Railways and rail transit are among the most important infrastructure in the country. Real-time monitoring of track health conditions is an effective guarantee for the safe operation of railway systems. Traditional electrical sensors have limitations such as poor anti-electromagnetic interference ability, limited signal transmission distance, and high costs for building sensor networks. Distributed optical fiber acoustic sensing systems integrate sensing and transmission functions, with multiple sensing units integrated on a single fiber optic cable. A single fiber optic cable can achieve long-distance, high-sensitivity, and distributed acoustic sensing detection. This technology has great application prospects in the field of railway health condition monitoring.

1. Fence Status
   • Monitoring fence conditions on both sides of railway/metro lines
2. Illegal Intrusion Detection
   • Monitoring illegal intrusions (theft, vandalism, etc.) on both sides of railway lines
   • Lateral distance monitoring from intrusion point to optical cable:
     • Theft within 5 meters
     • Vehicles within 10 meters
     • Digging within 20 meters
3. Illegal Activities in Railway Safety Protection Zones
   • Monitoring illegal excavation activities

• Monitoring of foreign object intrusion (falling rocks, landslides) on both sides of railway lines and at tunnel entrances
• Monitoring of sound barrier status (inclination intrusion) on both sides of railway lines

• Monitoring of train operation speed, up/downline spacing, train positioning, vehicle types, etc.
• Wheel-rail interaction status

• Dynamic detection and monitoring of wheel flats and broken rails

• Continuous recording of reflected waves generated by high-speed trains throughout the year
• Obtaining geological change information by comparing variations in acoustic spectrum characteristics along the railway line
• Timely detection of newly formed karst caves, flushed-out cavities, rock fractures, etc.
• Identification of karst cave existence based on existing acoustic characteristics of caves and cavities
• Overcoming issues such as spatial resolution and fading noise
• Long measurement distance with high measurement sensitivity

6. Structural Health Monitoring of Railway/Metro Tunnels:

• Fiber-optic cables are installed on both sides and the top of the tunnel, and HIFI-DAS is used for data acquisition and analysis. The imaging results can be used to explain the voids in shield tunnel segments and the health status of external spatial structures. Meanwhile, based on vibration energy, frequency, and phase information, external intrusion behaviors such as excavation and pile driving can be effectively identified.