Tekfen Engineering used the application to design the TBM segments at cross-passages.

Tasked with providing all design works for extending the metro in the Turkish city of Istanbul, multi-disciplinary engineering firm Tefken Engineering turned to geotechnical analysis software from Bentley to enable it to deliver the fast-track project by early 2032.

The İstanbul Metropolitan Municipality is spearheading the TRY2.34-billion ($278.6 million) metro line project to extend the main artery of the central transfer hub of İstanbul’s Anatolian region. The project consists of two intersecting metro lines: the Çekmeköy-Sancaktepe-Sultanbeyli (CSS) and Hastane-Taşdelen-Yenidoğan (HTY) lines.

Tefken Engineering is responsible for providing all the design works for the 17-km-long CSS-HTY project, which includes 13 stations. 

To meet this tight timeline, Tefken Engineering wanted comprehensive digital technology to help it determine an optimal tunnelling solution. The company found that simplified approaches would not provide the desired result, as it needed to overcome the technical challenges with the tunnelling and retaining systems due to the high seismic activity in İstanbul, according to a spokesman for Bentley. Tefken Engineering also needed technology that would allow it to carefully analyse the construction of its tunnel junctions.

After considering all its options, Tefken Engineering chose Plaxis 2D and Plaxis 3D to design the CSS-HTY tunnels and retaining walls. Plaxis 3D allowed it to perform finite element analysis of different construction scenarios, resulting in an optimal solution that minimised the impact on aboveground structures.

“By utilising Plaxis 3D, we analysed different construction schemes and discussed them with the owner to reach the best solution with minimal impact to aboveground structures,” says Berk Demir, Senior Geotechnical Engineer, Tekfen Engineering.

The company used the application to design the tunnel boring machine (TBM) segments at cross-passages, determining the stress concentration around openings and specifically designing segments for these locations. With Plaxis 2D and Plaxis 3D, it was able to consider seismic activity when developing its design.

Using Bentley’s geotechnical application to easily create 3D models helped all parties visualise and understand the effects of potential underground solutions, avoiding damages to existing buildings, says the spokesman.

“Tefken Engineering realised that Plaxis simplified 3D geotechnical modelling, alleviating previous industry fears, and helped it to have confidence in using 3D modelling and analysis for future projects. Plaxis’ ability to conduct transversal and longitudinal seismic analysis allowed the team to investigate the effects of these activities on the design, finding that simplified approaches resulted in unsafe structural forces,” he says.

Tefken Engineering worked with the client to create the best solution that would have a minimal impact to the aboveground structures, reducing the need for improvements and streamlining construction. This helped them avoid damaging the existing buildings. Showing the design in 3D, in addition to the user-friendly interface, made it easier for project stakeholders to understand the full design, the spokesman adds.

The project is on track to be completed by 2023.