The Gaasperdammertunnel - Geotechnical Challenges in Amsterdam-Paper

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The Gaasperdammer Tunnel is a three-kilometre cut-and-cover tunnel built as part of the A9 motorway expansion in Amsterdam. Its foundation works involved nearly 10,000 piles and extensive investigation, including more than 800 cone penetration tests (CPTs), to reduce design uncertainty and identify buried obstructions.<br /><br />A major challenge was landfill containing large concrete fragments beneath parts of the existing motorway. These deposits threatened installation of a long sheet-pile wall through the motorway’s central reservation. A trial site was used to select a suitable pre-drilling method, crusher and bentonite-cement mixture. The method successfully broke up the concrete and allowed the sheet piles to be installed.<br /><br />The tunnel was founded on cast-in-place vibro piles. Although a heavy impact hammer was selected using conservative drivability analyses, a limited number of piles had lower-than-expected driving blow counts. Engineers assessed these piles individually, considering whether they could be driven deeper and comparing driving records with nearby CPT data. Where capacity remained uncertain, additional CPTs were conducted after excavation and pile installation; these indicated adequate bearing capacity.<br /><br />The study also found that CPT resistance reductions following excavation appeared closer to a square-root method than the linear reduction required by the applicable Eurocode provisions. However, the limited post-excavation data were insufficient to justify using this more favourable method across the project, so the standard design rules were retained.<br /><br />Careful preparation, test installations and on-site geotechnical decision-making helped manage these challenges and limit delays. The authors recommend collecting and sharing more post-excavation CPT data to assess whether design guidance should be updated.

Keywords

Gaasperdammer Tunnel

Amsterdam

A9 motorway expansion

cut-and-cover tunnel

geotechnical investigation

cone penetration tests

sheet-pile wall

landfill obstructions

vibro piles

Eurocode design rules