Mixed Ground TBM Tunneling in Mexico City
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The Mexico City Metropolitan area with its 21 million people is one of the most populated places on earth. The population growth together with the sinking of some parts of the city are now challenging the capacity of the infrastructure connected to wastewater, urban runoff and flood control in downtown Mexico City. As a measure to solve this problem a gigantic tunnel for wastewater is under construction. The Tunel Emisor Oriente (TEO) would be 63-km long tunnel with a 7.0-meter inner-diameter bringing wastewater from Mexico City to a wastewater treatment facility in Atotonilco. The great length of the tunnel together with strict requirements to the tunnel alignment has led to the tunnel must cross some areas with very challenging ground conditions. This thesis is investigating the machine performance and cutter life in the mixed ground encountered in the TEO project. The challenges connected to mixed face TBM boring have been investigated thoroughly to look for a correlation between machine operating parameters and the corresponding cutter life. In a 2.2 km long tunnel stretch, the geological conditions are extremely complex, changing between basalt (UCS up to 95 MPa), soft ground (silt and clay) and mixed face. The length of the zones are varying from only a hundred meters to about 900 meters making the boring process very challenging. The cutter change reports have been used to back-calculate the instantaneous cutter life in the different geological zones, making this the basis for the machine parameter study. The main machine operating parameters focused on in this study are the thrust, torque, RPM and penetration rate. Together with the geological pre-investigation and lab-tests, a wide range of aspects connected to the boring process and ground conditions have been included. The analysis indicates that correlations can be found between the geological conditions and the cutter life. However, the analysis shows few correlations between the TBM operating parameters and cutter life. Only the torque gives results which indicates a relation between the applied torque and the overall condition of the cutter tools.