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

Paper

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The Stockholm Bypass is an 18 km road tunnel forming part of a 55 km rock-tunnelling project around Stockholm. Because the rock mass proved more hydraulically conductive than expected, the project faced a significant risk of exceeding allowable water ingress. The paper describes a flexible pre-excavation grouting design developed to manage geological uncertainty and improve sealing.<br /><br />The design applies the observational method: predictions of geology and environmental sensitivity are compared with observations during drilling and grouting, and the results guide further action. Continuous rock-fissure grouting uses cementitious, microfine grouts and Swedish Real Time Grouting Control principles to set grout pressures and injection times. Grouting is organized into three classes, with increasing numbers of rounds and tighter hole spacing for more challenging conditions.<br /><br />Each grouting fan is assessed against acceptance criteria expressed as six control parameters. These include water inflow and drilling data, grout take, connections between holes, surface leakage, and results from control-hole water-pressure tests. Flow charts specify how to verify the selected grouting class, approve a fan, or require additional rounds and investigations. A fan is accepted only when all applicable criteria are met.<br /><br />The approach aims to make decisions consistent, transparent, and responsive to actual ground conditions, reducing the risk of inadequate sealing while improving efficiency. Its implementation depends on reliable monitoring and documentation, and presents practical challenges, particularly the need for flexible payment arrangements and uncertainty in predicting completion schedules.

Keywords

Stockholm Bypass

road tunnel

pre-excavation grouting

rock tunneling

hydraulic conductivity

water ingress control

observational method

microfine grout

grouting control

geological uncertainty