Tunnelling Solutions

Backfilling Technology

Plant solutions for tunneling and underground structures.

The tunnel construction technique has been increasingly evolving over the years, with new methodologies, especially when it is necessary to operate in loose soils with or without groundwater.

The excavation methods performed with TBM (Tunnel Boring Machine) require a special attention to the completion of several operative phases and in particular it is very important to take care of the technique of filling of the annular space between the inner concrete lining and the natural soil.

This technique is defined “Backfilling” and for its application is usually required the preparation of a “Bi-component” MIXTURE.

A common “bi-component” MIXTURE is composed with:

A. Cement and bentonite storage of custom dimensions

B. High capacity mixing group with water and admixtures integrated dosing systems

C. Mixture agitated storage with transferring pumping group

Main parameters for plants design

Thanks to our wide experience in the concrete precast business, our solutions are developed with particular regard to innovation, in order to achieve the best quality through design and process optimizations.

The batching plant design is always customized upon the specific project requirements in terms of site layout, factory process flow and traffic management, other than climate and environment.

Mixtures design and physical features.

Geometric and topographical characteristics of the longitudinal profile of the tunnel.

Features of the pipes for the mixtures transfer.

Geometric features of the excavation and of the lining.

Advancement speed of the TBM and expected times for the various operations.

Logistic conditions outside the tunnels, for fixed installations.

Logistic conditions inside the TBM.

Monitoring systems for equipment and data transferring.

Duration of the works and evaluation of the spare parts warehouse and reserve equipment.

Operative main steps



High productivity automatic mixing set.



Big size agitators.



Transferring pump with high flow rates and working pressures.



Small and flexible grouting injectors.

Mixing unit

The first step, usually performed outside the tunnel, consists in the preparation of the fluid mixture with: water + bentonite + cement + retarder.

For its preparation, it is required to have:

Backfilling technology Mixing Unit containerized or on basic skid.



Big tank agitators

Once packaged, the primary mixture must be stored and accumulated inside large agitators which, through shafts with mixing blades and recirculation pumps, keep the mixture in motion, ready to be transferred to the TBM through the transfer pumps.

This operation is essential to avoid separation and bleeding in the mixes and also to always have an adequate volume of mix ready according to the needs of the TBM.


Transfering pumps

The transfer of the bicomponent mixtures from the storage buffers to the TBM takes place through pumps with suitable flow and pressure characteristics.

The injection rates are generally based on the geometry of the excavation and the lining segments, as well as of the advancement speed of the TBM.

The working pressures, to be evaluated according to the required flow rates, are generally sized in consideration of the type of pipe, the pipe diameter and the linear and altimetric development of the TBM excavation path.

According to the project features, a range of pumps is available, always considering the redundancy with one or more stand-by pumps to be used in the event of breakdowns,in order to avoid by any means slowdowns or interruptions of the TBM.

Clivio CLV12

Maximum working pressure: 230 bar

Maximum flow rate: 170 l/min


Grouting pumps

Once the TBM is reached, the Bi-component mixtures can be injected on the back of the concrete segments of the tunnel lining.

The filling of this annular void is carried out by means of small injectors, positioned inside the mechanized excavation equipment, in which the pressure and flow parameters can be managed very accurately through electro-controlled valves.

MCT Italy partners with Clivio Srl for the supply of the optimal type of grouting pumps, which most suitable for this application are the following: DP / OL4 and ID / OL2.

Clivio DP/OL4


Piston diametermm85
Piston strokemm120
Max strokes n.Strokes p.m.85
Pressure (LP) adjustablebar0 – 40
Delivery (LP) adjustablelitre p.m.0 – 30
Maximum pressure (HP)bar85
Delivery (HP)Litre p.m.9
Inlet Mouthgas1”1/2
Outlet Mouthgas¾”
Electric PowerkW3

Clivio ID/OL2


Piston diametermm85
Piston strokemm125
Max strokes n.Strokes p.m.75
Pressure (LP) adjustablebar0 – 55
Delivery (LP) adjustablelitre p.m.0 – 50
Maximum pressure (HP)bar90
Delivery (HP)Litre p.m.9
Inlet Mouthgas1”1/2
Outlet Mouthgas¾”
Electric PowerkW5,5

Data monitoring and transmission

In the technology for back-filling systems, data recording systems are no longer seen as simple “data-loggers” but as a more complex and interconnected electronic management system.

All the equipment, in particular the mixing and pumping units, are equipped with electronic systems, connected and accessible from a single, remote interface, with the possibility of viewing, in real time, the data and operating parameters.

The electronic control system provides for the remote transmission of data, wireless mode, thus making them accessible remotely from distant offices and different operating locations, such as the TBM operations center.

The monitoring of pumping units usually controls the following parameters:

The monitoring of mixing units usually controls the following parameters:

Any questions?

Contact our specialists today for any information and solutions concerning your concrete technology improvement.

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