The use of distributed fiber optic sensors (DFOS) for the monitoring of civil structures and infrastructure opens exciting new possibilities unmatched in conventional sensor systems. Several technologies within the DFOS umbrella have developed to varying maturities in the last decade. These technologies include distributed strain sensing (DSS), distributed temperature sensing (DTS) and distributed acoustic sensing (DAS).
Distributed Strain Sensing – DSS
Engineering design limits are often based on strain and/or stress developing in the structure. For structures interacting with soil, the ground loads are distributed spatially (not point loads); therefore, the state of the structure cannot be fully understood unless the complete in situ strain condition is known. This is where DSS technology shines. A single optical fiber with a length of up to 10 km of continuous sensing makes it possible to obtain a body of invaluable information on the distribution of civil infrastructure assets. Our group deploys DSS technology in laboratory and field applications to monitor natural in-situ, field load tests, and laboratory test conditions. We are also developing a dynamic Brillouin-based DSS system that has been used for detecting dynamic strains in the pavement.
Distributed Temperature Sensing – DTS
Infrastructure such as levees, dams, pipelines, natural gas wells, and water distribution systems rely on their ability to avoid or at least control leakage. DTS technology provides the ability to monitor subtle temperature changes due to fluid flow using optical fiber. Up to 50 km of linear assets can be monitored for distributed temperature. This gives engineers the real-time capability to monitor subsurface flow within the geotechnical infrastructure. Our group is working on deploying DTS technology in geotechnical infrastructure so better data analysis methods can be developed, and more information can be known about the condition of infrastructure.
Distributed Acoustic Sensing – DAS
Many events that are of interest to civil engineers have acoustic signatures. Earthquakes, landslides, vibration, excavation, and tunneling are just a few examples. DAS technology can measure the specific waveform of an acoustic signature along with an optical fiber 10s of km long. This technology is revolutionary in infrastructure monitoring, asset management, and even security. The problem is how we make use of exorbitant amounts of data. Our group is working on deploying DAS in infrastructures such as levees, pipelines, and wellbores. We plan to develop methods for systematic signal processing and data analysis that will identify acoustic signatures of interest. Our group also plans to unite DSS and DAS technology so that static and dynamic strains can be monitored on demand and in synchrony.
Applications: pile foundations, tunnels, pipelines, pavements, levees, and dams
At present, the high cost of analyzers is the major obstacle barring the widespread application of DFOS. However, recent developments in digital electronics and photonic integrated circuits provide an opportunity to transform the conventional analog-based system into a digital-based system. The group develops the next generation of DFOS analyzers. Our new system has the following unique characteristics (i) low cost using an advanced digital architecture replacing the conventional microwave synthesizer, (ii) a special pulse and modulation to reduce measurement time for real-time dynamic sensing, and (iii) use of small gain stimulated Brillouin scattering with fast data management. This invention allows strain data to be captured at a high sampling rate. The current prototype system achieves a 2cm read-out interval, 2m spatial resolution, and about 20µε accuracy with 23Hz continuous monitoring.
- Levee Performance Monitoring using Distributed Acoustic Sensing in Black Hawk, Louisiana
- California Energy Commission Offshore Wind Turbine Monitoring Project
- Kaolin Clay Beam Test
- Development of a Distributed Strain Sensing System for an HDPE Water Pipeline Crossing the Hayward Fault
- Distributed Acoustic Sensing of Wind Turbine Towers for Structural Health Monitoring
- Fiber Optic Monitoring of Base Grouted Piles
- Natural Gas Storage Safety Monitoring with Autonomous Reflectometry Technologies
- Distributed Strain Sensing of a Critical Natural Gas Pipeline
- Creating Subsurface Strain Cross-Sections using Distributed Strain Sensing: Application to Working Platform Design
- Miniature Pore Pressure Transducer
- Road Event Detection Using Distributed Acoustic Sensing
- Long-term Health Monitoring of Levee Cutoff Wall
- CPT Installation of Fiber Optic Cable for Settlement Monitoring
- Test Pile Curing and Strain Measurement at Millennium Tower
- Fiber Optic Monitoring of Sand Boil Development