Inside the Fortezza TBM Order: Hard-Rock Design Choices Behind CRCHI's Italian Export

Introduction

When two 9.68-metre-diameter single-shield tunnel boring machines (TBMs) were completed in Changsha in March, the headline figure was the export milestone: machines number 11 and 12 supplied to the Italian market. For the engineers and project planners who will actually run such equipment, however, the more instructive story lies beneath the headline. The Fortezza railway tunnel in northern Italy combines hard rock, long single-drive distances and multiple fault zones — a combination that stresses cutter life, main bearing duty and machine availability far more than headline diameter suggests. This article examines the engineering logic behind the machine specification and what the design choices imply for TBM selection and operation in comparable hard-rock projects.

Project Context: Why Fortezza Is a Demanding Duty

The two machines are destined for the Fortezza railway tunnel, a twin-tube, double-track railway tunnel. According to the project information released at the machine rollout, each TBM will bore approximately 12.75 km, with the two machines driving the parallel tubes. That single-drive length is significant. In hard rock, a long continuous bore without intermediate access points concentrates wear on the cutterhead, the cutter bearings and the main drive, and it limits opportunities for intervention. Every hour of unplanned downtime becomes more expensive when there is no alternative access to the working face.

The published project description also notes hard ground conditions and several fault zones along the alignment. This is a familiar but difficult combination: abrasive, high-strength rock rewards high thrust and robust cutter design, while fault zones demand the ability to control instability at the face and to pass through fractured ground without overloading the machine. A single-shield TBM, which relies on the shield to support the ground immediately behind the cutterhead and on segmental lining erected within the shield tail, must be specified to handle both extremes.

Reading the Specification: What the Key Figures Tell Engineers

The disclosed parameters are concise but informative. Each machine has an excavation diameter of 9.68 m, an overall length of about 175 m and a total weight of about 2,600 t. In practical terms, the diameter places these machines in the medium-to-large range for railway tunnels, where the finished internal profile must accommodate double-track operation plus services and lining thickness. The length reflects the full back-up system — segment handling, ventilation, power supply, grouting and conveyor or muck transport — rather than the shield alone.

For selection engineers, the more meaningful indicators are those tied to the ground. CRCHI states that the cutterhead structure, rock-breaking efficiency and wear resistance were specifically designed for the project's hard-rock conditions. That is a design statement rather than a performance guarantee, and it should be read as such: it indicates that cutter spacing, cutter type, face opening geometry and wear protection were adapted to the expected geology, but it does not by itself confirm achieved penetration rates or cutter consumption.

Technology Choices and Their Operational Meaning

The announcement lists several systems fitted to the two machines: permanent magnet synchronous motors, simultaneous thrusting and segment erection, automatic segment lifting and transport, and adaptive power management. Each has a practical implication for a long hard-rock drive.

Permanent Magnet Motors and Energy Efficiency

Permanent magnet synchronous motors are increasingly used in TBM main drives because they can offer high torque density and efficient operation across a range of speeds. For a project of this length, drive efficiency affects not only energy cost but also heat generation in the tunnel and the sizing of ventilation and cooling systems. The choice is consistent with the stated aim of meeting EU environmental and safety requirements, although the announcement does not provide motor ratings or measured efficiency figures.

Simultaneous Thrusting and Segment Erection

In conventional single-shield operation, boring stops while a ring of segments is erected. Simultaneous thrust and erection systems allow part of the thrust to be maintained while segments are installed, reducing the time lost per ring. Over a 12.75 km drive, the cumulative effect on schedule can be substantial. The trade-off is greater mechanical and control complexity, and the method must be matched to the ground's ability to stand while the shield is only partially advanced.

Automation of Segment Handling

Automatic segment lifting and transport reduces manual handling in the shield tail, where space is tight and the risk of injury during ring building is real. Combined with improved access walkways and ergonomic controls mentioned in the announcement, these features target both safety and consistent cycle times. They do not remove the need for experienced ring-building crews; they change the nature of the work.

Hard-Rock TBM Selection: Lessons for Comparable Projects

For engineers specifying machines for similar alpine or hard-rock railway tunnels, several general principles emerge from this project profile. These are established industry considerations rather than claims about this specific machine's measured performance.

• Match cutterhead design to the abrasivity and strength of the rock. Cutter spacing, disc diameter and wear protection should be set from geological and petrographic data, not from diameter alone.
• Plan for fault zones explicitly. Probe drilling, forepoling capability, face support options and the ability to control thrust and torque rapidly are more important than nominal thrust figures.
• Treat long single drives as a reliability problem. Main bearing life, backup system redundancy, ventilation and muck removal capacity all become schedule-critical when there is no intermediate access.
• Evaluate energy and ventilation together. Efficient drive systems reduce heat load, which can lower ventilation demand in long tunnels.
• Confirm performance claims against project-specific data. Manufacturer design statements should be verified through reference projects in comparable geology and through contractual performance mechanisms.

What the Export Context Does and Does Not Show

CRCHI states that its products have now been exported to more than 50 countries and regions, and that these two machines are the 11th and 12th TBMs supplied to Italy. That is a meaningful indicator of repeated market presence rather than a first entry, and repeated supply into a demanding European market implies familiarity with EU safety, environmental and documentation requirements. It does not, on its own, demonstrate technical superiority over established European suppliers, and buyers should continue to evaluate machines on project-specific evidence.

The Fortezza project will ultimately be judged on boring progress, cutter consumption, availability and settlement control. Those results will only become visible as the drive advances, and they will be the most reliable guide for future selection decisions in comparable ground.

Sources and References

• The Paper — report on CRCHI TBM rollout for the Fortezza railway tunnel project

Frequently Asked Questions

What is a single-shield TBM and where is it used?

A single-shield TBM is a hard-rock machine that excavates the tunnel and erects a segmental lining within the protection of a shield. It is typically used in rock that can stand temporarily but requires immediate support, and it is well suited to long railway and transport tunnels in competent to fractured hard rock.

Why does a 12.75 km single drive matter for machine design?

Long drives without intermediate access concentrate wear on cutters and the main bearing and limit opportunities for maintenance. Designers therefore place greater emphasis on reliability, wear protection, backup system redundancy and efficient logistics for muck removal and segment supply.

Does the use of permanent magnet motors guarantee lower energy consumption?

Permanent magnet synchronous motors can offer high efficiency and torque density, but actual energy consumption depends on the load profile, ground conditions and overall system design. Efficiency should be assessed from measured data for the specific machine and project, not from the motor type alone.

How should buyers verify TBM performance claims?

Buyers should request reference projects in comparable geology, review documented boring records where available, and structure contracts with performance mechanisms tied to availability and advance rates. Design statements alone are not a substitute for project-specific evidence.