Leak detection at underground building sites
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Imperfections in water resistant screens surrounding an underground building site can cause the occurrence of a leakage as a consequence of an artificially lowered groundwater level at this site. Leakages in a water resistant screen can be detected by active or passive testing methods. An active testing method is presented in which piezometer measurement data from a pumping test are used for characterizing the diaphragm wall of Vijzelgracht Station in Amsterdam. The conditions under which such a pumping test must be performed are highly demanding and are generally not met in practice. Hereafter, a passive testing method is presented in which the configuration of piezometers outside the building site is optimized in order to timely localize an occurring leakage by spatially interpolating their measurement data. This analysis is done for several values for aquifer properties and leakage discharge. The procedure results in an optimal piezometer configuration, namely a row of piezometers parallel to the building site for all scenarios tested. The optimal distance from this row to the site and the optimal mutual distance between piezometers depend on the aquifer properties. Subsequently, this method is applied in a case study at Vijzelgracht Station, confirming the use of the method. Finally, an active method for leakage detection using geoelectrical measurements is presented. As a case study, this method is applied to the sheet piling at a building site in the province of Overijssel in the Netherlands.