500 meters of outlet pipe in soft marsh soil

The solution was found in a research project with BAYO.S Screw Foundations

Rebild Utility installs outlet pipes from basins where bog terrain without load-bearing capacity makes conventional pipe laying impossible. The solution was found in a research project with screw foundations.

In connection with the installation of an outlet pipe from two rainwater basins at a new residential area in Støvring, Rebild Utility had to pull the pipe through a soft bog area. Unfortunately, a geotechnical investigation by the partner Andreasen & Hvidberg revealed soft layers down to a depth of 10 meters, where the bearing capacity could only be established. That’s why they had to think outside the box.

– Normally you dig up the old soil and replace it with sand, but that would be impossible to do with the depth conditions. On top of that, we experienced iron plates sinking into the area over a weekend, so we were worried about the bog soil bearing the weight of a pile driver for piling concrete piles, although we had that in mind at first. Therefore, there was uncertainty about the use of concrete piles, says Michael G. Jørgensen, who is a civil engineer at Rebild Forsyning.

Screw piles were the solution

To meet Rebild Forsyning’s request for pile foundations, Jens J. Porsmose, CEO of Andreasen & Hvidberg A/S, suggested using experience from a research project with screw piles. A project that geotechnical expert and screw foundation manufacturer BAYO.S is working on together with Aalborg University and Innovation Fund Denmark.

– We first turned to geogrid, which is used to create a stabilized layer that increases the bearing capacity of the subsoil, but Rebild Forsyning requested pile foundations as a solution as it is settlement-free. That’s why I presented the screw foundations as they matched the criteria well, where we can secure the outlet pipe – both against future buoyancy and settlements. “We carried out a geotechnical assessment and dimensioned the piles based on the experience from the research project for the design,” says Jens J. Porsmose.

The advantages of screw foundations over concrete piles or geogrids are that there is no excavation, no soil removal, no vibrations and fast installation. On top of that, the materials and equipment for installation are lightweight and won’t sink into the soft bog terrain.

March 2023