Fiber optic method for health assessment of pipelines subjected to earthquake-induced ground movement

Natural disasters, in particular earthquakes, can cause damage to pipelines with disastrous humanitarian, social, economic, and ecologic consequences. Thus, real-time, automatic, or on-demand assessment of damage to pipelines after the earthquake is essential for early emergency response, efficient preparation of rescue plans, and mitigation of these disastrous consequences. This article presents the development of a method for buried pipelines health assessment based on distributed fiber optic sensors, which are sensitive to strain at every point along their lengths. The sensors are both bonded to pipeline and embedded in the soil, in the proximity of the pipeline. The research includes determination of sensor topology, identification of required sensor properties, selection of sensors, development of installation procedures, implementation, and validation. The validation of the method was made through a large-scale testing: a 13-m-long real-size concrete segmented pipeline was assembled in a large test basin filled with soil and was tested under simulated permanent ground displacement. The basin consisted of two parts: the movable north part and the fixed south part. The movable north part of the test basin was attached to four hydraulic actuators, which were used to apply controlled displacement of the basin, and it induced damage to the pipeline by crushing the joints between adjacent pipeline segments. As a part of validation, the results obtained from distributed sensors were compared with resistive strain gauges. Two validation tests were performed: the first in 2010 and the second in 2011. The method is presented in detail, and the most significant results of both tests are analyzed, compared, and discussed. The validation tests confirmed the capacity of the method to reliably detect and localize the damage on pipeline and the displacement in the soil.