Investigation of deformation coordination between optical fibre and borehole sand backfill

Land subsidence has threatened the safety of municipal infrastructures and even that of inhabitants. As one of the deformation monitoring methods, distributed optical fibre sensing (DOFS) technology has been developed for the investigation of land subsidence. The deformation coordination between the optical fibre and soil (DC_f-s) under different conditions is critical for land subsidence monitoring with DOFS. In this paper, a medium-sized triaxial apparatus was modified for testing the DC_f-s. Consolidated drained triaxial tests were conducted to investigate the effect of sand types on the DC_f-s. By linearly fitting the deformation of the sensing cable with that of the triaxial specimen, the other factors that affect the DC_f-s, such as the confining pressure, dry or wet state of the soil and cyclic variation of the loads, can be discussed. The experiments reveal that better DC_f-s comes with a larger particle size, poor gradation of sand and larger confining pressure. The DC_f-s of wet sand is better than that of dry sand. The DC_f-s coefficient tends to be stable with an increase of loading cycles. The DC_f-s obtained and its dependence on influencing factors can be used to modify the measured cable strain in practical land subsidence monitoring with DOFS.