The Stockholm Bypass – A Grouting Design in Accordance with the Observational Methodpre-Excavation Grouting by Means of Rock Fissure Grouting with Cementitious Grouts-PPT Presentation

PPT Presentation

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The Stockholm Bypass is a 21 km section of the E4, including 18 km of tunnels and 55 km of rock tunnelling overall. The northern area presented major challenges: in 2017, unexpectedly poor rock conditions and highly conductive weak zones made it difficult to meet contractual water-sealing requirements. The existing approach was insufficient, so the project introduced a revised pre-excavation grouting design and launched post-grouting work.<br /><br />The new design uses flexible grout-hole fans, microfine cement, and calculations to ensure adequate grout spread. It applies an observational method that combines predictions about geology, sealing needs, and environmental sensitivity with drilling and grouting data. Each grout hole contributes information used to decide whether to approve a grouting round, change the grouting class, add rounds, or take other measures.<br /><br />Clear decision criteria, control parameters, and termination criteria guide these choices. Contractors and construction management assess results at defined stages, including water inflow, drilling indicators, grout consumption, connections between holes, leakage, and water-pressure tests. The design can adapt to observed conditions, with compatible grouting classes and options for additional grouting, post-grouting, monitoring, or recharge wells.<br /><br />The approach supports consistent, evidence-based decisions and reduces the risk of inadequate sealing despite uncertain geology. Its main drawbacks are the need for flexible payment arrangements and challenges in predicting the construction schedule.

Keywords

Stockholm Bypass

tunnel construction

pre-excavation grouting

post-grouting

rock tunnelling

water sealing

microfine cement

observational method

geological uncertainty