TY - JOUR A1 - Bore, Thierry A1 - Wagner, Norman A1 - Lesoille, Sylvie Delepine A1 - Taillade, Frederic A1 - Six, Gonzague A1 - Daout, Franck A1 - Placko, Dominique T1 - Error analysis of clay-rock water content estimation with broadband high-frequency electromagnetic sensors—air gap effect JF - Sensors N2 - Broadband electromagnetic frequency or time domain sensor techniques present high potential for quantitative water content monitoring in porous media. Prior to in situ application, the impact of the relationship between the broadband electromagnetic properties of the porous material (clay-rock) and the water content on the frequency or time domain sensor response is required. For this purpose, dielectric properties of intact clay rock samples experimental determined in the frequency range from 1 MHz to 10 GHz were used as input data in 3-D numerical frequency domain finite element field calculations to model the one port broadband frequency or time domain transfer function for a three rods based sensor embedded in the clay-rock. The sensor response in terms of the reflection factor was analyzed in time domain with classical travel time analysis in combination with an empirical model according to Topp equation, as well as the theoretical Lichtenecker and Rother model (LRM) to estimate the volumetric water content. The mixture equation considering the appropriate porosity of the investigated material provide a practical and efficient approach for water content estimation based on classical travel time analysis with the onset-method. The inflection method is not recommended for water content estimation in electrical dispersive and absorptive material. Moreover, the results clearly indicate that effects due to coupling of the sensor to the material cannot be neglected. Coupling problems caused by an air gap lead to dramatic effects on water content estimation, even for submillimeter gaps. Thus, the quantitative determination of the in situ water content requires careful sensor installation in order to reach a perfect probe clay rock coupling. KW - Wassergehalt KW - Ton KW - Zeitbereichsreflektometrie KW - Impedanzspektroskopie KW - Dielektrische Spektroskopie KW - water content measurement; TDR probe; clay-rock; dielectric spectroscopy; frequency domain finite element modeling Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20170418-31248 UR - https://www.scopus.com/inward/record.uri?eid=2-s2.0-84964200266&doi=10.3390%2fs16040554&partnerID=40&md5=26e537724db3b28e237009acde7676cd SP - 1 EP - 14 ER - TY - JOUR A1 - Bremer, K. A1 - Wollweber, M. A1 - Weigand, F. A1 - Rahlves, M. A1 - Kuhne, Michael A1 - Helbig, R. A1 - Roth, B. T1 - Fibre Optic Sensors for the Structural Health Monitoring of Building Structures JF - Procedia Technology 26 N2 - In this work different fibre optic sensors for the structural health monitoring of civil engineering structures are reported. A fibre optic crack sensor and two different fibre optic moisture sensors have been designed to detect the moisture ingress in concrete based building structures. Moreover, the degeneration of the mechanical properties of optical glass fibre sensors and hence their long-term stability and reliability due to the mechanical and chemical impact of the concrete environment is discussed as well as the advantage of applying a fibre optic sensor system for the structural health monitoring of sewerage tunnels is demonstrated. KW - Structural Health Monitoring KW - crack sensor; fibre optic sensor; humidity sensor; SHM Y1 - 2016 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20170331-30912 UR - http://www.sciencedirect.com/science/article/pii/S2212017316304121 SP - 524 EP - 529 ER - TY - JOUR A1 - Scheuermann, Alexander A1 - Huebner, Christof A1 - Schlaeger, Stefan A1 - Wagner, Norman A1 - Becker, Rolf A1 - Bieberstein, Andreas T1 - Spatial time domain reflectometry and its application for the measurement of water content distributions along flat ribbon cables in a full-scale levee model JF - Water Resources Research N2 - Spatial time domain reflectometry (spatial TDR) is a new measurement method for determining water content profiles along elongated probes (transmission lines). The method is based on the inverse modeling of TDR reflectograms using an optimization algorithm. By means of using flat ribbon cables it is possible to take two independent TDRmeasurements from both ends of the probe, which are used to improve the spatial information content of the optimization results and to consider effects caused by electrical conductivity. The method has been used for monitoring water content distributions on a full-scale levee model made of well-graded clean sand. Flood simulation tests, irrigation tests, and long-term observations were carried out on the model. The results show that spatial TDR is able to determine water content distributions with an accuracy of the spatial resolution of about ±3 cm compared to pore pressure measurements and an average deviation of ±2 vol % compared to measurements made using another independent TDR measurement system. KW - Damm KW - Infiltration KW - Bodenfeuchte KW - Transient and time domain; Dams; Infiltration; Soil moisture; calibration; levee model; soil moisture measurement; spatial time domain reflectometry Y1 - 2009 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20170425-31601 ER - TY - JOUR A1 - Wagner, Norman A1 - Bore, Thierry A1 - Robinet, Jean-Charles A1 - Coelho, Daniel A1 - Taillade, Frederic A1 - Delepine-Lesoille, Sylvie T1 - Dielectric relaxation behavior of Callovo-Oxfordian clay rock: A hydraulic-mechanical-electromagnetic coupling approach JF - Journal of Geophysical Research: Solid Earth N2 - Water content is a key parameter to monitor in nuclear waste repositories such as the planed underground repository in Bure, France, in the Callovo-Oxfordian (COx) clay formation. High-frequency electromagnetic (HF-EM) measurement techniques, i.e., time or frequency domain reflectometry, offer useful tools for quantitative estimation of water content in porous media. However, despite the efficiency of HF-EM methods, the relationship between water content and dielectric material properties needs to be characterized. Moreover, the high amount of swelling clay in the COx clay leads to dielectric relaxation effects which induce strong dispersion coupled with high absorption of EM waves. Against this background, the dielectric relaxation behavior of the clay rock was studied at frequencies from 1 MHz to 10 GHz with network analyzer technique in combination with coaxial transmission line cells. For this purpose, undisturbed and disturbed clay rock samples were conditioned to achieve a water saturation range from 0.16 to nearly saturation. The relaxation behavior was quantified based on a generalized fractional relaxation model under consideration of an apparent direct current conductivity assuming three relaxation processes: a high-frequency water process and two interface processes which are related to interactions between the aqueous pore solution and mineral particles (adsorbed/hydrated water relaxation, counter ion relaxation and Maxwell-Wagner effects). The frequency-dependent HF-EM properties were further modeled based on a novel hydraulic-mechanical-electromagnetic coupling approach developed for soils. The results show the potential of HF-EM techniques for quantitative monitoring of the hydraulic state in underground repositories in clay formations. KW - Lehm KW - Relaxation KW - Wassergehalt KW - Reflektometrie Y1 - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:gbv:wim2-20170428-31681 SP - 4729 EP - 4744 ER -