Tunnel construction encompasses the planning, tunnel excavation, tunnel support and lining of underground voids for transport, utilities and infrastructure. It combines geology, construction methods engineering and occupational safety in a particularly sensitive environment: confined workspace, constrained construction logistics, stringent vibration and noise control, and strict procedures for handling water, dust and explosives. Under these conditions, precise, controlled, low-vibration working methods are crucial. Tools and systems from Darda GmbH are used above all in rock demolition and tunnel construction, in concrete demolition and special demolition as well as in building gutting and cutting, for example concrete pulverizers for selective secondary demolition and hydraulic wedge splitters for controlled splitting of rock and concrete.
Definition: What is meant by tunnel construction
Tunnel construction comprises all processes for the creation, maintenance and, where applicable, the deconstruction of underground structures. This includes excavation methods (mechanized or conventional with drill-and-blast), geotechnical support measures (shotcrete, anchors, lattice girder beams), the lining (segment rings or cast-in-place concrete shells), sealing and drainage, as well as construction monitoring. The term also covers cross-passages, shafts, caverns, niches and safety rooms. In addition to construction, subsequent conversion and refurbishment works play an increasing role: profile corrections, enlargement of the excavation, replacement of damaged concrete, removal of equipment, and separation cutting of reinforcing steel and built-in components.
Construction methods in tunnel construction: conventional and mechanized
In conventional tunnel construction (often referred to as NATM/Austrian method), excavation proceeds in stages via top heading, bench and invert, typically using excavators, milling machines or drill-and-blast. Mechanized excavation uses roadheaders or tunnel boring machines (TBM) with immediate support and lining. Regardless of the method, tasks arise that require precise, low-vibration removal of rock or concrete: profile finishing, removing shotcrete overbuild, demolition of test specimens, opening niches and cross-passages, or the deconstruction of temporary supports. Depending on the construction state, concrete pulverizers are used for secondary demolition and hydraulic wedge splitters for the controlled splitting of rock or massive concrete components.
Materials, support and lining in the tunnel
Central building blocks are the geological composite and the temporary support. Shotcrete provides short-term stabilization; anchors, lattice girder beams and spiles provide load redistribution; segment rings or inner shells ensure durability and watertightness. Even during construction, profile correction is often necessary to ensure target dimensions and to balance over- or under-profiles.
Shotcrete and profile correction
Protrusions, noses and accretions of shotcrete can be removed with low vibration in the confined tunnel cross-section. Concrete pulverizers offer high edge control on the excavation shell without unnecessarily loading adjacent support elements. For massive areas where a separating cut is not expedient, hydraulic wedge splitters with inserted rock splitting cylinders allow targeted widening of boreholes and controlled fracturing of the structure.
Reinforcement, built-ins and segment rings
During lining works, steel reinforcement, lattice girder beams and temporary steel components must be separated. Depending on material thickness and accessibility, combination shears, steel shears or Multi Cutters are suitable. In segment ring tunnels, different tasks arise: opening segments for breakthroughs, removing grout cones, or controlled removal of damaged areas, for which concrete pulverizers in combination with hydraulic power units deliver precise, reproducible results.
Secondary demolition and deconstruction in the tunnel
Underground, limits for noise and vibrations are particularly important. In the special demolition of inner linings, chambers or cross-passages, a selective approach is required: components are divided into logical segments, reinforcement and built-ins are separated in a targeted manner, and adjacent structures are protected. Concrete pulverizers allow biting concrete with well-controlled break edges. Hydraulic wedge splitters create crack lines in thick-walled components that can then be separated with minimal force. For cutting massive sections or pipelines in tunnel operations, Multi Cutters, steel shears and, for special tank and jacket plates, a cutting torch are available. Power is typically supplied via hydraulic power packs adapted to limited ventilation and transport within the cross-section.
Rock breakout and tunnel construction: controlled splitting instead of blasting
Not every section can be blasted economically or safely. In sensitive areas—such as inner-city locations, beneath existing buildings, or near critical infrastructure—hydraulic splitting offers a low-vibration alternative. Hydraulic wedge splitters create controlled separation joints via pairs of boreholes. The resulting blocks can be removed with smaller equipment. This method reduces secondary damage, minimizes follow-up support, and facilitates compliance with strict limits for vibrations and airborne sound.
Planning, geotechnics and monitoring
Excavation and support decisions are based on ground models, prediction classes and measurement programs. Deformations, convergences and strengths are recorded during construction and compared with the target behavior. For interventions in existing structures—such as cross-section enlargements, structural repair or opening breakthroughs—work methods must be chosen to suit the specific geology, lining state and required operational safety. Tools such as concrete pulverizers and hydraulic wedge splitters can be integrated into such monitoring concepts, as they enable reproducible interventions with well-documentable parameters.
Occupational safety, emissions and logistics underground
Underground work requires special measures for dust, noise, vibrations, ventilation, lighting and emergency escape routes. Depending on the project, different codes and regulatory requirements apply; specific requirements must be verified for each site. In general, hydraulic methods favor a dust- and noise-reduced way of working. This applies both to biting concrete with concrete pulverizers and to drilling and splitting with hydraulic wedge splitters. For construction logistics, the weight, dimensions and hose routing of the equipment are decisive, as is the compatibility of the hydraulic power packs with the available power supply and ventilation.
Typical tasks in tunnel construction and suitable tools
- Profile finishing on shotcrete shells: concrete pulverizers for controlled edges, combination shears to separate smaller built-in components.
- Creating cross-passages and niches: drilling, hydraulic wedge splitters for forming separating crack lines, followed by targeted removal.
- Deconstruction of temporary steel structures: steel shears and Multi Cutters for sections, meshes and beams.
- Refurbishment of damaged inner linings: removal with concrete pulverizers, exposing the reinforcement, selective cutting with combination shears.
- Rock excavation in sensitive environments: hydraulic wedge splitters for low-vibration block formation.
- Gutting and cutting of pipelines and built-in components: Multi Cutters and, for special jacket materials, a cutting torch.
Special boundary conditions: inner-city and in existing structures
Under urban areas, limits for vibrations and airborne sound are often very low, while requirements for construction monitoring and third-party protection are high. Methods with limited propagation of vibrations—such as hydraulic splitting or biting with concrete pulverizers—support compliance with these specifications. When working in existing tubes during partial operation, compact, mobile units with hydraulic power packs and short setup times are advantageous.
Quality assurance and documentation
Documented work parameters and acceptance processes are required for dimensional accuracy and durability: target-actual comparison of geometry, evidence of concrete removal to the defined depth, logged separation cuts and splitting sequences. Tools with well-controllable forces—such as concrete pulverizers and hydraulic wedge splitters—facilitate reproducible results and seamless documentation of the work steps.
Sustainability and resource efficiency
Resource-conserving methods reduce material losses, energy demand and transport. Low-vibration methods mitigate consequential damage and follow-up support. Controlled splitting produces blocks with favorable transport dimensions; selective removal with concrete pulverizers preserves adjacent components and facilitates clean separation of concrete and steel—an essential prerequisite for high-quality recycling. In the sense of the circular economy, this supports efficient utilization of the excavated material.
Special use cases in tunnel construction
In special situations—such as emergency measures, exposing incident areas, or opening service caverns—fast, controlled separation and opening is required. Depending on the material mix, combination shears, Multi Cutters and steel shears offer flexible options. Where closed tank or jacket structures must be processed underground, a cutting torch can be part of a safety-compliant plan. The selection and application of such methods must always align with the applicable regulations and project-specific approvals.