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.