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Increasing roadway bearing capacity on peat
and marine clay

Location of work/project:



Germany, Hennickendorf / expansion L23 Hennickendorf to Torfhaus


The road from Hennickendorf to Torfhaus had to be upgraded, but layers of peat and marine clay in the subsoil presented a challenge. These were in a thickness of up to 5m and across a length of 400m. It was unsuitable for the L23 extension project without a unique design.

The solution was to design in piled foundation and a geogrid- reinforced load-distribution layer. The grouted vibro piles were installed in a square grid of 1.7m x 1.7m through the organic soil and to a depth of 11m into the underlying firm sand. The geogrid reinforcement forms a load-distributing layer on the columns. The structure over the pile caps was as follows:

• 10cm sand levelling layer
• Secugrid® 500/50 R6 laid in transverse direction
• Secutex® 151 GRK 3 as a separator laid in longitudinal direction
• 20cm sandy gravel
• Wrap-around of the lower Secugrid® 500/50 R6 layer with a length of 2m
• Secugrid® 500/50 R6 installed in longitudinal direction with an overlap of 6m, as required by the design

The requirements of the reinforcement were exactly specified. Design engineers from BBG Bauberatung Geokunststoffe geosynthetic consulting verified the suitability of Secugrid® 500/50 R6 with design calculations in accordance with EBGEO. The calculations took account of product-specific reduction factors for Secugrid® R6. In particular, the laid and welded geogrids showed reduction factors for creep-rupture behavior, installation damage, and chemical resistance. The installation plan took into account, adapting to include overlap and wrap-around lengths in the transverse and longitudinal layers with the Secugrid® 500/50 R6 geogrids. Optimal roll lengths were determined to be 40m to 52m. NAUE manufactured the rolls to the specification to maximize installation efficiency and reduce cut-off waste for the contractor. The design also improved the carbon footprint of the construction works by reducing the amount of aggregate needed in the design. To help in the installation, the contractor’s experienced team was given the custom installation plan. This ensured a speedy and successful installation in the spring of 2018. A total of 11,200m² of Secugrid® 500/50 R6 geogrid and 3,700m² of Secutex® nonwoven geotextile were used.

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