Evaluation of the Grouting Methodology used in the Stockholm City Line Project

University essay from KTH/Jord- och bergmekanik

Abstract: As part of the Stockholm City Line project a grouting design was conducted and documentedduring the planning phase, based on theoretical grounds. This comprehensive design is the first of its kind for a tunneling project in Sweden. Due to the scale of the undertaking, the general design was ordered by the Swedish Transport Administration (Trafikverket) to apply for the pregrouting operations at the City Line’s rock tunnels. During the local design however, the grouting work developed differently within each sub-project from what was prescribed by the original design. This thesis project was carried out in cooperation with Trafikverket and concerns subjects related to the general grouting design for the City Line. The emphasis is on describing the general design, its theoretical background, and further to investigate what modifications were made during the local design. It was also to discuss the reasons and justifications for the changes at each sub-project. A detailed analysis of the grouting results at chosen sub-projects of the City Line has been performed, including: Vasatunnel & Odenplan Norrmalmstunnel Norrströmstunnel Södermalmstunnel The evaluation of results featured a calculation of sealing effects for the track tunnels at the different sites, which were then compared to the inflow requirements set by the Swedish Environmental Court. Further, a section of each sub-project was analyzed with respect to both pumping time and grout consumption. In total 96 pre-grouting fans, including approximately 2900 grouting holes were analyzed for this purpose. The goal was to identify the most economical method of grouting at the City Line, which still met all the demands regarding inleakage. The performed study showed that for all sub-projects the local grouting proceedings evolved considerably, although to varying extents, from the originally designed grouting concepts. In general the designed concepts were quite conservative, and not entirely applicable for grouting at large parts in its unchanged form. However they were hugely beneficial as excellent basis for local modifications made considering site specific conditions.Performed calculations showed that the grouting works at all the sub-projects provided sealing which fulfilled the requirements set by the Environmental court. However the pumping times and material consumption were different between all of them, which provided a basis for a discussion on how economical the grouting was at each site.If documenting of grouting methods and designs is carried on in future tunneling projects, especially of similar scale as the City Line, the knowledge gained can be transferred from one project to the next. Thus consistently building up further understanding on the complexities of hard rock grouting.

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