Moles

Moles are tunnel boring machines designed to excavate hard or medium rocks, without much need for support. Their fundamental difference with the shields is that they are not equipped with a steel cylinder behind the cutting wheel that performs the temporary shoring function.

The thrust force is transmitted to the cutting head by cylinders (thrust cylinders). The reaction produced is transmitted to the gable end of the tunnel through the grippers (anchor force). The grippers also compensate for the torque produced by the cutting head, which is transmitted to them through the main beam.

When a forward cycle has been completed, it is necessary to reposition the grippers, for which the main beam rests on the rear support. Once the grippers are anchored in their new location, the rear support is released and a new forward cycle begins.

Shields

Shields are tunnel boring machines designed to excavate soft rocks or soils, terrain that systematically requires the placement of support. Unlike the topos, the shields have an external metal casing (which gives the name to this type of machine) that provisionally supports the ground from the front of advance to something beyond where the definitive support is placed, normally consisting of rings formed by about 7 voussoirs. In this way, the stability of the tunnel is guaranteed at all times. They are often prepared to advance below the water table.

If it is a rotating head tunnel boring machine, it is usually equipped with picks, battens or "rippers" (elements that tear out the soil) and cutters (elements that break the rock by indentation). It also has a series of openings, often adjustable, through which the torn material passes into a chamber located behind the cutting wheel and from where it is subsequently transported to the outside of the machine.

Behind this chamber are housed the motors and the machine's command post, spaces completely protected by the metal casing.

Next is the entire drilling system: first the perimeter cylinders (with a distance between 1.20 and 1.50 m). These perimeter jacks rest against the last placed ring of voussoirs of the final lining of the tunnel. When the travel of the advance cylinders ends, a new ring of segments is placed (inside the casing, which extends somewhat further, so that the tunnel is always supported) and a new excavation cycle begins. An injection of mortar "Mortar (construction)") or grease is necessary to fill the 7 to 9 cm thick void between the segments and the excavated ground.

Two large groups of shields are distinguished, among which the typologies explained below are distinguished:

Double Shield

Another type of tunnel boring machine is the so-called Double Shield, capable of working as a mole or as a shield, depending on the quality of the rock mass, being the best solution for masses with sections of variable soil-rock typology. In this type of tunnel boring machines, the shield is divided into two parts, the front one where the cutting head is located, and the rear area where the ring of segments is assembled.

The movement of these two parts of the shield is independent, with the "grippers" being placed in an open space between them, so the head can dig while the rings of voussoirs are mounted on the tail of the shield. In this way the performance achieved with this system is much higher than with a simple shield. This system is applied in those terrains capable of resisting the pressure transmitted by the grippers. At the same time that the main thrust cylinders drive the head shield forward and the cutting wheel carries out the excavation, a new ring of support voussoirs sheltered from it is mounted on the rear shield.

When the ground is weaker and is not capable of resisting the pressure of the grippers, the tunnel boring machine works as a simple shield, closing the gap of the grippers, and the tunnel boring machine resting, by means of auxiliary cylinders, on the last ring placed, in order to obtain the necessary reaction for the thrust of the cutting head (that is, as a normal shield works). Therefore, working in shield mode, it is not possible to simultaneously excavate with the assembly of the ring of voussoirs.

Contenido

Se distinguen dos grandes grupos: los topos y los escudos, aun cuando también existen tuneladoras mixtas como las que excavan actualmente la línea 9 "Línea 9 (Metro de Barcelona)") del Metro de Barcelona.

Moles

Moles are tunnel boring machines designed to excavate hard or medium rocks, without much need for support. Their fundamental difference with the shields is that they are not equipped with a steel cylinder behind the cutting wheel that performs the temporary shoring function.

The thrust force is transmitted to the cutting head by cylinders (thrust cylinders). The reaction produced is transmitted to the gable end of the tunnel through the grippers (anchor force). The grippers also compensate for the torque produced by the cutting head, which is transmitted to them through the main beam.

When a forward cycle has been completed, it is necessary to reposition the grippers, for which the main beam rests on the rear support. Once the grippers are anchored in their new location, the rear support is released and a new forward cycle begins.

Shields

Shields are tunnel boring machines designed to excavate soft rocks or soils, terrain that systematically requires the placement of support. Unlike the topos, the shields have an external metal casing (which gives the name to this type of machine) that provisionally supports the ground from the front of advance to something beyond where the definitive support is placed, normally consisting of rings formed by about 7 voussoirs. In this way, the stability of the tunnel is guaranteed at all times. They are often prepared to advance below the water table.

If it is a rotating head tunnel boring machine, it is usually equipped with picks, battens or "rippers" (elements that tear out the soil) and cutters (elements that break the rock by indentation). It also has a series of openings, often adjustable, through which the torn material passes into a chamber located behind the cutting wheel and from where it is subsequently transported to the outside of the machine.

Behind this chamber are housed the motors and the machine's command post, spaces completely protected by the metal casing.

Next is the entire drilling system: first the perimeter cylinders (with a distance between 1.20 and 1.50 m). These perimeter jacks rest against the last placed ring of voussoirs of the final lining of the tunnel. When the travel of the advance cylinders ends, a new ring of segments is placed (inside the casing, which extends somewhat further, so that the tunnel is always supported) and a new excavation cycle begins. An injection of mortar "Mortar (construction)") or grease is necessary to fill the 7 to 9 cm thick void between the segments and the excavated ground.

Two large groups of shields are distinguished, among which the typologies explained below are distinguished:

Double Shield

Another type of tunnel boring machine is the so-called Double Shield, capable of working as a mole or as a shield, depending on the quality of the rock mass, being the best solution for masses with sections of variable soil-rock typology. In this type of tunnel boring machines, the shield is divided into two parts, the front one where the cutting head is located, and the rear area where the ring of segments is assembled.

The movement of these two parts of the shield is independent, with the "grippers" being placed in an open space between them, so the head can dig while the rings of voussoirs are mounted on the tail of the shield. In this way the performance achieved with this system is much higher than with a simple shield. This system is applied in those terrains capable of resisting the pressure transmitted by the grippers. At the same time that the main thrust cylinders drive the head shield forward and the cutting wheel carries out the excavation, a new ring of support voussoirs sheltered from it is mounted on the rear shield.

When the ground is weaker and is not capable of resisting the pressure of the grippers, the tunnel boring machine works as a simple shield, closing the gap of the grippers, and the tunnel boring machine resting, by means of auxiliary cylinders, on the last ring placed, in order to obtain the necessary reaction for the thrust of the cutting head (that is, as a normal shield works). Therefore, working in shield mode, it is not possible to simultaneously excavate with the assembly of the ring of voussoirs.