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Excavation systems

The microtunnels, can be performed by different technologies, all of them included within the so-called Trenchless technologies or No-Dig.
These technologies, according to the ISTT, are the following:

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Cara de roca

This technologies  have very different application ranges and they can be distinguish by the usual work diameters as shown in the following table (from Trenchless technology: Planning, Equipment and Methods - Mohamed Najafi, completed by own elaboration):

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Besides the description within the previous table, the available ranges for each technology may vary depending on the region or specific needs of a project.

TBM Microtunneling

A Tunnel Boring Machine TBM is a machine which is able to perform a full-face excavation of a tunnel and, simultaneously, it contributes to the ground support of the excavation either  temporarily or definitively.

The TBM’s may be classified as shown in the following figure:

  • Moles :

A mole is a type of hard rock tunnel boring machine that has a cutter head capable of excavating the entire face in a single pass. The cutter head is driven by struts that push in a radial direction against the rock of the tunnel gables, advancing sequentially in two phases (ITA).

- Excavation (the struts remain fixed).

- Advance (the struts retract and the assembly advances the excavated distance).

Topo-type tunnel boring machines are used exclusively in specific geological conditions, always in competent hard rock terrain. Gripper TBM video

  • Shields :

The general principle on which a shield is based is that it is a cylindrical piece of steel that is pushed along the axis of the tunnel while the ground is being excavated. The steel piece supports the excavation opening until the lining is installed.

The shields can be differentiated according to the type of excavation element, support and extraction of the material extracted from the face or according to the type of lining of the excavation:

- Open Shield: Natural hold and dry extraction

- Hydroshield

- Earth Pressure Balancing Shield


  • Double Shields :

The microtunnelling process by means of a TBM, regarless its type, will always start from a launching shaft and will pierced the ground to get an exit shaft or final position where the TBM will be recovered by lifting it by means of cranes from this location.

The most usual auxiliary rigs pairing the TBMs during the excavation are:

  • Control and guidance systems

  • Spoils handling and treatment equipment

  • Thrust or jacking systems

  • Equipment for perforation, lubrication and lining inyection and preparation

  • Power supply equipment

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Open shield

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Double shield


Horizontal directed drilling

Auger Boring

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Close shield

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Excavation ancillary equipment

Direct Pipe

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Impact moling

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Hinca neumática

Excavation methods

From among all the Trenchless technologies included in the ISTT, only the New Instalation technologies are relevant to us because none of the substitution or rehabilitation technologies can be considered as microtunnelling proceses as the are performed within previously existent excavations

Métodos de excavación
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