Fibre‐optic supported measurement methods for monitoring rock pressure

Abstract

Like every civil engineered structure tunnels are subject to an ageing process. The reasons for the degrading of the condition are manifold: not fully completed stress redistribution, deterioration in the rock mass quality through long‐term exposure (creeping), weathering or dynamic loads and stresses, to name but a few. All this processes lead to a deformation of the surrounding bedrock and the lining. For a continuous monitoring of a tunnel condition the measurement of the deformation is necessary. Conventional methods are elaborate and time‐consuming and require almost always a shutdown of the tunnel for traffic. Therefore, an inspection is done selectively with large time gaps. A continuous condition assessment becomes hardly possible. Currently no robust method for permanent monitoring of tunnels exists. With a fibre optic measuring method many of these restrictions can be overcome. In the course of this research project, a novel and innovative measuring methodology has been developed to continuously and extensively measure rock deformations. The measurement results were evaluated performing laboratory tests. Subsequently, they were installed in the course of a field test at the Semmering Base Tunnel. With complementary technologies such as laser scanning, the measurement methodology could be verified for its applicability.

Direct and Distributed Strain Measurements Inside a Shotcrete Lining: Concept and Realisation

“…Alternately, a special temperature sensing cable could be used [for details see e.g. Henzinger et al (2018)]. The applicability of different fibre-optic sensing cable types has been investigated within a pre-test on a simple sprayed concrete slab [for details see Wagner (2017)].…”

Distributed fiber optic shape sensing along shotcrete tunnel linings: Methodology, field applications, and monitoring results

“…Although 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 convergence analysis [4,10], but do not deliver concepts for fully distributed shape analysis along the lining. This paper introduces a distributed fiber optic shape sensing and evaluation approach, which utilizes DFOS strain measurements along different sensing layers in combination with pointwise displacement readings for fully distributed shape assessment along curved structures, such as tunnels.…”

150 years reliable railway tunnels – Extending the hybrid method for the long‐term safety assessment

“…At the same time, displacement measurements at the surface of linings were complemented by strain measurements inside the linings, e.g. by means of embedded strain gauges or fibre-optical sensors [13,14]. Such methods provide quantitative access to strain distributions across a dense grid of up to thousands of measurement points spanning both the circumferential and longitudinal directions of a tunnel (Fig.…”