Construction of a beltway in Bremen progresses case study


Courtesy of NAUE GmbH & Co.KG

Geogrids secure embankment reinforcements
The western bypass around Bremen is not scheduled for completion until about 2011. Section 1 of the second construction phase has been under construction since 2002. The 3.3 km long core stretch of A281 is construction section 2/1. Its most prominent structure will be a 127 m long cable-stayed bridge supported by 50 m high pylons to be built over the airport embankment. The bridge's abutments and access ramps are located on very heterogeneous subsoil. Fill and river sediments were found in the upper layers, which had partially been pre-consolidated for previous industrial utilization of the premises, whereas other areas had been used without any pre-consolidation.

This is why a decision was made for a piling foundation with mortared, vibration-driven piles. It was especially important to have the bridge abutments well supported on the lower-lying Weser Sand which has good load-bearing properties. The installation plan called for the pilings to be placed at 2 m intervals. Geogrids were part of the plan from the outset - to absorb expansion forces and to improve load distribution across the piling heads. The contractor had to have evidence provided by the manufacturer of the geogrid to be used.

Evidence was provided by the geosynthetic consulting firm Bauberatung Geokunststoffe (BBG) for Secugrid® 60/60 Q6. Their analysis showed that this NAUE geogrid met the necessary requirements for force absorption at the specified elongation as well as requirements for long-term force absorption. The Secugrid® 60/60 Q6 geogrid used in the project is a flatlaid geogrid of oriented monolithic flat bars with welded junctions. Due to the nature of its production and the raw materials (polyester/ PET) used, this geogrid is able to absorb extremely high forces even after only minimal elongation. These product characteristics provided proof that the geogrid met the specified requirements with only a single layer being used.

Secugrid® Q geogrids are, unlike the NAUE R geogrids, designed to absorb biaxial tensile forces. The overall construction of the bridge's ramps can be described as follows. Above the vibration- driven pilings, a 50 cm leveling layer of gravel and sand mix (grain size 0/32) was laid down and consolidated. The Secugrid® Q geogrid was then laid on top of this layer. Weser sand was used for embanking up to a height of 5 m. The required material was taken from along the route. This was then covered with a 1 m thick layer of frost protection sand. The final road surface layer will have an overall thickness of 0.80 m. The use of Secugrid® Q geogrids allows the construction companies to work economically, quickly and safely.

Year of construction:2004
City / Country: Bremen, Germany
Installed products:
Secugrid® 60/60 Q6 28.000sqm

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