Experimental investigation on the deformation coordination between an optical fibre and backfilling sand of borehole

Abstract

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 (DCf-s) under different conditions is critical for land subsidence monitoring with DOFS. In this paper, a medium-size triaxial apparatus was modified for testing the DCf-s. Consolidated drained triaxial tests were conducted to investigate the effect of sand types on the DCf-s. By linearly fitting of the deformation of the sensing cable with that of the triaxial specimen, the other factors that affect the DCf-s, such as the confining pressure, dry or wet state of the soil, and cyclic variation of the loads, were discussed. The experiments reveal that better DCf-s comes with a larger particle size, poor gradation of sand, and larger confining pressure. The DCf-s of wet sand is better than that of dry sand. The DCf-s coefficient tends to be stable with increasing of loading cycles. The obtained DCf-s and its dependence on influencing factors can be used to modify the measured cable strain in practical land subsidence monitoring with DOFS.