Drilling for the tallest residential building in Denmark

Building what will be the tallest residential tower in Denmark present a unique set of challenges for the foundation works, which ground engineering specialist Aarsleff is equipped to take on

 Aarsleff’s Bauer BG 55 operating on the water-side Aarhus Ø project site in Denmark

Aarsleff’s Bauer BG 55 operating on the water-side Aarhus Ø project site in Denmark

The ground engineering contract for what is to become the tallest residential tower in Denmark is underway with Aarsleff Ground Engineering installing the drilled pile foundations for the 143m high Lighthouse 2.0 in Aarhus located at Aarhus Ø overlooking the waterfront.

Aarhus Ø is the newest part of Aarhus and has become a charming district of modern architecture separated by water canals. The Lighthouse will keep in line with Scandinavia's iconic architecture, built among other stand-out developments along the harbour such as The Iceberg and Dokk1.

Clay of high plasticity, complex logistics, wind factor and high-rise challenges were embraced wholly by Aarsleff Ground Engineering, which reviewed various foundation solutions and proposed that the building could be founded on deep drilled piles. This foundation method allows the structural load to be transferred to the subsoil, which has deeper load-bearing soil stratum to prevent long-term settlement of the building.

Highly monitored test piles - 2No. - to full depth and full diameter were carried out in the months prior to the main drilling works to ensure that all calculations were accurate and to optimise on the most effective drilling method both in respect of time and money.

On-site drilling

Aarsleff is currently on-site drilling 28No. piles with a diameter of 2,000mm and a total maximum length of 70m - the deepest bored piles ever to be executed in Denmark as production piles.

Ground conditions comprise a 10 - 12m layer of sand followed by clay of high plasticity. Generally, this soil type has numerous problems due to its low strength, high compressibility and high level of volumetric changes. Clay of high plasticity is typically found in coastal regions around the world.

Aarsleff Ground Engineering is responsible for overseeing the drilled piles at The Lighthouse project. The team on-site are 14 members strong, including one full-time health and safety inspector.

Aarsleff's Bauer BG 55 rig equipped with all necessary tools of a diameter of 1,860mm and 2,000mm diameter casing has been mobilised to undertake the main drilling works. This is the largest machine in Aarsleff's fleet and in Northern Europe. Beside that 2No. Hitachi (80t and 100t) mobile cranes and 2No. dumper trucks assist in the daily work.

Due to the high plasticity of the clay, the casing is not installed to full depth and as a result, bentonite was used to stabilise the drilled hole. The bentonite will be cleaned before concreting to achieve the correct amount of sand content according to European Standards.

A project of this scale within the inner city of Aarhus requires accurate and robust planning as well as logistics and thorough communications between all parties involved throughout the project duration. To reduce traffic congestion, Aarsleff designed a programme to only cast piles outside of rush hour thus ensuring the supply of fresh concrete, totalling 5,900m3, could always be delivered on time and without disruption.

Mobile laboratory

To ensure the quality of the piles and provide assurance to the main client, Aarsleff set up a mobile laboratory on-site to provide a transparent means of guaranteeing the quality of the product. The laboratory, equipped with modern technologies, is operated by qualified technical personnel who conduct tests and analysis of the concrete before installation.

Aarsleff also conducted tests such as SONICaliper for the verticality and cross-hole sonic logging for the integrity of the concrete.

Due to the site's restricted space, Aarsleff's newest technologies - Virtual Design and Construction (VDC), has been utilised in planning stages to model the construction site. This enabled the team to co-ordinate effectively the logistics on site, including the execution, transport, and stationing of workers and material to achieve the project both safely and efficiently.

The Lighthouse projects mark another ‘One Company' collaboration, whereby Aarsleff has involved several departments and companies of the Aarsleff Group to draw versatile expertise and experience from.

Building the entire Lighthouse project is expected to run over the next three years, and final completion is expected in 2022.

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