Quantifying Fiber-Optic Cable–Soil Interfacial Behavior Toward Distributed Monitoring of Land Subsidence

Abstract

Land subsidence is often associated with strata compaction, which can be measured by InSAR, GPS or extensometers. Despite considerable efforts, recording detailed subsurface deformation using these methods has proven to be difficult in some cases. The distributed fiber-optic sensing (DFOS) technique may overcome this dilemma by distributed strain measurement at kilometer scales and beyond. However, one crucial issue remains to be solved is the mechanical coupling between borehole backfill and embedded fiber-optic (FO) strain-sensing cable, which affects the quality of strain measurements. Here we perform laboratory pullout tests using a self-devised apparatus to investigate the interaction mechanism between FO cable and soil under confining pressures (CPs) up to 1.6 MPa. Our results indicate a critical CP that ensures a good cable–soil coupling, which has a direct application to the analysis of groundwater extraction-induced land subsidence in Shengze (Suzhou, China). A simple estimation of the CP exerted on the borehole-embedded cable suggests a strong coupling of the cable to the backfill for the main compaction zone. Taken together, these findings provide a basis for monitoring land subsidence and the associated strata compaction using the DFOS technique.