The construction of the M4 was a complex engineering project, requiring state-of-the-art technologies and specific expertise. The tunnels were excavated with six TBMs (Tunnel Boring Machines) that dug at an average depth of 20m from road level, up to a maximum of 30m.

Soil consolidation was achieved even through the artificial soil freezing, a state-of-the-art technique used in the construction of the M4 tunnels, which prevents subsidence during excavation. This technique involves freezing groundwater through the use of liquid nitrogen  at -196° and makes the soil compact like a rock, facilitating excavation.

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