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  EPB Shield Tunnelling Through a Volcanic Chain In Mexico

  The contribution gives insight to the challenges and respective engineering measures in the MexicoToluca Interurban Train tunnel project. Each of the twin tunnels has a length of 4.7 km and is excavated with two EBP shield machines of 8.57 m diameter. The tunnel overburden varies from 1 diameter up to 130 meters and hydrostatic pressures up to approximately 6.0 bar are expected. The geology of the region is composed of rock of andesitic spills, interspersed with brecciated horizons that are, in turn, interspersed with tuffs and lytic tuffs of variable thickness. The tunnel face is highly heterogeneous and varies both along the alignment and within the tunnel horizon. It is composed of volcanic rock, fractured rock, presence of blocks, open discontinuities and geological faults, rock with different degrees of weathering, breccia, and tuffs. The biggest challenge of the project is the heterogeneity of the tunnel face. It is partly unpredictable and impedes TBM operation. The characteristics of this type of tunnel face and its unpredictability lead to a high risk of tool wear, excessive consumption of tools and long durations of interventions. In addition, if tool wear is not properly controlled, both cutter head and screw conveyor can be easily damaged. The key to success of the project is the permanent adjustment of the operation mode and the main excavation parameters of the TBM by real-time analysis. This allows to minimize the reaction time, to optimize and control the excavation parameters, and to improve the control of water inflows as well as the TBM steering. EPB Shield, Heterogeneous Ground, Volcanic Rock, Mixed Face, High Groundwater Pressures. The Mexico Toluca Interurban Railway Project is located at approximately 3000 m above sea level, has an extension of 57.7 km and 6 stations. It will connect the metropolitan zone of the Valley of Toluca with the west zone of Mexico City. This modern and fast means of transportation will promote the use of non-motorized transportation and sustainable mobility providing a mass public transport to serve 230 thousand of passengers per day.

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