The application of tunneling, in a general, and of backfilling in particular, are used in the construction of tunnels (hydraulic, railway, road and other)

When we talk about tunneling, we refer to the different construction techniques used for the construction of tunnels that can be excavated "traditionally", for example with the "drill and blast" and "cut and cover" techniques and according to the "mechanized excavation" through the use of TBM (Tunnel Boring Machine).

METAX equipment are mainly used both for the consolidation of the soil crossed by the tunnels, and for the annular gap filling (backfilling) behind the tunnel lining segments.


Depending on the degree of water presence, the aforementioned techniques will be adopted, with important variations on the composition of the injection admixtures.

The main objective of the consolidation techniques described above is to modify the physical and mechanical conditions of natural soils, in order to allow them to be excavated safely and economically.

1. Sub-horizontal jet-grouting and / or sub-vertical jet-grouting

  • Execution of a hole, through the use of a specific drilling / injection string, which will be performed by mean of:
    • Common drilling rigs also used in the construction of jetting columns in the open field
    • Drilling rigs specifically designed and built to perform jetting columns in underground and open fields
    • "Single-mast" or "double / triple mast" drilling rigs designed and specifically built for the execution of major underground works
  • Injection from the bottom, at high pressure, according to the common jet-grouting technique through the use of triplex pumps and adequate mixing plants for the preparation of consolidating admixtures.

2.Sub-horizontal and / or sub-vertical Injectoins

  • Execution of an hole through the use of drilling machines according to the above described types;
  • Insertion inside the hole of a " TAM pipe”;
  • Execution of a first phase of "plastic" injection to make the "TAM pipe" integral with the surrounding ground;
  • Execution of one or more injection phases through the valves present along the "TAM pipe" (generally no. 02 or no. 03 valves per linear meter). (All injections will be performed through the use of injection "packers" and systems for preparing and pumping the consolidating admixtures)

In tunneling, when we talk about "mechanized excavation" carried out through the use of TBM (Tunnel Boring Machine), it is necessary to open a specific chapter relating to the backfilling application.

Backfilling technique, for tunnel construction, is closely linked to "mechanized excavation".

For "mechanized excavation”, and therefore for backfilling, special machines (TBMs) are used that are capable of:

  • excavate the circular section of the tunnel
  • to lay, almost simultaneously with the excavation, the internal lining of the tunnels itself.

Once the tunnel lining has been laid, it is necessary to fill in the annular space that remains “free/empty” between the excavation profile in the ground and the external surface of the reinforced concrete lining.

The filling of the “free” annular volume, eliminates the possible settling of the ground surrounding the excavation which could induce differential subsidence of both the tunnel and any existing superficial structures. It also significantly increases the degree of waterproofing of the tunnel itself.

In general, two-component mixtures are produced and injected on the back of the lining segments:

Component A

A": admixture of water, bentonite and cement, improved with retarding additives, to ensure long "workability" times of up to about 72 hours and therefore allow it to be pumped for a long time and long distances.

Component B

accelerating additive, which is transferred to the TBM as the Component "A" and then injected, together with it, on the back of the segments, in order to obtain a rapid hardening and setting action of the injected "bi- component ” final admixture.

Would you like more information on tunnelling
and backfilling technology or machines?


METAX | Geotechnical, Drilling and Oilfield Division of Cima SpA, since 1987 is specialized in the construction and design of high-pressure triplex motor pumps, mud pumps, mixing and injection plants, mixing plants and storage equipment for cement-based admixtures for the following applications: soil consolidation by means of jet grouting, tunneling & backfilling, drilling and guided drilling.

*I authorise the processing of my personal data to respond to my requests as indicated in the Privacy policy

Success! Your message has been sent correctly.
Errore! Error! Unable to send message, contact site owner.