Geosynthetics are used in railway construction predominantly in the field of earthworks. Thus, in Germany they are subject to the technical guideline “Ril 836 – Planning, constructing and main-taining earthwork constructions and other geotechnical structures” of Deutsche Bahn AG (German Rail-ways). In addition to Ril 836 there is a new guideline “Technical requirements for geosynthetics in rail-way constructions (DBS 918 039) published in November 2015. Within this new DBS 918 039 several geosynthetic applications and the corresponding technical requirements are defined. Besides the conven-tional applications, like filtration and separation (geotextiles) or reinforcement (geogrids), there are also new applications like groundwater protection where geosynthetics are used. In application no. 3.11 (DBS 918 039) the geosynthetic clay liners (GCL) are regulated as sealing elements for groundwater protection and in application no. 3.12 (DBS 918 039) the geomembranes are defined as sealing elements. The geo-synthetic clay liners and the geomembranes, respectively, work as a sealing underneath the railway track to protect groundwater e. g. in water protection areas.