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Ed. Züblin Deploys Digital Geotechnical Solution to Transform Center of Stuttgart

Case Studies

Ed. Züblin Deploys Digital Geotechnical Solution to Transform Center of Stuttgart

PLAXIS 3D’s Reliable Analysis and Versatile Visualization Capabilities Improves Project Efficiency, Leading to Significant Cost Savings

Tower Project Meets Sustainability Initiatives

Set on a triangular 1,800-square-meter site, the 66-meter-high Tower on Milan Square in Stuttgart, Germany will have a gross floor area of 21,000 square meters. The footprint will house two premier hotel brands, and include retail and dining space and an underground parking garage. The tower is being built close to major buildings and Stuttgart Central Station.

The GBP 150 million project of STRABAG Real Estate GmbH, Germany will be instrumental in shaping the center of Stuttgart with its distinctive and environmental architecture. The Tower on Milan Square will be designed and constructed with the latest sustainability trends in mind, including roof garden spaces, pockets of greenery planted in the stone façade, and ample public space. Grapevines will be planted in the stone niches and irrigated with collected rainwater.

Excavation Exposes 2 Underground Tunnels

Ed. Züblin AG was tasked with building the tower 20 centimeters above two operating underground train tunnels that were constructed using the cut-and-cover method. During excavation, the underground tunnels were uncovered and partially excavated at one side so that one tunnel forms a step in the excavation floor.

Along the outer tunnel wall, the number of underground floors changes from three to two, and the bottom slab of the new building is adjusted to the existing tunnels. One challenge the project team needed to overcome was that the tunnel owner stipulated that the geotechnical team could not excavate them only at one side, as it would cause asymmetric horizontal earth pressure on the tunnel. The demand was almost impossible to achieve, because it would tremendously impact the complexity of the excavation pit and the cost-effectiveness of the construction process.

Applying Digital Solutions for a More Robust Analysis

To address the construction challenges, Ed. Züblin AG needed to deploy a reliable digital solution to perform more robust geotechnical analysis and calculations that would lead to the most efficient excavation strategy.

Further, the digital solution had to allow for analysis and calculations to be translated during the construction process, the results of which could not deviate from the recommended limitations of the geotechnical analysis. Therefore, the geotechnical software must allow for robust construction project management.

Above all, the digital solution had to allow for clear and easy communication with important stakeholders to gain approval for the proposed construction approach.

PLAXIS 3D Used for Complex Deformation Analysis

PLAXIS 3D geotechnical software was used to fulfill all project requirements and allow for reliable analysis, powerful 3D staged construction modeling, and versatile visualization capabilities. PLAXIS 3D was crucial to performing complex deformation analyses of the excavation pit and the two underground tunnels.

As a result, a three-dimensional finite element model was generated to simulate all the excavation phases, including required structures and the installation of four levels of ground anchors. In addition, the foundation piles of the new building have been included in the model and act as lateral support to reduce potential horizontal displacements.

Tower Project Meets Sustainability Initiatives

Set on a triangular 1,800-square-meter site, the 66-meter-high Tower on Milan Square in Stuttgart, Germany will have a gross floor area of 21,000 square meters. The footprint will house two premier hotel brands, and include retail and dining space and an underground parking garage. The tower is being built close to major buildings and Stuttgart Central Station.

The GBP 150 million project of STRABAG Real Estate GmbH, Germany will be instrumental in shaping the center of Stuttgart with its distinctive and environmental architecture. The Tower on Milan Square will be designed and constructed with the latest sustainability trends in mind, including roof garden spaces, pockets of greenery planted in the stone façade, and ample public space. Grapevines will be planted in the stone niches and irrigated with collected rainwater.

Excavation Exposes 2 Underground Tunnels

Ed. Züblin AG was tasked with building the tower 20 centimeters above two operating underground train tunnels that were constructed using the cut-and-cover method. During excavation, the underground tunnels were uncovered and partially excavated at one side so that one tunnel forms a step in the excavation floor.

Along the outer tunnel wall, the number of underground floors changes from three to two, and the bottom slab of the new building is adjusted to the existing tunnels. One challenge the project team needed to overcome was that the tunnel owner stipulated that the geotechnical team could not excavate them only at one side, as it would cause asymmetric horizontal earth pressure on the tunnel. The demand was almost impossible to achieve, because it would tremendously impact the complexity of the excavation pit and the cost-effectiveness of the construction process.

Applying Digital Solutions for a More Robust Analysis

To address the construction challenges, Ed. Züblin AG needed to deploy a reliable digital solution to perform more robust geotechnical analysis and calculations that would lead to the most efficient excavation strategy.

Further, the digital solution had to allow for analysis and calculations to be translated during the construction process, the results of which could not deviate from the recommended limitations of the geotechnical analysis. Therefore, the geotechnical software must allow for robust construction project management.

Above all, the digital solution had to allow for clear and easy communication with important stakeholders to gain approval for the proposed construction approach.

PLAXIS 3D Used for Complex Deformation Analysis

PLAXIS 3D geotechnical software was used to fulfill all project requirements and allow for reliable analysis, powerful 3D staged construction modeling, and versatile visualization capabilities. PLAXIS 3D was crucial to performing complex deformation analyses of the excavation pit and the two underground tunnels.

As a result, a three-dimensional finite element model was generated to simulate all the excavation phases, including required structures and the installation of four levels of ground anchors. In addition, the foundation piles of the new building have been included in the model and act as lateral support to reduce potential horizontal displacements.

Securing Approval from the Tunnel Owner

PLAXIS 3D allowed geotechnical engineers to achieve safe construction according to desired parameters and to create an innovative construction and geotechnical approach.

Sound computation

The PLAXIS 3D analysis results showed that only small horizontal deflections as well as settlements of the tunnel can be expected with no critical differential displacements occurring at the segment joints.

Trusted Information for improved collaboration

Once presented with calculation results, the tunnel designer agreed that the predicted displacements are within the limits set for the tunnels. Based on this assessment, the tunnel owner accepted the adapted excavation concept, including the resulting asymmetric earth pressure.

Robust construction modeling and management

This decision enabled important simplifications that helped design the excavation pit and the construction sequences.

The most critical situation during construction was to arise at the point where one of the tunnel segments diagonally intersects with the retaining wall. Therefore, to avoid incompatible deformations, the team designed a lateral support for this segment. The steel construction connects the tunnel roof slab to the bottom slab of the new building, whereas the basement levels are under construction. While the steel struts are installed, a berm laterally supports the tunnel segment. Once the struts are installed, the supporting berm is removed.

“The special situation, that for this project, one building has to be built on existing tunnels, makes PLAXIS 3D a very powerful tool to examine geotechnical issues in such projects. Using PLAXIS 3D allowed us, together with the building owner, to find more economic ways to fulfil the demands of this project by building trust with the tunnel owner. Together we could also widen the predefined boundaries that would have produced immense conflicts during the construction process.” — Jörg Schreiber, Team Leader, Geotechnical Engineering.

Fast Facts

Milan Tower is a 66-meter high rise built within a dense urban environment.

The team had to work with a limited triangular construction site space with multiple adjacent structures.

The geotechnical analysis had to account for two tunnels located at 20 centimeters under the foundations.

The project team faced strict stakeholder requirements on the construction process and outcome.

ROI

  • Using PLAXIS 3D, the project team improved efficiency across the project leading to significant savings.
  • Reliable modeling based on trusted analysis adhered to stakeholders’ requirements.
  • The geotechnical team had to preserve the adjacent buildings and reduce construction risk.
  • Gaining the trust of stakeholders improved collaboration and lowered project risk.

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