The Consultant company ÅF Infrastructure AB and Stockholm County Council (Stockholms läns landsting)
Extend a subway-line through a marine environment
In the project of extending a subway line in Stockholm Sweden, the bedrock quality in the bay of Saltsjön needed to be investigated.
The project creates additional challenges in finding the most appropriate method for a marine environment that can handle potential gas pockets and is resistant enough to various electric disturbances frequent in urban areas.
The resistivity method was chosen, complying with the requirements and complexity of the project.
The system used in the survey consists of ABEM Terrameter LS with 12 channels and marine cabling with 64 take-outs at 7 meter spacing, complemented by SAS LOG300 to measure the variance in water resistance.
For data processing, Res2Dinv was used. The resistivity cable was placed on the sea bottom and the take-outs acted as electrodes.
Five (5) parallel profiles were measured for the survey and Pole-Dipole array was used for increased depth.
The processed data concluded the variations of the bedrock, from weak or eroded bedrock to good quality bedrock as well as seeing the effects of the existing dockside construction. The planned building start of the subway extension is 2018/2019.
For more in-depth information on the Subway extension project download the PDF – Resistivity/IP – Marine geophysical Survey
We would like to thank Stockholm County Council and ÅF for allowing the use of information, images from the publications made in their pre-studies for the new subway line to Nacka Sweden