Technical specifications
- 2600 m² soil mix wall,
- 17 m deep
185 vertical anchors
- VHP/HDI (Very High Pressure)
- Ø 1500 mm,
- 13 m long
This project involves constructing an underground space behind the existing museum and creating a connection between the new and existing buildings. Only vibration-free foundation techniques may be applied which do not reduce the soil tension or cause ground settlement. Lowering the adjacent groundwater level is also not permitted.
The new cellar is built in a construction pit bounded by a layer of natural water inhibiting clay to a depth of around 15.5 m, and a soil mix wall reaching down to 17.8 m.
The wall is 0.55 m thick and is reinforced with 15 m HE 320B beams, placed at 1m intervals. The combination of a water-inhibiting clay layer and 135 m of soil mix walling made it possible to excavate the building pit to a depth of approximately 5 m without affecting the nearby groundwater table. The concrete basement is pinned down by 195 vertical anchors up to 23 metres long. The anchors are drilled to a depth of 28 m below the surface using a Fundex 12SE machine. The anchors consists of 88.9 x 7.1 mm S355 steel tubes. After excavation, each anchor is fitted with a 300 x 300 mm plate, welded to the tube at the correct height for anchoring the cellar.
The connection between the new basement and the existing museum is partly within the existing buildings. Damage to adjacent properties is prevented by 1.5 m thick, 13 m deep jet grout walls inserted below the existing walls. These walls are reinforced with 32 and 40 mm Gewirods. At the upper end the walls are anchored with 12 m grout anchors.
Inside the building pit with its jet grouting walls an ‘underwater concrete floor’ is then laid, anchored by 32 post-stressable anchors of 23m in length.
Franki Grondtechnieken has been involved in the Assen project since early 2009. In the first instance it was invited by the main contractor Geveke Bouw and the builders, Engineering Consultancy Wassenaar and Grontmij, to examine possible solutions. Then in November 2009 it came in to actually implement the project.
