ABSTRACT
Oslo’s Fornebu Line metro project – part K2A consists of 2.5 km of tunnelling and four shafts excavated through Cambro-Silurian sedimentary rocks intruded by volcanic dykes, located in a densely populated urban environment. Challenges on the project involved the excavation of large underground caverns with complex geometry and overburdens as low as 3 m with numerous fault zones, including a soil section of the tunnel, excavated by conventional methods.
A major challenge was the strict requirements for ground permeability and water ingress. This paper outlines the grouting strategy which was initially devised in connection with the production of the design, contract and tender documents. The paper then details the different materials and procedures used for the complex grouting and monitoring program.
The grouting and monitoring work was overseen by the Client, ‘Oslo municipality, Fornebu Metro Line’. It constituted a significant portion of both the project’s cost and timeline. Due to the proactive approach of the Contractor Implenia Norge, state-of-the-art equipment, and the use of different grouting materials tailored to the conditions, the project successfully met the stringent leakage criteria. This reduced the permeability of the ground to such an extent that it eliminated the requirement for a concrete lining with a waterproof membrane in parts of the project most vulnerable to ground settlement.
