4 Strain Measurement

Strain, or the relative deformation due to loading, is an important hydrogeologic process. Vertical strain due to pumping in a well is a foundation of the concept of specific storage, and the field of geomechanics has taken on greater importance in the fields of geodesy and seismology in recent years as we recognize the relationships between fluids, fluid pressures and large-scale earth motions. Localized strain can be measured with a wide variety of sensors, ranging from load cells to GPS, but are typically point measurements. Distributed strain sensing on optical fibers has been evolving over the past several decades and is now well established in landslide monitoring although mainly focused on borehole sensing, pile monitoring, crack meters for rock instability and monitoring of retaining walls (Schenato, 2017). On the contrary, monitoring of the spatial distribution of surface displacement has seen only a few proof-of-concept experiments.