Adaptation of the TBM-Shield EPB for Tunnels with High Overburden and High Water Pressure for the Metro Los Teques Line 2
For the excavation of Lot 3 of the Metro Los Teques Line 2 in Venezuela, a great chal-lenge must be overcome due to a change of the alignment with respect to the original design. The new ground conditions are not appropriate for the typical application of EPB shields, which is the methodology used so far in the previous lots. The 3 km Lot 3 is excavated in areas with high overburden, high water pressures up to 4.7 bar acting on the tunnel lining, and highly fractured rock partly weathered and partly with high strengths. This paper aims to analyze the studies and the important TBM-shield technology adaptations to these extreme conditions, focusing on operation modes, confinement pressure control, requirements for grouting and soil conditioning, cutter wear, lowering of the ground water level, and the upgrade of the TBM for a nominal EPB pressure of 5 bar and water drainage systems, besides the verification of the tunnel lining design. KEYWORDS: Metro Los Teques, TBM-shield, High water pressures.