Dimensioning Groundwater levels - A case study of the TK Geo method

Abstract

Dimensioning groundwater level is a term that is used within the area of geo-construction and infrastructure projects. The level is used to calculate the water pressure that an underground construction should resist. The concept of dimensioning groundwater levels is implemented in Eurocode and governing documents from the Swedish Transport Administration (Trafikverket) and it implies a similar treatment as other loads to the construction in terms of safety. Groundwater levels fluctuate resulting in difficulties deciding on a single value as a dimensioning groundwater level. It is not only the evaluation method that arise questions within the industry. It has also arisen questions of who is responsible for these assessments and how should the levels be dealt with in large infrastructure projects where the whole landscape is affected, and the hydrogeological conditions are changed fundamentally? There is no simple answer to these questions but in an attempt to contribute to the industry, this master thesis aims to perform a case study where one common evaluation method for dimensioning groundwater levels is tested and compared to a statistical analysis. The master’s thesis project also includes a literature study that describes the fundamentals about groundwater level fluctuation. The literature study also gives an overview of how loads and groundwater levels are treated according to Eurocode and Swedish regulations. The tested evaluation method for dimensioning groundwater levels in the case study is the method presented by the Swedish Transport Administration in their governing document, TK Geo. The method is developed by Chester Svensson and Göran Sällfors in the 1980s and is an easy way to establish dimensioning groundwater levels for construction sites mainly. The method is notated the TK Geo method in this report. The TK Geo method uses measurement series from a reference well to estimate groundwater levels at a site. In this thesis project, the TK Geo method is used to estimate the dimensioning groundwater levels at two case study sites. The results are then compared to statistical analysis of measurement series from the case study sites. The results show that the TK Geo method can predict dimensioning groundwater levels with reasonable accuracy if the reference well is representative for the case study site. The case study is too limited to enable a general conclusion about the accuracy of the method, but the results indicates that there are risks associated with the hydrogeological conceptualization and that there are possible improvements to the description given in TK Geo.