New harbour lock in Bremerhaven: Safe constructions on weak soils using Secugrid®

As part of urban and port development in Bremerhaven, the New Harbour Lock – connecting the Weser River and Neuer Hafen – was constructed between 2003 and 2005. The project also included a road ramp over the outer lock head, directly adjacent to the historic Loschenturm lighthouse. The challenge: the subsoil consisted of up to 20m of highly compressible clay and soft soil layers. With a planned ground elevation of up to 5m, the project required a solution that would limit settlement and ensure long-term stability to protect the sensitive existing structures.

Engineering challenge: controlling settlement – structurally and on schedule

Given the deep soft soils, settlements of up to 60cm were expected. However, the maximum permissible residual settlement was just 5 to 7cm. Preloading techniques and lightweight fill materials, such as expanded clay, were ruled out due to unfavourable soil conditions. The adopted solution: a load-bearing foundation system comprising mortared piles in combination with a geogrid-reinforced load distribution layer.

The solution: Secugrid® 80/80 Q6 for geogrid-reinforced load transfer

For the northern ramp, a foundation system was implemented using mortar piles installed 2m deep into load-bearing sand, topped by a geogrid-reinforced pad. The embankment load is transferred onto the piles via a double-layer load distribution system made of Naue Secugrid® 80/80 Q6 geogrids and a load-bearing soil arch. The result: efficient load transfer into deeper, stable soil layers – and a maximum settlement of less than 4cm at the ramp centre.

Why Secugrid®?

• High stiffness: With a tensile stiffness of ≥ 2,000kN/m at up to 2% strain, Secugrid® effectively supports the load transfer mechanism and relieves the soft subsoil.
• Biaxial strength: Stiff, force-locked junctions ensure reliable load transfer – even under non-orthogonal stress directions.
• Proven performance: Long-term monitoring using strain gauges and pressure sensors confirmed the effectiveness of the system throughout the construction phase.

Results and transferability

The foundation system proved successful in both practice and theory. While conventional design models significantly overestimated geogrid strains, an advanced method based on Zaeske’s approach provided realistic and conservatively safe predictions. These findings enabled further refinement of the design methodology for future projects with similar subsoil conditions.

Conclusion: The combination of Naue Secugrid® geogrids with a column-supported load transfer system allowed for a safe, cost-effective and timely construction process under extremely challenging ground conditions. A transferable solution – especially suited for infrastructure projects in soft clay soils, such as those found in northern Germany and similar regions.

01132