Abstract
For almost two decades, distributed optical fibre sensors are well-known for an alternative to conventional instrumentation in geotechnical engineering applications. However, the technology is yet to be fully implemented due to uncertainties of attachment method or the best way to deploy optical fibre for geo-structure health monitoring. Thus, a project of a 1g model of soil slope was intiated and was constructed with three layers of optical fibre that were horizontally embedded in the soil slope mass in order to observe strain development due to a surcharge load. The strain mobilizations were measured by using Brillouin Optical Time-Domain Analysis (BOTDA) sensing system during the incremental loading on the slope crest until a failure feature had been initiated. The aim of study is to evaluate the development of horizontal strains from Brillouin-based optical fibre sensor subjected to soil slope deformation which lead to slope failures. The results showed that the measurands of optical fibre were highly accumulated at the position of 0.3m depth from the slope crest. The development of high strain at this position was because of soil-fibre interaction to the overburden imposed load in perpendicular direction of optical fibre placement. Therefore, it can be concluded that the optical fibre strain in the soil-strain field were well-responded to the particle soil movement. In addition, the significant trend of positive strain curves were illustrated when the soil was under compression due to external load from a surcharge load plus self-weight of the soil material.
Highlights
Optical fibre technology has been employed in structural health monitoring industry in more than two decades and seemed has been positively appraised by the users
As for the subsequent loading of 7kN and 9kN, the incremental microstrains were seen to maximised at position of Layer 2 (L2) and optical fibre at position Layer 3 (L3) was seen not responsive to the seqeuential loadings
The incremental microstrains were slightly increased when load at 9kN for both layer 2 (L2) and layer 1 (L1) and a downward pattern of strain curve was perceived at layer 3 (L3)
Summary
Optical fibre technology has been employed in structural health monitoring industry in more than two decades and seemed has been positively appraised by the users. There were several types of optical fibre sensor used in civil engineering application includes Fibre-Bragg grating sensor, SOFO (long-gauge optical fibre sensor) and the timedomain reflectometry-based sensor (distributed optical fibre sensor). The measurement principles of a Bragg grating is when a Bragg wavelength, λB was shifted proportionally with axial strain or temperature variation due to changes of the sensor segment through a periodic variation of refractive index along the length of the fibre [3] As for SOFO, Leung et al, 2013 has mentioned that the sensor includes two single-mode fibres which located in a tube and attached to the host structure; one is named as measurement fibre (attached to the structure) and the other named as reference fibre positioned in a loose condition. The optical time-domain reflectometry system (OTDRs) was designed for telecommunications industry and known as the basic of distributed optical sensing technology
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