residential building atop of it would have minimal influence on the tunnel lining. Advancing Geotechnical Modeling and Analysis As a PLAXIS user for almost a decade, SAIDELEngineering knew that Bentley’s geotechnical application was the best choice for this project. “PLAXIS 3D analysis was the natural step for us to take,” commented Nicolau. Using the software, they performed plane strain analysis and developed 3D models for improved accuracy and optimization, com- paring the 3D analysis with the original 2D models to provide further confidence in the project’s foundation. They evaluated the feasibility of using a simple raft or raft on piles, considering various diameters and lengths, with or without base enlargement. They also analyzed the possibility of using a 15-centimeter-thick layer of Styrofoam under the raft between the foundation piles that encase the tunnels. For the soil structure interaction, they performed nonlinear analysis using the unique constitutive soil modeling feature in PLAXIS. To overcome the modeling obstacles, SAIDEL Engineering utilized additional advanced capabilities within PLAXIS, including hexagonal prisms to model the piles and a rigid bodies feature for the pier loads to ensure convergence. The software enabled them to accurately model and analyze potential solutions and their influence on the tunnel lining throughout all stages of construction and lifecycle operations, resulting in a design concept approved by the subway operator. The accepted solution is a 1.5-meter-thick raft on 37 piles, with a 1,080-millimeter diameter, and 18 meters in length. The firm 3D calculation showed that this design resulted in just over approximately 6 millimeters of uplift during excavation and settlement during building service, minimally impacting the subway tunnels. The application’s advanced geotechnical modeling and analysis features accelerated finite element modeling and ensured accurate deliverables. Photo: SAIDEL Engineering
Using PLAXIS, SAIDEL Engineering delivered a design solution that achieved the subway operator’s approval within three months. Photo: SAIDEL Engineering
Unlocking Potential for Future Development Using PLAXIS facilitated highly accurate modeling and analysis that enabled SAIDEL Engineering to achieve approval of the project and get it back on track in just three months, after a lingering two-year hiatus. The software’s highly advanced soil models and dynamic con - struction simulation provided a fast, user-friendly, and reliable engi- neering environment that accelerated precise finite element modeling, improving overall geotechnical and structural iterations. “Our team members have been successfully using PLAXIS since 2000 for various international projects and the most complex deep excava - tion works and foundation systems for tall buildings in Romania,” explained Ion Răileanu, executive manager and head of design at SAIDEL Engineering. “Through monitoring during both the construc- tion and service periods, the results of the geotechnical analyses were confirmed. Thus, expertise was gained in safe and economical model- ing for the benefit of our clients and of the environment. The features of PLAXIS software—namely advanced constitutive models for the simulation of nonlinear behavior of soils, joint elements to model soil- structure interaction, staged construction enabling a realistic simula - tion of construction, and other special elements—make it suitable for the numerical analysis of all geotechnical analyses.” With their design solution, SAIDEL Engineering reduced the influence on the tunnel lining by 50 percent in terms of displacements and struc- tural forces. The analysis results led to a decision to reduce the number of building stories from 10 to nine, minimizing seismic loads on the tunnels. Furthermore, it resulted in the reduction of raft thickness from 2 meters to 1.5 meters, using less concrete and reinforcements. As a pioneer residential project for the city, it unlocks the potential for future development over the Bucharest subway tunnels. Through their successful 3D geotechnical modeling solutions supported by PLAXIS, SAIDEL Engineering increased their visibility as an organization, driving emulation of their methods and geotechnical competition. The project provides a model for future endeavors to follow.
“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.” - Serban Nicolau, FEM Design Engineer, SAIDEL Engineering
JANA MILLER is manager of Product Marketing and Structural Analysis at Bentley Systems.
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November 2021
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