Highway Safety Monitoring Application
I. Overview
Recent incidents on domestic expressways, such as the "collapse of a highway bridge in Zhashui, Shanxi" and the "road collapse on MeiDa Expressway in Guangdong", highlight the urgent need for a comprehensive monitoring and early warning system to enhance the safety of roads and bridges. Puniu Technology's expressway safety monitoring system includes typical bridge modal frequency monitoring to monitor bridge structural changes in real-time; and underground imaging functions for fiber optic laying sections to provide early warnings for underground structural changes. Through these measures, we will build a road safety monitoring system based on fiber optic sensing, effectively improving the safety and reliability of infrastructure and protecting people's lives and property.
II. Technical Background
Distributed Acoustic Sensing (DAS) technology is an innovative sensing technology that can continuously monitor the distribution of vibrations and acoustic fields. When vibrations occur and propagate in the optical fiber cable, the fiber will stretch or compress due to strain. This change causes variations in the amplitude and phase of Rayleigh scattered light through the photoelastic effect of coherent laser in the fiber. By capturing and decoding these changes in backscattered light, we can obtain detailed information about vibration waves.
DAS technology is known for its distributed characteristics, high integration, wide sensing range, strong environmental adaptability, anti-electromagnetic interference capability, and meter-level resolution. It enables long-distance, high spatiotemporal precision monitoring of environmental vibrations and acoustic fields interacting with the fiber.
Puniu Technology has successfully developed a high-precision distributed fiber optic acoustic sensing system by combining optical frequency domain reflectometry with time gating technology and utilizing optical wave tuning control technology. This system has achieved remarkable results in fading suppression, bandwidth improvement, and spatial resolution optimization. It has overcome technical challenges such as spatial resolution and coherent fading noise, reaching the highest performance standards in the industry.
The outstanding feature of this system lies in its superior performance throughout the entire sensing fiber length, demonstrating high sensitivity, low noise, and high fidelity.
III. Main Functions of the System
The system includes functions such as GIS map management and display interface, traffic flow statistics, tunnel monitoring, bridge monitoring, settlement monitoring, collision accident alarm management, accident statistics, etc.
- Traffic Flow Management Function. This function enables monitoring of traffic volume and vehicle speed on specific sections of expressways. The monitoring results include monitoring time, monitoring point location, maximum and minimum speed monitoring, average speed monitoring, and traffic volume monitoring. Users can select monitoring locations, filter time periods, generate data charts, export data, and create real-time curve graphs.
Figure1： Real-time Curve of Expressway Safety Monitoring System
2. Tunnel Safety Monitoring Function. This function allows users to specify tunnel passages and, with the help of the documentation manual, assess real-time conditions within the tunnels.
3. Bridge Structural Health and Safety Monitoring. This function includes real-time status and historical status. If the first vertical bending frequency of the bridge structure changes beyond a certain threshold, it indicates that there is a problem with the bridge. The first modal vertical bending frequency of the bridge shown below is around 3.88Hz, and it has remained unchanged since the system was deployed.
4. Road Settlement Safety Monitoring
Figure2： Sectional Tomographic Image of a Road Segment
As shown in Figure 2 above, the S-wave velocity range within 100 meters below the measurement point is generally 200-1000 m/s, with some lateral variations in wave velocity. According to the analysis of shear wave velocity range, in the channel 1501-2500 diagram, the overall wave velocity changes uniformly without any abnormal phenomena. Along the depth direction, stratification is obvious: within 5-20 meters of the shallow layer, the velocity is within 200 m/s (belonging to Class III soft soil); at 30-40 meters, the velocity reaches 400 m/s (belonging to Class II medium-hard soil, hard loess); after 60 meters, the velocity reaches 800 m/s (belonging to Class I0 rock). In the channel 2501-3500 diagram, at the lateral position of 125 meters (around channel 2750), the lateral velocity shows a concave shape, indicating a possible minor collapse.
5. Vehicle Collision Accident Monitoring. This function provides real-time monitoring of road vehicle collision events and displays collision locations on GIS maps.
6. Real-time Audio Playback Function. The sensor can detect and transmit sounds with frequencies below 2000Hz within a range of 25 kilometers. It supports single-channel audio playback and allows users to upload various filters generated by MATLAB software in the range of 0～2000Hz.
