Distributed fibre optic sensing of stabilised soil

A frequently adopted method to improve engineering properties of soft soils is the dry deep mixing method, where dry binders like lime and cement are mixed with the soil using a rotating mixing tool. To date, the properties of improved soil are predominantly measured using destructive methods and based on locally constrainedmethods. Latest sensing technologies such as distributed fibre optic sensing (DFOS) are promising tools to map temporal and spatial changes of geotechnical structures. However, the use of DFOS for stabilised soil has received scant attention. There is a lack of detailed investigations onmonitoring curing temperature anddetecting weakness zones in stabilised soil using distributed temperature sensing (DTS) and on the strain transfer mechanism between afibre optical cable and the stabilised soil. This paper experimentally examines DFOS to quantify the integrity and the stress-strain relation of stabilised soil. Samples with layers of stabilised and remoulded clay were instrumented with a loose tube fibre optical cable to monitor changes in the curing temperature. The results indicate that untreated soil layers with a thickness of a fewcentimetrescan effectively be identified when installing a fibre optical cable during the first hours after soil improvement. To address the strain transfer mechanism, composite fibre optical strain cables were directly embedded into stabilised soil samples and tested in unconfined compressiontests. The obtained data show that the stiffness differences between the stabilised soil and the fibre optical cable resultedin a complicated strain transfer,which requires further investigation. The findings from this research suggest that DFOS can provide a means of evaluating the engineering performance and safety of stabilised soil.