WEB EXCLUSIVE: Additional 150 piles for Copenhagen metro

Metroselskabet, the owner and operator of the metro system in Copenhagen, Denmark, is to extend its ground investigations for the city's new DKK 15 billion (€ 2 billion) underground circle line, the Cityringen.

Specialist geotechnical contractor GEO-Aarsleff is to sink an additional 150 boreholes to depths of 55 m. This is in addition to the 350 boreholes already sunk for the initial geotechnical and hydrogeological survey.

The new boreholes will be drilled at the locations of the new stations and shafts and have been requested by Cityringen's team of consultants to gather further geotechnical and hydrogeological information at these specific locations.

Geo-Aarsleff is using six rigs in situ for the drilling of boreholes of between 150 and 300 mm diameter. The boreholes range between 5 and 55 m in depth and are being drilled through Moraine clay and sand overburden to penetrate up to 30 m into the underlying limestone bedrock.

"We're using a combination of cased shell and auger drilling, core drilling with the Geobor S sytem and down-the-hole hammer drilling combined with the Symmetrix technique," said GEO-Aarsleff project manager Jesper Furdal.

"Even with the original 350 boreholes, this was the largest geotechnical and hydrogeological survey ever undertaken in Copenhagen. The additional 150 boreholes, which require a more comprehensive programme of geophysical logging than the initial 350 bores, makes it so much bigger and we have a team of 35 personnel on site and report the data findings to Metroselskabet on a daily basis," added Mr Furdal.

The large amount of data collected from the geophysical logging and thousands of soil and water samples will be used by Cityringen's team of engineers and consultants to design the underground stations, the deep access and ventilation shafts and the main twin-bore running tunnels.

GEO-Aarsleff expects to finish drilling, sampling and testing work by the middle of April and then submit its final report by June. The Cityringen is scheduled to commence passenger services in 2018.