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Post-grouting is a difficult task. It is often coupled with high costs and a result that is difficult to quantify. An infrastructure tunnel in an urban city in southern Sweden was used to develop and implement design methodology for post-grouting. The water inflow measured in weirs prior to post-grouting was about 3.8 l/min/100 m. The task of sealing low water inflows to achieve even lower ones takes a lot of effort and determination. The tunnel was built in the 1970s using the traditional drill-and blast method. During the pre-investigations of the project the analysis showed very good pre-grouting, giving a sealed zone of almost 10 meters. The tunnel had a large, sealed zone with a smaller hydraulic gradient and only narrow fractures were left unsealed. The grout chosen was the newly developed silica sol for the presumed narrow fractures and a robust cement grout if large inflows were hit by the grout holes. The tunnel is small, roughly 12 m 2 and heavily congested with cables and heating pipes, making it difficult to use traditional machinery. The tunnel section, 90 m in length, was divided into three different sub-sections, each with specific goals. The result showed that the strategy developed worked well and production was more rapid than presumed. The targeted water inflow rate of 1 l/min was met.

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