EXPERIMENTAL STUDY ON DISTRIBUTED MONITORING OF SOIL SHEAR DISPLACEMENT CONSIDERING DEFORMATION COMPATIBILITY

The shearing failure of rock and soil masses is reckoned as a common trigger for geohazards, and it is therefore a critical issue to monitor the shear displacements of rock and soil for disaster prevention and mitigation in geotechnical engineering. Fiber optics sensing technology can be potentially used for shear displacements monitoring owing to its high sensitivity and distributed strain sensing(DSS)features. In this paper, we carried out an experimental study to investigate the feasibility of soil shear displacements based on the fully distributed Optical Frequency Domain Reflection(OFDR) and Particle Image Velocimetry(PIV)technologies. Taking into account the deformation compatibility of directly embedded optical fiber cables and the surrounding soil, the relationship between the distributed strain measurements and real soil shear displacements is explored, and we proposed the strain integral method to realize the conversion. The test results show that while the optical fiber cables are well coupled with soil, there is a linear relationship between the calculated elongation and soil shear displacements, indicating that it is feasible to use the high-accuracy and high-spatial resolution OFDR technology to monitor soil shear displacements. Installing tube-type anchorages on optical fiber cables or increasing the confining pressure can effectively enhance the soil-cable coupling capability, and help to obtain more reliable shear displacement measurements.