Proceeding of the 2018 DFI-EFFC International Conference on Deep Foundations and Ground Improvement, Rome, Italy, (DFI, EFFC)
The Gaasperdammertunnel - Geotechnical Challenges in Amsterdam
D. Grotegoed, Geotechnical Engineer and N. Goedhart, Deep Foundation Specialist
The Directorate-General for Public Works and Water Management of the Netherlands (Rijkswaterstaat) has planned to increase the capacity of the motorway corridor between Schiphol Airport, via Amsterdam to Almere. A subproject was awarded to IXAS, a consortium consisting of Fluor, Ballast Nedam, Heijmans and investment partner 3i Infrastructure in 2014. This subproject concerns the expansion of the A9 motorway in Amsterdam between the junction Holendrecht and Diemen. A large part of the new expanded road will be constructed below ground level in a three kilometre cut-and-cover tunnel, the Gaasperdammer tunnel. For the foundation design of the tunnel a large scale soil investigation was carried out with more than 800 Cone Penetration Tests (CPT’s). The soil investigation was intended to reduce uncertainty in the foundation design of nearly 10,000 foundation piles. In addition, a series of CPT’s was performed to identify “dump” zones. Specific areas in the existing A9 motorway appeared to be founded on landfill consisting of large concrete fragments. This was not only a problem for the foundation piles, but also for the 10,000 tonnes of sheet piling that had to be installed over a length of nearly three kilometre in the central reservation of the existing A9. Based on the results of the soil investigation, it was decided to mobilize pre-drilling rigs with bentonite and some crushers. During pile driving, another problem was encountered. The blow count of a few piles corresponded to the lower bound values of our predictions. Limit values were imposed to the operational manager on site. For piles with low blow counts the option of driving deeper was discussed immediately with the geotechnical engineer on site. In specific cases, driving deeper was not an option. For those cases, CPT’s were carried out after excavation and pile installation to investigate whether the bearing capacity was reached. Some CPT’s that had been performed afterwards, appeared to be even more favourable compared to CPT’s before installation with a theoretical reduction for excavation. In 2015 the first pile was driven and in the spring of 2017 the foundation works were completed. This article addresses several challenges during the preparation and execution of the foundation works of the Gaasperdammer tunnel.
|article #2980; publication #1040 (ROME-2018)|