Fiber-Optic Extensometer Array in a Small Alcove at 1.25-km Depth in the Sanford Laboratory at Homestake, Lead, South Dakota

We are establishing a dense array of fiber-optic sensors in a small alcove at 4100-ft (1250-m) depth in the Sanford Laboratory at Homestake in Lead, South Dakota. The monitoring array will measure deformation in intact rock and serves also as an experimental site for research in structural health monitoring of deep underground spaces. Our GEOX boolean AND TM (Geological Optical eXtensometers and Tiltmeter) collaboration has installed approximately 10 Fiber Bragg Grating (FBG) strain and temperature sensors, which each house between 2 and 12 FBG gages, as well as distributed temperature sensing cable (DTS) in an alcove measuring 2 x 3 m and 2 m high and in the associated drift.