Pressure and thermal effects on Rayleigh fibre-optic strain measurement for soil–structure interaction

Abstract

Optical strain sensing for structural health monitoring is sometimes deployed for field and laboratory study of civil structures. Rayleigh backscatter devices (ROFDR) are presented for use with geotechnical centrifuge research since they offer distributed sensing capabilities, and through this study are shown to have negligible interference from external pressure effects. A comparison between a single channel and multi-channel fibre optic rotary joint (FORJ) is presented in the context of transmitting optical strain data across a rotating interface. The orthogonal pressure effects of a free-floating fibre under isotropic pressure was <0.32 με/kPa and that the pressure effect on a fibre bonded to a metal surface was below the detection limit of the instrument, 1 με, for an applied pressure of 60 kPa. The ROFDR system showed highly repeatable measurement of a constant temperature reading in a water bath experiment. The system is stable to ±10 microstrain within 2-sigma for a >12 h constant temperature test. An example case of a pipeline buried in a slope experiencing a landslide is presented using fiber pairs to capture pipe stress / strain. Geotechnical centrifuge modelling in a 1 m drum was carried out using a multi-channel FORJ coupled with an ROFDR system.