the length of optical fiber covered by each channel is called the gauge length. The gauge length determines the spatial resolution of the sensing unit.

[0031] Channel Spacing: There is a certain spatial offset between adjacent channels, which is called channel spacing.

[0032] Channel Pair: Any two channels form a channel pair, which serves as the basic unit for dv / v analysis.

[0033] The core of this solution lies in the precise division and flexible selection of fiber optic channels: Adjacent channel pairs: These consist of two adjacent channels, which is the most direct method of analysis. (For example, Channel A: i0 and Channel A: i0+1).

[0034] Arbitrary channel selection: Allows the selection of two non-adjacent channels to form a channel pair (e.g., Channel A: i0 and Channel A: i0+n, where n>1) to achieve multi-scale spatial exploration. Figure 1 The examples clearly demonstrate this strategy: by flexibly adjusting channel spacing and compensation settings, subsurface anomalies at different scales or depths can be detected, thus avoiding missed detections caused by a single fixed spacing. This indicates that the scheme has extremely high flexibility at the software level, can be optimized according to actual geological conditions, and is an algorithm-based spatial multi-scale detection strategy.

[0035] (2) Single-line double-sided fiber optic deployment scheme ① Physical deployment method like Figure 2As shown, two parallel optical fiber segments, fiber A and fiber B, are laid along both sides of the road and connected at one end to form a U-shaped optical fiber line. A DAS demodulator is located at one end of the line, simultaneously acquiring data from both fiber segments. A channel spanning the road is constructed using fiber segments A and B to monitor the geological structure below the road surface. For example, one channel from fiber segment B can be combined with multiple channels from fiber segment A to form a "ray-like" channel pair, enabling comprehensive detection of the area between the two optical fibers. Alternatively, a single-sided optical fiber can be used... Figure 1 This method monitors cavities in geological formations beneath optical fibers. This dual-analysis mode elevates one-dimensional linear sensing capabilities to planar detection capabilities. Based on this physical deployment, the traditional one-dimensional linear DAS sensing capability is fundamentally upgraded to two-dimensional sensing capabilities with planar detection. Traditional single-line deployments can only sense changes in vibration wave velocity along the fiber's direction, making it difficult to accurately pinpoint the lateral location of cavities, while U-shaped deployments provide the physical basis for achieving cross-path lateral sensing.

[0036] ② Dual-mode anomaly analysis The U-shaped deployment scheme enables the system to implement two different and complementary methods for monitoring underground cavities, thereby significantly improving the accuracy and coverage of detection: Mode 1: Single-sided fiber segment analysis Similar to the single-line, single-sided deployment scheme, this mode involves independent dv / v calculations for fiber segment A and fiber segment B. Within each fiber segment, channel pairs (including adjacent channels and arbitrary channels) can be flexibly selected, and the traversal step size for each channel pair can be arbitrarily set. This method is primarily used for precise monitoring of underground cavities beneath the fiber.

[0037] Mode 2: Analysis of dual-sided fiber optic cross-road channel pairs This is the core technological innovation of the U-shaped deployment scheme, specifically designed for monitoring voids located between two fiber segments. The core of this scheme is an innovative channel pair selection strategy. For example... Figure 2 As shown, the system can select a specific channel in fiber segment B (e.g., Channel B: i0) and sequentially form a channel pair with a series of channels within a specified range in fiber segment A (e.g., Channel A: i0 to Channel A: i0+n+1). In this way, a "ray-shaped" or "fan-shaped" channel pair selection range can be formed.

[0038] An underground cavity is a single acoustic anomaly point. When seismic waves or environmental vibrations pass through this cavity, they generate a disturbed wave field that simultaneously affects a series of channels on two parallel optical fibers. By pairing one channel of fiber segment B with multiple channels of fiber segment A using an algorithm, the system effectively creates multiple "virtual detection paths" spanning the path. This collection of virtual paths is a concrete manifestation of the "ray-like" or "fan-shaped" concept, extending the detection range from the linear projection of the optical fibers to the entire area between the two fibers. By analyzing the continuity, amplitude, and spatial distribution of dv / v anomaly signals on these virtual paths, the system can perform a "multi-overlay localization" analysis. This allows the system to fuse and verify the consistency of anomaly signals from multiple channel pairs, rather than relying solely on the anomalies of a single channel pair. This multipath, multi-channel consistency verification elevates the detection accuracy from simple channel projection to higher-dimensional spatial localization, effectively eliminating the influence of single random noise.

[0039] This combination of dual analysis modes enables the U-shaped deployment scheme to simultaneously measure signals from the same cavity location but via two different sensing paths. This design provides robust signal redundancy, cross-validation, and self-testing capabilities, allowing the system to perform "multi-fiber fusion judgment," meaning that an alert is only triggered when both corresponding channel pairs of fiber A and fiber B detect anomalies. This mechanism significantly improves the confidence level of the judgment, effectively suppresses false alarms caused by localized interference in a single fiber, and solves the "interference sensitivity" problem in the background technology.

[0040] Single-line single-sided and single-line double-sided fiber optic deployments are not interchangeable, but rather designed to address different engineering needs. Single-line single-sided deployments are suitable for cost-sensitive wide-area surveys, while single-line double-sided deployments provide the highest level of accuracy and reliability for critical areas. This tiered technology approach allows the invention to meet diverse application requirements with a flexible platform, demonstrating its high adaptability in engineering applications and commercialization.

[0041] In this embodiment, the multi-level fusion determination step includes: Level 1: Multi-channel Fusion: In the initial verification phase, the system requires that multiple adjacent channel pairs corresponding to the void region continuously detect dv / v anomalies. For the U-shaped deployment scheme, multiple "ray-like" superposition analyses are also required to ensure signal consistency. This filtering layer can effectively eliminate random noise on a single channel. It should be noted that the "superposition analysis" does not refer to the mathematical superposition and averaging of dv / v anomaly measurements of multiple channel pairs, but rather a multi-signal fusion judgment based on spatial distribution characteristics. That is, the system analyzes a series of "ray-like" virtual detection paths composed of a single second fiber segment channel and multiple first fiber segment channels (or a single first fiber segment channel and multiple second fiber segment channels). When a potential anomaly occurs, the system will examine whether the dv / v anomaly signals independently detected by multiple channel pairs within this fan-shaped detection range exhibit continuity in spatial distribution and consistency in anomaly amplitude and trend. Since a single random noise or localized interference typically affects only a very small number of channel pairs, while changes in the underground medium caused by a real underground cavity can affect a continuous area, resulting in mutually corroborating anomalous responses from multiple virtual paths covering that area, the system only determines that these independent measurements constitute a mutually supporting chain of evidence when a certain number of channel pairs simultaneously detect spatially continuous and characteristically consistent anomalous signals. This completes the "superposition" confirmation of the anomalous signals, improving the reliability and accuracy of event determination.

[0042] Level Two: Multi-fiber fusion for U-shaped deployments: As the final and highest-confidence determination, the system requires that the two parallel fiber segments corresponding to the void location must simultaneously and consistently exhibit dv / v anomalies before triggering an early warning. This cross-verification mechanism effectively eliminates misjudgments caused by sporadic interference (such as local vibrations from passing vehicles) in a single fiber, and is a key guarantee for the system's extremely high reliability in practical applications.

[0043] Level 3: Historical Baseline Comparison: The current DV / V anomaly signal is compared with long-term historical baseline data to eliminate signal fluctuations caused by short-term environmental changes (such as sudden temperature changes), further reducing the false alarm rate. This multi-layered adaptive decision-making mechanism enables the system to maintain high reliability even in complex and ever-changing urban environments, systematically solving all the interference problems pointed out in the background section.

[0044] To establish a reliable dv / v threshold, this invention employs a dual verification mechanism that combines virtual simulation with real-world environmental data. A three-dimensional finite element model is constructed to simulate underground cavities of different sizes, depths, and geological conditions, and their impact on the dv / v propagation of sound waves on optical fibers is calculated. Through large-scale numerical simulation, the abnormal threshold range of dv / v under ideal conditions can be obtained. In actual road environments, small cavities are artificially created to collect real-world abnormal dv / v values. This field data is used to verify and correct the threshold obtained from the numerical simulation, making it more consistent with actual engineering applications. The dual verification mechanism disclosed in this embodiment ensures the scientific validity and practicality of the threshold, reducing the false alarm rate at its source.

[0045] To ensure the long-term stability and accuracy of the system, this invention also introduces a dynamic calibration and reference signal mechanism. After the initial deployment, the system needs to collect baseline signals during a period of stable traffic and environment, using these as initial reference data. Since the urban environment is a dynamic system, factors such as geological subsidence, large-scale construction projects, and seasonal temperature differences can cause slow changes in the geological medium and sound wave propagation characteristics. If the reference data remains constant, these normal environmental changes may be misjudged as anomalies, leading to false alarms over time. Therefore, this invention introduces a mechanism for periodically and automatically updating the reference data (e.g., quarterly updates), combined with manual testing for correction. This adaptive and self-correcting dynamic system design is key to ensuring the system maintains high reliability in long-term applications.

[0046] This invention also introduces a dynamic compensation mechanism, fundamentally solving the problem of traditional methods being susceptible to environmental interference. The system collects environmental parameters in real time, such as temperature, rainfall, and traffic load, and automatically adjusts the dv / v judgment threshold accordingly. For example, during peak traffic hours, the system will raise the threshold accordingly to avoid false alarms caused by traffic noise; on rainy days, the system will consider the impact of moisture infiltration on the sound velocity of the foundation and make corresponding corrections. This adaptive decision-making mechanism enables the system to maintain high reliability even in complex and ever-changing urban environments.

[0047] This invention innovatively connects two parallel optical fiber segments, fiber A and fiber B, which are respectively deployed on both sides of the road, at one end of the road to form a U-shaped optical fiber line. The DAS demodulator is located at one end of the line, simultaneously collecting data from both optical fiber segments, and providing a physical basis for multi-fiber fusion determination, reducing construction difficulty and cost, and providing optical fiber self-testing and fault tolerance capabilities.

[0048] It should be noted that the software modules of this system are all embedded in the storage media of the data processing equipment; they are the means of implementing the hardware functions, not independent protected objects. The innovation of the system lies in the fiber optic deployment structure and equipment connection method; the software is only used to assist hardware operation.

[0049] Example 2

[0050] This embodiment discloses a method for identifying, locating, and issuing early warnings for underground cavities in urban roads, such as... Figure 3 As shown, it includes the following steps: S1 continuously collects vibration signals from beneath the road via sensing optical cables and a DAS demodulator installed on the road.

[0051] S2, preprocess the signal, including filtering, detrending and other operations, to remove high-frequency noise and low-frequency drift in the environment, and calculate the rate of change of sound wave velocity dv / v.

[0052] S3 acquires a baseline signal as an initial reference when the system is stable. The system automatically updates the baseline periodically (e.g., quarterly) to adapt to long-term environmental changes.

[0053] For each channel pair, the cross-correlation and time stretching algorithm is used to accurately calculate the rate of change of acoustic wave velocity dv / v.

[0054] A three-dimensional finite element model was constructed to simulate the impact of voids and determine the theoretical threshold range. Artificial voids were then placed in actual roads, and real data was collected to verify and correct the theoretical threshold in order to obtain the dv / v threshold.

[0055] A multi-level fusion judgment mechanism is used to verify abnormal signals.

[0056] The multi-level fusion determination mechanism is as follows: L1 compares the calculated rate of change of acoustic wave velocity (dv / v) with a preset dynamic threshold. This threshold is not a fixed value but is adjusted in real time according to environmental parameters (such as traffic load, temperature, and rainfall) to suppress false alarms caused by environmental interference. If the dv / v value does not exceed the threshold, the road condition is determined to be normal with no risk of underground cavities, and the process ends; if the dv / v value exceeds the dynamic threshold, the process proceeds to the L2 multi-channel fusion judgment stage.

[0057] L2 performs multi-channel fusion judgment when the dv / v of a certain channel pair exceeds the threshold.

[0058] Check if multiple adjacent channels around the anomaly point also show continuous and consistent dv / v anomalies to rule out random noise and local interference.

[0059] If multiple adjacent channels do not simultaneously exhibit consistent anomalies, the anomaly is determined to be likely caused by local interference, the process ends, and it is concluded that there are no underground cavities in the road.

[0060] If multiple adjacent channels are found to be continuously abnormal, for single-sided straight-line fiber optic cables, proceed directly to L4 historical baseline comparison; for U-shaped fiber optic cables, proceed to L3 multi-fiber fusion judgment.

[0061] L3, multi-fiber fusion judgment is only applicable to U-shaped fiber optic deployments, used to achieve cross-verification and reduce false alarms.

[0062] Determine whether the two parallel fiber segments exhibit anomalies simultaneously and consistently, i.e., whether consistent dv / v anomaly signals are detected at the same spatial location. If the determination is yes, then the spatial location and extent of the underground cavity are determined, and the process proceeds to L4 historical baseline comparison. If the determination is no, then it is determined that there is no underground cavity in the road area between the fiber segments, and the process ends.

[0063] L4, Historical Baseline Comparison. The system compares the current dv / v anomaly signal with long-term historical baseline data to eliminate the effects of slow environmental changes and seasonality.

[0064] Ultimately, only abnormal signals that successfully pass all the above judgment stages and are confirmed to be not caused by environmental interference will be recognized by the system as real underground cavity risk events, generating early warning information of different risk levels and outputting it to early warning and display devices.

[0065] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A system for identifying, locating, and issuing early warnings for underground cavities in urban roads, characterized in that, include: The sensing optical cable is laid along the road to be measured and connected to the DAS demodulator. A distributed fiber acoustic sensor (DAS) demodulator is connected to the sensing optical cable and is used to collect scattered signals along the optical fiber. Data processing and storage devices are communicatively connected to the DAS demodulator; The early warning and display device is communicatively connected to the data processing and storage device. The sensing optical cable is deployed in one of the following two structures: Structure 1: Single-line single-sided structure, the sensing optical cable is a single optical fiber, laid in a straight line along one side of the road, and the DAS demodulator collects the vibration signal under the road on one side through the single optical fiber; Structure 2: U-shaped loop structure. The sensing optical cable consists of optical fiber A segment and optical fiber B segment laid in parallel along both sides of the road. The optical fiber A segment and optical fiber B segment are physically connected at one end of the road through optical fiber fusion splice or connector to form a U-shaped loop, and are connected to the same DAS demodulator, so that the DAS demodulator can synchronously collect vibration signals below both sides of the road.

2. The system according to claim 1, characterized in that, For the single-line, single-sided structure: the single optical fiber is divided into multiple continuous sensing channels, and any two of the sensing channels constitute a monitoring unit.

3. The system according to claim 1, characterized in that, For the U-shaped loop structure: the sensing channels on optical fiber A segment and optical fiber B segment that correspond to each other form a monitoring channel pair for cross-verification, realizing multi-scale spatial detection.

4. The system according to claim 3, characterized in that, In the U-shaped loop structure, a specific sensing channel on the B segment of the optical fiber, together with a series of continuous sensing channels on the A segment of the optical fiber, forms a fan-shaped monitoring channel group, enabling planar spatial detection and multiple superimposed positioning of the area between the two optical fibers.

5. The system according to claim 1, characterized in that, The data processing and storage device includes: The data processing module receives the raw electrical signal from the DAS demodulator at its input end and outputs a filtered and de-trending digital signal at its output end. The cavity identification and positioning module generates a cavity positioning command based on the digital signal and sends the command to the early warning and display device. When the sensing optical cable is laid out as a single line on one side, the cavity identification and positioning unit processes the signal from a single optical fiber path; when it is laid out in a U-shaped loop, the cavity identification and positioning unit simultaneously processes and merges the signals from optical fiber segments A and B.

6. The system according to claim 1, characterized in that, The early warning and display device is communicatively connected to the data processing and storage device, and is used to receive and display the void space location, range and risk level information output by the device; the early warning and display device includes a local photoelectric alarm device, a local monitoring and display device, and a mobile device for receiving early warning information.

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