Abstract
Deformation monitoring and structural reliability assessment are key components in modern conventional tunneling. The state-of-the-art monitoring design is usually based on displacement measurements of geodetic targets using total stations paired with pointwise geotechnical sensors inside the tunnel lining. In recent years, distributed fiber optic sensing (DFOS) has become more popular in tunneling applications. DFOS measurements basically deliver internal strain and temperature distributions, but no direct relation to the tunnel shape’s behavior. This paper introduces a novel sensing and evaluation concept, which combines DFOS strain measurements and geodetic displacement readings for distributed shape assessment along curved structures, such as tunnel cross-sections. The designed system was implemented into shotcrete tunnel cross-sections as well as shaft linings and enables the determination of displacement profiles with high spatial resolution in the range of centimeters. Evaluations of continuous monitoring campaigns over several weeks as well as epoch-wise measurements performed by different DFOS sensing units in combination with stochastic analysis demonstrate the high potential of the developed approach and its capability to extend traditional monitoring methods in tunneling.
Highlights
The design of excavation and supporting methods in modern tunneling is usually based on geotechnical monitoring and reliable data interpretation to enable an assessment of the structural integrity and, to guarantee a safe construction and operation
Distributed fiber optic sensors (DFOS) are advantageous as the cable itself acts as the sensitive element and distributed measurements can be performed along the entire sensing fiber
This paper introduces a distributed fiber optic shape sensing and evaluation approach, which utilizes distributed fiber optic sensing (DFOS) strain measurements along different sensing layers in combination with pointwise displacement readings for fully distributed shape assessment along curved structures, such as tunnels
Summary
The design of excavation and supporting methods in modern tunneling is usually based on geotechnical monitoring and reliable data interpretation to enable an assessment of the structural integrity and, to guarantee a safe construction and operation. The sensing cable installation procedure is critical due to the harsh tunnel environment, DFOS have already been successfully implemented inside shotcrete tunnel linings. These existing installations are mainly focused on investigations of mechanical stress as a result of creepage, shrinkage, and/or rock pressure [9, 19, 28], as well as Journal of Civil Structural Health Monitoring (2021) 11:337–350 convergence analysis [4, 10], but do not deliver concepts for fully distributed shape analysis along the lining. The outcomes are concluded and an outlook on future research aspects is given (sect. 5)
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