Underground Car Parks comparative study in Germany

We announce the availability in English, of the comparative study for Underground Car Parks in Germany.

The study, conducted by GRBV Ingenieure im Bauwesen for ArcelorMittal, compared four retaining wall systems for a hypothetical two-storey underground car park in Germany: permanent sheet pile walls (V1), temporary sheet pile walls (V2), secant bored pile walls (V3), and diaphragm walls (V4). The key findings are summarized below:

1. Economic Superiority of Sheet Pile Walls

• Most Cost-Effective: Steel sheet pile solutions are significantly more economical than concrete alternatives. The temporary sheet pile wall (V2) was the cheapest, while the permanent sheet pile wall (V1) was only 3% more expensive.

• Concrete Costs: The secant bored pile wall (V3) and diaphragm wall (V4) were found to be 18% and 24% more expensive, respectively, than the permanent sheet pile solution.

• Total Investment: These costs include manufacturing, earthworks, and shell construction.

2. Execution Speed and Construction Logistics

• Fastest Installation: Sheet pile walls offer the shortest construction time because they are prefabricated and can be loaded immediately upon installation. Their execution speed can be up to twice as high as that of other materials.

• No Preparatory Work: Unlike concrete systems, sheet pile walls do not require time-consuming preparatory measures like concrete guide walls (for diaphragm walls) or drilling templates (for bored piles).

• Minimal Site Footprint: Sheet pile walls require much less site installation surface, whereas diaphragm walls require extensive space for separation plants, pumps, and mixing equipment.

3. Maximum Usable Floor Space

• Slim Profile: The permanent sheet pile wall (V1) provides the largest usable floor space because of its slim cross-section and the fact that it serves as the final exterior wall, removing the need for an additional concrete basement wall.

• Space Loss in Alternatives: Compared to the permanent sheet pile wall, other variants result in a 6% to 9% reduction in usable space. In dense inner-city environments, this lost area represents a significant loss of potential long-term income over the car park's 50-year service life.

4. Sustainability and Life Cycle

• Preferred Sustainable Choice: The permanent sheet pile wall was rated as the most sustainable solution.

• Resource Efficiency: Steel is lighter and offers higher strength with lower material volume than concrete. Furthermore, concrete production is limited by the scarcity of aggregates like sand.

• Circular Economy: Steel components are highly reusable and recyclable. Temporary sheet piles can be pulled and used in other projects, and permanent walls can be easily recycled at the end of the building's life.

5. Technical Performance and Risks

• Durability: Both steel and concrete systems can meet the required 50-year service life. Sheet pile durability is managed through corrosion allowances or coatings, while concrete relies on reinforcement cover.

• Ground Obstacles: Bored pile walls (V3) are the most robust against obstacles in the ground, as they can usually drill through them, whereas obstacles pose a higher risk of bending or declutching for sheet pile walls.

• Deformation: Rigid systems like diaphragm and bored pile walls offer lower deformation than flexible sheet pile walls, making them highly suitable for sites very close to settlement-sensitive neighboring buildings.

Study Conclusion

According to the evaluation matrix, the permanent sheet pile wall (V1) is the preferred option. It achieves excellent ratings across investment costs, construction time, space utilization, and sustainability, performing slightly worse only in the category of execution risks regarding ground obstacles.