Underground car parks

Underground car parks

Detailed Design | The Netherlands

Technical & Cost Analysis

The impact of the wall type on the overall costs is significant, but within a bandwidth of less than 10 %. The walls themselves have a much bigger bandwidth in costs but will also bring additional costs later on in the construction process, such as fire safety protection and duration of construction. Since the installation of the wall is a basic requirement in order to proceed with the construction, the installation/curing of the wall is always on the critical path. This implies that any time saved on the wall construction has an immediate impact on total construction duration and the related investment, cashflow and duration of hinderance. 

From this analysis it can be concluded that the pressed in sheet pile retaining wall is the most cost-effective solution: lowest cost, fastest execution and high quality in terms of watertightness and impact on surrounding structures. The D-Wall provides a robust solution but appears too expensive and too heavy for a 2-level car park solution. In sandy soil with a shallow groundwater table, the secant pile and the SoilMix retaining walls should not be used because of the risk of the lack of watertightness. They could be considered in other situations.

Underground car parks

Guide Book | The Netherlands

Comprehensive study of Steel Sheet Pile Walls

Steel sheet pile walls are the most sustainable alternative for underground car parks (UCP) with 1 to 4 levels below ground in the Netherlands: typical Dutch soft soil conditions, high groundwater table and the long-lasting experience of Dutch driving companies. The most efficient solution is to utilise the sheet pile walls for the temporary and for the permanent phase. Besides, sheet piles can transfer vertical loads to the soil, thus acting as a retaining wall and as a foundation, which reduces the number of columns inside the peripherical walls. The execution methods that can be envisaged are the classical bottom-up, and the unique top down.

Generally speaking, compared to alternative solutions, steel sheet piles are up to 50 % cheaper, and the execution of the retaining wall is up to 2 times faster. 

In city centres, an additional advantage of steel sheet piles compared to alternative solutions is the reduced amount of trucks that deliver material to the job-site, as well as the little space required for storage and installation: less traffic congestion, less disturbance to neighbours.