In western Bucharest, a developer initiated a EUR 2.5 million project to construct a 10-story residential building with a basement, above the existing subway tunnels. It is the first time that a structure is being built over these city tunnels. The project presented an irregular footprint, complex geotechnical challenges, and requirements from the subway operator regarding tunnel displacements and structural forces. SAIDEL Engineering was tasked with reducing the overall influence of the building on the tunnel lining, providing a safe and cost-effective solution. They needed to determine an excavation plan and conceptual design for the foundation that met the subway operator’s approval so that the project could proceed.
Meeting Displacement and Structural Demands
Because the entire footprint of the building is located in the subway tunnel protection zone, SAIDEL Engineering performed 2D analysis to determine feasible solutions for excavation and foundation that complied with the subway operator’s displacement and structural demands. While they received approval for excavation based on their 2D models, SAIDEL Engineering sought to increase the safety of the conceptual foundation design and implement 3D geotechnical modeling for the foundation, due to the project’s significance. Given the size of the model and the desire for increased accuracy and quality, they faced numerous challenges when modeling the piles and pier loads, which featured more than 1.1 million elements and 1.5 million nodes.
Finding Success with PLAXIS
As a PLAXIS user for almost a decade, SAIDEL Engineering knew that the software was the best geotechnical application for this project. Using PLAXIS, they performed plane strain analysis and developed 3D models for improved accuracy and optimization, providing further confidence in the foundation design and its reduced influence on the tunnels. The advanced design and analysis features facilitated evaluation of soil structure interaction and the usage of hexagonal prisms for the piles, as well as ensured convergence modeling for the pier loads. With Bentley’s geotechnical software, they modeled and analyzed various solutions and their influence on the tunnel lining throughout all stages of construction and lifecycle operations, resulting in a design concept that was approved by the subway operator.
3D Geotechnical Modeling Drives Industry Standard
Using PLAXIS, SAIDEL Engineering got the project back on track in just three months, after two years of lingering to find a solution that the subway operator found acceptable. The approved foundation system meets the requirements for minimal influence on the tunnels in terms of displacements and structural forces. The analysis results led to a decision to reduce the number of stories from 10 to nine, thus limiting the seismic loads on the tunnels as well. It also allowed SAIDEL Engineering to reduce raft thickness from 2 meters to 1.5 meters. As a pioneer residential project for the city, it unlocks the potential for future development over the Bucharest tunnels. Through successful 3D geotechnical modeling solutions backed by PLAXIS, SAIDEL Engineering increased their visibility into the project, driving emulation of their methods, geotechnical competition, and new industry standards in the country.
Project Playbook: PLAXIS
SAIDEL Engineering was tasked with providing geotechnical and structural design for the first residential building being constructed over West Bucharest subway tunnels.
They used PLAXIS to deliver an excavation plan and conceptual design of the building foundation, which was approved by the subway operator within three months.
The advanced software features facilitated accurate, reliable modeling and analysis, proving that displacements and structural forces will have minimal influence on the tunnel lining.
The cost-effective solution serves as a benchmark for potential future developments over tunnels in West Bucharest.
“PLAXIS is the best tool the geotechnical software market has to offer to expert geotechnical engineering teams who want a competitive edge over their peers.”
FEM Design Engineer