Innovative hybrid EPB tunnelling in Rio de Janeiro

The Line 4 South being constructed in Rio de Janeiro crosses complex geology that includes a long stretch of sand bounded by two stretches of hard, highly abrasive rock. These geological conditions, combined with the fact that the project is located in a distinct urban area, creates a demanding project scenario where special care needs to be taken. After carrying out an evaluation to determine whether to use earth pressure balance or slurry technology, the design of a convertible EPB boring machine that can excavate both rock and soils was developed. This paper outlines the technical difficulties of the project and describes the decision-making process and the solutions adopted. A technical description of the different operation modes of this hybrid TBM and the conditioning process related to each of them is provided.