Abstract
The impact wave response of soil due to a ball drop is monitored on a 30.5 cm by 30.5 cm square soil box using a fiber sensor with dynamic strain sensing capability. The experiments are conducted in real time using a simple one-laser one-modulator configuration with stimulated Brillouin scattering. The embedded BOTDA sensor grid successfully monitored the distribution and evolution of the inner strains of a sand bed during a mass impact on its surface. The measurement of the distributed dynamic strains was possible in several milliseconds and with 1 cm actual location resolution. This paper presents a time-domain signal analysis utilized for determining the dynamic strains in embedded fiber sensor. The results demonstrate the method to be a promising one for detection of subsurface vibration and movement in geotechnical Structure Health Monitoring (SHM).
Highlights
The availability of various sensing techniques has become increasingly important in health monitoring of the underground infrastructure and the environment [1,2,3,4,5,6]
The time domain signal is based on the 11.20-GHz fixed modulation frequency and is recorded for the total length of the fiber
It is noted that when the modulation frequency is close to local Brillouin frequency shift, there should be 30 visible peaks, each one corresponding to one of the stretched fiber strands embedded in the sand
Summary
The availability of various sensing techniques has become increasingly important in health monitoring of the underground infrastructure and the environment [1,2,3,4,5,6]. The sensors used to capture sightless geo-events in the subsurface must be buried at a certain depth Most of these sensors are targeted at monitoring multiple indices including moisture, temperature, pressure, vibration or other physical variables. Among the commonly used sensors, wired ones are often visible and can be prone to failure due to extreme environmental factors, which makes these sensors unsuitable for security and distributed applications. Ogawa [11] used Brillouin amplification to measure dynamic strain with a low spatial resolution of 100 m in a period of 2 s. The low cost and passive features (i.e., external detection and data acquisition) of a single mode fiber (SMF) make this design attractive for distributed applications in the subsurface
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