Publication Abstract

SuperPile 2017 Online Proceedings, (DFI)

Underpinning of a city street, with CAP, Stockholm, SWE
Tanja Bojovic, M. Sc.

A block in Stockholm City, Sweden had, for some time, been exposed to ground vibrations, causing discomfort to residents in the area. After complaints from the residents, measurements were performed by the Stockholm City Traffic Authority. The results indicated that the vibrations occured due to heavy vehicles passing on the adjecent street, e.g. trucks and city buses, and that they exceeded the allowed limit value for traffic induced vibrations in buildings. Golder Associates (technical consultant) was assigned to investigate and evaluate the reasons behind the ground vibrations and present measures for reducing the vibration levels below the allowable limit value (0,4mm/s). The investigation resulted in several possible mitigating measures. Measures related to vibration damping, due to uncertainties in the soil profile and soil properties, as well as measures involving taking actions in the buildings, due to legal regulations, were not regarded feasible. Thus separating the street from the buildings was considered the best option. It was decided to perform underpinning of the existing street, which was carried out as a concrete slab underneath the street founded on rock socketed bored piles. The bored piles were in this particular case performed as point bearing Cased Auger Piles (CAP), a piling method never before used in Sweden. The piling method had been proven successful in the south of Europe. Although one should bear in mind that the quality of the rock mass and the geotechnical conditions are somewhat diferent in Sweden, where especially the bedrock is significantly harder. The presence of the hard rock and a crushed zone, required compementary pre-drilling with a down the hole hammer and core drilling for a detailed verification of the bedrock level and its quality. With a close collaboration between the client, consultant and the contractor and a number of technical challenges later, a successful result was achieved, i.e. the vibrations in the buildings were no longer an issue.

 article #2685; publication #1031 (SP-2017)