Hydraulic motors for the tunnel machine

Hydraulic motors for the tunnel machine
Marginal Column

How the tunnel extension works

The construction concept: In the existing tunnel (black) a provisional protection tunnel is created (blue) from concrete segments. The extension of the tunnel (red) can take place while traffic is moving.

While traffic flows through the temporary tunnel, a saw cuts the new arch of the tunnel in the mountain. The gap is filled with shotcrete, then excavators remove the rock.

A second machine then lines the new ceiling of the tunnel with prefabricated concrete segments.


November 2016


Machine builder Palmieri has developed a new type of machine for an unusual tunnel project in Italy. Bosch Rexroth designed and delivered the hydraulic system for it.

Slowly the saw descends, the chain begins to rotate around the guide bar and eats its way little by little through a meter-thick reinforced concrete block as though it were ordinary wood. This saw is by no means ordinary. It looks like a normal chainsaw with gigantic dimensions – eight meters long, with a chain that is half a meter long. It is standing in a production hall at the Italian Palmieri Group, a manufacturer of tunnel construction systems. Once the huge saw has gone through its trial by fire, it still needs to prove itself in the field. “The saw is part of a machine concept intended for a tunnel expansion project. In order to test it, Palmieri completely assembled the system to ensure nothing could go wrong on the construction site,” says Andrea Novello, Sales Engineer at Bosch Rexroth in Italy. He has been overseeing the project from the outset.

A tunnel in a tunnel

Just a few weeks after the test run in the production hall, you can view the task for which the Palmieri machine is intended. On the Autostrada Adriatica or the A14 highway, which connects the north of Italy to the heel of the boot, the two tunnels of the Montedomini Tunnel, which are around 280 meters long will be widened from two to three lanes near the port city of Ancona. “While the expansion in itself is nothing special, the construction work here is to be carried out while traffic is still flowing,” says Novello. Normally you need to close the tunnel for such work and divert the traffic. However, the A14 is a busy road and closing the tunnel would result in traffic chaos. The responsible municipality did not authorize the building of a another tunnel. Autostrade per l’Italia S.p.A, which is the operator of the Italian highway network, commissioned the road construction company Ghella S.p.A. to widen the tunnel without having to close the road. So far, there has only been one comparable project in Italy and that was the Nazzano Tunnel project near Rome at the beginning of the millennium. The technique used there served as the model for the Montedomini project. In the existing tunnel a further tunnel is built through which the traffic can keep flowing while people and machines work in the cavity between the two tunnel ceilings.

Extreme conditions

Ghella wanted to further optimize this technique for the Montedomini Tunnel and commissioned the Palmieri Group to design a new machine for the expansion work. “While the Nazzano project only had one machine carrying out all of the work, Palmieri used two that are able to work separately,” explains Novello. Both look like two curved portals, whose dimensions more or less correspond to the desired tunnel diameter. They drive into the tunnel on rails, while below the cars rush by beneath a protective concrete shield. The first portal carries the gigantic saw, which saws a semi-circular, half-meter-wide cleft in the rock above the old tunnel ceiling. The resulting gap is then filled with shotcrete. Conventional excavators then remove the material from under the new semicircle. The next machine can now move forward where it lines the new tunnel ceiling with prefabricated concrete segments. Once this task has been completed, the saw continues with its work. “The two machines enable us to reduce standstill periods due to the fact that one can be serviced while the other one resumes its work,” explains Novello. The technology is faced with extreme conditions: the machines need to endure a lot of dust, heat and moisture.

The two machines enter the Montedomini tunnel.

The two machines enter the Montedomini tunnel.

The Hägglunds hydraulic motor from Rexroth has a torque of 80,000 Nm at 50 rpm.

The Hägglunds hydraulic motor from Rexroth has a torque of 80,000 Nm at 50 rpm.


Robust hydraulics

Palmieri required components for the two machines that also worked reliably under extreme conditions. The drive for the chainsaw in particular needed to be extremely resilient. “Palmieri originally considered using an electro-mechanical solution, but that would not have worked in this harsh environment,” explains Novello. The tunnel machine builder therefore settled for one by Hägglunds. Hydraulic motors from Rexroth with a displacement of 20,100 cubic centimeters and a torque of 80,000 Newton meters at 50 revolutions per minute. In addition to this, Palmieri also needed a hydraulic system to drive the motor. It was at this point that the cooperation with Bosch Rexroth began. For Novello, this job was a premiere in two respects: “Although Palmieri had already previously obtained Rexroth components from our dealers, they had never worked directly together with us. Also new was the fact that we had never before had anything to do with a hydraulic system of these dimensions”. Bosch Rexroth worked in close cooperation with Palmieri to develop and design a closed hydraulic system, through which the fluid was pumped using two axial piston variable pumps. “The hydraulic system was required to hold out for 3,000 hours. I am convinced that it is also capable of more,” says Novello with certainty.

One meter per day

The hydraulic system successfully survived the work on the Montedomini Tunnel and the machines from Palmieri advanced by one meter a day. The expansion work to widen each tunnel to three lanes took only six months. The saw was in use for approximately 1,000 hours. “In principle, the machine can also be used again for other similar tunnel projects. In Italy, there are still many sections with only two lanes,” says Novello.