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.
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, 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.
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.
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.
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.
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.
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.
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.
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
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 pack ensure the energy supply in confined environments and facilitate logistics in the tunnel.
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.
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:
- Adjustments to segment openings (e.g., cable penetrations, ventilation cross-sections)
- Deconstruction of temporary concrete components in the entry/access shaft
- Relief cut on inverts and upstands prior to lifting
- 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.
Further tools and power units in the TBM environment
Hydraulic power pack
Hydraulic power pack supply mobile tools with energy. Criteria include flow rate, pressure, operational safety, exhaust and noise emission, as well as transportability on narrow site routes.
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.
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.
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
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.
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.
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.
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.
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