BTS | PRAGUE METRO LINE D
Q&A
Following his presentation to the BTS meeting, Petr Makasek took questions from the audience.
Q: Matthew Hubble, Mace Dragados: Given the incredibly impressive scale of the tunnels, is this the most economical way to build them, or more of an architectural statement piece for the city? A: Who knows? Maybe more architectural than understandable from the technical point of view. There is a preference for this one cavern system and because there is good rock it can be constructed. This is the result of many discussions with the client.
Q: Nick Lock, London Bridge Associates: Looking at the escalator shaft what is access for construction? Secondly, what is the programme for the complete construction? A: The complete construction programme for the station is five years: two years for primary linings, and the rest for casting the secondary linings and internal structure. As two years is a short construction period the team will use all available access points (shafts, escalators) to launch headings in parallel. The ventilation shaft for the track is situated close to the problematic part at the turnout area, that’s the reason why we are going via the shaft.
Q: Hayden Davis, Retired (tunnel engineer): Are you assuming the successful contractor will use Drill & Blast? Has the vibration risk to nearby structures due to the blasting been considered? A: Yes, blasting is expected in competent rock but is subject to environmental assessment constraints in the city. The effects of vibration on the surrounding buildings have been assessed; one building is scheduled for demolition during the works.
Q: Nick Chittenden, Independent: You have a huge amount of shotcrete works ongoing for the temporary works. What sort of volumes are you anticipating and have you looked at specifying any certification for the operators to ensure quality, efficiency and optimisation for the application? A: Sprayed concrete is standard practice in the Czech Republic; contractors are certified, although industry-wide shortages of skilled operatives are a concern. I do not remember the total volume.
Q: Mike McConnell, Retired (Balfour Beatty): Temporary works design will play a very central part in this, and I would be appreciative if you could elaborate on how the actual Contractor´s contract is linking in here. It would be good to have the temporary works design wholly under the Contractor´s brief, if that is possible. How is it to be designed and managed? A: Designer will undertake temporary works design within an established division of responsibilities; contractors bring methodology and means in construction design.
Q: Ali Mahdi: Considering the high hydrostatic head, please elaborate on the approaches employed to ensure watertight and waterproofed connections and joints. A: A combination of sheet membrane and spray-applied systems is envisaged, with details to be finalised at the construction stage.
Q: I have made some correlations from our experience in Egypt and, regarding the previous question, sharp corners usually suffer from water ingress inside. How was numerical modelling validated? Do you specify monitoring during construction to ensure your design is safe? How will unsymmetrical lateral loading be handled as the station seems to be in areas fully congested but with zones that are vacant to one side (not loaded) and heavy loaded to the other side, considering you are designing for both short- and long-term? A: Monitoring is part of the NATM method, so the monitoring design and instrumentation were considered and settlement limits set at all construction stages. Critical 3D staging was modelled in MIDAS; Plaxis was also used and secondary linings were checked in other tools (e.g., Revit). Several different software packages were used for validation. Designs were independently checked to validate the design. Water ingress during primary lining construction is not
expected as we are dewatering but secondary lining design has considered full water load.
Q: Was conventional rebar used or GFRP? What did you use for the diaphragm walls? A: We used conventional steel reinforcement. Fibreglass reinforcement was used in the tunnel eyes for the future branch lines.
Follow-on Q: Is Prague a seismic zone? A: No, we don’t have earthquakes.
Follow-on Q: What constitutive models were used in analysis of the lining and the surrounding soil? A: Several were used, Mohr-Coulomb for soil, and Hoek-Brown for rock.
Q: Jen-Li Chu, Morgan Sindall: What is the impact of OSD pile foundations on the station? A: The Over Site Development (OSD) was proposed following the completion of our design and this was an issue. The team limited the OSD basement depth and verified station–OSD interaction to keep effects within design allowances; certain initial proposals for deeper basements were rejected.
Follow-on Q: With hindsight knowing there would be an OSD would you have adopted a station box? A: The building foundations will consist of retaining walls around the station. The secant pile walls around will not affect the station.
16 | April 2026
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