Underground car parks. Part 2 | Life Cycle Assessment

Detailed Design | The Netherlands

The technical and economic analysis of this case study was performed by the Dutch consulting engineers Witteveen & Bos for ArcelorMittal in 2020. The design assumptions were determined for a two level below grade underground car park in soil conditions that are typical for the region of Amsterdam in the Netherlands. The design assumptions were the same for the four alternatives. From an engineering point of view, such simplified assumptions for a soil can be used for a feasibility study or for a comparison of different alternatives.

ArcelorMittal emphasizes on the fact that Witteveen & Bos performed an objective and unbiased case study. The analysis is a purely hypothetical case study with its limitations on reliability on costs and techniques, since these aspects can be very dynamic in markets and different subsoils.

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In this case study, the conclusion is that the EcoSheetPile™ steel sheet pile wall has the lowest carbon footprint, the difference being 88 % compared to the cutter soil mix wall (CSM), and much more compared to a secant pile wall and a diaphragm wall. A sensitivity analysis showed that modifying some key parameters did not impact significantly the gaps, and in no case reversed the result.

The main objective of the study is to evaluate the influence of a structural solution on CO2-eq. emissions considering the life cycle of an underground car park structure. It proposes a comparison of four alternative solutions through LCA.

In order to provide a sound comparison of a steel sheet pile wall with alternative solutions a simple but realistic case study was carried out. The case study is based on a hypothetical geometry of a 250 meter long by 30 meter wide underground car park (UCP), with two levels below grade that would be built in the city of Amsterdam in the Netherlands. 

Following retaining structures were analysed 

  • steel sheet pile wall (SSP);
  • cutter soil mix wall (CSM), also known as deep soil mix in other countries;
  • secant pile wall;
  • diaphragm wall (D-Wall). 

The comparison of the indicators shows a sufficient difference between the four alternatives to justify the statement that “the environmental impact of steel sheet piles is lower than that of other solutions”. Indeed, assuming a 5 % uncertainty on each input of the study, a difference of minimum 10 % is essential to demonstrate a clear difference between alternative solutions. This condition is observed for the indicators that were analysed.

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UCP. Part 2 | Life Cycle Assessment