FOS - Gebirgsdruck - Fiber-optically supported measuring methods of observation of mountain pressure

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 respectively 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. At the moment no robust method for permanent monitoring of tunnels exists. Currently deformation measurements in tunnels are carried out with geotechnical sensors (e.g. rod-extensometers, vibrating wire sensors) or with geodetic techniques. Geotechnical sensors are usually electric sensors and a large number of measurement points can only be realized with a huge amount of cables and wiring effort. Geodetic methods on the other hand rely on laser scanners or total stations and need a direct line of sight between instrument and object respectively the prisms. A continuous measurement is hard to realize and one has to tackle several problems e.g. the pollution of the prisms. With a fibre-optic measuring method many of these restrictions can be overcome. It is possible to put several optical sensors on one optical fibre. The signal is transmitted through the optical cable and thus a direct visual contact is not necessary. With fibre optic measuring methods it is possible to integrate a monitoring system directly into the tunnel structure. Around a measuring section one is able to measure changes in strain, deformation and convergence. The forces in the tunnel lining let us draw conclusions on the ground load or ground pressure and record changes. With a permanent monitoring an automated recording and assessment of the conditions becomes feasible without interruption of infrastructure operation. Objective of this project is to develop a new and innovative measurement method for ground load and demonstrate it in a field experiment (new-build and renovation projects). With complementary technologies as laser scanning the method will be verified on its practicability. Since for tunnels, similar to bridges, many individual requirements have to be taken into account since many parameters have to be considered for a condition assessment. It is another project goal to identify the necessary observations and provide the customer with an easy to use tool for an overall assessment and evaluation of tunnel linings.