The railway line was 6 kilometres and the station in the rock was 260 meters long and included an elevator shaft in the rock and construction during the day. The work included zoning plan and detailed engineering and construction plan, tender documents and assistance during construction.

NGI's work comprised

  • planning of ground investigations and stress measurements in the rock formation
  • geophysical ground surveys
  • core logging
  • engineering geological mapping
  • stability analysis and design of required safety measures in the 35 m wide station hall with an adjacent 22 m wide rock cavern, and a 100 m long section with a width weakness zone sub-parallel to the tunnel
  • assessment and design of tunnelling construction methods in large cross-sections, including systematic pre-injection
  • design of anchoring of heavy steel cladding (water and frost protection, noise reduction) inside the rock cavern (station hall)
  • geotechnical design of various surface facilities in challenging ground conditions (local quick clay zones)
  • assessment of rockfall risk and safety needs in connection with an 80 m high rock slope centrally located in the construction area
  • hydrogeological assessments and determination of permeability and seepage requirements for tunnels and station halls
  • geoscientific assistance for the preparation of seven tender documents
  • installation of multi-point extensometers (MPBX, deformation measurements) from terrain to rock cavern and from rock cavern and 20 m out, and assessment and follow-up of measurement results
  • scanning of the station hall with LiDAR in several rounds for monitoring deformations to assess stability and need for supplementary protection and safety measures.
Holmestrand stasjon ferdig 500

Picture of completed Holmestrand station in the rock cavern

The project was challenging with strict requirements for a progress plan, and challenging ground conditions with large fault and soft clays. NGI contributed to the project being planned on time and the construction work being completed on time.

Systematic follow-up with deformation measurements performed by NGI documented that the large cross-sections, 600 m with a width of 30-40 m, were stable and constructed according to the design.