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Movements in geological areas are often caused by shear zones deep in the underground or by hardly observable slipping zones. Detection of movements reaching critical values is of crucial importance to avoid losses and harms. Optical sensor fibers with gauge lengths of several meters or even distributed fiber-optic sensors with gauge lengths of hundreds of meters allow detecting deformation of such zones with quite good resolution. The paper presents a new technology of detecting deformations and movements in soil or rock massifs. The core part of the sensing system is a tiny pultruded rod with an outer diameter of 3 mm to 6 mm. It contains two fiber-optic sensor systems. One sensor system is used for permanent online measurement and provides integral strain information along the whole length of the rod; in case of critical deformations, it provides a warning signal. The second sensing system uses fiber-optic Bragg grating (FBG) strain sensors located close to the expected shear zone. This measurement system will be activated after the warning signal has been initiated by the integral strain measurement system. The FBG strain sensor system records then resulting deformations in detail. The sensing rod containing both sensor systems can be installed in a borehole to detect beginning soil movements automatically. The electronic equipment is powered by a solar panel; the amount of deformation in soil or rock formations can be estimated from the strain change measured in the sensor fibers. The effectiveness of this warning system will be shown using the example of a critically sliding slope in an open brown coal pit in Germany.
Measurement and data recording systems are important parts of a holistic Structural Health Monitoring (SHM) system. They are often based on modern measurement and data communication technologies for which standards (or at least guidelines) do not exist yet. A lack in standardization, however, makes the establishment of new sensing and application technologies - and thus up-to-date SHM systems - substantially difficult. Successful commercialization and wide acceptance of SHM systems needs widely accepted standards and guidelines. Standards help to design SHM systems in an optimal way. Currently, standardization gets increasing attention in civil engineering field; there are some activities e.g. in ISHMII, IEC and ISO groups to develop standards for the most important components of SHM systems.
The paper gives an overview on current activities in standardization to propose sound and safe procedures for assessment of the existing structure's behavior and for estimation of its residual life. Special attention is paid in this paper to newly developed standards for fiber-optic measurement systems; important aspects of such sensor systems are mentioned.
The contribution is aimed at owners of structures that have to be assessed as well as at developers of sensors and monitoring systems who have to select appropriate effective sensing technologies. Using standards, both parties find recommendations how to proceed in development SHM systems to estimate the design or residual life, and how to find out the optimal maintenance strategy. The usefulness of standardized procedures is shown using the example of risk-based management of structures.
Durch die Absenkung des Chromatgehaltes der Zemente verändern sich die elektrochemischen Reaktionen von verzinkten Betonstählen in der Frischbetonphase. Mit Hilfe von elektrochemischen Messungen sowie Stabauszugsversuchen wurde an chromathaltigen und chromatreduzierten Zementen die Auswirkung des Chromats auf die Deckschichtbildung am Zink und auf das Verbundverhalten untersucht. Mit den Ergebnissen konnte eine Beeinträchtigung der Verbundzone als Folge der Chromatreduzierung für die Zementarten CEM I und CEM II nachgewiesen werden. Die Störung der Verbundzone ist in Bezug auf die sich ausbildende Porenstruktur als dauerhaft anzusehen. Die Auswirkungen auf das Verbundverhalten werden mit zunehmendem Betonalter weitgehend kompensiert. Die Ergebnisse der bezogenen Verbundspannung bei Verschiebewegen von 0,1 mm und 0,5 mm liegen trotz der Gefügestörung noch im Bereich der Erwartungswerte für den unverzinkten Betonstahl. Unter baupraktischen Gesichtspunkten muss die auftretende Gefügestörung hinsichtlich der Verbundspannung daher keine Berücksichtigung finden.
Monitoring of PAH in aqueous samples - a comparison of different sample preparation techniques
(2011)