Tunnel boring machine

A tunnel boring machine – often also referred to as a shield machine, TBM shield or hard-rock machine – is the central piece of equipment for mechanized tunnel construction. It enables underground tunnel excavation for infrastructure projects such as traffic tunnels, utility adits or relief sewers. Parallel to the mechanized advance, tasks for selective removal, re-profiling and lining regularly arise. In the environment of Darda GmbH, hydraulic wedge splitter and concrete pulverizer in particular come into play for controlled, low vibration levels and precise work in entry and access shafts, emergency bays, connection structures or for the deconstruction of auxiliary structures. The approach supports emission control underground and allows dimensionally accurate work where settlement-sensitive surroundings require reliable containment of impacts.

Definition: What is meant by a tunnel boring machine?

A tunnel boring machine is a large-scale advance system that mechanically excavates the ground at the tunnel face, conveys the excavated material, and – depending on the method – installs the lining directly behind. Core components are the cutterhead (for rock with disc cutters, for loose ground with ripping and scraping tools), the shield for ground support, conveying systems (screw conveyor, conveyor belt), drive and control systems, plus the backup with supply, logistics and lining equipment. In shield tunnelling, precast concrete segments are frequently assembled into a segment ring. Complementary work in the tunnel and shaft areas requires handheld or carrier-mounted cutting and splitting tools, for example for adjustments, openings or the deconstruction of temporary components. Terminology varies: TBM commonly denotes the entire system, while the term shield highlights ground support and lining within the excavation unit.

Design and mode of operation of a tunnel boring machine

The heart of the system is the cutterhead, which attacks the tunnel face. In hard rock, disc cutters act with high point loads; in loose ground, ripping tools engage and support is provided via earth pressure or slurry pressure (EPB, mixshield, slurry). Behind the cutterhead is the shield, which supports the surrounding ground and takes up the reaction forces for thrust. A screw conveyor or belt transports the material to the backup, where it is hauled away via conveyor belt, skips or muck cars. At the same time, the internal lining is installed with segment rings: segments are positioned, bolted and sealed while the shield advances hydraulically. Essential is the coordination between advance, support pressure, haulage logistics and lining to avoid settlements, blockages or overbreak. In the vicinity of shafts, cross-passages, equipment niches or obstacles, additional selective removal methods are required – here, hydraulic wedge splitter or concrete pulverizer are often used to work to the contour and with low vibration levels.

Modern systems integrate sensor-based monitoring of pressures, torques, volumes and alignment to keep the face stable and the ring build watertight. This process control, together with clean spoil management and careful handling of gaskets, reduces rework and safeguards advance rates.

Machine types and limits of application

Different machine types are used depending on geology. Hard-rock machines (gripper or double-shield machines) operate dry and use disc cutters; earth-pressure balance and mixshields stabilize the tunnel face with soil pressure; slurry shields rely on support fluids and separation plants. The choice depends on grain-size distribution, strength, groundwater conditions and the required lining technology. Limits arise with strongly alternating strata, large boulder content or foreign objects. In such situations, controlled, small-scale interventions are necessary. A concrete pulverizer enables precise removal on concrete elements in entry and access shafts, while a hydraulic wedge splitter introduces targeted tensile cracks in rock or concrete to separate components by splitting – with low vibration levels and good dimensional accuracy.

• Hard rock: High-strength formations favor gripper or double-shield TBMs with disc cutters and robust mucking logistics.
• Mixed and soft ground: EPB and mixshield concepts maintain face stability via pressure balance and conditioning measures.
• Challenging interfaces: Boulders, obstructions and variable groundwater require contingency tools and clear intervention procedures.

Geotechnics, support and lining

The interaction of ground, support pressure and lining determines advance safety. In loose ground, the tunnel face is stabilized by earth pressure or slurry; in rock, the shield skin, jacks and temporary linings provide support. Lining is often carried out with segment rings made of reinforced concrete. Typical follow-up work includes creating openings, removing protrusions or re-profiling transitions. For such work, a concrete pulverizer is suitable for gentle adjustments to concrete components, and a hydraulic wedge splitter is suitable where rock is encountered, e.g., at portal areas or cross-passage connections. Sealing systems at segment joints and around penetrations require careful handling to maintain watertightness; clean edge geometry minimizes repair grouting and reduces lifecycle risks.

Construction sequence: entry shaft, advance, access shaft

Entry shaft

In the entry shaft, the machine, backup and logistics are assembled. Openings, foundations, anchor points and temporary installations are created. When adapting shaft geometries or removing concrete upstands, a concrete pulverizer is helpful for selective removal. In rocky subsoil, a hydraulic wedge splitter can prepare the profile without affecting surrounding structures through vibrations. Early interface checks for transport paths, ventilation and power routing streamline the launch and reduce idle time.

Advance phase

During the advance, obstructions (e.g., boulders, embedded objects) are to be expected. Small-area interventions at the tunnel face or in the area of the conveying line require equipment that is compact, precise and safe. Low vibration levels splitting technology reduces risk to adjacent components and lowers the load on personnel and equipment. Clear exclusion zones, reliable signalling and defined permit steps enable rapid, controlled interventions with minimal production impact.

Access shaft

At breakthrough or during retrieval of the shield, confined space and high safety requirements are typical. The deconstruction of temporary concrete and steel structures is efficient with a coordinated combination of a concrete pulverizer, steel shear or Multi Cutters. For thick steel plates or tanks in auxiliary-plant areas, suitable tank cutters are an option; power is supplied by hydraulic power pack. Attention to sequence, lifting points and fire protection is crucial for a safe and timely demobilization.

Interfaces to handheld and carrier-mounted tools in tunnel construction

Even with fully mechanized advance, work steps remain that are not covered by the tunnel boring machine. These include:

• Creating openings in segments (e.g., for cable duct routes, cross-passages)
• Follow-up works on inverts and upstands
• Deconstruction of temporary formwork, ribs and beams
• Exposing utilities or anchor points
• Rescue and special interventions in case of incidents
• Chamfering, edge finishing and re-profiling at segment joints for sealing integrity

For these activities, a concrete pulverizer and a hydraulic wedge splitter are central options. They are complemented by steel shears, combination shears, Multi Cutters and tank cutters that sever steel and composite components. Compact hydraulic power packs ensure the energy supply in confined environments and facilitate logistics in the tunnel. Short hose runs and protected routing reduce pressure losses and improve ergonomics.

Hydraulic wedge splitter in mechanized tunnel construction

Splitting technology uses hydraulically generated tensile and compressive stresses to open rock or concrete along defined lines. In tunnel construction, this method is appropriate when:

• Vibrations and secondary damage must be avoided (near existing structures, in sensitive facilities)
• Contour accuracy is required (re-profiling, fit-up)
• Confined spaces restrict the use of large demolition works equipment

Typical applications include removing rock noses in niches, opening concrete webs in shafts and exposing connection cross-sections. Due to the small-scale working method, control over crack path and fragment size remains high. Proper drilling-pattern planning is important to steer the splitting effect precisely. Managed staging of drilling, wedge insertion and load cycles improves reproducibility and minimizes clean-up.

Concrete pulverizer for selective removal and lining work

A concrete pulverizer enables separating and crushing interventions on reinforced concrete with well-controllable force transmission. In the TBM environment, it is suitable for:

1. Adjustments to segment openings (e.g., cable penetrations, ventilation cross-sections)
2. Deconstruction of temporary concrete components in the entry/access shaft
3. Relief cut on inverts and upstands prior to lifting
4. Gentle breakout of small elements near sensitive installations

With reinforced concrete, combining with a steel shear can be useful to cut reinforcement selectively. This reduces rework, minimizes sparks and facilitates material separation for disposal. Choice of jaw profile and attention to bite sequence further protect gaskets and embedded parts.

Further tools and power units in the TBM environment

Hydraulic power pack

Hydraulic power packs supply mobile tools with energy. Criteria include flow rate, pressure, operational safety, exhaust and noise emissions, as well as transportability on narrow site routes. Remote controls and quick-coupling manifolds increase flexibility in tight headings.

Combination shears, steel shears, Multi Cutters

These tools cover the cutting of structural steel, plate, mesh and composite elements. They are used, among other things, for the deconstruction of temporary support structures, opening enclosures or sizing down bulky items. Proper matching of jaw geometry and material thickness enhances cutting performance and reduces tool wear.

Tank cutters

When dismantling vessels, shafts or large-diameter pipelines, tank cutters are an option. Protective measures against sparks and fire loads must be observed; the specific application requires safe work planning. Shielding, fire watches and media isolation are to be coordinated with ventilation and evacuation concepts.

Occupational safety, organization and ergonomics

Work in tunnels places special demands on safety, escape and rescue concepts, lighting, ventilation and communication routes. For handheld removal work, the following applies:

• Safe standing areas and stable positioning of power units
• Hazard analysis including vibrations, noise, dust, media leakage
• Coordination with the advance sequence (exclusion zones, permits, signals)
• Personal protective equipment and dust extraction and/or water spray system for dust control
• Silica-compliant dust management, lighting levels appropriate to task and minimized manual handling distances

Legal requirements may vary by project. The information provided here is general and non-binding; the applicable regulations, standards and official requirements are decisive.

Quality assurance and segment finishing

The dimensional accuracy of segment rings, gasket joints and anchor points is crucial for watertightness and durability. Follow-up work should be as minimal as possible. A concrete pulverizer allows controlled breakout of small areas; a hydraulic wedge splitter helps release protrusions smoothly and without transferring vibrations. Documentation of interventions and surface quality supports acceptance and future operation. Survey control, photographic evidence and punch-list tracking provide traceability across shifts.

Environmental aspects: vibrations, noise, dust and water

Reducing emissions is key. Splitting technology generates low vibration levels and is therefore advantageous in densely built environments. When processing reinforced concrete, hydraulic shears reduce noise and dust compared to percussive methods. Water and slurry management must be planned so that conveying and separation systems are not impaired. Recycling of spoil and proper disposal routes for reinforcement and concrete fractions support sustainability targets in mechanized tunnelling.

Special operations and contingency management

When foreign objects are in the cutterhead chamber, screw conveyors are jammed or geometries deviate from plan, fast, safe solutions are required. Handheld tools with hydraulic power pack enable targeted interventions in tight spaces. Hydraulic wedge splitter release stuck boulders; a concrete pulverizer removes interfering concrete remnants. A clear permit and communication chain is indispensable. Predefined isolation steps, rescue access routes and equipment readiness shorten response times and reduce risk.

Overview of related application areas

• Rock demolition and tunnel construction: Splitting technology for contour-true removal in niches and connections.
• Concrete demolition and special deconstruction: Concrete pulverizer for the deconstruction of temporary components in shafts and excavations.
• Building gutting and cutting: Selective removal for breakthroughs, openings and adjustments in interior works.
• Natural stone extraction: Parallels to splitting technology in the quarry, transferable to rock works in the tunnel environment.
• Special operations: Tool assortment for contingencies and unforeseen situations with limited accessibility.
• Shaft construction and rehabilitation: Selective interventions in linings, penetrations and interfaces under confined conditions.

Planning and best practices for the interface between TBM and ancillary works

• Early coordination of geometries (segment openings, niches, floor elevations) to minimize follow-up work
• Define drilling patterns and cut lines for splitting and pulverizer work
• Logistics concept for tool and power-unit transport in confined drives
• Coordination with conveying, ventilation and power supply systems
• Ongoing quality assurance and clean handovers between advance and lining
• Interface matrix for permits, lockout-tagout and access control for safe, fast interventions
• Training and toolbox talks focused on tool-specific risks, dust suppression and emergency procedures