The central section of the Warsaw 2nd Metro Line required preventive measures to protect buildings located in the Praga district above the tunnel alignment. The sections passing below buildings with EPB machines were certainly one of the most critical points. It was decided to carry out ground treatment in order to consolidate the subsoil around the tunnels. For this purpose grouting holes up to 261 m long were drilled by HDD following the tunnel path. Tunnelling did not affect the structures located above the ground, which always remained under close supervision with the use of specialist and multithreaded monitoring.