Detecting scour and liquefaction using OBS sensors

This work examined the performance of Optical Back-Scatter (OBS) sensors for detecting sediment movement around a model subsea structure. Three types of tests were conducted using a circular cylinder model equipped with 16 OBS sensors. The sensor recorded a dramatic reduction in back scatter when it became unburied (due to sediment movement) and was exposed to clear water. Based on this feature, the sensors were used to investigate the scour processes around a model pile, and the spanwise scour rate of a partially buried model pipeline. The test results agree well with existing knowledge. When the sensors were fully buried in sand, it was also observed that the sensor readings fluctuate noticeably when sand particles move local to the sensors. Based on this feature, the OBS sensors were used to detect sediment movement induced by seabed liquefaction. Through the tests presented in this paper, it has been demonstrated that the sensor can be used as a new device to detect local scour and liquefaction in laboratory tests. © 2016 Taylor & Francis Group, London.