Use of Distributed Fiber Optic Sensing to Measure Differential Settlements Induced by a Normal Fault

Ground deformation monitoring is essential for the safe operation of critical infrastructure and urban construction activities. Advances in distributed fiber optic sensing (DFOS) technologies offer potential improvements to traditional ground deformation monitoring techniques, particularly in terms of accuracy, spatial resolution, and sensing length. This paper presents the results from a laboratory test inducing ground deformations above a normal fault to evaluate the effectiveness of buried strain-based DFOS instruments for monitoring the resulting differential settlements. The investigation included five different types of commonly used fiber optic cables as well as a novel distributed fiber optic strip sensor capable of measuring axial strain and curvature, which can be used to approximate the deformed soil profile. The strains measured along the single buried fiber optic cables are used to estimate the fault offset following a recently proposed method. The axial strain and curvature measurements along the strip sensor are compared to independently measured strains along an adjacent buried pipe. The deformed soil profile inferred from the deformed shape of the strip sensor remains within 5% of the soil profile measured by digital image correlation and shows promise for determining soil deformation characteristics in both laboratory and field applications.