THE PROBLEM

To complete the ring road around the city of Odense, Odense Municipality faced a challenge as the remaining section had to cross marshland in order to connect to the city canal bridge. The marshland, consisting of weak, variable soils with varying thickness and strength, was expected to result in an extended period of settlement, as well as uneven settlement due to the variation of subsoil conditions.

The site was a challenge as marshland of 8-9m in depth overlay solid ground, as well as enduring high water levels for most of the year. In order to mitigate differential settlement, a stiff structure had to be constructed to bridge soft and hard spots which would result in an even settlement with high bearing capacity. It was necessary to reduce settlement time in order to open the access road to local traffic as soon as possible.

THE SOLUTION

The subsoil was reinforced with a 1m deep, three dimensional Tensartech Geocell Foundation Mattress. Tensar Geocells confine the soil placed within the cell structure and increase the stiffness. Additionally, the Tensar uniaxial geogrid component provides sufficient tensile strength to ensure equilibrium with the acting forces from the road embankment. The geocell spreads the load horizontally throughout the layer, resulting in reduced pressure on the subsoil and therefore reduced settlements. After the Tensartech Geocells were filled, perforated vertical drains (PVD's) were installed to further accelerate consolidation time. A sand blanket was placed over the geocell to ensure sufficient drainage of the excess water due to the consolidation of the underlying marshland.

PROJECT DESCRIPTION

The city of Odense is located close to the northern coast on the island Funen in Southern Denmark. The area is characterised by a flat moraine landscape. Odense Municipality has extensive plans to modernise the infrastructure in the area in order to meet the increased challenges of transportation requirements. One of the most ambitious projects would transform parts of the city center into a car free zone that relies heavily on public transport. This requires a capacity increase of the surrounding roads, as well as a functioning ring road.

The marshland surrounding the city canal connected the city with the sea to the north.  It was necessary for the contractor to stabilise the road foundation before constructing the last part of the ring road which included a bridge canal. The contractor suggested the use of a proven embankment foundation solution, comprising a 1m deep cellular mattress, rapidly fabricated and installed on site - the TensarTech Geocell Foundation Mattress System. This resulted in a reduction of settlement and achievement a more even road surface in comparison to alternative horizontal geosynthetic foundations.

After one year, the area had settled evenly with lower total settlement than initially expected.