The project TEO “Tunnel Emisor Oriente“ in Mexico city 
The paper gives firstly a general presentation about the project TEO, currently under excavation in Mexico City. Secondly, the tunnel Section included between the Shafts 5 and 6 is approached more in details. In particular, the TBM excavating such a section includes the extraction of the muck with the use of a solid matter pump. The pump works properly and with acceptable pressures only when high amounts of water are added to the muck. In order to avoid so high consumptions of water (that lead to several problems from economic and social points of view), a solution was found with the injection of a high-lubricating polymer, diluted in water at very low concentration before its use.