Experimental Research on Strain Transfer Behavior of Fiber-Optic Cable Embedded in Soil Using Distributed Strain Sensing

Abstract

The strain transfer between fiber-optic cable and soil plays a critical role in the deformation characteristics of a cable–soil interface. Existing findings cannot provide a clear understanding of the effects of key influencing factors including horizontal confining pressures, anchorage property of cables, and saturation of soils on the strain transfer and shear characteristics at the interface. A group of pullout tests of cables in soil were conducted to examine the strain transfer efficiency using the optical frequency domain reflectometry (OFDR) technique. Two kinds of cables were pulled out from sandy soil and sand–gravel–clay mixtures under the confining pressures of 0–1.2 MPa. Typical strain-hardening behavior was observed for cables with confining pressure and anchorage, and the interface shear strength could not be evaluated within the strain measurement range. To address this problem, the so-called interface shear coefficient was adopted, and the key influential factors were discussed quantitatively. The interface shear coefficient keeps a linear relationship with the confining pressure, and that of the anchored cable in saturated backfill mixtures is 2–3 times than that of the unanchored cable. These findings will guide the methods of gaining reliable data for revealing the failure mechanism of geostructures via distributed strain sensing.