Overview
Currently there is neither experience nor the validated test methods for the determination of long-term behavior of tunnel sealing systems.
The main aim of the project is to define an experimental evaluation procedure for the determination of the long-term ageing behavior of polymeric waterproofing systems for tunneling applications and the performance of this evaluation on selected, improved materials for waterproofing systems. A comprehensive analysis of the existing data and experience from the NEAT tunnels evaluation procedure for polymeric waterproofing systems shall yield an improved evaluation procedure that then will be applied to selected, commercially available waterproofing systems to determine their long-term ageing behavior.
The analyzed materials were stored for 3 to 5 years in water at 55 or 70 ° C with or without bubbling air. Furthermore, ageing for one year in acid and alkaline media were carried out. After ageing, samples were taken at defined time intervals and their visual appearance and the mass changes in the wet and dry state were investigated. For geomembranes mechanical properties were determined from tensile and tensile impact tests and compared with results from the extended 10-year storage of the evaluation procedure. Additional tests such as determination of oxygen induction time OIT were performed on selected materials.
Funding
Results
The question of whether the sealing systems of NEAT, actually meet the demands placed on them, were asked in this project. The two-year evaluation process, which was conducted prior to construction, also went to this question. Originally investigated materials of sealing systems could, however, not meet the requirements set after one year. Therefore, improved products were investigated in detail in a revision stage during one year. Further optimizations of the products allowed their approval for installation in the NEAT. The long term behavior of these products could not be investigated prior to construction. This gap should be closed in the present study.
Therefore, on the one hand the geomembranes 1702/2369 (PE/EVA) and the drainage materials 1801/2302 (PE-HD) in its original form (at the beginning of the evaluation process)/and in optimized form, as used in the sealing system of Gotthard tunnel, were chosen. On the other hand, the PVC geomembranes 1712/2385 (original / optimized) and the drainage materials made of PP 2304/2355 (original/optimized), which were combined as sealing system in the Lötschberg tunnel, were selected for the present study. Two other geomembranes, a PVC membrane 2 and a PE roof waterproofing membrane 3, were also investigated.
The materials were stored for 3 to 5 years in water at 55 or 70 ° C with or without bubbling air. Furthermore, ageing for one year in acid and alkaline media were carried out. After ageing, samples were taken at defined time intervals and their visual appearance and the mass changes in the wet and dry state were investigated. For geomembranes mechanical properties were determined from tensile and tensile impact tests and compared with results from the extended 10-year storage of the evaluation procedure. Additional tests such as determination of oxygen induction time OIT were performed on selected materials.
The PE/EVA-based waterproofing membranes showed after 5 years of storage only moderate mass changes and little change in mechanical properties. An unfavorable behavior was observed already in the evaluation procedure for the original geomembrane 1702 after storage under alkaline conditions. For the improved sealing sheet 2369 a more favorable attitude after storage in alkaline media could be determined. OIT measurements are indicative of a more effective stabilization with respect to thermo-oxidative processes in comparison to the original membrane 1702.
Significant increases in weight when wet and partially also in t