Tunnel Boring Machines, also known as TMBs, are the most versatile, adaptive and technologic methodology to perform tunnel excavations. In the last years, the demand for tunnels has progressively increased and these machines are being continuously improved to face greater challenges, to improve safety and to reduce environmental impacts. Through the main features of TBMs, there is surely the backfilling, that is an operation that is performed between the gap that is created during the excavation because of the bigger dimension of the cutterhead respect to the body of the machine, to minimize surface settlements. Two – component grout is, by far, the most used technology in modern backfilling practices, composed by two components: one cement – based (component A) and one accelerant (component B) that, mixed and injected at the tail of the machine, starts to gel in a few seconds.